text:
|Publication number
|Publication type
|Application number
|Publication date
|May 27, 1986
|Filing date
|Oct 1, 1984
|Priority date
|Oct 1, 1984
|Fee status
|Publication number
|Gary A. McCorkle
|Original Assignee
|United Technologies Corporation
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (4), Referenced by (39), Classifications (13), Legal Events (7)
|External Links: USPTO, USPTO Assignment, Espacenet
This invention relates to a signal conditioning circuit for linear variable differential transformers (LVDTs) or rotary variable differential transformers (RVDTs).
Commercially available displacement sensors produce either digital or analog outputs. The analog output types include variable resistors, capacitors in single-coil units, and multiple-coil inductive sensors. Among the later type, the linear variable differential transformer (LVDT) and the rotary variable differential transformer (RVDT) are iron-core transformers with a moveable core having three windings which sense a linear displacement. LVDTs and RVDTs are used to measure linear or angular displacement and are connected mechanically between the object being sensed and a reference object. The analog output voltage is proportional to the displacement of the moveable core. It can be used to measure motion or position.
The primary winding is energized with an AC voltage source. The LVDT's secondary windings are to produce opposing voltages and are connected in series opposition to produce an output voltage which is the difference of the two secondary voltages. With the core centered in a neutral or zero position, the two secondary voltages are equal and opposite and the differential is theoretically zero. This is the balance or null position. If the core is displaced, the magnetic coupling between the primary and one of the secondaries increases and the coupling between the primary and the other secondary decreases. Thus, an output voltage is produced which increases as the core is moved further away from the null position. The phase between the input voltage and the output voltage increases or decreases as a function of the direction in which the movable iron-core is moved. At the null point, movement of the core in either direction across the null boundary produces a 180� phase reversal. The amplitude of the secondary output voltage forms a V-shaped curve when plotted versus core displacement. At the V's "knee", corresponding to the null point, the phase angle abruptly reverses by 180�. The voltage at the "knee" is not exactly zero. A small residual null voltage contains a component 90� out of phase with the fundamental and higher harmonics of the input voltage.
Demodulator circuits are normally used to eliminate the residual voltage at the null and to produce a DC output from the secondary winding which may then be used with standard DC instruments. As mentioned above, RVDTs are also commercially available for angular displacement measurement where the movable iron-core rotates about a fixed axis. The principles of operation of the LVDT and the RVDT are basically the same.
LVDTs and RVDTs have a frequency dependent phase shift associated with the particular characteristics of the device. This phase shift is in addition to the 180� phase shift which occurs when passing through the null position. Two methods are used in the prior art to compensate for the secondary phase angle shift. The first method is to adjust the excitation frequency in a manner to cause the secondary voltage to be in phase with the primary excitation. If the primary excitation is referenced to the synchronous demodulator, optimum rectification occurs at zero phase differential between secondary AC phase and demodulator switching, relative to the waveform zero crossings. In addition, according to the prior art, exciting the L/R VDT at its zero phase angle frequency results in minimum sensitivity to frequency and temperature variations.
Another way of providing phase compensation is to use a variable phase shift network between the excitation output and the synchronizing reference input to the L/R VDT signal conditioner. In this case, the excitation frequency remains fixed and a potentiometer in an RC circuit is tuned for optimum demodulator phasing. According to the prior art, proper phasing of the synchronizing reference signal to the demodulator results in optimum sensitivity and linearity.
The phase error described above is a characteristic peculiar to the synchronous demodulator (product detector) scheme used in the prior art. Basically, a coherent, in-phase reference is needed by the product detector to enable it to output a full wave rectified signal wherein the baseline of the rectified signal is at a reference point. If there is a phase error, the output signal will have excursions on the wrong side of the baseline. This means that the filtered DC output which is representative of the L/R VDT position will be in error, inasmuch its amplitude will be off relative to the baseline reference voltage, since the signal has to average out for those portions on both sides of the reference baseline. Since the L/R VDT is an inductive device with the usual phase shift of an AC signal, phase shifting is used to put the product detector reference signal back into phase with the L/R VDT output signal to be demodulated. The prior art solution described above, using an RC filter introduces component inaccuracies and temperature coefficients of these elements which must be considered.
If the temperature range which the LVDT or RVDT must be capable of operating within is relatively large, e.g., -40� C. to +85� C. a simple RC circuit will give, according to the prior art, roughly plus or minus 5% stability over the temperature range. This figure can be considerably higher in many cases.
In addition, frequency accuracy is also a factor in the phase shift. A typical prior art device might exhibit a 6� phase shift at 2.5 KHz or 12� at 5 KHz.
The phase shift tolerance from device to device can vary by as much as 0.5%. Phase shift will also be affected by temperature as R and L vary and since the sensitivity error due to temperature can be approximately +0.7%, the overall worse case phase shift error can be as high as about +1.2% at 5 KHz.
Another item to consider in phase shift is the accuracy of the excitation frequency itself. If a simple RC oscillator is assumed, the best that can be hoped for in accuracy over the temperature range (with 1% components) is roughly 5%. A 5% shift in frequency translates to, for all practical purposes, a 5% shift in phase for RL elements involved. A reasonable breakdown of this figure into ambient and temperature coefficient percentages would likely be roughly 4% and 1%, respectively.
Although the temperature coefficient of the oscillator components and the phase shifter components should be the same, resulting in some tracking, causing the phase shift elements to shift in a roughly compensatory manner, this cannot be determined with any exactness so worse case conditions must be assumed.
In addition, the simple RC oscillators used in prior art devices produce non-linear, non-sinusoidal signals with significant harmonic content. These harmonics produce even more voltage and phase shift errors in the output of the product detector. Where non-linear networks have been used to produce approximations to a sine wave output, the harmonic distortion typically remains at 5% because of the inexact nature of the non-linear approximation techniques.
The overall phase shift error thus can be as high as approximately 12% (about 10% for spread and 2% for temperature deviations). It is difficult to put an exacting percentage of error that this phase shift error has on the product detector output. However, it is evident that for 12% of a half wave period, the polarity of the demodulator output signal will be in error.
The next errors to consider in the prior art LVDTs and RVDTs are demodulator errors. These include linearity, offset, offset temperature coefficient, and reference accuracy. The linearity error it is often as much as 0.5% over the temperature range. The offset voltage worst case over temperature range may be as high as 100 mv in a +5 volt device. The offset temperature coefficient can be as high as 0.25 millivolts per degree centigrade. The reference voltage error can often be as high as +3% of Vcc/2. Since the reference is derived by a resistive divider in the prior art, there has to be a temperature coefficient based on temperature coefficients on IC resistor to resistor variations as a function of temperature, and the reference source temperature coefficent should be on the order of 0.01%/�C. This translates to roughly �0.6% at the temperature extremes.
Other items to consider include the temperature sensitivity of the output buffer stage typically used in the prior art, conversion errors associated with the analog to digital converter used, the deviation of the sensitivity of the device from unit-to-unit, the distortion of the excitation signal due to the LVDT transformer, and excitation amplitude. This last includes simple output amplitude accuracy, the amplitude temperature coefficient, and the sensitivity to power supply variations.
When taken in their totality, the accumulative effects of all of these sources of error can be extremely high in the worst case.
A new circuit design approach is required in some cases in order to avoid many of these sources of error.
The object of the present invention is to utilize a variable differential transformer in a unipolar mode and to condition the signals associated therewith in such a way as to avoid many of the sources of error in the prior art.
According to the present invention, a variable differential transformer used for measuring linear or rotary displacement is used in its linear region only, on one side of the null point only, and a special peak detector is used in both excitation and output stages in order to measure, on a ratiometric basis, the signals representative of the displacement to be measured, in a signal conditioning circuit having an oscillator incorporated therein using the L/R VDT prinary as the inductive element of the oscillator.
In further accord with the present invention, offset error may be determined and subtracted out by external circuitry by momentarily shutting down the oscillator and measuring the DC components to the signal conditioner and excitation outputs.
Since the displacement is measured only on one side of the null point, there is no need to use a product detector for sensing phase reversal when passing through the null point. This eliminates the concerns for frequency stability and phase matching plus temperature effects for the same. As has been disclosed, a special peak detector is sufficient. The special peak detector is disclosed and claimed separately in copending application Ser. No. 656,568 entitled "A LINEAR SLOPE PEAK DETECTOR" invented by Gary McCorkle and assigned to the assignee of this invention, and is hereby expressly incorporated herein. A varity of other techniques may be used in this unipolar approach to eliminate most of the other errors.
For all practical purposes, the two aforementioned features of the present invention eliminate all but the linearity sensitivity error, the output signal conditioning gain error, and errors associated with annalog to digital conversion resolution. To quantify these errors, using a unipolar design with a peak detector the only errors remaining are attributable to LVDT linearity on the order of �0.5%, an LVDT temperature coefficient on the order of �0.7%, output buffer gain error on the order of 3%, and ADC resolution.
To illustrate what the remaining errors amount to in terms of positional measurement accuracy, it is necessary to consider what the impact is on a point-by-point basis. This allows selection of a linear region in the LVDT most suited for the task. It can be intuitively appreciated that near the null point, offset errors of any sort having a devastating effect on percentage of accuracy; but in terms of magnitude of error, purely in terms of displacement, the limits of the range are most error prone. In terms of relative accuracy, the offsets are significant on a percentagewise basis as the LVDT approaches the null point where displacement and corresponding LVDT output voltages are small. These same offsets diminish in the magnitude of their percentage effect on accuracy as displacement increases and LVDT output voltages approach maximum. Thus, there are two ways to view the effects of these errors. One is on a percentage basis and the other is on a strict plus or minus positional units basis. In the former case, the percentage of error is dramatic near the null point and asymptotically approaches a minimum percentage of error figure as overall displacement increases. In the later case, the displacement error in positional units, e.g., step or motor steps, starts off as a minimal figure and linearly increases to a maximum at maximum displacement of the LVDT. This follows a typical mx+b curve where "m" is the percentage error and "b" is the offset.
Restricting the physical operating range of the LVDT or RVDT so as to not pass through its null point, and designing a circuit most suited to unipolar operation, is a functional philosophy change which is found to reduce the unacceptably high measurement errors of the prior art. The principal failings of the prior art approach involving such things as the accumulation of temperature coefficient effects from a complex circuit, lack of true and simple ratiometric sampling of excitation versus output, distortion and phase errors associated with the synchronous (product) detector scheme, and the inability to determine and factor out offsets, are obviated by the present invention. Since unipolar L/R VDT operation does not require any recognition of phase reversal, the need for a synchronous detection scheme is not needed. Simple peak detection and ratiometric measurement of both the excitation and LVDT or RVDT output eliminates the errors introduced by excitation amplitude and frequency/phase errors, both fixed and temperature dependent, and also eliminates the prior art demodulator linearity and phase errors (associated with compensation networks), both fixed and temperature dependent. Of course, the restriction of the L/R VDT operation to one side of the null may have disadvantages in some cases. In such cases, the disadvantages may outweigh the advantages of the present invention and the prior art signal conditioning circuitry must be used.
A custom circuit designed to generate a cleaner sine wave which may be incorporated in the signal conditioning circuit of the present invention is recommended using the LVDT or RVDT primary as an inductive element in the oscillator stage. Using the L/R VDT primary directly as the inductive element in an LC oscillator, which is inherently sinusoidal, eliminate those harmonics (odd) that would affect the peak detector's ratiometric accuracy. Where harmonics are present, the L/R VDT would act as a filter so that L/R VDT output peak would not be proportional to excitation peak on account of odd harmonics being inductively filtered out. This technique reduces the effects of distortion to a negligible amount.
In addition, by periodically suspending LVDT excitation, the DC components of both the excitation and L/R VDT output channels up to and including the analog to digital converter are measured and may be factored out of subsequent measurements which takes care of fixed, aging, and temperature dependent effects throughout the life of the signal conditioning unit.
As mentioned, the technique of the present invention reduces the measurement errors to those introduced by temperature dependent characteristics and aging of the gain of the system (LVDT), output peak detector (ADC channels for example), and the ever present ambiguity of the ADC itself in terms of its resolution. If maximum amplitude output of the LVDT is scaled to be reasonably commensurate with the full range of a Vcc referenced ADC, the positional error will be ambiguous to an extent determined by the LVDT sensitivity and an arbitrary integer gain picked to roughly fit a Vcc reference in an ADC, and power supply margin. This is a constant positional error throughout the entire linear LVDT displacement range.
Initial gain disparities can be determined by end of line calibration. This leaves temperature dependent drift to be considered. Typical inter-resistor drift is on the order of 0.01%/�C. for the usual P-type diffusion resistors on board IC's. In the excitation source, the circuit design provides for temperature tracking and adequate bandwidth between the oscillator and filter elements so that distortion is kept supressed. This leaves the gain disparities in the excitation and LVDT output peak detectors and/or any pre/post amplification buffers to consider. This is principally the input and feedback resistor networks. Assuming the worst problem would be one amplifier increase in gain as much as temperature deviation would cause (about plus 0.65%) and another decrease similarly (-0.65%) for a -40� C. temperature the overall temperature dependent gain shift is about �1.3%. Channel gain disparities of the ADC might be on the order of +0.6%. This produces an overall gain error of �1.9% total. This is a percentage of point error throughout the linear range of the LVDT or RVDT. Once the device begins operation, internal heating will diminish the cold temperature deviation. The +85� C. deviation is a lesser �0.6% amount, yielding a gain error of �0.8% overall which, of the two temperature extremes, would be the more persistent.
Converting the �1.9% gain error to a physical displacement error in an LVDT having a maximum displacement of one half inch, the gain error is �0.095 an inch. Adding the ADC ambiguity of +1.5 LSB or, in this case, �0.0034 inch, the measurement error would be +0.0129 inches maximum at one half inch displacement of the LVDT. At +84� C. the error is only slightly less at a calculated +0.0124.
These and other objects, features, and advantages of the present invention will become more apparent in the light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawing.
FIG. 1 is a simplified block diagram illustration of an LVDT signal conditioning circuit utilized according to the prior art;
FIG. 2 is a simplified block diagram illustration of a signal conditioning circuit according to the present invention;
FIG. 3 is a simplified block diagram illustration of a signal conditioning circuit similar to the circuit of FIG. 2 except additionally incorporating an oscillator within the signal conditioning circuit;
FIG. 4 is a simplified block diagram illustration of a signal conditioning circuit similar to the circuit of FIG. 3 except additionally incorporating a shutdown circuit within the signal conditioning circuit; and
FIG. 5 is a simplified schematic block diagram illustration of a signal conditioning circuit according to the present invention incorporating all of the features of FIG. 4.
FIG. 1 is an illustration of a prior art signal conditioner 1 for use with a linear variable differential transformer 2 (LVDT). The circuit includes a low distortion amplitude stable triangle wave oscillator 3 with programmable frequency to drive the primary 4 of an LVDT; a converter 5 converts the triangle wave to a sine wave; a synchronous demodulator 6 converts the LVDT output amplitude and phase information from a pair of secondary windings 7 on a line 8 to position information; and an output amplifier 9 provides gain and filtering.
An external dual tracking-regulator 20 provides a positive DC level on a line 22 to the triangle wave oscillator 3 which generates a triangle waveform on a line 24. The triangle output is then converted into a sine wave by the sine converter 5, the output of which, on a line 26, is applied in phase opposition to the primary 4 of the LVDT 2.
The synchronous demodulator 6 performs full wave rectification in phase synchronism with the above oscillator output. In order to extract true position information, the phase relationship of the LVDT secondary must be obtained. This means that as the LVDT core passes through the null, an abrupt 180� phase change occurs. Once full wave rectification is accomplished, the resulting signal carrier frequency must be removed by filtering. Demodulator output on a line 36 is provided to an active filter 38 incorporating an auxiliary op amp 40. The objective is to provide the original position information ripple free on a line 42 which may be presented for readout purposes on a chart recorder 44 or a digital readout 46.
Other functions include buffer amplifier feedback on a line 48 in the oscillator circuit. The loop is closed with negative feedback around both amplifiers operating at unity gain.
An oscillator timing capacitor 50 controls the frequency. The frequency is related by an equation fOSC =110/C(microfarads).
As noted above in the background art section, the typical prior art LVDT signal conditioning circuit, as exemplified in FIG. 1, is designed for use with an LVDT having an actuator that is permitted to cross over the null point. As described in detail in the background art section, this approach introduces a degree of complexity which is necessary as a result of using a bipolar transfer function.
In the prior art circuit, there are two methods of biasing the signal conditioning circuit 10. The first method is to provide a fixed reference voltage (not shown) such as +8 volts on a line 52 to bias circuitry 54. This "fixed" reference voltage will vary with an incoming poorly regulated supply. This might occur in automotive applications, for example. With supply voltage variations, the DC voltage on the line 42 will not vary with the supply but will vary within the common mode limits of the amplifier 40 as the LVDT core traverses its path. The output voltage on the line 42 at the LVDT null will be the voltage on the line 52 divided by two. Thus, for the case mentioned with eight volts applied, the null voltage will be +4 volts. Depending on the size of the linear portion of the transfer function, the maximum linear swing might be, for example, 1.5-8.5 volts around this value.
An alternate method of biasing, as shown in FIG. 1, is known as the "ratiometric" mode. In this case, the DC level on the line 22 is connected to the bias circuit input line 52. Since the signal on the line 22 controls the DC common mode voltage of the demodulator and the oscillator RMS output, these magnitudes will now change with supply voltage. The DC output from the auxiliary amp 40 on the line 42, using a single ground referenced supply, will be "ratiometric" with the supply voltage and centered within the common mode range of the output amplifier when the LVDT transducer is at null.
FIG. 2 is an illustration of an linear/rotary variable differential transformer (L/R VDT) signal conditioning circuit 100, according to the present invention. The circuitry is designated "linear/rotary" because the circuitry design principles are equally applicable to either a linear or a rotary variable differential tranformer. The signal conditioning circuit 100 receives a rectified sine wave output on a line 102 from an oscillator 104 external to the signal conditioning circuit 100. The oscillator is an LC type having a tank circuit that utilizes the primary winding 106 of an L/V VDT 108 as the inductive element in the tank circuit. The secondary windings 110 of the L/R VDT provide output signals on lines 112, 114 to the signal conditioning circuit 100.
The signal conditioning circuit 100 includes an excitation peak detector 116 that provides a signal indicative of the peak excitation on a line 118 to an excitation output amplifier 120. An output signal on a line 122 from the output amplifier 120 is indicative of the present value of the peak excitation voltage.
An output peak detector 124 provides a signal on a line 126 indicative of the magnitude of the peak output voltage from the secondary winding 110. The signal on the line 126 is amplified by an output amplifier 128 which provides an output signal on the line 130 indicative of the displacement being measured.
The peak detectors 116, 124 are of a specially designed type, to be disclosed in more detail below, and may be characterized as linear slope peak detectors. They are more accurate than the typical RC peak detectors of the prior art.
It should be understood that although the oscillator 104 of FIG. 2 has been described as providing a rectified output signal on the line 102 (thereby assuming that a rectifier of some kind is contained within the oscillator 104) the oscillator could as easily provide a pure sine wave on the line 102 which may be rectified within the signal conditioning unit 100 before being applied to the peak detector 116. Similarly, although the secondary winding 110 of the L/R VDT has been described as providing a signal on the lines 112, 114 which, in the illustration would indicate that a pure sine wave is applied to the peak detector 124, it should be understood that the sine wave output of the secondary must be rectified at some point before being applied to the peak detector 124. Thus, a rectifier should be assumed in FIG. 2 to be within the peak detector 124. However, it should be understood that the rectifier could as easily be external to the signal conditioning unit 100.
Similarly, it should be understood that the boundaries of the signal conditioning unit shown in FIG. 2 are not necessarily restricted, in the practice of the invention, to the particular blocks shown. For example, in FIG. 3 the oscillator circuit 104 is shown as part of the signal conditioning unit 100. In fact, the incorporation of the oscillator circuitry within the signal conditioning unit 100 is probably the best way to produce such a signal conditioning circuit at low cost. In addition, various engineering considerations would militate in favor of placing the oscillator 104 within the signal conditioning circuit 100. The point is, the boundaries of the signal conditioning circuit 100 should not be thought of as limited by the descriptions contained in FIGS. 2-6. They are merely illustrative of various circuits that embody the inventive concepts involved.
As a further elaboration upon the inventive concepts, FIG. 4 is provided to illustrate a signal conditioning circuit 100 that includes a shutdown circuit 132. The shutdown circuit responds to an externally applied signal on a line 134 which is applied periodically for the purpose of shutting down the oscillator. The shutdown circuit provides a signal for this purpose on the line 136 in response to the signal on the line 134. The oscillator 104 is shutdown in response to the signal on the line 136 in order to measure, by means of external circuitry (not shown), any DC offsets which may exists and which may be factored out once their magnitudes are determined.
A more detailed simplified schematic block diagram of the circuitry of FIG. 4 is shown in FIG. 5. The outline of the L/R VDT 108 of FIGS. 2, 3, and 4 is shown in broken lines 108a and 108b in FIG. 5. In other words, the primary winding 106 and the secondary windings 110 are shown separately, although they are the same physically as in the previous figures.
The circuitry shown in FIG. 5 is capable of IC implementation and of meeting positional accuracy requirements over a temperature range of -40� C. to +85� C. The circuit can be used by a wide variety of LVDT/RVDT types operating in a unipolar mode. The design philosophy departs from traditional synchronous demodulator/product detector methods of converting the L/R VDT's AC output into position proportional DC voltage in order to eliminate the numerous error sources in those methods and to be able to determine intrinsic DC offsets and changes in excitation amplitude. The temperature sensitivity of circuit gains are insignificant in their effect on system accuracy. In addition, the device is capable of positional accuracy to 0.013 inch or less in a phalf inch device. This takes into account effects of L/R VDT and circuit linearity, temperature, conversion resolution, and intrinsic circuit DC offsets.
The LVDT/RVDT signal conditioning circuit shown in FIG. 5 consists of three main sections. These are: (a) the LVDT/RVDT primary coil excitation oscillator; (b) the LVDT/RVDT primary coil excitation signal peak detector; and (c) LVDT/RVDT secondary coil output signal peak detector.
The primary coil's excitation oscillator is a Colpitts type consisting of a transistor 150, a resistor 152, a resistor 154, a resistor 156, and the LVDT/RVDT primary coil 106 as the inductor and a capacitor 158 and a capacitor 160 as the capacitive elements in the LC tank circuit. Fixed base bias is used and oscillations are sustained by emitter feedback. The components used yielded a resident frequency of roughly 5 KHz with a sine wave peak-to-peak voltage of roughly 2.5 to 3 volts across the LVT/RVDT primary coil. This technique results in considerable simplification over the more traditional approach of an external oscillator, wave shaper or filter, and driver forcing the external oscillator, wave shaper or filter, and driver forcing the LVDT/RVDT primary. It also makes excitation performance less dependent upon the matching and stability of resistive and capactive elements such as are involved in external oscillators and filters used to obtain a useable sine wave to drive the primary. In addition, most of the energy used to provide the excitation is stored in the tank circuit elements with only a small amount used to sustain oscillations, resulting in far less dissipation in the overall excitation circuit than is typically dissipated by external oscillator/driver schemes.
A resistor 170 and a transistor 172 form a simple gating circuit that shuts down the oscillator 104 if a TTL "high" level voltage from an external source drives an input line 174. This is accomplished by transistor 172 saturating and essentially dropping the transistor 150 bias so low that transistor 150 ceases to conduct. The purpose of this gating circuit is to permit elimination of all AC components in the signal processing circuits, both excitation and L/R VDT output, so intrinsic circuit DC offsets may be measured and later factored out when positional calculations are being made.
The AC component of the oscillator signal on a line 176 is coupled to the peak detector stage 116 following. There are a number of considerations and tradeoffs involved in coupling the oscillator output to the peak detector. First, the impedance seen by the oscillator at the collector of transistor 150 must be sufficiently high that the oscillator is not loaded down. Second, resistors 178, 180, 182, and 184 provide both a signal path to ground and a current path for the inputs of the peak detector 116. Since a DC voltage is applied across a capacitor 186 via Vcc through the primary 106 of the LVDT/RVDT 104 through the aforementioned resistors, there is a time constant for an exponential decay of this DC voltage to consider when oscillator shutdown is effected by an external signal on the line 174 and a change in the applied DC level occurs (i.e., transistor 150 no longer conducts and no longer provides a voltage division with respect to the LVDT/RVDT). The tradeoff is such that there first must be sufficient impedance to not load the oscillator but, at the same time, a fast enough time constant to permit the DC level shift that occurs on oscillator shutdown to exponentially decay out to a value so insignificant that it does not measureably affect the accuracy of subsequent measurements.
After passing through the capacitor 186 the signal appears on a line 188 and is next clipped just below ground level by a diode 190 so the peak detector 116 will not distort as it would if two large a signal went below ground level at an op map 192 input. Again, to preclude loading the oscillator too much, resistor 184 provides a sufficiently high load to the input signal on the line 184 so that the clipping of diode 190 does not affect oscillator performance. Positive peaks appear across resistors 180 and 182. Given that capacitor 186 is, in this example, 0.0039 microfarads, the net loss in signal due to network attenuation is roughly 8%. This loss is not important inasmuch as end of line calibration will determine the overall system sensitivity (LVDT/RVDT and circuitry together) to be used in positional calculations.
The circuitry shown in FIG. 5 is a representation of a successful breadboard embodiment of the invention. In other words, the circuit represents in FIG. 5 is an engineering model. It will be noted that LM 124 and LM 139 type devices are used in the circuit of FIG. 5. Although the invention is not necessarily restricted to usage of such devices, it should be understood that are several reasons behind the choice of these devices to model the circuit. These reasons include the fact that both are low powered devices with very low offsets; they do not need external offset adjustments; and the gain is such, particularly on the LM 139 comparator, that uncertainty is insignificant compared to the desired resolution. In addition, for both devices, the Common Mode Voltage Range (CMVR) is (for a 0 to +5 volts single power supply scheme) from 0 to +V-1.5 volts or, in in other words, 0 to 3.5 volts. These devices are preferred over other types whose CMVR has deadbands of from 1 to 1.5 volts inside the power supply rails at both the +V and -V ends. Typically, these deadbands are relatively fixed amounts rather than proportional to the power supply span in the case of a single power supply. This would mean that the usable range for other devices could be as small as between 1.5 volts and 3.5 volts (5-1.5 volts) for a total dynamic range of only 2 volts, centered about the one half Vcc level or 2.5 volts typical. In addition, the circuit design is simpler due to being able to reference, for example, both the excitation and the LVDT/RVDT output to ground when the output to their respective peak detectors rather than build in some 1/2Vcc reference source to offset both signals in order to stay away from a deadband near ground. Also, the absence of a -V deadband allows a wider dynamic range (i.e., 3.5 volts) in which the useful signal, the positive peaks from their 0 crossup, may operate if necessary. It will be seen below that the absence of the -V deadband is most useful when coupled with techniques to minimize the +V deadband to the point of enhancing the amplitude and resolution of the positional measurement signal. Because of these considerations, it would be a considerable undertaking, resulting in more complex circuitry, to use devices other than those of the LM 124 and LM 139 genre or their equivalents.
The peak detector 116 consists of a comparator 192 and a switched input integrator 194. A clipped input signal on a line 196 goes to the inverting input of the comparator 192 and the output of the integrator 194 on a line 198 ultimately goes to the noninverting input of the comparator. Whenever the inverting input exceeds the noninverting input, the comparator 192 will, in effect, switch a resistor 200 into the integrator with ground as the driving signal (bear in mind that for single power supply configurations, the op-amp quiescent levels are 1/2Vcc or 2.5 VDC for a five VDC power supply; hence, both ground and Vcc are active driving signals relative to the quiescent level). This causes the integrator to ramp in the positive direction until a scaled version of its output on a line 201 equals or exceeds the inverting input level to the comparator 192. When this condition is reached, the comparator goes into a high impedance state and resistor 200 no longer connects to ground, leaving only a resistor 202 connected to a driving voltage (Vcc) on a line 204. Since resistor 202 is much larger than resistor 200 and is also connected to Vcc, the integrator 194 slowly ramps (decays) down between each postive going peak from the input. Gain in this stage is provided by the voltage division of a resistor 206 and a resistor 208. Essentially, the output of the integrator has to be that level that when applied to the voltage divider resistors 206, 208 results in a match to the input signal to the comparator. In the breadboard configuration illustrated in FIG. 5, for oscillator components used and using a Schaevitz E500 LDVT at 5 KHz, the gain was set to 1.2. This yields a 2.2 peak volt signal at the output of the integrator with roughly 2.5 volt margin above ground.
The peak detection technique disclosed is used in preference to the typical op-amp driven RC circuit for a number of reasons. Since changing signals may involve either an increase or decrease in peak amplitudes, the peak detector must be responsive to maximum input signal peak amplitude slew rate on either the increase or decrease. Next the error from peak refresh to peak refresh must be constrained to some specified maximum. This is because the LVDT/RVDT output may be sampled by an ADC (not shown) anywhere from at the moment the peak occurs when a minimum error condition would exist to just before the next refresh when the peak detector "droop" error would be at a maximum. Concurrent to the ability to respond to a maximum signal input signal peak slew on a decreasing level, it is desirable to have the peak detector be able to go to whatever the intrinsic circuit DC level is within a reasonable and predictable time subsequent to the reception of an oscillator shutdown signal on the line 174.
A conventional peak detector with a bleeder resistor to allow decay to successively decreasing amplitude peaks has a different relationship between its decay slew rate and the steady state peak refresh to peak refresh error than the comparator/integrator peak detector disclosed herein. The initial objective, based on a 5 KHz excitation frequency (which translate to 200 microseconds between refresh), was to minimize droop to approximately 25 mV. This number was based mostly on the design goal of a maximum of just slightly less than 2.5 V for a full scale signal on the peak detector outputs of both channels. This would amount to a one percent error at full scale or 0.005 inches in a one half inch travel L/R VDT device. A quick calculation for both the conventional peak detector with a bleeder resistor, and the method used shows that for a 220 K resistor and a 0.082 microfarad capacitor, the droop voltage at full scale is 27 mV. However, there is a dramatic difference in slew rate capabilities. If one assumes a full scale slew time of 100 ms, it can be shown that the conventional peak detector with the bleeder scheme has asymptotically approached the final near 0 V level to within 10 mV at 100 ms whereas the method using the comparator/integrator has gone directly to and held at the final valve in only 18.2 ms. What this means is that for a given error limit, the comparator/integrator method slews faster and holds to a final level far better than the conventional peak detector. This also means that for the comparator/integrator method, a sizeable increase in the decay slope resistors could be tolerated to decrease the slew rate and still be compatible with the position slew rate with a decrease in the droop error by the same proportionality (e.g., decrease slew rate by a factor of two and decrease droop by the same factor: 18.2 ms to 36.4 ms full scale slew period, 27 mV to 13.5 mV droop). To try to improve the slew rate of the conventional peak detector by decreasing the bleeder resistor will cause more droop error. In summary, the linear slope derived by the comparator/integrator method disclosed herein offers more advantages in the droop error versus slew rate tradeoff than the exponential slope that one gets with conventional peak detector methods.
The attack time (i.e., the slew rate when responding to a peak) is on the order of fifty times faster than the decay rate. This permits the peak detector to track the profile of the sine wave peak whenever the input signals exceeds the present value at output of the integrator. The practice of the invention is not restricted to such an exact figure, however.
Periodic oscillator shutdown via an external circuit presenting a shutdown signal on the line 174 is desirable to measure the DC offsets which vary as a consequence of temperature changes and aging. A conventional peak detector only asymptotically approaches the DC offset level because of the nature of the exponential decay. With the values used, the conventional method was shown to be only within 10 mV of the final value after 100 ms, whereas the comparator/integrator method had ramped down to and held at the final value in 18.2 ms. Again, if affected by slew rate versus droop error tradeoffs, the comparator/integrator method still offers the advantage of eliminating the ambiguity of the asymptotic approach of the conventional peak detector to the final value.
Another important consideration in the droop error versus slew rate tradeoff is the excitation frequency itself. Droop error is directly affected by the excitation frequency. In effect, the longer the period between peak refresh, the larger the droop regardless of peak detection method used. Slew, on the other hand, is dictated by the rate of positional change of the LVDT/RVDT. Picking a slew rate in the peak detector to be compatible with the positional change slew rate then fixes what the droop error will be for different excitation frequencies. What this says, in effect, is that for a peak detector slew rate that is just inside of that of the positional slew rate, the droop error will be twice as much for 2.5 KHz excitation as it would be for 5 KHz excitation. It is reasonable, therefore, that if nothing is lost in the LVDT/RVDT performance by going to a higher excitation frequency, the higher frequency should be used to both reduce droop error and the size of tuning capacitors used in the oscillator.
Note that there is a certain amount of signal "dither" around the DC level when the shutdown signal is imposed. This is because the integrator always has the decay rate imposed because of the permanent hookup of the integrator resistor affecting decay to Vcc. Accordingly, once the DC level is acquired, a decay will occur until the comparator detects sufficient difference between the DC level input to itself and the integrator output and restores the integrator output to a proper level. The periodicity and amplitude of this "dither" is a function of comparator and op-amp gains plus propagation delays. Observation of this "dither", which shows up as a saw-tooth waveform on a oscilloscope, shows it to have an amplitude of roughly 25 mV, or roughly the same error as the droop error at 5 KHz.
In addition, certain timing constraints dictate when measurements are feasible after effecting oscillator shutdown and reenabling the oscillator with the removal of the shutdown signal along the line 174. From a maximum output condition and using the current integrator RC components, it will take roughly 18.2 ms for the peak detector to decay down to the DC level. This is true for both the excitation and the LVDT/RVDT output channels. The Q of the Colpitts oscillator tank circuit using the LVDT/RVDT is low enough that oscillation damp out in one half of a cycle. However, on turn-on there is almost a fifty percent overshoot on the peak of the first cycle. For the excitation channel, and for the LVDT/RVDT output channel at a significant displacement, the peak detectors will only partially ramp up toward the peak on the attack slope. Observations shows that for maximum signals, it takes roughly 1 ms for the convergence of the signal damping down to steady state and the peak detector finally tracking the peaks to occur. At lesser signals nearer to the null point of the RVDT/LVDT output channel, the initial overshoot is readily acquired by the peak detector, but successive peaks and the steady state level takes some time for the peak detector to acquire since it has to decay down to that level and the decay slope rate.
Although the period of time is not completely necessary for the component values shown in FIG. 5, it is suggested that the use of the shutdown input on the line 174 and the sampling of DC levels be synchronized externally with the timed activities of the external controller. For instance, if the controller's activities are timed to sample the LVDT/RVDT position at 40 ms intervals, the shutdown signal could be asserted on a selected 40 ms event. Upon the next 40 ms event, the sampling of the excitation and the LVDT/RVDT channel would occur. The next 40 ms event following the completion of the channel sampling (assuming conversion times are taken into account) would disable the shutdown signal thereby enabling the oscillator to resume operation. At the 40 ms period then following, normal excitation channel and LVDT/RVDT output channel sampling for positional measurements could resume. Since the overall period of time involved is relatively lengthy compared to other events, the scheduling of the shutdown event would be on the order of once every few seconds or more.
Once any DC level has been established by the peak detector 116, it is fed on the line 198 to an output amplifier. The configuration used is best explained after the trade-offs of various op-amps is described. First, one can get op-amps with conventional, single stage inputs which have dead zones roughly 0.6 V inside the power supply rails. The low level signals that may exist near ground make this type of dead zone undesirable. One can also get PNP darlington input op-amps (such as the LM 124) wherein inputs can go all the way to ground, but cannot get any higher than Vcc minus 1.5 VDC. For a 5 volt power supply, this means that the dynamic range is limited to 0 to 3.5 volt. Ideally, one would like to operate over a wider range on the output so the bit to inch resolution of the following ADC would be finer (i.e., smaller displacement intervals per bit). If one is constrained to a 3.5 volt range representing the entire displacement span of the LVDT/RVDT, then the bit to inch resolution is coarser if the output dynamic range could more closely approach the +V rail (+5 VDC). Given that with the PNP darlington inputs, the ground level dead band is eliminated, it is the +V rail dead band that needs to be minimized in order to expand the dynamic range to obtain finer resolution.
To do this, a special output stage is added. This consists of a PNP transistor 210 which, when driven by an op-amp output signal on a line 214, provides an output signal on a line 216 which can approach +V rail as close as saturation voltage across the PNP will permit. A pair of resistors 218, 220 divide the output of the op-amp 212 in half. Normally, if the input to the op-amp 212 is around 0 volts, the output will limit out at around 3.5 volts. Since the PNP emitter is at Vcc or +5 VDC, the applied voltage across resistor 218 and the base emitter junction would be roughly 1.5 volts. Without resistor 220, transistor 210 would always be in some state of conduction and the output voltages for near zero input voltages would be in error. By putting resistor 220 between the base and emitter, two things occur. First, a modest pullup to op-amp 212 occurs which helps diminish the dead band. Second, the voltage division is such that with the pullup assist, the base emitter voltage is below Vbe. Therefore for a 0 volt input, it is possible for transistor 210 to cease conducting, resulting in a 0 volt output. For anything greater than a 0 volt input, the op-amp 212 will drive the base of transistor 210 the requisite amount since it now can control base drive all the way from cutoff to saturation. When the peak detector outputs a voltage to the op-amp 212 inverting input, the output of the op-amp 212 will drive transistor 210. The collector current through transistor 210 causes a voltage to appear across a resistor 222 and a resistor 224. Because resistors 222 and 224 are equal, the voltage at the collector of transistor 210 (which is the output point), with respect to ground, is twice that of the node 226 connecting resistor 222 and resistor 224. To satisfy the op-amp, this node voltage must also equal the input into inverting side of the op-amp. Therefore, this is a gain 2 stage wherein the output point at the collector of transistor 210 is always twice the input voltage to op-amp 212. Important to note, however, is the fact that the output is capable of operating from ground to almost +V, eliminating the greater percentage of the +V deadband. By design, all preceding stages do not produce a voltage greater than 2.2 volts and thusly are well guarded against getting into the device deadbands. By tailoring these stages to approach, at a maximum, 2.2 volt outputs, making the last stage a gain 2 function was simply assumed since the saturation voltage across transistor 210 can be kept to less than 0.5 volts (permitting a maximum output of 4.5 volts) and the gain to function on a maximum of 2.2 volts inputs would yield a 4.4 volt output: a value reasonably and safely less than theoretical maximum output. A resistor 228 and a capacitor 230 provide degenerative AC feedback to eliminate oscillations that otherwise occur without this compensation.
The LVDT/RVDT secondary output signal conditioning circuit is, for the most part, identical to the peak detector 116 and output stage of the oscillator/excitation stage just described above. The only significant difference is that the gain is four which will amplify the peak detector output up to a maximum of near 2.2 volts for a maximum input from the secondary. A resistor 232 provides just a slight DC offset from ground by a simple voltage division with the 31 secondary winding 110. The peak detector 124 and output stages are otherwise identical to the oscillator/excitation stages just described above.
The circuit design utilizes ratiometric means to set gains. By properly placing the gain setting resistors in any IC, drifting as a function of temperature changes will uniformly and proporationally affect these elements. Accordingly, changes in gain as a function of temperature will be minimum.
By having a measurement channel for both excitation and LVDT/RVDT output, true ratiometric measurement of position is possible. The LVDT/RVDT output is a function of both the excitation voltage and the position along with a sensitivity factor. End of line calibration of the overall system by using calibration displacements will yield an overall sensitivity factor that includes both the LVDT/RVDT and the circuit which can be stored in controller memory and applied to measured excitation and measured output to determine position.
The circuit design shown in FIG. 5 was tailored to a Schaevitz E500 LVTD with 5 kilhertz excitation. To adjust to other LVTD or RVTD with different inductive values in the primary, or to change the excitation frequency, it will be necessary to change the values of capacitor 158, 160, resistor 152, resistor 154, and resistor 156. The ratio between capacitors 158 and 160 should remain the same (i.e., close to a 3:1 ratio as standard values permit) with absolute values adjusted to whatever puts the tank circuit on or about the desired excitation frequency. Note that the bias of transistor 150 in conjunction with the emitter resistor establishes the power amplification which, in turn is reflected as the excitation amplitude in the tank circuit. A change in the load (i.e., tank circuit) requires a change in the other elements to keep the same excitation levels in terms of current and voltage (i.e., power).
Functional testing of the breadboard verified the validity of the concepts being used. The circuit demonstrated response over the entire linear range. For the particular LVDT and circuit breadboard, the demonstrated sensitivity was nominally 7.2 V/inch (7.2 mV/0.001 inch) with demonstrated linearity with less than one percent error over the region between 0.100 inch and 0.500 inch. In terms of resolution, the above sensitivity at a convergence value of 19.5 mV/bit yields a resolveable incremental position change of roughly 0.0027 inches/bit over this 0.400 inch span. Temperature testing of the most sensitive item, the oscillator section, demonstrated that over the prescribed temperature range (-40� C. to +85� C.), using CKO5 type capacitors for capacitor 158, capacitor 160, and capacitor 186 and RN 55 type 1% metal film resistors for resistor 152, resistor 154, and resistor 156, at design values the degradation in oscillator amplitude, and hence excitation, amounted to less than 0.25 volts peak at temperature extremes. Substituting resistors and capacitors with �30% deviations from design values indicated that these same resistors would best be kept external in an IC implementation for accuracy, temperature stability and flexibility if changing to different LVDT/RVDT's. While the oscillator remains operational at these simulated component tolerance deviation extremes at temperature extremes, amplitude was degraded too much. Since IC variations can typically amount to �30%, the external component route for resistors 152, 154, and 156 was empiricaly determined to be a better engineering practice and choice. This choice was also only at the cost of one extra IC pin.
In addition, other external component decisions were made. The next was the peak detector gain setting resistors 206, 208, and their counterparts resistors 234, 236 and peak detector 124. Since different LVDT/RVDT's may be used with different sensitivies from the Schaevitz E500 used in the demonstration, a generic IC would have to adapt to greater or lesser sensitivity and oscillator amplitude to maintain the same approximate system sensitivity, accuracy, and resolution. Finally, the output stage phase compensation was left entirely external inasmuch as the difference in needed compensation for a breadborad versus an actual IC is not known at this time.
Although the invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of this invention.
|Cited Patent
|Filing date
|Publication date
|Sep 8, 1969
|Aug 17, 1971
|Daniel Ind Inc
|Method and apparatus for linearizing the signal output of an lvdt responsive to nonlinear input motion
|Oct 1, 1976
|Oct 11, 1977
|Systron Donner Corporation
|Oscillation means for generating a differential AC signal proportional to movement of a conducting member
|Jun 24, 1976
|Aug 22, 1978
|A. O. Smith Corporation
|Position sensing differential transformer system with means to convert the output to an absolute value
|Oct 1, 1981
|Dec 13, 1983
|Burroughs Corporation
|Self oscillating acoustic displacement detector
|Citing Patent
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|Aug 20, 1987
|Oct 25, 1988
|Nec Corporation
|Carrier recovery circuitry immune to interburst frequency variations
|Sep 14, 1987
|Aug 15, 1989
|Conoco Inc.
|Method and apparatus for indicating the position of a core member of a variable differential transformer
|Sep 2, 1988
|Jan 1, 1991
|Allied-Signal Inc.
|Position transducer apparatus and associated circuitry including pulse energized primary winding and pair of waveform sampled secondary windings
|Apr 7, 1989
|Nov 19, 1991
|Sundstrand Data Control, Inc.
|Apparatus and method for sensing displacement using variations magnetic flux linkage
|Dec 2, 1991
|Jan 19, 1993
|Honeywell Inc.
|Proximity sensor with reduced temperature sensitivity using A.C. and D.C. energy
|Feb 8, 1991
|Sep 7, 1993
|Sundstrand Corporation
|Differential angular velocity sensor that is sensitive in only one degree of freedom
|May 24, 1993
|Oct 8, 1996
|Cj Design & Engineering, Inc.
|Force sensor
|Feb 2, 1995
|Apr 1, 1997
|Otis Elevator Company
|Industrial contactless position sensor
|May 7, 1999
|Jul 25, 2000
|Airpax Corporation, Llc
|AC current sensor having high accuracy and large bandwidth
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|Aug 14, 2001
|Teradyne, Inc.
|Remote test module for automatic test equipment
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|Mar 8, 2005
|Goodrich Pump & Engine Control Systems, Inc.
|System and method for processing a signal
|Jul 20, 2004
|Aug 8, 2006
|Infinia Corporation
|Displacement sensing system and method
|Jan 27, 2006
|Jul 24, 2007
|Alliant Techsystems Inc.
|Digital method and apparatus for sensing position with a linear variable differential transformer
|Feb 21, 2006
|Jun 24, 2008
|The Boeing Company
|Linear variable differential transformer (LVDT) system using an inductance of an LVDT primary as a micro-power excitation carrier frequency to lower a drive power
|Apr 24, 2009
|May 3, 2011
|Honeywell International Inc.
|Quarter cycle waveform detector
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|Sep 18, 2012
|Asylum Research Corporation
|Linear variable differential transformer with digital electronics
|May 13, 2011
|Apr 29, 2014
|Honeywell International Inc.
|Method and apparatus for detection of LVDT core fallout condition
|Sep 24, 2010
|Oct 14, 2014
|Broadcom Corporation
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|Dec 23, 2014
|Panasonic Corporation
|Phase-shift detection device, motor drive device, brushless motor, and phase-shift detection method
|Aug 30, 2010
|Jan 6, 2015
|Broadcom Corporation
|Variable gain control transformer and RF transmitter utilizing same
|Jun 9, 2010
|Aug 18, 2015
|Broadcom Corporation
|Adaptive powered local oscillator generator circuit and related method
|Feb 8, 2013
|Dec 27, 2016
|Hamilton Sundstrand Corporation
|Transformer based sensor arrangement
|Jan 29, 2002
|Jul 31, 2003
|Mcbrien Gary M.
|System and method for processing a signal
|May 27, 2003
|Mar 25, 2004
|Dan Bocek
|Linear variable differential transformer with digital electronics
|Aug 28, 2003
|Mar 3, 2005
|Tulpule Bhalchandra R.
|Reconfigurable sensor signal demodulation system
|Jul 20, 2004
|Jan 26, 2006
|Stirling Technology Company
|Displacement sensing system and method
|Jan 27, 2006
|Aug 2, 2007
|Stolan John A
|Digital method and apparatus for sensing position with a linear variable differential transformer
|Feb 21, 2006
|Aug 23, 2007
|The Boeing Company
|Low power LVDT orthogonal magnetic signal conditioner
|Apr 24, 2009
|Oct 28, 2010
|Honeywell International Inc.
|Quarter cycle waveform detector
|Aug 30, 2010
|Mar 1, 2012
|Broadcom Corporation
|Variable gain control transformer and RF transmitter utilizing same
|Jun 30, 2011
|May 9, 2013
|Panasonic Corporation
|Phase-shift detection device, motor drive device, brushless motor, and phase-shift detection method
|Feb 8, 2013
|Aug 14, 2014
|Hamilton Sundstrand Corporation
|Transformer based sensor arrangement
|Dec 12, 2014
|Jun 18, 2015
|Robert Bosch Gmbh
|Safe Position Measuring Apparatus
|Feb 3, 2014
|Nov 4, 2015
|Hamilton Sundstrand Corporation
|Transformer based sensor arrangement
|Mar 12, 1990
|Oct 18, 1990
|Sundstrand Data Control, Inc.
|Low distortion linear variable displacement transformer
|May 7, 1999
|Nov 11, 1999
|Airpax Corporation, L.L.C.
|Ac current sensor having high accuracy and large bandwidth
|May 7, 1999
|Apr 6, 2000
|Airpax Corp L L C
|Ac current sensor having high accuracy and large bandwidth
|May 27, 2003
|Dec 4, 2003
|Asylum Research Corporation
|Linear variable differential transformer with digital electronics
|May 27, 2003
|Jan 29, 2004
|Asylum Research Corp
|Linear variable differential transformer with digital electronics
|U.S. Classification
|327/104, 324/207.18, 327/336, 327/65, 340/870.36, 327/91
|International Classification
|Cooperative Classification
|European Classification
|Oct 1, 1984
Owner name: UNITED TECHNOLOGIES CORPORATION, HARTFORD, CT., A
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:MC CORKLE, GARY A.;REEL/FRAME:004319/0508
Effective date: 19840924
|Oct 6, 1987
|Certificate of correction
|Oct 16, 1989
|Fee payment
Year of fee payment: 4
|Aug 1, 1991
Owner name: HAMILTON TEST SYSTEMS, INC., ARIZONA
Free format text: ASSIGNS THE ENTIRE INTEREST, SUBJECT TO LICENSE RECITED;ASSIGNOR:UNITED TECHNOLOGIES CORPORATION;REEL/FRAME:005782/0820
Effective date: 19901213
|Jan 4, 1994
|Maintenance fee reminder mailed
|May 29, 1994
|Lapse for failure to pay maintenance fees
|Aug 9, 1994
|Expired due to failure to pay maintenance fee
Effective date: 19940529


text:
Massage Away
The Studio
Gillam House Yard
07570 865234
Massage Away
The Studio
Gillam House Yard
07570 865234
Massage Away
The Studio
Gillam House Yard
07570 865234
Massage Away
Holistic Health and Beauty
My name is Tara Linkowksa. I am a fully qualified Spa and beauty therapist who provides holistic massage and beauty treatments in Ulverston, Cumbria.
I use a selection of the finest quality products in my massages, facials and other body treatments to suit the individual needs of my clients. Botanicals personal care and wellness products are blended by hand using only carefully selected natural and organic ingredients - and absolutely no petrochemicals or synthetic additives.
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OCR Level 2 NVQ in Customer Service
VTCT Level 2 in Aromatherapy (using pre-blended oils)
VTCT Level 3 Spa Therapy
VTCT Level 2 in Beauty Therapy
Access to Higher Education Level 3 Diploma (Allied Health)
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A wonderfully relaxing massage to soothe the mind body and soul. The time will be spent focusing on your area of need.
45 minute appointment required
Swedish 30 minute massage
A more vigorous and firm massage for those with deep seated tension. We can focus on back, neck and shoulders or lower body and legs.
45 minute appointment required
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Time to unwind and spend some time focusing on yourself. A relaxing massage for the whole body.
90 minute appointment required
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A deeper massage to be rid of all those aches and pains of daily life.
90 minute appointment required
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A luxury treatment with unrivaled benefits. The use of aromatherapy oils, carefully selected to suit your particular needs on the day. Take it to the next level with Chakra balancing for ultimate re-energizing. A massage from head to toe and back again.
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Can include the use of Chakra analysis and placement of Semi-precious stones along with the hot basalt stones and cold marble or marine stones for total well-being.
45-90 minute appointment required
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Ayurvedic therapy at its finest. The main pressure points are worked on to begin, opening the energy pathways through the body. With massage focused on the head neck and shoulders.
60 minute appointment required
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Cleanse, tone and exfoliation
finished with the application of moisturiser
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The full works; cleanse, tone, exfoliation, mask, massage and moisturise
The application of professional make-up. Perfect for any special occasion
Make-up Lesson
The application of make-up along with personal tutorial
Bridal Make-up
Care and attention is focused on the bride for this most special occasion.
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A slimming and contouring body wrap with the best proven results. See it to believe it.
£35 for 1
£200 for 6 sessions
Manicure & Pedicure
File, cuticle removal and application of polish
Luxury Manicure
File, cuticle removal, mask and massage finished with the application of polish
File, cuticle removal and application of polish for the toes £12.00
Luxury Pedicure
File, cuticle removal, foot soak, removal of hard skin, mask and massage finished with the application of polish
Nail Art/French Polish supplement Add some dazzle to your manicure or try the ultimate in manicure elegance
Gel Polish A basic manicure with the application of gel polish, up to 14 day wear and chip resistant £18.00
Gel Nails
The application of tips covered with a gel overlay to give a natural look
Acrylic Nails
The application of tips finished with acrylic overlay. Allows to sculpt the clients requirements £20.00
Waxing & Eye enhancements
Half leg wax
Removal of hair up to the knee using warm wax
Full leg wax
Removal of hair up to the bikini line using warm wax
Bikini wax
Removal of hair from the bikini area using warm wax
Eyebrow wax
Removal of hair to help shape the natural brow line
Eyebrow Tint
Colouring of the brow to enhance the appearance
Eyelash tint
Tinting of the lashes to enhance for a fuller look
Lash and brow tint
Including brow shape
Weekend Lashes
The application of individual flare lashing to enhance the appearance of the eyes
Holistic Health and Beauty Therapy
Spa in itself is so diverse. Think of all the different types of massage, where the origins of those techniques came from and how they are put into practice in our modern world. There are always new techniques coming into the industry but they can all be traced back to thousands of years ago when massage and beauty products were used by ancient civilizations like the Egyptians.
As far back as 5000BC in India Ayurvedic medicine (including massage) was practiced and this is where many of the other healing systems, including those developed in China, Tibet and Greece are said to have been derived.
3000BC water therapy and herbal treatments were used by the Egyptians and later this knowledge was passed over to the Greeks who believe the physical properties of water had unique healing powers and this then passed down through the Romans and Turkish people.
Later, European spa's where water is used again, were developed for their healing properties.
A Swedish masseur, Peter Henry Ling, Developed the Swedish massage technique. This is one of the most popular massage treatments within spa's today. He believed that there needs to be underpinning knowledge when it comes to applying massage, i.e. Anatomy and Physiology and the way the body systems work.
Since the 1900's many other masseuses developed their skills and it was decided certain standards of practise for safe massage and regulations were set. In 2000, Spa therapy qualifications were developed as the industry has grown so large.
Aromatherapy has been used for thousands of years, but over the past 10 years it has increased in popularity within spa's. Aromatherapy, as its name implies, is the use of aroma's (smells) during a treatment. The aroma's are made from the extraction of essential oils from plants, trees' and fruits. Their individual properties are known to benefit particular physical and psychological problems, e.g. lavender is said to be good to treat stress and minor skin problems.
The massage itself uses slow rhythmic strokes and pressure points to help release any blocked energy within the body.
There are specific contra-indications to aromatherapy massage, as the oils can be quite potent. Certain oils can not be used on clients who may be pregnant or who are breast feeding for example.
If you have been diagnosed with or suspect you may have a pre-existing medical condition you should consult your GP for advice, diagnosis and treatment and always inform your health professional before starting any alternative or additional therapies, treatments or making any major changes in your diet or exercise programme.
|Sign language:
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subset: commoncrawl


text:
Hermes Silk Scarf '' Concours d` etriers '' Authentic Pre Owned
Authentic: Pre Owned
This is an authentic pre owned Hermes Silk Scarf. Featurin Blue, and Gold It won't last long!
- Condition: Like New
- Color: Gold
- Length: 35 in.
- Width: 35 in.
Product Code: 1983024
All photos are of actual item being sold. This Hermes® item is guaranteed to be authentic. Hermes is a registered trademark of Hermes. LuxeDH is not affiliated with or represents Hermes in any way or form.
New Arrivals


text:
For you my friend by hiaamirWatch
©2013-2017 hiaamir
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Beautiful birthday gift, dear Aamir!


text:
Home near Lake Eloika w/ 3 bedroom and 2.5 baths, 2 car garage on 9.27 acres with 20x36 shop/barn. Large living area with wood burning fireplace & built in bookshelves, vaulted beamed ceiling with dormer window. Open kitchen w/ beautiful cabinets, eating bar, double ovens, secretary counter w/ abundance of natural light. Master has 2 separate sinks, tiled, jetted tub, large shower & walk in closet. Spacious utility room with cabinet sink. Gargage is sheet rocked & taped. Additional adjoining lots available.
Listing courtesy of SARMLS / Live Real Estate, LLC
Listings last updated . All information provided is deemed reliable but is not guaranteed and should be independently verified.


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You know how I like comfy outfits and I'm definitely not a dress code girl, so you see what I wear everyday and here is an outfit from more than two weeks ago, when my vacation just started. I lost count on how many times I've worn this skirt, and every time I enjoy to wear it, even with my silk pajama shirt and new Topshop X Adidas Originals sneakers.
Thanks for stopping by and have a great week ahead! See you in my next post! xo
Marks&Spencer pajama shirt, Denim Co skirt, Topshop X Adidas Originals sneakers, Proenza Schouler ps11 bag


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8951 Tasting Notes
first cup of the morning because i really wanted to start the day with something i knew that i love. With so many samples in my cupboard, it's hard not to rush through them all…but since they can be hit or miss, it's nice to have a few cups of things i like for sure.
:) at least i'm finally getting to a point after 2.5yrs that i know what the old favourites are that i want hahaha
I can see why ost might not have liked these. Again, i'm finding the teas from What-cha to be just a little different than other teas that i've had from other companies. Not bad, just different…i'll have to look in to whether it's the regions or what…though i know on some of them that IS the difference.
These are deep, heavy pearls….they do have a malty taste to them but there's also a note in here that isn't honey…it's a bit of a sweetness – maybe cherry? with something that could almost be smoke if you thought too hard about it lol
Description on this one says stunning chocolate aroma and taste. All that makes me want to do is see if omgsrsly gets dirt from this one too. dry, this really does smell like chocolate/cocoa. However, i get more of a metallic, earthy sort of taste to this while drinking it. it'll be intersting to see how others find this one…as it's another "different" tea. having fun with these what-cha samples.
I really need to stop looking at What-cha's site or my resolve is going to break down and I'm going to place another order.
Another one from MissB as i desperately need to finish up those teas so that i can get them parcelled out and shared with everyone else lol I wasn't a huge fan of this one…it tasted more like a generic "christmas spice" sort of tea than anything else. It wasn't bad, but nothing i'm dying to have again or keep around…
this was a sample included in my dragon tea house order and one that i would totally pick up again, though it's VERY similar to other teas that i love for the same reasons…malty, cocoa-y, dark and delicious. So price would factor in..also the shipping…DH took over a month to get to me, which makes me a sad panda.
I'mfinding tjhast custos is holding Chinese packages for quite a while recently. They held teavivre for close to a week and one of my Ali purchases for close to three weeks. I wonder if they're back logged or it's a work to rule thing going on? Neither would surprise me.
I couldn't resist picking this one up from what-cha during their sale, because of the name lol. What exactly does and old lady tea taste like? well in this case, there's a fruitness here, which i guess you could call citrus, but i have a hard time distinguishing specific citrus tastes a lot of the time. this has echoes of your typical "red rose" tea but feels fancier and with more depth. Over all, a nice little cup for my first experience with What-Cha
i told omgsrsly that i would try this one today since we both ended up ordering it from CS during their sale the other week. This tea has super cute little curly buds that made me smile as i wasn't expecting that today.
So i don't actually get cocoa from this one…it's more of a slightly sweet, malty tea..with a hint of "dirt?" lol maybe there's a little cocoa there in the background if i concentrate, but this one is vastly different from other cocoa/chocolatey teas that i've had. I'll have to try this one gonfu as well to see how that changes things up.


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Wallström presented the ruling centre-left Social Democrat-Green coalition government's foreign policy declaration for the year in the Riksdag on Wednesday morning, continuing an annual tradition.
One of the key points is that the government will appoint a diplomat to work full-time on the Israel-Palestine conflict. The special envoy is to establish contacts and represent Sweden in international talks about the conflict.
"This year marks 50 years of the occupation of Palestine. Sweden continues to work for a resolution of the Israeli-Palestinian conflict and will appoint a special envoy," Wallström told the Riksdag.
"When I visited Palestine in December it was noticeable that hope can turn to despair, and this features heavily in the consultations that Sweden is holding with almost 150 Israeli and Palestinian civil society organizations," she added.
Sweden's relationship with Israel has been increasingly frosty in the past few years. In 2014 it recognized Palestine as a state, and Israeli officials have routinely refused to meet Wallström after she called for investigations into "extrajudicial" killings of Palestinian assailants by Israeli forces.
Wallström also addressed Britain's decision to leave the EU in her speech, saying that Sweden will act according to what best serves Swedish and European interests once Brexit negotiations start.
Without mentioning US president Donald Trump by name, she also said that "relations with the new US administration remain important for our trade and our security", adding, "but the White House's actions raise questions about the role of the United States in the world".
Wallström is set to meet her Russian counterpart in the near future, and the Foreign Minister insisted that Sweden will "maintain a political dialogue, take a long-term view, urge Russia to pursue cooperation rather than confrontation, and promote people-to-people contacts".
Sweden is currently a non-permanent member of the UN Security Council. The foreign policy declaration to parliament is seen as the country's official stance on international affairs and is usually attended by foreign diplomats as well as members of parliament and Swedish officials.


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If you're interested in learning more about our advisory services, please fill out the form below and a member of our team will be in touch!


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The historic Philo Lock #9 is open again after receiving repairs.
It temporarily closed when a concrete wall collapsed back in February. The Ohio Department of Transportation says only some minor work remains on the project, which deals with land-based construction.
Ellis Lock #11 near Dresden still remains closed and has for the past decade.
These historic locks, located along the Muskingum River are operated by Ohio State Parks. They were built back in the 1840's and still need to be operated by hand.


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Yesterday a group of anti-capitalists joined forces to protest the G-20 summit in Pittsburgh, PA. The police broke them up because, here's a shock for you, the anarchists didn't have a permit! Well, the AP calls this "a group of anarchists," but we know who this really is and I think I can prove it. Just to get a feel for how this group approaches the art of protest, here's a description from the AP.
Protesters split into smaller groups. Some rolled large metal trash bins toward police, and a man in a black hooded sweat shirt threw rocks at a police car, breaking the front windshield. Protesters broke 10 windows in a few businesses, including a bank branch, a Boston Market restaurant and a BMW dealership, police said.The AP concludes that the group is a collection of anarchists because they were holding anarchy symbols. However, if you saw a group of people holding signs that said, "No borders. No banks," "No Hope in Capitalism," and "Kick capitalism while it's down!" wouldn't you think this was either the Michael Moore fan club or a gathering from your local young Democrats club?
And who do we find at the protest?
Billy Talen - Where to start? I'll let his wiki page explain it to you if you're interested. If you want the twitter description: "A questionably insane liberal activist who uses often illegal public disturbances to get his message across."
T.J. Amick - This guy might actually be an anarchist. His facebook page says he like sour gummy bears, Adam Sandler, and he has the Ramen Noodles app installed. I think he showed up at the protest because he heard there was a 60% chance of weed.
The National Lawyers Guild - The article describes them as "a liberal legal-aid group," so I'm thinking they're probably not anarchists.
Stephon Boatwright - According to his Facebook page he is a fan of "The Socialist Party USA" (AKA unlikely an "anarchist"). I dare you to look at their website. Aside from the terrible layout and overuse of red, it could easily double as a website for a Democrat PAC. In case you were wondering, they do favor universal health care, which seems to be the opposite of anarchy, right?
So the tally at the end of the day is one socialist, one crazy person (counts as a liberal), one liberal legal defense group, and one normal-sounding dude (possibly an anarchist.)
So you're probably wondering how I could see this protest as a group of leftist radicals. You see, liberals are often found at events like this because they can rarely tell the difference between anarchy, socialism, and their own positions because the liberal position falls somewhere in the middle of socialism and anarchy.
Remember Amanda Duzak from just a few weeks ago? She's the environmental activist who challenged Michael Steele in order to promote universal medicine. Then her MySpace page had a picture of her holding an anarchy symbol at a protest.
The mind of a liberal is a sad and confused place.


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Category: Template, Business Cards
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text: Does anyone have it? I noticed it missing from fresh1.0. I still see it under wireless settings. I activated it and my laptop found it as something like "EVO B1****" (* = random numbers). It asked for a password, so I tried "00000000", and it would actually connect for a second and instantly drop.


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After the war lots of left wingers attempted to harbour or hide weapons in dumps which had been made available by the government because they believed that it would be necessary to ensure that any future election of a labour party with a popular left wing agenda "safe", either from establishment "strikes", betrayals under pressure from capital flight, the military or communist infiltrators.
Winteringham, or winterington, I cant remember which is the right spelling, was a member of a break away party called commonwealth, which was itself a break away from the independent labour party, a left wing fringe group which Orwell was assisted by in passage into and escape from Spain, they resisted war with Germany for a long time on the basis that it would involve raining bombs on German socialists organising a fight back against Hitler from with Germany.
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Thread: Random Thought Thread
01-28-2013, 03:17 PM #31581It is a luxury to be understood - Ralph Waldo Emerson
Those who can make you believe absurdities, can make you commit atrocities - Voltaire
A kind thought is the hope of the world - Anon
01-28-2013, 03:52 PM #31582It is a luxury to be understood - Ralph Waldo Emerson
Those who can make you believe absurdities, can make you commit atrocities - Voltaire
A kind thought is the hope of the world - Anon
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Mia: I appreciate your eloquent post, you're clearly an intelligent guy who I actually enjoy reading (not many people on TypoC I enjoy reading).
In this case though, that eloquence just serves to cover up complete underlying confusion.
In addition to what @Lark said (which I did not know, and I thank him for the historical information):
However, he did not, because a "people's militia" controlled by the central government and military command, and completely subordinate, is not dependent on "the right to bear arms" in peace time. In fact many of the totalitarian regimes which US gun nuts frequently cite as an example of the tyranny that arises when there is no right to bear arms - the Soviet Union, Iran, Venezuela (well not sure if this is totalitarian - yet - but you get my point) have "people's militias".
Not to mention Iraq (and look how well that went for them).
If the gun-loving Americans had not joined the war you'd very likely be speaking either German or Russian.
But what's the relevance of this? I love guns too - in the right hands. I have no issue at all with the US being a military superpower. But I am struggling to see the relevance of your right to buy over the counter rifles, to the fact that the US has the world's most advanced military technology.
This was only 70 years ago. Those who do not learn from history are doomed to repeat it dude.
it won't ever happen, either. *wink wink*
Having said this - if any military power was successful enough to get past the British Army, a nuclear superpower and one of the world's best equipped militaries and wealthiest states, with one of the world's largest arms production industries at its disposal and 10's of millions of healthy young men and women potentially ready to be conscripted - then it would take a bit more than some over the counter rifles to deter them AFTER all that. Don't you think?
By the way:
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01-28-2013, 05:30 PM #31585garbageGuest
01-28-2013, 07:56 PM #31586GlycerineGuest
I want to drink... vodka.
Peace of mind, how it proves elusive.It is a luxury to be understood - Ralph Waldo Emerson
Those who can make you believe absurdities, can make you commit atrocities - Voltaire
A kind thought is the hope of the world - Anon
Japanese soca/hip hop/reggae? Ok.
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Also, my sub-point that the citizens are the final defense in such a situation also stands, regardless of how you want to classify their organization.
If it makes you happy to own a gun then who am I to tell you otherwise? Maybe I should be clear, I don't wish to dictate to your country what you should do, and maybe I have come across that way.
However you guys should be aware of your tone as well. When you tell people that tighter gun control will lead to tyranny and invasion, the rest of us who experience otherwise - and who enjoy the same freedoms as you do - will call bullshit. Maybe some of your population believe those scare stories, and I think they have a right to know the truth.
So again, I don't want to take your guns away, it's your country and I respect it. But don't expect people to accept the argument that it's a defence against tyranny or invasion. You might as well learn karate or buy a bow and arrow. Warfare has moved on since 1776.
Nice try, doll. I'll take the kiss, though.
Soon may the Wellerman come and bring us sugar and tea and rum.Masquerading as a normal person day after day is exhausting.
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In this paper, we examine the impact of adopting a comprehensive school health (CSH) approach on reducing anxiety and depression of school-age children. We use the data from 245 schools that received government funding support to adopt a CSH approach in order to build health promoting school environments in Alberta.
Read the full paper here!
Anaylisis of TTFM data presents statistical associations between social-emotional wellbeing and bullying.
Click here to view the report!
Findings related to the relationships/correlations between wellness indicators and students' academic achievements. A summary of the reports can be found here.
TTFM Report Version 1
TTFM Report Version 2
The Alberta Healthy School Community Wellness Fund has developed a number of resources to assist in the development of healthy school communities. These resources have been compiled to create the Developing Healthy School Communities Handbook. Check back from time to time for updates to the handbook.
The Wellness Fund is pleased to offer the Developing Healthy School Communities Handbook in French.
Manuel Développement de Communautés Scolaires en Santé (PDF)
Developing and Sustaining a Healthy School Community:
Essential Elements Identified by Health Champions
Key concepts, approaches and strategies used by Wellness Fund Projects developing Healthy Relationships among grade 7-12 students while addressing responsible sexual behaviour.
Click here to view the report!
The Wellness Fund introduced high school wellness grants to provide support for Alberta's high
schools to embed health and wellness cross-curricular using a whole school approach, following a
comprehensive school health framework.
Click here to view the report!
In school communities everyone has a responsibility for wellness because healthy students are better learners and better educated students are healthier. Amendments to The School Act in Alberta require that students, parents and school authorities share the responsibility for ensuring welcoming, caring, respectful and safe learning environments that respect diversity and nurture a sense of belonging and a positive sense of self.


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Letter to the editor: Legislature should honor the intent of the voters
As the former chief medical officer at the North Dakota Department of Health, I know from experience the influence the tobacco industry and their allies can have on the Legislature, Health Department and governor's office. Because of this past influence, an independent advisory committee will be much more effective than the health department in administration of the funds allocated by Measure 3 for a comprehensive tobacco use prevention program.
The voters passed Measure 3 in November and Measure 3 established an advisory committee and executive committee. If the Legislature bypasses these new committees, they will be altering the voters' intent. The people have spoken and the Legislature should honor and respect their vote.
Stephen McDonough


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Imagine a picture of a forest from above, full of life. What if I then gave you the information on every single plant, tree, flower, animal, insect and weed in the area, how could you possibly make sense of it all?
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What if there was a better way to search for your images other than trying to describe what you are looking for and then hoping that someone has tagged or labelled that image with the right information. This is the future of Zegami, over the next year in conjunction with Oxford university and our development team we are going to turn Zegami from not just an amazing visual experience that enables you to intuitively search on your data but also search based on the image itself or parts of the image. Currently no other enterprise level software gives users that flexibility or functionality.
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Use the sliders to filter based on a numeric range or plot two ranges as a scatter plot and just draw around the area of interest.
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text: Hello, I am a full time student and have setup as self employed and in April 2011 will be launching a small business. I don't have much capital to start the business but obvoiusly I need a logo which will be strong and clear, as well as look professional. I know that a logo designer will not just design me a logo for free, so was wondering if there are other students who are looking to build a portfolio for University? I understand that when applying for a Graphic Design course at university the student has to provide a portfolio at their interview, which includes logo designs - so thought that this would be a good opportunity on both side. Are there any student designers on here or do you know of any? Many Thanks :up:


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About Get Involved! Power Hour: Come join difference makers and passionate leaders at the Get Involved! Power Hour. Each quarter we bring together difference makers to brainstorm ways to positively influence the region, assist each others businesses and organizations, and develop connections. We also feature panelists who share about ways that you can Get Involved! and make a difference.
Reserve your spot by RSVPing to Councilman Baker at email@example.com
We will have a terrific panel focused on being active in the community at our 56th Get Involved!, Inc. POWER HOUR on Monday, January 25, 2016! Power Hour will take place at CLADDAGH (407 Cinema Drive – next to SS Works movie theatre) in the South Side this quarter. Power Hour is hosted by Councilman Tom Baker and Laura Amster.