is detected and decoded by monitoring changes in inductance of an AC circuit that includes an inductive coil sensor. Maxon makes an example (rotary encoder) product (the MILE encoder). Without scales Optical image sensor The sensors are based on an image correlation method. The sensor takes subsequent pictures from the surface being measured and compares the images for displacement. Resolutions down to a nanometer are possible. Applications There are two main areas of application for linear encoders: Measurement Measurement application include coordinate-measuring machines (CMM), laser scanners, calipers, gear measurement, tension testers, and digital read outs (DROs). Motion systems Servo controlled motion systems employ linear encoder so as to provide accurate, high-speed movement. Typical applications include robotics, machine tools, pick-and-place PCB assembly equipment; semiconductors handling and test equipment, wire bonders, printers and digital presses. Output signal formats Incremental signals Linear encoders can have analog or digital outputs. Analog The industry standard, analog output for linear encoders is sine and cosine quadrature signals. These are usually transmitted differentially so as to improve noise immunity. An early industry standard was 12 μA peak-peak current signals but more recently this has been replaced with 1V peak to peak voltage signals. Compared to digital transmission, the analog signals' lower bandwidth helps to minimise EMC emissions. Quadrature sine/cosine signals can be monitored easily by using an oscilloscope in XY mode to display a circular Lissajous figure. Highest accuracy signals are obtained if the Lissajous figure is circular (no gain or phase error) and perfectly centred. Modern encoder systems employ circuitry to trim these error mechanisms automatically. The overall accuracy of the linear encoder is a combination of the scale accuracy and errors introduced by the readhead. Scale contributions to the error budget include linearity and slope (scaling factor error). Readhead error mechanisms are usually described as cyclic error or sub-divisional error (SDE) as they repeat every scale period. The largest contributor to readhead inaccuracy is signal offset, followed by signal imbalance (ellipticity) and phase error (the quadrature signals not being exactly 90° apart). Overall signal size does not affect encoder accuracy, however, signal-to-noise and jitter performance may degrade with smaller signals. Automatic signal compensation mechanisms can include automatic offset compensation (AOC), automatic balance compensation (ABC) and automatic gain control (AGC). Phase is more difficult to compensate dynamically and is usually applied as one time compensation during installation or calibration. Other forms of inaccuracy include signal distortion