# Signal conditioning for a wire-wound pot

#### dandedandelion

##### New Member I am having difficulties with solving question number 2.

Below is the circuit that was provided in the mark scheme. I am having a hard time understanding the circuit.
1. I believe R_s is the sensor, i.e. the potmeter described in question 1, am I right? In that case, why would we place it here?
2. Why do we have a voltage divider at the beginning of the circuit. And why is the input to the inverting amplifier set to -1.0V? Is the potmeter on the far left just used for tuning?
3. Why do we have an inverting amplifier and a differential amplifier RIGHT AFTER? I don't understand why we would want that as their use is very similar. (Is it just to multiply by -1? (Don't know if this makes sense...))

Is this the easiest solution? Wouldn't it be easier to just measure the voltage over the wire-wound pot and then fix the range?

How should one think when approached with a question like this?

All help is very much appreciated!

#### Ramussons

##### Active Member
This is a Homework question, the schematic is given. Don't waste time questioning the setup.
1. I believe R_s is the sensor, i.e. the potmeter described in question 1, am I right? In that case, why would we place it here?
Yes, it is the sensor. Why cannot it be placed here?
2. Why do we have a voltage divider at the beginning of the circuit. And why is the input to the inverting amplifier set to -1.0V? Is the potmeter on the far left just used for tuning?
That voltage divider with that voltage exists.
Presume that the resistors used in that divider have values far less than the 25K of R2.
3. Why do we have an inverting amplifier and a differential amplifier RIGHT AFTER? I don't understand why we would want that as their use is very similar. (Is it just to multiply by -1? (Don't know if this makes sense...))
That is the given schematic. Analyse the schematic, determine the output with the given values.
See what needs to be changed to get the required output.

The first opamp has a gain with an offset, the second is another opamp with a fixed gain and 2 inputs.

Just do a brush up on OpAmp fundas.

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