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I am working with 40 sensors and almost all the sensors are mechanical. I have some potentiometers converting mechanical displacement into voltage but the resistance of the voltage source is changing dynamically in field. The potentiometers I am using are in the range of 10K to 10M ohm.

It seems that I can't place a passive impedance matching circuit there so anybody tell me what is effective way of impedance matching in this type of case?

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  • \$\begingroup\$ why do you need impedence matching for potentiometers? \$\endgroup\$ – KyranF Oct 31 '14 at 9:32
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    \$\begingroup\$ Op amps configured as voltage followers \$\endgroup\$ – Scott Seidman Oct 31 '14 at 10:32
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I agree with Scott Seidman in his comments here, I think the easiest way is to just use a buffer with general purpose op-amps to provide extremely high input impedance. The input input impedance will allow you to detect the voltage given out by the various potentiometer's wipers, without affecting the circuit by having any other loads in parallel.

It does not matter what the resistance of the potentiometer used is, if you are only interested in the wiper's variable voltage output between 0 - 100% (which is probably what you are doing).

Shown below is a non-inverting voltage follow/buffer, and the series 1K resistor is to help limit input current if something goes wrong on the potentiometer. You may want to throw a few low value capacitors in there too, to help with noise immunity. The value R2 being 10K is just arbitrary, to reduce overall power consumption but depends on your ADC's preferred input impedance.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ You can very easily buy 6-8 buffers pre-configured for less PCB space in one package. look for non-inverting Hex buffers. Just whack 5-6 of these on a PCB and interface all your sensors to this, and then off to your controller \$\endgroup\$ – KyranF Oct 31 '14 at 14:39

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