Connecting A Linear Potentiometer To A NI 9215

[Mark321]

Hi,

Could anyone recommend how to connect a 10k linear potentiometer to a NI 9215 with the DAQ Express software and have it read the resistance of the potentiometer throughout its full range fairly accurately. I currently have 5V running across the connection with the current parameter at 1mA.  I'm try to use the linear pot as a rough measure of distance.  The output signal does not read out linearly as the resistance goes from 0 to 10K.  As expected it reads fairly accurately around 5k, then it spikes up or down from there.

Thx,

Mark

[Henrik_Volkers]

Some points come into my mind:

potentiometer linearity:

For a common pot in the 1% to >5% range depending on type, so a calibration would make sense. If not build for angular or length sensing, the end points can be very nonlinear .. one idea would be to use a 10 turn precision potentiometer, even if you only use a fraction of it, the linearity is usually speced (and better) and I assume the resolution is limited by mechanics anyway 😉  (hysteresis, friction)

input impedance of the 9215:

if you habe the BNC version the input impedance is 200k Ohm, that influences your measurement.

Spikes:

Dust on pot and/or wiper lift-off (speed and dust) ? Or spikes on the 5V ?

Depending on the dynamics of your measurement, filter can help, I would try a median filter against spikes and a mean filter over at least one line frequency periode if possible.

So an individual calibration would be recommended, depending  on the result, make a fit with an apropriate polynom or a lookup table with interpolation.

I have never seen a non broken/abused/burned/dirty  potentiometer with a non monotone output. Keep in mind that potentiometer are build for quite rare use. Industrial potentiometer sensors have a price for a reason 😄

Finally, since you measure a voltage ratio, it's alway a good idea to measure both voltages ; )  so if you have a spare channel, measure pot supply and wiper output.