Potentiometer linearity test using create and limit

[Toro]

We need to test for an open pot (this happens only for briefs moment). I am appling 5VDC @ 10mA to the 10K pot and using a manual crank and gear  arrangement we rotate the pot. When the pot is rotated we get a slop signal at the scope. I am trying to use create VI and the limit VI to check for the voltage drop but it seems it only work with waves signals not voltage. Any ideas.

[unclebump]

I modified the waveform create and limit mask vi's to work on array data instead of waveforms. I can attach them when I get back to my desk.

[unclebump]

See if the .llb file in this thread helps.

http://forums.ni.com/ni/board/message?board.id=170&message.id=145550&view=by_threading&page=2

[Toro]

Thanks for the reply. I can not open the llb or the vi they are on the wrong version of LabView I am still using Ver 6.1. Could you make it Ver 6.1. Thanks

[unclebump]

I think this will work in 6.1

[Henrik_Volkers]

---

@Toro wrote:

@...I am appling 5VDC @ 10mA to the 10K pot ...

---

should be 0.5mA ... or 100V ... or 500R  or simply U=R*I shouldn't it

If you go for a linearity test : does the absolute value matter ? Do you correlate (angle) position to voltage or move the wiper at constant speed and look at dU/dt?

If it's 'just' linearity (how is it defined?), i would take the hole slope and calculate the linearity instead of having a good / bad window.

[Toro]

I am testing an a constant speed. I may use the wrong words to describe what I want it to said.

We are not to worry about the linearity of the pot. What we are more concern is the lost of signal during the pot running.

Because of a design problem with pot the wiper has a tendency to loos contact with the surface of the resistance area of the pot.

Because of the constant speed, the signal shows up as an  angle, I totally forgot I could do dU/dt, thanks for the eye opening.

[AnalogKid2DigitalMan]

Toro:

You may want to take note of the axial force the crank/gear mechanism applies to the shaft of the potentiometer. If you are experienceng intermittant opens on the wiper, forces exerted through the shaft to the wiper can affect your results, depending on how mechanically robust the design is. I have seen opens in pot wipers that are very repeatable until you press on the shaft, at which point the opens magically disappear