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UniMeasure Linear potentiometer display voltage and length via Ni9237 and Ni9215.

I currently have a UniMeasure Linear Potetiometer which has a 50" cord length and a senstivity of 19.54 mV/V/Inch.  The voltage that is supplied is 10V and the impedence is 1000ohms.


I am supplying the voltage excitation via the NI 9237 and trying to read the voltage via an analog input on NI 9215. But when I attach a voltmeter to the same hook up I am not reading the correct voltage on the waveform chart.


Then I need to convert the voltage to mm to display length of the cord extended.


1. Am I not scaling the input right?

2. Do I have a high sample rate?


I have attached my VI to have you look at it.

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Hi sbpfit51,


I just wanted to ask a few clarifying questions to further understand the unexpected measurements you are receiving.


What are some typical readings on your voltmeter and how do they compare to the output on Waveform Graph 1?


Have you verified the output of the NI 9237 and confirmed the expected 10V output?


To answer your numbered questions:

1. If I am not mistaken, based on what you have described, you should divide your measurements collected by the NI 9215 by 7.6929 in order to convert the voltage to mm.


2. Your sample rate all depends on the application. Without knowing your application, I still am going to assume 50,000 samples per second (50k Hz) is probably plenty fast enough.

Sam Burhans
Senior Product Manager
National Instruments
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