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What does the gain do on a 6023E?

I want to measure an analog singnal that varies between 0 and +10V in the field. No problem using LabView and MAX, but I have recently tried talking to the card driver using Visual Basic. My signal at 6.81V (confirmed within MAX) pegs the ADC at 2047 or 4.99V. MAX interprets the signal correctly because I set the range to 0 to 10V within the MAX software. Apparently, when talking to the 6023E from VB, the MAX config is ignored, and the range defaults to the bipolar -5V to +5 range. The solution appears to be setting the polarity to unipolar by calling AI_Configure. No luck, and there is a suggestion here that unipolar is not an option on the 6023E. Odd, in that this is in contradiction to the NI-DAQ Function Reference documentation. As
suming that it is impossible to set the 6023E to unipolar, I am left with the option of setting the gain. Will setting the gain to 0.5 cause the ADC to convert +10V in the field to 2047? Or will it just map 2047 to +10V internally causing my 6.81V field signal to evaluate to 10V?

Thanks,
Doug
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The 6023E does in fact not support unipolar mode. Setting the gain to 0.5 however will properly sample your signal. The input amplifier divides your input signal by half before it is passed to the ADC. (The range of the ADC is +-5V.) When the resulting binary value is scaled to volts, the gain factor is compensated by multiplying the result by two. This is done automatically in the driver.
authored by
Christian L, CLA
Systems Engineering Manager - Automotive and Transportation
NI - Austin, TX


  
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