Why is voltage incorrect?

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Guest

Why is voltage incorrect?

Post by Guest » Wed Jan 21, 2009 6:21 pm

When using the supplied example in LabView, the reported voltages are incorrect.

The voltages are calculated as=
(value*(voltage/2^0))/MaxADC ,
but two simultaneous examples, measured on channels 1 and 3 (differential)

-30850*2500/524287 = -147 , correct value is -163 mV

-16046*2500/524287 = -76,5 , correct value is -235 mV

so it doesn't seem to be a scaling problem. any clues?

gruntman
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Post by gruntman » Wed Jan 21, 2009 11:59 pm

Hello,

How are you obtaining the values that are correct? Describe your testing setup for us so we can track down the source of the problem. Thanks!

Regards,

Richard Boyd
Crag Technologies, Inc
http://www.pc-oscilloscopes.com

Guest

Post by Guest » Thu Jan 22, 2009 6:31 am

using picorecorder and a voltmeter, both give the same and correct values, but using the HRDL vi gives incorrect values. i use a ADC-20 with the circuitboard extension, and i only measure voltages, no currents and/or resistors are involved.

Guest

Post by Guest » Thu Jan 22, 2009 7:59 am

i just found in the labview thread something about 20bit and the default example using 16bit inputs, will try to change this and then report back.

Guest

Post by Guest » Thu Jan 22, 2009 1:24 pm

this was the problem. Please note that in the HRDL vi you supply in your development pack adc20 uses 16bit integer to register a 20bit int.

/ Mark

gruntman
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Posts: 109
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Post by gruntman » Thu Jan 22, 2009 4:27 pm

Mark,

Thanks for the update. I'll be sure that we get our example updated to fix this. Thanks!

Regards,

Richard Boyd
Crag Technologies, Inc
http://www.pc-oscilloscopes.com

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