Re: Analog issues for a non hardware person.

This sounds what our channel measurements look like when our hardware is 
not set to the right reference mode. What kind of signal are you trying 
to measure? Is the signal's reference (ground) isolated or with respect 
to the wall socket? Isolated signals are those such as those from a 
battery powered device, isolation amplifier, electrophysiology 
amplifier, thermocouple, etc., the key is that they provide their own 
reference point which you would want to connect to AISENSE pin on your 
daq board and make sure that your board is running in the NRSE mode 
(likely AREF_COMMON with your hardware). If the signal you are trying to 
measure is with respect to the wall outlet, though, such as that of a 
function generator, D/A device, etc., then you do not want to provide a 
physical ground (if you plug a ground input into AIGND you'll probably 
create a ground loop, it's a ground output). All you need to do is make 
sure that your daq board is running in RSE mode (likely AREF_GROUND with 
your hardware), the DAQ hardware provides the ground for you.

The NI literature can be contradictory on the issue. At least the 
previous is how my PCI-6052E works, and seems the most logical answer: 
NRSE == non-referenced == supply your own ground (as isolated signals 
do), RSE == referenced == referenced to wall socket ground like the 
signal you're measuring in a non-isolated signal. The whole referenced 
vs. non-referenced nomenclature seems a little silly, every time you 
measure a voltage signal you're measuring with respect to some reference.


Regards,
Ryan

Ford, Ingi A. CIV NAVAIR wrote:

>I have been banging my head over an analog issue with a National Inst PCI-6025 board (DIO works fine).  I am a software person and not a hardware person.  We have set up though their SCB-100 wireing box some hardware that gives power while in its neutral position of aprox 2.5 volts DC between AIGND (pin 1) and ACH0 (pin 3) that is measurable with ease with a multimeter.  We also have the same powersource on another item that goes though the device and gives a second reading on pin 5 (ACH1) (its a Aircraft stick which has a lat and long pot).  We have a second power source that drives a third device between AIGND and pin 13 (ACH5) that reads about 4 volts in its current position (throttle).  The problem is that trying to read the chanels (currently have a program that is reading all 16 channels with comedit_data_read_delay at range 1 (-5 v to +5 v), AREF_GROUND, and a delay of 40000) I get pretty much random noise of -1v to 1v on all channels except chanel 5 which bounces from -3 volts to 2 volts to 4 volts and back and fourth.  I figure this is a hardware wireing issue and have tried moving the grounds to AISENCE instead to see if that helps anything which it does not.  Another test I ran was I tried to change the aref to AREF_COMMON, about 1/3 of the readings are pegged at 5 volts (on all 16 channels).
>
>Any assistance would be appriciated,
>
>Ingi A. Ford
>
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Received on 2005-11-17Z21:15:30