Urgent_Ground pins on usb 6008

[Miaa]

Hello everyone,

I am using USB6008 DAQ board to read analog voltages from my electrical system. The way i have set it up now is like:

The analog voltage to be measured is the ouput of the senor on electrical system. And I have 8 such sensors on my electrical system. analog pins AI-0 to AI-7 on USB6008   will be connected with the 8 output pins of sensors. Now there are also some ground pins on USB DAQ board..... I have connected all the ground pins together and connected it with mypower supply. ( see the attached document ) .

WHY AM I GETTING NEAGATIVE voltages on labview software which is reading the analog voltages of pin AI-0 and AI-7 ?? where as if i connect my voltmeter to the same DAQ pins EXTERNALLY ( ie not using labview ) i get positive voltages.

can we connect all GND terminals of DAQ board together as i did in my attached document ? or is there any calibration required for the USB 6008 before taking measurements ? 

[Wayne.C]

Miaa,

Can you give specifics on the sensors you are using?

[Chris_Rake]

Are you using single-ended or differential mode to read the signals?  Based on the configuration you described you want single-ended.

[Miaa]

yes i am using single ended mode.After looking the diagram is there anything i have to change ??

[Chris_Rake]

Can you post your diagram?

[Rod42]

A few things to try...

Double check your wiring - It may seem obvious, but I've been caught out that way!

Try connecting just one input, pin 1 = GND, pin 2 =AI 0

The voltage you are trying to measure is within range (-10V to +10V) isn't it?

Quit YOUR LV program and use the test panels. (An easy way to start them is to unplug the device, wat a few seconds and plug it back in. Select run test panels) That will let you know if your LabVIEW is at fault, or if the device is really returnung the 'wrong' voltages.

If that doesn't help, the device has +2.5V and +5 V (pins 30 and 31) output references. Disconnect all inputs to the device and try reading those voltages with the test panel. If those voltages are wrong, you may need a new 6008!

Rod.

[Ben]

Is it just me or are itmes "3" and "4" flip-floped in figure 5 of the 6008's pdf?

It looks like the diff and single end labels are wrong.

Ben

[Rod42]

I think you're right Ben.

NI seem to think so too, check out https://www.ni.com/docs/en-US/bundle/usb-6008-6009-feature/page/introduction.html

Rod.

[Chris_Rake]

Yes there was a typo in that version of the user manual

[RavensFan]

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Ben wrote:

Is it just me or are itmes "3" and "4" flip-floped in figure 5 of the 6008's pdf?

It looks like the diff and single end labels are wrong.

Ben

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I agree.  Also, for the differential mode, the label should be AI0  (letters A and I, number 0) but they have it as A10  (letter A, numbers 1 and 0).