DAQCard-6062E

[Dale_Olson]

I'm teaching a course on Computer Interfacing using LabVIEW and a DAQCard-6062E.  My students, and I, are having a problem with the MAX >> Analog In test panel.  When the Terminal Block is connected as 'Differential Input' (AI0 and AI8), and the corresponding mode is selected in the Analog In test panel, we cannot measure the voltage of a battery.

In contrast, we have complete success with RSE (Referenced Single Ended Input; AI0 and AI GND).

A few more details:

This morning I've successfully installed five DAQCards.  Each immediately appeared in MAX and passed the self-test, (except for one where it was necessary to uninstall the DAQCard in the Control Panel, and then restart the computer).

Then I connected an 8,4 volt battery to each terminal block, and, in MAX >> Test Panels,  selected Analog In, RSE (Referenced Single Ended).  Every one of three 'modes' worked: 1. On Demand, 2. Finite and 3. Continuous worked.  I used 5 samples at 1 sample per second for both the Finite and the and Continuous modes.

Then, for several computers I tried using Differential input.  Here there seems to be a problem. Differential mode seemed not to work in the test panel.  (Again, I used AI0 and AI8 for differential.  I used AI0 and AI GND for RSE.)  Does anyone have a suggestion please?

Thanks much for any help.

[crossrulz · Accepted solution]

First of all, what do you mean by "not working"?  Are you getting an error?

The likely problem here is that each side of the differential voltage needs a reference to the AI ground.  A typical setup will have a high resistance from each side of the signal to ground.  There's a good chart here for how you measurements should be setup:http://www.ni.com/white-paper/3344/en.

[Dale_Olson]

I used the advice you provided, and contained in Figure 11 of the White Paper.  Two 100k resistors, one between AI0 and the DAQ-Card ground, and the other between AI8 and the DAQ-Card ground.  The result was very good.  Our differential measurement of an 8.4 volt LiPo battery is up and running.

Thanks much for your time and your good guidance.

[Dale_Olson]

I should add:  What I meant by "not working" is that the reported voltage, using differential mode, would wander all over, over a range of volts.