New USB1608G questions

[Stephen Durbin]

Hi,

I have set up a new USB1608G connected to a Linux computer. I reached the point where I can run the example program AIn. The numbers I see, however, aren't what I expect. When the input is about zero (VDC), the display reads around 8-9 VDC. I have experimented with single-ended and differential inputs but the results are about the same. Any advice? Is this a faulty device?

I find in the manual a reference to "channel-gain queue" but no information on where this is. Is this relevant to my issue above? How is it created or modified?

I look forward to your response. Thanks....

 

....Steve Durbin

Professor of Physics, Purdue University

 

[JRys]

Hello Steve,

When left open (unconnected), the USB-1608G inputs will float as high as 9 or 10 volts. Regular operation is to connect the inputs to a low-impedance source. For test purposes, connect the inputs to AGND and retry the measurement. This will force them to read close to zero.  If you're using the differential mode, connect both the high and low sides to AGND. If you're still encountering strange values and have a Windows computer handy, use our DAQami program to test it. 

So that you know, the screw terminal top doesn't make a good connection unless it is screwed down or anchored on a wire. 

Best regards,
John

[Stephen Durbin]

Thanks. Shorting the inputs does give zero VDC. The problem was my source, which was not low impedance. A different source worked fine.

So, how do I access the "channel-gain queue"?

Thanks again,

...Steve

[JRys]

Hello,

The ulAInLoadQueue function works in conjunction with ulAInScan. It must be called before AInScan because it lets AInScan know to ignore its first channel, last channel, and range parameters. If you're programming with C, please look at the example AInScanWithQueue.c. The Python version is a_in_scan_with_queue.py

best regards,
John