I'm trying to read torque and speed (in the form of a DC-ish voltage) from a 700 Series Himmelstein torque cell reader, wired to a torque cell. The voltage is output on pins 14 and 15 of a VGA connecter, with pin 13 being used for ground, with the other pins being used mainly for logic stuff that I haven't touched nor do I use. I have a VGA cable running from the reader to a female VGA connector, and wires soldered to the back of the connector pins running to a 9205 AI cDAQ card, in a 9139 chassis. The torque feeds into AI0 and speed into AI1, and I have the pre-wiring for torques and speeds from two other readers (now, physically wired between the 9205 and the female VGA connector, but no connection to the readers (yet)). So, on my 9205, we have:
AI0 - T1 (connected to reader)
AI1 - S1 (connected to reader)
AI2 - T2 (not connected to reader)
AI3 - S2 (not connected to reader)
AI4 - T3 (not connected to reader)
AI5 - S3 (not connected to reader)
Now, enough about the setup (because I doubt it's the problem, as you'll see) and onto the interesting stuff. We sent out torque cell and reader out for cal, brought it back, put it in place (didn't touch the wiring except for disconnecting the VGA cable from the reader), and, long story short, saw that whichever output voltage was higher (torque or speed), both channels were reading that value (ie., at low speeds, where the corresponding output voltage from the reader might be ~0.1 V for the speed channel, and high torque, where the corresponding output voltage from the reader might be ~4 V, both channels read ~4 V on the 9205. The same sort of thing happens at high speed and low torque). In my tinkering, I found that when I plugged the VGA output into plugs 2 and 3 (which correspond to AI2&3 for the second reader and AI4&5 for the third reader), the same thing was happening. Tried two other VGA cables with the same reults. I confirmed that the output from the reader was outputing the right voltages. I then made a simple VI that measures the first 8 of the 16 channels on the 9205 and saw that, when I applied a 4 V signal from an adjustable DC power supply to AI0 through the female VGA connector:
AI0 (directly connected to PS) immediately goes to ~4V
AI1 (connected to the same VGA connector as AI0) slowly goes to ~4V
AI2-5 (connected to other VGA connectors, but wiring runs along with AI0 and AI1 wiring) slowly go to ~4V
AI6&7 (completely open) slowly go to ~4V
I have another 9205 card that I tried and got the same results. I tried putting the card in different slots with the same results. When I separate out the torque and speed channels to two different 9205 cards on AI0 on both cards, I can get what I need at the moment (seeing as some tests I can run measuring just torque and speed as my only AI's), but obviously I can't use one card per channel going forward.
In the past, I've seen channels slowly oscillate between +/- full scale when not connected to anything, but I've never seen any behavior like this. Has anyone else? Any idea what causes this and how to fix it?
Thanks,
Jim
