PCI-6259 AIs always registering -5 Volts

[1N4001]

Greetings, Our setup has a PCI-6259, SCC-68, and LabView of course. After having not used the setup for a while (and after the hard drive crashes of two of the previous computers it was installed in) I reinstalled LabView and tried to read some analog values. However, all LabView will read for any analog input value is -4.9505 volts, no matter in Diff, RSE, or NRSE modes. I'm able to read DIs and correctly output voltages on AOs. With nothing connected, using a multimeter I see approx. -15 volts between any AI and AI GND. Connecting a 1k resistor between any AI and AI GND causes the voltage to pretty much disappear, so I allow for the possibility of stray bias current which goes away when connecting something, but that still seems suspicious. I also tried connecting my SCC-68 to the other half of the card, which we've never used, but I see the same behavior. I know that this card has previously had RS-232 voltage levels (up to 15 V) connected to it, which may have damaged the AIs. Is behavior as noted consistent with damaged AI circuitry? If so, shouldn't the other half of the card's channels be operational yet, or is there common circuitry there? Is there protection in the SCC block which could be damaged instead? And in the end, I wonder if my knowledge of LabView is lacking and I'm missing something with how to read the AIs. Advice is welcome.

[taper]

There are 2 physical connectors but all analogs go back to a single A/D converter and share the same grounds(AI Sense for NRSE or AI GND for RSE).  15V is right at the limit for this device's overvoltage, could have broken something.

Look at Table 1 in the Field Wiring Guide.  Which configuration are you trying to use, and do you have the correct biasing resistors?  Can you probe on the SCC with your real signal attached and see how it looks?

https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

[1N4001]

My wiring setup is as noted in Figure 12a. In my case, the device on the left is an isolated power supply. If my power supply is set to ~4 volts and connected, the display on the power supply curiously goes up to ~9-10 volts. I confirmed this with a multimeter. Putting the same 1k resistor across the terminals brings it back down to 4 volts, also confirmed with a meter. LabView's reading remains the same (-4.9505) before, during, and after the test. I haven't measured current, but lack of movement on the power supply's current readout (precise to 10mA) suggests nothing seems to be shorting out.

[taper]

The AI on a DAQ card should not be pulling a power supply up to 10V, something's definitely wrong there.  Try ohming out the path and make sure nothing's shorted on the SCC.  Is your power supply isolated?  Not just that it says isolated, but actually is?  Nobody added a ground/chassis wire or an internal short to case?  Are you using +/-5V scale?  Could be railed low if so, or the common mode voltage high enough to push the signal out of range.

You could try connecting signal with the DAQ unpowered, if you still read -5V with a meter on the unpowered DAQ setup you know there's a hardware problem somewhere.  As long as you keep it within +/-10V input you won't damage the card.

[1N4001]

Continuity check on the SCC with the cable unplugged showed an open circuit ("overrange" on my meter). Same with a test between my power supply's earth ground and the power ground. Scale in LabView is set to +/-10V, so the existence of -5V is indeed odd. I'm not sure I understand your latter question. I powered down the SCC (switched to nonexistent External Power), and with nothing on the AI, still read the same ~-5 Volt value in LabView. To my knowledge, I can't power down the PCI DAQ card. I can accept that this would be damaged hardware, I guess I just wanted to be sure I wasn't missing something obvious since my LabView experience is light.

[tyagiy]

Iam using NI pci 6259 M series DAQ card with bnc 2110 connector. My problen is that iam unable to read analog input in measurement and auotmation explorer.I have  installed driber softaere and hardwre but with no success. The reading shown in  measurement and auotmation explorer is 3.11 volt in all analog channels irespective of analog input. Any help will be greatly appreciated. Y Tyagi

[James-K]

Tyagiy,

I would recommend creating a new forum post for your question so that this thread does not get off topic and so that you get more responses to your question.