PCI-7833R Analog Output Voltage Level when PC Unpowered

[gt7319c]

Hello,

Is it possible to define the voltage levels of the analog outputs of the PCI-7833R DAQ card when the PC is unpowered?  I have an application where an analog ouput is being used to drive an LED circuit with arbitrary waveforms.  The LED driver circuit is powered independantly from the PC and remains powered even if the PC containing the DAQ card is turned off.  I would like to ensure that a 0 V level is seen at the analog output of the DAQ card under this scenario so that the LED remains unenergized.

Thank you.   

[jareds]

Hi gt7319c,

There is no way of specifying the voltage level of the analog output when the computer is powered off.  Are you seeing a voltage on the card that is far from 0 V that is turning the LED on?

Jared S.

Applications Engineer

National Instruments 

[gt7319c]

Hi Jared,

Thank you for responding.  Unfortunately, the system in question was delivered to our customer and we don't have access to it right now to troubleshoot.  We delivered it back in October, and they didn't start seeing the problem until the last month.  We plan on visiting them to troubleshoot the problem, but as of now, all we know is that the LED lights up when the PC is powered down.  When the PC is powered up, everything returns to normal.

Chris

[jareds]

Chris,

So it was operating normally until now? It sounds like something might not be functioning properly in the LED circuit. What else is in the circuit other than the LED. Also, is there a reason for keep this circuit powered without the computer on? That would probably be the simplest solution.

[jareds]

Have you been able to look at your customer's system to troubleshoot the problem any further?

[gt7319c]

Hi Jared,

Not yet.  We are traveling to their facility tomorrow.  I will let you know what we find out.  As a backup solution we are taking a remotely controlled AC power switch to install with the rack enclosure containing our LED circuitry, so that the instrument can be powered down when the PC is powered down.

Best regards,

Chris

[jareds]

Chris,

I think that is good workaround, since it's hard to tell what the lines should be when the computer is powered down. 

[gt7319c]

Hi Jared,

I wanted to let you know that we installed the remote power switch yesterday, which has taken care of the problem.  Unfortunately, we decided not to troubleshoot the output voltage on the unpowered DAQ card as we had a solution that works, and we didn't want to risk damaging anything by opening up the enclosure and poking around with a multimeter.  Thank you for your followups on our initial question.

Best regards,

Chris

[jareds]

You're welcome.  I'm glad to hear that you've worked out a solution to this problem.