6211 Voltage lockup on AO0 and AO1 outputs

[CHS]

I have a situation with a USB-6211 DAQ card where I am using it to send a 0-10VDC signal to a heater control.  It worked fine for 2 or 3 months then one channel locked up and would send a static voltage (when measured with a volt meter) even though the program was telling it to send a different amount.  This problem persisted on AO1 and could be temporarily fixed by either rebooting the computer or by unplugging the USB connnector to the card and connecting it again.  It has gotten to a point where it seems to lock up from every other day to maybe as long as a week or so.  This morning the problem has now shown up on the AO0 channel as well.  I have used this card in this application before and it has not caused a problem which leads me to believe that it is not a problem with the software.

Thanks for any help.

CHS

[Wayne.C]

CHS,

It sounds like the output is latching up.  A lot of times this is caused by electrical noise or voltage spikes.  Can you describe the heater and the connections between it and the DAQ device?

[CHS]

Thanks for the responce, the heater control is a Watlow DINAMITE-C SCR with the 0-10VDC option.  The cabling is about an 18 or 20 guage 2 conductor shielded wire of about 20 feet, until it gets into the box with the SCR mounted, it is not really near any high voltage high current lines.

CHS

[Wayne.C · Accepted solution]

CHS,

SCR in Watlow could generate some nasty hash that may be getting into the 6211.  Two ways to get in, power supply and connection between DAQ output and Watlow.

Since the problem usually happens just to the channel driving the Watlow, I would start there.  You said it was shielded wire.  Can you verify how the shield is currently connected?

[CHS]

The unit is in the UK and I will be flying over to take a look at it tomorrow.  One other thing that has come to my attention is that a week or so before we started having problems, the electricians had wired in an interlock to the airhandler so if the fan went out on the air handler, the heater would shut down.  I don't know what they did or how they did it so I will have to take a look at that.  Likewise I will have to confirm where the shield is draining.

Thanks

CHS

[CHS]

The wire was installed but the shielding was not connected, that was connected and we have been running for quite some time with no problems so it seems to be solved.  Thanks for the input

[AnalogKid2DigitalMan]

Centerbolt:

Good remote troubleshooting advice there. Kudos to you!

"Captian, shields are back online..."

-AK2DM

[Wayne.C]

CHS,

Glad you got the problem figured out.  Hope you enjoyed your visit to the UK.

AK2DM,

Thanks.  It seems I remember the painfull lessons from the past the best.