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2700 resistance changes when LabView connects

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clegett
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Joined: March 10th, 2016, 7:33 am
Country: United States

2700 resistance changes when LabView connects

Post by clegett » March 10th, 2016, 7:49 am

I'm using a 2700 connected to three different thermocouples to monitor the temperature of different parts of a lab setup. Ch 101 and 102 are read in ohms, 103 is read using the TEMP function.

When I start my LabView VI, sometimes the Ch 101 and 102 noise goes through the roof, and the resistance values begin to climb, sometimes by as much as the equivalent of 25 C temperature change (70 C nominal temp).

As long as I don't monitor the instrument from LabView, the resistances are ok. Once the values go haywire, I have to power off the 2700 for a few minutes and start over before they resolve.

What could be causing this? I'm relatively inexperienced, and have barely been able to figure out the LabView code necessary to get this far. I've attached my VI if it helps.

Any suggestions are greatly appreciated.
Attachments
FTIR Monitor.vi
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Dale C
Keithley Applications
Keithley Applications
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Re: 2700 resistance changes when LabView connects

Post by Dale C » March 14th, 2016, 7:31 am

I connected resistors to channels 101 and 102 and a TC to channels 103.
I see the VI works just fine. How long before the issue shows up.
Maybe there is some issue with the hardware of the 2700 and the card?
I notice the VI will only run one function at a time. Is this what you want?

clegett
Posts: 2
Joined: March 10th, 2016, 7:33 am
Country: United States

Re: 2700 resistance changes when LabView connects

Post by clegett » March 14th, 2016, 12:12 pm

I have since isolate the problem to something internal to the 2700's resistance measuring circuitry. We put the 7708 card in an identical 2700 and everything is working fine.

As far as the VI goes, ideally I would like to be able to log the two resistance channels simultaneously with the output file separated by channel. I have been unable to do that so far, but I think I'm getting close since I discovered the "All Data" switch on the sub-VI within the loop. If you have any suggestions on a better way to do this I would love to hear it!

Thank you for your post and email.

Dale C
Keithley Applications
Keithley Applications
Posts: 2845
Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: 2700 resistance changes when LabView connects

Post by Dale C » March 14th, 2016, 12:25 pm

I think the Advanced Scan VI in the Example section of the 2700 Labview driver would help with this.

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