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Unwanted voltage between the SENSE contacts

Models 2601, 2602, 2611, 2612, 2635, 2636
Models 2601A, 2602A, 2611A, 2612A, 2635A, 2636A
Models 2601B, 2602B, 2604B, 2611B, 2612B, 2614B, 2634B, 2635B, 2636B
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abattleofwords
Posts: 5
Joined: February 23rd, 2013, 1:15 am
Country: Singapore

Unwanted voltage between the SENSE contacts

Post by abattleofwords » February 24th, 2013, 8:29 pm

Hi, I did some tests on the 2636A and I found that there is always a voltage drop between the SENSE HI and SENSE LO contacts. This happens in both source-V-measure-I and 2 Wire source-I-measure-V modes. The voltage is about the same order as the voltage being sourced but always higher. This happens in both the channels. The SENSE contacts should not be involved at all in the two modes, so I do not think this is normal, but I just want to confirm.

Jane S
Keithley Applications
Keithley Applications
Posts: 114
Joined: November 10th, 2010, 5:45 pm
Country: United States

Re: Unwanted voltage between the SENSE contacts

Post by Jane S » February 27th, 2013, 7:09 pm

Hello,
I believed you also sent a similar concern regarding your compliance measurement. I believed it is a simalar issue with what I replied to you.

I think that the issue is more of a set-up issue than the measurement itself. Since you have a 2636A, you can actually use the TSP Express to do your specific measurement and settings. Another aspect of the TSP Express is that it can generate the code for you as well. Use this as your debugging tool to make sure that you achieved your measurement needs. Also make sure that you are actually connected properly (HI = RED on the triax alligator, LO = RED on the triax alligator).

See link below;
http://www.keithley.com/products/dcac/c ... B/tsp.html

abattleofwords
Posts: 5
Joined: February 23rd, 2013, 1:15 am
Country: Singapore

Re: Unwanted voltage between the SENSE contacts

Post by abattleofwords » February 27th, 2013, 7:28 pm

Hi Jane,

No I do not think it is a setup issue. If I just tun on the 2636A with nothing connected to the terminals, ask it to source a voltage and measure current, there will be a voltage difference between the SENSE HI and SENSE LO contacts.

We use LabVIEW because we need to control multiple instruments from different manufacturers at the same time.

Andrea C
Keithley Applications
Keithley Applications
Posts: 1468
Joined: October 15th, 2010, 10:35 am
Country: United States
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Re: Unwanted voltage between the SENSE contacts

Post by Andrea C » March 1st, 2013, 5:06 am

Hi,

It's not abnormal for there to be some voltage potential on the sense lines even when operating the instrument in 2-wire mode.
There are internal circuit elements, particularly for the contact check feature, that connect the HI to Sense HI and the LO to Sense LO. See figure 4-11 in the 2600AS-901-01 Reference Manual.

When using the instrument in 4-wire mode, additional internal relays would be closed and the sense lines would be directly connected to the voltmeter.
But in 2-wire mode, it is not expected that any connection is made to the sense lines.

Can you elaborate on why this poses a problem or was it was just an observation that you wanted to clarify?

Andrea

abattleofwords
Posts: 5
Joined: February 23rd, 2013, 1:15 am
Country: Singapore

Re: Unwanted voltage between the SENSE contacts

Post by abattleofwords » March 1st, 2013, 5:17 am

Hello Andrea,

Thanks for the clarification. This is a problem for me because I switch between 2-probe and 4-probe measurements and I used to leave the sense wires connected to the device even while I was doing 2-probe measurements. Is there any way around this other than disconnecting the wires or making my own switches?

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