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Is there a way to eliminate the guard functionality in the SMU2450?

Models 2450, 2460, 2461, 2470
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Gotleyb
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Is there a way to eliminate the guard functionality in the SMU2450?

Post by Gotleyb » October 24th, 2021, 1:15 pm

Hello,
I'm using a Triax to BNC adaptor to connect the force LO terminal of the SMU2450 to another voltage source. The problem is that the guard and the Line of this terminal are shortened and in the adaptor the guard and shield are shortened, therefore eventually the Line and the shield are shortened.
My questions are why this is the case in the force LO terminal but not in the force HI terminal?
And is there a way to eliminate this functionality so there won't be any crosstalk between the Line and shield?

Andrea C
Keithley Applications
Keithley Applications
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Re: Is there a way to eliminate the guard functionality in the SMU2450?

Post by Andrea C » October 26th, 2021, 9:51 am

Care does need to be exercised when selecting a triax to BNC adaptor.
Many of these from the general electronics market will short together the inner and outer shields of the three conductor triax side to the single shield of the two conductor BNC side.

When this is used on the force HI or sense HI, it connects the driven guard to the bnc outer shell. If that outer shell is not earth grounded, then you have a shock hazard. Also, the SMU may not operate properly if the guard is shorted.
When guard is not being used, leave it unterminated (floating).

The 7078-TRX-GND adaptor is what you want as it drops the inner shield:
https://download.tek.com/datasheet/PA-2 ... GND)_4.pdf

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