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SMU Verification

When verifying source-measure units, is it acceptable to use the UUT source function as the source for the measure verification via  comparison with a Ref. DMM (8508)? My concern is possible loading effects since there are effectively two meters in parallel when the SMU is set to both measure (meter 1) & source simultaneously, while monitored by the 8508 (meter 2). I have always used an independent source, typically a 5720, to verify the UUT measure function. Has anyone considered this scenario?

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Michael Schwartz

SMU Verification / Automation depending on the standards you have. Same thing with the Tektronix 70000D Scopes, and the problems we experience creating Automation for them years ago.

The problem is you can't load them (AT ALL). The simple act of Turning-On the calibrator or changing the settings will draw current and trip the instrument. The only way we found we could do this with a Fluke calibrator was to disconnect the calibrator set the voltage value then carefully connect it the UUT. Make the measurement. Then disconnect and turn off the calibrator. (Not what I would call Automated.)

What we did discover was that using the Keithey 2400 worked very well and was automatable. All we had to do then was create a driver for the standard and call it just like we call the Fluke Calibrators.

Mike

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david morgan

That's interesting. I've never had an issue using a 5720 as the source with the SMU in measure mode only.

I was curious if anyone had tried putting the SMU in source+measure mode with an 8508 (or 3458) connected to the SMU to monitor the true voltage (or current). Theoretically, the 8508 could be used to measure the source value of the SMU directly while at the same time comparing the SMU measure display to the 8508 to verify both source & measure function on the SMU simultaneously.

If there is no adverse interaction between the two meters while the SMU is in source+measure mode, this would be much more efficient since the UUT provides its own source for its measure mode verification; no external calibrator (source) required.

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Michael Schwartz

The 8508A Should have high enough input resistance.  But the problem is going to be the range switching. 

I tried something like this once with a 3458A on a diferent device and tripped the UUT...  Everytime It did a range change the UUT tripped its output.  On that project we didn't need to read above 10V so I just range locked the 3458A. 

Mike

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david morgan

Thanks for the feedback, Mike.

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