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I am constructing a high resistance four-point probe measurement system using the 6430 + preamp as a current source and two 6517B's as guarded voltmeters. The DUT is inside a vacuum chamber with triaxial feedthroughs (see attached figure). According to Keithley application note number 2615 and best grounding practices, the 4th probe should be connected to the low of all 3 instruments and then only one instrument's LO terminal is connected to ground. However, the outer shield of the 6517B is chassis ground and the outer shield of the 6430 is IN/OUT LO. Therefore, LO is connected to two different chassis grounds at the vacuum chamber and the LOs of the 6517B would be connected to another chassis ground in the back of one of the instruments.
Will this create a ground loop problem? Should I use adapters that disconnect the triaxial chassis grounds of the 6517B's from the sample chamber?
Thanks in advance
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