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HP34401: a possible IC killer, beware!

Question asked by dbovey on Sep 7, 2011
Latest reply on Sep 9, 2011 by dbovey
Hi,
I was innocently using an HP34401 to check for shorts in a circuit (Ohms -2wire), and I had strange results. I took a USD50 multimeter, and I had different results. Then I measured the voltage on the leads of the 34401, and I found between 2.5 and 5V!!! That voltage applied on a PCB with 1.8V-supplied circuits!!! I thought the 34401 must be failed, and looked in the spec: no, this is true, it is the spec! According to the service guide doc 34401-90013, page 98, and the open circuit voltage may be between 5 and 14V depending on the ranges, with a "compliance voltage" of between 2.5 and 10V. Even if the current source level varies between nanoamps and 1mA depending on the ranges, these voltages, applied to fragile low-voltage IC's, may damage them (electrostatically).
The USD50 multimeter, on the other hand, applies at most 0.4V; this is a healthy behaviour, and allows measuring passives in an electronic circuit with some accuracy, i.e. without putting the IC diodes in conduction, or not too much of it.
Agilent engineers: in new multimeters PLEASE measure resistance using current sources limited to 0.4V, or even better, to 0.3 or 0.2V.
Agilent product managers: put this open voltage figures prominently on  the spec, and warn the users!
I would like to get a a feedback on this from Agilent people. Thank you!  

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