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how to protect the current meter of 6487

Posted: December 8th, 2014, 4:13 pm
by txz033000
Hi, All,
I have been asking questions about current meter of Keithley 6487, so I will make it a separate post. I have an external voltage supply which could output up to 2KV. I want to use the --ampere meter of 6487 to measure the current in this loop, which should be no more than 100nA. ( if current was more than 100nA, my device burn first.) but 6487 manual said "MAXIMUM COMMON MODE VOLTAGE (between chassis and voltage source or ammeter): 505 VDC", then 2kV looks dangerous to the current meter. I wonder how I could protect the meter without overloading it. I could put a 100Mohm resistor in series if it helps.

regards,
tao

Re: how to protect the current meter of 6487

Posted: December 9th, 2014, 4:22 am
by Andrea C
Hi tao,

Not only common mode voltage, but also the voltage to the input pin should not exceed 505 VDC else damage can result to the 6487.

Here is an excerpt from the 7th Edition of the Low Level Measurements Handbook:
picoammeter_input_protection_LLHB.PNG
picoammeter_input_protection_LLHB.PNG (60.21 KiB) Viewed 18103 times
Andrea