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at this moment, I am using the - ampere meter of my 6487 unit to measure the beam current of an electron source. basically the electron source could emit electrons by excitation and I use a metal plate as a collector to collect those electrons, with the help of an external 2kV DC power supply. see the attached image. I am using the - ampere meter of my 6487 to measure the beam current. the beam current is in nA range. if I am doing the normal close-loop current measurement, I would not bother to ask. but for the incident electron beam current, could 6487's meter handle such kind of job?
my 2nd question: if the answer is yes, does it matter where I place the meter in the circuit? please see the attached -.
- to show.jpg (62.17 KiB) Viewed 18202 times
- measurement set up to show.jpg (74.76 KiB) Viewed 18206 times
While the 6487 is intended for this type of application a few things need to noted. Firstly the 6487 can not be floated above 505VDC, so the setup in your first diagram would not work as you would be trying to float the instrument up 2kV.
The setup in your second diagram, where the 6487 is behind the the 2kV source would be the proper setup however you must take into consideration a worst case scenario in which there would be a short between the metal plate to the electron source. To protect your system from this potential failure you would need to use Overload protection which is a series resistor with two diodes that would clamp the voltage in case of this failure. Attached is a paper outlining overload protection.
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