Might look into something like a Measurement Computing PCI2517 card,
which has 8 differential analog inputs.
Looking at the spec sheet, it says it has a 40pA bias current, and
20Meg input impedance, while measuring a 100mv signal. With proper load
resistors (if you even need them at these low currents), you could
probably measure currents in the Ua range with no problem.
David Dudley
>>> Heinrich du Toit <[email protected]> 11/26/2007 8:25 AM >>>
Hi guys
I'm looking for some information on how you solve this problem...
We need to measure currents.. from harps and slits and faraday cups.
All of this gives of currents that is important.
Some of the currents we measure with keithleys but it is way to
expensive to buy keithleys for harps as you will need 100's of them :)
We need to measure currents between nA and uA range for harps and
slits.
For faraday cups this sometimes goes to 100+ uA but our main problem is
harps/slits.
I hope that we are not the first to have this problem, is there some
cost effective method to solve this problem? That can give descent
results.
The problem can basically be given as:
How do I measure 50+ current inputs (harp = 96, 4 per slit-set) across
a
wide range (2nA fullscale = 50pA sensitive up to 100uA full scale)
still
have resonable accuracy especially between the lines and have a descent
update rate and not 2 high noise levels.
(I guess noise can to some extend be solved with a software filter if
updates are high enough)
Thanks for your support :)
-Heinrich
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