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<== Date ==> <== Thread ==>

Subject: Re: current measurement - hardware
From: Tim Mooney <[email protected]>
To: Heinrich du Toit <[email protected]>
Cc: EPICS Techtalk <[email protected]>
Date: Mon, 26 Nov 2007 09:10:41 -0600
I would give each current source its own current-to-voltage
preamplifier (e.g., an Analog Devices AD8609 -- see
www.analog.com/UploadedFiles/Data_Sheets/AD8603_8607_8609.pdf),
and read the output voltages with multiple-input ADCs (e.g., IP330)
or DMMs (e.g., Keithley 2000), depending on how you value speed vs.
accuracy. The AD8609 has such low bias current (~0.2pA) and offset voltage (~12 uV) that you might not even need to trim them.


--
Tim Mooney ([email protected]) (630)252-5417
Beamline Controls & Data Acquisition Group
Advanced Photon Source, Argonne National Lab.

Heinrich du Toit wrote:
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




References:
current measurement - hardware Heinrich du Toit

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