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Problem with Labview example - wrong data sent by 2420

Models 2400, 2401, 2410, 2420, 2425, 2430, 2440, 6430
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Joined: October 19th, 2010, 6:19 am
Country: Israel

Problem with Labview example - wrong data sent by 2420

Post by gurator » May 17th, 2011, 4:08 am

Recently we purchased KEITHLEY 2420 sourcemeter (S/N 1316717).
I'm using it in the conjunction with Labview 2009 SP1 on Windows XP PC.
I'm charging and discharging capacitors using NI/KEITHLEY provided
driver Revision: 1.1.1
My purpose: to charge and discharge capacitor using constant current
while the capacitors voltage is monitored.
I'm facing a problem with 2420 Labview driver (see “Keithley 24XX Read Single.vi”).
When I discharge the capacitor the voltage is either 0.211mv or 2.11V
regardless of the true capacitors voltage which is measured by DVM or oscilloscope in parallel
to 2420.
The correct voltage monitoring resumes when the voltage drops below this value.
In order to recreate problem:
1) Connect capacitor (capacitance as high as possible) to KEITHLEY 2420 terminals.
2) Run the example with following settings: Source Mode: Voltage, Output level= nominal voltage of a capacitor, Compliance level: 0.1 all other settings remain intact.
3) Run the same example but change the Output level to 0.1
4) Observe voltage indicator.

I looked into it myself and found that on low level of the driver VISA read module returns the same measurement regardless of true measured voltage. It looks like a hardware problem (probably communication module of a device).

Please instruct me how to solve this problem.

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