keithley 236 probelm

[elo85]

I want to ask why when I'm doing linear stair sweep source V measure I on a 330K resistor, for example, when source 10V , the measure current is 0.000014611 A.
From ohm's law, V=IR, if take the source voltage divide measure current, the resister value is about 2times of the actual value. Why?

Thanks

[Albert.Geven]

It is not the compliance that is too low?

[elo85]

i'm not sure with that.
by the way, what is the purpose of compliance current?
because the range i set to AUTORANGE.

[Albert.Geven]

compliance is a currentlimit to make sure there runs not more than is safe

[elo85]

okie..i get that..
but...why become like tat?
how to solve this problem?

Message Edited by elo85 on 09-12-2007 05:31 AM

[Brian F.]

Hello. 

Can you provide more information on your system setup.  From my understanding, you are sourcing voltage from a power supply and measuring the current through a resistor with a Keithley 236.  Is this correct?  Is the current reading that you are referring to on the front of the Keithley 236?  Or are you interfacing this instrument with a computer in some fashion? 

If I am accurate in assuming that the reading is being displayed on the front of the Keithley instrument, then as long as there is only the one loop in your circuit consisting of one voltage source and one resistor, V=IR should definitely hold. 

Brian F
Applications Engineer

National Instruments

[elo85]

ok...i'm using labview to control keithley 236 smu
i using Keith 236 Sweep Example.vi to run it. This file u can get it from the keithley driver inside
the compliance voltage and current is 10 and 0.1
so, i run a measure current over a resistor...
eg, when i source 10V over a 330k resister, it show 14.611e-6 A. ( which should b around 30e-6 from V=IR formula)

[AnalogKid2DigitalMan]

Is there a way to do the test manually at a fixed voltage on the 236 alone without the use of LabVIEW?

If it reads incorrectly with this method, then there may be an issue with the instrument. I am not familiar with the 236.

[elo85]

yes...i try manually also...
the result give the same as using labview.
by the way, is there any pro in using keithley 236 smu teach me how the setting in sweep for 330k ohms & 68 ohms resistor for example?
thx alot!!!

[Brian F.]

Hello.

Unfortunately, it seems like something is wrong with your instrument.  If the instrument is returning the incorrect reading without any other interactions taking place (i.e. interfacing with LabVIEW), then we can be confident that the instrument needs to be the target of our troubleshooting. 

I would recommend finding another multimeter and giving that a try.  The other possibility is that the Keithley instrument is ok, but the voltage being supplied or the resistor is inaccurate. 

Brian F
Applications Engineer
National Instruments