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low current measurement in low voltage environment

Posted: February 25th, 2019, 2:41 pm
by kjones3856
I have been using a Keithley 2400 Source Meter to take a low voltage measurement across a resistive load. The load is being powered by a very low watt source and what I am finding is the resultant voltage measurement becomes unreliable (doesn't agree with mathematical calculations) once it drops below about 150 micro volts. My question is; am I using the right meter? If so can you recommend a better meter to use for this application? Thanks!

Re: low current measurement in low voltage environment

Posted: February 25th, 2019, 5:48 pm
by Andrea C
The 200mV measure range of 2400 has an allowable offset error of 300uV. It can report small changes still as the magnitude drops below this offset error threshold value spec, but absolute accuracy and repeatability is called into question below 300uV.

You need a better voltage measuring tool. How small absolute value and how small of a change do you want to know about? Model 2182A or DMM7510 are excellent 7.5 digit meters.

Re: low current measurement in low voltage environment

Posted: February 26th, 2019, 6:43 am
by kjones3856
Thank you Andrea for confirming my suspicions. To answer your question I would like to be able to measure voltage down to 1.0 uV with a 0.5 uV accuracy. Will the two units you proposed be able to get me there?

Re: low current measurement in low voltage environment

Posted: February 27th, 2019, 5:56 am
by Andrea C
The 2182A is a specialty meter targeting nanovolt resolution measurements. It offers a 10mV range with 1nV resolution. The one year specs on this range indicate you could measure 1uV with a 40nV uncertainty.
It is provided with a highly engineered cable to minimize thermal EMFs. It terminates in copper spade lugs.

The DMM7510 is a terrific general purpose multimeter: volts, amps, ohms, temperature, etc.
It uses conventional banana cables.
The DC Voltage most sensitive range is 100mV with 10nV resolution. The one year specs on this range indicate you would have 900nV of uncertainty on a 1uV level.