High Speed measurements with the Keithley 2110 DMM

[trevwhite]

Hi all.

I wanted to test how well the KEITHLEY 2110 DMM works with high speed measurements. I decided to measure a 1KHz signal going in and take 1000 measurements - all being written to the internal store of the device.

The manual says to set the NPLC to 0.001 for a really low integration time - 20uS integration. It also states in the manual it is possible to take 50,000 readings per second so I think it should work.

Well I assumed I would end up with a set of results that would represent a square wave. But it didn't come out that way, it came out as a stable average voltage of 50% the peak square wave voltage. I do not know if the ADC is holding charge but can anyone help with setting the DMM up to make this type of measurement work? Maybe my understanding of the meter's performance is wrong?

My end goal is to measure uA current of a processor and measure changes of current over a few 100ms so I need to know the measurements are good and working. The 1KHz voltage signal is my way of checking I can set the DMM up properly and calibrate how fast the ADC converter tracks changes in input.

Really appreciate any help.

Thanks

Trev