Hioki DM7276-01 Precision DC Voltmeter (9 PPM)

[Alex Nikitin]

Here is another measurement result using the DM7275, in this case I was trying to do a 1000:1 transfer of resistance, from Fluke 742A-10K to my 10 Ohm DIY shunt (made using a TO-3 packaged Vishay Foil resistor). The Keithley 263 is used as 1mA current source to supply the Fluke and 10R shunt in series, the voltage on the Fluke was monitored by HP3456A and was stable at 10.00046V (double checked with the Hioki), the Fluke 742A-10K has a measured resistance of 10.00005K so the current was about +41ppm from 1mA. As a control option the ESI SR1010 resistor was used as a 10R shunt in place of my DIY one. Despite some meters of cables and numerous connections, the circuit offset at the shunt was measured below +/- 50nV average, 250nV p-p variations (the Keithley 263 has some useful features to change the current polarity and also switch it on/off so it was easy to measure offsets without disturbing the wires and connectors). The graph below shows two 15min runs with two 10R shunts in this configuration. The temperature variations (measured by Hioki) were below 0.5C). A linear trendline was added to each run to indicate a possible drift in time. Vertical scale is 100nV /div (=10nA/div, or 10ppm of value) , horizontal is samples/time , 1min/div, (=15 samples).

Cheers

Alex

[HighVoltage]

Your 1000:1 transfer results are very impressive with the old Keithley 263 as a 1mA source !
Please show a picture of your complete setup.

[Alex Nikitin]

I had to tidy up the cabling a bit  and let it settle for 10 min or so. Also today the lab temperature is somewhat higher and the HP3456A shows 10.00044V on 10K Fluke (and that is the HP tempco shows, the Keithley is stable as Hioki shows 10.000463 on the Fluke).

The Keithley 263 is a very stable and capable instrument even at higher currents, my unit is repaired and fully recapped, and for most part I use it over the newly acquired HP3245A, mostly for convenience reasons but it is not that far in DC performance and similar in the LF noise area.

Cheers

Alex

P.S. - on the photos, the first one is measuring the offset only (the current source is OFF), the second is +1mA current, the third is -1mA current. The Keithley is very symmetrical in polarity switching, due to its architecture.

[Alex Nikitin]

Here is a longer run (1mA from K263 into 10R DIY shunt) in the night time, the temperature change was about 1C over that period. The orange line is averaging for 5min (75 samples) . Vertical scale 50nV/div, horizontal - time.

Cheers

Alex

[Alex Nikitin]

Here in an interesting result with the same 10R DIY shunt and Keithley 263 supplying +/-100nA, so the voltage measured is +/- 1uV, with the HIOKI on FAST (NPLC1) speed (~30s/sec), 10 sec OFF, 10 sec +100nA, 10sec -100nA and last 10 sec OFF. The orange line is 5 samples moving average.

Cheers

Alex

[Alex Nikitin]

I rather like the temperature measuring feature. Strangely, if you copy data to a USB stick, the temperature measurements are what is on the screen, with 0.1C resolution. However if you request the data remotely, the resolution is 0.01C which does make a lot of difference! Below the results of an overnight run with the Hioki measuring the Fluke 731B 10V output and the room temperature at the same time. I plan to use the DM7275 together with a small DIY "temperature chamber" for tempco measurements on resistors and references.

Cheers

Alex