Keithley DMM7510 7.5-Digit Multimeter Review, Teardown & Experiments

[VintageNut]

The current noise floor of a resistor sitting on a table using unshielded cables is something like 1 nA. If you want the maximum digits of a 1G resistor, all of the cabling, connections and the device must be shielded.

If you want the offset of the cable leakage to be subtracted, you have to guard the cables and the device. A guard enclosure inside of a shielded enclosure will eliminate noise and leakage offset.

It is not surprising that a 7 1/2 digit DMM measuring a 1G resistor appears to be noisy. Its probably not the DMM's fault.

[splin]

It is not surprising that a 7 1/2 digit DMM measuring a 1G resistor appears to be noisy. Its probably not the DMM's fault.

Probably not. But getting on for 0.3% noise??? That isn't Johnson noise!

[VintageNut]

It is not surprising that a 7 1/2 digit DMM measuring a 1G resistor appears to be noisy. Its probably not the DMM's fault.

Probably not. But getting on for 0.3% noise??? That isn't Johnson noise!

The 1G ohm range forces 0.68 uA in parallel with 10 megohms. That creates 6.8V across the 1G resistor which causes 6.8 nA to flow through the 1G resistor. (ignoring the solving the exact current)

6.8 nA @ 0.3% is 20.4 pA. 20.4 pA of noise in that resistor subject to the 60 Hz flying outside of the DMM is totally believable.

*edit* 0.69 uA

[Andreas]

Hello,

without having seen the video there is one thing what would interesting to me:
how sensitive is a heated LTFLU1 Reference which is used in the DMM7510 against tilting?

All LM399-based Instruments that I have seen are more or less (depending on individual reference) sensitive if you change the orientation from left to right or over the top of the instrument.

A example for a HP34401A measuring a stable LTZ1000A reference with 7V is attached:
in the diagram. Blue: orientation 0 = normal.
Red individual measurements with 100 NPLC
5 minutes in total with 4 minutes setup time + last minute for averaging final value
Green: Average of the 15 measurement values of the last minute.

01.08.2015 tilting 34401A LTZ1000A #2 100NPLC

0 = norm  = 7.1849649  (flat on the table)
1 = right = 7.1849672  (standing on the right edge)
2 = left  = 7.1849691   (standing on the left edge)
3 = over  = 7.1849698  (top side down)
4 = front = 7.1849819  (standing on the front bumper)
5 = back  = 7.1849568  (standing on the back bumper)
0 = norm2 = 7.1849660
4 = front2= 7.1849802
5 = back2 = 7.1849574
0 = norm3 = 7.1849668

so the largest difference of around 3.5 ppm is between
standing on the front side and standing on the bumpers of the back side.

By the way i have found a Keithley 2000 where between left and right side there were around 28ppm difference.

with best regards

Andreas

[dr.diesel]

New FW for both the 7510 and 2450, 1.6.1a.

Change log is several pages long, but a very noticeable improvement to the touch interface/action.

[HighVoltage]

Thanks for this information.
I will update my 2450 tonight

[HighVoltage]

I just updated my Keithley 2450 to the new FW 1.6.1a

The annoying hesitation when swiping the screen is gone.
This alone is enough reason to update to this latest FW.

In addition I see some small enhancements

[technogeeky]

Can someone replicate the experiment Hugoneus did where you measure and capture the FFT of a large amplitude signal near DC and a small amplitude signal near a few kHz, and see if the spurs are still present in the modern firmware?

I'm curious to see that plot and how good it can look.