I measure 10-40pF across the jacks of 5 multimeters on DCV. Most are around 35pFexcept 34401a measured 680pF quite high. Adding test leads does not add much.
34401a 177pF and 112pF to PE.
I find DMM input capacitance an issue if measuring low impedance HVDC, say 500V I've seen multimeters blank out or crash when connecting the (+) probe and even a tiny spark can be seen. It's a bit scary. A few product recalls over this (Fluke included) where the MCU reboots due to the EMI of that.
Also important is the common-mode capacitance, the other electrode being the multimeter's shield and your hand, or your workbench, or the grounded metal the multimeter is resting on. The input capacitance from each input (+), (-) to shield is not symmetrical. Mains-powered bench multimeters can have a Y-cap to PE.
This is a problem at RF especially if the DMM is cheaper and has no foil shield.
I wasn't sure about interpreting "when measuring bench DMM +- input terminal capacitance wrt to ground."
CM wrt to earth-ground it varies widely with handheld meters, depending on where they are, in your hand, on the floor, foil shield etc.
It's always imbalanced, (-) input is higher capacitance I believe because it goes all over the circuit board and not like (+) going to the divider resistor.
Bench multimeters you are basically measuring the power transformer winding capacitance or their Y-cap.
I wasn't sure about interpreting "when measuring bench DMM +- input terminal capacitance wrt to ground."
CM wrt to earth-ground it varies widely with handheld meters, depending on where they are, in your hand, on the floor, foil shield etc.
It's always imbalanced, (-) input is higher capacitance I believe because it goes all over the circuit board and not like (+) going to the divider resistor.
Bench multimeters you are basically measuring the power transformer winding capacitance or their Y-cap.
That is why i wrote:
sitting on top of isolated desk is 5pF both
siting on antistatic mat 15pF
sitting on grounded metal plate 19pF both.
And made a comment of not holding it in a hand.
Yes we know why benchtop meters are asymmetric in this regard.
Mike wanted to make this fact popularized by discussing it.
What's wrong with referencing earth at the outlet?
I wasn't sure about interpreting "when measuring bench DMM +- input terminal capacitance wrt to ground."
CM wrt to earth-ground it varies widely with handheld meters, depending on where they are, in your hand, on the floor, foil shield etc.
It's always imbalanced, (-) input is higher capacitance I believe because it goes all over the circuit board and not like (+) going to the divider resistor.
Bench multimeters you are basically measuring the power transformer winding capacitance or their Y-cap.
That is why i wrote:
sitting on top of isolated desk is 5pF both
siting on antistatic mat 15pF
sitting on grounded metal plate 19pF both.
And made a comment of not holding it in a hand.
Yes we know why benchtop meters are asymmetric in this regard.
Mike wanted to make this fact popularized by discussing it.
Josh,
Those measurements seem very low. Try using your DE-5000 instead at 10KHz like we did. You can use short banana plugs & cables directly with DE-5000, and plug the negative DE-5000 end into your power supply Green ground terminal like 2N3055 did, or just connect to something that has earth ground.
No need to calibrate the DE-5000, we are just looking for relative capacitance, cable capacitance and such shouldn't matter.
Best,
Josh,
Those measurements seem very low. Try using your DE-5000 instead at 10KHz like we did. You can use short banana plugs & cables directly with DE-5000, and plug the negative DE-5000 end into your power supply Green ground terminal like 2N3055 did, or just connect to something that has earth ground.
No need to calibrate the DE-5000, we are just looking for relative capacitance, cable capacitance and such shouldn't matter.
Best,
I agree these are very low. It might be because LCR meter is mains powered.
I also want to see DE-5000, which is handheld like my UNI-T.
Floobydust made some good points..
What's wrong with referencing earth at the outlet?
Nothing if you get the Allen Wrench into correct terminal
SDM3055X-E:
DCV:
Negative Terminal: 1.47615pF
Positive Terminal: 0.55323pF
...
The capacitance would also depend on the voltage range setting, when the input divider is connected the capacitance from the "+" input terminal might drop significantly. My measurements with a hand held capacitance meter (1kHz) for the DC voltage mode only:
The capacitance would also depend on the voltage range setting, when the input divider is connected the capacitance from the "+" input terminal might drop significantly. My measurements with a hand held capacitance meter (1kHz) for the DC voltage mode only:
Interesting. I tried that on my SDM3055X-E, and the DCV ranges did have a small impact. 20V to 1000V was 10pF higher than 200mV to 2V.
No effect at all for ACV.
Interesting. I tried that on my SDM3055X-E, and the DCV ranges did have a small impact. 20V to 1000V was 10pF higher than 200mV to 2V.
No effect at all for ACV.
What do you see when switching from DCV to ACV wrt the capacitance between terminals and + or - terminal to ground?
I have a convenient outlet on my bench, so I used a hex key inserted as my ground reference.