Products > Test Equipment
Multimeters With Low Ohms Function
AVGresponding:
You had better luck than me! Trying it with the F289 data logger yielded no usable results. I might try it with a scope this weekend if I get time.
Alex Nikitin:
FWIW, my MetraHit 28S has the o/c voltage on all Ohms ranges ~0.62V at 23C room temperature, dropping to 0.3V with 10M connected on 30M range. The current on 300 Ohm range is ~0.2mA . The diode test mode has ~2.9V o/c (which I suspect is just the battery voltage at the time of measurement) and <1mA current (looks like a 3K resistor in series).
Cheers
Alex
BlackFX:
Hioki 3238
Ohms 6v Max, 20nA (100meg range) - 1mA (200ohm range)
Low Ohms 0.45v Max, 100nA (2000k range) - 100uA (2000ohm range)
alm:
--- Quote from: ermionesrl on January 26, 2022, 06:16:12 pm ---I tried ACV mode and (this was expected but not to this extent) 34401A is awful here with a fall time of 5.14s, that translates to an effective 240nF, not according to 34401A specs that say 1Mohm in parallel with 100pf. In the schematic (page 158 of the document 34401-90013) I see C301, a 220nF capacitor in series with a 1Mohm resistor going to a OPAMP virtual GND, thus we are reading the 220nF discharging to an effective R of 11Mohm, measuring it through a resistance divider 11M/10M. Taking everything in account, effective measured C is 230nF. Good, it's C301.
--- End quote ---
That's the AC coupling capacitor in series that has forms a high-pass filter together with the input impedance. The ACV range is specified from 3 Hz - 300 kHz. At 3 Hz, the 220 nF capacitor has an impedance of about 240 Ohms. So I'm sure this won't affect the 1 MOhm +/- 2% spec. A fall time of 5.14s is well within the spec for a 7 second settling time in AC mode with the filter set to slow (see attached table from page 51 of the 34401-90004 user manual). Although I'm not sure how this relates to Ohms measurement?
ermionesrl:
alm:
Yes, the 220nF capacitor is not a problem in real ACV measurements. It has nothing to do with ohm function but I found interesting it's possible to infer much about the input circuit with this simple setup.
It was interesting to know multimeter input capacitance to understand a supposed anomalous settling time in a measurement done by AVGresponding. Of course ideal would be to measure capacitance in ohm function, but I think it's very difficult to do it, so I did in DCV just to have at least an idea of the order of magnitude of the value.
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