Electronics > Beginners
Why don't Digital Ohmmeters have a zero initialization?
Hobby73:
My old analog multimeter had a control knob to zero the meter before measuring resistance. My understanding is that this adjustment would account for resistance in the test leads/probes, as well as changes in battery life.
Why don't DMM's have this function? I can imagine switching out test leads with different resistance that would seem to impact the reading, especially for very low resistance ranges.
IanB:
Many of them do have this function. It is usually on the button marked with Δ or Rel.
glarsson:
Common analog multimeters didn't have the resolution needed to see the test probe resistance. What they absolutely needed was a way to adjust the zero point as it varied substantially with battery voltage.
David Hess:
The state of the battery had a major effect on the ohms calibration so analog meters had to have an adjustment. But the constant current source used for ohms conversion in a digital meter is so accurate that this is not required.
As IanB wrote, the relative function can be used to remove the lead resistance if necessary.
wasyoungonce:
And old analog meter used moving coil as the meter which needed adjustment to zero.
We used to put them on amps and short across the probe inputs to make the meter coil form a reactive magnetic field if it moved during transport. This field would dampen the coil bouncing around. They were/are sensitive instruments.
Moving coils are still the easiest best way to measure pots etc for contact IMHO
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