Digital Multimeter accuracy?

[tempoct]

Hi,
When I short the test leads and measure the resistance, I got something around 0.2 ohm, should it be zero??

When I set to AC voltage but didn't connect the test lead to anything, I got very few micro volt.

Is this off? or it's normal. The meter is brand new Fluke 111.

Thanks,
tempoct

[jackinnj]

yes, you are measuring the resistance of the leads -- to null this out you need a "4-wire" ohm DVM -- something like an HP 3468, 3456, 34401, 3478 -- and various models from Fluke and others.

there are always microvolts of a.c. energy in the ethersphere -- that's what you are picking up.

[AndrewT]

Hi,
when checking the voltage ranges, both DC and AC, connecting the probes together should give 0V/mV on every range.
Most multimeters will give about 0.1 to 0.2 ohms on the lowest range when measuring the cables, connectors and internal resistances.
On the higher resistance ranges the meter will usually show 0r when connecting the probes.

The highest current range is almost certainly NOT fused. Take care particularly if you measure voltage when on a current range.

Another check that nearly always works is to reverse the probes when measuring a voltage source. The better meter should read +-same voltage.

[jackinnj]

Originally posted by AndrewT
Hi,
when checking the voltage ranges, both DC and AC, connecting the probes together should give 0V/mV on every range.

for A.C it depends upon the frequency range of the converter and whether the probes are shielded -- I can null my Keithley nanovoltmeter but it has a special shielded cable -- (and it also has a "null" button). for my Fluke and HP meters you will always pick up some EMI on the A.C. range if you don't use a coaxial cable. unshielded cables are like antennas.

unless you have to actually measure microvolts it really isn't an issue since the trailing digits get lost in the noise anyway.

[AndrewT]

Hi,
I am surprised that you have a lsd problem on voltage scales.
I have a range of very cheap through cheap to mid price DMMs. They ALL read zero volts on ALL scales when the probes are connected together. None of then have shielded cable nor a null facility and all are in unshielded cases.

I agree with the thread starter, disconnected probes regularly pick up interference and this shows as a wandering LSD which I believe is normal for these high impedance probes (aerials).

[tempoct]

Thank you guys. Just wanna make sure my new meter works fine.
The AC voltage I get is in micro volt range, not milli volt, so I guess it's the interference then.

[anatech]

Hi tempoct,
It sounds like your meter is fine. The better (83 series and higher) use a 4 terminal socket. The contacts in the jack are split in two. We check them with a copper shorting bar much shorter than your leads.

New Fluke meters are normally well within spec. when new. It would be rare to get one not working, but I have seen this.

-Chris