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Old 2nd February 2006, 01:47 AM   #1
tempoct is offline tempoct  United States
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Question Digital Multimeter accuracy?

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
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Old 2nd February 2006, 01:50 AM   #2
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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.
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Old 2nd February 2006, 09:10 AM   #3
AndrewT is offline AndrewT  Scotland
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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.
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Old 2nd February 2006, 12:34 PM   #4
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Quote:
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.
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Old 2nd February 2006, 12:59 PM   #5
AndrewT is offline AndrewT  Scotland
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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).
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Old 2nd February 2006, 10:25 PM   #6
tempoct is offline tempoct  United States
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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.
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Old 4th February 2006, 05:58 PM   #7
anatech is offline anatech  Canada
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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
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