my multimeter behaves strange.

[whiz115]

Just today i got a new multimeter and first thing i noticed a problem.
when i turn it on DC or AC voltage function the multimeter shows few
mV which they keep changing all the time instead of staying zero!

first thought was that the probes aren't ok... but then i noticed that if i leave it alone and i go away then it stays constant on a specific value, and if i try to aproach my hand over the probes it starts again.

when i cross the probes then goes to zero and if i leave them alone it starts again showing numbers.

generaly it works perfectly and the measurements are fine.

 

[dknguyen]

It's just because the probes are floating and measure whatever charge happens to build up on them. As long as the reading stabilizes to zero when you touch them you are fine. All multimeters and oscillcopes do this.

 

[whiz115]

first time i see that... my other digital ones don't do that...

so such thing is kinda good?

P.S what does "relative measurement" and "duty" means on multimeters?

thanks!

 

[Boncuk]

DMM problem

HI whizz,

your problem isn't a real problem. If the DMM is a high impedance type it will measure stray voltages in its vicinity. Take it out to the jungle where electric power lines are miles away and it will zero.

Shorting the test cables should zero it.

Boncuk

 

[whiz115]

it says that it has Input Impedance 10Mohm.

this means that it acts like an amplifier and amplifies whatever
small signals picks up from the probes?!

 

[Dean Huster]

It isn't amplyfying them -- it's simply MEASURING them. It will tend to be worse on the ACV function. If you go to the ACA or DCA (current) function, it won't do that because the shunt resistors are effectively shorting the probes together, "grounding" the signal out.

Since this is a "new" DMM, consult your instruction book for the answers to your "relative measurement" and "duty" question.

Dean

 

[I²R]

it says that it has Input Impedance 10Mohm.

Input impedance is an indication of the instrument's sensitivity. The higher the impedance, the less loading a meter puts on the circuit under test and therefor the more accurate your readings are. 10 to 20 megohms is typical of digital voltmeters while analog meters often have impedances in the low tens of kOhms.