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Author Topic: multimeter Question  (Read 5430 times)

Offline derwood

  • Newbie
  • *
  • Posts: 16
multimeter Question
« on: August 09, 2010, 03:36:07 AM »
I have two different multimeters and both give me readings that don't make sense. On the 200ma setting I get a reading of about 190ma but if I switch to the 10 amp setting it reads about 600ma. Both multimeters do the same thing. Does anybody else get this problem and which is the correct reading?


Offline truthbeknown

  • Jr. Member
  • **
  • Posts: 98
Re: multimeter Question
« Reply #1 on: August 09, 2010, 06:20:24 AM »
Are you measuring AC or DC Amps? Are your meters true RMS meters?

Offline fritznien

  • Sr. Member
  • ****
  • Posts: 293
Re: multimeter Question
« Reply #2 on: August 09, 2010, 07:04:44 AM »
I have two different multimeters and both give me readings that don't make sense. On the 200ma setting I get a reading of about 190ma but if I switch to the 10 amp setting it reads about 600ma. Both multimeters do the same thing. Does anybody else get this problem and which is the correct reading?
too many variables to say for sue. could be a bad meter.
or the resistance going from one range to the other changes enough so that each measurement is correct.
or you have a strange waveform or frequency, in which case a regular meter cannot measure properly.
regular meters are made for DC and 60 cycle sinewave.
fritznien

Offline mscoffman

  • Hero Member
  • *****
  • Posts: 1377
Re: multimeter Question
« Reply #3 on: August 09, 2010, 07:59:16 PM »

Multimeters have a unitary "trial resistor" that is set as
a compromise. Also, you cannot measure current with
a meter without an external load on the power source.

To get an accurate reading take a precision 1 ohm resistor
measured on the ohms scale of a DVM and put it in series
with the source and load. Then read the voltage across the
1 ohm resistor and use ohms law to compute the current.

For higher currents there is a device called a "resistive
standard shunt" that has a resistance of either .1 or .01
ohms used the same way.

Whatever voltage you read across the trial resister ends up
being unavailable to load device from the source. So the lower
the volts reading the better. This is part of the problem.

User Gotoluc did this successfully with a nichrome wire coil
in the link: "Self Running Coil"

http://www.overunity.com/index.php?topic=8892.0


:S:MarkSCoffman