Question about Multimeters

  • #1
Ideally does a perfect multimeter have infinite resistance when testing current and voltage?
 

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  • #2
Bystander
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  • #3
Ok so Voltage is potential difference between two points and current is flow of charge... so you would want ideally infinite resistance to test the current but maybe no resistance at all when testing voltage? Is this correct, I correct my mistake?
 
  • #4
dlgoff
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"And?"
Multimeters went by a different name when I was a kid.
 
  • #5
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Did you mean voltmeters? as thats what they were most often used for.

I recently had to get a new one and discovered the analog varieties can be quite pricey and that the digital ones look real cheesy. I eventually decided on a Triplett for $30 bucks at Fry's Electronics. The multimeter dial seems a little wonky though it appears to act like a push button switch but I couldn't figure out what it did if anything. Also when I tested continuity I discovered my hearing is so bad I could hear the beep until I had the meter next to my ear.

My two earlier meters were Radio Shack meters and they were excellent. My favorite was an analog meter, my first, I had in high school. It hurt when a friend borrowed it and dropped it, breaking the glass over the meter. Later I got an LCD one that worked well until the LCD turned brownish thru 30+ years of aging I guess.
 
  • #6
Tom.G
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the analog varieties can be quite pricey
I can't attest to their quality, only their existence. Harbor Freight has them available starting at single-digit pricing. Search for 'multimeter' on their site.

Cheers,
Tom
 
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  • #7
NascentOxygen
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Ok so Voltage is potential difference between two points and current is flow of charge... so you would want ideally infinite resistance to test the current but maybe no resistance at all when testing voltage? Is this correct, I correct my mistake?
Suppose you needed to test the voltage of your car battery, so connected the multimeter between the battery's red and black terminals. Would you like the battery to sense that you were connecting zero ohms or infinite ohms between its terminals to make this measurement?
 
  • #9
CWatters
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Correct. You want infinite resistance on the voltage ranges to avoid loading the voltage source. Some meters use the gate of a FET to achieve this.

You want zero resistance on the current ranges so you don't increase the resistance in the circuit an change the current you are trying to measure.

Tip: Before putting your meter away always set it to a high voltage range.
 
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  • #10
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Tip: Before putting your meter away always set it to a high voltage range.
... and ensure the probes are not left in the current measurement jacks.
 
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  • #11
dlgoff
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Multimeters went by a different name when I was a kid.
Did you mean voltmeters?
I knew them as VOMs,
https://en.wikipedia.org/wiki/Multimeter said:
A multimeter or a multitester, also known as a VOM (volt-ohm-milliammeter) ...
 
  • #12
rbelli1
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... and ensure the probes are not left in the current measurement jacks.
Forgot this on my Fluke recently They take a $15 - $20 fuse to repair. (And it is a 400mA fuse.... Unfortunately my last current measurement was 500mA)

Even more dangerous is that some don't have a fuse at all.

BoB
 
  • #13
CWatters
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I still have a meter that let smoke out when it was connected to a battery while set on the 10A current range by accident
 
  • #14
Merlin3189
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I met them as AVO meters. Whether the AVO was a clever bit of branding, or just a fortuitous coincidence, I don't know.
 
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  • #15
davenn
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Tip: Before putting your meter away always set it to a high voltage range.

actually for most multimeters these days, don't do that, switch (rotate) to off to stop battery going flat :wink:

granted, there are those that have a separate on/off button and since most are auto ranging these days
just setting to voltage position is a good idea :smile:
 
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