- #1
AchillesWrathfulLove
- 30
- 6
Ideally does a perfect multimeter have infinite resistance when testing current and voltage?
Question about Multimeters
- Thread starter AchillesWrathfulLove
- Start date
Click For Summary
Discussion Overview
The discussion revolves around the characteristics and ideal properties of multimeters, particularly in relation to measuring current and voltage. Participants explore the definitions of voltage and current, the implications of resistance settings in multimeters, and share personal experiences with different types of multimeters.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Personal anecdotes
Main Points Raised
- Some participants propose that a perfect multimeter would have infinite resistance when measuring current and possibly no resistance when measuring voltage.
- Others argue that infinite resistance is desirable on voltage ranges to avoid loading the voltage source, while zero resistance is needed on current ranges to accurately measure current without altering the circuit.
- A participant shares a personal anecdote about the evolution of multimeters, mentioning their previous experiences with analog and digital varieties.
- There is a discussion about the naming conventions of multimeters, with references to terms like VOM (volt-ohm-milliammeter) and AVO meters.
- Some participants mention practical tips for using multimeters, including setting them to a high voltage range before storage and ensuring probes are not left in current measurement jacks.
- One participant recalls an incident where their meter was damaged due to incorrect settings during use.
Areas of Agreement / Disagreement
Participants express differing views on the ideal resistance settings for measuring current and voltage, indicating that there is no consensus on the best approach. Additionally, there are varying opinions on the naming and history of multimeters.
Contextual Notes
Participants discuss the implications of resistance settings in multimeters without resolving the nuances of how these settings affect measurements. There are also references to personal experiences with different multimeter models, which may not reflect broader trends or standards.
Who May Find This Useful
This discussion may be of interest to individuals learning about multimeters, electronics enthusiasts, and those seeking practical advice on multimeter usage and characteristics.
- #2
Bystander
Science Advisor
Homework Helper
Gold Member
- 5,621
- 1,773
"And?" Think for a moment about the definitions.AchillesWrathfulLove said:
- #3
AchillesWrathfulLove
- 30
- 6
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
Science Advisor
Gold Member
- 4,458
- 3,265
Multimeters went by a different name when I was a kid.Bystander said:
- #5
jedishrfu
Mentor
- 15,681
- 10,477
Did you mean voltmeters? as that's 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.
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
Science Advisor
Gold Member
- 5,661
- 4,507
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.jedishrfu said:
Cheers,
Tom
- #7
NascentOxygen
Staff Emeritus
Science Advisor
Homework Helper
- 9,253
- 1,080
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?AchillesWrathfulLove said:
- #8
AchillesWrathfulLove
- 30
- 6
Ok so other way around I think
- #9
CWatters
Science Advisor
Homework Helper
Gold Member
- 10,546
- 2,324
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.
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.
- #10
Guineafowl
- 910
- 418
CWatters said:
... and ensure the probes are not left in the current measurement jacks.
- #11
dlgoff
Science Advisor
Gold Member
- 4,458
- 3,265
dlgoff said:
jedishrfu said:
I knew them as VOMs,
https://en.wikipedia.org/wiki/Multimeter said:
- #12
rbelli1
Gold Member
- 1,092
- 446
Guineafowl said:
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
Science Advisor
Homework Helper
Gold Member
- 10,546
- 2,324
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
Homework Helper
Gold Member
- 1,733
- 824
I met them as AVO meters. Whether the AVO was a clever bit of branding, or just a fortuitous coincidence, I don't know.
- #15
davenn
Science Advisor
Gold Member
- 9,724
- 11,806
actually for most multimeters these days, don't do that, switch (rotate) to off to stop battery going flatCWatters said:
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
