Products > Test Equipment

Multimeters With Low Ohms Function

(1/13) > >>

EEVblog:

--- Quote from: floobydust on January 11, 2022, 02:25:07 am ---I have seen multimeters malfunction doing Ohms measurement on a DC rail with capacitance and semiconductors present.

Starting at the lowest Ohms range, beep and charging happens until the multimeter upranges with the corresponding lower compliance current then causing the capacitor's voltage to start dropping. This can also be aggravated due to semi's becoming biased on and current drain increases as the voltage goes up. It's a non-linear load. Auto-ranging will oscillate between ranges hunting all the time.

I believe the test current on the Brymen is quite low now at 0.3mA compared to 1-4mA on other multimeters. I just manual range to look for shorts.

--- End quote ---

Some old school meters have a "Low ohms" function that has a compliance voltage below 0.6V so it doesn't switch on semiconductor junctions in-circuit. Seems to have fallen out of favour since the 80's and 90's. My first digital meter, a Soar had it.

EEVblog:

--- Quote from: EEVblog on January 15, 2022, 09:56:25 pm ---Some old school meters have a "Low ohms" function that has a compliance voltage below 0.6V so it doesn't switch on semiconductor junctions in-circuit. Seems to have fallen out of favour since the 80's and 90's. My first digital meter, a Soar had it.

--- End quote ---

e.g



And Metex:

rsjsouza:
The Keysight U1272A/U1273A have a very low ohms voltage - I did a comparison a while ago with a few other multimeters (U1282A, 189, UT61E) and was quite pleased to find out this.
AFAIK it is not configurable like your examples.

AVGresponding:

--- Quote from: EEVblog on January 15, 2022, 09:56:25 pm ---
--- Quote from: floobydust on January 11, 2022, 02:25:07 am ---I have seen multimeters malfunction doing Ohms measurement on a DC rail with capacitance and semiconductors present.

Starting at the lowest Ohms range, beep and charging happens until the multimeter upranges with the corresponding lower compliance current then causing the capacitor's voltage to start dropping. This can also be aggravated due to semi's becoming biased on and current drain increases as the voltage goes up. It's a non-linear load. Auto-ranging will oscillate between ranges hunting all the time.

I believe the test current on the Brymen is quite low now at 0.3mA compared to 1-4mA on other multimeters. I just manual range to look for shorts.

--- End quote ---

Some old school meters have a "Low ohms" function that has a compliance voltage below 0.6V so it doesn't switch on semiconductor junctions in-circuit. Seems to have fallen out of favour since the 80's and 90's. My first digital meter, a Soar had it.

--- End quote ---

This sent me down the rabbit hole investigating the continuity compliance voltage on all my meters (no small task!   :-DD  ).

I found some (to me) interesting results.

Most were in the range from 3-4.5V, with some outliers: F87V ~7V, Keithley 2015 6.6V, Gossen M242A 8.4V (running off 2 AA Ni-MH!), Fluke T5-1000 ~1.1V, UT139C 1.04V, and finally a winner-winner-chicken-dinner, the Mastech 2108A with 0.44V!
I had a strange result by accident when I tried my Fluke 99B S2, got around 500mV, but then realised it was in auto-ranging ohms mode, and not continuity. Put it in continuity, and it went right up to 3.2V!
Decided to try just ohms mode on a few other meters, and found pretty much the same thing; a compliance voltage of around 400-500mV, the one outlier I had there was the Tektronix DMM912 with ~850mV.
Obviously, using ohms instead of continuity has some drawbacks, like response speed, no audible signal (unless your meter has an audible output on %dev function, you could set that up), but it's worth bearing in mind, if you find something with continuity, check it with ohms too.

EEVblog:
I'm thinking of a vidoe titled: "What happened to the Low Ohms Function?"
I could dig my original Soar out of the archives.
It would be interetsing to know what modern meters with have such a function, or have a complaince volatge under 0.6V?

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version