Products > Test Equipment

Multimeters With Low Ohms Function

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kripton2035:
self-promoting, but this is really kick-ass to locate short circuits...
http://kripton2035.free.fr/Projects/shorty-display.html

Squarewave:
That Soar looks rather like the AVO DA212





--- Quote from: EEVblog on January 15, 2022, 09:59:53 pm ---
--- 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




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Kleinstein:
One can still test for shorts in circuit, if the open circuit voltage goes higher. A diode junction would still not measure very low ohms, but what you get with some 0.6 V at a resistor and this is usually quite high.

There are 3 points with a limited voltage/power: one is protecting sensitive parts that can not withstand a higher voltage and could be damaged (e.g. BE junction in reverse from more than some 6 V, some LEDs - at least according to the abs. max specs and some were actually sensitive to > 5 V).

The other point is measuring sensors like PTCs / NTCs, where the test current may already cause significant self heating. A small PT1000 tested with 1 mA test current is not ideal. A 10 K NTC with 1 mA test current can be way off. 

The 3 rd point is dry contact testing, so testing the low votlage performance of contacts, where a higher voltage can destroy an oxide layer at the contact and this way hide a contact problem. This dry ohms testing wants a rather low maximum voltage, often realized with a prallel resistor.

A high voltage is nice for diode testing to also measure a blue / white LEDs and maybe a 5 V zener.
On the other side high resistor ranges may need a relatively high voltage to gets low senstivity to hum.

AVGresponding:

--- Quote from: Neutrion on January 16, 2022, 04:34:58 am ---This reminds me of the discussion somwhere about why the low vs high continuity voltages are good or bad.
Although I don't remember any positiv point for the high ones apart from getting through dirt easyer.

AVGresponding: Did you also measure the currents?


On the other hand the voltage vs. semiconductors is just one thing, to not to have false alarm on capacitances would reqiere an other solution.

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I did not, but it's easily arranged. Give me a couple of days to perform the tests and tabulate the results though.

Regarding the issue of turning semiconductor junctions on, it's also worth mentioning that quite a few here like to tinker with older equipment, that may well be full of germanium transistors. None of the compliance voltages I've seen so far would be low enough to not turn a germanium junction on.

nali:
My Meterman 38XR circa 2005 vintage is about 480mV on all ranges

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