Could my multimeter be bad? Getting random/odd continuity beeps when testing leads

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I had a thread a while back where I was trying to figure out where the leads of an ATX like connector were terminating on a server motherboard and when I would test some connections I would get a short beep (about 1/4 - 1/2 second) the first time I touch a motherboard lead (with a lead connected to an ATX pin) and then it wouldn't happen again if I touched it in the next minute or so. I could test the same leads maybe 15-30+ minutes later and I'd get the same short beep. This didn't happen with all the leads just some, maybe 10-20% of the motherboard leads I tested.

I also just started testing some used 50v/4700uf caps & 25v/10000uf caps (about 300 total) and I'm getting the same type of error. I'm using alligator clips on the meter and they are not touching at all, and there is no charge in the caps. I'll get the initial short beep and then when I test it again it doesn't beep. I'm testing these b/c in some caps I've found that they can be shorted inside so I wanted to at least sort ones that had this short.

So I was wondering how continuity testing works, if it sends a "high voltage" through the 2 leads and if the circuit in the meter is completed, it beeps. So I'm wondering if there is something in the meter that is causing this or if the meter might be bad. BTW, it is a "Southwire" auto sensing meter (auto detects range of measurement) and was about $45-50 at Home
Depot. I do get some odd behavior on the meter at times, especially when testing ohms, but I think that might have to do with the auto-ranging feature as well as possibly the item being tested (it seems pretty good on "static" resistors though).
 

djsfantasi

Joined Apr 11, 2010
6,531
I think it perfectly normal behavior. An uncharged cap initially appears to be a dead short. As the charge builds due to the voltage used for the continuity test, the resistance appears to approach infinity.

If testing power leads, it’s likely that there is a filter capacitor in there somewhere. Initially, will appear as a dead short. Over time, not so much.

Remove the leads, and the charge on the cap dissipates from the cap. So, 30 minutes later - dead short!

Note: Damn autocorrect!
 
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Thread Starter

RogueRose

Joined Oct 10, 2014
375
I think its just the auto sensing function starting its sensing function too low.

Well the auto range sensing is once the mode is set, for example the dial position where I test continuity has the Resistance/ohm, Capacitance, continuity & diode testing - which is 4 modes. I select the proper mode (continuity is 3rd on my meter) and then within that mode, it has the auto-range sensing.

Like for voltage there is AC & DC mode the once on the mode I don't have to select 2v, 20v, 200v, 2Kv - it just auto senses the proper range to display. There is also a range button to allow you to select a range to set, so it is a little faster if you are testing the same thing over and over. It takes about 1/2-1 second to detect the proper range on the auto detect setting.
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I think it perfectly normal behavior. An uncharted cap initially appears to be a dead short. As the charge builds due to the voltage used for the continuity test, the resistance appears to approach infinity.

If testing power leads, it’s likely that there is a filter capacitor in there somewhere. Initially, will appear as a dead short. Over time, not so much.

Remove the leads, and the charge on the cap dissipates from the cap. So, 30 minutes later - dead short!
Thanks for sharing that. This makes sense and I'm wondering if some meters are a little more sensitive than others b/c I've used other meters that don't seem to do this beep nearly as often. Most of the time they are less expensive models so maybe that is the case. I have a good Fluke meter I have access to that I'm going to test the same units and see if I get the same results - it will be interesting to find if it acts the same.
 

Tonyr1084

Joined Sep 24, 2015
4,738
Is your battery getting old? Once verified, auto-ranging takes a little time to settle.
That was my first though too. A weak battery can be problematic in getting accurate readings.

Once we (neighbor and I) were trying to determine which circuit was draining his car battery. My method was to monitor the voltage while he removed one fuse at a time, then put it back. A significant jump in voltage would mean we found a likely candidate for parasitic drain. As the test was taking some 10's of minutes without explanation the meter began reading higher and higher voltages until it was clear the meter was in error. The voltage began to go up into the 14 volt range without the engine running. That just doesn't happen. Perplexed, I went and grabbed a different meter and the voltage was down where it should be. Figuring that I had a meter gone bad I decided to take the battery out and save it for something else. When I checked the 9V battery it read (if memory serves) down in the 7 volt range. Put a new 9V in the meter and all was good again.

As for capacitance and the audible continuity checker - try this: Take a cap, discharge it, then check it for continuity. You'll probably get a beep. Then within just a few seconds, reverse the test leads on the cap. You should get a longer beep. But as you've stated, the beep goes away.

When a cap is discharged and you touch the leads to it, there's a large draw of current. Enough to make the meter think it has found continuity. But as the charge in the cap goes up it draws less and less current, resulting in the momentary beep, but not a continuous ongoing beep. By swapping the leads you're now introducing some extra current into the meter, making it think it has an excellent conductivity. But that will also fade as the charge changes.

So as @Wolframore said, first thought was a bad battery. After hearing more explanation of the symptoms, you're probably checking continuity across a capacitor.
 
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