Electronics > Projects, Designs, and Technical Stuff
Is it safe to test for continuity with multimeter
kripton2035:
make yourself a simple continuity meter, like the "shorty" device.
http://kripton2035.free.fr/continuity-repos.html
c64:
--- Quote from: bdunham7 on July 16, 2020, 06:03:36 am ---
--- Quote from: c64 on July 16, 2020, 05:36:40 am ---Nope. I really mean 200M. In 200R range it's 0.25V / 0.5V
--- End quote ---
Wow! I just looked--that's fairly impressive for a $5 meter. I might just have to upgrade!
--- End quote ---
Yes it's quite good. But yours is still better value for money, because is costs infinitely less ($5/$0=∞) :D
H713:
--- Quote from: bob91343 on July 14, 2020, 04:10:12 am ---You are right. A continuity test should be reserved for cables and connectors, and not used on circuitry. The diode test is on many meters just so they can say they have it but I don't think it's a good thing. Read the manual and see how much current it supplies and you can judge from that how to use it.
--- End quote ---
If you're working on audio power amps or anything with lots of discrete transistors, you will use the diode test constantly. If an amp is blowing fuses (or making a lab supply current limit), one of the first things to check for a collector-emitter short on the output devices. Extremely common failure, especially in some amps. Diode test doesn't tell for sure that a transistor is good, but it will tell you if it is completely toasted.
You should also keep in mind that the capacitance in your scope input can be dangerous too, especially on circuits with high voltage rails. An obvious example would be a modern high voltage power supply. You may have 600V for the power section (not all that rare to find a power supply that can output 600V), but also some sensitive 3.3V logic. It's very easy to blow things up by charging that capacitance up to a high voltage, then probing a logic circuit or other low voltage solid-state part.
Mind you, it's also easy to blow things up by slipping with a probe.
The point I'm trying to make is that you always need to be careful when taking measurements to ensure that you're 1) not interfering with the circuit you're trying to measure, thus affecting your measurements, 2) causing damage to your DUT, and 3) not causing damage to the test equipment and 4) not causing damage to yourself. If you're only dealing with digital logic circuits, #3 and #4 are probably not all that likely, but if you're dealing with a big power amplifier (be it audio or RF), you may need to carefully consider all four.
You should never just assume that your test equipment is invisible to the circuit you are testing.
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