how do you feel about measuring resistance or continuity in circuits that a re hot, i see people doing it all the time, and it seems to work, but somet hing about it doesn't seem right... is it an ok thing to do? or is it ok on ly in so and so situation, or you should never do that?
thoughts?
hot, i see people doing it all the time, and it seems to work, but something about it doesn't seem right... is it an ok thing to do? or is it ok only in so and so situation, or you should never do that?
seems like a bad idea, unless you have a good meter that doesn't fail if you abuse it. Even then, the readings you can get could be questionable.
I should probably test what it takes to trick a fluke meter into beeping on the continuity test, it's probably not very much.
hot, i see people doing it all the time, and it seems to work, but something about it doesn't seem right... is it an ok thing to do? or is it ok only in so and so situation, or you should never do that?
hot, i see people doing it all the time, and it seems to work, but something about it doesn't seem right... is it an ok thing to do? or is it ok only in so and so situation, or you should never do that?
Here's a thought experiment for you. What's the resistance of a battery? Put your Fluke on it. How many ohms does it measure? Does that agree with your expectation? What does that say about the wisdom of trusting ohms measurements on a live system with a Fluke?
Are you sure you're not seeing people measure resistance in-circuit with the power off, or measuring voltages? Both of those are valid things to do.
Ohm meters work by injecting a current into the part then measuring the voltage developed. Some circuits will be upset by having the current injected into them, and most circuits will have some standing voltage between most of the nodes -- so the readings will be off and the circuit won't be working right.
I could see it being valid if you were making a DC measurement to a spot in the circuit that was known to be AC-coupled -- but that rules out a whole lot of opportunities.
-- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
hot, i see people doing it all the time, and it seems to work, but something about it doesn't seem right... is it an ok thing to do? or is it ok only in so and so situation, or you should never do that?
If you need to ask, don't do it.
t are hot, i see people doing it all the time, and it seems to work, but so mething about it doesn't seem right... is it an ok thing to do? or is it ok only in so and so situation, or you should never do that?
yeah i don't think the people doing it are asking, but good advice
you know, it's really more the continuity test I see people do with live circuits, not the resistance measurement... and it's the continuity test that seems to work most of the time.... scratch resistance out of it, just continuity
It's even more spectacular to measure the resistance of the mains with an AVO. (I'm told the flames are purple.)
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
are hot, i see people doing it all the time, and it seems to work, but something about it doesn't seem right... is it an ok thing to do? or is it ok only in so and so situation, or you should never do that?
Sure, it really comes down to the knowledge (or lack of) of the operator. All methods are valid if used in the right context. To read resistance directly in a live circuit using the meter set for resistance would at least be wrong and as mentioned leading to a world of pain :-)
Yes they are but the last time I did that was in 1954, yes 59 years ago. 8-o 8-o 8-o
-- John G
I don't want to encourage dangerous behavior (so, don't do this!), but consider a live* circuit with a series switch of some kind. When the switch is open, you can measure the load R, perhaps even measure it accurately depending on common-mode voltage and rejection. Close it, deliberately or accidentally, and you may well experience a "Joerg moment" or much worse. Google 'arc flash' and 'arc blast' for examples.
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