digital multi meter question

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qwerty7

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#112888 25-Dec-2012 23:31

I have a dmm which says on the back .. this meter must not be connected to high energy sources which have transient voltages greater than 1000v. This includes 240v mains supply.

What does that mean, how does it work explain it?
I can understand if the meter cannot handle over 1000 volts but ..
a) What would happen if i connected it to more than 1000 volts
b) Why does that include 240 volts mains supply ? or do they just say that to protect people who don't really know what they are doing

sleemanj

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#737257 26-Dec-2012 02:41

Answers:
a) Anything from nothing, to KABLAM and take off your fingers.
b) Probably it's just C-Y-A, the 240v mains line could technically have a massive spike, but you'd hope not.

Edumacational material for you from the king of Multimeter teardowns, reviews and rants, Dave Jones:
http://www.youtube.com/watch?v=M-FZP1U2dkM#t=6m13s (blowing up meters with 4kv)

http://www.youtube.com/watch?v=Ewyf9mzIfi0#t=55s (Dave ranting about a meter that blew up on 240v)

http://www.youtube.com/watch?v=zUhnGp5vh60 (all about Input Protection)

---
James Sleeman
I sell lots of stuff for electronic enthusiasts...

gregmcc

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#737280 26-Dec-2012 09:11

because the insulation on the test leads and multimeter is only rated to 1000V above that and you start getting leakage voltage which will give you and electric shock

Radiotron

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#737376 26-Dec-2012 14:55

It appears the multimeter does not have sufficient protection to safely break high fault currents (such encountered with the AC mains), this means in worst case scenario, when internal protection device such as a fuse opens, there is risk of arcing, fire, and harm to user. If you plan on regularly using a multimeter, and going anywhere near the AC mains with it, buy a quality brand such as Fluke, they are expensive, but last almost forever. And, use the maker's own leads that came with it.
Otherwise, just keep the cheapie strictly for low voltage measurements.

In order to get the right answer, one must ask the right question

gzt

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#737380 26-Dec-2012 15:17

I bought a $20 cheapie a while back. Quality of the leads and probes absolutely awful. Measurement accuracy varies wildly depending on battery voltage and multiple other factors.

Decent ones start from round $100 at jaycar. Fluke are great but expensive for a general purpose model.

qwerty7

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#737414 26-Dec-2012 17:10

cool thanks, i understand it now