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Discuss Multimeter help needed in the Electrical Tools and Products area at ElectriciansForums.net

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i am hoping you may be able to help. I’ll try to explain my problem, any help gratefully received.

Part of what I do is train fire alarm engineers and as part of the practical is battery calculations, which we need to measure the stand by and full alarm load off the battery leads.
So the process is swap leads to mA position and switch to mA reading, connect leads in series to the battery disconnect main power so now mA is displayed for stand by the press sounder button on fire panel and you have alarm load.

Despite every time explaining not to do anything different & not to do it until I say etc etc nearly every course some one will either not change the leads or something stupid and bang as a minimum fuse blown.

What I am asking, is there a multimeter that does not need leads switching or as some sort of non fuse blowing feature that will allow non listening people to not blow meters?.
 
D

Deleted member 26818

Was about to say yes, then realised the multimeters are connected in series.
I doubt very much that you’ll find a multimeter that can withstand being connected in series.
You may be able to obtain an ammeter that can, but the size and cost will be large.
Would it not be better to use an Amp Clamp?
 

Rob

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Arms Access
You can get low range current clamp meters, however because you're measuring DC current they will not be as widely available as the AC versions.
Something like this would do:

https://www.amazon.com/General-Technologies-Corp-CM100-Current/dp/B001TCWL1E

Maybe worth contacting the site sponsor test-meter.co.uk and see if they can recommend something for you. You also get a discount for being a member.
 
The last time I say a multi meter that could with stand that sort of abuse with out blowing was 30 odd years ago and the meter was an "AVO - 8 " with built in resetable circuit breaker. You may be able to find a few old one's floating around, but they are collectors items now days.
 

telectrix

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Arms Access
The last time I say a multi meter that could with stand that sort of abuse with out blowing was 30 odd years ago and the meter was an "AVO - 8 " with built in resetable circuit breaker. You may be able to find a few old one's floating around, but they are collectors items now days.
i've still got 2 of them. one is actually in calibration. there's always a few on ebay.
 

SparkyChick

Moderator
Staff member
TA
Arms Access
Esteemed Member
Do you supply the multimeters? If so, I would stop providing them and make a course pre-requisite that they have their own, people take more care when they've had to shell out for the gear.

And maybe take an old meter and blow it up with a small stage pyrotechnics device, film this and play it to them to demonstrate what could happen if they get it wrong. Bit OTT perhaps but will lighten the mood. Could even maybe make it really good and include a ballistics gel hand, overpower the explosion so it damaged fingers :D
 

Rob

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Arms Access
Fused leads, if available for the meters you use, with a fuse rated lower than the internal one.
Good idea, but they must follow a strict proving routine if they use the multimeter for dead testing. This is the main reason multimeters are not recommended for this purpose.

If they manage to pop the fuse in the test lead, they will never read voltage.
 
T

The Ghost

Just an idea, but how about you dispense with that method altogether. Instead just assay the load each point demands from the manufacturer (say 80ma) and so 10 call points 800ma and just test the battery disconnected out of the box on the table separately?
 
  • Thread Starter Thread Starter
  • #14
Don't allow them to energise the circuit until the test connections have been checked by yourself
That’s what I have had to resort to, however sometimes they decide they know better and alter the leads.
 
[QUOTE="dmxtothemax, post: 1515525, member: 88482".....]
May be able to find a few old one's floating around, but they are collectors items now days. [/QUOTE]
-------
A) Being a bit heavier they don't enjoy mechanical shock ..
(1.2 Metres onto concrete )..as well
-Less bounce-
B) ---Using a cheap replaceable external shunt ---
.... could try measuring voltage across a 10 Ohm 2W resistor...
..but that's not the real test 0.95V
( -ten times bigger in mV-)
and may burn fingers if put across 12V !
C) A virtual environment "meter" ..may be the only fix for this "pretend listening" behavior (testing the tester)
 
Last edited:
D

Deleted member 26818

I think, that unless you insist all student supply their own meters, you’l just have to factor in replacing fuses into your pricing structure somehow.
 

Lucien Nunes

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TA
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Esteemed Member
There are meters with an 'alert' function, that makes a beeping noise and/ or flashes up 'LEAD' if you select a voltage range with red lead still in the current socket. Of course, if you also leave the meter on a current range and try to measure the voltage, that's no help.

But what are these people doing? I swap the leads on mine from current to voltage many, many times a day, every day, and haven't made this mistake for a decade or more. You need to drill into them the significance of checking the connections and settings for every setup bar none.

It's a good job they aren't trying to use a vintage valve tester. You can destroy a valuable AVO VCM instantly (beyond economic repair as the special panel meters haven't been made for years) just by turning one of its dials one click too far. FWIW the girls who used to help out on a Saturday never seemed to have any difficulty using them accurately.
 

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