Multimeter help needed

[Diver233]

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?.

 

[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?

 

[Diver233]

Do the amp clamps go as low as 95mA?

 

[Bobster]

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.

 

[dmxtothemax]

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]

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.

 

[davesparks]

Don't allow them to energise the circuit until the test connections have been checked by yourself

 

[SparkyChick]

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

 

[bill01803]

Di-Log do one

 

[snowhead]

Fused leads, if available for the meters you use, with a fuse rated lower than the internal one.

 

[Deleted member 105166]

And maybe take an old meter and blow it up with a small stage pyrotechnics device, film this and play it to them

... not forgetting to ensure your organ is on full display in the background throughout...

 

[Bobster]

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.

 

[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?

 

[Diver233]

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.

 

[static zap]

[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)

 

[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.

 

[davesparks]

Make them all aware that they will be charged if they damage the multimeter

 

[KWCFC]

I've been working in security for 5 years and still do it... you've got no hope mate lol

 

[Lucien Nunes]

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.

 

[ian.]

I replaced the low current range fuse with a resetable one for this exact reason: https://uk.farnell.com/c/circuit-protection/thermistors/pptc-resettable-fuses

 

[ian.]

I replaced the low current range fuse with a resetable one for this exact reason: https://uk.farnell.com/c/circuit-protection/thermistors/pptc-resettable-fuses

 

[Lucien Nunes]

That's a pragmatic solution, but the minimum resistance of a Polyfuse that has a low enough trip current to protect the shunt, is likely to have a higher cold resistance than the shunt itself, and much higher than the conventional fuse it replaces. If one needs the lowest possible voltage burden from the current ranges, it's something of a compromise.

 

[MJPD29]

My fluke doesn't need leads changing for any tests

 

[Diver233]

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.

I have ordered one of these from USA so will let you know how accurate it is when it arrived.
Thank you all for your input.

 

[Diver233]

My fluke doesn't need leads changing for any tests

Which fluke is it I’ll have a look

 

[MJPD29]

Which fluke is it I’ll have a look

Fluke 116, hopefully it will do what you need I've been impressed with it

 

[alasdairp]

Fluke 116, hopefully it will do what you need I've been impressed with it

The Fluke 116 only measures up to 600 microamps (AC or DC). i.e. 0.0006 Amps. That is while the rotary switch is adequate. It won't suit here at all!

 

[MJPD29]

The Fluke 116 only measures up to 600 microamps (AC or DC). i.e. 0.0006 Amps. That is while the rotary switch is adequate. It won't suit here at all!

Ok alasdair calm down only trying to help

 

[alasdairp]

Ok alasdair calm down only trying to help

Sorry - I felt calm enough at the time! Few glasses of home-made red wine inside now and I am certainly calm. The 116 is an unusual meter for electrical work - more an electronics multimeter. In fact I was amazed that it only goes to 600 microamps.

 

[Adrian1958]

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?.

Maybe you need to start the course with some basic use of test instruments.
How to measure Volts , Amps , ohms , difference between AC and DC , lead swapping etc.
When i was responsible for teaching mechanical service engineers basic electronics , i started the training on how to use test instruments multimeters , oscilloscopes etc. All instruments were labelled with , CHECK TEST LEAD CONFIGURATION BEFORE CONNECTING TEST LEADS TO THE CIRCUIT.
Its education from the trainer.
It sounds like its a regular mistake by students and it shouldnt be with the correct training, yes a mistake will happen, but this should not be occurring on a regular basis.

 

[Diver233]

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.

Was thinking about your answer and yes you have summed it up completely.
“You haven’t made this mistake for a decade or more”.
Trouble is these are mainly brand new engineers on short courses and they probably won’t make the mistake again for a decade or more, how do I stop them doing their first and last time at my expense ️️Lol

 

[SparkyChick]

how do I stop them doing their first and last time at my expense ️️Lol

Make it a course pre-requisite that they have their own test gear and that they use it.

I suspect the reason that most of us don't make the mistake very often is because we've blown up our own gear and had to suffer the consequences, which as you clearly know involves spending money

 

[Diver233]

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.

Rob you are a genius, the meter arrived today, it works an absolute dream. Had to come from USA and was a bit pricey but no more students blowing multimeters up.
Thank you.

 

[Bobster]

Rob you are a genius, the meter arrived today, it works an absolute dream. Had to come from USA and was a bit pricey but no more students blowing multimeters up.
Thank you.

No problem, like I mentioned though I'm sure someone @Test-Meter could have gotten you an equivalent from the UK with a forum discount applied too.

Maybe worth baring in mind if you need more for your staff.

 

[Diver233]

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.

Rob you are a genius, the meter arrived today, it works an absolute dream. Had to come from USA and was a bit pricey but no more students blowing multimeters up.
Thank you.

No problem, like I mentioned though I'm sure someone @Test-Meter could have gotten you an equivalent from the UK with a forum discount applied too.

Maybe worth baring in mind if you need more for your staff.

Now I know it works I will try find in uk, I did message them regards one of their clamp meters to see if it would do the same, they just sent back a data sheet didn’t answer my question sadly

 

[Bobster]

Now I know it works I will try find in uk, I did message them regards one of their clamp meters to see if it would do the same, they just sent back a data sheet didn’t answer my question sadly

Give them a call, I'm sure they would be glad to explain.

Or, post up the data sheet an I or someone on here will tell you if it can do the same.

Edit: This meter is actually quite cheap for measuring DC current like this. Hall effect measuring is a lot harder to produce and be accurate as standard clamp meters.

 

[Diver233]

Rob have a look at

AEMC CM605 Low Current AC/DC Clamp Meter (100A) - https://www.test-meter.co.uk/aemc-cm605-low-current-dc-clamp-meter/

Looks fairly much like the same unit maybe re badged.
If it’s the same as the amazon one it would fit the bill. Checked the amazon one against my new calibrated flukes and it was within a few mA.

 

[Bobster]

Rob have a look at

AEMC CM605 Low Current AC/DC Clamp Meter (100A) - https://www.test-meter.co.uk/aemc-cm605-low-current-dc-clamp-meter/

Looks fairly much like the same unit maybe re badged.
If it’s the same as the amazon one it would fit the bill. Checked the amazon one against my new calibrated flukes and it was within a few mA.

Yes, that will do the job.

Like I said, they look costly but are actually very cheap for what they are doing. So the accuracy is going to be not as good as what the flukes, in series measurement will be. Error will be less the larger the current you are trying to read.

However, it solves your problem, an If they get an errant reading or one that's on the boundaries of being permissible, they can use the fluke to check under supervision if necessary.

 

[Adrian1958]

Good news , Martindale do some good stuff, worth giving them a call.

Martindale Electric Co Ltd, Metrohm House, Imperial Park, Imperial Way, Watford, Hertfordshire, WD24 4PP
T: +44 (0) 1923 441 717
F: +44 (0) 1923 446 900