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Author Topic: Multimeter Nightmare  (Read 9385 times)

barryfoote

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Multimeter Nightmare
« on: September 04, 2008, 01:29:14 PM »

Guys, Some of you....names not be mentioned......put me up to buying one of these little boxes....Well I have done so. The only problem is that  do not have a clue how to use them and all the technical gubbins in the instructions, leave me dead. I don't know the difference between AC current and DC Current, just to give you an idea of my ignorance. Now please don't laugh too much at me as there must be others in my position who would benefit from simple and clear destructions :D...sorry I mean instructions...

I Need Help.... :embarrassed: :embarrassed:

Looking at the photo I have worked out that the section marked with a V (top left) is to test volts and indeed when I connect it to a battery I do get a reading that looks like volts i.e 1.5 on a 1.5 battery and 6.1 on a 6 volt battery.... The section top right marked with an A, I assume is for amps, but I do not know where to stick my prongs to get a reading (No rude remarks please)or what setting to use in that section. Help :embarrassed: :embarrassed:

I also assume that the bottom left section measures resistance, but don't know what this means or how to use it. Any help will be gratefully received.

Other questions are:

How do I measure what charge a battery has left in it?

With regards to mains electricity...How do I test whether power exists in a particular cable or not? Using those illuminating screwdrivers is not really an option out here in bright sunlight!!

Now please don't use anything that remotely resembles technical jargon.....Imagine you are talking to the village idiot.......but then again maybe you will be... :D

Cheers guys in advance.

Barry
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DickyD

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Re: Multimeter Nightmare
« Reply #1 on: September 04, 2008, 01:52:14 PM »

Great Barry, thats the one I've got, now I might find out how to use it. O0
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dreadnought72

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Re: Multimeter Nightmare
« Reply #2 on: September 04, 2008, 02:21:17 PM »

Looking at the photo I have worked out that the section marked with a V (top left) is to test volts and indeed when I connect it to a battery I do get a reading that looks like volts i.e 1.5 on a 1.5 battery and 6.1 on a 6 volt battery....
Hey Barry - you're an expert! That's fine for DC volts. With the prongs where they are you can measure the voltage across things: batteries, motors, etc.

The section top right marked with an A, I assume is for amps, but I do not know where to stick my prongs to get a reading (No rude remarks please)or what setting to use in that section. Help :embarrassed: :embarrassed:
Here you need to put the probes in line with things. Between a motor terminal and the wire leading to it, for example, making sure that the multimeter is taking all the current. And in that instance (big amps) imove the red cable to the 10ADC socket and turn the dial to that 10A position. Don't try to measure thirty amps with it!

I also assume that the bottom left section measures resistance, but don't know what this means or how to use it. Any help will be gratefully received.
In the resistance mode stick the red cable back in the V/ohms/mA socket, and measure the resistance of an item by touching the component's terminals with the probe. You could have a couple of minutes of fun by measuring your skin resistance on the highest sensitivity settings! Before the novelty wears off.  :D

How do I measure what charge a battery has left in it?
I'm open to others' suggestions on this - but I'd measure a charged battery voltage and a flat battery voltage and determine where on that scale your "unknown" (but same type of) battery voltage is.

With regards to mains electricity...How do I test whether power exists in a particular cable or not? Using those illuminating screwdrivers is not really an option out here in bright sunlight!!
Be very very very careful with mains electricity.  :o

The safe way to test it: plug a fused tool or light in that you've tested elsewhere. Do not use meters like this for mains. I know it can (we're all looking at that 500 V AC bit at the top right) but please don't, if you've any concerns about your knowledge.

Regards,

Andy
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andrewh

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Re: Multimeter Nightmare
« Reply #3 on: September 04, 2008, 02:22:06 PM »

Footski

I've grabbed the pic, and will mark it up a bit and repost it with some Janet-and-John step-by-steps.

In the meantime PLEASE don't go anywhere near mains voltage with it.  It will detect and measure mains, but you do need to know what you are doing, and the consequences of getting it wrong could be exciting

It won't btw directly measure what is left in a battery (unless its one of the many Lithium batteries) but it will help in this task - tell us what kind of battery and what its doing ( example 6-cell Nimh drive battery, or 7AH SLA or whatever) and I'm sure lots of experts will pitch in and make it crystal -simple.

andrew
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Sandy Calder

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Re: Multimeter Nightmare
« Reply #4 on: September 04, 2008, 02:58:35 PM »

Voltage and current connection for a meter:-
http://www.doctronics.co.uk/meter.htm
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FullLeatherJacket

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Re: Multimeter Nightmare
« Reply #5 on: September 04, 2008, 04:06:20 PM »

Many thanks for that link, Sandy. It should be mandatory reading for all R/C boat modellers.
FLJ
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Sandy Calder

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Re: Multimeter Nightmare
« Reply #6 on: September 04, 2008, 04:23:54 PM »

Lesson 2 in the series   {-)
http://www.doctronics.co.uk/scope.htm
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Bunkerbarge

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Re: Multimeter Nightmare
« Reply #7 on: September 04, 2008, 05:36:17 PM »

Barry as far as this unit is concerned don't get too wrapped up in resistance at this stage.  Suffice to say that resistance is nothing more than that, the resistance to current flow.

I always think of electricity in terms of water in a hose because it is exactly the same.

Voltage is pressure, and is even referred to in that way in some circles.  Think of the pressure in the hose pipe as the same as voltage.

Current is the same as flow in the hose.  You can have a high voltage (pressure) but a low current (flow) or a low voltage but a high flow and you can even have a high voltage and a high flow but think of them in terms of the hose pipe.

Now add the resistance bit!!  Restrict the hose with your fingers and the pressure goes up and the flow goes down.  In just the same way increase the resistance and the voltage goes up and the current goes down.  You can therefore see that they are all related but for the purposes of what you want you are very unlikely to be measuring specific resistances.  You will however find the resistance range usefull for continuity testing.  If you measure the resistance between two points in a circuit and you get zero resistance then you know you have electrical continuity between those points.  If you get an infinate resistance reading then you know that you have a break in the circuit. 

You can use this for testing fuses quickly and easily.  If you get zero resistance the fuse is OK but if you get an infinity reading the fuse is blown.  Just to familiarise yourself with this range put the probes across a micro switch and flick the switch on and off.  You will see the resistance reading vary from zero to infinity.

For the sake of what we do in a model boat just think of DC current.  A battery generates DC (direct current) as the current flows around the circuit in the same direction all the time from the positive to the negative terminals on the battery.

AC (alternating current) is found in your mains and flows backwards and forwards at a rate according to the frequency of the circuit, round about 50 times a second, or 50 htz.

In any electrical circuit there is always a relationship between violtage, current and resistance according to V=IR but for the sake of your model boat applications just think of the hose pipe and the volts and current and simplify resistance to either zero or infinity for now.

A couple of things to remember:

Voltage must be measured across a load or supply, i.e. in parallel to the load and current must be measured in line with the load or in series.  For a simple motor, switch, fuse and battery circuit  the voltage must be measured across the battery terminals (parallel) and current must be measured by disconnecting one of the battery terminals and putting your meter leads one to the battery and one to the disconnected wire (series)

I would set up a small motor with a 1.5 volt battery and a switch and have a play with your meter in varying different ways around this simple circuit.  You will soon get the hang of it and find it quite interesting.

Never measure resistance across a live circuit, most modern meters have protection but older ones will go bang and you've lost the meter.  Trust me, I've done it!!

Always check the scale is set correctly before you touch the probes to anything.  Once again most meters nowadays have protection but putting the meter set at 12 volts across 240 volts would have traditionally been quite entertaining.

When testing resistance or continuity touch the probes together to check they read zero ohms first.

A battery voltage should only be measured when it is under load, measuring a battery voltage across it's two terminals may give you a suitable voltage reading but as soon as you connect it to a load, if the battery is not fully charged the voltage will immediately drop off.

Battery charge is a measure of current not voltage, don't get too wrapped up in volts anyway as you know what it should be by what it says on the cover!  You need to know a battery's state of charge however by measuring it's current and you can only measure that when it is discharging to a load.

I hope this all helps a bit.  Apologies if it makes things more confusing but if so than ask more questions! 
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barryfoote

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Re: Multimeter Nightmare
« Reply #8 on: September 04, 2008, 07:05:34 PM »

Looking at the photo I have worked out that the section marked with a V (top left) is to test volts and indeed when I connect it to a battery I do get a reading that looks like volts i.e 1.5 on a 1.5 battery and 6.1 on a 6 volt battery....
Hey Barry - you're an expert! That's fine for DC volts. With the prongs where they are you can measure the voltage across things: batteries, motors, etc.

The section top right marked with an A, I assume is for amps, but I do not know where to stick my prongs to get a reading (No rude remarks please)or what setting to use in that section. Help :embarrassed: :embarrassed:
Here you need to put the probes in line with things. Between a motor terminal and the wire leading to it, for example, making sure that the multimeter is taking all the current. And in that instance (big amps) imove the red cable to the 10ADC socket and turn the dial to that 10A position. Don't try to measure thirty amps with it!

I also assume that the bottom left section measures resistance, but don't know what this means or how to use it. Any help will be gratefully received.
In the resistance mode stick the red cable back in the V/ohms/mA socket, and measure the resistance of an item by touching the component's terminals with the probe. You could have a couple of minutes of fun by measuring your skin resistance on the highest sensitivity settings! Before the novelty wears off.  :D

How do I measure what charge a battery has left in it?
I'm open to others' suggestions on this - but I'd measure a charged battery voltage and a flat battery voltage and determine where on that scale your "unknown" (but same type of) battery voltage is.

With regards to mains electricity...How do I test whether power exists in a particular cable or not? Using those illuminating screwdrivers is not really an option out here in bright sunlight!!
Be very very very careful with mains electricity.  :o

The safe way to test it: plug a fused tool or light in that you've tested elsewhere. Do not use meters like this for mains. I know it can (we're all looking at that 500 V AC bit at the top right) but please don't, if you've any concerns about your knowledge.

Regards,

Andy

Andy,
Thanks for that and I will not go near the mains.....Been banned by SWMBO..

Barry
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barryfoote

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Re: Multimeter Nightmare
« Reply #9 on: September 04, 2008, 07:06:39 PM »

Footski

I've grabbed the pic, and will mark it up a bit and repost it with some Janet-and-John step-by-steps.

In the meantime PLEASE don't go anywhere near mains voltage with it.  It will detect and measure mains, but you do need to know what you are doing, and the consequences of getting it wrong could be exciting

It won't btw directly measure what is left in a battery (unless its one of the many Lithium batteries) but it will help in this task - tell us what kind of battery and what its doing ( example 6-cell Nimh drive battery, or 7AH SLA or whatever) and I'm sure lots of experts will pitch in and make it crystal -simple.

andrew

Andrew,

Thanks that would be very useful. The batteries I am using are both 6volt 4.6amp lead acid.
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Colin Bishop

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Re: Multimeter Nightmare
« Reply #10 on: September 04, 2008, 07:13:40 PM »

Quote
Thanks for that and I will not go near the mains.....Been banned by SWMBO..

Now you know she REALLY loves you. (or relies upon the cash flow....)  ;)
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barryfoote

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Re: Multimeter Nightmare
« Reply #11 on: September 04, 2008, 07:16:38 PM »

Barry as far as this unit is concerned don't get too wrapped up in resistance at this stage.  Suffice to say that resistance is nothing more than that, the resistance to current flow.

I always think of electricity in terms of water in a hose because it is exactly the same.

Voltage is pressure, and is even referred to in that way in some circles.  Think of the pressure in the hose pipe as the same as voltage.

Current is the same as flow in the hose.  You can have a high voltage (pressure) but a low current (flow) or a low voltage but a high flow and you can even have a high voltage and a high flow but think of them in terms of the hose pipe.

Now add the resistance bit!!  Restrict the hose with your fingers and the pressure goes up and the flow goes down.  In just the same way increase the resistance and the voltage goes up and the current goes down.  You can therefore see that they are all related but for the purposes of what you want you are very unlikely to be measuring specific resistances.  You will however find the resistance range usefull for continuity testing.  If you measure the resistance between two points in a circuit and you get zero resistance then you know you have electrical continuity between those points.  If you get an infinate resistance reading then you know that you have a break in the circuit. 

You can use this for testing fuses quickly and easily.  If you get zero resistance the fuse is OK but if you get an infinity reading the fuse is blown.  Just to familiarise yourself with this range put the probes across a micro switch and flick the switch on and off.  You will see the resistance reading vary from zero to infinity.

For the sake of what we do in a model boat just think of DC current.  A battery generates DC (direct current) as the current flows around the circuit in the same direction all the time from the positive to the negative terminals on the battery.

AC (alternating current) is found in your mains and flows backwards and forwards at a rate according to the frequency of the circuit, round about 50 times a second, or 50 htz.

In any electrical circuit there is always a relationship between violtage, current and resistance according to V=IR but for the sake of your model boat applications just think of the hose pipe and the volts and current and simplify resistance to either zero or infinity for now.

A couple of things to remember:

Voltage must be measured across a load or supply, i.e. in parallel to the load and current must be measured in line with the load or in series.  For a simple motor, switch, fuse and battery circuit  the voltage must be measured across the battery terminals (parallel) and current must be measured by disconnecting one of the battery terminals and putting your meter leads one to the battery and one to the disconnected wire (series)

I would set up a small motor with a 1.5 volt battery and a switch and have a play with your meter in varying different ways around this simple circuit.  You will soon get the hang of it and find it quite interesting.

Never measure resistance across a live circuit, most modern meters have protection but older ones will go bang and you've lost the meter.  Trust me, I've done it!!

Always check the scale is set correctly before you touch the probes to anything.  Once again most meters nowadays have protection but putting the meter set at 12 volts across 240 volts would have traditionally been quite entertaining.

When testing resistance or continuity touch the probes together to check they read zero ohms first.

A battery voltage should only be measured when it is under load, measuring a battery voltage across it's two terminals may give you a suitable voltage reading but as soon as you connect it to a load, if the battery is not fully charged the voltage will immediately drop off.

Battery charge is a measure of current not voltage, don't get too wrapped up in volts anyway as you know what it should be by what it says on the cover!  You need to know a battery's state of charge however by measuring it's current and you can only measure that when it is discharging to a load.

I hope this all helps a bit.  Apologies if it makes things more confusing but if so than ask more questions! 

Thank you very much for your efforts. it must have taken some time to type all that out and I do appreciate it. I have tested resistance as you suggest. I get a reading of either 000 or 1. I assume 0 is fine and 1 is the infinity you talk about, meaning the circuit is broken?

Now to test the current of say a boats motor. Do I set the dial to say 20m and put the positive prong to the positive of the battery and the negative prong to the negative of the motor, thus getting a reading in amps? Sorry to be a nuisance but I am learning....slowly.

Barry

PS    Colin,

If I was brave enough I would ask her which it was!!!!
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Bunkerbarge

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Re: Multimeter Nightmare
« Reply #12 on: September 04, 2008, 07:26:17 PM »

It did and that was my lunchbreak!!

Zero resistance should be a completed circuit, I'm not sure about the 1 as it should read infinity if the circuit is open.  Have a look in the book!

For your motor, disconnect the positive wire and connect the positive lead fromm your meter to the positive of the battery and the negative lead from the meter to the cable that you disconnected.  Then run the motor and your meter should show the current draw.  Obviously in this scenario the motor is not loaded and the current should be low but with this all set up and running put your fingers on the motor shaft and slowly apply pressure.  The motor will slow down and the curent will rise on your meter.  If in doubt set the current to the highest range and then bring it down until you get a usefull reading.
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jules64

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Re: Multimeter Nightmare
« Reply #13 on: September 04, 2008, 07:46:20 PM »

Barry

When measuring the current as Bunkerbarge described, you must also put the positive probe in the (10A) Amp socket on your meter. (Leave it in the normal socket for all other measurements.)

Best wishes
Jules64
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tigertiger

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Re: Multimeter Nightmare
« Reply #14 on: September 04, 2008, 08:53:30 PM »

000 = Zero

1 = the AVO that you are measuring is beyond the scale of the meter, or change to a higher setting.
So if you look at the DC volt range you will see several settings. Best to start at a higher setting and work down. The further down the range the more accurate the reading.

Exactly 1v would read 1.00 or 1.000 etc depending onn the range you are in.

A reading of '   1' for anything is out of range. This might be your infinity, but it may not.
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barryfoote

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Re: Multimeter Nightmare
« Reply #15 on: September 04, 2008, 09:12:48 PM »

Hey thanks guys, got that bit and will do Bunkerbarges test in tomorrow.....Had a bit too much vino tinto to start with electrics now..

The resistance reading on any setting is either 1 or 000, so I assume on this model that 1 is infinity.

I really appreciate all the effort and hpe Dickyd is also learning from thi!!

Barry
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sheerline

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Re: Multimeter Nightmare
« Reply #16 on: September 04, 2008, 09:20:27 PM »

Barry, everyone is pitching in for you here... I told you they would and before long you will get the hang of things. A small but important point worth mentioning when measuring current: When you have finished using the current reading facililty on the meter... ALWAYS take the red lead out of the 10Adc socket and put it back into the V,A, ohms socket! If you leave it there and inadvertantly try to read volts.. say your 12v drive battery, it will not like it and will blow the internal fuse rendering the Adc socket inoperable. Should you do this (we all have at some time), you can undo the small screw on the back casing and having prised it off you should find a small glass fuse in there which will have blown. The size of fuse will be stamped on one of the metal end caps so the next trip out will be off to a stockist of 20mm fuses. Buy a pack of five as you WILL do it again some time, there is no shame in this.. it's a fairly common error.

Here's a good test for your boat:

Red lead in 10Adc
Black lead in com
Meter knob set to 10Adc

Remove the red  + lead from your boat battery and connect black meter lead to it.
Connect red meter lead to your meter to the + battery terminal.

With boat in bath, slowly open the throttle and watch the reading (in Amps) slowly rise on your meter scale and note how many Amps the boat is drawing from your battery at full throttle.

Now you have a maximum current reading (Amps) which is great but fairly meaningless unless you know what to do next.

Look at your battery, somewhere on it, it will state the voltage and current capacity of the pack. IE   '12 Volt 5Ahr'
Now divide the battery capacity (5Ahr) by the max current reading you obtained from your meter.

If for example your meter reading was say.. 2.5Amps then 5Ahr(battery) divided by 2.5Amps (motor reading) equals 0.5. Therefore, at full throttle your boat should theotretically run for 0.5 hrs on a fully charged battery!

You may well say, "I knew that anyway, Iv'e bin running the thing for the past year!" but now at least you have the means to determine how long your boat should run on any given battery.


Another small test whilst the boat is in the bath:

Re-connect red + wire for motor to boat battery as per normal boat running set-up
Place red meter wire  back into V,A,ohms socket
Set meter to read  20 Vdc (your battery is lower voltage than that on the scale so the meter will not be overloaded).
Black meter lead to Neg  battery terminal.
Red meter lead to Pos battery terminal
Note the battery voltage

Now fire up the boat and go for throttle up with the meter still connected and watch the battery voltage.
You will notice it will fall off very slightly .. even on a fully charged battery.
Give the boat a good caning at full throttle for a few mins and keep an eye on the voltmeter.
If the battery is fully charged and in good nick, the voltage will not be seen to drop very much and will hold up for a considerable period. If the battery is in poor condition or low on charge, the voltage will start dropping quite dramatically.

I hope this helps with the basic idea of using your meter and even if you never bother with the other functions on the front scale, these two functions on their own will tell you most of which you need to know about your boats setup and and running times.

Sorry Barry if it all sounds a bit long winded but it's easier to do than write about.. in fact doing it takes moments when you are familiar with it. Keep us posted on progress.

REMEMBER TO TAKE THE RED LEAD OUT OF THE 10A SOCKET!!











 
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barryfoote

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Re: Multimeter Nightmare
« Reply #17 on: September 04, 2008, 09:27:05 PM »

Thanks Sheerline.

Let me put it this way.  now know more than I did a few hours ago, so that is progress thanks to you chaps. I will give your plan a go tomorrow too. All in the name of science and learning.

Barry
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sheerline

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Re: Multimeter Nightmare
« Reply #18 on: September 04, 2008, 10:10:19 PM »

Barry, avoid doing it with a hangover!!
Good luck..........Chris
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barriew

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Re: Multimeter Nightmare
« Reply #19 on: September 05, 2008, 08:46:10 AM »

Barry,

Just to confirm your assumption, on all the "cheap" Digital Multi-meters I have seen, on the Resistance Ranges 1 is infinity. It is cheaper to display a 1 than try to display the infinity sign, which would probably require a special LCD {-)

Barrie
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malcolmfrary

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Re: Multimeter Nightmare
« Reply #20 on: September 05, 2008, 10:26:52 AM »

The really nice thing about a digital meter is that when you connect the leads back to front, it still gives a reading, it just puts a "-" in front of the number, rather than doing the needle type meter thing where the needle tries to go the wrong way and crimps itself round the stop. 
It helps to remember to switch it off after use (and switch it on before - dont ask) as the battery will last a long time, but its not infinite.
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sheerline

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Re: Multimeter Nightmare
« Reply #21 on: September 05, 2008, 11:43:33 AM »

Ah, bent needle references Malcolm, do I detect an ex AVO man in that remark? 'Bin there done that' as they say and I was also responsible for filling the scale area with smoke when I was an apprentice!
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Bunkerbarge

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Re: Multimeter Nightmare
« Reply #22 on: September 05, 2008, 07:10:57 PM »

It was an absolutely beautifull huge old Avo meter that I once put across a power supply while it was still set to resistance.  It didn't half make me jump :o

The electrical engineer was not a happy teddy!!!
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sheerline

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Re: Multimeter Nightmare
« Reply #23 on: September 05, 2008, 08:15:21 PM »

The little pop up button designed to protect the meter movement just wasn't fast enough for the likes of us, eh Bunkerbarge!
I have to say that I suddenly discovered that I no longer posess a moving coil multimeter and recently had desperate need of one.
I was working on my re-built Morris Vedette boat engine, trying to sort out the dynamo charging arrangements with the engine running. This engine has a magneto and using a digi meter in close proximity to that unit was as much use as a chocolate firegaurd as the radiated interference drove the digi nuts, with spurious readings all over theplace. The leads act as aerials and pump all sorts of muck into the sensitive measuring circuitry. I found an old Sparkrite dwell meter with a proper moving coil unit and used it as a voltmeter instead. Digi meters are great bits of kit but they can have their own little set of limitations. 
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OMK

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Re: Multimeter Nightmare
« Reply #24 on: September 05, 2008, 09:56:06 PM »

<Footski> "Wife, wife! Come quick! Look... I finally got the hang of this multi-met....................."


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