MULTI METERS and using them !

[dom2466]

hi guys. am a plumber and gas engineer in the making and was wondering if any of you electrians out there could give me the idiots guide to using a multimeter. photos would help but not essential

( i know you shouldnt mess with electirics but am just interesed in how to check how components are working or not, and check for voltage)

 

[bhm1712]

Best thing to do is to buy one and read the manual ( i know us blokes have a reputation for throwing it away before even looking, but they sometimes help)

otherwise, they are pretty self explanatory. Normally you have a dial on the front which has all of the different functions on it, with a small icon to identify what function is what

Usually they consist of ( on a basic meter) off, ohms, ac volts, dc volts, amps. some have smaller resolutions as well like Millivolts ac/dc and Milliamps. There are usually 3 terminals on the meter, a common in the middle and then either side will be a terminal for amps and volts/ohms. To measure different things, you have to swap the leads between the 2 outer terminals depending what you want to measure.

otherwise they are as easy to use as you expect...to measure volts, select AC position ( providing it is ac you want to measure) and use the leads to go between your live and neutral or earth. Ohms is used to measure the resistance of a circuit or component, for example a heater element. to measure the resistance of a heater element you would measure between the live and neutral terminal of the element. You can also use a multimeter as a basic way of checking for continuity between say a gas pipe and earth. If your trying to measure for signing off a job, a multimeter is not the ideal piece of kit. Thye should be used only as a basic piece of test equipment. multimeters should not be used to prove a circuit isolation. they are prone to picking up spurious voltages and displaying incorrect figures.

they come in handy when you are trying to identify unmarked cables between 2 places, say the consumer unit and a socket, you can use the ohms function to "bell" the cables out to indentify which cables are which.

 

[dom2466]

ive got the manual that came with the multi meter.
could you explain what i would be looknig for and how to test for it, say for example. testing to prove a pump was working.
or a compent like a switch was working ( what reading come on the multimater ?)

 

[wingcoax]

You would know a pump was not working when it did'nt. Sorry just joking. use th meter on a/c volts to see if it is getting power and on ohms to check the windings. Use the meter on diode (the little icon) to use the continuity check, hold across the switch terminals and you should get a bleep if the switch is ok. MAKE SURE YOUR POWER IS OFF FIRST.

 

[dom2466]

ok, thanks for your help and ill try it out on my boiler later.
ill let you how i got on. thanks alot. enjoy your Sunday.

 

[wingcoax]

Oh Yes I am, NOT WORKING!

 

[jmshep]

Hi
You may find this useful:
http://www.airborn.com.au/circuits/meter.html
If you Google for "using a multimeter" you will find a few similar sites but a quick look suggests this is not a bad one for starters. Although it relates to a particular make of multimeter the instructions apply to just about all similar types.

 

[Taylortwocities]

The site above will tell you how to make measurements.
IMO there is no point making measurements unless you know what you would expect to measure. Otherwise you cannot interpret if the measurement is correct.

You therefore need to have at least a basic understanding of electric circuits.

In the central heating I would expect that you would mostly be using the AC Voltage range. This would allow you to check if there is a supply at a particular point (across the terminals of a pump, for instance).
You can then say, with some confidence, say that the pump is knackered if you measure the correct voltage and the pump is not running.

Your issue is when you measure across the pump terminals and there is no voltage. You will then need a circuit diagram and apply some logic to determine where the problem may be.
It a logical process, something like this:

Is there power coming into the wiring centre
Is there power going to the programmer
Do you get power when the CH and/or DHW is selected
Does that power operate the valve
Does the valve's output contacts operate so you get power to the pump

So you'll need to read up on electric circuits as well as how to work the meter.
Pull up heating Plan diagram from the honeywell site and see if you can work through it, on paper. You may then be able to apply the principles to your home system, using your meter

 

[dom2466]

oh god this sounds more complicated than i first thought.
ill have to stick my head in some books then in my own boiler ( not the oven yet) and see what readings/measurements i get from the pump, fan etc.
cheers for the help ( i need it )

 

[ban-all-sheds]

If you Google for "using a multimeter" you will find a few similar sites but a quick look suggests this is not a bad one for starters. Although it relates to a particular make of multimeter the instructions apply to just about all similar types.

Also there are a lot of links at the end of the Wikipedia article.

 

[conny]

Don't forget, only have the power on when checking for voltages.
For continuity/resistance checking the power MUST BE OFF!

Otherwise you may get a nasty bang and a black mess where your meter was.
BE CAREFUL!

If in doubt, ask someone on here explaing what you want to do/check.

Good luck.