How to use amp meter

[Joker56]

 
I'm a complete novice when it comes to using amp meter , would it be possible for the wise ones to do an idiots guide to using please , I switch it on , place the probes , no idea of what I should be seeing voltage wise etc which of the click settings to use .
Many thanks in advance, apologies if already covered
Peter B

[Sprintex]

Google is your friend


Paul

[Ray Haddad]

An amp meter measures current, not voltage. What you most likely have is a multimeter. Not knowing the brand, I can't advise you about the knob settings but I can tell you how to take a measurement.

A multimeter can have many functions but the basic ones you need for most use are voltage, amperage and resistance. Almost every meter I have ever used has had at least those three. Some others have capacitance, inductance and component testing for transistors. Those last are of very little use to a beginner.

They all have something in common. A black (negative) lead and a red (positive) lead. Remember that and be sure the black is in the Negative or Common receptacle and the red in the Plus. Some meters make you move the red lead for current measuring. Read your manual for that.

Moving on, the two leads will be used differently for each type of measurement. For voltage, you adjust your meter to the range you believe your reading should be. For example, if you believe your voltage is 12V DC, you set it for a range that exceeds that. Normally the 20vdc range will do. Put the black lead on the negative side and the red on the positive and you should see a reading of 12vdc (if digital, the numbers will appear - if analog, your meter will deflect to the mark of 12vdc). For AC, you have to change your range to the appropriate AC voltage. If reading mains power, your meter should be set for the 400v AC range and you put one lead on either side of the mains line (not the bottom ground plug) and the other lead in the other mains receptacle. When measuring mains power, be sure to never touch exposed metal on your leads. Don't play around. Unless you need to test it, stay away from mains power.

The next thing in this informative little post is resistance readings. For that, all power must be removed before you use your meter. If you try to measure resistance on a live circuit you will blow a fuse inside the meter and that will cost you in time and money. So remember, all power off when measuring resistance. For reading a resistor, your readings will be inaccurate if you measure them in the circuit but you often have no choice. You first have to know the value of the resistor or what it should be. For that you will need to look up the resistor color code and learn how to determine if a part is a resistor or not. The leads go on either side of the part and you should get a close but not exact reading. There are many electronic formulas out there that will explain why the inaccuracy occurs but that requires a classroom and hours of study so we won't go any further right now.

Amps are measured in series with a circuit under test. If you want to see how much current an engine draws, for example, you would set your meter to read amps and making sure the red lead is in the right place, take your measurement in series with your load. The engine is your load. I recommend you set up a test oval of track and try this. Put your engine on the track and test that it runs in an oval like it should. Then remove one of the leads going from the power pack to the engine. This is for DC only, not DCC. Remove the negative lead, put the black meter lead on the power supply terminal and the red lead on the wire that you just removed. The meter is then between the power supply (power pack) and the track. If you have alligator clips, that is helpful. Run the engine and look at the meter to see how many amps it draws when running. Set it first on the 10 amp range for locomotives. For larger train scales, you might draw more but that's not likely.

This is by no means a full lesson for you. Take your meter to your next club meeting or drop in on another modeler and ask about it. Or, find a local amateur radio operator in your area for some hands on advice.

[Malc]

A very comprehensive set of instructions for the novice Ray, well done.

[Joker56]

Ray
Many thanks for your reply , I think you may be correct as in not amp meter Doh !! Told you folks I didn't know what to do with it, will try again over the weekend , it's that mysterious world of electrickery ( catweasle)

[Ray Haddad]

Joker, it sounds complicated and for the first time, it is. Over time it will become a trusted friend and become much easier. After more than 50 years in electronics, I still occasionally forget to remove power when checking a resistor. I still sometimes use my leads in reverse making a 12vdc look like a -12vdc. Modern meters are far more forgiving than the old analog meters.

It bears repeating to be very careful around mains power. I don't recommend it unless you absolutely must do it. Call a sparky and let them do it while you watch. Those guys live long and prosper because they obey the safety rules around mains power.

[AndyGif]

It bears repeating to be very careful around mains power. I don't recommend it unless you absolutely must do it. Call a sparky and let them do it while you watch. Those guys live long and prosper because they obey the safety rules around mains power.

if its dangerous they get the apprentice to do it......

Reminds me of the time the factory sparks told me i was ok to cut through an armoured cable on a 3 phase pump motor as he had the fuses in his pocket
Only to find out in a shower of  sparks and disintegrating hacksaw blade that he in fact had removed the fuses from the online running pump, not the one due to be relocated. 

Some choice words were exchanged during a brief chase out of  the factory, theres a reason the switch room has a lockable door, its so the sparks can hide!!!!

[Ray Haddad]

Andy, there are FAR easier ways to change a hacksaw blade.

I'd laugh if it wasn't so tragic. Glad you are still among us.

[AndyGif]

Just as well it was armoured cable, or it would probably have been a different story.
This is the same sparks that used to put his rollup ciggie on the live busbars in the switch panels when working on them, he had very very dry skin and didn't get shocked.
We (the fitting staff) used to think that he'd had fried his brain a long time ago.

[Ray Haddad]

Andy, I'm also guessing that you had a rubber or plastic handle on the saw too or the situation would have been far worse.

[AndyGif]

no, good steel and ali framed hack saw.

was probably wearing red pvc industrial gloves though, the place i worked at was foul, we dealt with liquid waste from the meat industry.

[Ray Haddad]

Well, Andy, that explains it. You were very lucky, mate. I once unscrewed a burned out bulb from a string of Christmas tree lights and the bulb cracked. My fingers touched the element inside and the next thing I remember is having to stand up while leaning against the couch. And that was only a 115v mains. Nothing like what you had there.

Thankfully that was my only experience with mains power going astray on my body. Although, I was assigned to climb and repair an antenna on a naval station radio tower that had come undone during a storm. Despite the rain and 50mhp winds, I managed to get everything squared away and when I asked for a test of the radio, the static electricity and the low signal gave me a whopper of a shock. Thank God for my safety harness. I wobbled back down the service ladder and downed about 3 pots of coffee afterwards.

[REGP]

Ray

Thanks for that Tutorial found it both interesting and useful and already printed off.

Ray (REGP)

[gorebridge2001]

When I first left school and went to work with an electrical company, the boss told me electricity's perfectly safe until you forget it's dangerous! Nearly 50 years later I always remember those words, even when performing the simplest task.

[James C]

During my first aid training we were taught that the electricity is not off until the fuses are in YOUR pocket. Don't trust even the "professionals" to say it's ok if you're the one going to be doing the actual dangerous bit!