How ampere meter works?

Answer 1

Amperes of electrical current is analogous to pressure of water in a water pipe. The higher the "water pressure", the higher the amperage. An Ammeter ("amperage meter") measures "the water pressure" (the pressure of electrical current).

I use to teach Electronic Theory to Armature/Ham Radio operators and to computer techs at one company. So I can recite this suff in my sleep.

It depends on the kind of Ammeter you are talking about. There is one used for AC/alternating current and another for DC/Direct current. In DC measurements there is one or more resisters inside the meter. Usually precision resisters measuring less than an ohm. The meter measures the voltage drop across that resister and using the formula current(I) equals voltage(E) divided by resistance(R). It calculates current. Again this is for DC measurements This all comes from Ohms law. There are strict current limits for these meters too. For measuring High current you usually have to buy a special meter or a very accurate meter and an expensive & very accurate resister that looks like a copper bar. Also to protect this measurement circuit in the meters there is usually a fuse or the like Also many if not most meters have to be hooked up red to positive and black to negative. There may also be a diode or something to protect the meter from being hooking it up wrong. It will blow the fuse if you hook it up backwards. Warning! When measuring HIGH CURRENT the resisters get very hot rule of thumb the bigger the resister the hotter it gets.

For AC current measurement there is a ring on the meter that can open and reconnect around the AC wiring. There it does a similar measurement using an Inductive connection rather than a direct connection. This is the easiest way to measure an inductive load also.

Hope this helps.