# Ammeter Explained #### What Do Ammeters Measure? - Leading Electrical Questions

An Ammeter is a measuring device that is used to measure the flow of electricity in the form of current in a circuit. Electrical currents are then measured in the form of amperes, hence the name, "ammeter". The term "ammeter" is sometimes used incorrectly as "ampmeter".

Ammeters are designed, (as well as ohmmeters and voltmeters), to be used with the use of a sensitive current detector such as a moving coil in a galvanometer. In order to measure the electric current flow through it, an ammeter is placed in series with a circuit element. The ammeter is designed to offer very low resistance to the current, so that it does not appreciably change the circuit it is measuring. To do this, a small resistor is placed in parallel with the galvanometer to shunt most of the current around the galvanometer. Its value is chosen so that when the design current flows through the meter it will deflect to its full-scale reading. A galvanometer full-scale current is very small: on the order of milliamperes.

An Ammeter is analog. It is not mechanical, or digital. It uses an analog to digital converter (ADC) to measure the voltage across the shunt resistor. The ADC is read by a microcomputer that performs the calculations to display the current through the resistor.

One problem with ammeters is the need for these meters to be inserted into the circuit and become part of it. Be warned: an ammeter connected in series or connected in parallel with a electrical circuit will probably blow the fuse, which can possibly damage the ammeter and cause injury.

An ideal ammeter has zero resistance so that the the circuit in which it has been placed is not disturbed. An ideal ammeter is a short circuit. However, as with the voltmeter, no ammeter can ever be ideal, and therefore all ammeters have some ( hopefully) small internal shunt resistance.

One problem with ammeters is the need for these meters to be inserted into the circuit and become part of it. Mistakenly placing ammeters in parallel with a circuit will blow the fuse, possibly damaging the ammeter, causing a voltage drop and causing injury.

An ideal ammeter has zero resistance so that the the circuit in which it has been placed is not disturbed. An ideal ammeter is a short circuit. However, as with the voltmeter, no ammeter can ever be ideal, and therefore all ammeters have some ( hopefully) small internal resistance.

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