What is an Ammeter

Ammeters are measuring devices that can be used to measure the electrical current in a circuit. They are available in many different designs. Effects of the electric current are used in ammeters of various types.
Ammeter, also current strength or ammeter called, measuring instruments, with which one can measure the electric current in a circuit are. They are available in many different designs. Different effects of the electric current are used in ammeters of different designs.
Ammeters must always be connected in series with the electrical device or component on which the amperage is to be measured. This is necessary so that the current flows through them, the strength of which is to be measured (Fig. 2).
As a flow meter using, Moving Coil. They differ in their structure and in their mode of operation.

Circuit of an ammeter

Moving coil measuring devices

In moving-coil measuring devices, a rotatably mounted small coil is in the magnetic field of a permanent magnet. A pointer is connected to this coil. If a current flows through the small coil, it becomes a magnet itself and interacts with the magnetic field of the permanent magnet. The greater the current through the coil, the stronger the resulting magnetic field and the stronger the deflection of the coil and thus the pointer (Fig. 3). The magnetic effect of the electric current is used.

Moving coil measuring mechanism

Moving iron gauges

Moving iron gauges, also known as soft iron gauges, have a fixed iron plate in a coil and a rotatable iron plate connected to the axis and the pointer (Fig. 4). If current flows through the coil, the two iron sheets are magnetized in the same direction and repel each other. The repulsion and thus the deflection of the pointer is greater, the greater the current through the coil. The magnetic effect of the electric current is used.

Moving iron measuring mechanism

Hot-wire gauges

In hot-wire meters, a pointer is connected to a thin platinum wire that is firmly stretched between two connections (Fig. 5). If a current flows through this wire, it heats up and expands. This expansion is transferred to a pointer. The greater the current that flows through the wire, the greater the expansion. So the thermal effect of the electric current is used.

Multimeters

Nowadays, multimeters are mostly used to measure voltage or current. Multiple measuring devices are often moving-coil measuring devices in which the measuring range can be changed and which are suitable for measuring direct current as well as measuring alternating current.
If you use a multimeter to measure the current, you should follow the steps below:

  • Set the type of current (direct current or alternating current) on the measuring device that is present in the circuit!
  • Set the largest measuring range for the amperage on the measuring device! This is especially necessary if you do not know how big the current is.
  • Connect the measuring device in series to the electrical device in the circuit in which the current is to be measured! With direct current, make sure that the negative pole of the electrical source is connected to the negative pole of the measuring device and the positive pole of the electrical source is connected to the positive pole of the measuring device.
  • After closing the circuit, switch the measuring range down so that the last third of the scale can be read as far as possible. Then the measurement error is due to the measuring device being the smallest.
  • Read the amperage! Please note that the set measuring range indicates the maximum value on the scale!
Hot-wire measuring mechanism