Ammeters for Current Measurement
Demonstrative Video
Ammeters
The ideal ammeter has zero internal resistance.
But practically the ammeter has small internal resistance.
The measuring range of the ammeter depends on the value of resistance.
Working Principle & Connection
The working principle of an ammeter depends on the current flowing along with its resistance.
Very little impedance is used inside the ammeter as it must drop the least amount of voltage attached to it.
It is connected to the series of circuits as the current in the series circuit is the same.
Types of Ammeter
Depending on their design
Permanent moving coil ammeter.
Moving iron/coil ammeter.
Electro-dynamometer ammeter.
Rectifier type ammeter.
By the type of current flowing
DC ammeter
AC ammeter
Permanent moving coil ammeter
used only for the measurement of the direct current
conductor is placed between the pole of the permanent magnet.
When the current flows through the coil, it starts deflecting.
The deflection of the coil depends on the magnitude of current flows through it.
Moving iron/coil ammeter
measures both the alternating and direct current
coil freely moves between the poles of a permanent magnet. When the current passes through the coil, it starts deflecting at a certain angle. The deflection of the coil is proportional to the current passes through the coil.
Electro-dynamometer ammeter
measurement of both AC and DC
The accuracy of the instrument is high as compared to the PMMC and MI instrument.
The calibration of the instrument is same both for AC and DC, i.e. if DC calibrates the instrument then without re-calibration, it is used for AC measurement.
Rectifier type ammeter
used for measuring the alternating current.
The instruments using the rectifying instrument which converts the direction of current and pass it to the PMMC instrument.
Such type of instrument is used for measuring the current in the communication circuit.
Ammeter Shunt
The high current directly passes through the ammeter which damages their internal circuit.
This problem can be removed by connecting the shunt resistance in parallel with the ammeter.
The major portion of the current passes through the shunt resistance.
The shunt resistance will not affect the working of the ammeter, i.e., the movement of the coil remains same.
Effect of Temperature in Ammeter
Ammeter is sensitive to the surrounding temperature which causes the error in the reading.
This can reduce by swamping resistance.
The resistance having zero temperature coefficient is known as the swamping resistance.
It connects in series with the ammeter.
The swamping resistance reduces the effect of temperature on the meter.
The ammeter has the inbuilt fuse which protects the ammeter from the heavy current.
If substantial current flows through the ammeter, the fuse will break.
Ammeter would not measure the current until the fuse is replaced