Thermal Ammeter

Definition - What does Thermal Ammeter mean?

A Thermal Ammeter, also known as a hot-wire ammeter, is a device that is used to measure the true RMS for an applied AC current. There is also an arrangement for the measurement of small expansion caused in the wire when it is heated. This is achieved by attaching one end of the wire to an index lever and the other to a fixed support. The elongation of the wire causes a rotation in a mirror from which a ray of light is reflected, and the movement of this ray over a scale will then provide the necessary means of indication.

Petropedia explains Thermal Ammeter

A thermal ammeter or a hot wire ammeter works when current passes through a wire which expands as this wire is heated. Although these instruments have slow response time and low accuracy, they were at times used in measuring radio frequency current. These ammeters consist of a wire through which current is passed and measured.

The following are some of the uses of thermal ammeters:

  • They are used for measuring low frequency AC and continuous currents.
  • They are used when there is no temperature correction.
  • They are used with AC when no correction is needed for frequency, unless that frequency is very high.
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