The hot-wire ammeter

Explanation:

The Hot-Wire Ammeter

• A hot-wire ammeter is a device used to measure current in a circuit. It operates based on the principle of thermal expansion of a wire when heated by the electric current passing through it. The instrument is designed to measure the effective value of the current in both alternating current (AC) and direct current (DC) circuits.
• When an electric current flows through the wire in the hot-wire ammeter, the wire heats up due to the resistive power loss. The heat causes the wire to expand, and this expansion is mechanically translated into a movement, which is measured and displayed on a calibrated scale. Since the heating effect of the current is proportional to the square of the current and independent of its direction, the hot-wire ammeter can measure the effective value of AC or DC current without differentiation.

Advantages:

• Can measure both AC and DC currents without requiring separate instruments.
• Insensitive to the waveform of AC, as it measures the effective (RMS) value of the current.
• Simple construction and operation, relying only on the thermal expansion of the wire.

Disadvantages:

• Limited accuracy compared to other types of ammeters, such as moving-coil ammeters.
• Slow response time due to the thermal inertia of the wire.
• Susceptible to environmental factors such as temperature variations and vibrations.

Applications: Hot-wire ammeters are typically used in situations where measuring the effective value of current is more important than waveform analysis. They are suitable for measuring currents in AC circuits with complex waveforms and for DC circuits where simplicity and reliability are prioritized.