Short Answer

Dynamometer-type instruments are electrical measuring devices that work on the principle of interaction between magnetic fields produced by current-carrying coils. They use two coils to produce a deflecting force.

These instruments can measure both AC and DC quantities such as current, voltage, and power. They are commonly used as wattmeters due to their accuracy.

Detailed Explanation:

Dynamometer Type Instruments

Meaning of Dynamometer Type Instruments

Dynamometer-type instruments are measuring instruments used in electrical engineering to measure various electrical quantities like current, voltage, and especially power. They operate on the principle of interaction between the magnetic fields of two current-carrying coils.

These instruments consist mainly of two coils: a fixed coil and a moving coil. When current flows through these coils, magnetic fields are produced. The interaction between these magnetic fields creates a force, which causes the moving coil to rotate.

A pointer is attached to the moving coil, which moves over a calibrated scale to indicate the measured value. The amount of deflection depends on the strength of the currents in the coils.

Dynamometer-type instruments are widely used because they can work on both alternating current (AC) and direct current (DC), making them versatile.

Construction and Working

The construction of a dynamometer-type instrument includes fixed coils, a moving coil, springs, a pointer, and a damping system.

The fixed coils are usually connected in series with the load and carry the load current. The moving coil is placed inside the magnetic field produced by the fixed coils and carries a current proportional to the voltage.

When current flows through both coils, magnetic fields are produced. These fields interact with each other, producing a torque that causes the moving coil to rotate.

The deflecting torque is proportional to the product of the currents in the two coils. In the case of a wattmeter, this makes the deflection proportional to power (since power = voltage × current).

A controlling torque is provided by springs, which balance the movement of the coil. Damping is usually provided by air friction to prevent oscillations and allow the pointer to settle quickly.

These instruments have a uniform scale and provide accurate readings, especially for power measurement.

Dynamometer-type instruments are commonly used as wattmeters in electrical circuits. They are also used as ammeters and voltmeters, although less commonly.

One advantage of these instruments is that they can measure both AC and DC without modification. They also provide high accuracy and are free from errors due to hysteresis.

However, they are more delicate and expensive compared to other instruments like moving iron instruments. They are also affected by external magnetic fields, so proper shielding is required.

Despite these limitations, they are widely used in laboratories and industries for precise measurements.

Conclusion

Dynamometer-type instruments work on the interaction of magnetic fields produced by two coils. They are accurate and versatile instruments used for measuring AC and DC quantities, especially power. Their reliability makes them important in electrical engineering applications.