In which instrument the deflecting torque depends on the frequency
In Induction type instrument instrument the deflecting torque depends on the frequency.
In induction type instruments, the deflecting torque is proportional to the square of the current flowing through the instrument coil.
At low frequencies, the current through the coil is almost in-phase with the applied voltage, resulting in a high current and a correspondingly high deflecting torque.
As the frequency increases, the current through the coil lags behind the applied voltage due to the inductance of the coil, resulting in a reduced current and deflecting torque.
At very high frequencies, the current through the coil is greatly reduced, resulting in a negligible deflecting torque.
Therefore, while the frequency of the current flowing through the coil does affect the current and, indirectly, the deflecting torque in induction type instruments.
To compensate for this frequency error, a non-inductive shunt can be connected in parallel with the instrument coil.
The shunt provides a low-resistance path for the high-frequency components of the current, effectively reducing the effective impedance of the instrument coil at high frequencies and reducing the frequency error in the measurement.