When power is transmitted by a shaft, the shaft undergoes a torsional twisting through an angle which is proportional to the transmitted torque. A digital torque meter coupled to non-contact type electroMagnetic Detectors facing gears mounted at two points on the shaft detects the torsion angle as the phase difference between two AC signal voltages. Some ingenious digital processing, referenced to a highly accurate and stable crystal oscillator, converts the phase difference into a measurement of the transmitted torque.

The torsion angel can be detected by inserting a torque detector at a point on the torque transmission shaft or direct detection by coupling a torque detector to a shaft. A motor rotates a suspended rotating column of a torque detector and an internal-toothed gear coupled to it, so even when the shaft (externally toothed-gear) is stationary, there is a speed differential between the two gears. The magnetic flux in the coil therefore fluctuates as the internally-toothed gear turns through its circular pitch, generating an AC voltage with a sine waveform. And then torque applied to a stationary shaft can also be measured.

The above drawing shows the interior structure of a torque detector. It is configured with a rotating shaft, phase difference plates where a drive coil and detection coils are located face to face. A magnetic signal that flows from the excited drive coil to the phase difference plates is converted into an electric signal by the two detection coils. When torque is applied to a rotating shaft, the rotation torque is twisted. Change of torsion angle appears as a phase difference of magnetic flux in the magnetic circuit. The magnetic signal is converted into voltage signals by the two detection coils and amplifier while the drive coil is excited. And then, the TH-5100 torque meter calculates the torque value from the phase difference.