In the technique described a resistance strain gauge bridge is used. The output from the bridge is amplified and used to pulse-width-modulate a 20 kHz square wave. The modulated waveform is extracted from the shaft, using split brass rings and carbon-copper brushes, and demodulated to give a continuous record of shaft torque. In this way distortion of the torque signal by electromagnetic radiation and variation in contact resistance between brushes and slip rings is eliminated.