The wave frequency is dependent upon the spacing of the teeth in the array and the direction of wave propagation is at right angles to the teeth. Therefore, any change in its length, caused by the dynamic forces of the shaft’s rotation, alters the spacing of the teeth and hence the operating frequency. To measure the torque in a rotating shaft, two SAW sensors are bonded to a shaft at 45° to the axis of rotation. When the shaft is subjected to torque, a signal is produced, which is transmitted to the adjacent stationary pick-up via the RF couple.
Interestingly, SAWs were first detected by 19th century gentleman–scientist and Nobel Laureate Lord Rayleigh when he was investigating the cause and effects of earthquakes.
8. Selection of the type of torque transducer will be based on many considerations including: the working environment, the expected length of operation, the rotational speed of the driveshaft, mechanical connection options and costs. There is no overall ‘best’, but an optimum choice for each individual situation.
9. Positioning a torque sensor can be a complicated decision if a true reading is to be obtained. Inaccuracies can creep in due to the effects of adjoining elements in the drive train, the damping effect of the driveshaft’s own end couplings and drag caused by contact-type sensors.
10. The final piece of advice is that expert help is usually available through the company supplying your torque sensor. Availing yourself of this service will probably save time, money and frustration.
