Non-Contact Torque Sensor

Getting the facts on rotating shafts

What’s the power of a spinning shaft? A calculation is simple to generate, but what about a real-time, in situ measurement? And let’s say that the critical shaft is deep within layers of machinery and casings, so that access is near impossible to an exposed end. And add in a hostile local environment, to make things interesting. While there are a few partial solutions to this type of problem, delicate devices like strain gages can be quickly ruled out.

FAST Technology, Livonia, MI, has introduced a line of sensors using Embedded Magnetic Domain technology, which combines magnetic induction and electronic processing for direct torque measurement. The EMD technology applies a small zone of the shaft with specific magnetic patterns, then measures the field alterations generated through the twisting of the shaft as torque is applied. The output signal is proportional to the applied torque. This does necessitate several requirements of the system being tested—1) the shaft material must be capable of being magnetized, 2) the shaft does not reach Curie point during operation—i.e., the temperature at which magnetic properties of a material change, 3) the shaft is not permanently bent or similarly damaged, and 4) the system is not exposed during operation to a strong magnetic field.

The FAST system measures torque in real-time from shafts rotating at speeds up to 100,000 rpm. With this method, sensor placement can be as far as 10mm from the rotating shaft, and measurements can be made through dirt, fluids and other non-magnetic materials, with minimal hysteresis and accuracy of 0.5% full-scale. Standard sensors are packaged as sleeves fitting round or square shafts, with measurement capabilities presently up to 150 Nm (110.6 lb/ft)(300, 500 and 1000 Nm versions are in the works). The basic package, seen in the above photo, can be modified for custom versions to suit shafts that are solid cylinders, tubes or discs. Their low power consumption and ability to function in tough environments makes them suited for applications ranging from automotive and aerospace to oil well and mining equipment.—RM