How Does a Torque Sensor Work?

From opening a jar, or tightening a screw, to the proper functioning of the electromotor, torsion of the materials, torque, is present everywhere around us. As torque is present in various aspects of our lives, in different industries, and around everyone, it is important to know how to measure torque.

What is the Torque and How is it Related to the Torsion?

The quick answer would be that the torque represents applied force and torsion is the result of applied torque, the torsion deformation. The same value of the torque may result in different deformations of the shaft, depending on the chosen material and its geometric properties. Torque is measured in Nm and torsion can be expressed as level of deformation. There are different types of torque sensors and each of them has its advantages and disadvantages. We will take a look at some of the torque sensors.

Types of Torque Sensors

1. Torque Gauge Sensor

Strain gauges used in the torsion measurement are called torque gauges. The strain gauge is adhesively attached to the shaft, or material that is being deformed. The torque gauge is being deformed as well, which results in the change of the electric response, which is calibrated to the corresponding values of the applied torque. Application of this kind of torque sensor is problematic due to wiring from the sensor to the reader of the response.

2. Rotary Transformer Torque Sensor

One of the most precise sensors, with large scales up to 15,000 RPM (Slip ring type) or up to 10,000 Nm (Clamp on type), represents the rotatory transformer torque sensor. In the sensor, there are two transformer windings, while one is stationary the second one is rotating altogether with the shaft that is being measured. The rotation induces the voltage at the transformer’s ou­tput, which is proportional to the torque. These kinds of sensors are used mostly for testing of the shafts in laboratory conditions, as they need skilled operator, and they are large for the actual application in motors.

3. Optical Torque Sensor

As the previous sensor used electrical quantities that correspond to the applied torque, the optical torque sensor uses the light’s polari­sation for the measurement. Sensor by itself is represented by the optic cable which is wrapped around the shaft on which the torsion is applied. The applied torque is proportional to the measured polarisation of the light.

4. Resonant Frequency Torque Sensor

Resonant frequency torque sensor represents a special type of micro-electromechanical system – MEMS based on quartz resonator and is usually used for micro-scaled materials, thus in laboratory testing conditions. This kind of torque sensor measures the resonant frequency of the shaft, which is proportionally changing with the applied torque.

5. The MicroWire Sensor

RVmagnetics introduces the MicroWire , the smallest passive sensor in the world. Thanks to its dimension it can be attached to the surface of the shaft, similarly as in the strain gauge type of torque sensor, however with no need for wiring. Contrary to the torque gauge sensor which works perfectly on static shafts, the contactless MicroWire sensors can be used even on the rotating shaft without any need for the commutator. The sensor is based on magnetic principles and the data acquisition device can gather the data from the MicroWire from a distance of up to 10 centimetres. Spatial limitations? No problem! RVmagnetics’ MicroWire adds no volume and mass to the shaft and the sensing head can be prepared in various shapes and sizes according to the client’s restric­tions and requirements. The sensor is able to provide real-time data, which can be used to protect the shaft from overload or adjust the power of the motor to save energy. The properties of the MicroWire torque sensor enable to measure not only the intensity of the torque on both static and rotating shafts, but also the direction of applied torque.

Conclusion

The selection of a suitable torque sensor depends on your requirements. RVmagnetics provides fully tailor-made solutions, fulfilling the client’s needs with the smallest passive, contactless torque sensor in the world. Are you intrigued? Visit our webpage: torque application section