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Torquing sense about power & control

30 June 2021

Why are engineers like dictators? Answer: they both obsess about power and control! For dictators it's about ruling the world, but for engineers it's about making machines run as smoothly and reliably as possible. Mark Ingham torques power

TORQUE IS power in rotary form, as produced by the motors and engines that drive the vast majority of machines in the world today. Those machines vary from microdosing systems used in pharmaceutical manufacture to the flood control pumps that handle millions of gallons of water an hour, from electronics etching machines to cement production plants and the precision robot arms used in automotive assembly.

Each such machine requires optimum amounts of power, so intelligent sensors that measure and adjust torque can be used to maintain peak performance. There are three main types of torque sensor, wheatstone bridge, surface acoustic wave (SAW) and optical. Each has its own advantages and strengths, so can be matched to given application needs.

Wheatstone bridge sensors, such as Sensor Technology’s SGR series, use a four-element strain gauge bridge, connected to a miniature shaft-mounted analogue-to-digital converter and microcontroller. When the host shaft rotates two gauges go into tension and two into compression. The microcontroller, mounted as close to the gauges as possible to minimise external noise pick-up, measures these levels and creates a real-time digital data stream. This stream is transferred wirelessly from the rotating shaft to a to a second static microcontroller which performs calibration and temperature compensation to produce an accurate torque reading.

Bridge based sensors are robust, reliable and easy to use

Bridge based sensors are robust, reliable and easy to use. Being wireless, Sensor Technology’s units are easy to install and quick to reset between reading.

SAW sensors, like the TorqSense RWT, are based on a patented technology that measures the resonant frequency change when a shaft twists under torque. Again, Sensor Technology’s SAW sensors collect the signal using a wireless RF rotating couple rather than slip rings and the same electronic processing and calibration is used to generate precise torque measurements.


SAW devices have a high immunity to magnetic fields allowing their use in motors and other electronically-hostile environments. They are bi-directional and provide fast mechanical and electrical responses. As the method is non-contact it has also complete freedom from brushes or complex electronics.  

The technology for optical torque sensors, for example Sensor Technology’s ORT units, is based on a measurement principle whereby two discs with segmented gratings are positioned on the shaft so that the opaque sectors on one disc partially obscure the clear sectors on the other. Light passes through these sectors and is detected by photovoltaic detectors.

The intensity of light beams, which is constantly monitored, is modulated by the applied torque and produces an electrical output that is used to provide a precise indication of the torque transmitted by the shaft.

The use of this measurement technique results in a transducer being able to sense torque bi-directionally. Very high full-scale sensitivity can be achieved with fast electrical responses up to 50kHz and low inertia. Again Sensor Technology’s offering in the optical field is non-contact.

Between these three methods of measuring torque, virtually every requirement for sensing, measuring and analysing torque can be met. Alongside its comprehensive range of torque sensors and solutions, what gives Sensor Technology the edge that has enabled it to become a leader in torque measurement is its down-to-earth practical approach to every application or project – the company's non-contact or wireless solutions cut out all the fiddling with brushes and slip-rings than can add time and frustration to any job.

Mark Ingham is sales engineer at Sensor Technology

Key Points

  • There are three main types of torque sensor –  wheatstone bridge, surface acoustic wave (SAW) and optical
  • SAW sensors are based on technology that measures the resonant frequency change when a shaft twists under torque
  • Sensor Technology's non-contact or wireless solutions cut out the complication of dealing with with brushes and slip-rings