Choosing the right torque transducer

Interfaceforce offers an extensive range Torque transducers in various designs and capacities to meet all types of torque measurement testing requirements. When choosing the right torque transducer, it is important to first understand how a torque transducer works and then determine the best type, design, model, assembly, capacity and specific features for your needs.

A torque transducer, like a load cell, consists of a metal spring element or a bend. Strain gauges are applied to the flexure in a Wheatstone bridge configuration. The torque applied to the sensor causes a bending or shear strain in the measured area and produces an output voltage signal proportional to the torque.

To help you select the right torque transducer, you will receive a copy of our Torque Measurement Guide as a reference for your selection process.

Reaction or rotation type

There are also two different types of torque transducers: reaction and rotary. A reaction torque transducer, also called a static transducer, measures torque without rotating, while a rotating torque transducer rotates as part of the system. A rotation sensor, sometimes called dynamic torque, is just a reaction sensor that can rotate.

Typically, a reaction sensor has a cable attached that supplies the strain gauge bridge with an excitation voltage and outputs the mV/V signal. The rotation of these sensors is prevented by the attached cable. To circumvent the connected cable problem, a variety of rotating sensor methods have been used. These methods include slip rings, rotating transformers, rotating electronics, rotating digital electronics and radio telemetry.

Design with shaft or flange

Torque transducers typically come in one of two main mechanical configurations, shaft or flange. Shafts can be either plain or keyed, with keyed shafts available in single or double keyed versions. Flange sensors are usually shorter than shaft sensors and have a centering device on the flange surface.

Smooth shafts offer several advantages over their keyed counterparts, including a more even introduction of torque into the measuring shaft, easier assembly and disassembly, and freedom from backlash. A coupling designed for use with smooth shafts has some form of clamping on the shaft. This is typically achieved using split collars or shrink disk hubs. Shrink disk hubs typically have features that make them easier to remove from the shaft.

Hubs for keyed shafts are simpler than those for smooth shafts and cost less, but can be susceptible to wear due to backlash, especially in reciprocating applications. To avoid backlash, the hub must be assembled onto the keyed shaft with an interference fit, which is typically achieved either by heating the hub before assembly or by pressing the hub onto the shaft.

Fixed or floating mounting

There are also two main methods for mounting torque transducers: fixed or floating. Fixed mounting applies only to sensors with bearings and involves attaching the sensor housing to a fixed support. In floating mounting, the sensor is supported only by its drive and load side connections, which are usually single flex couplings. A flexible band prevents the torque transducer housing from rotating. By definition, bearingless sensors are always floating.

For fixed mounting, the sensor housing must be provided with a device for attaching it to the bracket. Sometimes the mount is an option on the sensor, sometimes the foot or base mount is part of the sensor. The simplest fixed mount sensors have a flat, machined surface on the housing with threaded holes. Double flexible couplings must be used for permanently mounted sensors.

capacity

Once you have determined the type, design and installation, how do you choose the right sensor for your project? One of the most important considerations is choosing the right capacity. If you choose a measuring range that is too large, the accuracy and resolution may not be sufficient for the application. On the other hand, if you choose a size that is too small, the sensor can be damaged by overloading, which is an expensive mistake. No manufacturer wants you to overload the sensor.

To choose the right size, you must first determine the torque you want to measure. This can be easy or difficult depending on the application. A simple example would be a torque application where a specific torque needs to be applied to a screw. A more difficult application might be figuring out how much torque is required for a newly designed wind turbine.

This is just a quick overview, there are many other variables to consider when selecting a torque transducer. For a complete overview, see our Torque Measurement Primer white paper. And as always, you can call us to speak directly with our application engineers and learn more: 480-948-5555.

With more than 36.000 product SKUs in Interfaceforce's extensive catalog, choosing the sensors that exactly meet your needs can be a daunting task. Luckily, we're here to help you with that! There is a wealth of content, including product brochures, white papers, case studies and application notes, allowing easy comparison of different product types and categories. These resources, as well as our product data sheets with specifications, will help you navigate the options and common solutions for different industries.