Choosing the Right Torque Transducer
Interface offers an extensive line of torque transducer models in different designs and capacities to fit all types of torque measurement testing requirements. The first thing to understand when choosing the right torque transducer is how an actual torque transducer works in order to then determine the best type, style, model, mounting, capacity and special features for your requirements.
A torque transducer, like a load cell, consists of a metal spring element, or flexure. Strain gages are applied to the flexure in a Wheatstone bridge configuration. Torque applied to the sensor causes bending or shear strain in the gaged area, generating an output voltage signal proportional to torque.
To assist you in choosing the right torque transducer, get a copy of our Torque Measurement Primer for reference in your selection process.
Reaction or Rotary Type
There are also two different types of torque transducers: reaction and rotary. A reaction, also known as static, torque transducer measures torque without rotating, while a rotary torque transducer rotates as part of the system. A rotary sensor, also sometimes called dynamic torque, is merely a reaction sensor that is allowed to rotate. Normally, a reaction style sensor has a cable attached to it for supplying excitation voltage to the strain gage bridge and for output of the mV/V signal. Spinning of these sensors is prevented by the attached cable. To get around the issue of the attached cable, a variety of methods have been used for rotary sensors Some of those methods include slip rings, rotary transformers, rotating electronics, rotating digital electronics and radio telemetry.
Shaft or Flange Style
Torque transducers typically come in one of two major mechanical configurations, shaft or flange style. Shafts can be either smooth or keyed with keyed shafts coming in either single or double-keyed versions. Flange style sensors are typically shorter than shaft style, and have pilots on their flange faces as a centering feature.
Smooth shafts offer some advantages over their keyed counterparts, including more uniform introduction of the torque into the measuring shaft, ease of assembly and disassembly and zero backlash. A coupling designed for use with smooth shafts will have some method of clam ping to the shaft. This is commonly accomplished with split collars or shrink-disk style hubs. Shrink-disk style hubs usually include features to aid in their removal from the shaft.
Hubs for keyed shafts are simpler than those for smooth shafts and cost less but can suffer from wear due to backlash, especially in reciprocating applications. To prevent backlash, the hub must be installed on the keyed shaft with an interference fit, which is usually accomplished by either heating the hub before installation or pressing the hub onto the shaft.
Fixed or Floating Mount
There are also two main methods of mounting rotary torque transducers, fixed or floating. Fixed mount applies only to sensors with bearings and involves attaching the sensor housing to a fixed support. In floating installations the sensor is supported only by its drive and load side connections, which are typically single-flex style couplings. A flexible strap keeps the torque transducer housing from rotating. By definition, bearingless sensors are always floating mount.
Fixed mounting requires that the sensor housing have a means to attach it to the support. Sometimes the mount is an option on the sensor and sometimes the foot or pedestal mount is built as part of the sensor. The simplest fixed mount design sensors include a flat machined surface on the housing with threaded mounting holes. In fixed mount installations, double flex couplings must be used.
Capacity
Once you have determined the type, style and mount, how do you choose the right transducer for your project? One of the primary considerations is selecting the right capacity. On one hand, if you choose too large a range, the accuracy and resolution may not be enough for the application. On the other hand, if you choose too small a size, the sensor may be damaged due to overload, which is an expensive mistake. No manufacturer wants you to overload the sensor.
To select the proper size, first determine the amount of torque you want to measure. This can be easy or hard, depending on your application. An easy example would be a fastener torque application, where a certain amount of torque is to be applied to a fastener. A more difficult application might be trying to figure out how much torque is required for a new design wind turbine.
This is just a brief overview, there are many other variables to consider when choosing a torque transducer. To get a full rundown, check out our white paper Torque Measurement Primer. And as always, give us a call to speak directly with our applications engineers to learn more at 480-948-5555.
With more than 36,000 product SKUs in Interface’s extensive catalog, it can be a daunting task choosing the sensors that fit your exact needs. Fortunately, we’re here to work you through it! There is an abundance of content, including product brochures, white papers, case studies and application notes, for easy comparing of different product types and categories . These resources, as well as our model product datasheets with specifications can help navigate the options and along with common solutions by industry.
Our application engineers are just a phone call away and can help you determine the off-the-shelf products or custom solutions needed for your specific application. To learn more about our torque transducer selection, you can also visit www.interfaceforce.com/product-category/torque-transducers/.
ADDITIONAL RESOURCES
A Comparison of Torque Measurement Systems White Paper
Aircraft Yoke Torque Measurement
Insights in Torque Testing Featured in Quality Magazine
Torque Measurement for Electric Vehicles
