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Choosing the Right Torque Transducer

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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

New Twist on Torque Webinar

AxialTQ

Latest Spin on AxialTQ

A Comparison of Torque Measurement Systems White Paper

Rover Wheel Torque Monitoring

Aircraft Yoke Torque Measurement

Insights in Torque Testing Featured in Quality Magazine

Torque Measurement for Electric Vehicles

 

Couplings 101

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One of the biggest challenges in the force measurement is dealing with misaligned loads. Misaligned loads can result in bad data and damaged test equipment. Therefore, it’s important to understand the affect these types of loading conditions can have on a force test and know of the ways to fix or account for it.

For every force test, there is typically a piece of equipment designed to deal with misaligned loads. Whether it’s simply applying the force device properly or if misaligned loads are unavoidable, using the right tools to reject misaligned load. Learning more about couplings is a great place start in knowing how to this power tool is designed to deal with misaligned loads in torque testing.

Couplings are a critical component to be used alongside torque transducer that ensures the isolation of torque loads. A coupling is a mechanical element that connects two shafts together to accurately transmit the power from the drive side to the driven side while absorbing the mounting error of misalignment of the two shafts. Essentially, they allow and compensate for misalignment in a torque test. It is one of the topics we discuss in our online webinar, New Twist on Torque.

For instance, if two shafts are coupled together and the center shafts aren’t aligned, measuring torque without a coupling may ruin the test, affecting the longevity of the parts and the performance of the measurement. With a coupling, the shafts don’t have to be perfectly aligned in length and can still provide an accurate torque test.

There are two main categories of couplings used in force measurement and the biggest difference in the two is the degree of freedom needed for the application. The categories are single-jointed and double-jointed. A single-jointed coupling allows for angular and axial misalignment, while double-jointed coupling allow for an additional radial misalignment. For floating mount installations, Interface recommend single-flex disk couplings. For fixed mount installations, double-flex disk couplings are required.

Couplings should be used in all applications and the selection of the coupling type is based on the speed of the application. For higher speed applications, Interface recommends a high-quality coupling with a flexible, yet sturdy construction made from premium metals.

Interface offers a wide variety of torque transducers and can provide couplings off the shelf or in a custom solution when necessary. One of our most popular torque solutions, which includes a coupling, is the Interface Model T1 Torque Coupling Rotary Torque Transducer. This solution integrates torque measurement with a robust double flex coupling.  The coupling and sensor are completely hollow, allowing the shortest possible distance between the coupled shaft ends. On-board digital electronics provide a ±5V output, low-noise signal. Powered by 12-28V DC, the strain gage based T1 Torque Coupling offers precision rotary torque measurement in a bearing-less, contact-free design. Covering ranges from 50 to 1000 Nm (443 to 8.85K lbf-in), the T1 ships with factory bored hubs to mate precisely with the customer’s shaft ends.  Both smooth and keyed shaft style hubs are available.

Examples of a torque solutions using a coupling in the field can be found in our application notes section of the website. We’ve provided an example of one such application below.

Fuel Pump Optimization – Rotary Torque

A nationally renowned race team was using a flow bench to measure fuel pump performance. They wanted to determine if they could reduce the power consump­tion of the pump by further analyzing the precise torque it produced. An Interface Model T25 High Speed Rotary Torque Transducer was integrated into the pump drive to directly measure the torque required to spin the pump. Interface Shaft Style Torque Transducer Couplings we’re also used to marry the shafts to the T25. Using this data collected from the T25 in conjunction with the pressure and volume measurements of the fuel flow, the race team was able to characterize fuel pump performance versus drive line torque, and then minimize the required drive power while maintaining the needed pressure and flow for efficient fuel delivery.

Couplings are an integral part of any torque test project. To learn more about couplings and their application in a wide variety of projects, reach out to Interface at 480-948-5555 or contact us here. We can suggest a combination of off-the-shelf transducers, couplings and data acquisition devices or work with you to develop a custom solution necessary for your goals.

ADDITIONAL READING: TORQUE TRANSDUCERS 101

Source: Keith Skidmore

Torque Transducers 101

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Torque is defined as the rotational equivalent of linear force. It’s a measure of how much a force acting on an object causes that object to rotate. This is one of the key measurements for engineers doing design, test, and manufacturing. It’s critical to understand how to identify torque if you’re doing product development with rotating systems such as engines, crankshafts, gearboxes, transmissions, and rotors.

Interface develops more than 50 different kinds of reaction and rotary torque transducers, as well as custom transducers for our customers. All our torque transducers also referred to as torque sensors, are precision-machined and use our proprietary torque sensors for the most accurate data possible, quality and reliability.

Here are some frequently asked questions and details about torque transducers, including key terms and descriptions of reaction versus rotary, shaft and flange style torque, couplings, and floating and fixed mounts.

What is a torque sensor (transducer)?

A torque sensor is a transducer that converts a torsional mechanical input into an electrical output signal.

Reaction versus Rotary

There are two types of transducers that Interface sells, reaction and rotary transducers. Reaction torque transducers measure static torque, or torque without rotating, and are widely used in process control and testing. Rotary torque transducers like AxialTQ measure dynamic force and are used in applications where the torque transducer must rotate when attached to a spinning shaft. A rotary torque transducer provides a method of getting the signal off of the rotating element without an attached cable, while a reaction transducer uses an attached cable.

Shaft and Flange Style Torque

The shaft or flange is the component taking the torque measurement. Shaft style torque offers convenient mounting and has a longer installed length than flange style. It comes in two different versions, smooth and keyed shafts. A smooth shaft provides ease of assembly and disassembly, with zero backlash. Keyed style shafts are simple and less expensive; however, they can suffer from wear due to backlash. The flange style is typically shorter than the shaft style and has pilots on its flange face as a centering feature. This style has better resistance to overhung moments and can be more convenient to mount.

Coupling

Couplings are a critical component to the torque transducer that ensures the isolation of torque loads. Couplings should be used in all applications, and the selection of the coupling type is based on the speed of the application. For higher speed applications, you will want to look for high-quality couplings. The coupling helps to prevent error and/or damage from extraneous loads.

Floating and Fixed Mounts

Floating Style

There are two common types of torque transducer mounts, floating and fixed mounts. For high-speed applications, fixed and supporting mounting is mandatory. For safety reasons, floating mounts should only be used for low-speed applications. In floating mounts, the sensor is supported only by the drive and load side connectors, and a flexible strap keeps the sensor from rotating. Fixed mounts apply only to sensors with bearings, and it involves attaching the sensor housing to fixed support for added stability.

For more information on Interface’s wide selection of torque transducers, please visit www.interfaceforce.com/product-category/torque-transducers/.