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Torque Measurement Primer Review

Choosing the ideal torque transducer for your project can be a daunting task. Fear not. Interface has several torque measurement tools and resources to help you navigate your options and gain confidence in the selection process.

Interface’s advanced technical Torque Measurement Primer is an excellent resource to review and save for reference.  The expert guide takes you step-by-step, from torque transducer basics through complex capacity calculations to fixture and mounting considerations.

This technical reference offers considerable detail and diagrams regarding critical topics that impact the performance and accuracy of torque transducers. Interface engineer and measurement application specialist Keith Skidmore provides extensive information about defining capacity requirements, performance factors and considerations, mechanical configurations, outputs, resolution, mounting, and coupling selection tips.

Understanding Torque Transducers

A torque transducer consists of a metal spring element or flexure like a load cell. 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.

Two Main Types of Torque Transducers

  • Reaction (static) measures torque without rotating, which is ideal for stationary applications.
  • Rotary (dynamic) rotates as part of the system, suitable for dynamic measurements.

Normally, a reaction-style sensor has a cable attached to it to supply excitation voltage to the strain gage bridge and to output the mV/V signal. The attached cable prevents the spinning of these sensors. Various methods have been used for rotary sensors to get around the issue of the attached cable. Some of those methods include slip rings, rotary transformers, rotating electronics, rotating digital electronics, and wireless telemetry. More basics are available in our Torque Transducers 101 post.

Selecting the Right Transducer Capacity

When choosing a torque transducer, one of the primary considerations is selecting the right capacity. The key is not to overload the sensor. If you choose too large a range, the accuracy and resolution may not be enough for the application. If you choose too small a size, the sensor may be damaged due to overload, which is an expensive mistake. First, determine the amount of torque you want to measure to select the proper size. Use Interface’s Torque Transducer Selection Guide to review capacities and dimensions.

Mechanical Configurations

  • Shaft: Smooth or keyed, offering uniform torque introduction and ease of assembly and disassembly.
  • Flange: Shorter, with centering pilots, commonly used in limited space applications.

Reference the Torque Measurement Primer to Review Factors in the Selection

  • Determine average running torque
  • Understand load service factors (1-4) and drive service factors (1-4)
  • What is the required accuracy
  • What signal resolution do you require: analog and digital

Beyond the basics, take a deeper dive into advanced torque considerations by reviewing the following:

  • Mounting methods (fixed vs. floating)
  • Couplings (single and double flex)
  • Environmental factors (temperature, moisture, dust)
  • Variable-frequency drive applications
  • Maximum RPM rating
  • Bandwidth and sampling rate

Use the Interface Torque Measurement Primer to explore these factors comprehensively with technical references. It is an essential test and measurement resource for making informed torque transducer selections. Whether you are an experienced lab technician or engineer, the details of this primer are advanced and full of resourceful tips.

Torque-Measurement-Primer-2024-Edition-1

ADDITIONAL RESOURCES

Torque Transducers and Couplings are the Perfect Pairing

Understanding Torque Transducers for Motion Control Systems

New Interface Torque Transducer Selection Guide

Interface Introduces New Torque Coupling Guide

Miniature Torque Transducers 101

Understanding Torque Transducers for Motion Control Systems

A motion control system is an integrated set of components that work together to control the movement of a machine or device. It typically includes four main elements: controllers, sensors, actuators, and drives.

Torque transducers are essential components in motion control systems. They are important in controlling rotating machinery by providing real-time feedback on the applied torque accurately and efficiently.

Selecting the right torque transducer for a motion control system depends on several major factors, including use case, measurement range, accuracy requirements, speed, and environment.

Industry use cases of motion control systems require different torque measurement capabilities. For example, a robotic arm may need a torque transducer with a high resolution and fast response time. In contrast, a wind turbine may need a torque transducer with a high torque capacity and a long lifespan.

Motion control systems have the same basic goal: to control the movement of a machine or device in a precise and controlled method. Evaluation of the type of torque transducer for your motion control system is important based on type, measurement capacities, accuracy, and speed. Do you need a rotary torque transducer or a static device, known as a reaction torque transducer?

Torque Transducers for Motion Control Systems

Rotary torque transducers are designed to be mounted directly on a rotating shaft. These dynamic transducers are ideal for measuring torque in motors, pumps, and turbines.

Reaction transducers measure the torque applied to a stationary object. These static transducers are ideal for measuring torque in automotive applications such as brakes and clutches.

The torque transducer should withstand the environmental conditions it will be used, including factors such as temperature, vibration, and chemical exposure. These details should be easily identifiable in a review of the transducer’s specifications.

TIP: Use Interface’s Torque Transducer Selection Guide for easy device comparisons.

Why are torque transducers used in motion control systems?

Closed-loop control: Torque transducers enable closed-loop control of motors and drives. By measuring the actual torque output, the control system can compare it to the desired torque and adjust the motor speed or power output to maintain it. This ensures precise and consistent operation of the system, regardless of load variations.

Overload protection: Torque transducers can protect motors and other components from damage caused by excessive torque. By monitoring the torque in real-time, the system can shut down the motor or activate other protective measures if the torque exceeds a predetermined safe limit. This prevents costly equipment failures and downtime.

Optimization and efficiency: Torque transducers help optimize the performance of motion control systems by providing valuable data for analysis and improvement. Engineers can identify areas where the system can be more efficient by measuring the torque at different operating points. This can lead to reduced energy consumption, improved productivity, and increased product quality.

Safety: In safety-critical applications, torque transducers play a vital role in ensuring the safe operation of machinery. The system can take appropriate action to prevent accidents or injuries if the torque exceeds a safe limit by providing data on the torque applied to safety-related components.

Motion Control Applications

Here are four examples of how torque transducers are used in different types of motion control systems:

ROBOTICS: Torque transducers are used to control the movement of robotic arms with high precision. They ensure the robot arm applies the correct force to move objects without damaging them.

MACHINERY: Torque transducers control the spindle speed and feed rate of CNC machines, ensuring accurate and consistent machining operations.

ENERGY: Torque transducers are used to monitor the torque output of wind turbines and optimize their performance. This helps maximize energy production and ensure the safe operation of the turbines.

EV: Torque transducers are used in the drivetrains of electric vehicles to control the torque delivered to the wheels. This enables efficient and smooth acceleration and deceleration.

Should you use torque couplings instead of key shafts in motion control systems?

If your motion control system demands high precision, efficiency, and reliability, removing key shafts and employing torque couplings might be beneficial.

Keyless solutions can reduce downtime and associated costs in applications requiring frequent maintenance. Compact torque couplings can be a better fit than bulky key shafts in tight spaces.

If perfect shaft alignment is challenging, flexible torque couplings can compensate for misalignment and prevent potential problems.

TIP: Visit Torque Coupling Selection Guide for options.

Reviewing your use case to determine if key shafts are necessary for your motion control system is important. There are advantages to keeping key shafts. Replacing key shafts with torque couplings can offer several advantages, including:

  • Elimination of keyways: Keyways are slots cut into the shaft and hub to accommodate a key. This weakens the shaft and can lead to stress concentrations and fatigue failures. Torque couplings eliminate the need for keyways, improving the strength and integrity of the shaft.
  • Reduced maintenance: Keys can wear and loosen over time, requiring periodic maintenance and replacement. Torque couplings, on the other hand, are generally maintenance-free.
  • Improved performance: Torque couplings can transmit torque more efficiently than keys. This can lead to improved performance and efficiency in the overall system.
  • Reduced noise and vibration: Keys can cause noise and vibration, especially at high speeds. Torque couplings can help to reduce noise and vibration levels.
  • Simplified assembly and disassembly: Keys can be difficult to install and remove, especially in tight spaces. Torque couplings are generally easier to assemble and disassemble.
  • Increased flexibility: Some torque couplings can accommodate misalignment between shafts, which can be helpful in applications where perfect alignment is difficult to achieve.

Whether to use torque couplings to replace key shafts depends on the specific application. However, torque couplings can offer significant advantages in strength, performance, and ease of use in many cases.

Torque transducers are versatile tools that play a vital role in various motion control systems. They provide accurate and reliable data on the applied torque, enabling closed-loop control, overload protection, system optimization, and enhanced safety.

ADDITIONAL RESOURCES

Trends in Torque Transducer Applications in the Auto Industry

Interface Introduces New Torque Coupling Guide

Torque Transducers and Couplings are the Perfect Pairing

Miniature Torque Transducers 101

Choosing the Right Torque Transducer

A Comparison of Torque Measurement Systems: Download the white paper.

AxialTQ for Anything That Turns and Needs Testing

New Interface Torque Transducer Selection Guide

Interface produces content to help our customers in choosing the right force measurement products for their exact application requirements. From our Force Measurement 101 Series to the weekly Interface IQ posts, our focus is in building a repository of support resources that meet the needs of test and measurement professionals across all types of industries.

Our new Interface Torque Transducer Selection Guide helps to quickly evaluate the range of Interface’s torque transducer models based on whether you need a reaction (static) or rotary (dynamic) style. The guide assists in selecting best torque sensor based on features and capabilities, such as bearingless, contactless, compact, miniature, force and torque, overload protected, wireless, and USB output options.

Interface’s new web resource covers several types of torque sensors including flange mount, shaft type, square drive, hex drive, and couplings. If you’ve read our blog Choosing the Right Torque Transducer, which would also be a good place to start, you will understand how important it is to choose the right product, options and accessories for the job.

A torque sensor selection guide is typically used by engineers or technicians who need to choose a torque sensor for a specific application. Here are four easy steps to follow when using the Interface Torque Transducer Selection Guide:

  1. Determine the requirements of your application: Before selecting a torque sensor, you need to understand the specific requirements of your application. This includes the torque range you need to measure, the type of torque reaction versus rotary, shaft or mounting of the components you will be measuring, the environment in which the sensor will be used, and any other relevant factors related to the type of device you choose.
  2. Choose the type of torque sensor: There are several types of torque sensors available, including reaction or rotary, shaft or flange, shaft style, floating or fixed, and bearings or bearingless. The selection guide provides information about the features of each type, so you can choose the one that is best suited for your use case.
  3. Consider the accuracy and resolution: These both are key factors to consider, especially if you need to make precise measurements. The selection torque guide helps deliver specification details for each torque sensor, so you can choose the one that meets your requirements.
  4. Evaluate the physical characteristics: The physical characteristics of the torque transducer includes the size and shape of the sensor, the mounting options, and any distinctive features such as temperature compensation or overload protection.

By following these steps and using the information provided in the Interface Torque Transducer Selection Guide, it is easier to choose a sensor that is well-suited for your application and provides accurate and reliable measurements you require.

The Interface Torque Transducer Selection Guide helps to define the right product, as well as provide supplemental help and answers to frequently asked questions, including:

  • What is a torque transducer?
  • Reaction versus Rotary?
  • Shaft versus Flange?
  • Floating versus Fixed?
  • Bearings versus Bearingless?
  • Dual Range
  • RPM Considerations
  • Accuracy and Resolution
  • Coupling Types

Unsure of where to start? Check out Torque Transducers 101 or Recap of New Twist on Torque including the complete webinar below. In addition to our standard products, Interface has a custom solutions group that can collaborate with you to customize torque transducers, instrumentation, and complete measurement systems to fit your exact needs.  Contact Interface’s torque expert application engineers if you need assistance or require a quote.

ADDITIONAL RESOURCES

 

Miniature Torque Transducers 101

Choosing the Right Torque Transducer

A Comparison of Torque Measurement Systems White Paper

Torque Measurement Primer

Aircraft Yoke Torque Measurement

Fuel Pump Optimization & Rotary Torque

CPG Dental Handpiece Torque Check

Torque-Transducer-Brochure

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

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