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Measuring Torque

Measuring Torque

Assess Your Testing Needs

Many measurement sensors, such as accelerometers and load cells generate DC voltages that can be measured. There are considerations that come along with each measurement and sensor type. This guide will explain general DC voltage measurements that do not involve sensor setup. Voltage is the simplest of the different types of analog measurements, and yet still presents unique challenges regarding noise considerations.


Research & Select the Right Equipment

Research and select the right equipment and software for your testing process. Consider factors such as test accuracy, test speed, ease of use, scalability, and compatibility with your existing manufacturing process. Consult with experts in the field, attend trade shows and conferences, and request demonstrations or trials to evaluate different options.


Design Test Fixtures

Design test fixtures that securely hold the PCBs, provide proper alignment and contact, and allow for easy insertion and removal of the boards. Consider the specific requirements of your PCB designs and ensure that the test fixtures can accommodate different board sizes and configurations. Test the fixtures with sample PCBs to ensure proper functionality.


Develop Test Sequences & Parameters

Develop test sequences and parameters that accurately reflect your testing requirements. This includes defining the order of tests, the specific measurements and analysis to be performed, and the pass/fail criteria. Consider the complexity of your test procedures and ensure that the automated testing system can handle them accurately and consistently. Test the sequences and parameters with sample PCBs to ensure accurate and reliable results.


Deploy and Validate

Develop test sequences and parameters that accurately reflect your testing requirements. This includes defining the order of tests, the specific measurements and analysis to be performed, and the pass/fail criteria. Consider the complexity of your test procedures and ensure that the automated testing system can handle them accurately and consistently. Test the sequences and parameters with sample PCBs to ensure accurate and reliable results.

Measuring Load

This guide helps you understand the fundamentals of load measurements and how different sensor specifications impact load cell performance in your application. After you decide on your sensors, you can consider the required hardware and software to properly condition, acquire, and visualize load measurements. You can also consider any extra signal conditioning you may need.

What is Torque?

Force is the measure of interaction between two or more bodies: for every action there is an equal and opposite reaction. Force is also described as a push or pull on an object. It is a vector quantity with both magnitude and direction. 


Torque is the tendency of a force to rotate an object about an axis. Similar to force being described as a push or pull, torque can be described as a twist to an object. The SI unit for the measure of torque is Newton-meters (Nm). In simple terms, torque is equivalent to force times distance, where a clockwise torque or twist is usually positive and a counterclockwise torque is usually negative. Torque sensors are composed of strain gages that fixed to a torsion bar. As the bar turns, the gages respond to the bar’s sheer stress, which is proportional to the torque.


The two common ways to measure torque are: reaction torque sensors and rotary torque sensors.


Measuring Torque


Reaction Torque Sensors

Reaction torque is the turning force that is imposed on the stationary portion of a device by the rotating portion as power is either delivered or absorbed. As the load source is rigid while the drive source is trying to rotate, the torque is created. Reaction torque sensors are restrained so they cannot rotate 360 degrees without the cable wrapping up because the housing or cover is fixed to the sensor element. These sensors are commonly used to measure torque of a back-and-forth motion. These types of sensors do not use bearings, slip rings, or any other rotating elements in their installations.

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Rotary Torque Sensors

Rotatory torque sensors are complimentary in design and application to reaction torque sensors except that the torque sensor is installed in line with the device under test. As the shaft of a torque sensor is rotating 360 degrees they must have a way to transfer the signals from the rotational element to a stationary surface.


This is accomplished by using one of three mounting methods: slip rings, rotary transformers, or telemetry.

Slip Ring Method:

The slip ring method entails that the strain gage bridge is connected to four silver slip rings mounted on the rotating shaft. Precision brushes make contact with these slip rings and provide an electrical path for the incoming excitation and the outgoing signal. You can use either AC or DC to excite the strain gage bridge.

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Rotary Transformer Method:

For the transformer method, the rotating transformer differs from conventional transformers by the primary or secondary winding rotating. One transformer is used to transmit the AC excitation voltage to the strain gage bridge and a second transformer is used to transfer the signal output to the nonrotating portion of the sensor. This means two transformers replace multiple rings, and no direct contact is made between the rotating and stationary elements of the transducer.

Digital Telemetry Method:

The digital telemetry method requires no contact points since it consists of a receiver-transmitter module, coupling module, and signal processing module. The transmitter module is integrated into the torque sensor. It amplifies and digitizes the sensor signal into a radio frequency carrier wave that is picked up by the caliper coupling module (receiver). The digital measurement data is then able to be recovered by the signal processing module.


Torque sensor selections primarily depend on your capacity and physical requirements.


Choosing the Right Torque


Capacity—When taking note of application capacity, determine the minimum and maximum torque you expect. Extra torque and moments can increase the combined stress, which increases fatigue and affects overall sensor accuracy. Any load other than an axial, radial, or bending torque, is considered extraneous and should be noted beforehand. If you cannot design or build your setup to minimize the effects of these loads, consult the sensor guide to verify the extraneous loads are within the sensor’s ratings.


Physical and environmental requirements—Evaluate any physical constraints (length, diameter, and so on) and the way the torque sensor can be mounted. Consider environmental factors will be exposed to ensure proper performance across wide temperature ranges, and possible contaminants (oil, dirt, dust).


Revolutions per minute (rpm)—For rotary torque sensors in particular,  it is important to understand how long the torque sensor will be rotating and at what speed to calculate the RPM.

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