Torque Frequently Asked Questions

Torque is an incredibly important factor to understand and measure when designing products in the automotive, aerospace and defense, industrial, and even the medical sector in some cases. In order to arm our customers with critical information on torque and torque measurement, we created a Q&A of frequently asked questions from our resident experts and contributor to this post, Keith Skidmore.

How can you tell the direction of rotation from the output voltage?

The output of a torque sensor is most often bi-polar, which means the output reverses polarity as you cross through zero in your measurement. This has nothing to do with the direction of rotation, it only affects the direction of the torque. You cannot tell the direction using the voltage; however, in many cases, torque sensors can have an encoder installed in them in order to assess the direction of rotation.

What contributes to uncertainty for a torque calibration?

Often it is the actual application of the torque. When you are testing and doing comparison calibration, there are a lot of factors that can affect the results. You might think you are controlling for variances, but subtle differences can affect results.

How do you address unknown issues such as “start-up torque” and unknown torque transient spikes?

In general, start-up torque can be minimized by using a “soft start” on a motor and controlling the startup process. If there is a lot of inertia involved, you must be careful as starting up or powering down quickly can damage the torque sensor. Transient spikes would be factors that arise during testing such as compressor cycling or pulses from an engine.

It is most important to remember that torque sensor capacity should be selected so everything falls within a capacity range, and which sometimes means making an educated guess. Torque sensors always have a safe overload range. The overload range should be reserved only for accidental use. In addition, torque sensors have limits on how high they can go in terms of measurement, and that might be a lot less than their safe overload range.

You must size the sensor to measure appropriately. You can make estimates using horsepower, rpm, and some other factors to calculate torque to come up with an average and then you can factor in spikes. Just remember that starting conditions and spikes can be up to 10x running torque, so it’s very important to consider these.

When designing a rotary torque transducer into an application, do you think the pedestal-mount or the general-purpose floating rotary torque transducer is the best approach?

Generally, we would recommend floating-mount installations. The sensor should always be protected by appropriate couplings. On a floating installation, there should be single-flex couplings on each end of the sensor, and on pedestal or foot-mount, there should be double flex couplings at each end. The sensor is never intended to be used as a bearing block. In some applications, such as high rpm or when test setups need to be changed often, a pedestal-mount will make more sense. Additional design elements and considerations must be factored in.

How do you minimize slippage at the mating surfaces for torque cells that measure in both directions?

This is an issue that is not always considered but can be a big deal. It can affect the measurement and damage the hardware. There are really two considerations. First is the effect on measurement and second is damage to the mating surfaces, and they both need to be considered.

Ultimately, it depends on the types of couplings used and the types of sensors. For example, in flange connections, it’s not the bolts themselves that prevent slippage, but the friction between the mating surfaces. Surfaces must be clean and dry, and hardware torqued to spec.

Are there sensors available that can measure both applied load and torque simultaneously?

Yes. Interface calls these types of sensors axial torsion. In most cases they are static or reaction type torque sensors. Typically, they do not rotate or only rotate within a limited range.

Is there any reason to use a load cell over a torque transducer to measure torque?

Yes, there are several reasons. The main one is that a load cell is often less expensive. In some cases, you can get better accuracy (or the same) with a load cell. The downside is mounting considerations. Measuring torque using a load cell can be easy in some cases or in some cases prove difficult or impossible. Some applications will require a torque sensor for accurate measurement.

Is there any protection in case the test torque goes over the expected capacity?

Certain torque sensors have protections built-in, and that would be a mechanical stop that protects them. Those are typically lower capacity reaction style sensors.

Have additional questions regarding torque?

The Interface team is always here to help with all your torque needs! And to end 2019, Interface is offering a special discount to all our valued customers. We are offering a 10% discount on Interface Rotary Torque Transducers and Reaction Torque Transducers. We have multiple models and capacities in stock and ready to ship now. Contact our Application Engineers today and mention the promo code TORQUE2019.

*Please note that Interface’s AxialTQ Rotary Torque is not part of this promotion. Orders must be placed by December 31, 2019. 

CONTRIBUTOR:  Keith Skidmore, Regional Sales Director

Torque Brochure


Torque Transducers 101

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.


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