Shaft Torque Transducers – FAQ

Shaft torque transducers are true all-rounders used in a wide range of technical applications, from engine test beds to production lines. This FAQ covers important questions and answers about their installation, setup, function, strengths, and limitations.

A shaft-type torque sensor, also known as a torque measurement shaft, is an  instrument used to measure torque. These transducers are typically used in test benches, production lines or other technical assemblies to measure the applied torque.

Most torque transducers are based on strain gauge technology. The basic design includes a shaft that deforms slightly when external loads are applied. This deformation is measured and processed, allowing for reliable measurements  as it is known how much the shaft deforms in relation to the known loads. If torque is involved, the applied load generates  torsion, or twisting of the measuring body.

A torque transducer is made up of three main components:

• A shaft (rotor) that is connected to the measurement line of the test bench, where the actual measurement is performed
• Electronic components and circuit boards for signal conditioning and energy supply
• Housing (stator) that encases the shaft and electronics, and that can be mounted on the test bench

The transducer can, for example, be attached to the test bench via the housing using holes in the base or side. Precise alignment is crucial to ensure that the ends of the measurement shaft align with the drive and output shafts of the measurement line of the test bench. Alternatively, the measurement shaft can be installed in a suspended position, supported by the drive and output shafts, which is more suitable for lower rotational speeds.

The measurement shaft must be installed in or connected to the measurement line of the test bench or system using:

• Positive locking connections, such as interlock systems, square or key connections
• Force-fit connections, such as clamped bellows couplings or shrunk-on multiple-disk couplings

Shaft torque transducers typically measure nominal (rated) torques of ranging from 0.5 to 200 Nm. There are only a few applications for even lower ranges. For higher torques, measurement flanges are often used.

A downstream electronic system is required, as a torque transducer usually lacks its own display. Depending on the application, results can be shown on a simple display device . An electronic system can record and process the measured values, or a complex control system can be implemented. Output signals may vary depending on the situation, but they are often frequency or voltage signals. A new version of a shaft torque sensor is also available with a digital IO-Link interface.

IO-Link is a standardised IO technology that enables consistent, bidirectional communication between the control system and the sensor. When combined with a torque sensor, the interface provides torque data as well as auxiliary data like speed, angle, power and temperature. Users can perform comprehensive diagnostics or configure IO-Link devices during operation, benefitting from multiple measured quantities, reduced operation costs, and transparent data exchange down to the sensor.

Shaft torque sensors offer several advantages, including simple operation and universal application options. Their protected design, with housing around the measurement shaft, is particularly suitable for small measurement ranges. Additionally, they are generally more cost effective than comparable measurement flanges.

One unavoidable design-related disadvantage of shaft torque sensors is the bearing friction they generate. Typically, the mounting space required for a measurement shaft is slightly longer than that of a measurement flange. Measurement flanges are more suitable for very large torques in the kilonewton and meganewton range due to their design.

Shaft-type torque transducers are primarily used to measure torque, but some models include an option to determine rotational speed and/or angle of rotation. Recording other measured quantities, such as temperature, is also possible.

Providing a comprehensive answer to this question requires consideration of all key aspects. Start by considering the measurement range and the maximum expected rotational speed. It is also important to consider the required level of measurement accuracy early on. Additionally, don’t overlook environmental temperature conditions.

To further assess whether a measurement shaft is suitable, we recommend reading the technical data sheet and consulting the mounting instructions, which contain detailed and essential information.

When replacing shaft torque transducers in existing systems, it is essential to consider the geometric dimensions, including the mounting hole pattern and shaft diameter. Additionally, the signal output must be compatible or easily adaptable. Since torque transducers often share similar dimensions and commonly use voltage and frequency outputs, only few adaptations are typically required, making installation straightforward.