A torque transducer, often called a torque sensor or torque cell, is a device used to measure and convert a twisting force (torque) into a measurable electrical signal. It measures the rotational force applied to an object, typically in units like Newton-meters N.m

There are two primary types, distinguished by their method of transmitting the signal:

• > Rotary (Dynamic) Torque Transducers: These are inserted into a rotating drivetrain or shaft and are used to measure torque while the shaft is turning (e.g., measuring engine power). They require a means to transfer the signal from the rotating part to the stationary sensor housing, often using slip rings or a non-contact (wireless) system.
• > Reaction (Static) Torque Transducers: These are fixed in place (non-rotating) and measure the resistance or reaction torque applied to a fixed object (e.g., measuring the torque required to loosen a bolt or turn a valve). They are simpler, more robust, and do not require slip rings or telemetry.

Most industrial torque transducers use strain gauge technology, similar to a load cell:

1. Strain Gauges: Thin, resistive foils (strain gauges) are bonded to the surface of the shaft or measuring element.
2. Torsion: When torque is applied, the element twists (torsion), causing the strain gauges to slightly stretch and compress.
3. Resistance Change: This mechanical deformation changes the electrical resistance of the gauges.
4. Signal Output: The gauges are wired into a Wheatstone bridge circuit, which converts the resistance change into a tiny, proportional voltage signal (mV), which is then amplified and measured.

Torque transducers are essential for quality control and efficiency testing across numerous industries:

• > Automotive: Measuring engine and motor performance, transmission efficiency, and drive shaft torque.
• > Aerospace: Testing propeller, rotor, and turbine performance, and ensuring fastener integrity.
• > Manufacturing: Calibrating and monitoring automated screwdrivers, wrenches, and assembly tools.
• > Testing: Testing pump efficiency, mixer output, and material fatigue under torsional stress.

Since the raw output signal from the strain gauges is very small (a few millivolts), additional instrumentation is required:

• > Torque Indicator/Amplifier: This device supplies the excitation voltage (power) to the transducer, amplifies the small mV output signal, digitizes it, and displays the torque reading (e.g., on an LED screen).
• > Couplings (for Rotary Sensors): Precision couplings are required to connect the rotary sensor between the motor/driver and the load/brake, ensuring perfect alignment to prevent bending moments or excessive vibrations.
• > Data Acquisition (DAQ) System: For high-speed measurements or automated testing, a DAQ system is used to log the amplified torque signal alongside other parameters (like RPM or speed).