Torque sensors and torque instruments are used to measure torque in a variety of applications. Torque sensors are categorized into two main types, reaction and rotary. Reaction torque sensors measure static and dynamic torque with a stationary or non-rotating transducer. Rotary torque sensors use rotary transducers to measure torque.

Important specifications to consider when searching for torque sensors include maximum torque, accuracy, and temperature compensation.  Torque is defined as the moment of a force, a measure of its tendency to produce torsion and rotation about an axis.  Temperature compensation prevents measurement error due to temperature increases or decreases.

The technology of torque sensors can be magnetoelastic, piezoelectric, and strain gauge.  A magnetoelastic torque sensor detects changes in permeability by measuring changes in its own magnetic field.  A piezoelectric material is compressed and generates a charge, which is measured by a charge amplifier.  To measure torque, strain gage elements usually are mounted in pairs on the shaft, one gauge measuring the increase in length (in the direction in which the surface is under tension), the other measuring the decrease in length in the other direction.

Torque sensors can be many different types of devices including sensor element or chip, sensor or transducer, instrument or meter, gauge or indicator, and recorder and totalizers.  A sensor element or chip denotes a "raw" device such as a strain gage, or one with no integral signal conditioning or packaging.  A sensor or transducer is a more complex device with packaging and/or signal conditioning that is powered and provides an output such a dc voltage, a 4-20mA current loop, etc.  An instrument or meter is a self-contained unit that provides an output such as a display locally at or near the device. Typically also includes signal processing and/or conditioning.  A gauge or indicator is a device that has a (usually analog) display and no electronic output such as a tension gage.  A recorder or totalizer is an instrument that records, totalizes, or tracks force measurement over time.  Includes simple datalogging capability or advanced features such as mathematical functions, graphing, etc. 

Common outputs for torque sensors include analog voltage, analog current, analog or modulated frequency, switch or alarm, serial, and parallel.  Other parameters to consider include operating temperature, maximum shock, and maximum vibration.