A torque tester is used as a quality control device to test or calibrate

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

controlled tools. This includes electronic

torque wrenches A torque wrench is a tool used to apply a specific torque to a fastener such as a nut, bolt, or lag screw. It is usually in the form of a socket wrench with an indicating scale, or an internal mechanism which will indicate (as by 'clicking', a ...

, click torque wrenches, dial torque wrenches, electric screwdrivers, air screwdrivers, pulse tools, cordless screwdrivers, nutrunners, and torque screwdrivers. Today's advanced torque testers include the ability to measure in clockwise and counter-clockwise directions, and potentially convert to engineering units (such as in·oz, in·lb, ft·lb,

N·m The newton-metre (also newton metre or newton meter; symbol N⋅m or N m) is the unit of torque (also called ) in the International System of Units (SI). One newton-metre is equal to the torque resulting from a force of one newton app ...

, cN·m, kgf·cm, gf·cm, kgf·fm). They can also have different modes of operation (such as peak, 1st peak, track), or include a certificate from a local regulator (such as

NIST The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sci ...

). Torque testers measure properties such as torsional strength and stiffness and are used in quality control of various fields including medical devices, metals, and aerospace.

Components

Transducer

A torque

transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and con ...

, similar to a load cell, is an electronic device used to convert torque into an electrical signal. This conversion is indirect and happens in two stages. Through a mechanical arrangement, the torque being sensed deforms a

strain gauge A strain gauge (also spelled strain gage) is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports ...

. The strain gauge converts the deformation ( strain) to electrical signals. A torque transducer usually consists of four strain gauges in a

Wheatstone bridge A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of the circuit is its ability to provid ...

configuration. Torque transducers of one or two strain gauges are also available. The electrical signal output is typically in the order of a few millivolts and usually requires amplification by an

instrumentation amplifier An instrumentation amplifier (sometimes shorthanded as in-amp or InAmp) is a type of differential amplifier that has been outfitted with input buffer amplifiers, which eliminate the need for input impedance matching and thus make the amplifie ...

before it can be used. The output of the transducer is plugged into an

algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...

to calculate the force applied to the transducer. There are several styles available for torque transducers. Rotary, stationary (reaction), and inline are used for different calibration and audit purposes.

Digital display

A key component of modern torque testers is the digital display. A digital display is used to measure the output signal from the transducer and calculates that reading into a torque value that is displayed on screen. In most cases the display and transducer are contained together inside a housing. This is known as a "Desktop Torque Tester". External rotary and stationary transducers can be used with portable displays (handheld torque analyzers).

Rundown fixture (joint simulator)

A rundown fixture, also known as a joint simulator, is used during the calibration process to help test power tools (electric screwdrivers, air screwdrivers, pulse tools, cordless screwdrivers, nutrunners, etc.). A joint simulator is placed on top of the transducers. An adapter bit is inserted into the power tool and is mated to the top of the joint simulator. By using springs of different stiffness or stacking

Belleville washer A Belleville washer, also known as a coned-disc spring, conical spring washer, disc spring, Belleville spring or cupped spring washer, is a conical shell which can be loaded along its axis either statically or dynamically. A Belleville washer is ...

s in set patterns, the joint simulator can replicate soft, medium, or hard joints. This is important when trying to repeat how a tool may be used during an actual process.

References

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External links

Brief History of Torque MeasurementFastening: How Tight Is Tight?
Wrenches Measuring instruments