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PROPRIETARY MATERIAL. 2009 The McGraw-Hill Companies, Inc. All rights reserved. No part of this PowerPoint slide may be displayed, reproduced or distributed in anyform or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their

individual course preparation. If you are a student using this PowerPoint slide, you are using it without permission.

METROLOGY & MEASUREMENT

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Anand K Bewoor & Vinay A Kulkarni

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Chapter 17

Force and TorqueMeasurement

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Force and torque instruments measure the real strength of the entity under

test..

INTRODUCTION TO FORCE AND TORQUE MEASUREMENT

Force and torque instruments are used to measure force, weight or torque. Some can measure

force and torque by changing the sensor/transducer. Force or weight measurements include

tension or compression loading; and the units are pounds, Newtons, etc. Torque measuring

instruments display torque units (in-oz, ft-lbs, etc.).

Important parameters to consider when specifying force and torque instruments are the force

measurement range and accuracy, and the torque measurement range and accuracy. Sensor or

transducer interfaces for force and torque instruments include strain gauge and piezoelectric

devices. For strain gauge devices, strain gauges (strain-sensitive variable resistors) are

bonded to parts of the structure that deform when making the measurement. These strain

gauges are typically used as elements in a Wheatstone bridge circuit, which is used to make

the measurement. For piezoelectric devices, a piezoelectric material is compressed and

generates a charge that is measured by a charge amplifier. The analog bandwidth is another

important specification to consider. The bandwidth is the frequency range over which the

device meets its accuracy specifications. Accuracy is degraded at lower and lower frequencies

unless the device is capable of dc response, and at higher frequencies near resonance and

beyond, where its output response rolls off. Frequencies in the database are usually the 3-dB

rolloff frequencies.

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Common configurations for force and torque instruments include handheld, portable, modularand battery-powered instruments. Measurement features of force and toque instruments

include tare, limits or set points, peak hold, controller functionality, temperature compensation,

biaxial measurement, and triaxial measurement. Units with tare can zero out reading to

measure differences for weighing. Limits and set points include hilo. Peak hold shows or

holds a peak measurement value. Controller functions in clude set limits, regulator, P/PI/PID,

etc. Instruments with temperature compensation have software or adjustments for

compensating for variations in temperature that may cause measurement errors. Force and

torque instruments with biaxial measurement have an accelerometer capable of measurementalong two, usually orthogonal, axes.

Force and torque instruments with triaxial measurement have an accelerometer capable of

measurement along three, usually orthogonal, axes. Force and torque instruments usually

have displays for users to interface with the unit. Common types of displays include analog or

dial displays, digital readouts, and video displays. Programmability is achieved through

manual operation, front panels, or computer interfaces. Instruments with software supporthave software specifically for running on a host computer, which can be a PC or MAC.

Advanced searching capabilities for force and torque instruments include outputs, digital

resolution and sampling frequency. General features found on force and torque instruments

include filters, event triggering, built-in self-calibration, self-test diagnostics, and extreme

environment construction. Force and torque instruments often come with data storage in non-

volatile memory, hard drives or removable storage. Very often these instruments are also

compatible on a network.

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