Brief history of torque measurement

An Industrial Measurements product story
Edited by the Engineeringtalk editorial team Dec 9, 2005

Industrial Measurements explains the development of industrial torque measurements from a wrench to a handheld instrument in two decades.

Up to 15 or 20 years ago, it was highly unlikely that anything more sophisticated than a mechanical torque wrench would be used on the production line to monitor the applied torque in fasteners.

Assembly tools, mainly pneumatic, were used to run home individual fasteners, followed by final tightening with a dial indicator or, more usually, a click action torque wrench.

This method had two problems, it was relatively slow and was prone to over-torqueing, usually due to an over enthusiastic operative.

Gradually, it was realised that it was more effective to monitor directly the torque output of the assembly tool, rather than perform break-away checks on individual fasteners after they had been driven.

This could be done using a rundown fixture over the top of a static transducer, thus allowing the tool to go through its normal cycle of operation in a reasonably close simulation of actual joint conditions.

The rundown fixture or joint simulator (usually a cap screw passed through a stack of disc springs) connected to the square drive of a static transducer is a method still used extensively today.

It is never a true recreation of the actual joint, but is a better representation than driving a tool directly into a bare transducer.

As measurement methods improved, so did the realisation that many of the assembly tools in use were simply not capable of maintaining the accuracy and repeatability necessary for modern production plants.

Tools, both pneumatic and electric, were developed which were torque controlled via internal inline transducers.

These were and still are invaluable for critical applications, but tended to be too expensive for general production work.

It was at this point that pulse tools came into use.

These tools, which were originally developed from impact wrenches, are fast and reactionless, but quite accurate enough for normal production use.

They can be easily checked using an external inline rotary transducer.

In addition to torque, an optical encoder within the transducer measures angle as an extra parameter to aid tool assessment.

Most modern production lines now have a mix of transducerised tools and pulse tools which are regularly checked on a weekly, daily or even hourly basis (depending on the importance of the particular application) using various torque monitoring equipment.

The most universal monitor is the hand held analyser which, while extremely portable, can be connected to a static or rotary transducer, a digital torque wrench or even a load cell.

This means the torque output of an individual tool can be checked on a joint simulator with a static transducer following repair or maintenance in the tool crib and rechecked on the production line with a rotary transducer.

Finally, if required, a breakaway test can be performed on the fastener itself using a digital torque wench, all done with the same analyser.

An example of this type of universal handheld analyser is the TM 2000 from Industrial Measurements.

Find out more about this article. Request a brochure, download technical specifications and request samples here.
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