How To Measure Torque
Download PDF: How To Measure Torque - A Definitive Guide
What is ‘Torque’
Torque Measurement in essence is a very simple mechanical process, in its most basic meaning it is a measure of the ‘force’ being used in turning (or attempting to turn) something. When a force or ‘torque’ is applied to a shaft; the shaft twists (by a very small amount). This twisting produces a ‘stretch’ in the material of the shaft, in a direction at 45 degrees to the axis of the shaft, between points on the shaft that are moved apart by the twisting motion. The material of the shaft also sees a ‘compression’ in the opposite 45 degree direction.
Datum Electronics utilise this shaft strain and measure the change in order to calculate the torque. This measurement is achieved by the use strain gauges bonded to the shaft, measuring the strain induced in the shaft by the applied torque or ‘force’. There are various methods of measuring this twist through a shaft; strain gauges are recognised as one of the most reliable methods, if you have the expertise to achieve this.
Definition of a Strain Gauge
A strain gauge is a small electrical ‘element’ printed on a non-conductive substrate. The pattern of the element is arranged so that if the gauge is stretched (or compressed) in one direction (along operating axis of the gauge), the resistance of the element increases (or decreases) in relation to that stretch. A stretch perpendicular to the axis of the strain gauge has little effect on the resistance of the element.
If a gauge is bonded to the shaft, with its axis aligned with the direction in which the shaft material stretches when a torque is applied, the strain gauge will also stretch and therefore the element will increase in resistance.
In the Torsionmeter, strain gauges making up four resistive elements are bonded to the shaft. Two elements are aligned with the direction of Tension (stretch). The remaining two are aligned with the direction of Compression.
The four resistive elements are electrically connected in a ‘Wheatstone Bridge’ configuration. The Wheatstone Bridge configuration is appropriate for measurement of the small resistance changes produced in the strain gauges, as the combination increases and decreases in resistance it produces a change in output voltage which is only proportional to excitation voltage and change of resistance between opposing elements, not to any overall change in resistance such as might be produced by a change in temperature.
Torque measurement can be used in a number of different applications and for different requirements, including monitoring and control, power management and increased efficiency savings. If you are looking to measure/control power, torque and speed then our range of torque instrumentation has been designed to help you.
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Torque Solutions from Datum Electronics
M420 Rotary Torque Transducer (with bearings)
FF420 Rotary Torque Transducer (without bearings)
RS420 Rotary Torque Transducer (without bearings)
FF410 Static Torque Transducer
Marine Torsionmeter Systems
Shaft Power Meters
Drive/Prop Shaft Torque
PTO / Power Take Off
Torque Trails Kit