The best in suspension testing tech
‘The principles of a load cell design are quite generic although there are different types depending on application specific factors,’ says Ian Papworth, applications engineer at Novatech Measurements Ltd. ‘We use foil strain gauges that are either etched or deposited depending on the production process of the supplier. Effectively, a strain gauge consists of loops of very fine wire, only microns thick. These are attached to a metal structure, and when this structure deforms under load, it either stretches or compresses the wire grid, therefore changing its length and cross-sectional area. All the time this deflection is occurring, the resistance of the wire is changing. The foil strain gauges are wired up in a Wheatstone bridge and any change
in resistance excites this bridge, forming a potential divide. The output signal is in the order of millivolts and is linearly proportional to the amount of load applied. Instrumentation is set up so that the calibrated output is displayed as an accurate force measurement.’
Foil Gauges
Novatech use foil strain gauges for four- and seven-post rig applications because they are
the most stable and versatile, although the needs of many other industries to measure low forces at the highest resolution has opened up the potential for other load cell technologies to be utilised in the future. ‘Piezoelectric devices are good for high frequency measurements
and semiconductor gauges allow much more signal for the same mechanical deflection,’ Papworth say. ‘This could potentially increase the resolution beyond what foil strain gauges are capable of. But the technology that some companies are currently taking more seriously
is fibre optics. They work almost like a radar gun where you measure the time taken for one pulse to travel down the fibre optic and bounce back. The strain element of the fibre optic wire can
be attached to a material and, when deflected, there will be a change in length of the section that the wave is propagating along so the return signal will be slightly out of phase. Fibre optics will come into their own in applications where large electromagnetic forces could severely effect the output of the load cell.’
Credit: By GEMMA HATTON