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Even if you’ve never come across the term “strain gauge” before, chances are you’ve used the device in question. A strain gauge is something that comes in handy whenever we need to measure how much something is compressed or stretched. Strain gauges are used in accelerometers and balances, as well as in storage tanks. They are extremely practical in the automotive industry, where they can be used to track a range of forces.
Strain gauges have several key advantages over the competition, in that they are extremely durable and accurate, capable of operating at very high temperatures and under considerable pressure.
What is a strain gauge?
A strain gauge can work in different ways. There are magnetostrictive, photoelectric, piezoelectric, capacitive, inductive and electroreceptive gauges. They are set up in three different ways, for the most part.
A tubular gauge uses a long piece of wire, covered with aluminum foil on both sides. As the wire stretches, it will become more or less resistive. Next we have the mesh strain gauge, which sees a series of parallel wires connected by copper strips. Finally, there is the foil gauge, which uses extremely thin metal foil, which is only possible with modern lithographic techniques.
So how do we use these devices to determine the charge? There are three different circuits that do the job in different ways.
Quarter Bridge Strain Gauge
These gauges use a Wheatstone bridge – which is a quartet of resistors arranged in a specific formation. In this case, one of the resistors is variable, while the others are fixed. This design tends to be preferable in cases where only one axis is measured.
Strain gauge rosettes
This is a setup that sees multiple strain gauges overlap to measure strain in multiple directions at once. This is often a cost effective way to get the job done. A biaxial rosette uses two different sensors, offset at different angles. In the case of a triaxial rosette, it is rather three sensors.
Rosettes can be arranged in a variety of ways – and original arrangements can be designed to meet the needs of a new specialist application. As such, it makes for an extremely adaptable way to get the job done.
piezoresistance
When making very small scale measurements, a piezoresistor is often the superior option. A piezoresistor works on very different principles from a strain gauge, which means you lose some of the defining benefits of the latter: namely durability at high temperatures and pressures. When considering the appropriate choice for a given application, designers will need to weigh these considerations.
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