Lab report strain gauge

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Lab report strain gauge

Strain gauges are usually based on a metallic foil pattern. The gauge is attached to the test piece with a special adhesive. As the test piece is deformed, so the adhesive deforms equally and thus the strain gauge deforms at the same rate and amount as the test piece.

If the adhesive cracks or becomes detached from the test piece any test results will be useless. Strain gauges are used not just for metals; they have been connected to the retina of the human eye, insects, plastics, concrete and indeed any material where strain is under investigation.

Modern composite materials like carbon fibre when under development are often constructed with strain gauges between the layers of the material. The strain gauge is effectively a resistor. As the strain increases so the resistance increases. In a basic sense a strain gauge is simply a long piece of wire.

Lab report strain gauge

Gauges are mostly made from copper or aluminium Figure 1. As the wire in the strain gauge is mostly laid from end to end, the strain gauge is only sensitive in that direction. When an electrical conductor is stretched within the limits of its elasticity it will become thinner and longer.

It is important to understand that strain gauges actually deform Lab report strain gauge a very small amount, the wire is not stretched anywhere near its breaking point. This is because resistance is a function of both cable length and cable diameter.

The formula for resistance in a wire is where is resistivity in ohm metres, is length in metres and in m2. For example, the resistance of a copper wire which has a resistivity of 1.

It is measured in ohm metres. In this example to 0. This example shows only the difference when the characteristics of the copper wire have changed.

It is not practically possible to stretch and extend a piece of copper wire by these amounts. The example merely shows how resistance changes with respect to length and cross sectional area and demonstrates that strain gauges, by their very nature, exhibit small resistance changes with respect to strain upon them.

These small resistance changes are very difficult to measure. So, in a practical sense, it is difficult to measure a strain gauge, which is just a long wire. Whatever is used to measure the strain gauges resistance will itself have its own resistance. The resistance of the measuring device would almost certainly obscure the resistance change of the strain gauge.

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A Wheatstone bridge Figure 3: With shunt resistor The solution to this problem is to use a Wheatstone bridge to measure the resistance change.

A Wheatstone bridge is a device used to measure an unknown electrical resistance. It works by balancing two halves of a circuit, where one half of the circuit includes the unknown resistance.

Figure 2 shows a classical Wheatstone bridge, Rx represents the strain gauge. Resistors R2, R3 and R4 are known resistances. Normally,or are used depending on the application.

For example if R2, R3 and R4 are and if the measured signal voltage between measurement points A and B was 0 Volts then the resistance of Rx is For our example we get This implies a perfectly balanced bridge.

In practice, because the strain gauge goes through different strain levels its resistance changes, the measured signal level between measurement points A and B is not zero. This is not a problem when using a system like the Prosig P as it can accurately measure the voltage between measurement points A and B.

It is necessary to know the relationship between resistance and voltage. Only then can the measured voltage be related to a resistance and, hence, a strain value. Figure 3 shows the addition of another resistor RS, called the shunt resistor.

The shunt resistor is a known fixed value, normally. The Shunt resistor is added for calibration purposes and is a very high precision resistor. By measuring the voltage between measurement points A and B with the shunt resistor across Rx, a voltage with the shunt resistor in place is known. Therefore the volt per ohm value is known for this particular bridge and this particular Rx.

In order to go one step further and calculate the strain from the resistance, the gauge factor must be known.

This is a calibrated number provided by the manufacturer of the strain gauge.MSE MECHANICAL BEHAVIOUR LABORATORY LIST OF EXPERIMENT 1. Determination of the tensile properties of different class of materials (Lab-1). Labeling theory is the theory of how the self-identity and behavior of individuals may be determined or influenced by the terms used to describe or classify them.

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A strain gauge is an electrical sensor which is used to accurately measure strain in a test piece. Strain gauges are usually based on a metallic foil pattern.

The gauge is attached to the test piece with a special adhesive. As the test piece is deformed, so the adhesive deforms equally and thus the. Cable Types and Their Differences Home audio conductors fall into two broad categories, interconnects and speaker benjaminpohle.com former connect the source (turntable, CD player, tape deck, music server, tuner, and so on) to the control center (preamp, receiver, or integrated amplifier), as .

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Strain Measurement MEASUREMENT EXPERIMENT 1. OBJECT The objective of this experiment is to become familiar with the electric resistance strain gage techniques and utilize such gages for the determination of unknown quantities (such as strain and stress) at prescribed conditions of a cantilever beam.

An ideal gauge for checking bearing alignment or shaft deflection without dismantling the engine. Useful as a strain gauge on engine frames. This inside measuring gauge checks the distortion of .

What Is A Strain Gauge?