Investigate and test a strain gauge sensor using different materials.

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Investigate and test a strain gauge sensor using different materials.

Aim

To test and evaluate a sensor using two materials, (steel and wood) to determine the sensitivity and accuracy. Response time and reliability of the sensor will also be tested and the ability of the sensor to detect small changes will show in the results.

Research

A strain gauge is a device capable of translating a deformation (strain) into an electrical signal. This can also be used to measure force, pressure load or weight.

Strain =Extension 

                 Area

The above equation is used to calculate the strain and has no units because they are cancelled out (meters/meters=nothing).

A strain gauge is connected in a wheatstone bridge it consists of 4 resistors arranged in a diamond orientation. An input DC voltage is applied between the top and bottom of the diamond and the output voltage is measured across the middle.

When the output voltage is zero, the bridge is said to be balanced. As the resistance of one of the leg changes, balanced bridge is now unbalanced. The unbalance causes a voltage to appear across the middle of the bridge. This voltage may be measured with a voltmeter.

The strain gauge it self works when stretched this increases the length therefore resistance increases, according to the relationship: Resistance=resistivity*Length.

                                                                        Area

Vice versa if the strain gauge is compressed then the length decreases so does the resistance, which can be seen when connected in the circuit and as the potential difference (P.D).

(A Strain Gauge).


A fundamental parameter of the strain gauge is its sensitivity to strain, expressed quantitatively as the gauge factor (GF). Gauge factor is the ratio of fractional change in electrical resistance to the fractional change in length (strain):

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The relationship between resistance and strain is:

                        GF= ΔR/R = ΔR/R

                                 ΔL/L      ε

GF= Gauge Factor, ε= is the strain, R is the resistance and L= length.

 

Fair Test

Making this a fair test will involve taking into consideration many factors as temperature will affect the results because Strain gauge manufacturers attempt to minimize sensitivity to temperature by processing the gauge material to compensate for the thermal expansion of the specimen material for which the gauge is intended for. While compensated gauges reduce the thermal sensitivity, they do not ...

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