A strain gauge is a type of accelerometer that measures the strain of different objects.
It is usually made of a metallic foil construction and bendable frame to which objects are attached. A series of parallel conductive strips are arranged in a way that multiply the experienced effects.
The resulting changes in shape to the device due to the attached object are then measured.
The first gauges were invented in 1938 by Arthur C.
Ruge and Edward E.
Simmons.
They were first created to measure stress levels on water tanks due to earthquakes.
The most common form of device is made of metallic foil material supported by an insulating and flexible backing. It is attached to the object wished to be measured by an adhesive.
An appropriate adhesive is cyanoacrylate.
Usually it is attached so that the gauge is in the vertical position, as it is much more precise at this angle.
Horizontal positioning adversely affects its sensitivity. After attachment, as the object becomes deformed so does the attached device.
These deformities create changes in its electrical resistance.
Lord Kelvin first noticed the mechanism behind this in the year 1856. He linked changes in shape to changes in electrical resistance.
When an electrical conductor is stretched but not permanently deformed, it lengthens.
This results in an increase in its electrical resistance.
If this same conductor is instead compressed but not smashed, it shortens and widens, decreasing its resistance.
Therefore, taking the changes of the gauge into account, the amount of force applied to it can be calculated.
Changes are measured with the use of a bridge tool. The resistance is then compared to strain using the gauge factor.
This factor is the product of the change in resistance divided by the resistance of the undeformed gauge, all divided by strain.
Metallic foil models usually end up with a resulting factor of slightly over two.
Other measurements can be calculated using a voltage of five to twelve volts passed to input leads attached to devices.
Readings are taken from output leads, and are generally in small quantities of millivolts.
This information can then be plugged into an equation.
Output voltages are equal to the bridge excitation voltage multiplied by the gauge factor and strain, all divided by four.
The stability of devices attached to a load cell could endure for decades.
Gauges instead used for short term experiments can be attached for days and require energy for less than an hour.
The operation of this short term gauge can last for less than one second.
The integrity of devices can be compromised by several factors.
One of these is temperature.
Increases in temperatures may cause objects to expand, which is interpreted as strain. Therefore the gauges resistance and the resistance of its connections alter. Luckily, they are available of specific alloy combinations that can cancel out the effects of the objects expansion.
However, the right alloy must be chosen.
Furthermore, the type of adhesive that is used also affects results.
This type of accelerometer accurately determines the forces at work upon objects.
The deformities it undergoes as a result is measurable.
Resistance and strain can be calculated from measurements determined by physical and electrical changes to the device.
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