What is Strain gauge and its types

What is a strain gauge and how is it a transducer

A strain gauge is a device that can be used to measure strain on an object. It can be described as a passive transducer that uses electrical resistance variation in wires to sense the strain produced by a force on the wire. It can be used to measure weight and pressure. Strain gauge will be attached to the object and when the object is deformed then the coil will be deformed, which will change its electrical resistance and this resistance change will be measured by using a Wheatstone bridge. A strain gauge is called a transducer because it can convert the mechanical stress of an object into its corresponding change in resistance so the amount of force on the object can be calculated.

How does a strain gauge works

The strain gauge will be connected to the object which is needed to be measured by a suitable adhesives strain gauge can convert the weight, pressure, tension, and force into a difference in electrical resistance which can be measured, if the object is under a lot of force or stress the material will begin to bend slightly and this could increase the electrical resistance, and mostly the change in resistance will be measured by Wheatstone bridge. The resistance which is measured can be converted to strain by using a gauge factor.

What are the factors which can affect the accuracy of a strain gauge

There are certain factors that can affect the accuracy of a strain gauge they are electromagnetic interference, humidity, and the environment. Temperature can be affected in many ways, for example, a rise in temperature can increase the object to expand and this change in size will be considered as a strain in the object by the strain gauge. Electromagnetic interference is affected by vibrating strain gauge their operating frequency will be affected by the electromagnetic interference and the humidity can cause the breakdown of the insulation between the gauge and the ground point this will affect the accuracy.

How do I choose a strain gauge

The two important factors to select the right strain gauge is sensitivity and precision. In order to get a quality and quick measurement, more strain gauges can be added but it could cost high.

How do you measure strain

Wheatstone bridge is used to measure the static and dynamic electrical resistance. In order to measure the strain, the device must be connected to an electric network which can measure small changes in resistance relative to strain

What are the types of strain gauges

Classification of strain gauges

  • Mechanical
  • Optical
  • Pneumatic
  • Acoustical
  • Electrical
  • Bonded
  • Un-bonded

Inductance strain gauge

Inductance strain gauges are very sensitive and it can be used to measure very small changes, in this, the member which is to be measured is connected to one end of a moveable iron armature and the long parts of the armature are placed between the two cores with wires coiled in between. If the strain produced makes the armature move towards the left core then it increases the inductance of the left-hand coil which is coil1 and decreases the inductance of coil2. The coils will produce an impedance in a bridge circuit and this produces an output voltage which is proportional to the input displacement and hence proportional to the strain.

Resistance strain gauge

Resistance strain gauges are used widely they are fabricated from metal foil it is used for characterizing small mechanical strains in force cells, scales for weighing and the engineering testing of metals and rigid composites. The change in the gauge resistor is characterized by using a Wheatstone bridge resistor network.

Foil strain gauge

This strain gauge consists of an insulating flexible backing which supports a mechanical foil pattern and the gauge is attached to the object by a suitable adhesive. When the object shape changes then the foil shape will change too which will cause its electrical resistance to change and the change in resistance is measured by Wheatstone bridge.

Mechanical strain gauges

These strain gauges are mostly known as extensometer and they can be used to measure the strain under static or gradually varying loading conditions. Extensometer has two knife edges and they are clamped in contact with the test component, during the strain of the test component the two knife edges will slightly undergo displacement and this displacement is amplified by using a mechanical linkage and the strain will be displayed on a calibrated scale.

Un-bonded strain gauge

In this type of strain gauge, a piece of wire is stretched in multiple folds between a pair or more insulated pins fixed to a moveable part of a body or a flexible part when strained then the wire will get strained too.

Acoustic strain gauge

This strain gauge consists of steel wire tensioned between two predefined supports variation in distance alter the natural frequency with a change in strain. In this strain gauge, the frequency change can be increased by decreasing the length or stress in the wire, these gauges are highly accurate and long term reliability. Structural strains can be measured by using this strain gauge, a wire is mounted in this device and its tension varies with strain. It can be used to measure the strain of concrete structures, steel structures, and rock.

Pneumatic strain gauge

It is a strain gauge which can be used to measure the dimension change of objects according to the flow rate of air escapes from a nozzle under pressure. This gauge can be used to measure 1mm, they are capable of static and dynamic measurements. These devices are very sensitive and reliable too.

What are the applications of strain gauge

  • Pressure measurement
  • Acceleration measurement
  • Temperature measurement