Types of Strain Gauge : Characteristics & Its Applications

The strain gauge is a passive transducer that converts the mechanical elongation and compression into the resistance strain. It is invented in 1938 by Arthur Claude Ruge and Edward E. Simmons. There are different types of strain gauges and they are used for finding the vibrations, used for the calculation of strain, and associated stress and sometimes it is also used to find applied force and pressure. In the geotechnical field, the strain gauges are the important sensors. The direction, resolution, and type of strain are the important factors that should be considered before selecting types of strain gauge or strain gage.  The different types of strain gauges & their applications are explained below. 

What is Strain Gauge? 

The strain gauge is a passive transducer used for the measurement of strain and stress, displacement, force, and pressure. It operates on the “Piezoresistive Effect” principle. The gauge is attached to an object by using an adhesive under stress.  

Basics of Strain Gauge

Everyday engineering building lighter and more efficient structures that still manage to maintain strict safety and durability standards. To achieve this balance of safety, durability, and efficiency, engineers use strain gauges to measure the stress limits of their raw materials. The gauges monitor the amount of surface stress that a material can handle. A typical strain gauge is made up of three layers are Laminate top layer, sensing element, and plastic film base layer. 

When a strain gauge is bonded to a surface under stress, it will distort or flex in unison with that surface causing a shift in electrical resistance proportional to the strain applied to the surface. A formula can then be used to convert the fluctuations of resistance to an accurate strain reading. The gauges come in different configurations, choosing the right strain gauge for your application depends on which direction the primary strain is running, what type of strain you are measuring, and the target measuring area. This is the basics of strain gauge. 

Strain

Let us take one object of length ‘L0’, apply force ‘F’ on both sides of an object. If we apply an equal amount of force to the object the length of the object will change. 

Previously the length of the object is L0, after force applied to that object the length is L. The change in length is taken as dL, where dL=L– L0. The strain is defined as a ratio of change in length and original length.  

Strain= Change in Length/Original Length=dL/ L0 

This is the formula for measuring the strain. There are two types of strains they are positive strain and negative strain. Suppose we are using the one electrical conductor or electrical wire in a strain gauge which can pass the electricity through it. Whatever the forces, vibrations, and pressures applied on gauges are on the wire, because of the vibrations, and applied force the dimensions of the conductor also change.

The change in dimension will also change in resistance, that change in resistance will find the applied force or vibrations or pressure. Here the change in the dimension is the strain. It is the main basic principle of the strain gauge. 

Types of Strain Gauges

There are different types of strain gauges which include the following.

LY Linear Strain Gauges

The LY linear strain gauges measure the strain only in one direction. The LY1-LY9 are the types of LY linear strain gauges with different sizes and geometrics. The DY11, DY13, DY1x, DY41, DY43, DY4x, are the double linear strain gauges. 

Strain Gauge Rosettes

The different types of strain gauge rosettes are membrane rosette, tee rosette, rectangular rosette, and delta rosette.  

Membrane Rosette Strain Gauges

The membrane rosette strain gauges are used to measure displacement, velocity, pressure, and force, as well as to measure the elastic strain of the developed materials and structures under dynamic and static loads. The strain gauges are used in railroad car manufacturing, mechanical engineering, aircraft, and missile production, and other industries. 

Tee Rosette Strain Gauge (0-900)

The Tee rosette is a two-element rosette strain gauge. In Tee rosette, the two grids are mutually perpendicular.  

Rectangular Rosette (0- 450-900)

It is also known as a three-element rectangular rosette strain gauge consists of three grids. The second and third grids are angularly displaced by 450 and 900 respectively. Delta Rosette: The delta rosette is also known as a three-element delta rosette strain gauge, the second and third grids are 600 and 1200 away from the first grid.  

The tee rosette, rectangular rosette, and delta rosette strain gauge figures are shown below. 

Quarter Bridge, Half Bridge, and Full-Bridge Strain Gauges

The quarter, half, and full-bridge type strain gauges are discussed below.

Quarter Bridge Type Strain Gauge

The quarter bridge type I and quarter bridge-type II provide information about quarter bridge strain gage configurations.  

Quarter Bridge Type I

The type I quarter bridge measures either bending strain or axial strain. The bending strain is also known as moment strain. The bending strain is defined as a ratio of bending stress and young’s modulus of elasticity. The strain gauges used in the moment strain configuration can be used to determine the vertical load. The axial strain is defined as a ratio of axial stress and young’s modulus, to determine the axial loads the strain gauges are used in axial strain.

In the type-I quarter bridge, a single strain gauge element is mounted in the direction of bending strain or axial strain. Where R1 and R2 (half-bridge completion resistors); R3 is a quarter bridge completion resistor and R4 is also an active strain-gauge element that measures tensile strain. The quarter bridge type I and type II axial strain, bending strain, and circuit diagrams are shown below. 

Quarter Bridge Type II

The type II quarter bridge also measures either bending strain or axial strain.  Where R1 and R2 (half-bridge completion resistors); R3 (quarter bridge temperature sensing element) and R4 (an active strain-gauge element which measures tensile strain).  

Half-Bridge Type Strain Gauges

The half-bridge type I and half-bridge type II provide information on half-bridge strain gage configurations. 

Half-Bridge Type I

It measures either bending or axial strain. In type I R1 and R2 (half-bridge completion resistors); R3 (it measures compression from Poisson effect); and R4 (it measures tensile strain). 

Half-Bridge Type II

It doesn’t measure axial strain only measures bending strain. In type II R1 and R2 (half-bridge completion resistors); R3 (it measuring compressive strain); and R3 (it measures tensile strain). 

The half-bridge type I and type II axial strain, bending strain, and circuit diagrams are shown below

Full-Bridge Type Strain Gauges

The full-bridge type I, type II, and Type III provide information about full-bridge strain gage configurations. 

Full-Bridge Type I and Type II

Type I and type II both measures only bending strain. In type I R1 and R3 (active strain gauge elements measure compressive strain); R2 and R4 (active strain-gauge element measures tensile strain). In type II R1 (active strain gauge elements measure compressive Poisson effect); R2 (active strain gauge elements measure tensile Poisson effect); R3 (active strain-gauge element measures compressive strain); and R4 (active strain-gauge elements measure tensile strain); 

Full Bridge Type III

 The type III full-bridge rejects bending strain measures only axial strain. Where R1 and R3 (active strain gauge elements measure compressive Poisson effect); R2 and R4 (active strain gauge elements measure tensile strain). The total active strain-gauge elements in type III are four, where two active strain gauge elements are mounted in axial strain direction (one is mounted on top and the other is mounted on bottom) and the other two elements act as a Poisson gauge.

Strain Gauge Products

Some types of strain gauge products with measuring range, brand, and cost are shown in the below table. 

Model Number	Brand	Measuring Range	Cost
UITM is the model number	Unitech scales and measurement	300 mm length, 28 mm width and thickness is 2.5 mm	9000Rs/-
IG 1100/1200	Innovative geotechnical instrumentation	+/- 1500 micro-strain	3000Rs/-
VMW-MSG	VMW	The measuring range of this product is 200mm	14,500Rs/-

 Characteristics 

The characteristics of the strain gauges are 

• The strain gauges are highly precise
• For long-distance communication, they are ideal
• They require easy maintenance
• They have a long operating life
•  For long term installation, the strain gauges are suitable 

Applications 

The applications of the strain gauge are 

• Aerospace
• Cable bridges
• Rail monitoring
• Torque and power management in rotating equipment
• Residual stress
• Vibration and torque measurement
• Bending and deflection measurement
• Tension, strain, and compression measurement 

Advantages 

The advantages of the strain gauge are 

• Inexpensive
• Affordable
• Accurate 

FAQs 

1). What is the range of gauge length? 

The range of gauge length is from 3 to 6 mm for common applications. 

2). What are the strain gauge selection considerations? 

The strain gauge selection considerations are gauges length and width, the configuration of the solder tab, availability, carrier material, number of gauges, and arrangement of gauges in gauge pattern. 

3). What is the range of strain gauge resistance? 

The range of strain gauge resistance is from 30 to 3k ohms. 

4). What is the young’s modulus? 

The young’s modulus is defined as a ratio of tensile stress ad extensional strain. 

5). What are the types of strain? 

The axial strain, bending strain, torsional strain, shear strain, and compressive strain are the five types of strain. 

In this article types of strain-gauge & their applications, advantages of the strain gauge, some strain gauge products with measuring range and model, characteristics, basics of a strain gauge, and different types of strain gauges with diagrams are discussed. Here is a question for you what are the features of strain gauge?