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Types Of Strain Gauges And Their Application Pdf

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A strain gauge was invented by Edward E. Simmons and Arthur C. Ruge, in

Strain Gauge Principle, Types, Features and Applications

The strain gauges are based on the resistive properties of the metal. Upon stretching, the metal material loses or increases its electrical resistance. The strain gauge foil is glued on the material, which will be tested using a specially adapted glue for strain gauges.

Due to the correct fit to the material being examined, the strain gauge is bent in the same way as the test material, so it reproduces the stresses. Strain gauge theory tells about resistance elements that are found in a large amount of electronic equipment. They are mainly used to measure different compressive forces, tensile forces and any stresses of materials. They are the main element of automatic systems when it comes to weight measurements e.

Properly set strain gauges allow mass measurements, measurements of product dispensing amount, etc. In order to properly choose the type of strain gauge, it should be determined in what conditions it will operate.

You need to know the type of load, the temperature at which it will be operating and the requirements it must have to endure cooperation in that system.

Their advantages are:. Strain gauges are attached to the substrate with a special glue, which bonds them together. The type of glue depends on the required lifetime of the measurement system. Main task of the strain gauge adhesive bonding material is to obtain the best possible connection between strain gauge and the surface of the tested sample or object.

Different measurement environments require other types of strain gauge adhesive, because each one influences the measurement process in different way. Aforementioned surface must be first smoothed e. Strain gauge must be glued immediately after this process to avoid oxidation or pollution of the prepared area. Without this process, the strain gauge adhesive binding to the surface may generate measurement errors and be unreliable.

The type of strain gauge adhesive and material used for the production of strain gauges are patented secrets of manufacturing companies, thanks to these material parameters the best accuracy and sensitivity are obtained.

There are three types of most popular strain gauges:. To obtain the best possible quality of the bonding between strain gauge and the substrate, different requirements must be met. In terms of operating temperature, this led to the availability of various types of strain gauge adhesive materials. To ensure correct strain gauge calibration process, it is important to know its most important parameters for the corresponding model:.

Electric strain gauges use physical relationships between electrical parameters and material deformation. Depending on the measured units, there is a division of strain gauges:. The electroresistive strain gauges are characterised by good accuracy and sensitivity of strain measurements of the tested sample. The distance of the test sample from the strain gauge can be large in the case of electric strain gauges, which also allows measurement in many measuring places for the material stresses of the test system.

Due to the very low value of the inertia parameter of the measurement system, electrofusion strain gauges are well suited for testing fast-changing strains. Block system measuring the load cell amplifier powered by AC voltage. Electrical strain gauges are based on the principle of changing the electrical resistance due to the change in the length of the metal used in the strain gauge.

The formula for the resistance of strain gauge metal is:. Where: R — strain gauge metal resistance, p — specific resistance of a strain gauge, l — strain gauge length, A — cross-sectional area of the strain gauge. In resistance theory strain gauge, their length is called the strain gauge base.

During the samples work, the length of the strain gauge base changes. At the same time, the length of the metal wire also changes, which directly affects the change of its resistance.

The formula defining changes in deformation in relation to resistance changes is as follows:. The two previous formulas describe the basic physical dependencies of the strain gauges electrical resistance. By plunging the Hooke law, it is possible to obtain a tension at a particular point of the sample:. A distinguishing feature of electric strain gauges is the method of obtaining deformation values from the material under test. In this process, the strain gauge is used together with a glue specially made for such tasks.

To fix the strain gauge correctly, clean the test surface. The whole process of choosing a foil, the shape of a strain gauge and sticking is long.

It is necessary to prepare everything carefully and calculate the places of sticking and the shape of the strain gauge. Electroresistive strain gauge works well as a subset of static, dynamic and moving samples. Their sensitivity is high and their own weight does not affect the discrepancy of measurements. By transmitting the deformations directly to the resistive wire, the transmission and the slippage are avoided. The values of results are dimensionless, so they do not depend on the value of the strain gauge constant.

Examination of several places of one sample is not a problem for electric strain gauge. In addition, results can be obtained live through the wireless connection. Thanks to the use of compensation strain gauges, the influence of moisture and temperature on the measurement results is removed. Three types of electric strain gauges are most commonly used: tubular strain gauges, mesh strain gauges, foil strain gauges, with which the foil is the most popular in the industry. The tubular strain gauge is made of a piece of wire that is covered with foil or paper on both sides.

The connectivity of the wire with the electrical circuit provides a copper strip connected to both ends of the wire. Its diameter ranges from 0. Tubular strain gauge. The mesh strain gauge is made of parallel-laid wires, which are connected by a copper band with a larger width and a lower specific resistance. Due to the use of tape with a larger cross-section, the resistance of the tape deformation is so small, that it is not measurable for the apparatus calibrated under strain gauges.

Consequently, the strain gauge has a much lower sensitivity when it comes to measurements in the transverse direction. The execution of wires is constant and their diameter does not exceed 50 micrometers. Connecting copper strips with wires is made using tin soldering. Tin is a problem in measurements at high temperatures above degrees Celsius. The base value of mesh strain gauges is 5 mm to 70 mm. Mesh strain gauge. The foil strain gauge is made of a metal foil, the thickness of which does not exceed 0.

The method of producing strain gauge foil is similar to printing circuits on flexible films. Thanks to lithographic technique, it is possible to create strain gauges with dimensions and shapes ideally suited to the examination.

Foil strain gauge. The strain gauge rosette is a set of strain gauges set in a previously planned way. The number of applied strain gauges depends on the values calculated during the selection of strain gauges to the sample under test. Strain gauge rosettes. The strain gauge rosettes can be divided into three types: rectangular rosette measures deformations in the multi-axis state , T-rosette measures biaxial stresses , screwed rosette measures torsion samples.

The strain gauge should be properly prepared by ideally gluing the strain gauge to the material being tested. The glue used should be specially prepared for use in the strain gauge. Its thickness should not exceed 10 micrometers.

The operation of the glue should isolate the wires from the material being tested. The glue should withstand high operating temperatures without changing its physical and electrical properties. After proper gluing of the strain gauge, the whole system is covered with a protection layer, it may be a wax.

Glued strain gauge. Mechanical strain gauges are among the most straightforward in the way of making and measuring. The method of measurement consists of measuring the elongation of the blades and reading this value on a scale magnified times, transmitted by means of mechanical levers.

The following figure shows the Huggenberger mechanical strain gauge, its construction consists of a movable, immovable blade, handles, pointer, and scale. Huggenberger mechanical strain gauge. Changing the deformation value activates the lever movement. The Huggenberger strain gauge has a strain gauge base with values ranging from 5 — mm. The strain gauges are a bit heavier because they weigh about 50 g. They are most often used in building constructions. The stress of the surface and the mass of the test material are measured.

The main element of a string strain gauge is a tightly tensioned string, adjustable by means of screws. It is placed between two blades. The measurement is carried out by means of vibrating and resonant vibrations. Strained strings stretched between the blades are subjected to testing. String strain gauge. Optical strain gauges predominate over mechanical strain gauges in terms of the resolution of strains under investigation.

Thanks to the large ratio, they are capable of performing more accurate measurements. The most popular types of strain gauge as optical is the Martens mirror strain gauge. The operation of the optical strain gauge is based on the study of the length of the measuring base. When changing the length of the base, the mirror rotates and the light falls on the scale, which is read with the telescope. During the operation of this strain gauge, very restrictive conditions must be maintained as to the mechanical shocks of the environment.

Martens mirror strain gauge.

Strain Gauge: Principle, Types, Features and Applications

Several types of strain gages depend for their operation on the proportional variance of electrical resistance to strain: the piezoresistive or semi-conductor gage, the carbon resistive gage, the bonded metallic wire, and foil resistance gages. The bonded resistance strain gage is by far the most widely used in experimental stress analysis. This gage consists of a grid of very fine wire or foil bonded to a backing or carrier matrix. The electrical resistance of the grid varies linearly with strain. In use, the carrier matrix is bonded to the surface, force is applied, and the strain is found by measuring the change in resistance. The bonded resistance strain gage is low in cost, can be made with a short gage length, is only moderately affected by temperature changes, has small physical size and low mass, and has fairly high sensitivity to strain. In a strain gage application, the carrier matrix and the adhesive must work together to transmit the strain from the specimen to the grid.

The strain gauges are based on the resistive properties of the metal. Upon stretching, the metal material loses or increases its electrical resistance. The strain gauge foil is glued on the material, which will be tested using a specially adapted glue for strain gauges. Due to the correct fit to the material being examined, the strain gauge is bent in the same way as the test material, so it reproduces the stresses. Strain gauge theory tells about resistance elements that are found in a large amount of electronic equipment. They are mainly used to measure different compressive forces, tensile forces and any stresses of materials. They are the main element of automatic systems when it comes to weight measurements e.

Strain Gauge Theory – Types, formulas and applications

Strain gauges may be used in "smart bridge" technology to detect structural problems early. Strain gauge technology has practically unlimited uses in the field. It can be used to test vehicles, ship hulls, dams, and oil drilling platforms. A simple civil engineering application using strain gauge technology is to install strain gauges on structural components in a bridge or building to measure stress and compare them to analytical models and stress calculations.

The main purpose of a strain gauge is to indirectly determine stress and its variation with time, quantitatively. Change in stress is determined by multiplying the measured strain by the modulus of elasticity. We have covered its working principles, characteristics, features, as well as, application areas. Strain GaugeStrain Gage measures the strain amount of contraction as well as expansion caused by external forces on any object. The strain gauge was invented in by Edward E.

It converts a force such as tension, compression, pressure, or torque into an electrical signal that can be measured and standardized. As the force applied to the load cell increases, the electrical signal changes proportionally. The most common types of load cell used are strain gauges, pneumatic, and hydraulic, pneumatic.

A strain gauge was invented by Edward E. Simmons and Arthur C.

What is Strain Gauge : Working and Its Applications

The bonded resistance strain gage is an analog electrical sensor ideally suited to the task of measuring surface stains on solid materials. The two most common devices are the popular etched-foil sensor, and the somewhat more exotic semiconductor gage. Strain gages work on the same principle as engineering strain; i. Foundational characteristics, including sensitivity, thermal response, and limiting properties, and use of these sensors in experimental stress analysis applications, including shear measurement, thermal expansion measurement, and principal strain measurement, are reviewed. Electrical circuits used in the interrogation of strain gages are discussed, along with special considerations and exploitation of specific circuit arrangements for solving unique problems.

The strain gauges are based on the resistive properties of the metal. Upon stretching, the metal material loses or increases its electrical resistance. The strain gauge foil is glued on the material, which will be tested using a specially adapted glue for strain gauges.


Strain Gauge Principle, Types, Features and Applications The main purpose of a strain gauge is to indirectly determine stress and its variation with time.


Strain gauges are devices that are commonly used by engineers to measure the effect of external forces on an object. They measure strain directly, which can be used to indirectly determine stress, torque, pressure, deflection, and many other measurements. Strain is a dimensionless measurement that is a ratio of the change in length to the original length of an object.

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Strain Gauge Theory – Types, formulas and applications

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What is Strain Gauge : Working and Its Applications

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