Electric strain gauges use physical relationships between electrical parameters and material deformation. The most widely used gauge is the bonded metallic strain gauge. Gauge factor is defined as the ratio of fractional change in electrical. January 27, 2016 comparing strain gage measurements to force calculations in a simple cantilever beam 4 p a g e mqp, hazel figure 1 stress strain graph showing elastic and plastic region davis stress when a body is loaded with a force, the material must compensate for this load by altering the shape of. A strain gage with a gf of 2 exhibits a change in electrical resistance of only 2 500 x 106 0. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. Measuring stress and strain, part 2 the electrical resistance strain gauge. A strain gauge takes advantage of the physical property of electrical conductance and its dependence on the conductors geometry. Scribd is the worlds largest social reading and publishing site.
Foil strain gages are usually made by a printedcircuit process. When bearing mechanical elongation or contraction, most metals undergo a change in electric resistance. A thin plastic base supports thin ribbons of metal, joined in a zigzag to. There are three steps in obtaining experimental strain measurements using a strain gage. Electrical resistance strain gauges are the most frequently used devices in experimental stress analysis today. Hi friends, in this article, i am going to describe you strain gauge working principle, gauge factor and strain gauge load cell working. Thus, in order to use it to determine strain, compensation has to be made for temperature effects. R change in strain gauge resistance due axial strain and lateral strain. Wilson introduction a strainsensitive material is one whose electrical resistance is proportional to the instantaneous spatialaverage strain over its surface. Strain gauges if a strip of conductive metal is stretched, it will become skinnier and longer, both changes resulting in an increase of electrical resistance endtoend.
The direction of strain which is measured is generally in longer direction of the strip means it ca. View test prep 4 strain gauge circuits repaired from mechanical 432 at egerton university. In this clip we will discuss that how does a strain gauge works. Only a differential resistance difference of resistance between the two strain gauges produced by physical force on the test specimen can alter the balance of the bridge. Automatic strain measurement is usually done with an electrical resistance strain gauge or gage. Jan 04, 2018 a2a strain gauges require the surface on which they are applied on to be of very good finish and clean. Most of the strain gauges are made of constantan alloy which cancel out the effect of temperature on the resistance. Effect of pressure on electrical resistance strain gages article pdf available in experimental mechanics 373. It operates on the principle, discovered by the british physicist william thompson later lord kelvin in 1856, that the electrical resistance of a copper or iron wire changes when the wire. When a fine metallic wire is pulled, it has its electric resistance. With the 2wire circuit, the strain gauges and the amplifier are connected via two wires. A strain gauge sensor is a thin waferlike device that can be attached to a variety of materials to measure applied strain. The finalization after bonding the gauge in the bolt is shown in this helpful article.
Other types of strain gages are acoustic, capacitive, inductive, mechanical, optical, piezoresistive, and semiconductive. However, since strain is an invisible infinitesimal phenomenon, the resistance change caused by strain is extremely small. An easeries gage with option le should not be used in a fatigue environment. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Strain gages are used to measure linear strains that occur at surface points of an object when it responds to.
Strain gauges are popular means to measure mechanical movements in micro components. Historical development lord kelvin in 1856 first reported on the relationship bw strain and the resistance of wire conductors. Transferring the extensional strain of the surface of a specimen into a proportional strain in the elements of a resistive strain gauge. Measuring strain gauge circuits in order to measure strain with a bonded resistance strain gauge, it must be connected to an electric circuit that is capable of measuring the minute changes in resistance corresponding to strain. Various means like mechanical, optical, acoustical, pneumatic or electrical can be used to measure deformation strain of an object. The electrical resistance of this grid material varies. Strain gages are used to measure linear strains that occur at surface points of an object when it responds to some actuating load, as shown in figure 1. Performance characteristics of metallic resistance strain. Mar 15, 2020 this is a common property of all the conductors. The most serious difficulty involves the change in electrical resistivity of the strain gage and lead wires as a result of the fastneutron dose. A strain gauge is a passive transducer, that converts mechanical displacement into the change of resistance. Comparing strain gage measurements to force calculations. The circuit diagram shows that the cable resistance is added twice feed and return to the strain gauge resistance this affects both the bridges zero point and its sensitivity. While such gages cant be identified from catalogs, estimated fatigue life for any micromeasurements gages can be obtained from our applications engineering department.
The length change of the piezoelectric stack alters the resistance of the strain gauge. This recommendation deals with metallic resistance strain gauges of the type used for determining the mechanical properties of materials, for stress analysis of structures, and as sensing elements in a variety of measuring instruments see appendix a. The resistance strain gauge is a valuable tool in the field of experimental stress analysis. Strain gauges of all types are essentially employed to measure the linear.
Introduction to strain gages instruments techno test inc. Strain gauge sensors or piezoresistive sensors piezoresistive means pressuresensitive resistance, or a resistance that changes value with applied pressure. Depending on the measured units, there is a division of strain gauges. Resistance strain gage is based on that phenomenon see sec. Our wide portfolio consists of more than 2,000 different strain gauge types and accessories, and our service makes hbm the perfect partner for your project.
It covers the installation of foil gauges using cyanoacrylate and epoxy adhesives, inspection of installations, the. When using these gages in a cyclic strain field, refer to micromeasurements application note tt604, leadwire attachment techniques for obtaining maximum fatigue life of strain gages, for the recommended method of leadwire attachment. The change in the resistance of a wire is directly proportional to axial sensitivity of the. A strain gage sometimes refered to as a strain gauge is a sensor whose resistance varies with applied force. Contents definition history working characteristics types advantages disadvantages application a strain gauge is a thin, waferlike device that can be attached to a variety of materials to measure applied strain. For example, the piezoresistive strain gauge is a semiconductor device whose resistance varies nonlinearly with strain. In order to convert force into electrical signals, we bond a sensor called a strain gauge to the load cell. Read the operation manual carefully before using bonding adhesives. Simmons at california institute of technology and ruge at mit independently discovered in 1938 that small diameter wires could be adhesivly bonded to a structure to measure surface strain. These gages should be avoided where cyclic endurance is important. Also explore the seminar topics paper on strain gauge with abstract or synopsis, documentation on advantages and disadvantages, base paper presentation slides for ieee final year mechanical engineering me or production automobile students for the year 2019 2020. Resistance type strain gauges like this were invented in 1938 by mit professor arthur ruge 19052000 to help with earthquake detection. The electrical resistance of an object is a measure of its opposition to the flow of electric current.
Methods for calibration of bonded electric resistance strain gauges. But some strain gauges are not of an isoelastic alloy. Resistancetype strain gauges like this were invented in 1938 by mit professor arthur ruge 19052000 to help with earthquake detection. History the electrical resistance of a metallic object changes due to pressure or tension. From strain measurements to load in an instrumented pile. Strain gauge working principle your electrical guide.
A thin plastic base supports thin ribbons of metal, joined in a zigzag to form one long electrically conductive strip. Principle of strain gages the strain gage is tightly bonded to a measuring object so that the sensing element metallic resistive foil may elongate or contract according to the strain borne by the measuring object. The electrical resistance strain gage is the most widely used device for strain measurement, its operation is based on the principle that electrical resistance of a conductor changes when its subjected to. Conversely, if a strip of conductive metal is placed under compressive force without buckling, it will broaden and shorten. There are numerous types of strain gauges available. Characteristics of strain gauges free download as powerpoint presentation. Oct 24, 2016 electrical resistance of a piece of wire is directly proportional to the length and inversely to the area of the cross section. Fatigue characteristics of micromeasurements strain gages. Electrical resistance strain gages are sensors made of thin foil or wiretype conductors that respond to variations in length with variations in electrical resistance. Develop a suitable method suitable for the conversion of resistance changes in the gauge element into a more readily observable quantity, in. Wire resistance doesnt impact the accuracy of the circuit as much as before, because the wires connecting both strain gauges to the bridge are approximately equal length.
Several types of strain gages depend for their operation on the proportional variance of electrical resistance to strain. The electrical resistance strain gauge is a resistance element which changes resistance when subject to strain. A typical strain gauge is made up of very fine wire, or foil, set up in a grid pattern in a way that produces a linear change in resistance when strain is applied along one axis. History in 1856, lord kelvin established the principle of electrical resistance strain gauges when he demonstrated that when stress. The resistance of a strain gauge varies with applied force and, it converts parameters such as force, pressure, tension, weight, etc. A strain gauge sometimes refered to as a strain gage is a sensor whose resistance varies with applied force.
Even with cables with lengths of few centimeters it is essential to allow for the cable resistance. January 27, 2016 comparing strain gage measurements to force calculations in a simple cantilever beam 5 p a g e mqp, hazel eq 3 where the stress vector is now equal to the normal and sheer stress components. The bonded resistance strain gage is an ana log electrical sensor ideally suited to the task of measuring surface stains on solid materials. A strain gage sometimes referred to as a strain gauge is a sensor whose resistance varies with applied force. It operates on the principle, discovered by the british physicist william thompson later lord kelvin in 1856, that the electrical resistance of a copper or iron wire changes when the wire is either stretched or compressed. The input and output relationship of the strain gauges can be expressed by the term gauge factor or gauge gradient, which is defined as the change in resistance r for the given value of applied strain materials used for the strain gauges. Successfully compensating for lead resistances hbm. This method is simple, fast, and requires no manual adjustments. Since the foil used in a strain gage must be very fine or thin to have a sufficiently high electrical resistance usually between 60 and 350 ohms, it is difficult to handle. Performance characteristics of metallic resistance strain gauges 1. Pdf effect of pressure on electrical resistance strain gages.
Strain gauge theory types, formulas and applications. Normally, this requires the use of heavy machinery, but the application of special electrical strain gauges provides a simplified solution for measuring the axial load on bolt elements. The change in resistance is proportional to the displacement of the pzt stack. A strain gauge is an electrical transducer which is used for measuring mechanical surface strain. Measuring strain with strain gages national instruments. A strain gauge is a thin strip of metal designed to measure mechanical load by changing resistance when stressed stretched or compressed within its. The most universal measuring device for the electrical measurement of mechanical quantities is the strain gage. Several types of strain gages depend on the proportional variance of electrical resistance to strain. For example, suppose a test specimen undergoes a strain of 500 me.
From strain measurements to load in an instrumented pile bengt h. In this experiment the strain gage will be utilized. These types of strain gauges are appropriate for a wide variety of environmental conditions. Moreover, a wheatstone electric bridge, which consists of two strain gauges on the pzt stacks and two resistors on the pzt housing, is used to obtain better stability and resolution. The strain gauge is a classic example of a piezoresistive element, a typical strain gauge element shown here on the tip of my finger. For example, lets calculate the resistance change on a strain gage caused by x106 strain. Thus strain gauges can be used to measure force and related parameters like displacement and stress. A strain gauge is a device that measures change in electrical resistance when a force is applied.
Strain gage technical data strain gage measurement the most universal measuring device for the electrical measurement of mechanical quantities is the strain gage. Below, the wheatstone bridge circuit will only be considered with respect to its application in strain gage technique. Figure 2 average cyclic endurance of wk strain gages. The strain gauge while there are several methods of measuring strain, the most common is with a strain gauge, a device whose electrical resistance varies in proportion to the amount of strain in the device. However, it will also change resistance when subject to a temperature change. Bonded resistance strain gages can be employed to measure both static and dynamic strain. Among strain gages, an electric resistance wire strain gage has the advantages of lower cost and being an established product. Explore strain gauge with free download of seminar report and ppt in pdf and doc format. An illustration of arthur ruges original electrical resistance strain gauge from a us patent he filed in september 1939. We can overcome this problem by using strain gauges that are self temperaturecompensated or by a dummy strain gauge technique. Apr 04, 2014 4 effects of nuclear radiation several difficult problems are encountered when electricalresistance strain gages are employed in nuclear radiation fields. Comparing strain gage measurements to force calculations in a. Basic principle of strain gauge when stress is applied to the metal conductor, its resistance changes owing to change in length and crosssectional area of the conductor.
Our wide portfolio consists of more than 2,000 different strain gauge types and accessories, and. Electrical resistance strain gauges overcome most of the disadvantages of mechanical gauges. Electrical strain gauge is a resistive elastic unit whose change in resistance is a function of applied strain. Introduction to strain gauges and their usage strain gauge applications strain gauges are used to determine or verify component or structure stresses, or by manufacturers of load cells, pressure and torque transducers, etc. Ideally, we would like the resistance of the strain gauge to change only in response to applied strain. This can be accomplished because a strain gauge changes resistance as it is stretched, or compressed, similar to wire. Gauge factor gf or strain factor of a strain gauge is the ratio of relative change in electrical resistance r, to the mechanical strain the gauge factor is defined as. Electrical resistance strain gauge an overview sciencedirect. When an electrical conductor is stretched within the limits of its elasticity such that it does not break or permanently deform, it will become narrower and longer, which increases its electrical resistance endtoend. The electrical resistance strain gage discussed in this chapter is basically a piece of very thin foil or fine wire which exhibits a change in resistance propor. Characteristics of strain gauges electrical resistivity. Like many of the other topics addressed in this chapter, strain gauge systems can become quite complex, and a full dissertation on strain gauges would be beyond the scope of this book. Strain analysis using resistance strain gauges the strain analysis course provides an introduction to electrical resistance strain gauges and the associated circuits for strain measurement and transducer applications.
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