A strain gauge is a long length of conductor arranged in a zigzag pattern on a membrane. For example, lets calculate the resistance change on a strain gage caused by x106 strain. Us2873341a electric strain gauge and resistance units. The differential voltage of the bridge produced by variation in strain gauge resistance is amplified using the ina333. In order to compensate for such changes which the instrumentation would interpret as mechanical strain the gauge itself should be chosen, if possible, as one having temperature compensation for the material being tested. The strain gage is one of the most widely used strain measurement sensors. This method is simple, fast, and requires no manual adjustments. Strain gages for composite materials, printed boards, plastics and rubber. Strain gages with preattached lead cables how to select strain gages selection based on measuring object material and measurement environment. Other articles where resistance strain gauge is discussed.
When external forces are applied to a stationary object, stress and strain are the result. Download as ppt, pdf, txt or read online from scribd. Therefore, if we replace r4 in figure 3 with an active strain gauge, any changes in the strain gauge resistance will unbalance the bridge and produce a nonzero output voltage. If the nominal resistance of the strain gauge is designated as rg, then the strain induced change in resistance. For strain gauges this latter represents a change in resistance. Electrical resistance strain gauges are the most frequently used devices in experimental stress analysis today. The two ratio arms of the bridge r 1 and r 3 are set equal to each other.
The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate. Generally, the sensing element of the strain gage is made of a copper. Certain backing and alloy combinations, along with special construction features, are designed as systems, and given gage series designations. Pdf application of strain gauges in measurements of strain. The resistance strain gauge is a valuable tool in the field of experimental stress analysis. 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. This gage consists of a grid of very fine wire or foil bonded to a backing. Resistance strain gauge the change in value of resistance of metal semiconductor due to elongation or compression is known by the measurement of torque, displacement or force. Measuring strain with strain gages national instruments. 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 it is stretched, its resistance increases and vice versa. This is the strain that we typically measure with a bonded resistance strain gage. Which strain gauge is the right one for your application. Strain gauges are used together with the corresponding gauge factor to relate the relative electrical resistance change of the strain gauge with the strain of the underlying material. Thus, with no force applied to the strain gauge, the bridge will be symmetrically balanced and the voltmeter will indicate zero volts, representing zero force on the strain gauge. Strain gauge is subjected to stressstrain to be converted to resistance variations component surface, because the member strain is generally less, in order to guarantee certain measuring accuracy, requires the sensitivity of surveying instrument can reach the 15 microstrain. Strain gauge is a passive transducer that converts a mechanical elongation or displacement produced due to a force into its corresponding change in resistance r, inductance l, or capacitance c.
Electric strain gauge and resistance units therefor download pdf info publication number us2873341a. Tupper bsc, ceng, rcnc, frina, whsch, in introduction to naval architecture fifth edition, 20. If a metal piece is subjected to a tensile stress, the metal length will increase and thus will increase the electrical. Electrical resistance strain gauge an overview sciencedirect. For example, strain gages require voltage excitation, which is only available. A strain gages electrical resistance varies in proportion to the. Electrical strain gauge is a resistive elastic unit whose change in resistance is a function of applied strain.
The gauge factor for many gauges is about 2, however, each gauge may have a slightly different gauge factor and it is therefore. When environmental temperature changes, the resistance of the strain gauge changes accordingly. Elastic stressstrain uniaxial mechanical behavior relations. If the nominal resistance of the strain gauge is designated as rg, then the straininduced change in resistance. R, since g f and r gauge factor and unstressed gauge resistance can be obtained from. It is a resistive elastic unit whose change in resistance is a function of applied strain. Many ships have been fitted with statistical strain gauges to record strain, most using electrical resistance gauges. 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.
Introduction a load cell is a transducer that is used to create an electrical signal whose magnitude is directly proportional to the force being measured. Strain gauge fixed to a structure under traction will exhibit an increase in length and, a change in the output parameter. Characteristics of strain gauges electrical resistivity. Standard resistance are 120 and 350 ohms, whereas 500, and 3000 ohms are for special purpose gauges. The change in resistance of the strain gauge can therefore be utilised to measure strain accurately when connected to an appropriate measuring and indicating circuit e. Strain gauges are available commercially with nominal resistance values from 30 to 3000. Nevertheless, the gauge factor depends on the stiffness of the calibration material and ideally the calibration should be done on a. But the loads can be different types and deflection can be. The products described in this manual, although zemic has carefully proofread and verified its accuracy.
A biaxial rosette composed of both resistance gauge 1 parallel to the direction x of external force and gauge 3 perpendicular to it was stuck on an infinite plate in figure 1. Correction of gauge factor for strain gauges used in. They operate on the principle that as the foil is subjected to stress, the resistance of the foil changes in a defined way. Strain gauge performance for inhomogeneous materials. Assuming the change in resistance can be measured, the strain gage provides a method for measuring. The gauge factor is found from a calibration on a stiff material steel. A strain gauge is basically used to measure the strain in a work piece. If a metal piece is subjected to a tensile stress, the metal length will increase and thus will increase the electrical resistance.
Pdf strain gauge principle, types, features and applications. Explore strain gauge with free download of seminar report and ppt in pdf and doc format. The strain gage applies this principle to strain measurement through the resistance change. If the area of cs is large, resistance is small and vice versa. Resistance thermometer the change in resistance of metal wire due to the change in. Design and construction of a strain gauge request pdf. In this application note, we will be more specific and define the term strain to mean deformation per unit length or fractional change in length and give it the symbol. 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. The general electric wire strain gauge that adopts is converted to. Once bonded to the surface of the material, any physical strain in the material is transmitted to the strain. Strain gauge lengths are usually chosen depending on the shape and size of the sample and expected strain distribution. As the resistance change of strain gauges is extremely small, it is indicated or recorded by means of an amplifier, except for special cases and semiconductor gauges. Contd further, as the length increases, diameter decreases. Stress, strain, and strain gages penn state mechanical engineering.
The active gauge r 1 is remote from the instrumentation, and both it and its associated wiring are subject to resistance changes brought about by any variation in temperature. This strain gauge reference design accurately measures the resistance of a strain gauge by being placed in a bridge configuration. The work of dummy gauge is to nullify the effect of the temperature changes. Hbms extensive strain gauge catalog provides 100 pages of information about our extensive choice of strain gauges ranging from standard strain gauges for experimental stress analysis through special strain gauges to strain gauge accessories you can be sure that you will get the. Strain gages for ultrasmall strain measurement semiconductor strain gages.
When bearing mechanical elongation or contraction, most metals undergo a change in electric resistance. Gauge length defnition gauge length of a strain gauge is the active or strain sensitive length of the grid. The bonded resistance strain gage is by far the most widely used in experimental stress analysis. The bridge excitation voltage and ina333 reference voltage is supplied using the ref5025. Thus, with no force applied to the strain gauge, the bridge will be symmetrically balanced and the voltmeter will indicate zero volts, representing. This article provides an instruction on how to install and use the 1lb1120zw strain gauge from hbm. Stress is defined as the objects internal resisting forces, and. When load is acted on a material, elongation or compression is happened. Strain may be either tensile positive or compressive negative. According to the elastic theory if the main stresses. Strain gauges are usually installed on a surface whether it is for stress analyses or sensor production, without any external forces applied to the surface. The resistance of a strain gauge varies with applied force and, it converts parameters such as force, pressure, tension, weight, etc.
Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The strain must be calculated using the original voltage. Electrical resistance strain gages can be used with this resolution and with an accuracy varying from numbers as low as 1% to as high as 0. Gauge factor needs to be found experimentally in strain gauge. It is difficult to bond a strain gauge to a bolt while measuring the tightening stress. Thus, in order to use it to determine strain, compensation has to be made for temperature effects. The discovery of the principle upon which the electrical resistance strain gauge is based was made in 1856 by lord kelvin, who loaded copper and iron wires in tension and noted that their resistance increased with the strain applied to the wire. A strain gauge of the same resistance and sensitivity as that of the actual gauge and is cemented on a separate piece of material of the same type and is kept in the unrestrained condition in the vicinity of that actual gauge called dummy gauge. However, it will also change resistance when subject to a temperature change. A strain gauge is a sensor whose resistance varies with applied force. As in the case of the strainsensitive alloy, the backing is not completely an independently specifiable parameter.
The ratio of the resistance variation to the length variation is designated kfactor or strain gain. Strain gauge seminar report, ppt, pdf for mechanical. They usually record the number of times the strain lies in a certain range during recording periods of 20 or 30 min. This type of strain gauge allows the measurement of axial load on bolt elements. The gauge length also plays an essential role in the. The electrical resistance strain gauge is a resistance element which changes resistance when subject to strain.
Strain gauges are used to measure the strain of a material. This change in resistance of the conductor can be measured easily against the applied force using strain gauge. Strain measurement strain can be measured using many techniques, but the resistance strain gauge is generally the most direct and convenient tool. The strainmeter is designed to convert the small resistance change of the strain gauge into a voltage output, amplifying it to. However, since strain is an invisible infinitesimal phenomenon, the resistance change caused by strain is extremely small. Conclusions glossary bibliography summary electrical resistance strain gages are sensors fabricated from thin foil or wiretype conductors that respond to variations in their length. Introduction to strain gages instruments techno test inc.
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