The wire is sealed in the tube by a set of double “O” rings fixed on each end piece. This process mainly includes a sensing element to sense the i… (10 marks] 5. There are many types of transducers displacement measurements, Linear variable differential transformer (LVDT), capacitive transducer, potentiometer transducer, resistive transducer, optical transducer, etc. Strain gauge directly is used for the measurement of load and indirectly it is used for the measurement of displacement. Even a small change in pressure of environment can affect the output because output from the strain gauge is amplified by 100. Any change of resistance will give value to output voltage. This results in the effect of oxidation, moisture, environmental conditions and any ingress of water being completely eliminated. When the core is displaced in one direction, the voltage in one coil increases as the other decreases, causing the output voltage0 to increase from zero to a maximum. The amount of deformation that occurs in an object is known as strain. As illustrated in figure 16, it can be seen that the value of output increase as the number of load increases. When an object deforms within the limit of elasticity, either it becomes narrower and longer or it become shorter and broadens. For example, a strain gage (aka strain gauge) signal conditioner must provide excitation voltage to the strain gage sensor. Encardio-rite primarily deals with five different types of strain gauges. In term of waveform generated, it can be seen as in figure 15 that during the zero turn, the output voltage is in same phase as input, except the amplitude is lower. It can be used to test deformity in multiple structures such as high-rise buildings, underground metro corridors, bridges, dams, deep vacations, railway lines, etc. The voltage used must be relevant depending to the load given. Strain gauge 1.1. A zero set may be incorporated in the circuitry or a reset to zero reading may be provided. Strain GaugeStrain Gage measures the strain (amount of contraction as well as expansion caused by external forces) on any object. The relationship between the input strain and the output voltage may be determined using the system sensitivity. This extendibility is produced by suitably die cutting a flexible but inherently inelastic insulative substrate. The voltage may then be amplified, thus reducing quantization errors. It is represented as N/m2. The strain gauge was invented in 1938 by Edward E. Simmons and Arthur C. Ruge. D Primary transducers. When an alternative current is applied into the primary coil, a voltage is induced in each secondary core; those voltages are directly proportional to the mutual inductance induced with the primary. The gauge is cemented to the surface of the strain element. Linear Variable Differential Transformer(LVDT): The linear variable differential transformer (LVDT) is a type of electrical transformer used for measuring linear displacement. Using 10 cent coin, the graph generated is as expected, a linear graph. So if R4 is to be change into active strain gauge, any changes in the gauge resistance will unbalance the bridge and produce nonzero output voltage. c = 0 because the values touches y axis at 0V. Change in stress is determined by multiplying the measured strain by the modulus of elasticity. The LVDT contains one primary winding, and two secondary windings connected to each other in series opposing manner as shown in the figure below. The Gauge Factor of a Strain Gauge is the sensitivity coefficient of strain gauges and, is given by the formula: ΔR = Change in the resistance caused due to strain. There are some differences in the values of the output of these two data. Well-instrumented bridges can alert responsible authorities about approaching failure so as to initiate preventive measures. The model EDS-11V strain meter is suitable for embedment in soil or concrete or surface mounting by welding on steel structures. The Encardio-rite vibrating wire strain meter basically consists of a magnetic, high tensile strength stretched wire, one end of which is anchored and the other end is displaced proportionally to the variation in strain. Strain Gauges have a long history in the safety of rails. The main advantages of mechanical strain gauges are the ease with which they can be used, their relatively low cost and the fact that they are reusable. Strain-gauge-based load cells are the most commonly used type. You can view samples of our professional work here. So, during the experiment, any electronic devices that produces magnetic field such as cell phone and notebook must be avoided to be close to the LVDT. In practice, strain measurement involves quantities larger than few milistrain, Therefore, to measure the strain; it requires accurate measurement of very small changes in resistance. This deformation in the shape is both compressive or tensile is called strain, and it is measured by the strain gauge. The strain is a unitless quantity since the values in the numerator and denominator always have the same units. To export a reference to this article please select a referencing stye below: If you are the original writer of this essay and no longer wish to have your work published on UKEssays.com then please: Our academic writing and marking services can help you! You will find such types of equipment in power plants, ships, refineries, automobiles and industries. In such cases, the error depends on the gauge length and the gauge width. The resonant frequency, with which the wire vibrates, is read by the readout unit. A strain gauge is a thin wire mounted on a piece of film. The disadvantages of LVDT also can be observed by doing this experiment, which are important to be learnt. LVDTs find uses in modern machine-tool, robotics, avionics, and computerized manufacturing. The transformer has three solenoid coils placed end-to-end around a tube. According to University of Massachusetts Lowell, strain gauge is a sensor used to transfer a mechanical strain to a quantifiable output. Copyrights Reserved Encardio-rite Electronics Pvt. The centre coil is … Figure 10 : electrical connection of strain gauge, Ten coins with similar weights(10 cent coins) are placed on the gauge and the gain fine control is adjusted to produce 7.0 voltage output, One coin is placed on the load platform and the value is recorded in table 2, Step #5 is repeated and all values are noted in the table. Model EDS-20V-E vibrating wire strain gage is designed to measure strain in underground cavities, tunnels, buildings, concrete and masonry dams etc. Strain gauge, LVDT and thermocouple are examples of. To measure such small change, strain gauges are always used in a bridge configuration with voltage excitation source just like the Wheatstone bridge shown below. Your email address will not be published. An inverse transducer is a device which converts. For example, Yamuna Bridge in Allahabad-Naini is a 630 m cable-stayed bridge across river Yamuna. / (10-0) = 0.713 V/turn, So the mathematical expression is: y = 0.713x; for 20 cent. The double ‘O’ ring seals suitably protect the strain gage against ingress of water. For +ve turn, averagely, m = (9-0.5) / (4-0) = 2.125 V/turn, So the mathematical expression is: y = 2.125x + 0.5; for positive turn, For -ve turn, averagely, m = -(8-0.5) / (4-0) = -1.875 V/turn, So the mathematical expression is: y = -1.875x + 0.5; for negative turn, Even though the output generated is increasing as the number of turns increases, but the pattern of output readings are not smooth just like the expected output. Study for free with our range of university lectures! Identify an application of displacement sensor (LVDT) and explain the working of LVDT in the selected application. It is one of the significant sensors used in the geotechnical field to measure the amount of strain on any structure (Dams, Buildings, Nuclear Plants, Tunnels, etc. Alternatively, strain gauge conductors may be thin strips of the metallic film deposited on a nonconducting substrate material called the carrier. A stainless steel foil tab fixed to each end block enables the gage to be spot-welded or fixed in place by epoxy. 2.1. A thermocouple is used to generate a voltage corresponding to the heat that is generated at the junction of two dissimilar metals. The tube is flattened in the middle to accommodate a sensor assembly in the constriction. It’s impossible to measure nonlinear strain fields without some degree of error being introduced because strains cannot be measured at a point with any type of gauge. The LVDT advantages might be useful for lots of project such as measurement process, silent process, and any process that needs fast output generation. In 1992, a patent on Strain gauge for medical applications by Bowman, Bruce R. (Eden Prairie, MN) is published. They operate on the principle that as the foil is subjected to stress, the resistance of the foil changes in a defined way. 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