The Measurement System - Lab Report Example

The measurement system was design to verify dimensional characteristics of the physical parameters. The physical parameters depict the shape, geometry, strength and other significant parameters, which shall be useful during experimentation and application. The intent of this report is to share the working principle of the methodologies essential for the calibration and standardization of the tools and dimensional units. The fundamental physical parameters are length, mass and time; whereas the other parameters are essentially derived from these fundamental units including velocity, momentum and force. The American and British measurement systems are two distinct and popular systems widely practiced internationally, the fundamental units for the American system for length, mass, and time is foot, pound and seconds respectively; whereas the British system has used meter, gram and seconds for the measurement of length, mass and time. The British units are also known as SI Units i.e. International System for Units. These units and their magnitude have been described against certain standard. The meter unit (for length) has been described as particular length of platinum bar at specific temperature and pressure condition; similarly the gram unit (for mass) has been quantified against mass of specific platinum bar against standard pressure and temperature conditions. The SI units are more popular internationally, and this has revolutionized the engineering practices of the researchers, scientists and engineer. The standardization of the measurement units have established and verified many scientific theoretical principles, which were previously unresolved due to variation of units. Table of Contents 1. Introduction 2. Stain Gauge Experiment: Calibration 3. Experiments 4. Linear Potentiometer: Calibration 5. Experiments 6. Conclusions Introduction The measurement system units have standardised. These measurement units have been tested and verified internationally; and are used exclusively in engineering practices. Such measurement units have provided technological edge to the contemporary scientists and engineers against the predecessors. The intent of this report is to discuss the calibration of the measurement system for some physical parameters through experiments, 1. Stain Gauge Experiment 2. Calibration of Linear Potentiometer The fundamental units have been identified by the scientists, and these fundamental units are related to form derived units. The fundamental units have their distinct property and characteristic, whereas the derived units are the function of these fundamental units (Richard, 1996). The fundamental units have been listed as follows, Quantity Unit Symbol Basic units Length Meter M Mass Kilogram Kg Time Second S Electric current Ampere A Temperature Kelvin K Luminous intensity Candela Cd Supplemental units Plane angle Radian Rad Solid angle Steradian Sr Stain Gauge Experiment: Calibration The stain is the change is length per unit length of an object when stresses are applied on the body. He application of stresses create stretch in the body, which in actual is responsible for the change of the length. The ration of change of length to the original length is termed Stain. The stain gauge experiment is employed to verify the stress bearing capacity of the objects. The operation of stain gauge is based upon the change in resistance detected by the sensor. The change of resistance will be function of the change in length. The stain gauge will therefore estimate the stain after evaluating the change in resistance of its system against the total resistance of the system, as detected by the sensor (Qasim ,1977). The resistance of the sensor wire is the function of the length of the wire L, the cross section of the wire A, and ℓ which is the resistivity of the material (George, 1993). The GAUGE FACTOR is the reflection of the performance of the stain gauge. The Gauge Factor is the ratio of change of resistivity of the sensor against the actual stain in the system (Richard, 1996). The semiconductor used for the sensing the stain of the system is piezoresistive, which is 100 times more sensitive against the average conducting wire. The Gauge Factor is the function of material, The high gauge factor reflects the reliability and accuracy of the stain gauge (Grigor, 1971). The stain gauge works on the principle of Wheat Stone Bridge, The variance of resistance depicts change in the voltage across the entire system. The output of the system is function of the excitation voltage and the gauge factor. If not change is traced by the bridge, the circuit produces no output. Such behaviour verifies that the magnitude of stain is negligible (Qasim ,1977). The working formula for the estimation of the Wheat Stone Bridge is, The possible factors which can influence the functionality of the stain gauge includes, 1. Cross-sensitivity i.e. the gauge acts not only in the direction of stain but also perpendicular to it. 2. Bonding faults i.e. the adhesives used shall be thin and continuous, and the surface shall be cleaned. 3. Dynamic loading i.e. the creep rate of the gauge element, the disintegration of the bonding element is suspected due to fatigue. 4. Hysteresis i.e. Impact loading and unloading, this shall result in the permanent damage to the gauge element due to over-strained. 5. Effects of moisture i.e. water absorb by the bonding adhesives can cause dimensional variations. The moisture can also act as high resistance and can cause reduction in the equivalent resistance of the bridge. 6. Temperature change i.e. the resistance of the material is function of temperature (George, 1993). The calibration of the stain gauge is the verification of sensitivity of the stain gauge against. Ideally the sensitivity of the stain gauge shall follow increasing trend with increase in load / stresses. The variation from the exact value can be only due to the already discussed potential failures or source of errors. The sensitivity is the ratio of change in output to the changes in input that produces the change in the output. Ideally, the sensor should have large and constant sensitivity (Grigor, 1971). Experiments The results of the experiment conducted are as follows, load(g) 1/4 bridge voltage (v) micro strain 0 0 0 100 0.11 0.13 200 0.21 0.23 300 0.31 0.32 400 0.41 0.44 500 0.51 0.53 600 0.61 0.63 700 0.72 0.74 800 0.82 0.85 900 0.93 93 1000 0.103 103 load(g) 1/2 bridge voltage (v) micro strain 0 0 0 100 0.2 0.22 200 0.4 0.43 300 0.61 0.63 400 0.82 0.83 500 1.02 1.03 600 1.23 1.25 700 1.42 1.44 800 1.63 1.66 load(g) full bridge voltage (v) micro strain 0 0 0 100 0.04 0.47 200 0.08 0.89 300 0.12 1.27 400 0.16 1.69 500 0.2 2.09 600 0.24 2.5 700 0.28 2.91 800 0.33 3.31 Linear Potentiometer: Calibration The potentiometer is potential divider; it divides the voltage by application of Ohms Law. The voltage at the required point can be estimated as, The linear potentiometers are useful for voltage break-down on linear circuit. The working formula is, VL= (x/L)VIN The calibration of the linear potentiometer against the provided graph, the voltage divided by the potentiometer shall be verified against the voltage supplied. The graph explains the relationship between the divided voltage and the linear length (George, 1993). The calibration of the linear potentiometer can be also conducted by verifying the applied voltage with voltmeter, and then applying the working formula for splitting of the linear voltage which is the function of distance covered linear (Alan, 2001). The distance can be measured through ruler etc. Experiments Distance (cm) voltage (v) 5.6 kΩ 1 kΩ 0 0.42 0.42 0.42 1 1.62 1.54 1.21 2 2.9 2.64 1.85 3 4.16 3.68 2.4 4 5.43 4.71 2.92 5 6.69 5.73 3.45 6 7.94 6.78 4.04 7 9.2 7.87 4.7 8 10.42 9.01 5.5 9 11.68 10.25 6.51 10 12.89 11.59 7.84 Conclusion From the given exercise it is proved that these experiments are substantial enough to produce real output. It is important to protect their measurement devices from the potential sources of error, and as long as this care is taken these measurement devices can offer reliable performance. References 1. George J Blcktey. Control Engineering. Technical Publications. 1993. pp. 23-27. 2. Grigor Wilson Marr, R. C. Layton. General engineering science in SI units. University of Wisconsin - Madison. 1971. pp. 134-187. 3. S. H. Qasim. SI units in engineering and technology. Pergamon Press. 1977. pp. 216-232. 4. Alan S. Morris. Measurement and instrumentation principles. Elsevier. 2001. pp. 56-64. 5. Richard W. Miller. Flow measurement engineering handbook. McGraw-Hill Professional. 1996. pp. 165-175. Read More