LAB_6 - Basic Measurements 2

LAB_6 - Basic Measurements 2 - Lab 6 Basic Measurements II...

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Lab 6 75 Basic Measurements II Summary The same factors that influence the measurement of length in the physical world also apply to the measurement of other physical quantities such as mass and force. Concepts such as accuracy, precision, least count and sensitivity that were explored in the previous lab will be reinforced in this lab in the con- text of mass and force measurements. Educational Objectives After performing this experiment, students should be able to: 1. Determine the accuracy, precision and sensitivity of the instruments. 2. Calibrate and use: a spring scale, an electronic scale and a strain gauge to measure mass. 3. Acquire, analyze and graph your data in a spreadsheet. 4. Analyze data to identify and minimize sources of error. 5. Select an optimum method of measurement for a given mass measurement application. Background - The Load Cell with Strain Gauge Transducer Of the measuring devices used in this experiment, the strain gauge is probably the most unfamil- iar to the student. A strain gauge is a transducer which converts a physical displacement into a voltage. By comparing the electrical outputs from the strain gauge to known inputs, the strain gauge can be cali- brated and used as a precision measurement device. Strain gauges are used to measure the stress applied to mechanical parts such as the structural members and surfaces of airplanes, ships, trains, buildings, bridges, etc. They are also the transducing elements in many commercially available scales and weighing instruments. Most electronic scales found in homes and deli counters use strain gauges. The strain gauge used in this lab is essentially a resistor, designed so that elastic deformation changes its resistance. In other words, it acts as a variable resistor when subject to external forces. In most strain gauge measurement systems, the strain gauge is used as the variable resistance in a Wheat- stone bridge circuit. When the output voltage is zero, this corresponds to the bridge circuit being in per- fect balance (no force being applied to the strain gauge). When a force deforms the strain gauge, its resistance is changed and the bridge circuit becomes unbalanced. This in turn produces a voltage at the output, which is read as a corresponding force, displacement, pressure, etc.
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This note was uploaded on 12/16/2011 for the course ENGR 102 taught by Professor Cattell during the Fall '10 term at Community College of Philadelphia.

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LAB_6 - Basic Measurements 2 - Lab 6 Basic Measurements II...

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