Mechanical Measurements 01

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UnknownPredefined Standard

Quantitative Comparison

Measurement (numerical result)

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Reference: Omega Engineering, Inc.

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Reference: Omega Engineering, Inc.

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Generalized Measuring System 

Most measurement systems consist of three stages: 

STAGE 1 STAGE 2 STAGE 3Measurand

(quantity to be measured)

detecting or sensing stage

intermediate or signal conditioning stage

terminating stage or readout

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Detect or sense measurand or detect changes in a variable.

Stage I:

Examples:

1. The tube of a Bourdon tube for pressure2. Piezoelectric crystal for acceleration3. Thermocouple for temperature.

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Stage II:

Signal conditioning stage. Purpose is to modify the sensed information so that it will be accepted by the third stage.

Examples:

1. Filtering2. Amplification3. Integration.

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Stage III:

Read-out stage - provides an indication or recording in a form that can be evaluated.

Examples:

1. Digital voltmeter2. Oscilloscope3. Data acquisition system4. Dial

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Chen, W., Lu, F., and Zhou, B., “A Quartz-crystal-embedded SplitHopkinson Pressure Bar for Soft Materials, Experimental Mechanics,Volume 40, Number 1, pp. 1-6, March 2000.

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Sali, S., and Kpac, J., “Measuring the Quality of Guitar Tone,” Experimental Mechanics,Volume 40, Number 3, pp. 242-247, September 2000.

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Yam, L. H., Gaun, D. H., and Zhang, A. Q., “Three-dimensional Mode Shapes of a Tire Using Experimental Modal Analysis,” Experimental Mechanics,Volume 40, Number 4, pp. 369-275, December 2000.

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There are two general methods available for solving engineering problems:

Features of theoretical method:

1. Often give general results2. Usually require simplifying assumptions (create a

"model" of the actual physical system) 3. May lead to complicated mathematical problems 4. Do not require extensive laboratory facilities 5. Usually requires less time than experimental method  

1. Theoretical2. Experimental

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Features of experimental method:

1. Often give results for a specific system 2. The true behavior of the test system is revealed

(i.e., no simplifying assumption) 3. Accurate measurements are necessary (must

understand characteristics of measuring system) 4. Actual system or scale model is required 5. Time consuming

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Types of experimental-analysis problems:

1. Testing the validity of theoretical predictions

2. Development of generalized empirical relationships where no adequate theory exists

3. Determination of material, component and system parameters

4. Study of phenomena with hopes of developing a theory

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Tag from audio/visualprojector recently purchased. Could apply to any instrumentation.