ENGR_201_Lab1_Measurements

ENGR_201_Lab1_Measurements - ENGR 201 Evaluation and...

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Page 1 of 11 ENGR 201 Evaluation and Presentations of Experimental Data I Spring 2011 Basic Measurements R. Carr, R. Quinn, Introduction to the Art of Engineering 1 1 Edited by K. Scoles, T. Chmielewski, D. Miller Summary All scientific and engineering knowledge about the physical world and its governing principles has been gained by observation and experimentation. The numbers used to describe physical phenomena and properties are called physical quantities. In order to be consistent each physical quantity must be expressed in some accepted units whose values are referred to some accepted standards. In any measurement of a physical quantity, there is always some experimental error. There are a variety of methods used to identify, control and minimize these errors. This experiment will provide an opportunity to measure length, a basic physical quantity, and develop skill in using a variety of instruments designed for this purpose. It will also provide an opportunity to learn and apply concepts, practices and procedures fundamental to all types of scientific and engineering experimentation. Educational Objectives After performing this experiment, students should be able to: 1. Determine the accuracy and precision of instruments. 2. Measure length using a linear scale (ruler), a vernier caliper and a micrometer. 3. Properly acquire and record data using these instruments. 4. Analyze data to identify and/or minimize error. 5. Select an optimum method of measurement for a given length measurement application. 6. Construct a histogram. Background Information All analog measurements have error and a consequent uncertainty. Errors are classified as systematic or random. Systematic errors are usually categorized as instrumental, personal, or extraneous. An instrumental error is due to faults or limitations of the measuring device. This includes improper calibration as well as broken devices. Personal errors vary from one observer to the next and indicate any bias the observer may have. Extraneous errors are introduced by the environment in which measurements are taken. For example, air currents from a fan or window may alter the readings of mass obtained on a mass scale. Hysteresis is another phenomenon that may contribute to error. An instrument is said to have hysteresis when it shows a different reading for the same measured quantity depending on whether the quantity is approached from above or below. Some of the systematic errors may be corrected using a calibration curve. A plot of the instrument reading against the standard being measured is called a calibration curve. 1 Carr, R. and R. Quinn, Introduction to the Art of Engineering , 7th ed., Wiley Custom Services, 2005.
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Page 2 of 11 We can imagine an ideal instrument for which each measurement exactly equals the quantity being measured. Thus the calibration curve fpr an ideal instrument is a line of slope one through the origin. Figure 1 depicts calibration curves for an ideal instrument, a non-ideal instrument and an instrument with hysteresis. Figure 1: Calibration curves for (1) an ideal instrument, (2) a non-ideal linear instrument,
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This note was uploaded on 05/18/2011 for the course ENGR 201 taught by Professor Miller during the Spring '08 term at Drexel.

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ENGR_201_Lab1_Measurements - ENGR 201 Evaluation and...

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