Instruments and Measuring Devices

Instruments and Measuring Devices - CONTENTS Page 1 2 3 4 5...

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2 Page 1. 3 2. 4 3. 6 4. 7 5. 9 6. 10 7. 12 8. 14 9. 16 10. 18 11. 19 12. 21 13. 24 Geiger-Müller Counter The Multimeter The Cathode Ray Tube Mechanical Wave Driver Function Generator/Amplifier Photogate Timers Precision Airtrack The Triple Beam Balance Electronic Timers and Reaction Time Quick Reference Guide for the Science Workshop CONTENTS Analog and Digital Devices The Vernier Caliper The Micrometer Caliper
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3 1. Analog and Digital Devices (1) Analog Devices: For illustration, consider the typical analog devices and scale shown below : 2 3 Typical analog devices and scale The scale shows a reading that is certainly greater than 2.40 units and certainly less than 2.50 units and the pointer is approximately half way between the markings . A conservative estimate of the reading would be 2.45 ± 0.05 units . Notice that the stated reading error (0.05 units) is half the smallest scale division (0.1 units) and is the maximum reading uncertainty on this piece of equipment . In practice, a skilled observer may be able to reduce the uncertainty to as low as 1/5 the smallest scale division . (2) Digital Devices: For illustration, consider the typical digital devices and display shown below: Typical digital devices and display A digital clock only indicates which division on the clock’s time scale has most recently passed . For example, in the figure, the display reads 1.23 s . One can only be sure that the elapsed time is greater than 1.23 s and less than 1.24 s . Thus, to encompass all possibilities, the measurement should be recorded as 1.235 ± 0.005 s . A similar argument can be made for any instrument with a digital readout .
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4 2. THE VERNIER CALIPER Inside caliper Main scale Depth gauge 0 1 3 4 5 0 1 2 3 5 6 8 9 10 11 12 0 1 Outside caliper Vernier scale Specifications: Range : 0-13 cm , 0-5 in.. Sensitivity: 0.01 cm , 1/128 in. Accuracy: max. 0.005 cm. Description: A versatile measuring instrument for making precise measurements of both interior and exterior dimensions of objects. Further, the vernier can be used as a depth gauge. Both inch and centimetre scales are provided and both may be precisely read by means of vernier scale. The Vernier Principle: In 1631, a Frenchman, Pierre Vernier, devised a way to improve the precision of length measurements. The vernier caliper, commonly called a vernier, usually consists of a main scale, a movable pointer, and a short scale (of usually 10 marks) attached to the pointer. This short scale is called the “vernier” scale and its divisions are spaced so that the whole vernier scale is one main-scale sub-division shorter than the corresponding division on the main scale. Thus, when the pointer (or vernier zero) is moved from one main-scale sub- division to the next, each mark on the vernier scale will move successively into and out of coincidence with a corresponding sub-division mark on the main scale. The vernier scale mark, which is coincident, gives the decimal fraction of the main scale sub-division.
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