Experiment1 - - Department of Electrical & Computer...

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- Department of Electrical & Computer Engineering - Course ECSE-291 EXPERIMENT I DC Meters and Measurements - 2003-2004 -1- Objective: To introduce the basic principles of DC meters and their use in measurement of voltage, current, and resistance. To study the loading effects of meters. Preparation: Study the background information in the Appendix and answer the following questions. 1. Consider the circuit shown In Fig. 1 (see p.10) (a) Determine the current and voltages in terms of R 1 , R 2 and E, then, calculate their values for: i. R 1 = 390 K , R 2 = 180 K , E = 9.50 V; ii. R 1 = 12 K , R 2 = 6.8 K , E = 9.50 V; iii. R 1 = 1.5 K , R 2 = 470 K , E = 0.95 V; (b) If an ammeter with an input resistance of 360 is used to measure the current, what will be the ammeter reading in each case (i, ii, iii)? (c) If a voltmeter with an input resistance of 100 k is used to measure all the voltages, what will be the meter readings in each case (i, ii, iii)? In which case does the meter have the least loading effect? 2. A permanent-magnet moving coil (PMMC) mechanism has resistance R m and a full-scale current of 100 μA. Use this to design a DC voltmeter with a 10 V full-scale deflection. Find the required multiplier resistance in terms of R m . 3. Design a DC ammeter with a 5.0 mA full-scale deflection. The PMMC mechanism has a resistance R m and full-scale current of 500 μA. Find the shunt resistance in terms of R m . The circuit shown in Fig. 2 can be used to calibrate the design ammeter, by comparing its readings with the corresponding measurements of a standard meter. The resistance R is required to limit the maximum current in the circuit to the full- scale value of your designed ammeter. Assuming negligible resistance for the ammeters, determine R for E = 9.50 V.
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- Department of Electrical & Computer Engineering - Course ECSE-291 EXPERIMENT I DC Meters and Measurements - 2003-2004 -2- Apparatus: 1 Microammeter (Simpsn Model 347) 1 DC power supply 1 Multimeter (Fluke 45) Circuit Assembly Apparatus (breadboard, cables and wires) Experiment: Answer ALL questions during the laboratory period, but those marked with an asterisk (*) may be answered later. NB : Cut the connection wires short – just a little longer than the minimum length needed, and lay them flat on the breadboard. In this way the circuit will be visualized more easily, you will be able to debug, TA’s will be able to help you and you will get more accurate results since less noise will be picked up. READ THE NOTES “DESCRIPTION OF SOME LABORATORY EQUIPMENT” BEFORE PROCEESING ANY FURTHER 1. Basic Measurements Turn the DC power supply “on”. Adjust the output voltage to 9.50 V by measuring it with the multimeter (Fluke 45), do not just read off the power supply scale. With the power supply “off”, assemble the circuit of Fig. 1 for R 1 = 12 k and R 2 = 6.8 k .
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Experiment1 - - Department of Electrical & Computer...

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