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Experiment3

# Experiment3 - Department of Electrical Computer Engineering...

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- Department of Electrical & Computer Engineering Course ECSE-291 EXPERIMENT 3 Resistive Circuits and Applications 2003-2004 -1- Objective: To study some common circuits and to introduce aspects of basic measurement and instrumentation. Preparation: 1. By using the Thevenin theorem, determine the current and the Consider the circuit shown In Fig. 1 for (a) v i (t) = -3.00 V, and (b) v i (t) = -2.50sin(2000 П t) V. 2. Input and Output Resistances (a) The input resistance of a device such as an oscilloscope can be determined by using the method illustrated in Fig. 2 if the presence of the known resistance R does not affect the normal operation of the device. Derive the equation given in the figure. (b) The output resistance of a device such as a sine wave generator can be determined by using the method illustrated in Fig. 3 if (i) the presence of the known resistance R does not affect the normal operation of the device, and (ii) the Thevenin equivalent source voltage can be measured accurately. Derive the equation given in the figure. 3. Wheatstone Bridge Bridge circuits are commonly used for precision measurement of resistance, inductance, capacitance, and other circuit parameters such as frequency. They are also extensively used in instrumentation with transducers to measure non- electrical variables. The Wheatstone bridge (Fig. 4) will be studied in this experiment for measuring resistance and temperature. (a) Balanced Bridge (i) When the voltage across points b and c in Fig. 4 is zero, the bridge is said to be balanced. Show that the balanced condition is R 1 R 4 = R 2 R 3 . (ii) From the balance condition, it is clear that the bridge can be balanced if one of the resistances is adjustable. Further, if three of the resistances have known values, the fourth can be determined. Let R 4 be an unknown resistance and R 3 be adjustable. If the unknown resistance lies in the range from 1 to 10 ohms and R 1 /R 2 = 33, what must be the range of values for R 3 ? (iii) For a DC source of 10 volts and the conditions given in (ii), find R 1 and R 2 so that the current is R 4 will not exceed 10mA. (Assume ideal source).

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- Department of Electrical & Computer Engineering Course ECSE-291 EXPERIMENT 3 Resistive Circuits and Applications 2003-2004 -2- (b) Unbalanced Bridge A thermistor is a semiconductor device that behaves like a resistor with a high (usually negative) temperature coefficient of resistance. It can be used in an unbalanced Wheatstone bridge as shown in Fig. 5 for temperature measurement. The thermistor to be used in this experiment has the resistance-temperature characteristic given in Fig. 5 over the range from 0 to 50 degrees Celsius. For a linear temperature scale, R 3 and R 4 should each be equal to the resistance of the thermistor at the mid range temperature. If V o should be zero for zero degree, what must be R 1 ?
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Experiment3 - Department of Electrical Computer Engineering...

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