 Department of Electrical & Computer Engineering
Course ECSE291
EXPERIMENT 3
Resistive Circuits and Applications
20032004
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 ECSE291
EXPERIMENT 3
Resistive Circuits and Applications
20032004
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 resistancetemperature
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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 Winter '03
 Khazaka
 Operational Amplifier, Thévenin's theorem, Resistive Circuits, Engineering Course ECSE291, Course ECSE291 EXPERIMENT, Department of Electrical & Computer Engineering Course

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