Due:
In class, Friday
April 18, 2008
Name(s)
(up to four students per homework set)
:
Section number(s)
1.
2.
3.
4.
For instructor or TA use only:
Problem
Score
Points
1
15
2
25
3
15
4
10
5
15
6
10
7
10
M E 345
Spring Semester, 2008
Homework Set # 10
Professor J. M. Cimbala
Total:
100
1
.
(15 pts)
An inverting amplifier is constructed using an opamp that has a GBP of 1.20 MHz. The input impedance of the
circuit is 1000
Ω
, and the theoretical gain of the circuit is 100.
(
a
) What resistors
R
1
and
R
2
are used to construct the circuit?
(
b
) As discussed in class, an opamp amplifier acts like a lowpass filter to high frequency input signals. Calculate the
effective cutoff frequency of the filter.
(
c
)
If the input signal is a sine wave of frequency 30.0 kHz, calculate the actual (true or overall) gain of the amplifier.
2
.
(25 pts)
A graduate student named Dilip needs to monitor the temperature of his experiment. The range of expected
temperatures is 10 to 40
o
C. He decides to use a standard 100
Ω
platinum RTD, along with a Wheatstone bridge circuit. He
constructs the bridge with resistor
R
3
as the RTD as sketched. The
power supply to the bridge is 6.00 V DC. The resistance of the two
lead wires is 0.685
Ω
each. He wants the bridge to be balanced
when
T
= 0
o
C so that the output voltage is exactly zero when
T
=
0
o
C. By definition, the resistance of the socalled 100
Ω
RTD is
100
Ω
when
T
= 0
o
C. So, he uses 100
Ω
resistors for
R
1
and
R
2
.
However, if he also sets
R
4
= 100
Ω
, the bridge would
not
exactly balance, because of the lead wires.
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 Spring '08
 staff
 Lowpass filter, Cutoff frequency, Dilip

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