INST 200 (Introduction to Instrumentation), Practice Exam – MASTERY
NAME:
#
1
2-3
4-5
6
7-8
9
Question type
Circuit sketching
DC circuits
Mathematics
Circuit fault analysis
AC and opamp circuits
Relay ladder logic circuit
1st attempt
2nd attempt
No credit will be given for mathematical answers unless your work is shown!
(1) Circuit sketching
Sketch wires connecting components together to form a circuit where the red lamp is controlled by
pushbutton switch “A” and the green lamp is controlled by pushbutton switch “B”. The control of each
lamp should be independent (i.e. the status of one lamp should not affect the status of the other):
Switch A
+
Switch B
Battery
Red lamp
+
Battery
Green lamp
Assume each lamp is rated to operate at 12 volts with a current draw of 50 mA, and that each battery
outputs 6 volts at a maximum current of 2 amps.
1
(2) DC circuit analysis
Calculate the amount of current through R1 in this series-parallel circuit, as well as the voltage between
points C and D. Assume all resistors are 1 kΩ in resistance:
R1
A
+
−
15 V
R3
C
R4
R2
B
E
F
D
IR1 =
VCD =
(3) DC capacitor/inductor circuit analysis
Suppose the switch has been left in the “down” position (as shown in the diagram) for a long time, and
then is suddenly toggled to the “up” position:
−
+
Moments after the switch transitions to its new state, identify the following:
• Voltage polarity across the inductor (+ and - symbols)
• Voltage polarity across the current-carrying resistor (+ and - symbols)
• Direction of current through the resistor (arrow pointing in the direction of conventional flow)
2
(4) Algebraic manipulation
The following formula describes the rate of liquid flow (Q) through a magnetic flowmeter having a tube
diameter d and magnetic flux density B, generating an induced voltage E across the diameter of the tube.
A “k factor” (k) having a value less than 1 accounts for imperfections in the device:
πdE
4B
Algebraically manipulate this formula to solve for k:
Q=k
k=
(5) Trigonometry
Use the “current triangle” to calculate the phase shift angle (Θ) between total current (Itotal ) and
resistor current (IR ) in this parallel resistor-inductor circuit:
IR = 8 A
θ = ???
IL = 14 A
8A
θ=
3
14 A
(6) Circuit fault analysis
Suppose the lamp refuses to light up regardless if the pushbutton switch is pressed or not. A voltmeter
registers 12 volts between test points E and F in the circuit while the pushbutton is released (not pressed):
A
C
E
12 volts
+
−
B
(0.25 amps
current-limited)
F
D
Identify the likelihood of each specified fault for this circuit. Consider each fault one at a time (i.e. no
multiple faults), determining whether or not each fault could independently account for all measurements
and symptoms in this circuit.
Fault
Open wire between A and C
Open wire between B and D
Open wire between D and F
Lamp failed open
Switch failed open
Lamp failed shorted
Switch failed shorted
Voltage source dead
Possible
4
Impossible
(7) AC circuit analysis
Identify the type of filtering behavior of the circuit shown in this diagram:
Vin
Vout
Next, identify the filtering behavior of this same circuit supposing the capacitor fails open. Place two
check-marks in the table below to identify each filtering characteristic (one for before the fault and another
for after the fault):
Filter type
Low-pass
High-pass
Band-pass
Band-stop
Passes all frequencies
Blocks all frequencies
Healthy circuit
5
Faulted circuit
(8) Opamp circuit analysis
Calculate the input voltage (Vin ) to this opamp circuit, given the amount of current shown in the
diagram. Assume the arrow points in the direction of conventional flow, and be sure to denote whether the
input voltage is a positive or a negative value (with reference to ground):
Vin
2.2 kΩ
−
+
1.5 kΩ
1.3 mA
Vout
Vin =
6
(9) Relay ladder logic circuit analysis
Assess the status of this relay circuit, given the following switch actuation statuses:
• Switch A = unpressed
• Switch B = unpressed
• Switch C = pressed
L1
L2
Switch A
Switch B
CR1
Red
Switch C
CR1
Green
Now, check the appropriate cells in this table indicating whether each of the specified components is
energized (powered) or de-energized (unpowered):
Component
Red lamp
Green lamp
CR1 coil
Energized
7
De-energized
Answers
Answer 1
This is just one possible solution:
Switch A
+
Switch B
Battery
Red lamp
+
Battery
Green lamp
Answer 2
IR1 = 9 mA
VCD = 6 V
Answer 3
−
+
Answer 4
k=
4BQ
πdE
8
Answer 5
θ = 60.26o (negative, if you wish to represent the angle according to the standard coordinate system
for phasors)
Answer 6
Fault
Open wire between A and C
Open wire between B and D
Open wire between D and F
Lamp failed open
Switch failed open
Lamp failed shorted
Switch failed shorted
Voltage source dead
Possible
√
√
√
√
√
√
Impossible
√
√
Answer 7
Filter type
Low-pass
High-pass
Band-pass
Band-stop
Passes all frequencies
Blocks all frequencies
Healthy circuit
√
Faulted circuit
√
Answer 8
Vin = -2.86 V
Answer 9
Component
Red lamp
Green lamp
CR1 coil
Energized
9
De-energized
√
√
√