INST 200 (Introduction to Instrumentation), Practice Exam – MASTERY
NAME:
#
1
2-3
4-5
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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
Red lamp
Green lamp
+
Battery
+
Battery
Assume each lamp is rated to operate at 12 volts with a current draw of 2.5 amps, and that each battery
outputs 12 volts at a maximum current of 10 amps.
1
(2) DC circuit analysis
Calculate the amount of current through R1 in this section of a circuit, as well as the voltage between
points A and B. Assume all resistors are 1 kΩ in resistance:
...
A
2.8 V
C
R1
D
...
R3
3.5 V
R2
B
...
IR1 =
VAB =
(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 capacitor (+ 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 failure rate (λ) for a well-maintained batch of devices may be calculated using the following formula,
based on the total number of devices (No ) in the batch, number of failed devices (Nf ) during the test period,
and the duration of the test (t):
λ=
Nf 1
t No
Algebraically manipulate this formula to solve for No :
No =
(5) Trigonometry
Use the “impedance triangle” to calculate the impedance (Z) of this series combination of resistance
(R) and inductive reactance (X):
Z = ???
R = 500 Ω
X = 375 Ω
X = 375 Ω
R = 500 Ω
Z=
3
(6) Circuit fault analysis
Suppose the lamp refuses to light up regardless if the pushbutton switch is pressed or not. A voltmeter
registers 0 volts between test points A and D 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 phase shift exhibited from input to output of the following circuit:
Vin
Vout
Next, identify the phase-shift behavior of this same circuit supposing the capacitor fails shorted. Place
two check-marks in the table below to identify each phase-shifting characteristic (one for before the fault
and another for after the fault):
Phase shift
Vout lags behind Vin
Vout leads ahead of Vin
Vout is in-phase with Vin
Vout is zero (no output signal)
Healthy circuit
5
Faulted circuit
(8) Opamp circuit analysis
Calculate the output voltage (Vout ) of 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
output voltage is a positive or a negative value (with reference to ground):
Vin +
−
2.2 kΩ
−
+
1.5 kΩ
0.6 mA
Vout
Vout =
6
(9) Relay ladder logic circuit analysis
Assess the status of this relay circuit, given the following switch actuation statuses:
• Switch A = pressed
• Switch B = unpressed
• Switch C = pressed
L1
L2
Switch A
CR1
Red
Switch B
CR1
Green
Switch C
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 (note that it is not necessary to connect both batteries, since just one
has enough current capacity to handle both loads):
Switch A
Switch B
Red lamp
Green lamp
+
Battery
+
Answer 2
IR1 = 6.3 mA
VAB = 9.8 V
Answer 3
+
−
Answer 4
No =
Nf 1
t λ
Answer 5
Z = 625 Ω
8
Battery
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
Phase shift
Vout lags behind Vin
Vout leads ahead of Vin
Vout is in-phase with Vin
Vout is zero (no output signal)
Healthy circuit
√
Faulted circuit
√
Answer 8
Vout = -0.9 V
Answer 9
Component
Red lamp
Green lamp
CR1 coil
Energized
√
√
9
De-energized
√