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Table 3.3 Air Compressor Operation
According to Selector Switch Position
Selector Switch
Position
Air Compressors
in Operation
0
None
1
1st
2
2nd
3
3rd
4
1st and 2nd
5
2nd and 3rd
6
1st and 3rd
7
1st, 2nd, and 3rd
Industrial Automation Synthesis
◾
113
Problems
3.1. Design two automation circuits corresponding to Figures 3.6 and 3.7a by utilizing pneu-
matic ON-Delay timers.
3.2. Design an automation circuit corresponding to Figure 3.7a by utilizing the pneumatic OFF-
Delay timer.
3.3. Design two automation circuits corresponding to Figure 3.8 by utilizing a pneumatic timer
for an ON-Delay and OFF-Delay type.
3.4. Redesign the automation circuit of Figure 3.13 in order to add an indicator of the machine’s
operation at each control panel.
3.5. Examine the operational difference of the following circuit in comparison with the circuit of
Figure 3.1d.
R
N
Stop
Start
C
C
50 Hz 230 V
R
RS
0–7
1
2
0
3 4
5
6
7
RS
0–1
Υ/Δ
N
1
e
1
d
0
e
3
3
e
2
2
2
3
4
d
1
5
d
2
6
d
3
7
d
0
d
0
d
0
d
1
d
1
d
1
d
2
d
2
d
2
d
3
d
3
Υ/Δ
Υ/Δ
Figure 3.36 Automation circuit for operation of three air-compressors with selectable
combinations.
114
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Introduction to Industrial Automation
3.6. Design an automation circuit for controlling the operation of a machine from multiple pan-
els (corresponding to that of Figure 3.13) by applying the logic of the circuit shown in
Problem 3.5.
3.7. Examine closely and explain the actual behavior of the following automation circuits:
R
N
C
C
R
N
C
C
R
N
C
1
C
C
1
C
2
C
2
R
N
C
1
C
2
C
3
C
3
C
1
C
2
C
3
3.8. Explain the consequent behavior of the two pumps described in Section 3.5.3 if the electrode
probes of the two electronic level switches are mounted as shown in the following figure:
ELS = electronic level switch
Pumps
ELS
2
ELS
1
E
2
E
1
ELS = electronic level switch
3.9. The sliding electric gate, described in Section 3.5.4, is controlled by the circuit of Figure 3.28.
Examine if it is possible for the moving gate to be stopped in an intermediate location by
normal mode and by an unconventional action. Design an automation circuit that will offer
to the user the possibility to stop the gate in any intermediate location, via an additive tele-
control signal (i.e., a 3-channel transmitter).
3.10. Design an automation circuit for a motor with two directions of rotation, which will permit
the direct change of rotation without the need to previously press the STOP button. Please
note that the circuit of Figure 3.19 does not have this feature.
3.11. Design an automation circuit so that the sliding electric gate, described in Section 3.5.4,
operates with only one tele-control signal (i.e., a 1-channel transmitter). Specifically, we
would like by pressing the transmitter button once, the gate will open. By pressing the same
button for a second time, the gate will close, and so on. During the gate movement, pressing
of the transmitter button will reverse the direction of its motion.
3.12. The automation circuit of Figure 3.9, for the periodic operation of a machine with two time
constants, presents the characteristics of reoperation. Design a similar automation circuit,
which will not reoperate after a power supply interruption or restoration.
3.13. A pump is going to empty a water tank continuously. The desired level of the water in this
tank is controlled by an electronic level switch with immersed electrode probes. Design the
required automation circuit and indicate the positioning of the electrodes into the tank for
the differential operation of the pump.
Industrial Automation Synthesis
◾
115
3.14. Design an automation circuit for starting up a Star-Delta motor via an SPST output contact
of a sensor (2-wire command).
3.15. Some air-compressors have two electrovalves in their compression chamber as safety exhaust
outlets. In order for the air compression in the chamber to be feasible, the two electrovalves
must be closed. Furthermore, the two electrovalves are used for a step-by-step start-up of the
air compressor, in order to avoid percussive loading of either the compressor or the power
supply network. Design an automation circuit so that after the Star-Delta starts the motor,
the first valve closes with time delay T
1
and the second one closes with time delay T
2
> T
1
.
Both time constants T
1
and T
2
are measured from the changing time instant from the Star-
Delta connection.
3.16. Redesign the automation circuit of Problem 3.15 with only one timer (except the timer
needed for the Y/Δ transition) and with the following time constants T
1
= T and T
2
= 2T.
3.17. Which of the following circuits are operationally correct or not and for what reason? All the
relays and lamps have nominal operating voltage +24 V DC.
0 V
0 V
0 V
0 V
+24 V
C
“C=ON”
RS
a
+24 V
C
“C=ON”
RS
b
C
1
“C
1
or C
2
=ON”
C
2
c
+24 V
RS
C
“C=ON”
C
d
+24 V
RS
3.18. In an industrial process where a general shutdown of the power supply network took place,
is it possible to get some form of electrical signal 3 minutes after an interruption while the
shutdown occurs? If yes, explain how to achieve it and design the required automation
circuit.
3.19. Although we accept that the indicator lamp of the circuit informs us if the machine M oper-
ates or not, this is not strictly true. Describe three cases of fault due to which the machine
M does not rotate while the lamp is on. Show how to make the indication literal, i.e., for the
lamp to show whether the machine M really rotates or not.
Μ
C
M
RS
Motor
operation
50 Hz 230 V
R
N
3.20. After an instant START signal from an NO button, the heating resistor R is connected to a
nominal supply voltage. After a period of 10 minutes required to heat the viscous fluid, the
pump starts to operate, and simultaneously the electrovalve V
1
opens in order to supply the
pipe network with the fluid. After an instant STOP signal from an NC button, the heating
resistor is disconnected, the electrovalve V
1
closes, the electrovalve V
2
opens, and the pump
operates for a period of 5 minutes. During this period, the pump supplies the pipe network
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Introduction to Industrial Automation
with water for its cleaning. At the end of this period, the pump stops and the electrovalve V
2
closes automatically. Design the required automation circuit.
V
1
Water
Pipe
network
Pump
R
Viscous
fluid
V
2
3.21. In a special machine tool, the carriage is equipped with a reversible motor, as shown in the
figure. Thus, the carriage can be moved between the two limit positions A and B, which
are detected by the two proximity sensors PS
1
and PS
2
, correspondingly. The carriage lies
initially at the left position (A) and we want it to be moved according to the following
specifications:
a. By pressing instantly button b1 the carriage moves right to position B.
b. When the carriage reaches point B (with a signal from PS
2
), it stops moving.
c. With the carriage at position B, the instant pressing of button b1 causes it to move left.
When the carriage reaches position A (with a signal from PS
1
), it stops. The steps (a) and
(c) can be repeated as many times as we want.
d. If the button b2 is pressed during the carriage’s movement in any direction, then the
carriage stops at its current location. By pressing button b
1
again, the carriage continues
moving in the same direction before it had been stopped.
Design an automation circuit to satisfy the described specifications.
A
B
b
1
b
2
PS
2
PS
1
M
Carriage
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