|
DI
MODULE
Number of
Inputs
230 V or 24 V
DO
MODULE
Number of
Outputs
230 V or 24 V
AI
MODULE
Number
of Inputs
AO
MODULE
Number of
outputs
Modules
per
Installation
Rack
Number of
Possible
Local
Expansions
PLC-A
4, 8
4, 8
2, 4
4
6
2
PLC-B
6
6
2
2
8
2
PLC-C
2, 4
2, 4
4
4
8
2
6.11. In the technical characteristics catalog of a digital input module with a nominal operating
voltage of 24 V DC, it is written,
“Input current for signal ‘1’ = 8.5 mA at 24 V DC”
Explain what exactly expresses this magnitude (8.5 mA) and if it has any possible
importance.
Basic Operating Principles of PLCs
◾
267
6.12. In a PLC with many digital I/Os and a large executed program, the scanning cycle
duration is 50 msec. The digital input device connected to the PLC is an SPST con-
tact output of a sensor which opens and closes with frequency 100 Hz. Explain if it is
possible to count the number of ON/OFF changes of the sensor output during a time
interval of 1 hour.
6.13. Four machines, C
1
–C
4
, operate according to the automation circuit shown in the figure,
either manually through buttons Start
i
/Stop
i
and the rotational switch RS
i
in place M or
automatically through command from the digital Output
i
of the PLC and the rotational
switch RS
i
in place A. In order to accomplish this operation, a digital output module is
available from the manufacturer that defines the connection in the diagram shown in the
figure (module view). Design how the outputs of the PLC will be connected to the conven-
tional automation circuit in order for the desired operation to be achieved. Note that the
conventional circuit may be modified suitably to facilitate the connection to PLC, but it
will not affect the desired operation.
R
“A”
“M”
“A”
“M”
RS
1
C
1
N
C
4
START
1
START
4
STOP
1
STOP
4
STOP
1
Digital output 4
PLC command
RS
4
6.14. Write the differences between a PLC and a general purpose computer from a hardware and
software point of view.
6.15. Write the basic differences between a digital input module and an analog input module of
a PLC.
6.16. The manufacturer of a digital output module with nominal operating voltage of 24 V DC
gives a connection pattern of the output devices as shown in diagram (e) of the figure.
Which one of the four connections (a, b, c, or d) of the output devices realized by a techni-
cian (shown in the figure) has a faulty connection? Explain your answer.
268
◾
Introduction to Industrial Automation
Digital output
module 4 × 24 V DC
1
2
3
4
6
5
1
2
3
4
6
5
1
2
3
4
6
5
1
2
3
4
6
5
1
2
3
4
6
5
(a)
(b)
(c)
(d)
(e)
24 V
24 V
24 V
6.17. The activation of the power relay C from a PLC is performed via a power transistor or a
triac which are in the digital output module. Suppose that the power transistor or triac
has been burned and is at short-circuit status. What problem arises concerning the func-
tion of the button STOP which must stop the operation of power relay C, and how it can
be addressed?
PS
C
P
U
STOP
C
PS
C
P
U
6.18. A modular type PLC is going to control a small system with 8 digital inputs, 8 digital out-
puts, and 1 analog input. What structural units (modules) do you have to buy in order to
implement the PLC-based automation system?
6.19. Which is the maximum time delay that may happen between the activation of a digital
input and the activation of a digital output which depends logically on the first?
6.20. The operation of the electromechanical equipment of a road tunnel is going to be controlled
via a central PLC. The electromechanical equipment includes general purpose lighting,
acoustic and luminous signaling, a ventilation system, a fire safety system, and a large num-
ber of sensors and meters. Although the machinery is relatively distributed along the whole
length of the tunnel, they may be grouped in the three points as shown in the figure. The
kind and number of I/O devices are also indicated in the figure. Configure and design the
I/O hardware system in detail, selecting the PLC placement first. In particular, determine
Basic Operating Principles of PLCs
◾
269
the local and peripheral hardware, the kind and number of required I/O modules, the
communication pattern between I/O modules and CPU, and the method of grouping I/O
points and modules, giving the corresponding diagrams.
The technical characteristics of the PLC are:
a. Each digital module contains 8 I/O points.
b. Each analog module contains 4 I/O points.
c. The maximum cable length for peripheral equipment is 900 m.
d. The maximum cable length for local equipment is 30 m.
e. The maximum cable length between a digital I/O module and digital I/O devices is
100 m.
f. Each installation rack may contain up to 6 I/O modules.
The automation and control system of the road tunnel will have a central selector switch
for selecting the manual or automatic operation of the system. All handling and indicating
devices must be installed at one of the two ends of the tunnel (on a control panel) indepen-
dently of the PLC location. All digital inputs and outputs have the same nominal operating
voltage of 24 V DC.
1 Km
1 Km
1
2
3
Motors DS
5
Motors IR
3
2
Outputs for lighting control
32
Sirens
4
Alarm buttons
12
Photocells
12
Flow and level switches
3
Analog inputs
8
Analog outputs
2
1 Km
1 Km
1
2
3
DS = direct starting
IR = inversible rotation
1 Km
1 Km
1
2
3
Two-speed motors
Motors DS
0
Motors IR
1
Two-speed motors
4
Outputs for lighting control
32
Sirens
4
Alarm buttons
12
Photocells
12
Flow and level switches
0
Analog inputs
4
Analog outputs
2
Motors DS
5
Motors IR
3
Two-speed motors
2
Outputs for lighting control
32
Sirens
4
Alarm buttons
12
Photocells
12
Flow and level switches
3
Analog inputs
8
Analog outputs
2
http://taylorandfrancis.com
Do'stlaringiz bilan baham: | 
