This document discusses various types of input/output interfaces used in programmable logic controllers (PLCs). It describes interfaces for analog, digital, and specialty signals like temperature sensors. Intelligent interfaces include PID controllers for closed-loop processes and positioning interfaces for machine axes. The document also covers serial communication modes and network interfaces that allow multiple PLCs to communicate over local area networks.

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5. Conversion of an analog signal by a
transmitter and transducer
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6. Single-ended input
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7. Differential inputs
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8. ANALOG OUTPUT SIGNALS
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11. Single-ended outputs
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12. Differential outputs
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13. Block diagram of bypass/control
backup unit
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14. The signal chain within a PLC
y y(i) y(i)
time time time
analog filtering analog- 011011001111
digital- analog
variable & sampling digital analog amplifier variable
(e.g. 4..20mA) scaling converter converter e.g. -10V..10V
1
processing
binary transistor
binary
variable filtering sampling or
variable
(e.g. 0..24V)
0001111
relay
non-volatile
counter memory
y
time
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16. Special function I/O interfaces
They provide the link between programmable
controllers and devices that require special types of
signals.
These special signals are not very common (only 5–
10% of PLC applications).
They are divided into two categories:
• direct action interfaces
• intelligent interfaces
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17. Direct action I/O interface application
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18. Intelligent I/O interface application
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19. FAST-INPUT/PULSE STRETCHER MODULES
•They detect input pulses of very short duration.
•They operate as pulse stretchers, enabling the input signal to
remain valid for one scan.
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20. Wire input fault module diagram
They are special input interfaces designed to detect short-circuit
or open-circuit connections between the module and input
devices.
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21. Fast-response interfaces
•They are extensions of fast-input modules.
•These interfaces detect fast inputs and respond with an output.
•The speed at which this occurs can be as short as 1 msec from
the sensing of the input to the output response.
•The output response time is independent of the PLC processor
and the scan time.
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22. Weight input modules
They are special types of analog interfaces designed to read
data from load cells.
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23. THERMOCOUPLE INPUT MODULES
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24. RTD INPUT MODULE
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25. PID MODULES
Proportional-integral-derivative (PID) interfaces are used in
process applications that require continuous closed-loop
control employing the PID algorithm.
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26. Block diagram of the PID algorithm
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27. Connection Diagram for
AB 1771-PID module
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28. POSITIONING INTERFACES
They are intelligent modules that provide position-related
feedback and control output in machine axis control applications.
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29. Encoder/counter modules interface
They interface encoders and high-speed counter devices with
programmable controllers.
There are two types of encoder/counter interfaces:
•Absolute encoders provide an angular measurement of the shaft.
•Incremental encoders measure shaft rotation over distance by
outputting a fixed number of pulses per shaft rotation.
The communication between the interface and the processor is
bidirectional. The module accepts the preset value and other
control data from the processor and transmits values and status
data to the PLC memory.
The interface also lets the PLC know when the marker and limit
switch are both energized, indicating a home position. 29

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31. STEPPER MOTOR INTERFACES
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32. Stepper motor with a position/velocity
feedback scheme
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33. SERVO MOTOR INTERFACES
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34. Servo motor interface connection diagram
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35. ASCII input/output interfaces
•They send and receive
alphanumeric data between
peripheral equipment and the
controller.
•Typical peripheral devices include
printers, video monitors, and
displays.
•The information exchange in either
type of interface generally takes
place via an RS-232C, RS-422, RS-
485, or a 20 mA current loop
standard communications link.
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36. COMPUTER MODULES—BASIC modules
•They also referred to as data-processing modules, are
intelligent I/O interfaces capable of performing
computational tasks without burdening the PLC
processor’s computing time.
•In contrast to other intelligent I/O interfaces, such as
servo controls, a BASIC module does not actually
command or control specific field devices.
•It complements the performance of the PLC system.
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37. Network interface modules
They allow a number of PLCs and other intelligent devices to
communicate and pass PLC data over a high speed local area
communication network.
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39. FUZZY LOGIC INTERFACES
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41. Data transfer between I/O modules
and fuzzy module
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42. SERIAL COMMUNICATION
(a) Unidirectional,
(b) half-duplex,
(c) full-duplex.
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