PLC-Chap04

8/13/2019 PLC-Chap04

1/24

Chapter 4: Input/Output Modules and

Computer Aided Manufacturing TECH 4/53350 1

8/13/2019 PLC-Chap04

2/24

Input/Output Modules

Understand

Wiring of typical sensors and actuators to PLC I/O modules

Surge protection for certain types of devices

Typical control cabinet layout

Typical installation wiring


8/13/2019 PLC-Chap04

3/24


Input/Output (I/O) Modules provide Physical Interface

between

PLC Processor and

Field Devices:

Switches, Lamps Valves etc

Common Characteristics of I/O Modules

Removable Terminal Blocks (Retractable) Wiring is connected to the terminal block

erm na oc s p ugge n o e mo u e

Isolation Isolates field wiring from the PLC internal circuitry

PLC power supply provides low-voltage power unlike a typical field wiring

Diagnostic Indicators Discrete Input modules display an indicator for each input channel that is on

Discrete Output modules display an indicator for each output channel that is

on


8/13/2019 PLC-Chap04

4/24


Isolation Barrier

Neutral

Fuse

PLCProcessor

Power

ne

OutputDevice

Neutral

InputModule

SupplyOutputModule

L1 Neutral

I/O modules provide isolation between field wiring and PLC internal circuitry:

Ground loops

Noisy electrical signals

Fault on I/O wiring

Isolation prevents events from interfering with the PLC and causing a module failure


8/13/2019 PLC-Chap04

5/24


What is Sinkin and Sourcin ?

The flow of current (power) when the I/O device is active

An Output Device is designated as Sourcing if current

flows OUT when the output device is active

An Output Device is designated as Sinking if current

flows IN when the output device is active


8/13/2019 PLC-Chap04

6/24


What is Sinkin and Sourcin ?

The flow of current (power) when the I/O device is active

An Input Device is designated as Sourcing if current

flows OUT when the output device is active

An Input Device is designated as Sinking if current flows

IN when the output device is active


8/13/2019 PLC-Chap04

7/24


A Sourcing f ield Sensor is usually

SourcingField

Sensor

SinkingPLCInput

Current SinkingField

Sensor

SourcingPLCInput

Current

connec e o a npu w y

SourcingPLC

SinkingField

Current Sinking

PLCSourcing

Field

Current

Output Device ev ce


8/13/2019 PLC-Chap04

8/24


Focus

Primarily concern with sinking PLC inputs and sourcing

ou pu s s nce a s e ma or y o ypes o

connections.

Note that most discrete sensors can be purchased in

either a sinking or sourcing configuration. Make sure youspec y e correc one


8/13/2019 PLC-Chap04

9/24

Discrete Input Modules

devices with only two states, ,

Switches - many kinds

Pushbutton

m Level

Proximity


e ay con ac s

8/13/2019 PLC-Chap04

10/24


Standard Discrete Input Voltages

v can an e e er

220 v AC/DC

10 - 30 v DC

10 - 30 v AC 20 - 60 v DC


8/13/2019 PLC-Chap04

11/24


Discrete In ut Module Block Dia ram

Powered from the field Powered from PLC

Threshold detector

When input device voltage > minimum-on-state voltage devised is sensed to be on

When device voltage < maximum-off state voltage devised is sensed to be off


8/13/2019 PLC-Chap04

12/24


Discrete Input Module Block Diagram

Powered from the field Powered from PLC

Optical Isolator Provides electrical isolation between field wiring and the PLC internal circuitry

Light-Emitting Diode & Photoelectric transistor

w c ose urren ow roug enera es g g r ggers curren ow ru o oe ec r c

transistor Sensed by PLC digital logic

Circuitry to the LHS of isolator powered from the field

Circuitry to the RHS powered from internal PLC voltage source


8/13/2019 PLC-Chap04

13/24


Discrete Input Module Block Diagram

owere rom e e owere rom

o se an s ur ance Capacitors and Resistors are typically used to form simple noise filter

r ge ec er Converts AC to full-wave rectified DC


8/13/2019 PLC-Chap04

14/24


L1(Line)

L2

(Load)I/O ModuleTerm. Strip

Black

(120 VAC)

White

(120 VAC)

Com

Some modules need thisconnection for balancing

AC Inputs Power flows into the Input Module when the field device is on

Hence the Input Module is characterized as a Sinking Module

There is a least one common per module. Some modules have a common for every 4input channels

Why would you need more than one common?


8/13/2019 PLC-Chap04

15/24

Discrete Output Modules

Used to turn real-world output deices either on or off Can be used to control any two state device

Available in AC and DC versions

Available in various voltage ranges and current capabilities

Indicator Lamps, Alarm Lamps

Motor Starters Electric Valves Electric Fans

Control Relays, Heater Relay


8/13/2019 PLC-Chap04

16/24


Standard Discrete Out ut Volta es 120 v AC

220 v AC

12 - 48 v AC

120 v DC

220 v DC

12 - 48 v DC

scre e u pu o u es an e on y c gna s

DC Discrete Output Modules handle only DC Signals

Relay output Modules handle both Ac and DC signals


8/13/2019 PLC-Chap04

17/24


Optical Isolator Provides electrical isolation between PLC and internal circuitry and field wiring

Circuitry on LHS of Optical Isolator powered by internal PLC voltage

Circuitry on RHS of Optical Isolator powered from the field


8/13/2019 PLC-Chap04

18/24


L2

(Load)

L1

(Line) I/O ModuleTerm. Strip

M

Common

AC Signals Output Modules that handle Ac signals are Sourcing Modules

Power flows out of the Module when the Switch (Triac ) is ON


8/13/2019 PLC-Chap04

19/24


r ng

Best to sketch the dia ram on a iece of a er before

wiring Easier to visualize the whole picture

uppose you ave many npu s o w re

Start the sketch with one input first

If you figure out the first, the rest will follow

Next simply add second input

third input etc


8/13/2019 PLC-Chap04

20/24


n ng nput o u e r ng

One Input

Power SupplyWiring Terminals

Input 0

Input 1

Input 2

Common


8/13/2019 PLC-Chap04

21/24


r ng n a mp e rcu t

Input 0

npu

Input 2

Input 3

Common


8/13/2019 PLC-Chap04

22/24


r ng t ona nput ev ce

Input 0

npu

Input 2

Input 3

Common

Wiring an additional input device


8/13/2019 PLC-Chap04

23/24

8/13/2019 PLC-Chap04

24/24


ree-w re ensor r ng

Complete Wired Circuit

PUT

Sourcin

Input 0

OU

- + Sensor

Input 1

Input 2

Input 3

Common


PLC-Chap04

Documents