What Is a Programmable Logic Controller (PLC)

Brands of PLC’c
A lle n B r a d le y
S ie m e n s
M it s u b is h i
T a t a H o n e y w e ll

A B B
A L S T O M
F E S T O
F u j i E le c t r ic

R e lia n c e
B & R
T o s h ib a
C u t le r H a m m e r

A n s h u m a n
S c h n e id e r
K o y o
S ig m a t e k

M e s s u n g
O m r o n
F a n u c
M o d ic o n

P.L.C.
Programmable Logic Controller

• CPU - Decision Making Unit

• Inputs-Digital/Analog/High Speed
• Outputs - Digital / Analog

• Power Supply - 24 VDC /
110VAC / 220VAC / +/- 12V

• Timers / Counters / Flags /
Registers / Memory

• Communication - Serial - RS232C
/ Equivalent

• Programming - Through PC /

Why to use PLC’s ?
• COST :- PLC can scan Digital &
Analog Inputs through relevant S .
It can execute the Logic w.r.t. the
Scanned Inputs, take necessary
decision and send it to Digital /
Analog Outputs. It can also
perform PID control Functions. The
cost of all this is much less than a
conventional DATA Logger !!

• Versatility :- The ability to
combine discrete (Digital) & Analog
logic is a powerful tool for the
Control Engineers. Control of
critical start-up parameters, such
as temperature and pressure, can
be precisely pre-programmed for
each start-up step.

• Expandability :- As a process
matures, it is inevitable that
enhancements will be needed.
These usually require more outputs.

For hard-wire Relays system this
usually necessitates extensive panel
changes, which generally are
problematic.

A PLC easily accommodates the
additional I/O’s without requiring
changes in the existing wiring.

If a PID loop is to be added, no
panel rework is necessary; only the
wiring of new points and some re-
programming to incorporate them is
required.

• Flexibility :- As a process goes
ONLINE and Refined, the Control
Equipment should be easily
reconfigured to accommodate such
modifications.

Bottling Plant Control, Traffic Light
Control, Process Control of Temp.,
Pressure, Level, Flow etc., Car
Parking Control etc. are all within
the Capabilities of PLC’s.

• As one common device (PLC)
performs multiple functions in a
Plant, fewer spare parts are
needed .

• The Digital nature and self-
Diagnostic capabilities are strong

Advantages of PLC over
Electro-mechanical Relays
• Ability to interface /
communicate with Computers
• Simple Programming

• Field Programming possible (HHT)
• High Reliability (Better MTBF)

• Easy Maintenance
• Rugged Construction - Can
operate in Extremely harsh
field conditions

• Smaller Size
• Easy Expandability (Due to
Modular Design)

Differences between -
PLC & PC / Computers

• Real Time Operation -
PLC’s are designed to
operate in a REAL-TIME
control Environment.
Most PLC’s have internal
clocks and built-in
“Watch-Dog Timers”.

PLC’s Vs PC’s
• Environmental Conditions

PLC’s are designed to
operate near the equipment
they are meant to control.
This means that they
function in hot, humid,
dirty, noisy and dusty
industrial environments.

PLC’s can operate in 60 Deg
C as well as 0 Deg C, with
tolerable relative Humidities
ranging from 0% to 95%
non-condensing.

PLC Vs PC
• Programming Languages &
Techniques -
• PLC - Ladder Diagram format
is read & understood world-
wide by maintenance
technicians as well as by
engineers.
• Unlike Computer Programming,
PLC Programming does not
require extensive special
training.
• Programme operation are
performed by the PLC in the
order they were programmed .
This allows easy programming
of Shift Registers

PLC Vs PC
• Maintenance & Trouble-shooting

• As PLC is a Plant Floor
Controller it has to be
maintained / serviced by plant
electrician or the Instrument
Technician.

• It would be highly impractical
to require computer type
maintenance service.

• Most PLC Components are
modular and simple to isolate,
remove-and-place (system

Digital I/O Devices
• Digital Input Field Devices

• Pushbuttons,
• Thumbwheel Swiches
• Limit Switches
• Selector Switches
• Proximity Sensors
• Photoelectric Sensors

• Digital Output Field Devices

• Discrete Outputs - Relays,
Solenoids, Contactors, Motors
starters, Annunciator Windows,
Pilot Lights etc.
• Register Outputs - Displays,

Various Types of
Transmitters

T r a n s m itte r s

T e m p e ra tu re T ra n s m itte rs

P re s s u re T ra n s m itte rs

F lo w T ra n s m itte rs

L e v e l T ra n s m itte rs

Analog I/O Devices
• Analog Outputs –
4 to 20mA / 0 to 5V DC –
Can drive signals to variable
speed drives etc., Control
Temperature, Pressure, Level,
Flow, pH, Conductivity etc.

• Analog I/P -
• 4 to 20 mA / 0 to 5V DC
• 12 Bit or better ADC
• 32 Bit Storage (For SCADA)
• Thermocouples T/C / RTD’s
• Flow Transmitters
• Temperature Transmitters
• Level Transmitters
• Pressure Transmitters
• Strain Guage

Digital / Analog I/O’s
• Digital Inputs - 1-4096 / more
• (Useful for sensing of entry of
CAR)
• (To Sense COIN in vending machine)
• (To sense if Door Bell is pressed)

• Digital Outputs – 1-4096 / more
• (To indicate Traffic Light Signals)
• (To display Alarm indication)
• (To display CAR is exiting parking)

• Analog Inputs - 1-4096 or more
• (To continuously Scan the Temp.)
• (To continuously Scan Level / Flow)

• Analog Outputs - 1-4096 / more

Digital I/O Voltages
• DC Input Modules -
24 V DC
48 V DC
10-60 V DC
120 V DC
230 V DC
5-50 V DC Sink /Source
5 V DC TTL Level
5/12 V DC TTL Level

• AC Input Modules –
24 V AC
48 V AC
120 V AC / Isolated
240 V AC / Isolated
24 V AC / DC

Analog I/O Voltages
Voltage Range Decimal Equivalent

-10 V to + 10V - 32768 to + 32767

0 to + 10V 0 to + 32767

0 to +5V 0 to + 16384

1V to + 5V 3277 to + 16384

Current Range Decimal Equivalent

-20mA to +20mA -16384 to +16384

0 to +20mA 0 to +16384

4 to +20mA 3277 to +16384

PLC
Programming
Languages
• Ladder Diagram Programming

• Function Block Diagram

• Sequential Function Chart

• Statement / Instruction List

• Structured Text

PLC Programming
[1] Edit / Write a Ladder Programme

[2] Simulate Programme using Simulator

[3] Change the Programme if necessary

[4] Download the Programme PC to PLC

[5] Execute the Programme in PLC

[6] Change Inputs to see effects on
Outputs

[7] Modify the Programme for different

field conditions & repeat steps
4,5,6.

PLC Applications using
Static Application Panels
• CAR PARKING
• TRAFFIC LIGHT CONTROL
• SOFT DRINK DISPENSER
• WASHING MACHINE
• REACTION VESSEL
• PROCESS CONTROL
• TANK LEVEL CONTROL
• DOOR BELL DIGITAL LOCK
• MICROWAVE OVEN
• BOTTLING PLANT
• SEQUENTIAL CONTROL MOTORS
• SWITCHING OF LIGHTS
• MIXING OF 2 CHEMICALS
• STARER CONTROL
• STAR-DELTA STARTER

Other Applications of PLC’s

[1] Control of SPM’s (Special

Purpose Machines - Like
Drilling M/c or Grinding

M/c or Lathes etc.

[2] Packing Machines Like -

Capsule Packing Machines

Tablet Packing Machines;
Milk Pouches Packing M/c.

While Chosing PLC for an
Application, following points
should be taken into
consideration
• Maintenance
• Spare Parts
• Operation
• Modifications
• Losses (Production,
Equipment, Personnel)
• Information Technology
• Space & Weight
• Flexibility
• Expandability
• Operability
• Cost of Control & Instrumentation

Aspects of
Control & Instrumentation

• Standardisation
• Speed of Response
• Hardware Variety
• Software Portability
• User Interface
• Memory
• Compactness
• Power Requirement
• System Integrity (Reliability,
Availability, Security)
• Control & Logic Algorithms

A Control Unit Should have
following capabilities as Standard
• Continuous Control
• Batch Control
• Logic
• Advanced Control
• Simulation
• Neural Network & Knowledge
based Systems
• A PC-Oriented Programming
Language
• Dual or Triple Redundancy
• High Scan rates (1 to 10 mS)
• High Resolution Time Stamping
(1 mS)
• A Communication Processor
that can handle popular
protocols

Safety Considerations
• The most important safety
feature, which is often
neglected is PLC system design.
This feature must be included
whenever a hardwired device is
used in order to ensure
operator protection against the
unwanted application of power.

• Emergency STOP function
should be completely
hardwired.

Software functions should not
be relied upon to shut-off the
process or the machine.

NOISE
• Electro-Magnetic Interference /
NOISE / Unwanted Electrical Signals
can generate problems for all solid
state circuits, particularly Micro-
processors.

Each PLC manufacturer suggests
methods for designing a noise-immune
system.

• I/O system are isolated from the
field, but voltage spikes can still
appear within the low-voltage
environment of the PLC if Proper
Grounding practices are not followed.

Often it is necessary to keep AC and
DC wiring bundles apart, particularly
when high-voltage AC is used at the
same time that low-level analog signals
are present.

Temperature
Considerations
• Installing any solid state device
requires paying attention to –
• Ambient Temperature
• Radiant Heat Bombardment
• And the Heat generated by
the Device itself.

• PLC’s are typically designed for
operation over a broad range
of Temperatures, usually from
0 to 60 Deg.C

• For Cooling, blowing filtered air
through the enclosure can
resolve minor difficulties.

Enclosures
• Enclosure of PLC protects PLC’s
from moisture, Oil, Dust Particles
and unwanted tampering.

• Most Manufaturers recommend
NEMA 12 Enclosure for the
Standard Industrial Environment.

• PLC’s are designed to be located
close to the machine or the process
under control. This keeps the wiring
runs short and aids in the trouble-
shooting procedure.

• It is not advisable to place a PLC
near a Virating Machine, Electrical
NOISE Interference or Excessive
Heat Environment conditions.

KEY-WORDS of PLC

• PLC - Programmable Logic Controller

• PID – Proportional + Integral +
Derivative Control Function.

• DCS – Distributed Control System

• SCADA – Supervisory Control &
Data Acquisition System

• RTOS- Real Time Operating System

KEY-WORDS of PLC
• RTC - Real Time Clock

• RTU – Remote Terminal Unit

• Timers – On-Delay
Off-Delay
Monoshot /
Monostable
Pulse
Flasher
Astable
Bistable

• Counters – Up / Down

KEY-WORDS of PLC

• Flags / Registers /
Latches / Memory Set-Reset
/ Retentive – Non-Retentive

• HHT – Hand Held Terminal
• HHP – Hand Held Programmmer
It is used for PLC
Programming at the
Installation site.

• MMI – Man-Machine Interface
• HMI – Human Machine Interface
Useful for ease of
operation of PLC by
operator/s.

H.H.T./ H.H.P.- Advantages
• Easy transfer of PLC Program
to HHT / HHP for editing or
troubleshooting.
• Easy transport of a program to
the field to update a current
machines program.
• Rugged and industrially
hardened for the factory
environment.
• Low cost, cheaper than a
notebook computer.
• Easy to use & easy to learn, no
software required.
• Compact Size (pocket size)
• Easy storage of Program
• Monitor resident PLC Program
for trouble shooting.

H.H.T./ H.H.P.– Disadvantages
• Not supported by some PLC’s.
• An HHP can hold only one
program at a time – whereas a
Laptop / PC can hold many
programs on its HDD.
• HHP’s usually require more
keystrokes to enter and get
the same information as
compared to a laptop / PC.
• Limited capability to display
ladder rungs due to screen size
• Documentation not displayed
• Different HHPs are needed for
different PLC manufacturers if
more than 1 PLC’s are in
field.
• If the Battery of the HHP
discharges, a program stored

KEY-WORDS of PLC

• Memory Cartridge / Module
Consists of either –

RAM ---- Random Access Memory.
(Volatile)

EPROM -- Erasable Programmable
Read Only Memory.

EEPROM -- Electrically Erasable
Programmable Read
Only Memory.

FLASH --- Non-Volatile

Softwired Vs Harwired
components of PLC

• Soft-wired Components –
Timers
Counters
Logic Circuits
Latches

• Hard-wired Components -
24 V DC Lamps
Relays
Contactors
Solenoid Valves

Scan-Time / Scan-Cycle

• Scan Time of PLC –
It is the time between an
Input being sensed & the
corresponding output.

• Single Scan Cycle –
Single Scan Cycle function
enables the circuit diagram to
run for one processing cycle
and then stop.

This is useful in analyzing the
circuit diagram and observing
how it works.

PLC Scan
• Input Scan – PLC
scans all
Inputs

• Logic / Process Scan
PLC goes through the
ladder program / logic

• Output Scan –
PLC sends Outputs as
per various Inputs and
the corresponding

Input Scan
• During the Input Scan
the CPU scans each
Input module for the
ON / OFF states of
each of the associated
input points.

• The ON / OFF input
states are stored in
the input status file.

Program Scan
• After the inputs are read and stored
in the input status file, the processor
will use this information to solve the
user ladder program.
• The processor scans the user program
starting at rung zero at the left
power rail, working left to right and
evaluating one instruction at a time
until the output instruction is reached.
• The Output status is the logical
resultant of the solved input logic for
that rung. The logical one or zero
output status is placed in the output
status file.
• After completing rung zero, the
processor goes on to rung 1,2,3… and
so on, sequentially, to the last rung
except in case of Master Control
Relay (MCR)
• At the end of the program, an END-
Rung is automatically inserted which
alerts the CPU the it has reached the

PLC – Concepts
• Forcing Inputs / Outputs

• RS232C / RS422 Ports

• Source-Sink Concept in PLC

• How to select a PLC for

a particular project ?

• PLC Types –

PLC – Concepts
• Online (Run) / Offline
Mode of operation.

• Uploading/ Downloading
of Programmes from -
PLC to PC & PC to PLC

• Display – LEDs / LCDs /
VFD – Vacuum
Florescent
Display.

PLC – Concepts
•MCR – Master Control
Relay Function

• File Handling /
Addressing System

•PLC Simulator
Software

Key-Words of PLC

• WDT - Watch-Dog-Timer –

In case of PLC control loss due
to EMI / NOISE, WDT brings
back control of CPU to a Known
State.

This Timer Circuit usually
resides on the CPU card itself.

It works like a MONOSHOT
PULSE GENERATOR of width
greater than MAXIMUM SCAN
TIME.

WDT - Watch-Dog-Timer
• In order to insure system
predictability a WDT is
used to insure that the
processor completes each
scan in a timely manner.
• WDT is a hardware timer
incorporated into the CPU’s
circuitry that monitors the
cyclical process / scan of
the CPU.
• WDT is a safeguard that
verifies the processor does
not become stuck while
scanning the user program
or for some other reason,
become unable to complete
the current scan.

WDT - Watch-Dog-Timer
• The WDT is reset at the end os
each Scan Cycle by the CPU when
the scan time is less than WDT’s
preset time.

• In case of one or more sub-
routines, program scan time can
exceed WDT time value. In some
cases increasing the WDT’s
preset value can solve the
problem.

• Some PLC’s have WDT with fixed
time intervals, while others are
adjustable within specific limits.

• A typical default time of 100 /
200 mS is standard for many
PLC’s with either fixed or

SLC-500 - Processor
operating modes
• Program Mode
• Run Mode
• Remote Run Mode
• Remote Program Mode
• Test Mode
• Single-Step Test Mode
• Single – Scan Test Mode
• Continuous Scan Test Mode

• Test Mode – Test Program
execution before allowing
the PLC to operate the
actual Hardware.

GE – 90-70 CPU -
Processor operating modes

• Run with Outputs Enabled

• Run with Outputs disabled

• Stop Mode

• Stop & I/O Scan Mode

• Run Mode Store Function.

Key-Words of PLC
• CCU - Central Control Unit -
It consists of a CPU + PALS-
GALS + RTOS + EPROM / RAM
/ EEPROM

• Process / Ladder Logic Memory
It could be integrated with
CPU or in a separate DATA /
MEMORY CARTRIDGE /
MODULE. Usually it is a
replaceable Cartridge.

• Optoisolation - Analog I/O’s
should be isolated otherwise
induction / pickup can lead to
malfunctioning of PLC

Digital Electronics

• Boolean Algebra
• Binary / Hexadecimal nos.
• Logic Gates & Truth Tables

• AND
• OR
• NAND
• NOR
• Ex-OR
• Ex-NOR
• NOT

L o g ic F u n c t io n s

A N D

O R

N A N D

N O R

N O T

E x - O R

E x - N O R

T I M E R

C A S C A D E T I M E R

S R F L I P - F lo p

C O U N T E R

PLC Programming
AND Timers APPLICATIONS
Astable
OR Monostable Traffic Light Control
Process Control
Bistable
NOT
Tank Level Control
Bottling Plant
NAND Counters
Digital Lock
NOR Flags Microwave Oven
Retentive
Ex-OR Non-Reten Washing Machine
Door Bell & Alarm
Ex-NOR
Registers Sequential Control
Retentive Silo Control

Functioning of
Timers / Counters / Flags / Registers

PLC

T IM E R S CO UNTERS FLAG S R E G IS T E R S
0 t o 2 5 6 in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n
M o n o s t a b le U p C o u n te r R e t e n t iv e R e t e n t iv e
A s t a b le D o w n C o u n te r N o n - R e t e n t iv e N o n - R e t e n t iv e

DCS / SCADA
•D.C.S. :-
Distributed Control Systems
•S.C.A.D.A.:-
Supervisory Control
And Data Acquisition
System. (Through Network
Data Acquisition,
Data Display,
Data Processing,
Data Storage,
Data Analysis etc.)

DCS Vs SCADA
• Generally supplied by • Normally supplied by
a single Vendor with Multiple / Competing
dedicated H/W & Vendors
S/W. • Competitive cost due
to Multi-Vendor
products.
• Costly due to • Can be applied to
redundent design very low cost
applications
• Application Areas - • Comm’n - Can cover
Large Mfg. Facilities larger geographical
area by use of
modems and T/p lines
• Comm’n - Confined to
factory premises (LAN
for H/W) • Small to medium
Analog I/O’s with /
without PID.
• Analog Processing -
Large Analog I/O’s • Programming - PLC by
using PID’s relay Ladder Diagram
or STL and SCADA
using built-in graphics
• Programming - by editor and drivers.
creating drawing like
charts called as
configuration diagram • Suppliers - PLC’s -
Siemens, Allen
Bradley, Omron etc.
• Suppliers - Honeywell, SCADA - Intellution,
NI-Lookout / Labview

Following Displays are available in
most Control Systems
• Overview
• Area
• Group
• Details
• Trends
• Configuration
• Diagnostics
• Alarm Summary
• System Status (LAN)
• Scratch Pad

Solid State O/P Switching
• Advantages –
[1] Fast Switching Speeds
[2] High Reliability
& almost infinite life
[3] Low Power required to energize
[4] No Contact Arcing
[5] Little / nil Switching noise
[6] +ve switching,
no contact bounce
[7] Can be hermetically sealed –
good for hostile environments.

• Disadvantages –
[1] May be destroyed by overload
[2] Tend to fail in ON state
[3] Heat dissipation
[4] Expensive to purchase
[5] Possibility of false trips from
electrical noise.

Relay O/P Switching
• Advantages –
[1] Contacts forgiving to a temporary
overload
[2] Immune to false trips from elec noise
[3] Little voltage drop across contacts
[4] No restrictions when connecting in series
or parallel configurations
[5] Difinite ON / OFF state, with contacts
physically open.
[6] No Leakage
[7] Contacts generate little heat
[8] Inexpensive to purchase

• Disadvantages –
[1] Mechanical switching is slow
[2] Mechnical life is limited by demands of

the load and the contacts.
[3] Require 50mA or more to energize
[4] Subject to contact arcing or welding
[5] Subject to contact bounce

PLC –
Reference Books
• Programmable Logic
Controllers.
– By – John Web

• Programmable
Controllers
– By – Richard Cox.

• Introduction to
Programmable Logic
Controllers
– By – Gary Dunning

Other Terms related to
Control Systems
• UCP - Unified Control Panel
• UCS - Unified Control System
• UCN - Universal Control Network
• UOC - Unit Operation Controller

• TDC - Totally Distributed
• Control System

• SOE - Sequence Of Events
• SP --- Set-Point
• SFC - Sequential Function Chart
• SAT - Site Acceptance Test
• SAS - Safety & Automation Systems

Other Terms Used in
Control Systems
RTU - Remote Terminal Unit
ROC - Rate of Change
PV --- Process Variable
PS --- Process Station
PSD - Process Shut-Down
PIU - Plant Interface Unit
PIN - Plant Interface Network
PCS - Process Control System
PFD - Process Flow Diagram
PCN - Process Control Network

Other Terms Used in
Control Systems
OBT - Optical Bus Terminal
OLE - Object Linking & Embedding
OLM - Optical Link Module

NIU - Network Interface Unit

MC---- Multifunction Controller
MTU - Master Terminal Unit
MCS - Master Control Station
MAS - Manufacturing Automation System
MAP - Manufacturing Automation Proto’l
MTBF - Mean Time Between Failure
MTTR - Mean Time To Repair

Other Terms Used in
Control Systems
• LLPIU - Low-Level Process
Control Station
• LCN --- Local Control Network
• LCR --- Local Control Room
• LAN --- Local Area Network

• ISA - Instrument Society of America
• ISO - International Standards Organization

• HSE ---- High Speed Ethernet

• HIPPS -- High Level Process
Protection System
• HAZOP - Hazard & Operability
Study

Other Terms Used in
Control Systems
• FAT- Factory Acceptance Test
• EUC - Equipment Under Control
• ESD - Emergency Shut-Down System
• EC --- Extended Controller

• DPS - Dynamic Positioning System

• AC --- Adaptive Control

• CFC - Continuous Function Chart

• C & I - Control & Instrumentation
• CCR -- Central Control Room

• Other Terms Used in
Control Systems

• BCL -- Batch Control Language
• BC --- Basic Controller

• AEC - Advanced Extended Controller
• AMC - Advanced Multifunc’n Controller

• CAD - Computer Aided Design
• CADAS - Computer Aided
Design Analysis &
Application

FF-Bus -Foundation Field Bus
• FF-Bus is a Digital Comm’n
System

• A Summary of improvements,
which FF-Bus will offer as it
becomes more widely applied
are –
* Higher Communication Speed
- 10 to 100 M Baud
* Higher nos. of modes per
branch to reduce cabaling &
termination effort

• More efficient Communication

• Better diagnostics & predictive
maintenance in field

FF-Bus
• More reliable Control System
because of better maintenance
& Higher distribution control.

• Faster Control System
Response.

• Saving in Hardware (Cabling,
I/O cards, Cabinets)

• Higher Accuracy because
Process Parameters are
Sampled Locally &
Transmitted Digitally to
local / remote Control Units.

• Major Improvements in System

FF-Bus
• Reduction in Documentation
(No. of Loop Diagrams,
Termination Schedules etc.)

• Possibilities od using
Multifunction Instruments -
Where one Transmitter
measures multiple variables
(e.g. A Corolis meter can
measure - flow, Density &
Temperature )

• A High Degree of Inter-
operability among system
Computers & Instruments
from different Vendors.

• DPS - Dynamic Positioning System

• Availability = MTBF / (MTBF + MTTR)

• Categories of Consequences
Definitions

• Catastrophic ---- Multiple Loss of Life

• Critical -------- Loss of a Single Life

• Marginal ------- Major injuries to one
or more persons.

• Negligible ------ Minor injuries at worst

Catagories of Likelihood
Categories Definition Failures
of Likelihood
(in System Life) Per Year
Frequent Many Times > 10-3

-4
Probable 10 to
Several Times
-3
10
-5
Occasional One Time 10 to
-4
10
-6
Remote Unlikely 10 to
-5
10
-7
Impossible Very 10 to
-6
Unlikely 10
Incredible Cannot believe < 10-7
it could
happen

* Analog Input :- DC models of

Pico are provided with two
analog inputs I7 and I8. The
permissible input voltages are
between 0 V and 10 V. The
measured data is evaluated by
an integrated Analog Value
Comparator relay.

* Circuit Connection:
Each line in the circuit
diagram display is a circuit
connection.

Circuit Diagram Elements:
The circuit diagram is made
up of circuit diagram elements
from conventional wiring
practice. These include input,
output and auxiliary relays as
well as function relays and P
buttons.

Contact/Coil Monitor:
The Contact/Coil Monitor is
a dialog for displaying and
forcing the logic states of
selected relays (contacts /
coils).

Device Test :-
The device test shows in plain
text the results of comparison
between the selected Pico
device and the circuit diagram.
All contact/coil elements that
are not available on the device
used will be listed, and the
number of circuit connections
used will be checked. If the
Pico device cannot properly
process the circuit diagram, a
device will be suggested on
which the circuit diagram can
be used successfully.

Function Relay :-
Function relays are used for
complex switching tasks. Pico
devices are provided with the
following function relays:
Timing relays (T), Time
switches (H), Counters (C),
Analog value comparators (A),
Text relays (D).

Impulse Relay :-
An impulse relay is one that
changes and then retains this
state if a voltage is
momentarily applied to it.

Input :-
External contacts are
connected to the inputs of the
device. Inputs are evaluated in
the circuit diagram via the
switching contacts I1 to I12
and R1 to R12. The 24 V DC
Pico models can also receive
additional analog data via
inputs I7 and I8.
Input Debounce :-
Input signals can be evaluated
by the device with a delay in
order to compensate for the
contact bounce of switches
and pushbuttons.

Interface :-
The device interface allows
circuit diagrams to be
exchanged and stored on a
memory card or PC. A memory
card saves both the circuit
diagram and device settings.
PicoSoft PC software allows
you to control the device from
the PC. The PC is connected to
Pico via the "1760-CBL-PM02"
cable.

I/Q Window :-
The I/Q window contains the
input simulator and the display
for Q and S coils. The input
simulator or I window is used
as a central tool in circuit
diagram simulation. It enables
you to create dynamic input
signal states for the simulated
circuit diagram. For this you
can also assign different
functions to the I and R
buttons.

I/R Function :-
The I/R Function determines
the switching function of the
elements I1 to I16 and R1 to
R16. These can be latching
make contacts, latching break
contacts, momentary make
contacts or momentary break
contacts.

Operator Buttons :-

The device features 8
operator buttons by which you
can select the menu functions
and also enter the circuit
diagram directly via the Pico
display. The centrally arranged
cursor buttons are used to
move the cursor in the Pico
display. DEL, ALT, ESC and OK
are also provided with
additional functions.

Output :-
The outputs are used to switch
loads such as contactors, lamps
or motors. The outputs are
controlled in the circuit
diagram via the output relay
coils Q1 to Q8 and S1 to S8.

Parameters :-
Function relays are assigned
particular parameters by the
user. Set values may include,
for example, switching times
or counter setpoints. These
are set in the Contact/Coil

P Buttons :-
The P buttons allow you four
additional inputs that are
switched via the cursor
buttons on Pico instead of
external contacts. The
switching contacts of the P
buttons are wired in the
circuit diagram.

Retention :-
This function allows data to be
retained in the device even
after its power supply has
been switched off. Retentive
data consists of: Device circuit
diagram, parameters,
setpoints, text, system
settings, password, actual
values of auxiliary relays
(markers), timing relays,
counters.

Signal Diagram :-
The Signal Diagram allows you to
display the behavior up to eight
selected relays along a time
axis. The diagram produced can
also be printed out for
documentation purposes.

Single Cycle :-
The Single Cycle function enables
your circuit diagram to run for
one processing cycle and then
stop. This helps you in analysing
the circuit diagram and observing
how it works. This function is
only available during Simulation.

Startup Behavior :-
The startup behavior is an
important help during
commissioning. The circuit
diagram may not be completely
wired when it is transferred to
Pico, or the system/machine to
be controlled is in a state in
which it cannot be controlled by
Pico. If Pico is then switched on,
it may therefore be desirable
for the outputs to remain
inactive. For this set the startup
behavior to STOP. If the
startup behavior is set to RUN,
Pico will start processing the
circuit diagram as soon as it is
switched on.

Stop Point :-
In order to analyse your
circuit diagram effectively,
you need a tool to interrupt
processing selectively, evaluate
the state of selected contacts
or coils and continue
processing. The Stop Point
function makes this possible.
It is only available during
Simulation.

Wiring via the Keyboard
PicoSoft also enables you to
wire up your circuit diagram
via keyboard commands.

Selecting Make/Break
Contact Behavior :-
Entering letters in lower case
selects make contacts, and
entering letters in upper case
selects break contacts.

Adding / Deleting Contacts :-
Position the cursor on the contact
field required and enter the contact
via the keyboard. Use the following
shortcuts for contacts & f’n relays:
i, I Controller Inputs
p, P Soft Inputs - Keypad
q, Q Controller Outputs
m, MInternal Marker Bits
c, C Counters
t, T Timers
h, H Time Switch Relay
a, A Analog Setpoint Compare
d, D Text Display
r, R Expansion Inputs
s, S Expansion Outputs or Internal
Marker Bits
To delete the contact, press the Del key

Adding / Deleting Coils
Position the cursor on the coil
field required and enter the
coil via the keyboard. Use the
following shortcuts for coils
and coil functions:
q Controller Outputs
m Internal Marker Bits
t Timer "Trigger" coil
c Counter "Trigger" coil
d Text Display "contactor" function
s Internal Marker
"contactor" function

To select the coil function
required, press the Shift key
and select the appropriate coil
function letter below:
Shift + E Impulse relay
Shift + S Latching (Set)
Shift + R Unlatching
(Reset)
Shift + D Direction coil for
counter
The default setting is for the
contactor function. To revert
to the simple contactor
function of the coil, press the
letter for the coil concerned.

To delete the coil,
press the Del key.
Connecting Inputs and Outputs
Use Shift+Cursor key to make
the connection between the
individual contacts and coils.

Adding Empty Lines
Position the cursor on the
circuit connection in front of
which you wish to add the
empty circuit connection. Press
Ctrl+I to add the empty circuit
connection.

Deleting Circuit Connections
Position the cursor on the circuit
connection you wish to delete.
Press Ctrl+D to delete the entire
circuit connection.

Deleting Connections
Position the cursor on the
connection you wish to delete.
To delete the connection,
press the Del key.

If the circuit connection contains
branches, the selected
connection will only be deleted up
to the next node.

What Is a Programmable Logic Controller (PLC)

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (14)

Similar to What Is a Programmable Logic Controller (PLC)

Similar to What Is a Programmable Logic Controller (PLC) (20)

What Is a Programmable Logic Controller (PLC)