An introduction to the PLC

PLC Programmable Logic ControllerDevices C R • A solid state electronic device that controls output devices based on input signals and a user developed program.. • Originally developed

Copyright © 2007 Rockwell Automation, Inc All rights reserved.

PLC Basics Agenda

1 Introduction to Terms / Concepts

4 Basic Selection criteria and Applications

2 Programming a PLC

3 Application Example

5 Hands-On Lab

How did the “PLC” get started?

• 1960 -> GM (Hydramatic Division) approached suppliers to help with a

problem:

– Relay “walls” covered the plant floor.

– Changes and Troubleshooting took weeks/months High costs

– Every change (model year) was major destruction and re-wiring.

GM needed the flexibility of “solid state”; a controller that could be programmed and maintained by plant engineers; and was rugged enough to withstand the factory environment and provided easy

PLC (Programmable Logic Controller)

Devices

C R

• A solid state (electronic) device that controls output devices

based on input signals

and a user developed program.

• Originally developed to directly replace relays used for discrete control.

Two types of I/O (Inputs & Outputs)

• Example: Temperature sensor.

• Range of values between two limits For example:

• 0°F represented by “0”

• 100°F represented by “4095” (example)

• Electrically: 4-20mA, 0-5VDC, -10 to 10VDC

• Digital

• Also called Discrete

• Has two possible states

• Represented by “1” or “0”

• Electrically:

• “0” is usually 0 Volts (AC or DC)

• “1” is a fixed voltage value such as 5VDC, 24VDC, 120VAC, etc.

• Technology: Relays, Triac, Transistor,

MOSFET, TTL

Electrical Characteristics of I/O

Type of Device

• Pushbuttons (Discrete)

• Selector Switches (Discrete)

• Motor Starter Contacts (Discrete)

• Relay Contacts (Discrete)

• Thumbwheel Switches (Discrete)

• Limit Switches (Discrete or Analog)

• Level Switches (Discrete or Analog)

• Photoelectric Sensors (Discrete or Analog)

• Proximity Sensors (Discrete or Analog)

• Temperature Sensors (Discrete or Analog)

What are “typical” Input devices for PLC’s?

Device Ratings Discrete

• 120/240 VAC

• 24 VDC

– Sourcing – Sinking

• 24 VAC

Analog

• 4-20mA

• 0-10VDC

What are “typical” output devices for PLC’s?

• Fans (Discrete or Analog)

• Valves (Discrete or Analog)

• Heaters (Discrete or Analog)

Device Ratings Discrete

• Relays

– 240 VAC – 85-120 VAC/VDC – 24 VAC/VDC

Isolation Barrier Isolation

Central Processor (CPU) What's really inside a PLC?

General PLC Concept

• PLC performs relay equivalent functions

• PLC performs ON/OFF control

• Ladder diagram program representation

single

board

contr ollers

.

PLC Basics Agenda

1 Introduction to Terms / Concepts

4 Basic Selection criteria and Applications

2 Programming a PLC

3 Application Example

5 Hands-On Lab

Memory Organization – Files used in Lab

0 1 2 3 4 5

– Two possible states: “1” or “0”

– Can be used as “storage” or to turn ON a real device.

– Purpose is similar to that of Control or Latching relays used in

“wired” control.

– For example, to “remember” that

a button was previously pressed.

Data Files – Bit File

0 1 2 3 4 5 6 7

0 1 2 3 4 5

– Used to store Integer values such

as number of Boxes of product produced during the current shift.

– Can be used as Individual bits.

Data Files – Integer File

0 1 2 3 4 5 6 7

0 1 2 3 4 5

Input (“I1” file of PLC):

– Two possible states: “1” or “0”

– Reflects the state (ON or OFF) of the Input device connected to the PLC.

Data Files – Input File

0 1 2 3 4 5 6 7

• I:Slot#/Bit# (ex I:0/0 )

– Slot# = 0 for embedded I/O

– Bit# is equivalent to “screw #”

in terminal block.

1

0 1 2 3 4 5

Input (“O0” file of PLC):

– Two possible states: “1” or “0”

– Drives the state (ON or OFF) of the device connected to the PLC.

Data Files – Output File

0 1 2 3 4 5 6 7

• O:Slot#/Bit# (ex O:0/0 )

– Slot# = 0 for embedded I/O

– Bit# is equivalent to “screw #”

in terminal block.

0

0 1 2 3 4 5

• TON: Timer On Delay

• TOF: Timer Off Delay

• RTO: Retentive Timer ON

Data Files – Timer

0 1 2 3 4 5 6 7

0 1 2 3 4 5

– Can count Up or Down

Data Files – Counter

0 1 2 3 4 5 6 7

Count Up CU

I:0.0 0

0 1 2 3 4 5

• Main “Ladder Logic” Program

– Called ladder due to it’s resemblance

of rungs on a ladder.

• Most important file

• Typically is where the “main” user program resides

• Must have some program logic

• Where jump to subroutines originate

] [

] /[

(C U) (D N)

] [

] /[

(C U) (D N)

] [ ( (R E S R E S) )

Conversion Example Relay Diagram to Ladder Logic

Conversion Example Relay Diagram to Ladder Logic

O / 2 VAC VDC

Addressing Input Instructions

False

True

Examine OFF -|/|- XIO

False

The instruction is:

The input bit is

Logic 0

Examine ON -| |- XIC

If the input device is

Open (0)

Closed (1)

These are not normally open (N.O.) and normally closed (N.C.) XIC = Examine If Closed, ON when voltage is present XIO = Examine If Open, ON when voltage is not present

SupplyVoltage

Unused COM I / 0 I / 1 I / 2 I / 3 I / 4 COM I / 5 I / 6 I / 7 I / 8 I / 9

Unused

LS 1

Addressing Output Instructions

Rung State

Output Bit

Output Terminal

Logical AND example

Copyright © 2007 Rockwell Automation, Inc All rights reserved.

PLC operating cycle

Understanding the PLC Operating Cycle

Each ladder rung is scanned using the data in the Input file The resulting status (Logic being solved) is written to the Output file (“Output Image”).

The Output Image data is transferred to the external output circuits, turning the output devices ON or OFF.

Internal checks on memory,

speed and operation

Service any communication

requests, etc.

PLC Basics Agenda

1 Introduction to Terms / Concepts

4 Basic Selection criteria and Applications

2 Programming a PLC

3 Application Example

5 Hands-On Lab

Example Application

How to program a real application

Typical PLC application – Mixer or Blender

Motor

Ingredient A Solenoid Valve 1

Ingredient B Solenoid Valve 2

Drain Solenoid Valve 3

Sensor 2

Ingredient B

Start/ Stop Station

Maintained Push Buttons

Ingredient A

Sensor 1

Typical PLC application – Mixer or Blender

Motor

Ingredient A

Solenoid Valve 1

Ingredient B Solenoid Valve 2

Drain Solenoid Valve 3

Sensor 2

Start/ Stop Station

Maintained Push Buttons

Sensor 1

Inputs

Outputs

Sequence of Operation Step 1 - Start/Stop Station

Most Start/Stop stations use momentary push-buttons and are wired as

“3-Wire” control.

When you press a button it is only ON while it is being pressed, if you remove

your finger from the button the button will turn OFF.

Stop Buttons are usually selected as normally closed (NC) contacts, this is to ensure that when you press the button you are breaking the contacts rather then making the contacts This is done to ensure that if a failure in the contact should occur you are not relying on trying to make a connection, but instead

by pressing the button you are forcing open/turning off the circuit.

Below is a standard Start/Stop 3-wire control we will use for our Mixer/Blender

Ladder Logic for Step 1

Sequence of Operation Step 2

Ingredient A Solenoid Valve 1 will open (turn ON) if:

• “Machine_Start” is ON

• “Drain Solenoid 3” is Closed (OFF)

• Sensor 2 is OFF

Solenoid Valve 1 will close or turn OFF

when Sensor 2 turns ON

Add ingredient A to the mixer, but only when the drain is closed, sensor 2 is OFF, and the start button is ON Stop adding ingredient A when Sensor 2 turns ON.

Add ingredient A to the mixer, but only when the drain is closed, sensor 2 is OFF, and the start button is ON Stop adding ingredient A when Sensor 2 turns ON.

Ladder Logic for Step 2

Sequence of Operation Step 3

Add ingredient B to the mixer only after sensor 2 is ON indicating enough of ingredient A

has been added, the drain is closed, The start button is ON Stop adding ingredient B

when Sensor 1 turns ON.

Add ingredient B to the mixer only after sensor 2 is ON indicating enough of ingredient A

has been added, the drain is closed, The start button is ON Stop adding ingredient B

when Sensor 1 turns ON.

Ingredient B Solenoid Valve 2 will open (turn ON) if:

• “Machine_Start” is ON

• “Drain Solenoid 3” is Closed (OFF)

• Sensor 2 is ON

• Sensor 1 is OFF

Solenoid Valve 2 will close or turn OFF

when Sensor 1 turns ON

Ladder Logic for Step 3

Motor

Sequence of Operation Step 4

Once ingredients have been added, mix for 30 seconds

Motor will turn ON for 30 Seconds if:

Sequence of Operation Step 5

After mixing the ingredients drain the vessel Close the drain after 1 minute.

Turn ON/Open Solenoid 3 for 60

seconds to drain the vessel if:

• Start Button is ON

• Mix/Blend Timer is DN

Ladder Logic for Step 5

PLC Basics Agenda

1 Introduction to Terms / Concepts

4 Basic Selection criteria and Applications

2 Programming a PLC

3 Application Example

5 Hands-On Lab

PLC’s Come in a Variety of Sizes

Today's applications require a high level of control capability and advanced features

• Arithmetic (Addition, Subtraction, Multiplication, Division, etc)

• Data Comparison (Equal, Greater Than or Equal, Less Than or Equal)

• Word Manipulation (Copy, Move, etc)

• Communications or Messaging data between PLC’s

• Sequencing

• Data Manipulation

• Proportional, Integral, Derivative (PID) Control

(Used for Temperature, Pressure, Speed, Flow regulation)

• Conveyor control

• Printed circuit board handling equipment

• SCADA(Supervisory Control And Data Acquisition)

– Remote pump/lift station (water/wastewater)

– Flow monitoring for leak detection (Oil & Gas)

• Strapping machinery / trash compactors

• Palletizers

• Compressor control

• Amusement park rides and attractions

• Hard-wired relay panels or Single Board Computers

• Many, many more

So where could you use a PLC?

What you must consider when selecting a

PLC

• Inputs/Outputs

– How many Inputs/Outputs? including

embedded, local expansion, and networked I/O

• Communications Networks

• DF1 Full Duplex, DF1 Half Duplex, DF1 Radio Modem, DH485, ModBus Master /

Copyright © 2007 Rockwell Automation, Inc All rights reserved.

Some of our favorite applications that have been solved

with MicroLogix

controllers?

• Customer: Tait Towers

– World renowned stage design

• Requirement: Solution to operate trendy “theater-in-the-round” set design with dramatic effects,

flexibility of stage height, plus trouble-shooting capabilities so the show can go on!

• Solution: 17 MicroLogix 1000s and 1 SLC 500 control and coordinate:

(Other products include: limit switches, motors, operator interface, contactors)

– Motor driven raising/lowering of 2 band risers with variable height options

Boot Scootin’

Monster Truckin’

• Customer: Dan Patrick

– Designer and driver of monster trucks

• Sampson

• Requirement: Cost effective solution that provides accident-

proofed muscle truck able to operate at max speed for most of

race, and not require race-day repairs

• Solution: 1 MicroLogix 1000 and Hand-Held Programmer

– Replaced relays

– Controls shifting mechanism

• Race 5-6 seconds long

• 1.5 seconds to shift from 1st to 4th gear with 100 shifts per night

– Keeps rpms steady by eliminating possibility of over-revving the motor

– $300 control solution protects $55,000 investment in transmission and motor

– Hand-Held Programmer trace key reduces troubleshooting time

“Operation MicroLogix”

Customer: United States Army

Requirement: Real-Time control of multiple targets on full scale 30 acre urban assault training site.

Solution:

330+ MicroLogix 1500 controllers and 1761-NET-ENI’s.

– Pop-Up targets and count successful hits.

– Communicate using Ethernet and Fiber Optic cables to all MicroLogix controllers.

– Interface to advanced human interface software for control.

Copyright © 2007 Rockwell Automation, Inc All rights reserved.

Questions?

PLC Basics Agenda

1 Introduction to Terms / Concepts

4 Basic Selection criteria and Applications

2 Programming a PLC

3 Application Example

5 Hands-On Lab

Demo Box – Button description for this Lab

I:0/0 - InputButton0

I:0/1 - StopButton

I:0/2 - StartButton

O:0/0 - Light0

O:0/1 - Motor1 O:0/3 - Running Light

I:0/3 - Motor On/Off Counter

Reset Button

O:0/4 - Motor Starting Light

Please leave the Lab guides for the Next participants

Continue what you’ve learned today by purchasing an Open Enrollment course with the 15% off coupon in your take away packet

Register at the Training Services kiosk by the registration tables on this floor.

Rockwell Automation Training Services