1 Introduction

MicroLogix Packaged Controllers

Programmable Controller BasicsIntroduction

Traditional PLC ConceptTraditional PLC Concept

• PLC performs relay equivalent functions• PLC performs ON/OFF control• Ladder diagram program representation• Designed for industrial environment• Designed for ease of use and maintenance

PLC AdvantagesPLC Advantages

• Ease of programming• Ease of maintenance• Designed for industrial environment• Quick installation• Adaptable to change

Today's Higher Level Control CapabilityToday's Higher Level Control Capability

• Arithmetic• Data Comparison• Word Manipulation• Master Control Relay Instructions• Program Skip Capability• Sequencing• Matrix Data Manipulation• Proportional, Integral, Differential (PID) Control

Programmable Controller

Inputs Outputs

CR

What Is A Programmable Controller?What Is A Programmable Controller?

• A solid state device that controls output devices based on input status and a user developed program.

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

Where do you Use a MicroPLC?Where do you Use a MicroPLC?

• 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• Replace hard-wired relay panels or SBCs• Many, many more

Other Types of ControlOther Types of Control

• MicroPLCs vs. Relays– above 2/3 relays cost becomes a problem

• panel space, cost– limited functions

• limited logic, no math, no application specific instructions• timers and counters cost $ to add• no communications

– difficult to “exchange” data– maintenance/reliability

• mechanical devices wear out, create and are affected by vibration– expensive to program

• time consuming, difficult to document, hard to “pass on” logic– difficult to troubleshoot

• requires skilled technician• “race” problems are common and difficult to deal with

Other Types of ControlOther Types of Control

• MicroPLCs vs. Custom SBC’s (single board computers)– High design costs

• Contract or Staff with overhead and maintenance issues associated with each

– Repair / Service nightmare for customers• Depending on markets served supplier must develop/support services

– High level of technical expertise required by technicians• Specialized circuit boards require specialized equipment and technical staff

– Not readily available through distribution (typically regional)• Suppliers sell the controller imbedded, replacement parts are not readily available even in emergency

situations

– Typically does not meet worldwide standards• Certifications cost money, typically a single controller does not warrant the investment. Volumes are not

high enough and re-certification on each revision is unrealistic

– Typically a “Domestic” product• Because of these issues many manufacturers limit themselves to a single market.

Input DevicesInput Devices

• Pushbuttons

• Selector Switches

• Limit Switches

• Level Switches

• Photoelectric Sensors

• Proximity Sensors

• Motor Starter Contacts

• Relay Contacts

• Thumbwheel Switches

• 120/230 VAC

• 24 VDC – Sourcing

– Sinking

Output DevicesOutput Devices

• Valves• Motor Starters• Solenoids• Control Relays• Alarms• Lights• Fans• Horns

• Relays– 120 VAC/VDC– 240 VAC– 24 VAC/VDC

• Triac– 120/230 VAC

• Transistor MOSFET– 24 VDC

CR

IsolationBarrier

IsolationBarrier

MEMORY

program data

HighVoltage

HighVoltage

Low Voltage

AC Power Supply85-264 VAC,

50/60Hz

Output

Circuits

ExternalDC Power Supplyor

Communications

Input

Circuits

CentralProcessor

Inside A PLCInside A PLC

PLC Application ConsiderationsPLC Application Considerations

• Inputs/Outputs– Type,

• AC, DC, sourcing, sinking, etc.

– Number of• 10, 16, 20, 32, 156

• Memory– Type

• Flash or Battery backed

– Size• 1k, 6k, 12k, 16k, 64k

• Functions required– Instruction set

• Messaging• PID• PTO, PWM

– Arithmetic– Communications

• DeviceNet, Ethernet• Remote I/O, DH+

– Report generation

PLC’s Come in a Variety of Sizes...PLC’s Come in a Variety of Sizes...

• Pico– Typically less than 20 I/O

• Micro– Typically less than 32 I/O

• Small– Typically less than 128 I/O

• Medium– Typically less than 1024 I/O

• Large– Typically greater than 1024 I/O

And a variety of shapes/configurationsAnd a variety of shapes/configurations

• Packaged– MicroLogix 1000,1200 and 1500

• Packaged with expansion– MicroLogix 1200 and 1500

• Modular (rack less)– MicroLogix 1200 and 1500

• Modular (rack based)– SLC 500 and PLC5

• Distributed– SLC 500 and PLC5

Packaged PLCPackaged PLC

• Power supply, inputs, outputs and communication port are enclosed in a single package. Input and output devices are wired individually to the packaged controller.

Packaged PLC With ExpansionPackaged PLC With Expansion

• Base is identical to the standard Packaged PLC, but it also has the ability to drive additional I/O. The most common form of expansion is a block of I/O that uses the same base, or makes use of different types of expansion “modules”.

Modular Rack-Less PLC’sModular Rack-Less PLC’s

• Identical in functionality to rack based PLC’s• Typically not as robust (packaging)• Typically found on “smaller” (small and medium) sized

PLC’s.• Will likely become the prevalent form of packaging in the

future.

+ +

Processor Base Unit Compact I/O

Modular PLC’sModular PLC’s

• Mix N Match Components– Processors, Power Supplies and I/O are plugged into a rack or

chassis– Available in Small, Medium, and Large platforms– Flexibility results in higher costs when compared to packaged

DistributedDistributed

• Rely on communications for EVERYTHING • All I/O is connected to the processor through a “High Speed”

data link.• Typically found on “larger” (medium and large) PLC’s.• For certain applications this type of form factor is very

advantageous.• Usually higher cost for hardware, but much lower cost for

system integration.• RIO (Remote I/O), DeviceNet are examples of distributed

control.

Why use a Micro PLCWhy use a Micro PLC

• Performance– Although small in size these products can perform the same tasks

as much larger PLC’s• Cost

– The price range for the entire family: $200-$800 List• Reliability

– Designed to meet existing industrial design standards• UL, CSA, CE• Designed & manufactured in ISO9000 facilities

• International Focus– Standard product available throughout the world

Motor Solenoid 1 Solenoid 2

Solenoid 3

Sensor 1

Sensor 2

Ingredient A Ingredient B

Typical PLC ApplicationTypical PLC Application

Motor Solenoid 1 Solenoid 2

Solenoid 3

Sensor 1

Sensor 2

Ingredient A

Ingredient B

Operation of MixerOperation of Mixer

• Solenoid 1– On = Sol 3 is off, and Motor is off,

and Sensor 2 is off, and Auto Switch is on

– Off = Sol 3 is on, or Motor is on, or Sensor 2 is on

• Solenoid 2– On = Sol 3 is off, and Motor is off,

and Sensor 2 is on– Off = Sol 3 is on, or Motor is on, or

Sensor 1 is on

• Motor– On = Sensor 1 is on, and Solenoid 2

is off, and Solenoid 1 is off– Off = Solenoid 3 on

• Solenoid 3– On = Sol 1 is off, and Sol 2 is off, and

Motor has run for 30 sec.– Off = Solenoid 3 has been on for 60

sec.

Terminal Block

1

2

3

4

5

6

7

8

9

Input Devices

L1

L1

L210

COM

PLC

IsolationBarrier

Input WiringInput Wiring

OUT 1

Output Devices

L2

L2

L1OUT 1

OUT 2

OUT 2

OUT 3

OUT 3

OUT 4

OUT 4

OUT 5

OUT 5

OUT 6

OUT 6

CR

L1PLC

Terminal Block

IsolationBarrier

Output WiringOutput Wiring

Input Scan

Program ScanOutput Scan

Housekeeping

START

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 status of external inputs (terminal block voltage) is written to the Input image (“Input file”).

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 Operating CyclePLC Operating Cycle