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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
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