Transcript Programming Logic Controllers

Programming Logic
Controllers
Selection, Components, & Communication - Chapter 2
PLC
• Process control computers
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no number crunching no graphics
• Event driven industrial control systems
• Environmentally hardened
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Dust, temp, noise (em)
• Easy
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Repair, operate, and program
PLC Selection
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Mfg support
Serviceability
Flexibility
Expandability
Programming software
Training
Documentation
Allen-Bradley SLC 500
• Fixed
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Single housing for power supply, cpu, I/O modules
• Modular
Allen-Bradley SLC 500 Components
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Chassis
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Rack / backplane for PLC and modules
Distributes power
slotted
Power Supply – sufficient for all components
Processor – chosen for memory and math
I/O Modules
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Digital I/O modules
Analog I/O modules
Specialty
Distributed / networking I/O modules
Addressing
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Slot 0 next to power supply
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CPU
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Slot 1+ hold other modules
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Each module has several ports/terminals
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I:1
(input module in slot 1)
O:2 (output module in slot 2)
I:3, O:4, I:5, O:5 May have many modules
I:1/2 input on module 1, terminal 2
O:2/1 output on module 1, terminal 1
A Fixed PLC may have both Input and output in slot 0
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I:0/0
O:0/0
Sourcing and Sinking
• Sourcing and Sinking refer to electrical
current flow
• Sourcing modules connect to sinking
modules and vice versa
• Sourcing occurs when current flows out of
PLC circuit
• Sinking occurs when current flow into PLC
port
PLC Memory Expansion and Usage
System memory (25%) User Memory (75%)
User Memory
• Ladder logic program(s)
System Memory
• Input status
• Output status
• Timers’ status
• Counters’ status
• Math and logic instruction status
Communications
• Channel 1 and Channel 0 occasionally
• Channel 0 for peripheral devices
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Bar code scanner
Printer
• Channel 1
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Communication with other plc/pcs
• RS232 interface for programming
• Ethernet or other network communications
Communications
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Baud Rate
Parity
DTE (initiate) and DCE (respond)
Simplex, Half Duplex, Full Duplex
Programming Modules
• Hand held
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Common for small devices
• Dedicated
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Part of the PLC circuit/station
• Computer
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Need a device to translate
States/setting
• Off/program/disabled/run/forced