Chapter 9
Putting Together a Modular PLC
Objectives
• Define rack, chassis, and baseplate and tell
how or why they differ.
• Select the proper type of I/O to interface a
specific input signal.
• Explain why power supply loading must be
determined as a PLC system is configured.
PLCs Come in Two Styles
• The I/O of a fixed PLC is built in and not
changeable.
• A modular PLC consists of user-selected I/O
modules, a processor, a power supply, and a
chassis.
Rack, Chassis, or Baseplate?
• Depending on the modular PLC
manufacturer, the term used to identify the
hardware device that holds all the modules,
processor, and power supply may vary.
• Some use rack, chassis, or baseplate.
Module Installation into a
Four-Slot SLC 500 Chassis (1 of 2)
Image courtesy of Allen-Bradley, a Rockwell Automation business
Module Installation into a
Four-Slot SLC 500 Chassis (2 of 2)
• The General Electric Series 90-30
incorporates the processor into the baseplate
for the low-end modular PLCs.
• Baseplates come in five-slot and ten-slot
models.
Series 90-30 PLC Model 331 CPU
Image courtesy of GE Fanuc Automation
Removing a GE Series
90-30 I/O Module
Image courtesy of GE Fanuc Automation
Local I/O Expansion
• When more I/O is required than a single
chassis can hold, additional chassis can be
added.
• Communications cable connects expansion
chassis together.
• There is no processor in expansion chassis.
• A power supply is required in all chassis.
• The expansion cable distance is limited.
SLC 500 3-chassis
Local Expansion
Image courtesy of Allen-Bradley, a Rockwell Automation business
Remote I/O
• Allows greater cable distance between
chassis
• Typically a serial link
• SLC 500 remote I/O maximum cable length
10,000 feet
• Baud rate of 57.6 K bits per second
SLC 500 Remote I/O Example (1 of 3)
Image courtesy of Allen-Bradley, a Rockwell Automation business
SLC 500 Remote I/O Example (2 of 3)
• SLC 500 uses 1747-SN scanner in local
chassis.
• SN scanner communicates with remote
chassis.
• 1747-ASB communication module is required
in each remote chassis.
SLC 500 Remote I/O Example (3 of 3)
• Remote I/O allows I/O to be “distributed”
around the plant floor.
• PanelView operator interface terminals as
well as variable frequency drives can be
connected on a remote I/O link.
PLC Networking
• A single chassis PLC can be part of a larger
factory-wide communication network.
• Each PLC has its own processor.
• Each device on the network is a node or
station on the network.
• Each node must have a unique identifier
known as the node address.
Advantages to Networking
• Multiple stand-alone PLCs networked
together
• Share information between processors
• Share control of the process
• Operator interface devices input or display
information from multiple PLC processors
• PLC control of other devices such as VFDs
Current SLC 500
Network Connectivity
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•
•
•
•
•
Remote I/O
Data Highway-485
Data Highway Plus
Control Net
Device Net
Ethernet
AB SLC 500
Data Highway-485 Network
Image courtesy of Allen-Bradley, a Rockwell Automation business
Selection and
Placement of I/O Modules
• Consider input and output signals
– Modules are divided into family groups.
– The appropriate input or output module is
selected by determining incoming and
outgoing signals.
– Match I/O signals to proper module.
Table for Determining
Input and Output Types
I/O Module Selection
from Input and Output Type
Power Supply Selection (1 of 2)
• Each modular PLC chassis, rack, or
baseplate must have its own power supply.
• Power supply is designed to handle specific
load.
• Power supply loading is dependent on
modules installed.
Power Supply Selection (2 of 2)
• Proper power supply sizing will help avoid
intermittent problems or power supply
shutdown due to an overloaded power
supply.
SLC 500 Power Supply
Specifications
Image courtesy of Allen-Bradley, a Rockwell Automation business
Determine Power Supply Loading
• Proper size power supply is selected to
handle load placed upon it by the I/O module
mix.
• Power supply loading can be manually
calculated using manufacturers’ tables and
module loading data.
• PLC programming software can provide
power supply loading calculation feature.
RSLogix 500
Power Supply Loading
Installing an SLC 500 Power Supply
Image courtesy of Allen-Bradley, a Rockwell Automation business
Series 90-30 Power Supply
Image courtesy of GE Fanuc Automation