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)

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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

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Removing a GE Series 90-30 I/O Module

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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

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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)

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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 • Remote I/O • Data Highway-485 • Data Highway Plus • Control Net • Device Net • Ethernet

AB SLC 500 Data Highway-485 Network

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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

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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

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Series 90-30 Power Supply

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