Chapter 2 PLC Selection Components and Communication

Chapter 2 PLC Selection, Components, and Communication

Objectives • Identify important questions to determine which PLC device to purchase. • Distinguish between Allen-Bradley fixed and modular SLC 500 processors. • Select modular Allen-Bradley SLC 500 series processor and chassis. • Select input or output modules for Allen. Bradley SLC 500 PLCs. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Objectives • Recognize how to connect sensors and switches to PLC ports. • Describe the different types of PLC memory. • Describe the method to connect PLC devices to programming modules. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Selection • Factors: – Manufacturer’s support. – Serviceability. – Flexibility. – Expandability. – Programming software. – Training. – Documentation. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Allen-Bradley SLC 500 Components • For Allen-Bradley SLC 500 PLC, select either: – Fixed PLC. – Modular PLC. • In a single housing, a fixed PLC has – the processor (CPU). – power supply. – I/O modules. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Allen-Bradley SLC 500 Components (Cont. ) • Modular Allen-Bradley SLC 500 PLCs: – Chassis. – Power supply. – Processor. – I/O modules. • Allen-Bradley refers to the central processing unit (CPU) as processor. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Chassis • In an Allen-Bradley SLC 500 modular PLC, provides electrical current to: – Processor. – Input module. – Output modules. (Used with permission of Rockwell Automation, Inc. ) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Chassis (Cont. ) • Four chassis sizes for the modular SLC 500 series processors: – – Four-slot. Seven-slot. Thirteen-slot. • Number of slots can be expanded to a maximum of 30 by interconnecting up to three chassis using cables. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Chassis (Cont. ) • When installing the PLC components in a chassis: – Processor must be placed in slot zero. – Input and output modules can be in any other slot. – Slot zero in the modular PLC is reserved for the processor. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Chassis (Cont. ) • A complete unit in an Allen-Bradley SLC 500 fixed PLC includes: – Power supply. – Processor. – I/O modules. • An I/0 module is referred to as Module Zero. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Chassis (Cont. ) • I/O port types and voltage or current rating cannot be altered. • However, a two-slot chassis can be added so two more I/O modules can be installed. – Fixed PLC power supply provides power. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Power Supply • Provides power to the chassis backplane, and thus to the processor, modules, and peripherals attached to the chassis. • Must be able to provide ample current to these components. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Processor • Allen-Bradley SLC 500 modular processors: © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

I/O Modules • Allen-Bradley SLC 500 series modules: – Digital (discrete) I/O modules. – Analog (variable) I/O modules. – Specialty I/O modules. – Distributed or networking I/O modules. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

I/O Modules (Cont. ) • Each input or output module has several ports, or terminals. • For example, input module one may have sixteen ports, and output module two may have eight ports. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

I/O Modules (Cont. ) • Ports on the modules: – Specified when they are specifically used in a ladder logic diagram. – Addressed by their module and port number. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

I/O Modules (Cont. ) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Wiring Connection Diagram © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Wiring • PLC I/O ports: – Typically rated for low amperage. – Ordinarily connected to I/O devices through American Wire Gauge size fourteen (AWG 14). • AWG 14 wire has more than sufficient ampere rating for carrying current for the PLC I/O ports. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Wiring (Cont. ) • In most applications, the output devices require larger voltage and current ratings. • A magnetic relay should be used to connect larger voltage and current equipment to the output device. • PLC output port provides voltage and current to the input coil of the magnetic relay. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Sourcing and Sinking • The way current flows through the input or output module DC circuit. • DC I/O modules labeled as sourcing or sinking. • Sourcing device always attaches to a sinking I/O module. • Sinking device always attaches to a sourcing I/O module. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Sourcing • Sourcing occurs when the current flows out of the PLC port. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Sinking • Sinking occurs when the current flows into the PLC port. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Memory Expansion and Usage • User memory: – Holds the ladder logic program. – About 75% of the total memory. • System memory: – Stores information needed to execute the user program. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Memory Expansion and Usage (Cont. ) • Input status: holds the status of discrete input ports. • Output status: holds the status of discrete output ports. • Timers’ status: holds the preset values and the accumulated values of the timers. • Counters’ status: holds the preset values and the accumulated values of the counters. • Math and logic instructions’ status: used for instructions such as addition, subtraction, multiplication, division, sequencer, shift registers, and comparison. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Memory Expansion and Usage (Cont. ) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Communication Systems • PLCs communicate with: – Industrial input and output devices. – Peripheral control components. • • • PCs. Printers. Display panels. Peripheral interfaces. Programming devices. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Communication Systems (Cont. ) • Allen-Bradley SLC 500 PLCs: – Channel 0 is used to attach peripheral devices. – Channel 1 is used to communicate with other PLCs and PCs. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Communication Systems (Cont. ) • All of the Allen-Bradley SLC 500 PLCs have a Channel 1, but only the SLC 5/03, 5/04, and 5/05 also have a Channel 0. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Communication Systems (Cont. ) • Network communications: – DH-485. – DH+. – Ethernet. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Communication Systems (Cont. ) • DF 1: – Provides serial communications through an RS-232 interface. – Can be used for remote communications through a modem or radio modem, monitoring PLC status, and programming. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Communication Systems (Cont. ) • Two types of DF 1 communications: – Full-duplex. – Half-duplex. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

PLC Communication Systems (Cont. ) • Full-duplex: – DF 1 allows for two-way communications between two devices. • Half-duplex: – DF 1 allows for communications in one direction at a time in a network of up to 255 devices. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

ASCII • Allows for communications with other devices that use the ASCII protocol. – Serial printers. – Bar code readers. • Takes place over the RS-232 interface or connector. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Serial Communication • Serial communication data: – Transmitted one bit at a time through one transmission medium. – Can be framed prior to transmission. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Baud (Bd) Rate • Includes framing bits. • A PLC communicates with its peripheral devices at different baud rates. – A PLC may operate at a rate of 19, 200 Bd with the CPU and 2400 Bd with a printer. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Framing • Process of indicating the beginning and ending of a transmission. • Ensures each byte of data is the correct transmission of data. • Device receiving the information is alerted when data transmission starts and ends. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Framing (Cont. ) • Framing bits include: – Start bit. – Stop bit. – Parity bit. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Parity • Parity bit: – Turned on or off to make transmitted data to have either an odd number of ones (i. e. , odd parity) or an even number of ones (i. e. , even parity). • Parity bit check: – Used to find transmission errors. • Errors come in the form of lost or changed bits. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Parity (Cont. ) • Even parity check. – Parity bit turns on or off to ensure the number of high bits in one byte (8 bits) of transmitted data is even. • Odd parity check. – Parity bit turns on or off to ensure the number of high bits in one byte of transmitted data is odd. • No parity check. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

DTE and DCE • Data terminal equipment (DTE): – Initiate communication by sending messages. • Device that initiates communication is also referred to as a master or initiator. • Computers or master PLCs. • Data communication equipment (DCE): – Respond to the messages transmitted by the DTE. • Device that responds to transmitted messages can also be referred to as a slave or responder. • Modems or slave PLCs. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

DTE and DCE (Cont. ) • Single master/multiple slave network: – Network with one initiator and several responders. • Multi-master network: – Network with more than one initiator. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Channeling Systems • Three ways to channel communication: – Simplex. – Half duplex. – Full duplex. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Channeling Systems (Cont. ) • Simplex channeling: – When the DTE either transmits data to or receives data from the DCE. – Will not do both. – Data flows only in one direction. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Channeling Systems (Cont. ) • Half duplex channeling: – DTE transmits data to and receives data from the DCE. – Transmission and reception of data cannot occur simultaneously. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Channeling Systems (Cont. ) • Full duplex channeling: – DTE transmits data to and receives data from the DCE through two separate transmission lines. – Data flow to and from DTE and DCE is simultaneous. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Programming Module (PM) • Three different types of PLC programming modules: – Hand-held. – Dedicated. – Personal computer. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Hand-held Programmer • Typically used for programming smaller PLC devices. • After programming the PLC, these temporary programming modules are disconnected from the system. (Used with permission of Rockwell Automation, Inc. ) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Dedicated Programmer Module • Used for larger PLC systems. • Permanently left in the PLC circuit. • Maintenance personnel can use it to modify or troubleshoot the PLC programs. (Used with permission of Rockwell Automation, Inc. ) © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Personal Computer (PC) or Laptop Computer • Can be used to program a PLC. • A device that bridges communication between two different interfaces must be used between the PC or laptop and the PLC. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Communication Settings • To prevent unauthorized personnel from running or altering a PLC program, most PLCs have different hardware and software communication settings. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Common Communication Settings – Off: System cannot run or be programmed. – Offline program: PLC’s program can be modified while the system is not running. – Disable: Turns all the PLC outputs off or sets them to the inoperable state. – Run: System can run, but its program cannot be altered. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Common Communication Settings (Cont. ) – Online Monitor/Run: Turns on to display the PLC program while the PLC is running. – Forced: Allows system to run and allows the program to be modified while the system is running. © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.

Forced Mode © Goodheart-Willcox Co. , Inc. Permission granted to reproduce for educational use only.