Programmable Logic Controller ELC 9060 Steve Moore- Lange stevem287@msn.com http://stevem287.googlepages.com

Define industrial automation: Industrial automation is a set of technologies that results in operation of industrial machines and system without significant human intervention and achieves performance superior to man operation

Sequence/ Logic control It is a class of control problems for systems where input, outputs and feedbacks are discrete set valued ( on/off) . In order to cause or prevent Particular values of outputs Particular values of outputs to obey timing restrictions Given sequence of output Given order between various outputs  

Event modeling Variables: Input, Output, State Finite number of Systems States State changes caused by Transitions External events (Inputs) Internal dynamics (Timers) State changes cause Events (Outputs ) to engage

Relay Logic PLC Hardwired logic Using relay switches Software logic   Relay Logic PLC Hardwired logic Using relay switches Software logic Using CPU and memory Difficult to upgrade and maintain Modular, easier to program Limited in terms of speed size, complexity, and reliability Superior in these terms   Dated technology Current technology

What is a PLC? Industrial PC with I/O (PLC) A device used to automate monitoring and control of industrial plant. replaced relays, cam timers, and drum sequencers in hard-wired control panels Widespread in industry Noise/Humidity/Temperature/Vibration/EMI resilient

Major PLC Manufacturers Allen Bradley Siemens Modicon General Electric – Fanuc Omron

PLC Types Rack - (up to 18” by 30” by 10”). Mini - PLC racks, but about half the size. Shoebox - A compact, all-in-one unit Micro - as small as a deck of cards. fixed quantities of I/O and limited abilities, but costs will be the lowest

Legacy 16 BIT AB Control System Rack Mini Micro

AB LOGIX 32 BIT SYSTEMS

PLC Architecture CPU Memory Programming Interface Communication Interfaces I/O Power Supply

PLC HARDWARE Power Supply - built into the PLC or be an external unit. 24Vdc, 120Vac, 220Vac. CPU (Central Processing Unit) - where ladder logic is stored and processed. I/O (Input/Output) - monitor the process and initiate actions. Indicator lights - power on, program running, and a fault.

The Chassis device which holds modules. SLC chassis- available in 4, 7, 10, or 13 slots, PLC-5 chassis in 4, 8, 12, or 16 slots. The processor is not included in the slot count. SLC and PLC support extended local I/O.  

The Power Supply supplies power to the modules on the backplane. Generally power from field devices DOES NOT come from the power supply. has a fuse which protects the AC side of the power supply. If this fuse blows, the power supply is probably defective and in need of repair.  

The Processor where the program is stored , reads the status of your equipment, makes a decision on what to control.  The Processor Consists of several Components:  1) The battery: The battery retains the processor's program  2) EEPROM is an on board backup of the processor's memory,. manually store changes to the EEPROM from the COMMS menu in RSLogix.  3) On the front of the processor, you will find several status lights:

1. RUN – Indicates RUN Mode 2. PROC – If flashing red, indicates a software problem. description in the S2 status file on the ERRORS tab. If the fault light is solid red indicates the processor lost it's program, or has a hardware problem.. 3. BATT-- Indicates the battery is low or missing 4. FORCE –flashing indicates forces are installed but not enabled... If solid indicates forces are installed, and enabled. 5.Communication lights-- to indicate when communications are active

I/O (Inputs & Outputs) Input devices are transducers that change events into electrical signals. Input devices are wired into an Input Module. Output devices are transducers that change electrical signals into events. Output devices are wired into Output modules * Transducer :an electrical device that converts one form of energy into another

There Are Many Trade-offs When Deciding Which Type of Input Cards to Use. • DC voltages are usually lower, and therefore safer (i.e., 12-24V). • DC inputs are very fast, AC inputs require a longer on-time. For example, a 60Hz wave may require up to 1/60sec for reasonable recognition. • DC voltages can be connected to larger variety of electrical systems.

• AC signals are more immune to noise than DC, so they are suited to long distances,and noisy (magnetic) environments. • AC power is easier and less expensive to supply to equipment. • AC signals are very common in many existing automation devices

Sinking & Sourcing Sinking - allows current to flow to a common ground. This is best selected when different voltages are supplied. (usually used for Inputs) Sourcing - current flows from a supply, through the output device and to ground. This method is best used when all devices use a single supply voltage. (usually used for Outputs)

Software A software based PLC requires a computer with an interface card, but allows the PLC to be connected to sensors and other PLCs across a network Rslogix 5 & 500 Software is use with AB Legacy System PLC 5 & SLC

RsLogix 5000 Software is use with AB newer Contrologix Systems

PLC languages Ladder Logic Function Block Diagram Structured Text Instruction List Sequential Function Chart

Self - Test Examine Inputs Update Program Update Outputs Processor Scan Self - Test Examine Inputs Update Program Update Outputs

Scan repeats 10 to 100 times per second OPERATION SEQUENCE Scan repeats 10 to 100 times per second

SELF TEST: all cards error free INPUT SCAN: Reads input values copies their values to memory. This snapshot avoids cases where an input changes from the start to the end of the program . changes in inputs that are too short in duration, can be missed by input scans  

LOGIC SOLVE/SCAN: program is executed 1 step at a time, modeled after relay logic, left-to-right, top-to-bottom OUTPUT SCAN: output table is copied from memory to the output chips. if output bits were changed as each bit was changed, the PLC would operate much slower  

Latching Circuit and Instruction