Class Notes - Year 4 - 2020-2021
Year 4

Lesson 412

Introduction to Programmable Controllers

IEC Manual 412


412.1 Recognize and Explain Basic Operation and Use of Programmable Controllers

Control logic
Inputs to programmable controllers can be mechanical or solod state devices
Outputs control loads
Discrete manufacturing
Output is countable, identifiable, measurable in distinct units
Make “things”
Process manufacturing
Blending, mixing, transforming
Make “stuff”

412.2 Recognize Programmable Controller Components and Explain their Operation

Programmable I/O’s can be analog or discrete
Analog I/O’s can have varying values
Discrete I/O’s are digital and can have only binary values
1/0, high/low, open/closed, on/off

Logic Gates

And, Or, Not, Nor, Nand
All switches must be closed to allow output to be energized
If any switch is open, output will be de-energized
Nor -
All switches must be open to allow output to be energized
If any switch is closed, load will be de-energized
Not -
Switch must be open to allow output to be energized
Switch must be closed to allow output to be de-energized
If any switch is closed, output will be energized
Both switches must be open to allow load to be de-energized
If any switch is open, output will be energized
Both switches must be closed to allow load to be de-energized

412.3 Demonstrate Basic Programmable Controller Applications


412.4 Explain Basic Troubleshooting Steps for Programmable Controllers

Inputs and outputs only
Logic is programmed
No device to device connections
Components must be programmed with unique address
Contacts and coils need matching address in program

EMC5 27-1 - Programmable Controllers

Developed to automate larger and more complex systems
Replaced CRs and TRs by consolidating them into one unit
Can be programmed and reprogrammed
First ones were called PLCs
Smaller, less expensive PLRs were soon developed
Computer integrated control systems are called programmable automatic controllers (PAC)

Programmable Controller Usage

Discrete parts manufacturing versus process manufacturing

Discrete Parts Manufacturing

Modular replacement of programmable controllers
Helps reduce startup and debug time
Can control speed of line, divert production to other lines when there is a problem, make product changes, and maintain documentation

Process Manufacturing

Systems must blend, cook, dry, separate, or mix
Automation opens or closes valves and controls motors in sequence
Programmable controller allows for easy modification
Can generate reports
Microunits to very large unis

Types of Programmable Controllers

Type can depend on application, size, and number of loads to be controlled, need for monitoring and reprogramming, amount of control required
Cost and knowledge level of personnel is also considered

Programmable Logic Controllers (PLCs)

Solid state control device designed to be programmed and reprogrammed
Primarily designed for harsher environments
Consists of:
Power supply
Processor section (CPU)
Output section
Designed to control circuits w/ many inputs and outputs
Typically 8, 16, 32, or 48 devices
Additional IO capabilities through expansion modules or interconnecting multiple PLCs
Most are programmed using line (ladder ) logic or function blocks
Programmed with manufacturer’s software

Programmable Logic Relays (PLRs)

Solid state control device that includes internal relays, timer, counters that can be programmed and reprogrammed
Basically small PLCs designed for more general applications that require fewer inputs (less than 10) and fewer outputs (less than 6)
Sometimes called smart relays
Designed to be programmed using line (ladder) logic or function blocks
Can be programmed by buttons, but best if by computer

Programmable Automatic Controllers (PACs)

Combination of PLC and CPU control device designed to operate in industrial environment
Can be programmed and reprogrammed using ladder logic or function blocks, or PC languages
Interconnected into larger systems that usually contain human machine interfaces (HMIs), remote monitors, data acquisition, motion control, or vision control type devices
Available in self contained units, including:
Power supply
Input or outputs parts
Available in rack mounts
Units can include basic parts like I/O modules and temperature modules
Can contain specialized modules like serial communication modules, servo/stepper motor control modules, data acquisition modules

Programmable Controller Selection

PLC is generally first choice
PLR can be considered when system does not have a lot of loads and requires less internal controllers
PAC can be considered when more advanced control is required

Programmable Controller Configurations

Can be used as stand-alone or configured into system
Systems can be programed PC, handheld programming device, operator interface panel

EMC5 27-2 - Programmable Controller Sections

4 basic sections
Power supply
Input/output (I/O)
Processor section
Programming section

Power Supplies

Powers internal operations
May provide power for I/O modules
Can be separate unit or built into processor section
Normally 120V or 240V to 5VDC through 32 VDC
Charges internal battery to prevent memory loss

Input/Output Sections

Input section receives info from pushbuttons, temperature switches, pressure switches, photoelectric and proximity switches
Output section delivers voltage to loads like alarms, lights, solenoids, and starters
Input signals are sent to processor section
Output section receives signals from processor
I/O section can be located onboard or part of expansion module

Discrete I/Os

Most common inputs and outputs
Use bits (on/off, open/closed, 1/0)
Input examples include buttons, switches
Output examples include lights, relays, solenoids

Data I/Os

More complex info than on/off
Example: temperature sensor number value, potentiometers, bar code readers, displays
Data I/Os produce and receive variable signal

I/O Capacity

Size of programmable controller is based on I/O capacity
Mini/micro (32 or fewer I/Os, but may have up to 64)
Small (64 to 128 I/Os, but may have up to 256)
Medium (256 to 512 I/Os, but may have up to 1023)
Large (1024 to 2048 I/Os, but may have thousands more)
Can be remotely located
Can be hardwired or FO

Solid-State Input Controls

Examples include proximity photoelectric controls

Electrical Noise Suppression

Electrical noise is unwanted signals present on wiring
Can be solved by placing controller away from noise generating equipment or with shielded cables

Processor Section

Organizes and controls activity by receiving inputs, performing logical decisions according to program, and controlling outputs
The brain
Central processing unit (CPU)
Scan is the process of evaluating I/O status, executing program, and updating the system
Scan time is the time it takes the programmable controller to make sweep of the program
Processor section has different modes
Used for developing logic
Used to execute program
Used to test program without energizing output

Programming Sections

Allows input into controller through keyboard
Offline programming uses separate PC

Programming Symbols


Programming Languages

Line diagrams are commonly used
Functional blocks
English statement
Input devices are either NO or NC
Classified as “examined if closed” (XIC), or “examined if open” (XIO)

Programming Rules

Rule 1: Inputs are placed on left side of circuit between left rung and output. Outputs placed on right side
Rule 2: Only one output can be placed on a rung. Outputs cannot be placed in series
Rule 3: Inputs can be placed in series, parallel, or combo
Rule 4: Inputs can be programmed at multiple locations in the circuit. Same input can be programmed as NO and/or NC at multiple locations
Rule 5: Standard outputs cannot be programmed at multiple locations in the circuit.There is a special output called “or-output” that allows output to be placed more than once

Developing Typical Programs

Step 1: Develop logic that is required of the circuit into line diagram
Step 2: Convert Line Diagram into Programming Diagram
Step 3: Enter Desired Logic into programmable controller

Storing and Documenting

Program can be stored digitally or printed

Controller Status and Fault Indicators

LED indicator lamps show condition of components
Can show condition of inputs, outputs, and operating condition of controller

Force and Disable

Force command opens or closes input device or turns on or off output device
Disable prevents output device from operating

Controller Communication Network

Utilized LAN

EMC5 27-3 - Programmable Controller Applications


EMC5 27-4 - Troubleshooting Programmable Controllers

Do not use NCVT

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