1. Lesson 1 PLC BASICS

2. PLC Definition  Programmable Logic Controllers are industrial computers that control machine and other applications.  PLC have replaced hardwired devices such as relays & contacts  Automation and Control: Real time I/O  Field device: switches, output devices and drives

3. Advantages of PLC 1. Less Space: PLC requires less space than a computer or a relay panel to do the same job. 2. Lower Cost: Can cost as little as 4 or 5 relays, but can replace hundred of relays 3. Resistant to Environment – Industrially hardened to withstand harsh environment 4. Direct Interface – Standard computers require a complex and limited system to interface to real world components. PLC interface is directly wired to components 5. Easy Programming – PLCs most often use ladder logic, language based on industrial standard symbols used in hardwired relays. 6. Flexible: programming can be changed quickly

4. PLC Applications PLC can control any number of applications:  Assembly Machines  Automatic Transfer Lines  Packaging Lines  Robots

5. Components of a PLC 1. Input modules 2. Output modules 3. Controller (Processor Module) 4. PLC power supply 5. I/O chassis 6. Programming device All industrial PLCs use similar configurations. 890-AB5500 PLC

6. Controller of a PLC PLC Processor Module, also called a controller, is the actual computer that controls the PLC. It consist of the CPU and memory. The program is stored in the processor memory. ControlLogix processors usually contain at least 2MB of user memory. Prominent processor components include alphanumeric display, LED status indicators, the energy storage module (ESM), SD card cover, and the USB communications port.

7. PLC PROGRAMMING  All PLC must have user develop project to operate. Projects can be entered into the PLC memory: 1. A personal computer 2. SD card 3. Handheld terminal

8. Personal Computers RSLogix 5000 software is used to develop ControlLogix projects, configure inputs and outputs, develop ladder routines, and transfer projects to the PLC and monitor its operation.

9. Secure Data (SD) Card  Used to store backup programs on nonvolatile memory cards to be restored to the controller if a memory failure occurs.  Program is developed in RSLogix 5000 software, downloaded to the PLC memory, and transferred to SD card.  The user configures the card for the conditions that cause the transfer of the program to the controller, such as a power and memory failure.

10. Handheld Terminal  Used to enter, monitor, or change PLC user programs.  Easy to carry  Not used with ControlLogix controller

11. Basic Operation of PLC  The basic operation of a PLC is to scan instructions, monitor the status of input devices, and produce outputs based on the status of the inputs.  The status of field input devices, such as limit switches, represent conditions in the machine or process.  Outputs provide control by turning on and off output devices, such as motor starters and solenoid valves.  PLC is a specialized computer that works with binary information.  There are 4 basic data types connected to the PLC: discrete input, discrete output, analog input, analog output. Hardware modules in the PLC chassis or rack use electronics and firmware to process the input signals and generate the output signals.

12. Discrete Signal  Discrete input represented by two-state, electricity flowing (T) or not flowing (F). The binary system relates this to 1 or 0 values of software.  Examples of discrete input signal are: switch, photocell, pushbutton, contact or proximity sensor.  The discrete input module would represent this presence or absence of electrical signal as a 1 or 0.  The discrete output is also also a 2 state signal, represented by electricity flowing or not. Examples are lamps, motor contacts and solenoid valves.

13. Analog Signal  Analog signals are represented by a range of electrical signals, such as 1-5 VDC or 4-20 mA. This electrical signal is generated by a transducer, which converts the field value to a proportional electrical signal. The analog input module samples the input signal and converts it to a 16 digit binary number in the range of 32,787. The low end would be represented as 0, while the high end of the signal 5V or 20 mA will be represented by 32787. The current value of the voltage or current is converted to a binary number which is proportional to the electrical signal between the two limits.  Analog outputs begin as internal 16 bit values, and are converted into an electrical signal of 1-5VDC or 4-20mA. Examples are valve positioners, turn drive speed controllers and any other variable control device.