A programmable logic controller (PLC) is a microprocessor based device used for automation processes, such as control of machinery on factory assembly line, or control of boxing machines and conveyor lines. A key feature of a PLC is the facility for input/output (I/O) which connect to sensors and actuators. Through these I/Os, a PLC can read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. A PLC can operate electric motors, magnetic relays or solenoids, pneumatic or hydraulic cylinders or analog outputs.
They are one of the most versatile and common device used for industrial automation.
They monitor the inputs, solve logic of a user program and control the outputs.
Data & Communications
A PLC has a wealth of information inside. Information such as math calculations or input state of a device are stored in PLC's data area. Data areas are internal memory registers of a PLC, each with it's own memory address. These data are accessible from external systems via communication ports built in a PLC. Usually, a PLC will have a 9-Pin serial RS232 port with Modbus included as one of the communications protocols. Optionally, they may have Ethernet ports or various filed buses such DeviceNet or Profibus. Example:the running state of a motor is available to the PLC via input 1. Depending on the make of
the PLCs, this input 1 may be addressed by the Modbus address 10001.
PLC & IntegraXor
IntegraXor is a tool to develop HMI/SCADA applications. IntegraXor has the communication drivers to exchange data directly with a PLC via it's communication port. Apart from PLCs, IntegraXor can also communicate with various other devices such as robots and drives that has the supported communication protocol and port.
SCADA Supervisory Control and Data Acquisition
It generally refers to industrial control systems : a computer system monitoring and controlling a process. The process can be industrial, in infrastructure or facility -based as described below:
Industrial processes include those of manufacturing , production, power generation, fabrication , and refining and may run in continuous batch, repetitive or discrete modes
Infrastructure processes maybe be public or private which includes water treatment and distribution, water collection and treatment , oil and gas pipeline , electrical power transmission and distribution, wind farms, civil defense siren systems, and large communication systems
Facility processes occur both in public facilities and private ones , including buildings, airports, ships, and space stations. They monitor and control HVAC , access, and energy consumption
Scada system consists of :
- A human machine interface HMI , this presents process data to a human operator, the human operator monitor and controls the process.
- A supervisory (computer) system for gathering and acquiring data on the process ans sending commands(controls) to the process
- Remote Terminal Units RTUs connecting to sensors in the process, converting sensor signals to digital data and sending data to the supervisory system.
- Programmable Logic controller PLCs used as field devices because they are more economical , versatile, flexible and configurable than special -purpose RTUs
Communication infrastructure connecting the supervisory system t the remote Terminal units
SUB systems of SCADA
SCADA / EMS subsystem
Inter-site Communication ICCP subsystem
Web Subsystem and the security Infrastructure
ISR subsystem HIS
Network managements subsystems
video projection systems VPS
User Interface UI subsystem
GPS Time & Frequency subsystem