(Programmable Logic Controller/Programmable Automation Controller)
PLC/PACs are the “brains” of the operation. These real time controllers are programmed to run the control logic behind a given process. They provide the hardware connection to the field devices, actuators, and motor loads. They scan inputs, compute the control loop logic, and set the outputs all in real time. Once programmed to a given functional description, they can run the process autonomously.
(Human-Machine Interface/ Operator Interface Terminal)
These devices are the “local” displays in a process. They are usually mounted in the field, and give operators a visual way to interface with a part of their process. They can monitor status, check and acknowledge alarms, and adjust operational set-points. These devices serve a similar function to a SCADA application; however their scope is usually limited to a specific part or piece of equipment that make up the overall process.
(Supervisory Control And Data Acquisition)
SCADA applications give operators an overall visual representation of their process. These PC based software programs allow operators to monitor their entire plants. These applications can data-log and trend process values, generate reports, allow operators to adjust set-points and operational modes, and manage alarming. The wealth of information these programs can gather and provide to an operator can greatly enhance the performance of their process.