PLC Controllers

General Information

• A Programmable Logic Controller (PLC) is a general purpose control that processes analog (temperature) and discrete inputs (such as pressure switch and motor overload) to sequence outputs (such as compressors and hot gas bypass valves).
• They are in widespread use in both simple machinery and complex production lines.
• Their appeal is their flexible configuration and field programmability.
• They are easily networked to provide complete plant-wide information management systems.

Application

• PLC controls can be optionally used to replace the Advantage Multizone III chiller control.
• The PLC will sequence the compressors, valves and pumps in the same way the MZC III does.
• The information in the PLC can also be shared with other PLCs and data collection monitors in a plant or cell network.
• The use of the PLC allows the control logic of the chiller system to be altered in the field.
• The PLC can be programmed to process information and make control decisions based on this information.

Hardware

• The hardware used in PLC controllers consist of input and output modules for receiving and sending various signals, an information processor (CPU) and an operator interface panel.
• Input and output modules are added to meet the specific requirement of the system to be controlled.
• A variety of operator interface panels are available from basic 2 line black and white text displays to color touch screen displays.
• There are many manufacturers of PLC hardware, including Allen Bradley (SLC-500), General Electric (90-30), Siemans, Square D (Modikon) and others.

Programming

• PLCs need custom programs to operate the equipment they are installed in.
• Programs are custom written by the user for each application.
• For chiller or tower systems, Advantage writes a custom program or uses an existing program written specifically for the equipment.
• A copy of the program is sent with the manual for the equipment when it is shipped.
• Programming changes can be made in the field using a notebook computer interfaced to the PLC.