Programmable Logic Controllers ( PLCS ) & Programmable Logic Controller

Some programmable logic controllers ( PLCS ) are equipped to solve problems involving mathematical functions such as sine, cosine, tangent, xy, y root of x, e sub x , natural logarithms, and common logarithms. Such calculations are often required for energy management, process control, process modeling, real-time error correction, and many other applications.

And while ladder logic is still the standard industry programming language for programmable logic controllers ( PLCS ), the trend is toward state logic, sequential function charts, graphics, and versions that are programmable in Basic, C, or other high-level languages.

The ability to handle analog signals along with arithmetic and other complex calculations has made programmable logic controllers ( PLCS ) suitable for the control of processes as well as for the control of machines. Typical applications for programmable logic controllers ( PLCS ) are mineral and chemical processing, water and waste treatment, and petroleum collection and distribution. In many of these applications a programmable logic controller ( PLCS ) can complement conventional analog control systems by handling sequence problems as well as a portion of the analog calculation and control. In support of those functions, some programmable logic controllers ( PLCS ) now have the ability to store recipes for batch processing, reducing the need for manual inputs.

In further support of their process-control capabilities, some programmable logic controllers ( PLCS ) can be equipped to solve complex equations such as proportional-integral-derivative equations required for the control of many processes. A sophisticated programmable logic controller ( PLCS ) is capable of performing these calculations on many different portions of a process simultaneously.

More powerful microprocessors have resulted in programmable logic controllers ( PLCS ) able to perform multiaxis control and able to link with sophisticated vision systems. One reason new programmable logic controllers ( PLCS ) are taking on such a wide range of duties is that they can be installed in modules, thus simplifying any needed customization and future expansion. Because each programmable logic controller ( PLCS ) contains its own internal communication highway or bus, a programmable logic controller ( PLCS ) can be upgraded with additional memory or processing capability and can be added by snapping in additional modules.

Various programmable logic controller ( PLCS ) modules add RS-232 communication ports, multiaxis control and fault annunciation.

Programmable logic controller ( PLCS ) software can be developed either on or off line; data-management and analysis programs are available. Many of the programmable logic controllers ( PLCS ) can be programmed from an IBM PC or compatible machine, and special industrially hardened programmers are also available when extreme temperature, dust, and vibration are problems. I/O stations can be located up to 2,000 ft from the CPU.

A programmable logic controller ( PLCS ) is no more powerful than the software available for it. Two relatively recent developments for programmable logic controllers ( PLCS ) are menu-driven software and concurrent operating systems, which have simplified programming and made it more useful. Programs using menus allow an operator with only minimal training to monitor, analyze, and manage processes. Concurrent operating systems switch back and forth between two different programs so fast that both appear to be running at the same time.