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Session 2663

Development of a Relay Ladder Logic Programming and Simulation Tool with Graphical User Interface Kevin M. Hubbard, Ph.D., CMfgE University of Missouri-Rolla

I. Abstract

Two software packages have been developed in the Computer Integrated Manufacturing Laboratory of the University of Missouri-Rolla's Engineering Management Department. The first, LadderCAD, is a relay ladder logic programming environment. It features:

• "Point and Click" graphical user interface based ladder logic program construction. • Forward Interpretation: The generation of an English-like representation of the control logic embodied by the ladder logic program. • Backward Interpretation: The generation of a ladder logic program from English-like control logic statements. • The use of assignable English device names in place of device addresses. • The generation of PC based data acquisition card device control code.

The second, SIM, is a simulation package. Using this software package, ladder logic programs may be tested, verified, and debugged off-line. Through a graphical user interface, the user may actuate/deactuate input devices, and monitor the state of output devices, counters, timers, and mathematical instructions in real time, or in "step mode". Once the ladder logic program has been verified, it may be used to run physical equipment.

Students receiving instruction in relay ladder logic programming may use LadderCAD's forward and backward interpretation routines to gain a more thorough understanding of the process by which these programs are written and interpreted. LadderCAD and SIM may also be used in the instruction of digital data acquisition card programming.

II. Background

Programmable Logic Controllers (PLC's) are used extensively for logic and sequencing control in a wide variety of applications. The demand for these controllers will continue to increase during the foreseeable future1. As a result, a demand exists in industry for engineers proficient in their use and programming. To satisfy this demand, many Mechanical, Electrical, and Manufacturing Engineering curricula contain courses dealing with PLC programming and applications.

Although a variety of programming methods for these devices are in use, the most common PLC language is relay ladder logic, a symbolic language in which the PLC is programmed to emulate the activity of a set of logic circuits. Relay ladder logic offers many benefits, but suffers from a number of disadvantages as well. Chiefly, these disadvantages lie in the areas of:

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Hubbard, K. M. (1998, June), Development Of A Relay Ladder Logic Programming And Simulation Tool With Graphical User Interface Paper presented at 1998 Annual Conference, Seattle, Washington. 10.18260/1-2--7035