The New Jersey Institute of Technology's
Electronic Theses & Dissertations Project

Title:	Relay ladder logic and petri nets for discrete event control design : a comparative study
Author:	Twiss, Edward
View Online:	njit-etd1996-026 (xi, 73 pages ~ 3.4 MB pdf)
Department:	Department of Industrial and Manufacturing Engineering
Degree:	Master of Science
Program:	Manufacturing Systems Engineering
Document Type:	Thesis
Advisory Committee:	Zhou, MengChu (Committee chair) Caudill, Reggie J. (Committee member) Chao, Xiuli (Committee member)
Date:	1996-05
Keywords:	Petri nets Production control Relay control systems Programmable controllers
Availability:	Unrestricted
Abstract:	In the 1960's and earlier discrete event systems (DES) were controlled by hardwired electromechanical relay systems. In 1969 an electronic programmable logic controller (PLC) was introduced. PLC's have been programmed utilizing relay ladder logic (RLL). RLL is a graphical programming language with software "devices" used to emulate electromechanical devices. RLL programs, however, often become large and difficult to understand because its graphical representation of physical switching devices obscures the discrete event dynamics inherent in the process to be controlled. Petri nets are a methodology for modeling discrete event systems (DES). Using a Petri net based controller, a control strategy could be developed that captures the discrete event dynamics of the process. This should result in a control strategy that is much easier to understand, troubleshoot, modify and evaluate.