106 research outputs found
Relay ladder logic and petri nets for discrete event control design : a comparative study
In the 1960\u27s and earlier discrete event systems (DES) were controlled by hardwired electromechanical relay systems. In 1969 an electronic programmable logic controller (PLC) was introduced. PLC\u27s 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
Methods of measuring the size and complexity of PLC programs in different logic control design methodologies
Currently there is a wide variety of logic control design methodologies used in industrial logic design. These methodologies include ladder diagrams, function block diagrams, sequential function charts, and flow charts, but driven by a desire for verifiability, academics are developing additional logic control design methodologies, such as modular finite state machines and Petri nets. Using these, important properties of programs can be verified and some logic can be generated automatically from a part plan. The main contribution of this paper is to define methods for measuring programs written in different methodologies, so that the performance of the methodologies can be compared.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45886/1/170_2003_Article_1996.pd
A new approach to the development and maintenance of industrial sequence logic
This thesis is concerned with sequence logic as found in industrial control systems, with
the focus being on process and manufacturing control systems. At its core is the assertion
that there is a need for a better approach to the development of industrial sequence logic
to satisfy the life-cycle requirements, and that many of the ingredients required to deliver
such an approach are now available.
The needs are discussed by considering the business case for automation and
deficiencies with traditional approaches. A set of requirements is then derived for an
integrated development environment to address the business needs throughout the
control system life-cycle.
The strengths and weaknesses of relevant control system technology and standards are
reviewed and their bias towards implementation described. Mathematical models,
graphical methods and software tools are then assessed with respect to the requirements
for an integrated development environment.
A solution to the requirements, called Synect is then introduced. Synect combines a
methodology using familiar graphical notations with Petri net modelling supported by a set
of software tools. Its key features are justified with reference to the requirements. A set of
case studies forms the basis of an evaluation against business needs by comparing the
Synect methodology with current approaches. The industrial relevance and exploitation
are then briefly described.
The thesis ends with a review of the key conclusions along with contributions to
knowledge and suggestions for further research
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