Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 74-76). Also available via the Internet.

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PLCs are extensively used for the discrete and continuous control of non-intelligent shop-floor devices. The debugging phase of ladder logic development for PLCs is very cumbersome and difficult. Most often on-line debugging which is expensive and time consuming is used for debugging. Computer simulation techniques applied to this problem, leaves much to be desired. The best technique developed for ladder logic debugging is the use of ladder-based triggers. A ladder-based trigger is a function which suspends simulation execution whenever a vector of ladder variables equates to a vector of predefined states. System-based debugging facilities are those which aid a programmer in error detection at the system level. System based triggers will identify system faults and set traps within a simulation model to detect their occurrence. This approach will provide information necessary for a faster correction of the ladder logic once a trigger is activated. The system based debugging tool developed is capable of scanning a boolean representation of a PLC program with input coils, counters, timers, "and" conditions, "or conditions and output coils. The program provides the following facilities: 1. Graphics programs can be attached to the simulation program for better visualization. 2. The simulation program allows interactive control over the test bed developed. In a non-interactive simulation it can be executed in a timed sequential mode or random mode. 3. Triggers can be set by the user depending on the conditions that are to be monitored. 4. The program stops execution whenever a trigger is activated. 5. The program provides a trace of the output that caused the trigger and also of the inputs to this output, along with their state values at the time of activation. The use of system based techniques and graphics in the debugging of PLC ladder logic is demonstrated. Further the use of an object oriented frame work in the development of the debugging software is also demonstrated. / Master of Science

A simulation model is developed for use in programmable controller ladder diagram testing. The developed model represent a physical flexible manufacturing system that can be controlled by different ladder logic diagrams. The model is capable of detecting initial ladder errors, displaying state changes in the ladder, and logging an operations history. As a result of the simulation development, insight into a generalized system descriptive language is obtained. This includes the language structure, specific data requirements, and an interface control method. The model also allows the user to locate optimal ladder solutions by comparing the results produced by different ladder diagrams. This thesis contains a literature review that establishes a history of programmable controller ladder testing and simulation modeling. The literature review provides impetus to the research by conveying the need for alternative methods of ladder diagram development, debugging, and testing. / M.S.

This thesis presents methodologies for the operation of a programming/documentation system for a Texas Instruments Model 530 programmable controller. The methodologies include: 1) a means to store information about the structure of a ladder diagram and display the ladder diagram on a CRT screen, 2) a means to convert the ladder diagram information into its equivalent Boolean code, and 3) a means to convert Boolean code into its equivalent ladder diagram information. / Master of Science

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Frequency response analysis (FRA) of transformers is universally accepted as a highly sensitive tool to detect deformations in its windings. This is evident from the fact that customized commercial equipment (popularly called FRA or SFRA instruments) are used and recently the IEEE has issued a draft trial-use guide. Nevertheless, use of FRA is still limited to only detection and there is little progress towards its use for localization of winding deformation. Toward this end, a possible approach would be to compare the healthy and deformed systems in a suitable domain, e.g., their respective models could be compared. In this context, the mutually-coupled ladder network is ideally suited because not only does it map the length of the winding to sections of the ladder network, but, also inherently captures all subtle intricacies of winding behaviour under lightning impulse excitations insofar as the terminal response, internal oscillations and voltage distributions are concerned. The task of constructing a ladder network from frequency response is not trivial, and so exploration of newer methods is imperative. A system can comprehensively be characterized by its frequency response. With this as the starting point, many approaches exist to construct the corresponding rational function (in s-domain). But, the subsequent step of converting this rational function into a physically-realizable mutually-coupled ladder network has, as yet, remained elusive. A critical analysis of the circuit synthesis literature reveals that there exists no analytical procedure to achieve this task, a fact unequivocally stated by Guillemin in his seminal book "Synthesis of Passive Networks". In recent years, use of iterative methods to synthesize such ladder networks has also been attempted with some degree of success. However, there exists a lot of scope for improvement. Based on this summary, the objectives of this thesis are as follows- _ Development of an analytical procedure, if possible, to synthesize a mutually-coupled ladder network starting from the s-domain representation of the frequency response _ Construction of a nearly-unique, mutually-coupled ladder network employing constrained optimization technique and using frequency response as input, with time-efficiency, physical realizability and repeatability as its features In Chapter 2, analytical solution is presented to convert a given driving-point impedance function (in s-domain) into a physically-realizable ladder network with inductive couplings (between any two sections) and losses considered. The number of sections in the ladder network can vary, but, its topology is assumed fixed. A study of the coefficients of the numerator and denominator polynomials of the driving-point impedance function of the ladder network, for increasing number of sections, led to the identification of certain coefficients, which exhibit very special properties. Generalized expressions for these specific coefficients have also been derived. Exploiting their properties, it is demonstrated that the synthesis method essentially turns out to be an exercise of solving a set of linear, simultaneous, algebraic equations, whose solution directly yields the ladder network elements. The proposed solution is novel, simple, and guarantees a unique network. Presently, the formulation can synthesize a unique ladder network up to 6-sections. Although it is an analytical solution, there are issues which prevent its implementation with actual FRA data. Keeping the above aspect in mind, the second part of the thesis presents results of employing an artificial bee colony search algorithm for synthesizing a mutuallycoupled lumped-parameter ladder network representation of a transformer winding, starting from its measured magnitude frequency response. The bee colony algorithm is modified by defining constraints and bounds to restrict the search-space and thus ensure synthesis of a nearly-unique ladder network, corresponding to each frequency response. Ensuring near-uniqueness while constructing the reference circuit (i.e., a uniform healthy winding) is the objective. The proposed method is easy to implement, time-efficient, ensures physical realizability and problem associated with supply of initial guess in existing methods is circumvented. Experiments were performed on two types of actual, single, isolated transformer windings (continuous-disc and interleaveddisc) and the results are encouraging. Further details are presented in the thesis.