logiccontrollers for machining systems typically have three control modes: auto, hand, and manual. Hand and manual modes are designed for various fault recovery operations in machining systems. In this paper, a unifi...
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logiccontrollers for machining systems typically have three control modes: auto, hand, and manual. Hand and manual modes are designed for various fault recovery operations in machining systems. In this paper, a unified formal representation of logiccontrollers with three control modes is provided using Petri nets. A modular logic controller structure is introduced and formalized for reconfigurable high-volume transfer lines. The modular logic controller consists of a control module for mode decision and control modules for station logiccontrollers. Each station control module is represented by connecting operation modules which are designed with respect to the fault recovery processes of operations;their connection algorithm is also provided. In our formal representation, each control module is represented by a live, safe, and reversible Petri net. A condition for the modular logic controller to generate a correct control logic is provided.
In most industrial plants, there is a strong drive to provide business applications with some access to real-time data generated from process control systems. Often, this has been in the form of a process historian da...
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In most industrial plants, there is a strong drive to provide business applications with some access to real-time data generated from process control systems. Often, this has been in the form of a process historian database server connected to both the distributed control systems/programmablelogic controller (DCS/PLC) systems and the business users. It can also take many other forms such as remote X-Windows sessions from the DCS, or direct file transfers from PLCs to users spreadsheets. Regardless of the method, it involves a network connection to both the process and the business side. These network connections are increasingly Ethernet based on both sides, rather than proprietary industrial protocols. At the same time, most control systems now use Ethernet networking as a critical component of their system architecture. This can be for controller-to-controller communications, controller-to-operator console communications or even I/O-to-controller communications. Losing any of these links will directly impact production.
This paper deals with the possibility of introducing exception handling mechanisms into the specification and code of industrial process control software. Although exception handling is a very important aspect of proc...
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This paper deals with the possibility of introducing exception handling mechanisms into the specification and code of industrial process control software. Although exception handling is a very important aspect of process control applications, in most cases it is treated in an ad hoc and unstructured manner - which is mainly caused by the lack of appropriate constructs in programming languages for programmable logic controllers. A high degree of mastery of the development process can be achieved by applying an engineering process based upon life cycle and domain engineering concepts. The main result of domain engineering is a conceptual model of the domain in question. One of the elements of the conceptual model is the specification language with a defined exception handling construct. The exception handling construct is illustrated by a real application excerpt. It would be useful to include this exception handling construct into the Structured Text controller programming language. (C) 2000 Elsevier Science B.V. All rights reserved.
This paper describes an HPLC procedure for the determination of tocopherols and tocotrienols in crude and edible vegetable oils. The sample preparation only involves a dissolution of the oil in n-hexane and filtration...
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This paper describes an HPLC procedure for the determination of tocopherols and tocotrienols in crude and edible vegetable oils. The sample preparation only involves a dissolution of the oil in n-hexane and filtration. The chromatographic separation was achieved using a normal phase column LiChrosorb SI 60 (5 mum;25.0 x 0.4 cm). Isocratic elution was carried out using n-hexane :2-propanol (99.7:0.3). The effluent was monitored by using diode-array and fluorimetric detectors. The determinations were performed in the following linear ranges: 0.5-7.5 mug/mL for alpha -tocopherol and beta -tocotrienol;0.5-10 mug/mL for beta -tocopherol;and 0.5-15 mug/mL for alpha -tocotrienol, gamma -tocopherol, gamma -tocotrienol, and delta -tocopherol. Extensive quality assurance of the proposed method was performed by the standard addition method in both crude and edible oil. For edible oil, the precision obtained (n=10) was better than 1.8, 2.0, and 1.4 CV% for alpha, beta, and gamma -tocopherol, respectively;for crude oil it was better than 1.9, 2.4, and 2.4% for alpha, beta, and gamma -tocopherol, respectively. Furthermore, for edible oil the mean recovery values were between 96-116%, 58-69%, and 111-115% for alpha, beta, and gamma -tocopherol, respectively;for crude oil recovery values were between 85-95%, 63-66%, and 99-103% for the same tocopherols, respectively. The proposed method appears to be an adequate method for quality control and helpful for authenticity verification by the official control in oil industry.
In recent years, inhomogeneous plastic deformation associated with the Portevin-Le Chatelier (PLC) has received a renewed attention. The PLC effect, commonly called 'jerky flow' or 'serrated yielding: is t...
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In recent years, inhomogeneous plastic deformation associated with the Portevin-Le Chatelier (PLC) has received a renewed attention. The PLC effect, commonly called 'jerky flow' or 'serrated yielding: is the result of dynamic strain ageing due to dynamic interactions between mobile dislocations, temporarily arrested at obstacles, and dissolved alloying atoms, which diffuse towards disclocations [1]. So, the microstructure can have an important role on the PLC phenomenon and efforts to understand these mechanisms were the subject of previous researches [2, 3]. In this work, essentially experimental, we have changed the ageing conditions in order to investigate the effects of precipitates on the jerky flow and its characteristics.
Signal Interpreted Petri Nets (SIPN) show good properties in modeling and analyzing control algorithms. With SIPN, logiccontrollers are modeled by places-setting output signals-and transitions between those places-de...
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ISBN:
(纸本)0780355199;0780355202
Signal Interpreted Petri Nets (SIPN) show good properties in modeling and analyzing control algorithms. With SIPN, logiccontrollers are modeled by places-setting output signals-and transitions between those places-depending on Boolean functions of input signals. This model has interesting dynamics: Firstly, several transitions can fire simultaneously. Secondly, there can be iterated firing of transitions before a new stable marking is reached. In standard PLC programming languages, there is no direct means to implement these dynamics. In this contribution a method for the generation of transparent PLC code from SIPN is presented (using Instruction List or Ladder Diagram). The code is transparent because there is a one-to-one correspondence between SIPN elements and code segments. A new analytical method to guarantee the correct dynamics of the implemented code is presented and compared to existing approaches. The new method results in a special ordering of the code segments. The presented analysis of the SIPN shows if a transition t(a) can fire in an iteration after transition tb In this case, the code segment describing tb has to be processed prior to the one of t(a). A solution for the case, where the analysis results in an impossible ordering is also presented.
This paper gives a summary of a project, which deals with methods for the proof of the demanded properties of user-written control software. Although these methods based on formal methods they are covered with user-fr...
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ISBN:
(纸本)0780365836
This paper gives a summary of a project, which deals with methods for the proof of the demanded properties of user-written control software. Although these methods based on formal methods they are covered with user-friendly interfaces. The document displays the modelling of a control-system, which consists of a programmablelogic controller (PLC), a user program and the environment, it demonstrates the description of the requirements for this system, and it explains, how we prove these requirements at the generated model.
The paper presents a resource control framework for active IP networks. Generic router resource abstractions are discussed to supporting network programming by a wide variety of active network services. Dynamic partit...
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ISBN:
(纸本)0769509126
The paper presents a resource control framework for active IP networks. Generic router resource abstractions are discussed to supporting network programming by a wide variety of active network services. Dynamic partitioning is described as an adaptive bandwidth allocation scheme to provide safe resource access and efficient multiplexing. Policy in the form of code is use to enable customization by operators via CORBA interface. The framework is a key module in an enhanced ORE, a middleware platform for active services, and can be dynamically installed as downloadable objects.
The goal of this paper is to present the design methodology for the modelling and synthesis of discrete-event controllers for compact, fast and reliable embedded systems, using related Petri net theory, rule-based sys...
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ISBN:
(纸本)0780366069
The goal of this paper is to present the design methodology for the modelling and synthesis of discrete-event controllers for compact, fast and reliable embedded systems, using related Petri net theory, rule-based system theory (conditional mathematical logic), and Hardware Description Languages (VHDL, Verilog), The well-structured specification, which is represented in the human-readable logic language, has a direct impact on the validation, formal verification and implementation of Application Specific logiccontrollers (ASLC) mapped into reconfigurable logic devices (FPGA). Reprogrammable logic controllers (RLC) may replace traditional PLCs in many industrial applications.
This paper describes the application of binary and multi-valued SPFD-based wire removal techniques for circuit implementations utilizing networks of PLAs. It has been shown that a design style based on a multi-level n...
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This paper describes the application of binary and multi-valued SPFD-based wire removal techniques for circuit implementations utilizing networks of PLAs. It has been shown that a design style based on a multi-level network of approximately equal-sized PLAs results in a dense, fast, and crosstalk-resistant layout. Wire removal is a technique where the total number of wires between individual circuit nodes is reduced, either by removing wires, or replacing them with other existing wires. Three separate wire removal experiments are performed. Either wire removal is invoked before clustering the original netlist into a network of PLAs, or after clustering, or both before and after clustering. For wire removal before clustering, binary SPFD-based wire removal is used. For wire removal after clustering, multi-valued SPFD-based wire removal is used since the multi-output PLAs can be viewed as multi-valued single output nodes. We demonstrate that these techniques are effective. The most effective approach is to perform wire removal both before and after clustering. Using these techniques, we obtain a reduction in placed and routed circuit area of about 11%. This reduction is significantly higher (about 20%) for the larger circuits we used in our experiments.
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