Programmable Logic Controller System Research Articles

Practical PLC Applications

تعتبر انظمة التحكم المبرمجة من الاجهزة الشائعة الاستخدام في العمليات الصناعية بسبب استجابتها السريعة وخصائصها الاخرى التي تميزها عن الاجهزة الاخرى. وقد تم في هذا البحث شرح ووصف اجهزة التحكم المبرمجة اضافة الى تنفيذ ثلاثة انظمة عملية باستخدام انظمة التحكم المبرمجة وهي:
 عملية التثقيب وعملية التحويل والمصعد الكهربائي
 ونلاحظ من خلال تنفيذ البرامج الخاصة بهذه العمليات ان اي خطأ يؤدي الى عدم عمل اي نظام وهذا يؤشر لنا مدى دقة هذه الاجهزة كما ان عملية تصحيح الخطأ او الصيانة أسهل نسبيا من الاجهزة الاخرى..

Specifying and verifying PLC systems with TLA+ : A case study

We report on a method for formally specifying and verifying programmable logic controllers (PLCs) in the specification language TLA+. The specification framework is generic. It separates the description of the environment from that of the controller itself and its structure is consistent with the scan cycle mechanism used by PLCs. Specifications can be parameterized with the number of replicated components. In our experience, the structuring mechanisms of TLA+ help to obtain clear, well-organized, and configurable specifications, finite instances of which are verified by the TLA+ model checker TLC. We have validated our approach on a concrete case study, a controller for fire fighting equipment in a ship dock, and report on the results obtained for this case study.

Design, Construction, and Testing of an Automated NIR In-line Analysis System for Potatoes. Part II. Development and Testing of the Automated Semi-industrial System with In-line NIR for the Characterization of Potatoes

An automated semi-industrial system with in-line near-infrared reflectance (NIR) for the characterization of the chemical composition of potatoes was designed and constructed, and its performance was tested. The system consisted of the following subsystems: sample crate manipulator, weighing unit for the gross sample weight, potato washing machines with a washing water recycling system, belt for visual inspection of the potatoes, unit for measuring the underwater weight (UWW), industrial rotary saw blade rasp for pulping the potatoes equipped with a sulfite dosage system for inhibiting enzymatic browning of the pulped potatoes, and industrial NIR system for the measurement of the potato composition. The whole system was controlled and operated by a programmable logic controller and process personal computer system. The system was able to process 12 potato samples per hour. Measurements were done to establish the sample carry-over in the system. The carry-over was proven to be well below the maximum acceptable level of 2%. The UWW values established with the automatic system corresponded very well with the UWW data obtained by manual weighting. The day-to-day reproducibility of the UWW system was tested with golf balls. These balls have about the same specific gravity and size as potatoes. The day-to-day reproducibility coefficient of variation of the UWW unit was 0. 4%. As a principle of proof, two tentative partial least squares calibration models, one for the starch concentration and one for the coagulating protein concentration in the potato samples, were calculated, applying leaving one out cross-validation. Both models were very promising. The by NIR-predicted starch concentrations showed to be at least as good or even better than the by UWW-obtained starch concentrations. The average difference between the by NIR-predicted and the chemically measured starch concentration was 0. 0 ± 0. 3% (w/w). For the coagulating protein concentration, the average difference between the by NIR-predicted and the chemically measured concentration was 0. 00 ± 0. 06% (w/w). In future years, potatoes of a wider range of varieties, growing locations, and growing seasons have to be added to the present tentative model, in order to get a robust NIR model. © 2010 EAPR.

Reliability Analysis of a Hot Standby Industrial System

Industries/plants, such as Fibre Optic plant and casting plants, often use programmable logic controllers (PLC) as a two-unit/two-PLC hot standby systems. Optimizing profit and avoiding the major losses are the main objectives of using a two-unit hot standby PLC system. In the two-unit system, one unit is operative and the other is a hot standby. The hot standby unit also fails, but with lower failure rate than the operative unit. The paper outlines a reliability analysis of a two-unit hot standby PLC system, and the real data from an industrial system has been used for the purpose. Four types of failure are seen in the PLCs: input module failure, digital relay burnt/power supply failure, complete unit burnt failure and failure due to corrupted software. The concept of inspection is introduced to detect the type of failure. The model developed is embedded by the types of failure actually depicted in the data and the real failure, repair, replacement, reinstallation rates are used for analysis. Measures of system effectiveness in terms of reliability indices are obtained using semi-Markov processes and regenerative point techniques. Profit incurred to the system is evaluated and related graphs pertaining to the case example are also shown.

Special automation and regulation strategies for enhancing sequencing batch reactor (SBR) performances

Dynamic simulation analyses of five different sequencing batch reactor (SBR) wastewater treatment plants (WWTPs) were used in order to optimise developed regulation strategies and to develop new strategies. The results were applied directly to 15 full-scale SBR plants. To do this, the cycle strategies were extended through the use of appropriate aggregates, or were anchored in the programmable logic controller (PLC) and process control system (PCS) with the help of online sensors. This enabled all regulation strategies to be introduced and automated without problems.

The CMS Tracker Detector Control System

The Compact Muon Solenoid DCS (CMS) Silicon Strip Tracker is by far the largest detector ever built in micro-strip technology. It has an active surface area of 198 m 2 consisting of 15,148 silicon modules with 9,316,352 readout channels read via 75,376 Analog Pipeline Voltage (APV) front-end chips and a total of 24,244 sensors. The Detector Control System (DCS) for the Tracker is a distributed control system that operates ∼2000 power supplies for the silicon modules and also monitors its environmental sensors. The DCS receives information from about 10 3 environmental probes (temperature and humidity sensors) located inside the detector's volume and values from these probes are driven through the Programmable Logic Controllers (PLC) of the Detector Safety System (DSS). A total of 10 5 parameters are read out from the dedicated chips in the front-end electronics of the detector via the data acquisition system, and a total of 10 5 parameters are read from the power supply modules. All these parameters are monitored, evaluated and correlated with the detector layout; actions are taken under specific conditions. The hardware for DCS consists of 10 PCs and 10 PLC systems that are continuously running the necessary control and safety routines. The DCS is a fundamental tool for the Tracker operation and its safety.

Application of PLC to dynamic control system for liquid He cryogenic pumping facility on JT-60U NBI system

The control system of the cryogenic facility in the JT-60 NBI system has been replaced by employing the PLC (Programmable Logic Controller) and SCADA (Supervisory Control And Data Acquisition) system. The original control system was constructed about 20 years ago by specifying the DCS (Distributed Control System) computer to deal with ∼400 feedback loops. Recently, troubles on this control system have increased due to its age-induced deterioration. To maintain the high reliability of the cryogenic facility, a new control system has been planned with the PLC and SCADA systems. Their attractive features include high market availability and cost-effectiveness, however, the use of PLC for such a large facility with ∼400 feedback loops has not been established because of insufficient processing capability of the early PLC. Meanwhile, the recent progress in the PLC enables to use the FBD (function block diagram) programming language for 500 function blocks. By optimizing the function blocks and connecting them in the FBD language, the feedback loops have been successfully replaced from DCS to PLC without a software developer. Moreover, an oscillation of the liquid He level, which often occurs during the cooldown mode of the cryopumps, can be automatically stabilized by easily adding a new process program in the PLC. At present, the new control system has worked well.

Reliability and Profit Evaluation of a PLC Hot Standby System Based on a Master-Slave Concept and Two Types of Repair Facilities

Programmable Logic Controllers (PLC) are frequently used by a good number of companies like steel plants, biscuit manufacturing companies, etc. Various plants/companies use two PLC at a time: one operative, and the other as a hot standby to avoid big losses. Analysis of the reliability, and profit of a hot standby PLC system is of great importance; and hence the present paper examines such a system wherein two PLC are working in master-slave fashion. Initially, the master unit is operative, and the slave unit is in hot standby. The slave unit can also fail, but with a lower failure rate than the master unit. The master unit has the priority of operation ∓mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp;mp; repair over the slave unit. While operating, the latest information from the master unit keeps on transferring to the slave unit. There are three types of failure: minor, major-repairable, and major-irreparable. The ordinary repairman who stays with the system repairs the minor failures. The expert repairman who is available upon demand repairs the major failures. Various measures of the system effectiveness, such as the mean time to system failure, steady-state availability, busy period of the ordinary as well as expert repairmen, expected number of replacements, etc. are obtained by using semi-Markov processes, and regenerative point Techniques. Profit incurred to the system is evaluated, and a graphical study is also made. Real data from an industrial application is used in this study.

Development of a compact sample pre-concentration system for the detection of a trace amount of volatile organic compounds (VOCs)

A new pre-concentration system was developed for a trace detection of VOCs by adopting a ceramic heater, a dc power supply, a three-way solenoid valve, a micro-diaphragm pump, and a programmable logic control system. The adopted ceramic heater was made by coating carbon powder onto the inner wall of a ceramic tube and by additional coating of silver paste both on the inside as well as outside of the rims of a ceramic tube to create electrical connection with dc power supply. Various adsorbing materials, such as charcoal powder, molecular sieve, and Tenax-TA, were packed inside the ceramic heater for pre-concentration of VOCs from a sample reservoir. The ceramic heaters were prepared to have a resistance ranging from 10 to 25 Ω, and the heating time was optimized from 8 to 16 s in order to maximize the thermal desorption of the adsorbed VOCs while avoiding any possible damage to the ceramic heater. The performance of the developed system was estimated by measuring the enhancement of ion signals for VOCs by using the pre-concentration system and the laser photoionization mass spectrometry. The signal enhancement was identified to be better than 40 when compared to the signals measured without the pre-concentration device.

Exceptions in a Programmable Logic Controller implementation based on ADA

In this work we propose an implementation of IEC 61131-3 Programmable Logic Controller (PLC) software model based on ADA programming language. The guidelines for an IEC 61131-3 to ADA translator are shown. This translator would allow obtaining executable code after compiling the ADA code. In this way, most error conditions that the standard foresees for PLC systems can be managed by the usual ADA compilers or the run-time environment, thus improving software quality. In addition, we show how to manage user- or system-defined error conditions in two ways: first, by proposing ADA-like exception statements in IEC languages; second, by showing an implementation of the error tasks that are explained in part 8 of IEC 61131 standard. Therefore, we conclude that ADA is a suitable target language for PLC.

New 30 kA Power System at Fermilab and Its Use for Measuring the Effects of Ripple Current on the Performance of Superconducting High Field Magnets

A new 30 kA, 30 V dc Power System was designed, built, and commissioned at Fermilab for testing Superconducting High Field Magnets. This system has been successfully supporting operations at the Fermilab Magnet Test Facility since April 2002. It is based on six commercial 150 kW Power Energy Industries power supply modules and the following in-house modules: six 720 Hz filters, two 15 kA/1 kV dc solid-state dump switch, and a 3 MJ/30 kA/1 kV dc dump resistor. Additional in-house electronic components were designed and built to provide precise current regulation and distribution of current and current rate of change. An industrial-type Programmable Logic Controller system was used to provide equipment interlocks and monitoring. This paper summarizes studies on the influence of characteristics of this new power system-such as ripple current-on the performance of High Field Superconducting magnets.

A Web-based programmable logic controller laboratory for manufacturing engineering education

This study presents the design and development of a Web-based programmable logic controller (PLC) system architecture that supports “hands-on” laboratory exercises in automated manufacturing systems control area for distance education. The system architecture allows remote users to access and control a PLC-based table-top manufacturing system via the Internet. A Web site has been designed and developed that facilitates interactivity and supports PLC programming and control. The architecture has been tested and implemented in the course Emgt 334 Computer Integrated Manufacturing Systems at the Integrated Systems Facility (ISF) in the Engineering Management Department at the University of Missouri-Rolla during Fall 2001. This study shows that software tools available in the market can be integrated to develop a fairly complex, yet effective, learning environment for distance education. The architecture presented in this paper is not dependent on specific PLC hardware or software configuration, it represents a generic infrastructure.

Bringing theory and reality together through CIM

Computer Controls and networks are at the heart of CIM (Computer Integrated Manufacturing) cells. The interdisciplinary nature of CIM cells brings Computer Science students together with Engineering Technology and other students face to face with real world problems. Texas A&M University Corpus Christi is currently developing a funded CIM cell laboratory that will be used in three Computer Science courses and four Engineering Technology courses. The courses include Manufacturing Processes, Programmable Logic Controllers, Control Systems, Capstone Projects, Systems Programming, and System Analysis and Design. The Mechanical Engineering Technology students benefit from the study of mechanical components, the design of tooling and fixtures, the selection of material handling equipment, pneumatic actuators and clamps, and the relationship of material selection to the manufacturing process. The Control Systems Engineering Technology students study the use of sensors, data acquisition, actuators, networking of equipment, robot controllers, programmable logic controllers, and the communication of the cell with overall factory operations. The Computer Science students will focus on the development of controlling algorithms, cell control, user interfaces, networking, and the manipulation and analysis of the data collected. The students of each of the three majors will benefit from working in interdisciplinary groups to solve real-world-like problems. [6,7]

Replacement of a multiple hearth by a fluid bed incinerator the Greensboro case history

The incinerator at the T.Z. Osborne Plant in Greensboro, North Carolina burns sludge from its own waste water treatment plant and sludge pumped from the nearby North Buffalo plant. The two plants have a combined capacity of 36 million gallons per day of wastewater. Because of the age of and increasing high maintenance on the existing multiple hearth incinerator, and the need to increase treatment capacity, the Osborne plant concluded a study in 1992 evaluating its options for future municipal sewage sludge disposal. Options which were evaluated during the study included; (i) rehabilitation of the existing eight-year old multiple hearth unit; (ii) addition of a new multiple hearth; (iii) addition of a new fluid bed system; (iv) drying, composting, or land application. The chosen option, based on both economic and environmental considerations, was a new fluid bed system with a capacity of 2.55 tons per hour, approximately double that of the existing multiple hearth. Design of the new fluid bed system began in December 1994 and equipment delivery for the incineration system was begun in April 1995. Initial operation occurred in August 1996. Primary and secondary sludge, dewatered to 28% dry solids by centrifuge, is delivered by piston pumps to the twenty-foot freeboard ID incinerator. A shell and tube heat exchanger recuperates heat from the exhaust gas and preheats the combustion air to 1250°F, resulting in minimal auxiliary fuel use. The air pollution control device is a high-energy Tandem Nozzle® scrubber. Greensboro was the initial installation of this scrubber design on a fluid bed incinerator and its characteristics and performance are discussed. Ash is dewatered in an ash thickener/belt press system prior to disposal to landfill. The system includes a state of the art Programmable Logic Controller (PLC) system for computer control of the operation. The unit was commissioned in August 1996 and has been in continuous operation since that time except for a one week inspection and maintenance shutdown in February 1999. The plant operates 24 h/day, 7 days per week. The initial performance test showed the system to readily meet federal and state air emission standards. Particulate released was 0.002 grains per dry standard cubic foot, carbon monoxide was 22.5 parts per million volumetric (ppmv) and opacity was 0.4%. These results show a significant emission reduction with the fluid bed when compared to the multiple hearth. Annual tests conducted since then and continuous emission monitoring have shown the unit to be in consistent compliance. Since the fluid bed system became operational, the old multiple hearth system has been maintained on standby as a backup, but its use has not been required. Operational experience is discussed, the most interesting of which is the relatively trouble-free operation. The minor problems which occurred and their solutions are detailed. Also included is a comparison of operation and maintenance experience of the fluid bed and the multiple hearth. Current sludge disposal actual cost data are also provided including the average cost per ton of dry solids treated. The almost three years of operational experience to date has shown that the decision to install a new fluid bed system was the correct one on both an environmental and economic basis. It has provided benefits to all interested parties — the wastewater treatment plant, the regulators, the taxpayers, and the surrounding community.

Grafcet revisited with a synchronous data-flow language

The Grafcet (or sequential function charts) language is a graphic language often offered in programmable logic control systems (PLC) used for industrial control-command applications. Modeling of Grafcet by the synchronous data-flow language Signal gives both explicit semantics, and the corresponding simulator. The translation into a graph of tasks makes it possible to execute the Grafcet program on any hardware architecture. Moreover, the use of Signal's proof tools allows verification of Grafcet properties, opening the field of critical applications to this very expressive language.

Design of a VMEbus-based programmable logic controller (PLC)

This paper presents an overall view of the architecture and design of a programmable logic controller (PLC). The main objectives of the work are to design, develop, and implement a versatile PLC processor module (PLCPM) based on an industrial open bus architecture called VMEbus (IEEE 1014 Versa Module Euro-standard). The controller is inserted inside the VME crate and controls the industrial process via input and output modules that reside in the crate. The PLCPM is designed to be an intelligent module through the use of a Motorola MC68000 CPU. A method of distributed arbitration protocol, based on an algorithmic state-machine design approach, is added to the design of this module. This facility makes PLCPM suitable to work inside a VMEbus environment. The PLCPM therefore becomes adequate for use in multiprocessing PLC systems. The controller uses a host personal computer (IBM-PC) as a versatile and indispensable system component for process development, monitoring, control and supervision. Software and firmware programs are developed and written for both host-PC and PLCPM using standard C-language and 68000 assembly language, respectively. This results in a sequential control algorithm for the PLCPM and windowing user interface for the host-PC. Ladder diagram programming language is supported by this user interface.

A hybrid, knowledge-based system as a process control ‘tool’ for improved energy efficiency in alumina calcining furnaces

This paper describes the development and implementation of a hybrid SCADA (Supervisory Control and Data Acquisition) system for the air suspension ‘flash’ alumina calciner at Aluminium de Grece St. Nicholas plant. The system includes two additional modules, an ‘expert system’ based on 10 years of commissioning and operating experience and a dynamic model continuously predicting the quality of the product. It is implemented on an industrial PC under an industrial control software environment and interfaces to the furnace through a programmable logic controller (PLC) system. The system guides the furnace operator to reduce sensible heat losses by operating with a marginal excess air flow rate, to take advantage of the higher energy efficiency at higher production rates and, at the same time, to avoid potentially dangerous operating conditions leading to loss of production and consequential energy losses. It also performs the traditional SCADA functions (data acquisition, maintaining history files for important parameters and display of important operating parameters in both a mimic process diagram and a series of graphs.) In addition to these tasks a simplified dynamic model gives the operator a prediction of the current value of the main product quality parameter, which can only be measured with laboratory equipment. Preliminary results have shown that reduction of secondary air flow rate and reduced downtime achieved by the operator under the guidance of the system can reduce energy consumption by as much as 10%. A similar, or even greater, improvement in energy efficiency can be expected by implementing a similar system to cement calcination kilns based on the same technology.

An event chaining relay ladder logic solver

Relay ladder logic (RLL) remains a dominant modeling language in programmable logic control (PLC) systems. RLL uses flow over a relay ladder structure as the control model state. Event chaining, a requirement for discrete systems, is applied to ladder solving. An event chaining relay ladder solver, the “Event Sweep”, is described in detail. The Event Sweep maintains a complete ladder flow state, and therefore supports on-line display of ladder logic. Scan times of existing ladder solving methods depend on the size of the ladder model. It is shown how RLL solving can be limited to flow calculation along “hot” flow paths, and to “eligible” networks in which contact switches can influence coil values. The Event Sweep algorithm limits solving to downstream changes in ladder flow caused by the opening and closing of contacts.

Kiss your PLC

The sage adage, “ Keep it small and simple,” provides a memorable acronym (KISS) and good advice for any venture involving complex computers. Yesteryear efforts to incorporate this technology into the traditionally conservative realm of water and wastewater engineering all too often overlooked this KISS approach, however, falling headlong into an electronic abyss that still haunts those plants that strayed too far too fast. Hence, the field has recently begun to shift downward in scale and sophistication, towards a hardware grouping largely dominated by a low-end product known as a programmable logic controller (PLC). Indeed, these PLC's systems appear to offer a prime opportunity for small-to-medium scale water and wastewater treatment facilities to explore a wide range of monitoring and control regimes with minimal financial risk…fully within the KISS context! This paper will, therefore, explore the conceptual development of three small-scale PLC applications that largely emphasize a process oversight or “caretaker” role, but which also have clear potential to incorporate additional missions and responsibilities relative to their affiliated control requirements.

Use of advanced programmable logic control systems in continuous production CIP plants: A. Freeman, (Stanstead Fluid Power Ltd., Stanstead, UK)

Use of advanced programmable logic control systems in continuous production CIP plants: A. Freeman, (Stanstead Fluid Power Ltd., Stanstead, UK)