Process Control Simulator using Programmable ...

Process Control Simulator using Programmable Controller Technology Iulia DUMITRU1, Nicoleta ARGHIRA1, Ioana FAGARASAN2, Segiu St. ILIESCU2 University Politehnica of Bucharest, 1{id.iulia, arghira.nicoleta}@gmail.com 2 {ioana, iliescu}@shiva.pub.ro

Abstract-The simulation of physical processes represents a modern and efficient direction for multifunctional testing platforms. This paper will present a Process Control Simulator and its applications in system simulation. The Process Control Simulator can be used for students training as well as for the conception, simulation and improvement of control schemes in modern technologies. The simulation of industrial processes reduces the cost and the amount of time needed for deploying the system. The various types of applications, with different complexity factors, are associated with several functional masks. The Process Control Simulator uses a simulation block and a microcontroller for all the applications with different replaceable masks according to the desired application.

The PLC is used for automation of industrial processes and replaces the circuits of sequential command in cable logic. II. The Process Control Simulator In this section we present the components of the simulator. The Process Control Simulator is divided into three sections: the PLC, the microcontroller board and the simulation block that holds a mask (an applied mask according to the desired application) with a large image of the process that is being simulated (figure 1). These three panels are connected between each other.

I. INTRODUCTION This paper will present a hardware and software integrated system that enables training and practical work (referred to as the “Process Control Simulator”). A Process Control Simulator can replace a vast number of expensive systems or functional models. It can be used for vocational training in order to practice programming of programmable logic controllers (PLCs) as well as for simulation, testing and analyzing command diagrams before the actual deployment of the solution [5]. The functional solution for the simulation of industrial processes is projected into an innovative system that implements the “hardware-in-the-loop” concept. This solution implies the use of dedicated structures – digital/sequential reprogrammable structures, PLCs, microcontrollers and PCs. The current trend in terms of design of the control and monitoring systems is the use of PLC and microcontroller units. Therefore it is important to study, develop and test their functioning. A programmable logic controller (PLC) or programmable controller is a control device, used for the control of applications, which employs the hardware architecture of a computer and a relay ladder diagram language [2]. The unit has to be connected to the various process input and output devices. A microcontroller (also microcomputer) is a small computer on a single integrated circuit consisting internally of a relatively simple CPU, clock, timers, I/O ports, and memory. The equipment simulates sequences that are initiated by inputs from the process, which then prompt the outputs to change the plant status. The Process Control Simulator has a hardware structure that ensures stability, accuracy and good transitions. These performances are obtained by the interconnection of PLCs and a PC.

Figure 1. The Process Control Simulator.

The actual process can be simulated only with the help of the corresponding mask, applied on the simulation panel, and the PLC program which can be obtained in two different ways: • using the program implemented by the user and transferred from the PC (The user interface – The programming software) into the PLC’s memory; • using the program implemented into the microcontroller memory and transferred into the PLC’s memory. Several programs, with the tasks that the system must perform, are implemented in the microcontroller’s memory; this is achieved by a set of software instructions. The connected and correspondingly programmed PLC system allows the user to study automatic functions, for which respective signals are generated automatically while controlling the actuators. These automatic functions depend on the assigned process. The exercises cover a wide range of levels of complexity. They range from the simulation of elementary control processes for complete beginners, with no previous know-

ledge of automation technology, right up to the simulation of the most demanding solution strategies. This is obtained by applying the complete operational spectrum of large programmable memory controllers. The individual examples are obtained with masks that contain a process flow chart and are applied to the simulation panel of the Process Control Simulator [1]. Three categories of exercises were developed: • Simulation of simple assignments using classical contactor circuits (reversing contactor, delta-star connection, reversing delta-star connection, Dahlander circuit, motor with 2 separate windings) [1]. • Simulation of medium difficulty assignments using industrial system models (conveyor belt system, heating control, tank system, coal grinder, embossing machine) [1]. • Simulation of complex assignments using industrial system models with the incorporation of analog functions (silo control, reactor, goods lift, pump control, monitoring of 3 pumps) [1]. A. The central unit (The PLC) All the inputs and outputs of the Modular Process Simulator have been designed to meet the industrial standards for control engineering: 24 V DC for digital inputs/outputs and from 0 to 10 V DC for analog inputs and outputs [7]. As a result, the simulator can be operated with the programmable logical controller systems of all major manufacturers. The PLC used in this case is a SIMATIC S7-300 series, a system which is able to withstand real industrial conditions during the entire simulations and training actions. The standard software used for configuring and programming Simatic programmable logic controllers is Step 7. The programming languages which can be used for the S7-300 are Ladder Logic, Statement List, and Function Block Diagram: • Statement List (or STL) is a textual representation, similar to machine code. If a program is written in Statement List, the individual instructions correspond to the steps by which the CPU executes the program. To make programming easier, Statement List has been extended to include some high-level language constructions (such as structured data access and block parameters) [3]. • Ladder Logic Diagram (or LAD) is a programming language primarily used to develop software for Programmable Logic Controllers (PLCs) used in industrial control applications. LAD represents a program by a graphical diagram based on the circuit’s diagrams of relay-based logic hardware. The name comes from the observation that the program language resembles ladders, with two vertical rails and series of horizontal rungs between them. Ladder allows you to track the power flow between power rails as it passes through various contacts, complex elements, and output coils [4]. • Function Block Diagram (FBD) is a graphic representation and uses the logic boxes familiar from boolean algebra to represent the logic. Complex func-

tions (for example, math functions) can be represented directly in conjunction with the logic boxes. Inputs and outputs of the blocks are wired together with connection lines, or links. The S7-300 is a modular control system for industrial solutions with a main emphasis on production engineering. The wide ranges of assemblies are ideally suited to cope with all required demands and a flexible application. The S7-300 contains the following types of modules: • Central processing units (CPU) • Power supply modules (PS) • Interface modules (IM) • Communications processors (CP); (for connecting to PROFIBUS) • Digital and analog modules which are now called “signal modules” (SM) [6]. As in a real application, the S7-300 modules are plugged into the profiled rail on the basic plate, fastened and connected to each other via the rear panel bus to be system compatible. The system is quickly and safely connected electrically to the inputs and outputs on the modules with the respective connector adapter. Due to its construction, the system is ready for future expansion. B. The microcontroller board Several applications are implemented in the microcontroller’s memory. Each application has an address memory. All the masks (all the processes) are assigned a specification number which can be found in the bottom left corner off the mask. The microcontroller is linked with the simulation panel with the help of the code switch. The same setting of the code switch with the one on the mask defines the address memory where the application is stored. The stored program is then transferred automatically to the PLC. Depending on the applied mask and the respective setting of the code switch, different industrial processes can be simulated. C. The simulation panel The simulation panel is operated with a stabilized DC voltage of 24 V, e.g. supplied with the power supply unit of the PLC system. The sockets are used to connect the sensors and switches on the system simulator to the PLC system. The safety sockets on the system simulator are connected to the sensors and switches according to the assignment. Each of these switches and sensors can physically act as make or break contact depending on the setting of the respective selector with the same marking. Sockets 0 to 7 are used to connect the actuators on the applied mask, e.g. relay and contactor coils to the PLC outputs. The operating state of an actuator is indicated with a LED assigned to the symbol. Sockets H1 to H4 are directly connected to the signal lamps or LEDs H1 to H4 on the control panel. All the switches, signal lamps and potentiometers required for operating the control circuit illustrated on the applied mask are clearly arranged on the control panel. Only the control elements labeled on the control panel are visible, corresponding to the applied mask.

The simulation panel contains LEDs to indicate the operating states of the actuators, such as relay and contactor coils. The LED strip, for example, clearly indicates filling levels and dynamic behavior. III. Case study In the following section, let us illustrate a relevant case study - the embossing machine - from the second specified category of applications. The characteristic and the operation of the process is depicted in a mask as figure 2 shows (the mask’s view from the simulation panel). In order to build the command procedure for this process, some steps need to be followed: drawing the PLC terminal diagram which contains pushbuttons and sensors (figure 3), drawing the process chart (table 1) and writing the PLC program (table 2). The final step is downloading the program into the PLC and then starting the simulation. The process can also be simulated using a second method. This method consists in the adjustment of the same setting of the code switch with the one on the application mask. Following this procedure the program will be transferred into the PLC unit and the simulation can start. A. The assignment The assignment consists of modeling an embossing machine that has 4 pistons - each cylinder is activated by a valve - four limit sensors (used to determine the extension and the retraction limits of the cylinders), one presence sensor and one light barrier. The user can control the embossing machine with the help off five pushbuttons. By pushing a corresponding button a voltage is applied to one solenoid valve and the respective LED is lit. After a few seconds, the piston rod is extended and the corresponding sensor is automatically activated. If the solenoid valve is disconnected from the voltage supply (the LED will turn off), the piston rod retracts within a few seconds (the compressed air in the cylinder can escape into the atmosphere via the nonconducting valve). When the machine is set in the initial position, all four valves are closed, so that the piston rod of the single cylinders springs back. The matrix is empty (a blank in the matrix is indicated as an LED segment). When the machine is switched to initial position, the automatic mode can be started by pressing pushbutton B1. The indicator lamp H1 will lit during the automatic operation. If an embossing cycle is started, valve V1 opens and a blank is moved from the dropping magazine into the matrix. When sensor S2 indicates that the matrix has been filled correctly, valve V1 closes and valve V2 opens. The coining die moves down and back to the initial position after the sensor signal from S3 has been triggered and after remaining in its position for 3 s. When the sensor S4 has been activated, the embossing process is finished, so that valve V3 opens and the embossed part is removed from the matrix. When sensor S5 is activated, valve V4 also opens to blow the embossed part into the collecting container. When the embossed part drops into the collecting container, the reflex light barrier S5 is triggered and valves

V3 and V4 close. If sensor S6 is triggered, a new embossing cycle can be initiated. After one embossing process is finished, the next one will be started automatically. If pushbutton B3 “Stop” is pressed, the started embossing process will be finished, but another embossing process will not be initiated. If pushbutton B0 “Stop” is pressed, the started embossing process is immediately stopped. The control can be changed to manual operation with pushbutton B2 “man”. This mode is indicated with the lit indicator lamp H2. The subsequent operational sequences are each started by pressing the pushbutton B5 “individual step” if the switching conditions are fulfilled. Each valve remains open during the corresponding operational sequence as long as pushbutton B2 is pressed. If you switch from automatic mode to manual mode during operation, the started embossing process will be interrupted, i.e. the control stops in the actual process stage. The remaining control sequence can be continued step by step with pushbutton B5. If, due to an incorrect PLC program, a blank is inserted into the matrix before an embossed part has been removed, a short alarm signal will be heard.

Figure 2. The mask for the embossing machine view from the simulation panel.

B. The solving procedure The PLC program must be set up using the PLC terminal diagram, the process chart, the assignment list according to the functional description and the used PLC. After that, the program will be downloaded into the PLC and then the simulation of the process can start.

Figure 3. The PLC terminal diagram

The process chart for the functional description is shown in the table below (table 1): TABLE I THE PROCESS CHART[8]

The PLC programming software used is STEP 7 V5.2. The program written in Statement List Language is shown in table 2: A

"B1" S "H1" AN "B0" R "H1" A "B3" S #Release A "B4" ON "H1" R # Release AN # Release A "H1" X( A "Clock" A #Step3 A "V2" A #Release ) = "H4" A "B5" AN "H2" O "H2" A #Release = #Var1 A "B2" FP #Merker1 X "H2" = "H2" A #Var1 A "S1" A "S2" A "S4" AN "V1" AN "V2" AN "V3" AN "V4" S #Step1 A #Step2 ON "H1" R #Step1 A #Step1 A #Var1 AN "B2" A "B4" S #Step2 A #Step3 ON "H1" R #Step2 A #Step2 A "B3" S #Step3 A #Step4 ON "H1" R #Step3 A #Step3 A #Var1 AN "B2" A "B4" A "Timer1" S #Step4 A #Step5 ON "H1" R #Step4 A #Step4 A #Var1 A "B6" S #Step5

TABLE II THE STEP 7 PROGRAM[9],[10] // On // System On // Off // System Off // Start // Stop // System On // System On

// Pilot lamp stop // Single Step // Pilot lamp manual operation // Pilot lamp automatic operation // Start variable // man./auto // Pilot lamp automatic operation // Start variable // Sensor 1 // Sensor 2 // Sensor 4 // Slide gate valve V1 // Ram piston valve V2 // Ejector valve V3 // Air nozzle valve V4 // Vane // System on

// Sensor 2 // Sensor 4 // Stamps

// Sensor 3 // Delay

// Sensor 2 // Sensor 4 // Ejector

// Sensor 6 // Air nozzle

A A A

A

A

A "B5" ON "H1" R #Step5 #Step1 = "Y1" #Step2 S "Y2" #Stept3 L S5T#3S SD "Timer1" A "Timer1" ON "H1" R "Y2" #Stept4 S "Y3" A "B5" ON "H1" R "Y3" #Step5 = "Y4"

// Light barrier

// Slide gate valve // Ram piston Valve

// Ejector valve // Light barrier

// Air nozzle valve

The Process Control Simulator can be used for vocational training in order to practice programming of PLCs. It can be used for testing and analyzing command diagrams before the actual deployment. The PLC systems can simulate the real processes with several masks, as shown in the case study. PLCs have the great advantage that the same basic controller can be used with a wide range of control systems. To modify a control system and the rules that are to be used, all that is necessary is for an operator to set a different set of instructions. There is no need to rewire. PLCs are optimized for control and command tasks and the industrial environment. The presented simulator has a hardware, as well as a software component, used for better transitions and stability during process functioning. The software component allows programming for different control assignments using one of the three languages: Ladder Logic, Statement List, and Function Block Diagram. The simulator is an “open” equipment as it can be developed further on future technologies. This characteristic allows an easy development of the system and can be use in future development by adding FPGA (Field-Programmable Gate Array) components. In this case the commands procedure or process simulator could be implemented using FPGA technology and the system will be used for training and testing using both technologies PLC and FPGA. REFERENCES

[2] [3] [4] [5] [6] [7] [8]

FJ.Molina, J. Barbancho, C. Leon, A. Molina, A. Gomez, Using industrial standards on PLC programming learning, Proceedings on Mediterranean Conference on Control & Automation, Volumes 1-4, Pages 390395, 2007 [10] Frank D. Petruzella, Programmable Logic Controllers, 3rd edition, McGraw-Hill Ed. US 2005, ISBN 0078298520 / 9780078298523, 482 pages

Biographies

IV. Conclusion

[1]

[9]

Fagarasan, I., S.St. Iliescu, I. Dumitru, “Process Simulator using PLC technology”, UPB Scientific Bulletin, Series C: Electrical Engineering, vol. 73, nr. 1, ISSN 1454-234X, 2010 W. Bolton, “Programmable Logic Controllers”, Elsevier Ed., July, 2006, ISBN-13: 978-0-7506-8112-4, ISBN-10: 0-7506-8112-8, 304 pages Popescu, D., “Automate programabile”, Editura Matrix Rom, 2005. Ivanescu, N., T. Borangiu, S. Brotac, “Automate programabile. Teorie si probleme rezolvate”, Editura Printech, 2002 *** Elwe – “Automation, Electrical machines”, Power electronics, 2007 *** Siemens – Programmable Logic Controllers S7-300 Module Data, 2004 *** Siemens – Central processing units, 1999 H. Jack, Automating Manufacturing Systems with PLCs, march 2008, http://www.eod.gvsu.edu/~jackh/books/plcs/pdf/plcbook5_1.pdf.

Sergiu Stelian ILIESCU has received the M.S. (1965) degree from the Power System Faculty, Automatic Control Department and Ph. D. (1979) degree in Computers- Electronics from University Politehnica of Bucharest (UPB). He has started his professional activity in execution and implementation of automatic control equipments and systems, within the Automatic Control System Execution Company (IMIA). The next step was to work as design engineer within Power Systems Studies and Design Institute (ISPE). Since 1968 he is part of the teaching and research team from Automatic Control and Computers Faculty, UPB and acts as Full Professor since 1995. He has experience in process computers (TU Dresden, 1971-1972) and coordinates collaborative research activities with TU Darmstadt (1992-2004), in two research field: in system theory, modelling, identification and control technical processes (Institute of Automatic Technique, TUD) and in power system control and monitoring (Institute of Electrical Power Systems, TUD). His research and teaching domain includes: automatic control theory, informatics system for supervision and control of industrial processes with concern to power system field and system engineering analysis. Ioana FAGARASAN received the M.S. (1996) degree in Electrical Engineering, Specialty - Control Systems and Informatics in Power Systems, and the PhD (2002) degree in Automatic Control from the University Politehnica of Bucharest (UPB). Since 1996 she has been Assistant Professor, Lecturer and is currently Associated Professor in the department of Control Engineering and Industrial Informatics at the UPB. She has participated in research cooperation programs between the University and the Institute for Automatic Control, Technical University of Darmstadt, in the Fault Detection and Identification (FDI) field with application to energetic processes. Between 2002 and 2004 she worked as associate professor at the National Polytechnic Institute of Grenoble (Automatic Control Laboratory) teaching automation control for power systems specialty. Her research interests include control system for technical processes, fault detection and isolation methods, diagnostic algorithms and fault tolerant systems in power system. Iulia DUMITRU received her BSs (2009) degree in Automatic Control from the University POLITEHNCA of Bucharest (UPB). She has participated at an Erasmus mobility at the University Polytech-Lille, France. She is an Associate Teaching Assistant, since the fall of 2009. Currently, she is also, researching for her PhD thesis in the field of control system for industrial and technical processes. Her research interest include fault detection, diagnostic algorithms and fault tolerant systems, automatic control theory, system modelling and identification. Nicoleta ARGHIRA graduated the Power Engineering Faculty, University POLITEHNCA of Bucharest in 2009. She has been an Assistant Professor in the Automatic Control and Computers Faculty since. Currently, she is researching for her PhD thesis in the Power Systems Contol domain. Her research and teaching interests also include automatic control theory and system modelling and identification.