Development of a Real Time Monitoring and Control System for PLC Based Elevator Erdal Irmak, Ilhami Colak, Orhan Kaplan, Ali Kose GAZI UNIVERSITY Faculty of Technology, Electrical and Electronics Engineering Department, 06500 Ankara, Turkey Tel.: +90 / (312) – 212.13.38 Fax: +90 / (312) – 212.13.38
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Keywords PLC, OPC server, Automation, Elevator.
Abstract In this study, real time monitoring and controlling of an elevator prototype based on PLC is developed. The software of PLC has been improved in Simatic Version 4.0 and the main control interface is also developed in Visual Basic as more visual. The system has been applied on a laboratory sized elevator prototype which includes a dc motor, sensors for every floor, gas-smoke detectors and temperature sensor. OPC Server protocol is used to transfer data between the PLC and the control interface. The system developed can be used for not only controlling and monitoring an industrial elevator system but also learning the basic principles of a PLC based system and control strategies of elevator systems as an educational material. .
Introduction As a result of rapid population growth at the cities and multi-stored buildings, need to elevators is being increased. With the rising life standards and attention to human and with the technologic developments, elevator systems are getting better, more fast, stronger and better quality elevators are produced. Previously, most systems were focused on the mounting of elevators, especially after the 1980s the need for elevator maintenance and fault staff have been started to increase [1]. For instance, automatic doors have being used instead of splash doors, microprocessor electronic cards have being used instead of cards with relay, double-speed or speed-controlled elevators have being used instead of one-speed elevators. Such developments provide to improve the quality in elevator systems, develop and diverse the used setting and maintenance or repair tools and instruments and therefore facilitation of the work compared to previous years and increase the reliability of elevator [2]. However, one of the issues is the lack of experienced personnel in the market. Mechanical knowledge for the exercise of the profession, as well as electrical, electronic and software knowledge is also required. The deficiencies in the existing training practical sets lead the education to shift towards more theory. The current test sets controlled only classical control systems have some disadvantages such as trying some failures on test sets experimentally is not possible due to mains voltage operation, the loss of integrity monitoring at the same time on test sets due to the actual size model of the elevators and need to take special safety. For large-scale enterprises, there are three different area of expertise as elevator mounting, elevator maintenance and elevator fault, but at small-scale enterprises mounting and maintenance can be done by the same people. The purpose of this study is to support the training of the trainers who could train the qualified workers about the elevator system. Based on this purpose, a visual and practical elevator education set has been realized based on PLC and up to date software technologies as well as control techniques.
The prototype elevator used in the system has 3 floors and operates on 24 V DC voltages. Siemens S7 200 CPU 224 model PLC with EM235 analogue module is selected as main controller. The system also includes cylindrical inductive sensors, MQ-7 Carbon Monoxide sensors and LM35 heat sensor. Thanks to the system developed, students can learn more skills such as detecting the required input and output elements of the system, connecting the input and output units to the PLC, writing any PLC program, making changes on the program, making the selection of appropriate sensors, operating and testing of the whole system, understanding the error messages and solving system faults.
Hardware structure The system presented consists of four main hardware units: a Programmable Logic Controller (PLC), an analogue module for PLC, an elevator prototype and different types of sensors. requested.
Programmable Logic Controller (PLC) PLC is an electronic device that suitable to realize the control circuits of industrial automation systems. It can control the system via input/output units and equipped with communication interfaces. Program runs under a suitable control system, inherent in the timing, counting, storage and arithmetic operations with the functions of an electronic device provides overall control [3, 4]. PLC is connected to the computer with the RS-485 port via the PPI (Point to point interface) cable and under 24V DC power supply [5]. The most important difficulty for education of the PLC is in the field of application. Some application models can be simulated with several computer programs and this gives great benefit [6]. However, simulation models are not as effective as the real models because students is usually like to touch to learn, so establishing a real-life model strengthens knowledge [7]. For these reasons, the PLCcontrolled elevator training kit presented in this study is designed and established in laboratory environment. Thus, students will learn not only an industrial application but also main ideas and programming techniques of a PLC. In this study, Siemens S7200 type of PLC has been used to realize the system. A general view of the PLC is given in Fig. 1 (a) and also a block diagram is given in Fig. 1 (b). As seen on this figure, input port of the PLC is used for receiving data sent by detectors as well as sensing signals that produced when a calling button is pushed. Output port of the PLC is used for moving the elevator in two ways (go up or go down), controlling the signal lamps and conditioning system, activating the alarm system when an alarm signal is sensed by detectors.
Fig. 1(a): A general view of the PLC
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Fig. 1(b): PLC connection scheme
EM 235 Analog Input Output Module While some of detectors operate under digital signals, some of them produce analogue type of output signals. Since the main CPU of PLC operates with only digital signals, it is required to convert analogue signals received from detectors to digital signals. This operation is performed by analogue modules in PLC based applications. There are three different analogue modules can be attached to the main block of the S7 200 PLC family: EM-231 with 4 analog inputs, EM-232 with 2 analog outputs and EM-235 with 4 analog inputs and 1 analog output. Analog/digital conversion calibration settings can be adjust to turn Offset adjustment potentiometer in Analog module produced reference voltage [8]. In this study, EM235 type analogue module is used for analogue/digital conversation operations.
Elevator System An elevator is a transport equipment moving vertically, which moves people or goods between levels of a building. Elevators are generally powered by electric motors that either drive traction cables or counterweight systems like a hoist, or pump hydraulic fluid to raise a cylindrical piston like a jack [911]. The main hardware unit used in the system presented is the elevator prototype. The prototype has three floors. There are calling buttons and inductive cylindrical sensors to sense the cabin on the each floor. Since the system is a small scaled prototype, a DC motor used to move the cabin over the rails. The status of cabin such as current floor can be seen by LED lambs placed on the each level and also placed on the cabin. Besides the buttons for each floor an "emergency stop" button is also installed into the cabin. A view of the prototype is given in Fig. 2.
Fig. 2: A view of the elevator prototype
Software structure Software structure of the system consists of two main parts: OPC server software for establishing communication between the computer and hardware units, Visual Basic software for designing a user interface.
OPC server OPC server’s mission is take data from the device or send data to the device according to OPC client commands. OPC clients work as a data receiver for starting communication with OPC servers and operating control processes [12-14]. OPC standard can be used on wind turbines, observing and managing energy, automobile factories, concrete and cement factories, building automation, textile industry, oil and gas industry, paper factories, iron-steel enterprises. Using an OPC server provides to communicate with lots of PLCs operating within the same network. Also communication capabilities can be extended using further drivers. In this study, the communication between the user interface and the PLC is established via the OPC Server. When the interface is connected to the OPC server, the information of elevator status is displayed on the screen and corresponding buttons are activated for controlling the elevator.
Visual Basic software User interface of the system has been designed in Visual Basic.NET. Status of the elevator can be monitored and invited for the desired floor through the interface via OPC server. The communication between hardware units and the user interface is provided through the serial port by the PPI cable. Flowchart of the software developed to control the system is given in Fig 3.
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Fig. 3: Flowchart of software
Implementation Overview of the system is shown in Fig. 4. It is needed to establish the connection with the OPC server before running the experimental implementation. This process is performed with "Connect to Server" button. When the interface connected to the OPC, the elevator status information will be displayed on the screen and corresponding buttons will be activated. If the connection of OPC can not be established, the interface program can be operated but calling buttons and emergency stop button will be inactive due to required data is not received from the elevator system. This status can be seen on Fig. 5. If the OPC server connection is established successfully, data received from the elevator is instantly displayed on the user interface as seen on Fig. 6. Status of the elevator cabin such as which floor it is at the moment, temperature in the cabin, and the warning message system will also be displayed on the screen in real time. As seen on the Fig. 6, current status of the elevator is being displayed in real time such as the elevator is on the 2nd floor, the cabin temperature is 25.504 degrees and the elevator has been called from the 1st floor. Since the elevator is called from the 1st floor, calling buttons of other floors are inactive. Fig. 7 shows a sample alarm status of the system. As seen on this figure, smoke or toxic gas leakage is detected by the sensors while the elevator is on the 3rd floor. So, a warning is displayed on the screen automatically under the "System Operating Status" section.
Three floored elevator prototype
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Fig. 4: Overview of the system
Fig. 5: A view of the user interface during the server connection is not established
Fig. 6: A view of the user interface while the system is operated.
Fig. 7: A sample alarm status of the system
Conclusion Elevator control with PLC is an important issue of Electrical and Electronic Engineering education and it is becoming a requirement for intelligent building applications. In this study, real time controlling and monitoring of a three floored elevator prototype based on PLC is realized. The system developed can be used either in industrial automation or educational purposes as an interactive and instructional material. As a novelty, a more functional as well as more visual user interface has been developed using Visual Basic which is an object-oriented programming language. The system can easily be adapted into various industrial systems with small changes in software. Thanks to using of the OPC, an international communication standard between PLCs and PC, the system has quite faster and reliable communication structure.
References [1] Toygar N.: Vertical Motion on the Horizontal Direction , Elevator World Magazine, volume 73, 2004. [2] Arıtan, T.: Elevator Control Systems, Kaynak Magazine, pp.29-32 [3] Çolak I., Bayındır R.: Electrical Control Circuits, Seckin Press, pp.74-128, Ankara, January 2007
[4] Siemens Simatic S7-200,: Programmable Logic Controller (PLC) User's Guide, 2005 [5] https://www.automation.siemens.com/_en/s7-200/Products/01CPUs/cpu224xp.html [6] Atıs S., Oral B.: PLC Systems and Automation Exhibition, Industrial Activities Week 15-18 March 2001, Istanbul. [7] Özerdem Ö. C., Samurkas T.: Laboratory Mechanism Design for the Purpose of PLC Training, PLCControlled Transport at the University of Cyprus, 2nd National Symposium for Electrical, Electronics, Computer engineering education 25-27 May 2005, Samsun. [8] Eken Ö.: PLC and PIC Controlled Elevator Automation ", 4th International Symposium on Advanced Technologies, vol 1, pp 297 [9] Ünalan E.: Control Systems in Elevators, Sektör Magazine, vol. 4, pp.29-32 [10] Öztürk T.: Control of Elevator System with Programmable Logic Controller , Master Thesis , 1996 KocaeliTURKEY. [11] İmrak E., Gerdemeli İ.: Elevators and Escalators , Birsen Publishing, Istanbul 2000 [12] Zheng,L., Nakagawa,H.: OPC (OLE for Process Control) Specification and its Developments" OPC Council. Japan (Yokogawa Electric), SICE02-0806 [13] http://www.opcfoundation.org [14] http://www.aspltd.net/opcturkiye/default.asp
