- Email: [email protected]
Remote Level Monitoring and Control Solution
June 1-3, 2016. Bratislava, Slovakia 11th IFAC Symposium on Advances in Control Education 11th IFAC Symposium on Advances in Control Education June 1-3, 2016. Bratislava, Slovakia Available online at www.sciencedirect.com June 1-3, 2016. Bratislava, Slovakia
ScienceDirect IFAC-PapersOnLine 49-6 (2016)and 194–197 Remote Level Monitoring Control Solution Remote Level Monitoring and Control Solution Remote Level Monitoring and Control Solution Maria de Fátima Chouzal *, Maria Teresa Restivo*, Fernando Gomes Silva*,
Fernando Gomes Almeida*, Tiago Faustino Andrade* Maria Maria de de Fátima Fátima Chouzal Chouzal *, *, Maria Maria Teresa Teresa Restivo*, Restivo*, Fernando Fernando Gomes Gomes Silva*, Silva*, Fernando Gomes Almeida*, Tiago Faustino Andrade* Fernando Gomes Almeida*, Tiago Faustino Andrade* *LAETA-INEGI, Faculdade de Engenharia, Universidade do Porto, Porto, Portugal (Tel: +351225081776; e-mail: [email protected], [email protected], [email protected], [email protected], [email protected]). *LAETA-INEGI, *LAETA-INEGI, Faculdade Faculdade de de Engenharia, Engenharia, Universidade Universidade do do Porto, Porto, Porto, Porto, Portugal Portugal (Tel: (Tel: +351225081776; +351225081776; e-mail: e-mail: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected]). [email protected]). Abstract: This work presents a remote monitoring and control solution for a level measurement system. The level This measurement system comprises two tanks in a solution closed loop watermeasurement circuit, somesystem. level Abstract: work aa remote and for aa level Abstract: This work presents presents remote monitoring monitoring and control control solution for on level measurementand system. transducers, detectors and two actuators. The developed solution is based microcontrollers web The measurement system comprises two tanks in loop water circuit, level The level levelThe measurement system comprises two tanksinteract in aa closed closed loop water circuit, some some level services. web interface allows the user to remotely with the level measurement and control transducers, transducers, detectors detectors and and two two actuators. actuators. The The developed developed solution solution is is based based on on microcontrollers microcontrollers and and web web system. services. The web interface allows the user to remotely interact with the level measurement and services. The web interface allows the user to remotely interact with the level measurement and control control system. © 2016, IFAC (International Federation of Automatic Control)system, Hostinglevel by Elsevier All rights reserved. Keywords: Remote experiments, web interface, embedded control,Ltd. remote control. system. Keywords: Keywords: Remote Remote experiments, experiments, web web interface, interface, embedded embedded system, system, level level control, control, remote remote control. control. principles, characteristics and limitations, in a closed loop 1. INTRODUCTION water circuit using two and tanks and twoin actuators. The principles, characteristics limitations, closed loop principles, selection characteristics and limitations, in aathe closed loop has to take into account adequate The increasing use 1. of INTRODUCTION computer-based communications and transducer 1. INTRODUCTION water circuit circuit using using two two tanks tanks and and two two actuators. actuators. The The water ranges for selection the present tank andinto to provide very distinct mobile devices use makes possible to offer communications online experimental transducer has to take account the adequate The increasing of computer-based and has tobehaviours. take into account the adequate The increasing use ofexperiments, computer-based communications and transducer features to selection force different In order very to house all activities. Remote being partexperimental of online ranges for for the present present tank and and to to provide provide distinct mobile devices makes possible to offer online ranges the tank very strongly distinct mobile devices makes possible to offer online experimental the transducers and detectors, the tank dimensions experimentation (Restivo et al., 2013), remotely access online a real features to force different behaviours. In order to house all activities. Remote experiments, being part to force different behaviours. In order to house all activities. Remote experiments, being partat aof ofdistance, online features compromise the and system dynamics. set-up, which can be monitored and controlled the transducers transducers detectors, the tank tank dimensions dimensions strongly strongly experimentation (Restivo et al., 2013), remotely access a real the and detectors, the experimentation (Restivo et al., 2013), remotely access a real compromise the system dynamics. through the internet. set-up, Therefore, the must be computationally light and thecontroller system dynamics. set-up, which which can can be be monitored monitored and and controlled controlled at at aa distance, distance, compromise through the internet. also enable the remote control of computationally the fluid level. Alight control Despite the the internet. relevance of remote experiments in education Therefore, the controller must be through and Therefore, the controller must be computationally lightzone and policy based on the use of an on-off controller with dead (Villa-Lopez et al., 2013; Wenshan et al., 2013; De la Torre also enable the remote control of the fluid level. A control Despite the relevance of remote experiments in education also hysteresis enable thewas remote control of the fluiddefining level. Athe control Despite the relevance of remote experiments education parameters et al., 2016) and the remarkable increase of in interest and and policy based based on on the the chosen. use of of an anAll on-off controller with with dead dead dead zone (Villa-Lopez et al., 2013; Wenshan et al., 2013; De la Torre policy use on-off controller zone (Villa-Lopez et al., 2013; Wenshan et al., 2013; De la Torre and hysteresis functions may be selected by the user. reported worksand in the area (Heradioincrease et al., 2016), as welland as zone and hysteresis was chosen. All parameters defining the dead et al., 2016) the remarkable of interest and hysteresis was chosen. All parameters defining the dead et al., 2016) and the remarkable increase of interest and The experimentation different parameter setsuser. and its significance for industrial, research and medical purposes, zone online and hysteresis hysteresis functionsofmay may be selected selected by the the reported works in the area (Heradio et al., 2016), as well as zone and functions be by user. reported works in the area (Heradio et al., 2016), as well as the observation of their influence on system dynamic there still are different problems related with the remote labs The online experimentation of different parameter sets and its significance for research medical purposes, The onlineisexperimentation of different parameter sets and its significance for industrial, industrial, research and and medical purposes, thus made possible. features due to hardware and software solutions (Fabregas et behaviour the observation observation of their their influence on on system system dynamic dynamic there still are different problems related with the remote labs the of influence there still are different problems related with the remote labs behaviour is thus made possible. al., 2011; Tawfik et al., 2013). At present, another important features due and software solutions (Fabregas et An embedded system on PIC® microcontrollers was is thus made based possible. features due to to hardware hardware andbeing software solutions (Fabregas et behaviour issue is preparing them for easily accessed by mobile al., 2011; Tawfik et al., 2013). At present, another important implemented for processing and web monitoring all signal al., 2011; Tawfik 2013). At present,etanother important An embedded system based on PIC® microcontrollers was devices (Štefka et et al.,al., 2016; Papadopoulos al., 2013). An embedded system based on PIC®systems. microcontrollers was issue of sensing and actuating The interface issue is is preparing preparing them them for for being being easily easily accessed accessed by by mobile mobile information implemented for processing and web monitoring all signal implemented for Monitoring processing and web monitoring allonsignal devices (Štefka et 2016; Papadopoulos al., 2013). Remote Level and Control was made Easy In this context, set-up hereinet used not of devices (Štefka the et al., al., 2016;described Papadopoulos ethas al.,been 2013). information of sensing sensing and and actuating actuating systems. The interface interface information of systems. The Javascript Simulations (EJsS) application (Christian et al., only as a system available for training the topic of level of Remote Remote Level Level Monitoring Monitoring and and Control Control was was made made on on Easy Easy In this the described herein has been used not of In this context, context,and the set-up set-up described herein has been used not 2011) to be easily integrated in a Moodle platform. This measurement control but also to be open to the Javascript Simulations (EJsS) application (Christian et al., only as for training the topic level Javascript Simulations (EJsS)EJSApp application (Christian et al., only as aa system systemof available available for training for the remote topic of ofaccess level integration requires tointegrated install plug in (De la Torre et implementation different solutions 2011) to be easily in a Moodle platform. This measurement and control but also to be open to the 2011) to be easily integrated in awith Moodle platform. This measurement and control but also to be open to the al., 2013), which can be combined the EJSApp booking experiments. integration requires requires to to install install EJSApp EJSApp plug plug in in (De (De la la Torre Torre et et implementation implementation of of different different solutions solutions for for remote remote access access integration system resource. al., 2013), which can be combined with the EJSApp booking experiments. In a first stage, a solution combining a PLC for controlling al., 2013), which can be combined with the EJSApp booking experiments. systemsystem resource. This is under use to give the students of the resource. and LabVIEW software for combining developing athe userfor interface was system In a first stage, a solution PLC controlling In a first stage, this a solution combining a PLC for controlling Instrumentation 2nd Measurement (2nd year, used. However, was an expensive approach. This system system is is for under use to to give givecourse the students students of the the and under use the of and LabVIEW LabVIEW software software for for developing developing the the user user interface interface was was This semester of Integrated Master in Mechanical at nd Instrumentation for Measurement Measurement course Engineering, (2nd nd year, 2nd used. was approach. year, the 2 for course (2 In theHowever, present this work, an expensive alternative solution based on Instrumentation used. However, this was an an expensive approach. the Faculty of Engineering of University of Porto), semester Master in Engineering, at semester of of Integrated Integrated Master in Mechanical Mechanical Engineering, at embedded systemswork, and web services is developed to provide opportunity to Engineering contact with an additional type the of In the present an alternative solution based on the Faculty of of University of Porto), In the present work, an alternative solution based on the Faculty of Engineering of University of Porto), the the monitoring and control of the closed loop water tanks measurement, transducers characterization and an easy embedded systems and web services is developed to to contact an additional type of embedded web services ismobile developed to provide provide opportunity opportunity to During contactthe with with an additional of system andsystems makeand it and easily accessed by devices. control strategy. Demo Session, results oftype theeasy use the monitoring control of the closed loop water tanks measurement, transducers characterization and an the monitoring and control of the closed loop water tanks measurement, transducers characterization and an easy of this remote experiment based onSession, a sample of around 320 system and make it accessed by devices. strategy. During Therefore, present set-up for testing level transducers and control system and the make it easily easily accessed by mobile mobile devices. control strategy. During the the Demo Demo Session, results results of of the the use use students will be available. of this remote experiment based on aa sample of around 320 detectors is a didactic test bench in both perspectives: as a of this remote experiment based on sample of around 320 Therefore, the set-up for testing and Therefore, the present present for implementing testing level level transducers transducers and students will training system and a set-up basis for new solutions In the present work, Section 2 describes the workbench, will be be available. available. detectors is a didactic test bench in both perspectives: as aa students detectors is access. a didactic test bench inofboth perspectives: as for remote Different types level transducers and comprising several levelSection transducers and detectors. Section 3 training system and a basis for implementing new solutions In the work, describes the training system and a basis new solutions In the present present work,adopted Sectionfor22making describes the workbench, workbench, detectors areaccess. available to putfor inimplementing evidence different working presents the solution the system remotely for remote Different types of level transducers and for remote access. Different types of level transducers and comprising comprising several several level level transducers transducers and and detectors. detectors. Section Section 33 detectors are available to put in evidence different working presents the solution adopted for making the system detectors are available to put in evidence different working presents the solution adopted for making the system remotely remotely
Copyright © 2016 IFAC 194 2405-8963 © 2016, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Peer review©under of International Federation of Automatic Copyright 2016 responsibility IFAC 194Control. Copyright © 2016 IFAC 194 10.1016/j.ifacol.2016.07.144
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Maria de Fátima Chouzal et al. / IFAC-PapersOnLine 49-6 (2016) 194–197
available. Section 4 provides details of the control algorithm implemented. Section 5 presents the user interface for remote access to the experiment.
195
for future developments. The acquisition and actuation module is associated to one of the microcontrollers and the web server module is performed by the second one. Synchronous serial communication in a master-slave mode is used between both microcontrollers, as shown in Fig. 3.
2. THE WORKBENCH One of the closed-loop water circuit tanks, the upper tank, is visible in Fig. 1. Different working principles of level transmitters (magnetostrictive, ultrasound and differential water level pressure) and detectors (conductive limit switch, vibrating limit switch), as shown in Fig. 1, can be perceived and their performance can be evaluated and compared in distinct perspectives. The transmitters’ characteristics can be observed on Table 1, where the dead zones are setup geometry dependent. The detectors present different hysteresis (of the order of 3 and 4 mm) that can also be observed.
Fig. 3. Modular architecture of the implemented system. 3.1 Acquisition and actuation module
Table 1. Transmitter characteristics Level transmitters
Sensitivity [µA/mm]
Nominal range [mm]
Dead Zone [mm]
Magnetostrictive
53.3
300
0 - 230
Ultrasound
36.3
60 - 500
0 - 44
Pressure
16.0
1000
—
The acquisition and actuation module deals with signals acquisition, processing data from transmitters and detectors, as well as with the valve and pump actuations for controlling actions. In this module, the microcontroller was selected considering the required number of analogue and digital I/Os, the range of the frequency pulse rate of the water flow transducer, the synchronous serial communication between both modules and the requirement of guarantying, at least, 1 mm resolution in the level measurement, with any of the transmitters. 3.2 Web server module This module is responsible for the communications and the web page hosting. It includes a microcontroller with an Ethernet controller that meets all of the IEEE 802.3i specifications. 4. CONTROL ALGORITHM A relay controller with dead zone and unequal pull-in and drop-out level error, with the general characteristic shown in Fig. 4, was chosen given its straightforwardness, its capability to control the process and its low computational load.
Fig. 1. Level transmitters and detectors workbench. The system also includes two electrical actuators: an on/off normally-closed (NC) outlet valve and a submersible circulation pump controlled by a DC motor. A flow transducer measures the pump water flow (range: 1.5 to 30 l/min). 3. IMPLEMENTED SOLUTION The embedded system includes two microcontrollers, in order to achieve a modular solution for two well-defined and distinct functions. The goal is to reduce the development and debugging time, make the system run faster, permit an easy replacement of any of the modules, expedite the testing of other solutions (in both modules) and have a scalable solution
Fig. 4. Relay controller with dead zone and hysteresis 195
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that enables up and uv simultaneousely ON in some conditions.
As the controller must provide two control actions, one for the DC pump, up, and one for the NC outlet valve, uv, it was implemented as two independent controllers enabling a high degree of flexibility in the overall controller behaviour. Both controllers act on the level error, e, which is the difference between the desired level set point and the actual measured level. Therefore, if e is greater than ep1 then up will be ON; if e is smaller than ep0 then up will be OFF; and if e is between ep0 and ep1 up will keep its previous state. In a similar way, if e is greater than ev0 then uv will be OFF; if e is smaller than ev1 then uv will be ON; and if e is between ev1 and ev0 uv will keep its previous state. By defining the values ep0, ep1, ev0 and ev1 different behaviours may be imposed. If these four variables are made equal to zero the result is a relay controller with neither dead zone nor hysteresis, as shown in Fig. 5.
Fig. 7. Relay controller with unusual behaviour. This flexibility enables the user to experiment with different controller configurations and observe its results without the constraints that must be introduced in a real process to ensure its survivability. 5. USER INTERFACE The user interface is a HTML5 web page for system monitoring and remote control. HTML language is a standard for developing web pages and offers great compatibility with different browsers, in both computers and mobile devices. The user interface is presented in Fig. 8.
Fig. 5. Relay controller without dead zone or hysteresis. A relay controller with hysteresis but no dead zone may be obtained, as represented in Fig. 6, if ev1 is given the same value as ep0 and ep1 takes de value of ev0. If these two values are symmetric, the hysteresis loop will also be symmetric around zero. Otherwise, a positive or negative bias will be introduced.
Fig. 8. User interface. Two operating modes are available for controlling the tank water level: Manual and Automatic.
Fig. 6. Relay controller with hysteresis but no dead zone.
In the Manual mode, the user will get control of the pump by clicking the “Filling” button and actuate the on/off NC outlet
Finally, if the four variables are given arbitrary values some strange behaviours may result, as the one presented in Fig. 7 196
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valve by clicking the “Draining” button. In addition, the user can select the suitable filling flow rate.
Foundation for Science and Technology under the project (PEst-OE/EME/LA0022/2013).
In the Automatic mode, two controllers are available: •
Hybrid Controller based on a P controller
•
Relay Controller with dead zone and hysteresis
197
REFERENCES Christian, W., Esquembre, F., and Barbato, L., (2011), Open Source Physics, Science, Vol. 334, pp. 1077–1078. De la Torre, L., Heradio. R., Jara, C. A., Sanchez, J., Dormido, S., Torres, F. and Candelas, F. A., (2013), Providing Collaborative Support to Virtual and Remote Laboratories, IEEE Transactions Learning Technologies, vol. 6, pp. 312-323. De la Torre, L., Sánchez, J.P., Dormido, S., (2016). What remote labs can do for you, Physics Today, vol. 69 no. 4, pp. 48-53. Fabregas, E., Farias, G., Dormido-Canto, S., Dormido, S. and Esquembre, F. (2011). Developing a remote laboratory for engineering education. Computers & Education, vol. 57, pp. 1686-1697. Heradio, R., de la Torre, L., Galan, D., Cabrerizo, F.J., Herrera-Viedma, E., Dormido, S. (2016) Virtual and remote labs in education: A bibliometric analysis, Computers & Education, 98, pp. 14-38. Papadopoulos, A.V., Leva, A., (2013) “Laboratories over the network: from remote to mobile”, 10th IFAC Symposium Advances in Control Education, Sheffield, United Kingdom. Restivo, M. T., Cardoso, A., (2013). Exploring Online Experimentation. Guest Editorial, iJOE, Vol. 9, pp. 4-6. Štefka, P., Žáková, K., (2016), Mobile Application for Remote Control of Thermo-Optical Plant, 13th International Conference on Remote Engineering and Virtual Instrumentation (REV’16). Tawfik, M., Sancristobal, E., Martin, S., Diaz, G., Peire, J. and Castro, M. (2013). Expanding the Boundaries of the Classroom: Implementation of Remote Laboratories for Industrial Electronics Disciplines. Industrial Electronics Magazine, IEEE, vol. 7, pp. 41-49. Villa-López, F. H., García-Guzmán, J., Enríquez, J. V., LealOrtíz, S. and Ramírez-Ramírez, A. (2013). Electropneumatic System for Industrial Automation: A Remote Experiment within a Web-Based Learning Environment. Procedia Technology, vol. 7, pp. 198-207. Wenshan, H., Guo-Ping, L. and Hong, Z. (2013). Web-Based 3-D Control Laboratory for Remote Real-Time Experimentation. IEEE Transactions on Industrial Electronics, vol. 60, pp. 4673-4682.
In the first one, the user may introduce the set-point value. The software will then automatically perform the preestablished procedure based on the implemented controller (Hybrid Controller based on a P controller). In the second (Relay Controller with dead zone and hysteresis), the set-point value and the control parameters may be introduced (or the default ones kept). The software will then automatically perform the pre-established procedure. The pump and/or valve indicator lights, if of green color, indicate that the pump and/or valve are actuated. This information can be observed in the relay controller status. The graphical presentation automatically displays the introduced parameter in order to allow the user a better perception. In each case, the user interface provides in the monitoring section the numerical value of the water level, the voltage output of each transmitter and the detectors state, while the live video of the real system permits the user to follow the level evolution. By using any of the two possibilities, manual actuation and the automatic mode using Hybrid Controller based on a P controller, the students may be able to perform the sensing devices characterization. For that purpose, a very simple animated indicator on the animation window gives the constant level value in the animated tank of the Monitoring Section of the user interface. 6. CONCLUSIONS This setup contributes with a new technological solution to the remote experiments of "online experimentation @ FEUP", (https://remotelab.fe.up.pt). This solution is presenting a very good performance. The flexibility allowed by the solution used for developing the interface is a valuable tool for adapting the remote experiment to different requirements of learning objectives. Combining both the use of HTML and the commitment to optimize the elements dimensions to the dynamic positioning, makes the application available through any mobile device. The system is under evaluation at present. The main electronic solution was the result of an Integrated Master in Mechanical Engineering thesis and, as such, it has also been a student project in a learning context. ACKNOWLEDGEMENTS This work has been funded by Calouste Gulbenkian Foundation under Project U-Academy and by the Portuguese 197
ScienceDirect IFAC-PapersOnLine 49-6 (2016)and 194–197 Remote Level Monitoring Control Solution Remote Level Monitoring and Control Solution Remote Level Monitoring and Control Solution Maria de Fátima Chouzal *, Maria Teresa Restivo*, Fernando Gomes Silva*,
Fernando Gomes Almeida*, Tiago Faustino Andrade* Maria Maria de de Fátima Fátima Chouzal Chouzal *, *, Maria Maria Teresa Teresa Restivo*, Restivo*, Fernando Fernando Gomes Gomes Silva*, Silva*, Fernando Gomes Almeida*, Tiago Faustino Andrade* Fernando Gomes Almeida*, Tiago Faustino Andrade* *LAETA-INEGI, Faculdade de Engenharia, Universidade do Porto, Porto, Portugal (Tel: +351225081776; e-mail: [email protected], [email protected], [email protected], [email protected], [email protected]). *LAETA-INEGI, *LAETA-INEGI, Faculdade Faculdade de de Engenharia, Engenharia, Universidade Universidade do do Porto, Porto, Porto, Porto, Portugal Portugal (Tel: (Tel: +351225081776; +351225081776; e-mail: e-mail: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected]). [email protected]). Abstract: This work presents a remote monitoring and control solution for a level measurement system. The level This measurement system comprises two tanks in a solution closed loop watermeasurement circuit, somesystem. level Abstract: work aa remote and for aa level Abstract: This work presents presents remote monitoring monitoring and control control solution for on level measurementand system. transducers, detectors and two actuators. The developed solution is based microcontrollers web The measurement system comprises two tanks in loop water circuit, level The level levelThe measurement system comprises two tanksinteract in aa closed closed loop water circuit, some some level services. web interface allows the user to remotely with the level measurement and control transducers, transducers, detectors detectors and and two two actuators. actuators. The The developed developed solution solution is is based based on on microcontrollers microcontrollers and and web web system. services. The web interface allows the user to remotely interact with the level measurement and services. The web interface allows the user to remotely interact with the level measurement and control control system. © 2016, IFAC (International Federation of Automatic Control)system, Hostinglevel by Elsevier All rights reserved. Keywords: Remote experiments, web interface, embedded control,Ltd. remote control. system. Keywords: Keywords: Remote Remote experiments, experiments, web web interface, interface, embedded embedded system, system, level level control, control, remote remote control. control. principles, characteristics and limitations, in a closed loop 1. INTRODUCTION water circuit using two and tanks and twoin actuators. The principles, characteristics limitations, closed loop principles, selection characteristics and limitations, in aathe closed loop has to take into account adequate The increasing use 1. of INTRODUCTION computer-based communications and transducer 1. INTRODUCTION water circuit circuit using using two two tanks tanks and and two two actuators. actuators. The The water ranges for selection the present tank andinto to provide very distinct mobile devices use makes possible to offer communications online experimental transducer has to take account the adequate The increasing of computer-based and has tobehaviours. take into account the adequate The increasing use ofexperiments, computer-based communications and transducer features to selection force different In order very to house all activities. Remote being partexperimental of online ranges for for the present present tank and and to to provide provide distinct mobile devices makes possible to offer online ranges the tank very strongly distinct mobile devices makes possible to offer online experimental the transducers and detectors, the tank dimensions experimentation (Restivo et al., 2013), remotely access online a real features to force different behaviours. In order to house all activities. Remote experiments, being part to force different behaviours. In order to house all activities. Remote experiments, being partat aof ofdistance, online features compromise the and system dynamics. set-up, which can be monitored and controlled the transducers transducers detectors, the tank tank dimensions dimensions strongly strongly experimentation (Restivo et al., 2013), remotely access a real the and detectors, the experimentation (Restivo et al., 2013), remotely access a real compromise the system dynamics. through the internet. set-up, Therefore, the must be computationally light and thecontroller system dynamics. set-up, which which can can be be monitored monitored and and controlled controlled at at aa distance, distance, compromise through the internet. also enable the remote control of computationally the fluid level. Alight control Despite the the internet. relevance of remote experiments in education Therefore, the controller must be through and Therefore, the controller must be computationally lightzone and policy based on the use of an on-off controller with dead (Villa-Lopez et al., 2013; Wenshan et al., 2013; De la Torre also enable the remote control of the fluid level. A control Despite the relevance of remote experiments in education also hysteresis enable thewas remote control of the fluiddefining level. Athe control Despite the relevance of remote experiments education parameters et al., 2016) and the remarkable increase of in interest and and policy based based on on the the chosen. use of of an anAll on-off controller with with dead dead dead zone (Villa-Lopez et al., 2013; Wenshan et al., 2013; De la Torre policy use on-off controller zone (Villa-Lopez et al., 2013; Wenshan et al., 2013; De la Torre and hysteresis functions may be selected by the user. reported worksand in the area (Heradioincrease et al., 2016), as welland as zone and hysteresis was chosen. All parameters defining the dead et al., 2016) the remarkable of interest and hysteresis was chosen. All parameters defining the dead et al., 2016) and the remarkable increase of interest and The experimentation different parameter setsuser. and its significance for industrial, research and medical purposes, zone online and hysteresis hysteresis functionsofmay may be selected selected by the the reported works in the area (Heradio et al., 2016), as well as zone and functions be by user. reported works in the area (Heradio et al., 2016), as well as the observation of their influence on system dynamic there still are different problems related with the remote labs The online experimentation of different parameter sets and its significance for research medical purposes, The onlineisexperimentation of different parameter sets and its significance for industrial, industrial, research and and medical purposes, thus made possible. features due to hardware and software solutions (Fabregas et behaviour the observation observation of their their influence on on system system dynamic dynamic there still are different problems related with the remote labs the of influence there still are different problems related with the remote labs behaviour is thus made possible. al., 2011; Tawfik et al., 2013). At present, another important features due and software solutions (Fabregas et An embedded system on PIC® microcontrollers was is thus made based possible. features due to to hardware hardware andbeing software solutions (Fabregas et behaviour issue is preparing them for easily accessed by mobile al., 2011; Tawfik et al., 2013). At present, another important implemented for processing and web monitoring all signal al., 2011; Tawfik 2013). At present,etanother important An embedded system based on PIC® microcontrollers was devices (Štefka et et al.,al., 2016; Papadopoulos al., 2013). An embedded system based on PIC®systems. microcontrollers was issue of sensing and actuating The interface issue is is preparing preparing them them for for being being easily easily accessed accessed by by mobile mobile information implemented for processing and web monitoring all signal implemented for Monitoring processing and web monitoring allonsignal devices (Štefka et 2016; Papadopoulos al., 2013). Remote Level and Control was made Easy In this context, set-up hereinet used not of devices (Štefka the et al., al., 2016;described Papadopoulos ethas al.,been 2013). information of sensing sensing and and actuating actuating systems. The interface interface information of systems. The Javascript Simulations (EJsS) application (Christian et al., only as a system available for training the topic of level of Remote Remote Level Level Monitoring Monitoring and and Control Control was was made made on on Easy Easy In this the described herein has been used not of In this context, context,and the set-up set-up described herein has been used not 2011) to be easily integrated in a Moodle platform. This measurement control but also to be open to the Javascript Simulations (EJsS) application (Christian et al., only as for training the topic level Javascript Simulations (EJsS)EJSApp application (Christian et al., only as aa system systemof available available for training for the remote topic of ofaccess level integration requires tointegrated install plug in (De la Torre et implementation different solutions 2011) to be easily in a Moodle platform. This measurement and control but also to be open to the 2011) to be easily integrated in awith Moodle platform. This measurement and control but also to be open to the al., 2013), which can be combined the EJSApp booking experiments. integration requires requires to to install install EJSApp EJSApp plug plug in in (De (De la la Torre Torre et et implementation implementation of of different different solutions solutions for for remote remote access access integration system resource. al., 2013), which can be combined with the EJSApp booking experiments. In a first stage, a solution combining a PLC for controlling al., 2013), which can be combined with the EJSApp booking experiments. systemsystem resource. This is under use to give the students of the resource. and LabVIEW software for combining developing athe userfor interface was system In a first stage, a solution PLC controlling In a first stage, this a solution combining a PLC for controlling Instrumentation 2nd Measurement (2nd year, used. However, was an expensive approach. This system system is is for under use to to give givecourse the students students of the the and under use the of and LabVIEW LabVIEW software software for for developing developing the the user user interface interface was was This semester of Integrated Master in Mechanical at nd Instrumentation for Measurement Measurement course Engineering, (2nd nd year, 2nd used. was approach. year, the 2 for course (2 In theHowever, present this work, an expensive alternative solution based on Instrumentation used. However, this was an an expensive approach. the Faculty of Engineering of University of Porto), semester Master in Engineering, at semester of of Integrated Integrated Master in Mechanical Mechanical Engineering, at embedded systemswork, and web services is developed to provide opportunity to Engineering contact with an additional type the of In the present an alternative solution based on the Faculty of of University of Porto), In the present work, an alternative solution based on the Faculty of Engineering of University of Porto), the the monitoring and control of the closed loop water tanks measurement, transducers characterization and an easy embedded systems and web services is developed to to contact an additional type of embedded web services ismobile developed to provide provide opportunity opportunity to During contactthe with with an additional of system andsystems makeand it and easily accessed by devices. control strategy. Demo Session, results oftype theeasy use the monitoring control of the closed loop water tanks measurement, transducers characterization and an the monitoring and control of the closed loop water tanks measurement, transducers characterization and an easy of this remote experiment based onSession, a sample of around 320 system and make it accessed by devices. strategy. During Therefore, present set-up for testing level transducers and control system and the make it easily easily accessed by mobile mobile devices. control strategy. During the the Demo Demo Session, results results of of the the use use students will be available. of this remote experiment based on aa sample of around 320 detectors is a didactic test bench in both perspectives: as a of this remote experiment based on sample of around 320 Therefore, the set-up for testing and Therefore, the present present for implementing testing level level transducers transducers and students will training system and a set-up basis for new solutions In the present work, Section 2 describes the workbench, will be be available. available. detectors is a didactic test bench in both perspectives: as aa students detectors is access. a didactic test bench inofboth perspectives: as for remote Different types level transducers and comprising several levelSection transducers and detectors. Section 3 training system and a basis for implementing new solutions In the work, describes the training system and a basis new solutions In the present present work,adopted Sectionfor22making describes the workbench, workbench, detectors areaccess. available to putfor inimplementing evidence different working presents the solution the system remotely for remote Different types of level transducers and for remote access. Different types of level transducers and comprising comprising several several level level transducers transducers and and detectors. detectors. Section Section 33 detectors are available to put in evidence different working presents the solution adopted for making the system detectors are available to put in evidence different working presents the solution adopted for making the system remotely remotely
Copyright © 2016 IFAC 194 2405-8963 © 2016, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Peer review©under of International Federation of Automatic Copyright 2016 responsibility IFAC 194Control. Copyright © 2016 IFAC 194 10.1016/j.ifacol.2016.07.144
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available. Section 4 provides details of the control algorithm implemented. Section 5 presents the user interface for remote access to the experiment.
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for future developments. The acquisition and actuation module is associated to one of the microcontrollers and the web server module is performed by the second one. Synchronous serial communication in a master-slave mode is used between both microcontrollers, as shown in Fig. 3.
2. THE WORKBENCH One of the closed-loop water circuit tanks, the upper tank, is visible in Fig. 1. Different working principles of level transmitters (magnetostrictive, ultrasound and differential water level pressure) and detectors (conductive limit switch, vibrating limit switch), as shown in Fig. 1, can be perceived and their performance can be evaluated and compared in distinct perspectives. The transmitters’ characteristics can be observed on Table 1, where the dead zones are setup geometry dependent. The detectors present different hysteresis (of the order of 3 and 4 mm) that can also be observed.
Fig. 3. Modular architecture of the implemented system. 3.1 Acquisition and actuation module
Table 1. Transmitter characteristics Level transmitters
Sensitivity [µA/mm]
Nominal range [mm]
Dead Zone [mm]
Magnetostrictive
53.3
300
0 - 230
Ultrasound
36.3
60 - 500
0 - 44
Pressure
16.0
1000
—
The acquisition and actuation module deals with signals acquisition, processing data from transmitters and detectors, as well as with the valve and pump actuations for controlling actions. In this module, the microcontroller was selected considering the required number of analogue and digital I/Os, the range of the frequency pulse rate of the water flow transducer, the synchronous serial communication between both modules and the requirement of guarantying, at least, 1 mm resolution in the level measurement, with any of the transmitters. 3.2 Web server module This module is responsible for the communications and the web page hosting. It includes a microcontroller with an Ethernet controller that meets all of the IEEE 802.3i specifications. 4. CONTROL ALGORITHM A relay controller with dead zone and unequal pull-in and drop-out level error, with the general characteristic shown in Fig. 4, was chosen given its straightforwardness, its capability to control the process and its low computational load.
Fig. 1. Level transmitters and detectors workbench. The system also includes two electrical actuators: an on/off normally-closed (NC) outlet valve and a submersible circulation pump controlled by a DC motor. A flow transducer measures the pump water flow (range: 1.5 to 30 l/min). 3. IMPLEMENTED SOLUTION The embedded system includes two microcontrollers, in order to achieve a modular solution for two well-defined and distinct functions. The goal is to reduce the development and debugging time, make the system run faster, permit an easy replacement of any of the modules, expedite the testing of other solutions (in both modules) and have a scalable solution
Fig. 4. Relay controller with dead zone and hysteresis 195
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that enables up and uv simultaneousely ON in some conditions.
As the controller must provide two control actions, one for the DC pump, up, and one for the NC outlet valve, uv, it was implemented as two independent controllers enabling a high degree of flexibility in the overall controller behaviour. Both controllers act on the level error, e, which is the difference between the desired level set point and the actual measured level. Therefore, if e is greater than ep1 then up will be ON; if e is smaller than ep0 then up will be OFF; and if e is between ep0 and ep1 up will keep its previous state. In a similar way, if e is greater than ev0 then uv will be OFF; if e is smaller than ev1 then uv will be ON; and if e is between ev1 and ev0 uv will keep its previous state. By defining the values ep0, ep1, ev0 and ev1 different behaviours may be imposed. If these four variables are made equal to zero the result is a relay controller with neither dead zone nor hysteresis, as shown in Fig. 5.
Fig. 7. Relay controller with unusual behaviour. This flexibility enables the user to experiment with different controller configurations and observe its results without the constraints that must be introduced in a real process to ensure its survivability. 5. USER INTERFACE The user interface is a HTML5 web page for system monitoring and remote control. HTML language is a standard for developing web pages and offers great compatibility with different browsers, in both computers and mobile devices. The user interface is presented in Fig. 8.
Fig. 5. Relay controller without dead zone or hysteresis. A relay controller with hysteresis but no dead zone may be obtained, as represented in Fig. 6, if ev1 is given the same value as ep0 and ep1 takes de value of ev0. If these two values are symmetric, the hysteresis loop will also be symmetric around zero. Otherwise, a positive or negative bias will be introduced.
Fig. 8. User interface. Two operating modes are available for controlling the tank water level: Manual and Automatic.
Fig. 6. Relay controller with hysteresis but no dead zone.
In the Manual mode, the user will get control of the pump by clicking the “Filling” button and actuate the on/off NC outlet
Finally, if the four variables are given arbitrary values some strange behaviours may result, as the one presented in Fig. 7 196
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valve by clicking the “Draining” button. In addition, the user can select the suitable filling flow rate.
Foundation for Science and Technology under the project (PEst-OE/EME/LA0022/2013).
In the Automatic mode, two controllers are available: •
Hybrid Controller based on a P controller
•
Relay Controller with dead zone and hysteresis
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REFERENCES Christian, W., Esquembre, F., and Barbato, L., (2011), Open Source Physics, Science, Vol. 334, pp. 1077–1078. De la Torre, L., Heradio. R., Jara, C. A., Sanchez, J., Dormido, S., Torres, F. and Candelas, F. A., (2013), Providing Collaborative Support to Virtual and Remote Laboratories, IEEE Transactions Learning Technologies, vol. 6, pp. 312-323. De la Torre, L., Sánchez, J.P., Dormido, S., (2016). What remote labs can do for you, Physics Today, vol. 69 no. 4, pp. 48-53. Fabregas, E., Farias, G., Dormido-Canto, S., Dormido, S. and Esquembre, F. (2011). Developing a remote laboratory for engineering education. Computers & Education, vol. 57, pp. 1686-1697. Heradio, R., de la Torre, L., Galan, D., Cabrerizo, F.J., Herrera-Viedma, E., Dormido, S. (2016) Virtual and remote labs in education: A bibliometric analysis, Computers & Education, 98, pp. 14-38. Papadopoulos, A.V., Leva, A., (2013) “Laboratories over the network: from remote to mobile”, 10th IFAC Symposium Advances in Control Education, Sheffield, United Kingdom. Restivo, M. T., Cardoso, A., (2013). Exploring Online Experimentation. Guest Editorial, iJOE, Vol. 9, pp. 4-6. Štefka, P., Žáková, K., (2016), Mobile Application for Remote Control of Thermo-Optical Plant, 13th International Conference on Remote Engineering and Virtual Instrumentation (REV’16). Tawfik, M., Sancristobal, E., Martin, S., Diaz, G., Peire, J. and Castro, M. (2013). Expanding the Boundaries of the Classroom: Implementation of Remote Laboratories for Industrial Electronics Disciplines. Industrial Electronics Magazine, IEEE, vol. 7, pp. 41-49. Villa-López, F. H., García-Guzmán, J., Enríquez, J. V., LealOrtíz, S. and Ramírez-Ramírez, A. (2013). Electropneumatic System for Industrial Automation: A Remote Experiment within a Web-Based Learning Environment. Procedia Technology, vol. 7, pp. 198-207. Wenshan, H., Guo-Ping, L. and Hong, Z. (2013). Web-Based 3-D Control Laboratory for Remote Real-Time Experimentation. IEEE Transactions on Industrial Electronics, vol. 60, pp. 4673-4682.
In the first one, the user may introduce the set-point value. The software will then automatically perform the preestablished procedure based on the implemented controller (Hybrid Controller based on a P controller). In the second (Relay Controller with dead zone and hysteresis), the set-point value and the control parameters may be introduced (or the default ones kept). The software will then automatically perform the pre-established procedure. The pump and/or valve indicator lights, if of green color, indicate that the pump and/or valve are actuated. This information can be observed in the relay controller status. The graphical presentation automatically displays the introduced parameter in order to allow the user a better perception. In each case, the user interface provides in the monitoring section the numerical value of the water level, the voltage output of each transmitter and the detectors state, while the live video of the real system permits the user to follow the level evolution. By using any of the two possibilities, manual actuation and the automatic mode using Hybrid Controller based on a P controller, the students may be able to perform the sensing devices characterization. For that purpose, a very simple animated indicator on the animation window gives the constant level value in the animated tank of the Monitoring Section of the user interface. 6. CONCLUSIONS This setup contributes with a new technological solution to the remote experiments of "online experimentation @ FEUP", (https://remotelab.fe.up.pt). This solution is presenting a very good performance. The flexibility allowed by the solution used for developing the interface is a valuable tool for adapting the remote experiment to different requirements of learning objectives. Combining both the use of HTML and the commitment to optimize the elements dimensions to the dynamic positioning, makes the application available through any mobile device. The system is under evaluation at present. The main electronic solution was the result of an Integrated Master in Mechanical Engineering thesis and, as such, it has also been a student project in a learning context. ACKNOWLEDGEMENTS This work has been funded by Calouste Gulbenkian Foundation under Project U-Academy and by the Portuguese 197