Elsevier

Sensors and Actuators B: Chemical

Volume 237, December 2016, Pages 509-520
Sensors and Actuators B: Chemical

A self-calibrated Wireless Sensing System for monitoring the ambient industrial environment. From lab to real-time application

https://doi.org/10.1016/j.snb.2016.06.118Get rights and content

Abstract

The sensing performance of a self-calibrated Wireless Sensing System (WSS) was evaluated under laboratory and real environment conditions. The Wireless Sensing Node consists of a sensor array based on chemocapacitors, which is integrated with appropriate low power consumption read-out electronics and is connected with appropriate wireless module. The sensing system was evaluated and calibrated under laboratory conditions with two different VOCs transfer methods: dynamic and static. The sensing unit calibration deals with changes of VOCs and/or humidity concentration and temperature variations, simulating the real industrial environment. Finally the WSS was placed in the workspace of a printed flexing packaging industrial installation and comparison with the already installed commercial detectors was performed. A very good agreement between the results of the two measurement systems is demonstrated. Additionally these results showed that the WSS is characterized by fast response with high repeatability and long-term stability. Concluding, this system is suitable for the targeted application.

Introduction

Wireless Sensing Systems (WSS) are of great importance for numerous applications in diverse fields such as medicine, transportation, agriculture, military surveillance, home health care and industrial process control, since they fulfill the requirements for small size and low cost devices and un-attended low power operation [1], [2], [3], [4], [5], [6], [7], [8], [9], [10].

The key component of WSS is the sensor node, also referred as mote, comprised of: sensors, radio frequency (RF) transceivers with microcontroller and power sources. The mote performs all three key functions: sensing, to some extend processing and communication with the other motes and the gateway [11]. The sensing module of the mote is a sensor or a sensor array where a change in a property of the sensing material is converted by a suitable transducer to a readable signal. The most common operation principles are based on radiant, electrical, mechanical and thermal energy transduction types [12]. Then, the output analog signal is converted to digital (analog to digital converter) and is transferred to the processing unit [11], [13]. Usually, the on-mote processing unit has limited computational power and memory. There the digital signal is processed to provide the desirable information about the sample of interest. With suitable RF communication modules (wireless nodes) the motes transfer the acquired responses to a gateway unit. This gateway unit sends the collected data to a base station, for further signal processing [14] as well visualization. The gateway units can also communicate with other computers via other networks such as Local Area Networks (LAN) or Internet, building Internet of Things (IoT) [15], [16], [17].

With the WSS technology measurements at the location of interest (in-line analysis) are attainable. The key benefit of wireless sensor systems stands in their ability to collect the data read by sensors wirelessly, thus allowing storage and analysis at a local facility. Adopting WSS for process in-line analysis provides great advantages over traditional off line analysis, such as: (a) elimination of pre processing steps (no need for sample handling or transformation) and (b) reduction of the overall cost of data acquisition (shorter time for sampling, handling and analysis) [10].

The monitoring, evaluation and control of the ambient environment, with the use of WSS, rather than collecting samples for off-line laboratory analysis appears to be a challenging task in industrial applications, where the demand for real-time measurements is apparent, as in the case of leakage of explosive or environmental harmful products.

In a previous study the development and the characterization under laboratory condition of such a system was introduced [18]. In that work, the WSS was tested only under laboratory conditions upon exposure to certain analytes of interest and the results were post processed with Principal Component Analysis (PCA), showing the potential discrimination between gaseous environments of different composition and different concentration.

In the present study the implementation of a WSS for real-time monitoring and evaluation of the ambient workspace environment of a flexing packaging industrial installation (Alfa Beta Roto SA, [19]) is the main objective. The main solvent used in flexing packaging processes is ethyl acetate (EtOAc). Therefore, effective safety precaution measures, relating both to the flammability of the solvent used [45% of the Lower Explosion Limit, (LEL)] as well as to the upper limit of safe exposure of the employees [Time Weighted Average, (TWA)] are required [20]. Furthermore, the concentration of the analyte should be monitored in real-time at various points of the factory with the option to easy install such a unit at a new point of interest. These objectives is hard to be reached by the standard ethyl acetate measurement units which are rather heavy and bulky and significant preparation actions should be carried out in advance to connect a new unit in the control system.

Moreover, towards the final application of continuous monitoring the gaseous environment composition in the working areas, the WSS has to be tested and characterized under laboratory conditions simulating in a more holistic perspective the real-time conditions. For that purpose two different VOCs transfer methods (static and dynamic measurements) were used. The tests included evaluation and calibration of the WSS under exposure to vapor concentration changes of humidity and EtOAc and to temperature variations. It should be noted that in the industrial facility of interest a commercial detector (TecnoControl, #TS293PX, [21]) calibrated for EtOAc vapor is already installed. This detector is also used for determining the EtOAc vapor concentration produced during the static measurements. Details about the technical characteristics of the commercial detector are shown in Table 1 of the supplementary part. Additionally the specifications/requirements of the pilot application, according to the technical manager of the industrial facility, are shown in Table 2 of the supplementary part. At this stage, our purpose is to supply the industrial facility with a complementary, portable and easy to install, sensing device, rather than to replace the already installed commercial detectors with the WSS. Therefore, the final evaluation in the real industrial environment was performed with the use of the WSS and the results were compared with those of the commercial detector in terms of sensitivity, response time, repeatability and long term stability.

Section snippets

WSS description

The WSS is shown in Fig. 1 [18]. Briefly, the sensing unit is a sensor array based on chemocapacitors, which is integrated with appropriate low power consumption read-out electronics and is connected with appropriate transceiver (wireless node) that is controlled by a gateway unit. The gateway unit collects the data and transmits them to a computer for monitoring and processing with suitable software.

The sensor array is fabricated to meet certain specifications: (a) suitable design of the

Evaluation and calibration of the WSS under laboratory conditions

The evaluation and calibration of the sensor array of the WSS was performed with measurements under laboratory conditions with dynamic and static VOCs transfer methods. During the measurement the WSS was exposed to vapors of pure components (Relative Humidity (R.H. (%)) and EtOAc (ppm)), as well as to selected binary mixtures of them at constant temperature. Additionally the temperature dependence of the sensors was also studied.

Performance evaluation in real-time industrial application

The WSS was appropriately packaged and installed in the workspace of Alfa Beta Roto S.A. industrial facility (Fig. 9). Details about the technical characteristics of the WSS are also shown in Table 1 of the supplementary part. The objective is the precise and accurate calculation of EtOAc vapor concentration in the ambient environment. The workspace is already equipped with commercial detectors (TecnoControl, #TS293PX, catalytic pellistors) selectively calibrated for this particular analyte

Conclusions

This paper demonstrates the operation of a self-calibrated WSS for real-time monitoring of the ambient workspace environment of a specific industrial facility. The objective is the accurate and precise detection of the vapor concentration of the industrial solvent (EtOAc) used.

In this study the WSS is evaluated and calibrated under realistic conditions, simulating the real-time industrial ones. For that purpose, two different vapor analyte transfer methods were used. Both dynamic and static

Acknowledgements

This work was supported by the research project entitled “Autonomous and Integrated system for insitu and continuous contaminant gases in industrial environments (ALEPOY)”, co-financed by the European Union (European Regional Development Fund - ERDF) and Greek national funds through the Operational Program “Competitiveness and Entrepreneurship” of the National Strategic Reference Framework (NSRF) – National Action “Support of New Enterprises & SMEs” (MIA – RTDI, Contract No. 19SMEs2010).

Dr. Petros Oikonomou received the B.Sc. degree in Chemistry from the Chemistry Department of Ioannina University (Greece) in 2003. He received the M.Sc. and the Ph.D. degree in “Polymers and their Applications” from the Chemistry Department of University of Athens in 2005 and 2012, respectively. Both M.Sc. and Ph.D. thesis research were performed at the Institutes of Microelectronics and Physical Chemistry at National Center for Scientific Research – NCSR, “DEMOKRITOS” – Greece. Currently, he

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    Antonis Olziersky received his B.Sc. in Physics from the Aristotle University of Thessaloniki, Greece, in 2000. He joined the Institute of Microelectronics of NCSR “DEMOKRITOS” in 2000 where he received both his M.Sc. and Ph.D. in Microelectronics from the Department of Informatics of the National University of Athens, Greece in 2003 and 2006, respectively. He has worked in the field of fabrication and characterization of nanocrystal memory devices and electron beam lithography. In 2007 he obtained a “Juan de la Cierva” postdoctoral position at the Electronics Department of the University of Barcelona in Spain. He has worked on characterization of amorphous metal oxide materials for large area electronics, inkjet printing of functional materials, focused ion beam patterning. In 2010 he moved back to the Institute of Microelectronics of NCSR “Demokritos” to work as a postdoctoral research associate in electron beam lithography. In November 2014 he joined the IBM Research Laboratory in Zurich, Switzerland. ([email protected].)

    Evangelos P. Hadjigeorgiou received his B.Sc. in Mathematics from the University of Ioannina (Greece) in 1985 and his Ph.D. in Applied Mathematics and Mechanics from the University of Aegean (Greece) in 1997. From 2007 he is an Assistant Professor in the Department of Materials Science and Engineering in the University of Ioannina. His research focuses on continuum mechanics with coupled fields and on smart composites. ([email protected].)

    Serafim Katsikas received his B.Sc. in Electrical & Computer Engineering from the National Technical University of Athens in 1998. He is the Head of Prisma Electronics R&D department. He has participated in a variety of research programs in Greece and internationally. He is member of the board of directors of the Hellenic Semiconductor Industry Association (Hellenic-SIA) while participates in various International Congresses. ([email protected].)

    Dimitrios Dimas received the B.Sc. degree in Physics and M.Sc. in Electronics from the Physics Department of Aristotle University of Thessaloniki (Greece) in 2004 and 2008, respectively. He has participated in a variety of research projects mainly focused in environmental sensing applications. Currently, he works as manager of the Installations Department of Prisma Electronics. ([email protected].)

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    Ioannis Raptis received his Ph.D. on e-beam lithography (1996) from Physics Department, University of Athens. The experimental part of his Ph.D. thesis was carried out at IESS-CNR (Rome, Italy). From 2003 he works at NCSR “DEMOKRITOS” as researcher on the implementation of technologies and electronic/photonic devices in the micro/nano scale for bio(chem) sensing applications. At the end of 2008 he co-founded Theta Metrisis as the first spin-off company of the Institute of Microelectronics NCSR ‘Demokritos’ exploiting technologies and methodologies that have been developed in his team. He is/was Key Researcher and Coordinator for several national and EU (FP6, FP7) funded research projects in the areas of nanotechnology and microsystems. He is program and steering committee member in several international conferences and serves regularly as reviewer in scientific journals and as invited speaker in conferences/summer schools. He is author of more than 130 publications in international journals and holder of 4 patents. ([email protected].)

    Dr. Merope Sanopoulou received her B.Sc. degree in Chemistry from the University of Athens in 1977 and her Ph.D. in Physical Chemistry from the same institution in 1984. She then joined the Institute of Physical Chemistry, NCSR “DEMOKRITOS”, currently being Head of the Laboratory of Transport of Matter Phenomena in Polymers. She has been engaged in extensive modeling and experimental studies of sorption and diffusion in polymer films, focusing in transport-related applications of polymers, such as controlled release devices, transport properties in polymeric hydrogels, characterization of polymeric membranes for separation processes, performance evaluation of polymer-based capacitive sensors. She is the author/co-author of more than 70 publications in peer-reviewed journals and has been key researcher or project leader in various National and EU research projects. ([email protected].)

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