Design of a methane monitoring system based on ...

Scientific Research and Essays Vol. 5(8), pp. 799-805, 18 April, 2010 Available online at http://www.academicjournals.org/SRE ISSN 1992-2248 © 2010 Academic Journals

Full Length Research Paper

Design of a methane monitoring system based on wireless sensor networks Abdullah Erdal Tümer1* and Mesut Gündüz2 1

Department of Computer Education and Instructional Technology, University of Selcuk, Turkey. 2 Department of Computer Engineering, University of Selcuk, Turkey. Accepted 25 March, 2010

Wireless sensor prototypes have varying hardware architectures and distinctive sensing principles. In this study, a prototype is developed for the purpose of monitoring leaks of methane (CH4), which has explosive properties and is the main constituent of the natural gas, in the refineries or buildings and work places heating. The prototype can be mounted on the walls as well as it is portable. System is composed of the integration of methane gas sensor module NGM2611 to MicaZ mote. The sensor module is pre-calibrated and is a product of FIGARO firm. The MICAz is a 2.4 GHz, IEEE/ZigBee 802.15.4; board used for low-power, wireless and sensor networks. By means of the designed sensor prototypes, wireless sensor networks are established indoors; hence, methane gas leaks are detected and sent to the base stations. Data received by base station is monitored by the software on a computer connected to the base station. This study explains the system structure, parts of hardware and software design in detail. The aim of the system is to implement a wireless methane gas platform. This platform can be used to real time monitoring of the methane leaks which would be crucial for critical conditions and helpful to decrease risk of death due to those leaks. Key words: Wireless sensor network, methane sensing system. INTRODUCTION Wireless sensor networks (WSNs) are used increasingly for an accurate monitoring of the physical environments exposed to fire; toxic and explosive gas leaks (Boukerchea et al., 2007). One of the explosive gases is methane which is the main constituent of the natural gas (Liua et al., 2008). Many houses in the UK and elsewhere in Europe employ a boiler fired by natural gas, which is used to heat domestic water and adjust the room temperature through room radiators (Boait et al., 2009). Monitoring methane gas is a type of gas which is widely used in the world is of great significance not only for industrial security but also for personal security. The existing methane monitoring systems use mostly cable network. That kind of network has poor performance of expansion. The cables are poor in aging and wearing resistance, and have high incidence of failures. With the

*Corresponding author. E-mail: [email protected]. Tel: +90 332 323 8220. Fax: +90 332 323 8225.

expanded working surface, a blind spot which causes an additional cost of installation and maintenance occurs. When an accident (e.g. explosion) happens, the sensors and cables are usually damaged fatally, and cannot provide information for rescue search and detection events (Wei et al., 2007). On the other hand, wireless gas sensor networks (WGSNs) do not need cables. This is a fact that reduces installation cost, as it brings a user-friendly design forward. Consequently, networks can quickly be expanded into wider and different areas. Even in the case of failure of any sensor nodes due to a died battery situation or similar problems; communication and monitoring will continue functioning through other sensors. In addition, sensor network systems may solve the key problems like bandwidth, mobile data communications, staff orientation and real time monitoring (Li-min et al., 2008). The control and monitor of indoor atmosphere conditions represent an important task. It is to ensure suitable working and living spaces for people (Chunga et al., 2006). The staffs who work in the places where there is methane can carry

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this platform easily and they can quickly get aware of gas leaks in the case of danger. The other staffs, who don’t work in the places where there are no gas leaks, can be informed about this danger with the help of their carrying sensors, which get information coming from other sensors. So, this situation will contribute to the staff’s security and motivation. This study surveys a prototype and accompanying software that is particularly designed to avoid negative influences of the possible leaks of CH4, the main constituent of the natural gas and to monitor the gas levels before an explosion takes place. Our prototype is designed by the integration of FIGARO NGM2611 CH4 sensor circuit to Crossbow 2.4 GHz MicaZ wireless module. Software is written for real time monitoring of the gas data sensed when transmitted to the PC through the base station which is connected to the serial port. Software provides both real time and retroactive monitoring of data which is stored in the database. Moreover, data can be monitored via internet anywhere if desired. Besides, it provides an accurate monitor of the physical environment in order to prevent accidents that may result in death of residents and employees and casualties before CH4 concentration comes to dangerous levels and helps rescue team to understand what is going on in field of leak and to take immediate precautions. It is certain that in such kind of scenarios, taking measures is of primary importance. WIRELESS MONITORING SYSTEMS One of the applications related to the monitoring of physical environments in the case of emergency situations is monitoring gas leaks. The main object of the developed hardware and software for wireless gas sensor network is not to risk life and health of the residents and employees in possible emergence of the poisonous and explosive gases in the environment resulting from many different reasons. For that reason, sensors such as temperature sensors, humidity sensors, CO2 sensors, CH4 sensors and wearable EKG sensors are connected to the RF transmitters in order to monitor indoor environmental conditions and healthcare (Chunga et al., 2006). There are already various studies made to develop prototypes for both wireless methane monitoring and many different sensors integrated to wireless modules in the literature. In this section, we intend to provide a brief overview of some of the related research work. Li-min et al. (2008) designed a monitoring system based on wireless sensor network for mining safety. S3C44BOX microcontroller terminal based on Samsung firm’s ARM7TDMI structure and CC2420 RF transceiver of Cipcon are used to gather data accompanied by data processing and RF receiver-transmitter, respectively. Niu et al. (2007) developed a heterogeneous hierarchical mine safety monitoring system to measure the methane gas concentration and determine the location of

of the miner in the mines. System uses hardware series developed by EASINET. Data is collected by the wired base station consisting of EZ210 communication board and EZ511 gate way board. EASINET node includes TinyOS operating system and sensor board supporting analog gas sensor (LXK-3) and EZ310 compatible EZ210. Node uses 8-bit 8 MHz microprocessor and 38.4 Kbps data rate operating at 433 MHz radio. Zhang et al. (2008) developed software for monitoring methane gas concentration and hardware node by using a mini intelligent methane sensor to form a real-time methane monitoring network based on NRF240. Network can be used both for data gathering and calibration purposes. Communication module consists of PCB antenna, NRF2401 data trans-mission and receiving module which can be connected. Tavares et al. (2008) mentioned wireless sensor network (WSN) which has the capability of measuring and processing different data for drivers. A MTS310 sensorial board which has on board light, aceleration and temperature sensor with a MicaZ module of Crossbow firm is used for signal processing and transmission. Instead of special software, open source software running on TINYOS operating system is used to monitor the data. Fulford-Jones et al. (2004) developed a mote-based oximetry module which collects data from noninvasive finger sensors and transmits it to a base station. For wireless transmission of the cardiac rhythm continuously, an EKG circuit is integrated into Mica2 node. Consequently available data can be easily received by PDAs, desktop PCs, or wireless enabled devices in a multitude of healthcare scenarios. The research consists of development and design of the hardware containing Mica2 platform integrated EKG circuit and software performing safe and wireless transmission of the EKG data to a nearby receiver. Chen (2008) designed a type of gas inspection tour as a system based on single chip microprocessor and wireless transmission technology. System uses LXY-3 methane gas sensor as the sensor, SCM MSP430F149 as the central core controller for data analyzing and processing and NRF401 as wireless transceiver for data communication between the field monitor and inspection tour equipment. Main controller is connected to the inspection tour equipment through a MAX232 interface. As easily understandable from the related work, researchers have integrated diverse compatible electronics equipment from different manufacturers (transmitters, receivers, sensors). After the hardware is ideally designed, either open source software or the software they developed themselves is used to monitor gathered information by the prototype from a central station. In this study, we present a prototype for wireless methane gas sensor systems. The system consists of integration of Figaro NGM2611 methane gas sensor which has never been used for

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platform can run with a 2.7-3.3 V external DC power supply or 2 AA batteries. Moreover, it easily allows connection to various sensor boards via the standard 51-pin expansion connector. Indoor radio transmission range is 20 - 30 m. TINYOS is an open source event-driven operating system which is the operating system running on MicaZ. The application for TINYOS can be written by using NesC, a C programming language extension. TINYOS operating system and NesC language are designed for the limited resource microprocessors. They aim to achieve efficient processing of events such as sensor data acquisition, radio transmission and data processing (Won-Suk et al., 2008). Sensor

Figure 1. NGM2621 pre-calibrated module for methane.

Table 1. Methane gas sensor equivalent output voltages.

voltage (V) 1,00 1,40 1,80 2,00 2,25 2,40 2,60 2,80 2,90 3,00

ppm 1.000 2.000 3.000 4.000 5.000 6.000 7.000 8.000 9.000 10.000

sensor node designs with Crossbow MicaZ wireless module and related software for monitoring. MATERIALS AND METHODS Integration materials The integration of three materials is essential in order to meet the needs of sensor node design; (i) wireless module; (ii) sensor and (iii) battery. The following is a brief explanation of the employed equipment and their usage motivations in the designed prototype.

Wireless module MicaZ mote developed by UC Berkeley, produced and marketed by Crossbow Technology Inc. has been chosen as wireless module for this gas sensor network study. MicaZ mote has embedded microcontroller (8 bit Atmega 128 L), 2.4 GHz low power radio transceiver (Chipcon CC2420), and modest amount of local storage in a package (4 kb EEPROM, 128 kb program flash memory). The

In our designed prototype, NGM2611 coded pre-calibrated methane gas sensor module of Figaro that has been used to integrate to MicaZ mote (Figure 1). The sensor is especially used in residencies; it has long life, low power consumption and high sensitivity for methane gas. NGM2611 methane gas sensor needs 56 mA heating current and runs with 5 V DC. There are three reasons for choosing this module. (i) It is calibrated: Calibration is a complicated and time consuming process which also requires a substantial investment in calibration equipment. (ii) It runs with 5 V DC voltages external power supplies. This is not appropriate for wireless sensor networks. As a consequence of this, we get the 5 V output voltage by using a MAX1595 charge pump regulator which is powered by 2 AA batteries running the wireless module. In this way, both wireless module and sensor are powered by one single power source. (iii) Output voltage can be adjusted: NGM2611 gas sensor outputs 0 - 5 v voltage values. Sensor’s output voltage value is dropped to an appropriate value by adjusting the potentiometer value to 1.33 kΩ through pre-calibration and applied to wireless sensor boards data input which accepts 8 bits and 3 v. Necessary output voltage is in order to measure the range between 1000 - 10000 ppm1 gas concentrations are given in Table 1. Design and implementation By consulting the datasheet of the MicaZ, pre-calibrated NGM2611 methane gas sensor and MAX1595 charge pump regulator, it is possible to verify how to connect them together. This work enables the connecting of the methane gas sensors to MicaZ via Digi-Key H2163-ND 51 pin expansion connector (Figure 2). In Figure 3a the designed gas sensor board printed circuit was seen. The pre-calibrated NGM2611 gas sensor on the sensor board powered by 5 V DC power supply. Micaz wireless module powered by 2 AA batteries. In Figure 3b by using the voltage of these batteries and MAX1595 charge pump both wireless MicaZ mote and NGM2611 methane gas is powered. Because MAX1595 charge pump has the ability to increase the voltage level of 2 AA batteries to 5 V. In this case, the wireless methane gas platform can be powered with only one power supply. There is no need for an extra power supply. Hence, the platform can be portable easily (Figure 4b. NGM2611 methane gas sensor converts the sensed 1000 -10000 ppm gas concentration values to 0 - 3 V voltage interval (Table 1) and transfers the data by means of 51 pin connector to MicaZ wireless module to be processed and then transmitted to base station.

1

A detailed investigation has been carried out on design of optical sensor for methane detection with a sensitivity of ~2% of the lower explosive level (LEL) for methane (1000 ppm-part per million) (Jun et al., 2007).

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Figure 2. Circuit schematic of 51 pin expansion connector, MAX1595 and NGM2611 gas sensor.

Expansion Connector NGM2611 MAX 1595

(a)

(b)

Figure 3. Methane gas sensor board printed circuit: (a) top surface (b) bottom surface.

Figure 4. Wireless sensor node: (a) MicaZ, (b) methane gas sensor board and MicaZ connected

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Sensor node is starting

No

If sensor started successfully?

Stop Yes Detect methane gas concentration continuously

Analyze Data If data>1.000 ppm

Yes

Send Signal to base station

No Is there any methane gas detected?

No

Yes

Figure 5. The program flow chart of the sensor node.

Table 2. ppm values as sensed bits.

BIT

V

ppm

1

1

1

1

1

1

1

1

3

10.000

1

1

1

1

0

1

1

0

2,9

9.000

1

1

1

0

1

1

1

0

2,8

8.000

1

1

0

1

1

1

0

1

2,6

7.000

1

1

0

0

1

1

0

0

2,4

6.000

1

0

1

1

1

1

1

1

2,25

5.000

1

0

1

0

1

0

1

0

2

4.000

1

0

0

1

1

0

0

1

1,8

3.000

0

1

1

1

0

1

1

1

1,4

2.000

0

1

0

1

0

1

0

1

1

1.000

Software In this section, the software developed for data acquisition and data collection are presented. Data acquisition The nodes in this network periodically switch on their sensors and transmitters, detect the environment and transmit the data of interest to base station. Necessary software has been developed

and written on the onboard microprocessor to digitize the sensed data by the gas methane sensor board on the MicaZ and to transmit the data to a base station through a RF antenna. Applications have been written by using a NesC programming language on a desktop computer, machine codes produced by a compiler are then transferred to each node through gateways. When the sensor node is switched on, the program runs automatically. Because nodes consume a limited energy during sensing, processing and transferring, developed program ignores the values below 1000 ppm to increase the lifetime of the nodes. The flow chart of sensor node program is given in Figure 5. Data collection and monitoring Software is written in Java in order to control the transmitted data from base station to computer serial port connected to base station. The node through which the sensed data is coming from is detected and the raw value sensed by the node is converted to physical values. Thus, sensed methane gas concentration in ppm by each node can be monitored in real time. Raw digital values are shown in Table 2 in ppm. The application permits both real time monitoring and identifying from the nodes where data is coming from. The application does not warn for the values between 1000 7000 ppm since it is below danger levels. But the values above 7000 are up to 10000 ppm, create the continuous flashes on the monitor and attract the attention of people in charge, so that, they can take necessary precautions. Another added property of the application is that, the data is stored in the database and can be monitored through a prepared web page from anywhere if desired. To collect and manage application server information and WSNs information, we use MySQL as a database management system. Flow chart of the program is shown in Figure 6.

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Start

Base station connected to serial port?

No

Stop Yes Detect methane gas concentration continuously

Is there an exceed Threshold? (if data>7000 ppm)

Yes

No No

Receive concentration of methane gas?

Yes

Send data and node ID

Send data and node ID with flag

Store Data

Figure 6. The program flow chart of information receiving and processing terminal.

RESULTS AND DISCUSSION Gas monitoring systems are widely used for situations such as environmental protection, processing control, forest fire prevention, family use of natural gas, and control systems as well as in agriculture, scientific research, medical, health, etc. This study presents a design of sensor system for monitoring indoor methane gas concentrations and thus, contributes to the wireless gas sensor network technology. Wireless gas sensor system design presented here has two components. First one is the MicaZ as the wireless module and secondly methane gas sensor board is powered up by the batteries of the MicaZ module and makes the gas sensor data suitable for MicaZ inputs. It also contains a user-friendly software for real time monitoring of sensed data from the computers serial port which is connected to base station, as well as analyzing data, saving of the data to a database and monitoring data from anywhere through an internet web page when desired. This system meets the requirements of the applications such as monitoring methane gas concentration value or determining the place where the gas leaks occur. During the experiments conducted to check the system, we manually actuated a device to release a proper amount of

methane to change the methane concentration, which can be regarded as a methane leakage. The experiments indicated that the accuracy of data communication between the methane gas sensor node and monitor terminal is very high. Conclusion The results of this study demonstrate that as the system can avoid costs of rewiring, it is more flexible and suggests a low cost installation cost. Wireless movement and topologic change will be easier. The effective communication and monitoring device will avoid losses, thanks to real time monitoring. Compared to the existing monitoring systems and developed system has a simpler structure and comes with a lower cost. ACKNOWLEDGMENTS This work has been conducted within the scope of a doctorial thesis and was supported by BAP coordinator ship of Selcuk University under Project No.09101011. The authors would like to thank Prof. Dr. Ibrahim USLU and

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Fevzi Yildirim for their constructive comments and suggestions. REFERENCES Boait P, Rylatt RM (2009). A method for fully automatic operation of domestic heating. Energy and Buildings 42(1): 11-16. Boukerchea A, Araujoa RB, Silvab FHS (2007). An efficient event ordering algorithm that extends the lifetime of wireless actor and sensor Networks. In Performance Evaluation an Int. J. 64(5): 480494. Chen Y (2008). Research and Design of Methane Gas Inspection Tour System Based on Low-Power SCM MSP430F149, Intelligent Information Technology Application, Second Int. Symposium 2: 503507. Chunga WY, Ohb SJ (2006). Remote monitoring system with wireless sensors module for room environment. Sensors and Actuators B: Chemical EASINET product series, http://www.easinet.cn/ products.htm 113(1): 64-70. Fulford-Jones T, Wei GY, Welsh M (2004). A portable, low-power, wireless two-lead EKG system. Engineering in Medicine and Biology Society, Annual International Conference of the IEEE. Figaro Inc. www.figarosensor.com 1: 2141-2144. Won-Suk J, Healy WM, Skibniewski MJ (2008). Wireless sensor networks as part of a web-based building environmental monitoring system, Automation in Construction, 17(6): 729-736.

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Li-min Y, Anqi L, Zheng S, Hui L (2008). Design of Monitoring System for Coal Mine Safety Based on Wireless Sensor Network. Mechtronic and Embedded Systems and Applications. IEEE/ASME International Conference, pp. 409-414. Liua X, Chenga B, Hu J, Qina H, Jianga M (2008). Preparation, structure, resistance and methane-gas sensing properties of nominal La1−xMgxFeO3. Micaz 2.4 GHz Datasheet, Crossbow Technology Inc., http://www.xbow.com/Products/Product_pdf_files/Wireless_pdf/MICA z_Datasheet.pdf. MySQL AB: The world's most popular open source database. www.mysql.comSensors and Actuators B: Chemical 133(1): 340-344. Niu X, Huang X, Zhao Z., Zhang Y, Huang C, Cui L (2007). The Design and Evaluation of a Wireless Sensor Network for Mine Safety Monitoring. Global Telecommunications Conference pp. 1291-1295. Tavares J, Velez FJ, Ferro JM (2008). Application of Wireless Sensor Networks to Automobiles, TinyOS, www.tinyos.net. Measurement Sci. Rev. 8(3): 65-70 Wei Y, Ying H (2007). Wireless Sensor Network Based Coal Mine Wireless and Integrated Security Monitoring Information System. Networking ICN pp. 22-28. Zhang X, Wang S (2008). Design a Wireless Sensor Network for Methane Monitoring System. Ind. Informatics pp. 614-618.