PROCEEDINGS OF ICETECT 2011
PIC18LF4620 Based Customizable Wireless Sensor Node to Detect Hazardous Gas Pipeline Leakage S. Edward Jero1, A. Balaji Ganesh2 Opto-Electronic Sensor Research Laboratory, Velammal Engineering College, Chennai -66, INDIA
[email protected],
[email protected]
Abstract— The paper describes the performance and functional characteristics of PIC18LF4620 based wireless sensor node in monitoring the parameters such as CO2, Oxygen, temperature, humidity and light around the pipeline structure. The system is deployed to monitor any deviations in these parameters with the standard atmospheric values eventually alert the user even to a remote location. The proposed system is a battery operated wireless sensor node which is interfaced with the external sensors to measure the parameters listed above. The distance range between sensor node and coordinator node is also tested. The signal conditioning module associated with detailed calibration procedure for the individual sensor is also described. Zigbee protocol stack is implemented to enable wireless transmission and performance of the same is evaluated. Keywords—PIC18LF4620, Wireless Sensor Node, Gas Pipeline Leakage Detection, Zigbee module
I.
INTRODUCTION
Obviously, the atmospheric air is composed of various gases including nitrogen, methane, oxygen and carbon dioxide etc in different percentage [1]. Industries are using gases like CO2, Oxygen, Nitrogen, Methane etc and commercializing it based on the requirements [2]. Gas pipelines take part of vital role in transmission and distribution of gases in industrial and domestic purposes [3]. Leakage of hazardous gas pipelines modifies the percentage of gas contents in the atmospheric air and causes undesirable effects in the environment. The proposed system used to monitor the concentration of CO2 and the percentage of oxygen, humidity and temperature in the atmosphere in the randomly selected locations in the pipeline. The proposed system is a PIC18LF4620 based wireless sensor node and it has the features of continuous monitoring of specified parameters with easy deployment procedures and increase the battery lifetime. Wireless connectivity is obtained by MRF24J40 zigbee module which enables data transmission of the system to the remote location [4]. II.
PROPOSED SYSTEM OF COMPONENTS
The proposed system consists of, Sensor module consists of sensor for each parameter and its respective power circuitry. Output voltages of the procured sensors are not found to be insufficient to have a better interpretation with Analog-toDigital Converter (ADC) and micro computer. Signal
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conditioning module amplifies the sensor output and the same is fed to ADC [5]. The chosen PIC18LF4620 is a low voltage, nano watt Micro controller unit. The microcontroller is interfaced with sensor modules, communication module. The required computations for the analog signals received from sensors, data transmission are done within micro controller unit. Wireless communication module consists of 2.4GHz IEEE 802.15.4 based MRF24J40 RF Transceiver zigbee unit which is used to establish the wireless connectivity of the system. The 9V Ni-MH rechargeable battery is used to power up the system [6]. In the mere future, a solar battery charging unit will be adapted to charge the battery. Voltage regulation is designed to provide the rated input voltage supply for each module. The block diagram representation of the proposed system is shown in the Figure 1.
Figure 1. Block Diagram Representation of Proposed System
III.
SENSOR NODE – HARDWARE COMPONENTS DESCRIPTION
The sensor node consists of various sensors to monitor the values of CO2 concentration, percentage of oxygen, temperature and relative humidity. The sensors to be embedded with the system are listed in Table 1 TABLE I.
SENSOR COMPONENTS DESCRIPTION
Sensor Type & Its Details
Measurand
TGS4161 (M/s Figaro, USA) KE-50 (M/s Figaro, USA)
CO2 Oxygen
ChipCap-L (M/s GE Sensing, USA)
Temperature and Humidity
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Each sensor outputs are amplified by the gain amplifier [7]. The maximum gain of an amplifier is selected to obtain the reference voltage of the analog to digital converter (ADC). The filter circuit is added with the output of the gain amplifier to reduce the noise level of the amplified output. The filtered analog signals are given as inputs to the 10Bit ADC modules of the micro controller. The block diagram of signal conditioning circuit is shown in Figure 2.
MRF24J40MA zigbee module used to establish the wireless connectivity of the designed system. Serial-Parallel Interface (SPI) communication protocol supports the interface between zigbee module and micro controller unit. The information required to be transmitted are loaded in the data frame and the payload is placed in the transmission buffer and ready to transmit. Wireless communication takes place when the requested node is founded as idle. The block diagram of interfacing zigbee module with micro controller is shown in Figure 4.
Figure 2. Block diagram of sensor module
Figure 4. Wireless Communication module
PIC18LF4620 Low power micro controller is contributed for computations, conversion and data transmission of the proposed system. The input power supply required to operate the micro computer is 3.3V. The current drawn by the micro controller is 11µA at run mode. Thirteen number of 10-bit ADC modules support the extension of the existing design; SPI module and ZigBee compatibility are the key features which are used by the proposed system. The 10bit ADC of the micro controller converts the analog input signal from the sensor module into digital value within the range between 0 and 1024. Computations are used for the conversion of digital values to its respective engineering units. The block diagram of microcontroller unit is shown in the Figure 3. The PICDEMZ Evaluation board is used for design verification of the proposed sensor node in programming and functionality. The Sensor modules are connected with the full function device node. The coordinator node is connected with the computer for monitoring the measured parameters from the sensor node. The ICD3 debugger provides hardware break points and supports hardware debugging while the execution of program.
IV.
SOFTWARE PROCESS MODEL OF SENSOR NODE
The MPLAB IDE with PIC C18 compiler is used to compose the programming part of the proposed system. The computed values of each sensor output parameters in PIC18LF4620 are obtained by the program written in Embedded C using PIC C18 compiler and loaded in the data fields D0, D1, D2 and D3 of the data frame. Data field D4 is loaded with the cyclic redundancy check value (CRC) which is calculated for all the computed sensor data. The transmission buffer of the zigbee stack is loaded with that data frame and ready to transfer the data on request as shown in the block diagram of Figure 5. The CRC value is used to verify the transmitted data of the sensor node at the receiving end.
Figure 5. Block diagram of software architecture Figure 3. Block diagram of microcontroller unit
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V.
RESULTS AND DISCUSSIONS
A four pin carbon dioxide sensor, which contains a heater with 70 ohm resistance. This sensor requires 5V voltage to the heater circuit and the response time of the sensor is calculated approximately 90 seconds. The EMF generated by the sensor is inversely proportional to the concentration of CO2 and measured through a high impedance operational amplifier TLC271 [8]. The proposed system is designed to measure the concentration of CO2 in the range between 350PPM and 3500PPM. EMF generated at 350 PPM of CO2 is one of the ranges between 220 mV and 490 mV. The EMF generated at 3500 PPM of CO2 by the range between 44 mV and 72 mV. The test environment for CO2 sensor to observe the variation in the concentration is created as the sensor is enclosed by the fiber box which contains an air vent; an exhalation through that air vent increases the CO2 concentration inside the enclosed area of the box result in changes in EMF. Figaro KE-50 Oxygen sensor provides a linear voltage output signal for the rate of oxygen present in the atmosphere. Test setup is obtained by the percentage of oxygen present in the plastic pot is reduced by exhalation and the sensor is closed by that pot. The test procedure is found that the output of the sensor at 21% of oxygen is within the range between 47 mV and 65 mV. The maximum output of the sensor is 260 mV at the maximum (100%) of oxygen. Accordingly the oxygen value is calculated from the linear relationship with oxygen of the sensor’s output. After each testing, oxygen sensor output is bring back to the approximately 20% of oxygen by kept it in the normal atmospheric air and then the next test is conducted. The Humidity and Temperature sensor ChipCap-L provides the linear output for temperature and humidity of the atmosphere in the range between 0 and 1 volt [9]. All the calibrated sensors are cross checked with the same type reference instruments. Several test case scenerios are performed to validate the functional charatestics of developed sensor node. Tests are conducted in both laboratory and outdoor environments. The results are obtained and also the parameters are tested by keeping the sensor node at a distance of 100 fts from the coordinator node without any dataloss. The results obtained are plotted and are shown in figures 6 and 7. The coordinator node comprises with a computer and a wireless access unit. The database is maintaind in computer for the offline future analysis. The hardwares which are selected to build this system to obtain higher performance with minimum hardware components and requirement of minimal cost. The proposed sensor node has the features of low power consumption and deal with minimal number of components with larger distance covarage. In the mere future, it is planned to construct a customizable sensor node with the advent of same identified hardware components such as microcontroller, signal conditioning circuits and communication module.
Figure 6. Carbon-di-Oxide Sensor Output
Figure 7. Sensors (O2, Temperature & Humidity) Output
VI.
CONCLUSIONS
The functionaliites and performance of PIC18LF4620 based wireless sensor node has been evalutead by interfacing the same with various sensors. The sensor node is successfully tested for the distance of 100 ft witout any dataloss. The individiual sensors such as Carbon-di-Oxide, Oxygen, Temperature and Humidity are calibrated and deployed for the estimation of hazarourdous gas pipe line leakage. The signal conditioning circuit for the individual sensor has been designed eventually tested. A ten byte of data frame is formed and its data fields are allocated to each measured parameter. ACKNOWLEDGMENT The authors gratefully acknowledge the financial support of TIFAC-DST through the centre ‘Pervasive Computing Technologies’ to Velammal Engineering College, Chennai. REFERENCES [1] [2] [3] [4] [5]
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