Zhi-qin WANG（Department of Information Engineering，Tangshan College，Tangshan 063000，China）

Design of ultra-low power wireless sensor network for temperature measurement of coke oven

Zhi-qin WANG*
（Department of Information Engineering，Tangshan College，Tangshan 063000，China）

Since it is difficult to set up the network in existing coke oven to measure the temperature and the cost is relatively high，the ultra-low power wireless sensor network for temperature measurement of coke oven is designed in this paper.Self-organizing network with a MESH structure for field environments are constituted of the protocols of a physical layer，data link layer，network layer，application layer，location-based routing protocol and the ultra-low power operation mode.The system has some advantages such as flexible，accurate，low cost and long survival.

Wireless sensor network，Temperature measurement，MESH structure，Ultra-low power，Self-organization

Hydromechatronics Engineering

http：//jdy.qks.cqut.edu.cn

E-mail：jdygcyw@126.com

1 Introduction

The wireless sensor network（WSN），highly integrated with the Short-range wireless communication technology，sensortechnology，embeddedsystem technology and network technology，has become an important research area of broad interest，and is increasingly used in a variety of area［1-3］.The ultralow power wireless sensor network for temperature measurement of coke oven replaces the traditional wire measurement with wireless sensor network.Hardware and software architectures are designed according to the topology of the industrial field environments.Ultra-low power operation of the system is achieved by using ultra-low power microcontroller，ultra-low power wireless communication ASIC，the power management module and the low-power mode.Self-organizing network with a MESH structure of the design is constitu-ted of physical layer protocol，data link layer protocol，network layer protocol，application layer protocol and location-based routing protocol for field environments.

2 System structures

2.1 Feature of the coke oven temperature measurement Coke oven is a kind of industrial oven which uses coal to produce coke.In order to ensure the quality of coke production，cake temperature of coke is measured by a thermocouple.The measurement results can be used as one of the input parameters for the automatic control system of coke oven.The traditional coke oven temperature measurement is wire communication，less measurement nodes and high cost of complex wiring.The wired system generally uses only 2-3 measurement points.The temperature of the cake inside the center of each coke oven hole is generally estimated without accuracy.The wireless communication system can increase the number of nodes，reduce costs and wiring difficulty.Depend on the installation environment，the location of the temperature measurement nodes is fixed and gathered relatively；for an example in an oven with 50 holes，each hole could be equipped with a node.It can improve the accuracy of temperature measurement.The coke ovens in factory are generally far from each other with a variety of architectural obstacles in the middle.The wireless communication requirements of the measurement system are the far distance and good penetration.

Coke oven system is a nonlinear system with a large time lag and inertia，so accurate temperature data have important implications for the accuracy of the control algorithm of automatic control systems.Cake temperature of coke is usually in the 900-1100 degrees Celsius，and temperature measurement error should be controlled within 1 degree Celsius.Real-time requirements are not very strict.One temperature data within every three minutes can meet the design requirements. Wireless measurement system needs long working hours to reduce the installation and commissioning work，usually for more than one year.The environments of the oven temperature measurement system with high temperatures，dust，corrosion，electromagnetic interference and other adverse conditions require protective measures of the equipment.

2.2 The network structure

According to the characteristics of the coke oven temperaturemeasurement，self-organizingnetwork with a MESH structure can effectively reduce the complexity of the system configuration.The wireless sensor network nodes of coke oven temperature measurement are divided into two types as temperature nodes and sink nodes.The temperature node can measure coke oven temperature by using the thermocouple circuit；the node has self-organizing capabilities to constitute MESH structure networks reducing the difficulty of configuration and organization.It can work for more than 1 year with a battery using low-power design. The sink node receives the transmission data and sent it to the host computer via RS485.The network structure is shown in Fig.1.

Fig.1 The network structure

2.3 The ultra-low power design

The ultra-low power design of wireless sensor network for temperature measurement of coke oven is achieved via two kinds of ways，the ultra-low power hardware design and software design.Ultra-low power hardware design includes how to reduce micro-processor power consumption by low voltage and sleep mode，using the power management module cutting off the peripheral circuits power supply when the system is sleeping，using the ultra-low power radio frequency circuits effectively reducing power consumption and ensuring communication distance and signal strength. Ultra-low power software design primarily reduce selforganizing routing time of the MESH structure network through software algorithms，and reduce system operating time for data transmission to save energy and balance the energy consumption of each node for extending the overall system surviving time.

2.4 The hardware structure

The hardware structure of temperature node includes the microcontroller module，thermocouple module，wireless RF transceiver module and power management module.The microcontroller module reads and stores the temperature data from the thermocouple module，sends data to the wireless RF transceiver module and receives data according to the network conditions.The battery and power management module provide protection for the low power operation of the system.

Fig.2 The hardware structure of temperature node

The ultra-low power，16-bit RISC mixed-signal processor MSP430F5418A is used as the microcontroller of the temperature node.It incorporates 128KB of internal FLASH and 16KB RAM to meet the complex procedures.It has an operation voltage range of 1.8-3.6 V，the standby power consumption of 0.5 μA. The processor clock and speed can be set flexibly for battery-powered low-power wireless sensor networks.

SX1212 which has very low power consumption of the receiver is used for wireless RF transceiver.The receiver current is typically 2.6 mA.It has long transmission distance and high sensitivity.Frequency range of SX1212 is from 300 MHz to 510 MHz.When the working voltage is 2.1-3.6 V，the maximum transmit power is+12.5 dBm［4-5］.SX1212 communicates with the microcontroller by SPI interface by using packet processing mode.

AK-type thermocouple is used to measure the cake temperature in the design，which is installed in an additional armour protection tube.The K-type thermocouple ADC MAX6675 converts the analogy signal into a digital data，which has cold junction temperature compensation.The high resolution，small size and good reliability of MAX6675 could meet the oven temperatureapplications［6-7］.Low-noiseLDO TPS78833 is used in the power management module. It can cut off the peripheral circuit power supply by using its control terminal port to ensure ultra-low power consumption when the system is sleeping.

The hardware structure of the sink node is similar to the temperature node.It includes a microcontroller module，wireless RF transceiver module，power module and RS485 serial communication module.The RS485 serial communication module sent temperature data to the host computer of the control system.The power module provides energy to the system for the long run.

3 Design of software

3.1 Network protocols overview

Complete network protocol architecture is required to design a self-organizing wireless sensor network with a MESH structure.The hierarchical network structure provides the functionality and reliability of the system. According to the OSI reference model，the design uses four-layer structure of network protocol，including the physical layer，data link layer，network layer and application layer［8-10］.Network protocols are shown in Fig.3.

Fig.3 Network protocoIs

3.2 The physical layer protocol

Physical layer uses 434 MHz with FSK modulation techniques for the carrier communication frequency.It has better anti-noise and anti-decay properties，long distance，and strong penetration ability.The frequency of RF communication transceiver SX1212 can be adjusted between 300 MHz to 510 MHz in a single communication channel to avoid interference according to their characteristics.The transmission speed is 25 kb/s.RF communication transceiver provides the channel frequency selection，data transmission and reception，activation and deactivation for the radio，the signal strength indication and carrier sense functions. The frame structure of physical layer uses variable length packet mode，shown in Fig.4.

Fig.4 The frame structure of physicaI Iayer

3.3 The data link layer protocol

The data link layer protocol includes the logical link control（LLC）sub layer and media access control（MAC）sub layer.LLC sub layer uses the IEEE802.6 standard definition.The collision avoidance Carrier Sense Multiple Access（CSMA/CA）is used for the MAC sub layer.S-MAC protocol is used as the MAC protocol.S-MAC protocol ensures energy efficiency by using periodically monitors and sleep mechanisms which are competitive MAC protocol for wireless sensor networks.The sleep cycles of the nodes converge by consultation.S-MAC has better expansibility［11-12］.

3.4 The network layer protocol

The network layer protocol is a key component of self-organizing wireless sensor network with a MESH structure.The network layer protocol of this design is based on the principle of location-based GRID routing protocol and LEACH clustering routing protocol according to the feature of the coke oven temperature measurement based on the location of nodes.Location-based GRID routing protocol separates the covered area with small grids.One node in a grid is selected as the head node in this grid；only the head node can retransmit route packets through the grid by routing method［13-14］.The disadvantage of this protocol is that the communication burden and energy consumption of the head node are heavy，so the design selects the head node randomly using LEACH principles within the grid，and re-selects another head node after working for some time［15］.When location information of the node based on the GRID algorithm is installed，each node has its own specific grid.It can reduce the complexity of randomly selecting the head node in the mesh.Equal probability of the head node balances the energy consumption.When the grid is set，which sink nodes belong，it can simplify the routing algorithm based on self-organizing GRID routing protocol.The routing protocol is shown in Fig.5.The coordinate（3，2）of the grids is close to the sink node.The disadvantage of location-based network routing protocols for this design is having a long time to build a network and large data traffic in the process of establishing networks.After the head node is re-selected，the mesh routing list should be transferred to the new head node.The depth of routing list is greater.The advantage of the network layer protocol is saving energy and extending the life of the nodes，and maintains a balanced for energy consumption according to the nodes’location.Network layer protocol has MESH structure，self-organizing capabilities，simple and reliable protocol，and better scalability. divided into three grids.The farthest distance of communication is 400 meters.The grid ID and node ID are set for all temperature nodes.It takes approximately 150 seconds to organize the network.Temperature data can be updated at least once within three minutes.Accurate temperature measurement and low loss rate of temperature data packet could meet the design requirements.Temperature node uses 2Ah battery in 1%duty cycle；the working time is up to 1 year. The temperature node keeps more than 1 meter distance from the heat source for the high temperature of the oven.Node protections and shielding measures of the device are set to reduce the effects of electromagnetic interference.Experimental results show that with the increase of network nodes，the packet number will increase，but the average loss rate will not be affected.There is no missing node，and the nodes have low average power consumption.The temperature errors are basically the same no more than 1 degree Celsius.

TabIe1 ExperimentaI resuIts

Fig.5 The network Iayer protocoI based on Iocation

3.5 The application layer protocol

The application layer protocol is designed according to the simplified application，including the underlying protocol interface，temperature data transmission functions，temperature calibration and data connection timeout functions.Various application interface functions serve the main function of cake oven temperature measurement.

4 Experiments

Experiments use 20 temperature nodes，which are

5 Conclusions

The ultra-low power wireless sensor network for temperature measurement of coke oven could be established by using the ultra-low power microcontroller，wireless communication ASIC，the power management module and the low-power mode.Physical layer protocol，data link layer protocol，network layer protocol，application layer protocol for field environments and location-based routing protocol make up the self-organizing network with a MESH structure.The system has some advantages such as low cost，flexible，accurate and long survival，therefore it could be extended to other industrial furnace.

Acknowledgements

This paper is supported by Tangshan City Science and Technology Support Program（No.12110235b）.

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超低功耗焦?fàn)t溫度測量無線傳感器網(wǎng)絡(luò)設(shè)計

王志秦*
唐山學(xué)院信息工程系，河北唐山 063000

針對現(xiàn)有焦?fàn)t溫度有線測量方式成本高、接線復(fù)雜的問題，超低功耗的焦?fàn)t溫度測量無線傳感器網(wǎng)絡(luò)將無線傳感器網(wǎng)絡(luò)技術(shù)應(yīng)用于焦?fàn)t的溫度測量，采用適合現(xiàn)場環(huán)境的物理層、數(shù)據(jù)鏈路層、網(wǎng)絡(luò)層、應(yīng)用層協(xié)議和基于地理位置的路由協(xié)議構(gòu)成MESH結(jié)構(gòu)自組織網(wǎng)絡(luò)，并采用超低功耗運行方式。該系統(tǒng)具有成本低、使用靈活、溫度數(shù)據(jù)測量準(zhǔn)確、使用壽命長等優(yōu)點，具有廣闊的應(yīng)用前景。

無線傳感器網(wǎng)絡(luò)；溫度測量；MESH結(jié)構(gòu)；超低功耗；自組織

10.3969/j.issn.1001-3881.2015.12.023Document code：A

TN919.2

1 November 2014；revised 16 February 2015；accepted 1 March 2015

*Corresponding author：Zhi-qin WANG，Lecturer.

E-mail：157152621@qq.com

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