International Journal Of Scientific Research And Education ||Volume||2||Issue|| 3||Pages 563-574|||2014|| ISSN (e): 2321-7545 Website: http://ijsae.in Development of Wide Range Temperature Monitoring WSN Node Using MAX31855 and JN5139 with K-type Thermocouple for Coal mine

Margaret Richardson Ansah, Qinghua Cao, Shu Yan School of Computer Science and Telecommunication Engineering, Jiangsu University, Zhenjiang, 212013, China Email: [email protected], [email protected], [email protected] [email protected]

ABSTRACT Wireless sensor network (WSN) has become useful in monitoring physical and environmental quantities in coal mines and many other industries. This has led to reduction of labour cost and brought efficiency and accuracy in data collection. However, development of WSN that can measure wider range of temperature is limited. This paper describes the design and implementation of a WSN node that fills the limitations of existing WSN nodes. A WSN node that measures very high and very low temperatures has been designed to address the gap and demand for monitoring very high temperature of coalfield fire. The JN5139 microcontroller, MAX31855 temperature sensor and K-type thermocouple are the main components of the design and the SSCOM32 serial port tool were used for the communication between nodes and PC. Sensing temperature, data processing and transmission are software-controlled by the JN5139 microcontroller, which is interfaced to the MAX31855 through SPI. The node is robust enough to withstand changes in environmental conditions. The node is able to provide readings of temperature range from -40o C to ~1200o C. Keywords- Wide range Temperature Measurement; MAX31855; JN5139; WSN Node; Coal Fire Monitoring. 1. INTRODUCTION Wireless sensor network (WSN) is a modern technology that combines sensing, control automation, information processing, digital transmission, and information storage technologies to make monitoring highly efficient and effective. It has become an option for reliable collection of physical environmental Margaret Richardson Ansah et al IJSRE Volume 2 Issue 3 March 2014

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quantities. The use of WSN to corporately monitor physical or environmental conditio ns such as temperature, sound, vibration, pressure, motion or pollutants has made humanly daunting tasks relatively easy. Off-the-shelf WSN node products generally use standard temperature sensors of -55o C ~ 125o C temperature range [1-3]. Many application research have therefore been done in such temperature range, such as pressure and temperature signals monitoring by Arshak and Jafer [4], room temperature monitoring in an oil industry [5], monitoring cold chain logistics [6], investigating permafrost with WSN in the Swiss Alps [7] and high temperature measurement in industrial equipment [8]. WSN technology is application related; therefore, development of special technology for special domain is an important part of WSN development. For instance, the main task in monitoring coal seam spontaneous combustion is to measure very high temperature in coal seam combustion evolution and the temperature of coal fire from cooling down to extinction or from heating up again to combustion after the coal fire has been put off. WSN node that is able to read a temperature range of 0o C ~ 1000oC for coalmine fire was developed by Li and Cao [9, 10]. However, in winter the temperature of the field goes down to -45o C, with an average winter temperature of -25o C, and during deployment, the thermocouple connected to the sensor is buried in frozen soil. It therefore became necessary to develop wide range temperature measuring WSN node for monitoring coalfield fire accurately. The WSN node that can measure a temperature range of -40o C ~ 1200o C. The result will provide useful information not only for coalfield monitoring but also for agricultural and other purposes. 1.1 Method Of Impleme ntation The entire system architecture consists of JN5139 microcontroller board, MAX31855, signal acquisition board which provides a good interface between the microcontroller and the MAX31855. K-type thermocouple was used to connect the node to the physical entity to be monitored. These components form the sensor node, a base station that is PC in this case was used to view real- time data. Data was viewed on a PC using the SSCOM32 serial port tool. The JN5139 micro-processor was adopted as the core component for the wireless sensor node. 1.2 Hardware design and functional modules a. JN5139 The Jennic microcontroller board is used for the implementation. JN5139 node has some desirable feat ures such as low power consumption, high stability and robustness that met the hardware requirement of this work. It also operates in the 2.4GHz wireless band that is compatible with IEEE802.15.4 and ZigBee standards which is responsible for the wireless communication between nodes. JN5139 also has the following features that informed our choice of microcontroller: 16MHz 32-bit RISC optimized for low power and efficient code density, 96kB RAM for shared program, data and routing tables, 192Kb ROM for program code, 4- input 12-bit ADC, 2 11-bit DACs, comparators, temperature and humidity sensor, 2 Margaret Richardson Ansah et al IJSRE Volume 2 Issue 3 March 2014

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application Timer/Counters, 3 system timers, 2 UARTs, SPI ports with 5 selects, 2-wire serial interface and 40 GPIO [11]. The transceiver features of JN5139 are: 2.4GHz IEEE 802.15.4 compliant, 128-bit AES security processor, sleep current of less than 5uA, receive current of less than 50mA, transmit current of less than 45mA etc. The internal structure of the JN5139 node and the chip pin layout are shown in figures 1and 2.

Fig 1: JN5139 architecture DIO0 DIO2 DIO4

1 3 5

DIO6 7 DIO8 9 DIO10 11 DIO12 13 DIO14 15 DIO16 17 DIO18 19 DIO20 21 MISO 23 SSZ 25 RESETN 27 C1M 29 C2M 31 DAC2 33 35 37 39

JN5139

2 4 6 8 10 12 14 16 18

DIO1 DIO3 DIO5 DIO7 DIO9 DIO11 DIO13 DIO15 DIO17

20 22

DIO19 SCLK

24 26 28 30

MOSI SSM C1P C2P

32 34

DAC1

36 38 40

VCC

Fig 2: JN5139 chip pin layout b.

The Temperature Sensing

MAX31855 thermocouple-to-digital converter temperature sensor from MAXIM was used. It was chosen because it has an in-built 14-bit analogue-to-digital converter. It also has an operating temperature range of 40o C to 125o C and sensing temperature range of -250o C to 1800o C depending on the version and the thermocouple type used. MAX31855 has other versions that use J, K, E, N, S, T and R type thermocouples [12]. There are notable features that make MAX31855 desirable for this work than other temperature sensors.

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The choice of MAX31855 temperature/humidity sensor was informed by the requirement of the research and the capability of the sensor. A previous work done in the same research area used MAX6675 which has the following limitations. Foremost, the temperature sensing range is limited to 0 o C ~ 1023o C. Again, the analogue to digital conversion resolution of the sensor is 12-bit. While the environment in which the sensor is going to be used requires a much higher operating temperature range, MAX6675 can only operate within the temperatures of -20oC ~ 85o C. MAX31855 is able to process data at a much higher rate as compared to MAX6675. These factors make MAX31855 suitable in terms of bit resolution, accuracy and speed. Figure 3 shows the pin layout of MAX31855 chip.

GND

8

1

T- 2

DNC

7 SO

MAXIM MAX31855

T+ 3 Vcc

6 CS

5 SCK

4

Fig 3. MAX31855 Sensor The main functional differences between MAX6675 and MAX31855 temperature/humid ity sensors are shown in table 1. Table. 1 Functional Differences of MAX6675 and MAX31855 Parameter Temperature range [ o C]

MAX6675 MAX31855 0 to1024

-250 to +1800

12 bits

14 bits

Temperature resolution (bits) Operating temperature range [ o C] Processor (CPU)

-

20

+85

16 bits

to

- 40 to +125

32

its

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c. Integrated signal acquisition board The device, shown in figure 6, is the power management section of the wireless sensor node. It also has on board MAX31855 temperature sensor. There are two power source te rminals, one for battery and the other for solar panel. The thermocouple connector is also on this board. MAX31855 connection with K type thermocouple and JN5139 are listed in table 2.

Table 2 Connection of chip JN5139 and MAX31855 with K type thermocouple

K-type

MAX31855

JN5139

SO

MISO

SCK

SCLK

CS

DIO0

Thermocouple

NC T+

T+

T-

T-

Table 3 MAX31855 SO temperature data output format

14-Bit

Reserv Fault

Thermocouple

ed

12-Bit Internal

Bit

Temperature

Reserv

SCV

SCG

Open

ed

Bit

Bit

Circuit

Temperature data Bit

D31 D30

… D18

Bit D17

D16

D15

D1

… D4

D3

D2

D1

D0

4 Valu

Sig

MS

LS

reserv

1=

e

n

B

B

ed

fault

MS

LS

reserv

1=

1=

1=

B

B

ed

Short

short

Open

to Vcc

to

Circuit

GND

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The signal acquisition board is shown in Fig 4.

Fig 4: Signal acquisition board

1.3 Software The JN5139 uses Jennic protocol stack to support its application development [11] with the help of integrated peripherals API user Guide and Integrated peripherals API reference manual from Jennic. The software digitally controls processes such as setting SPI communication interface between JN5139 microcontroller and MAX31855, reading data from the thermocouple and transmitting to the serial interface of the MAX31855, shifting of data to the microcontroller after A/D conversion and the wireless transmission of data. The main application function of the node was accomplished in C programming language on Jennic Code blocks software [13], and loaded onto the node with Jennic flash programmer. Fig 5 shows the various states in the program and how the node works Power Power on on Initialize Initialize all all parameters parameters

MAX31855 MAX31855 takes takes TC TC data data and and buffer buffer No

32-bits 32-bits received? received? Yes wait wait

Yes No

JN5139 JN5139 take take data data from from MAX31855 MAX31855 No

Wake Wake up up time? time?

SPI SPI stop/ stop/ Sleep Sleep

SPI SPI done done ??

Yes Yes Send Send To To PC/Clear PC/Clear buffer buffer

No

Data Data Sent? Sent?

Fig. 5: Node process

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MAX31855 has signal-conditioning hardware to convert the thermocouple’s signal into a voltage compatible with the input channels of the ADC. Below are the key steps of the program which shows the SPI configuration, Chip Selection of MAX31855 CS pin, data transfer etc. It is assumed all parts of the node are connected properly and the node power is tuned on.

a. JN5139 node SPI interface is initialized. The number of slave devices using SPI is selected as 1, the first is the high data transmission, transmit/receive data using SCLK rising edge of the clock with the clock rate of 0.25MHz, the SPI interrupt and automatic chip select functions are disabled.

b. Chip Select a device to transfer data and open it. This function causes a high-to- low transition of the MAX31855 CS pin to initiate data transfer.

c. JN5139 through the SPI interface sends command to the MAX31855 to take data from the thermocouple after the clock is activated. JN5139 need to wait for some time after sending data before the MISO pin read data from the MAX31855.

d. JN5139 through the MISO pin receives 32-bit data from the MAX31855. JN5139 actively use this function to read data from the MAX31855 for 32 clock period.

e. Received data is analysed and converted into decimals.

The MAX31855 received data is 32-bit D31 ~D0 as shown in Table 3. D3 ~ D0 are the fault bits and D15 ~ D4 are the internal cold junction bits. Here the 32-bit data is analysed to see if there is any fault. The fault may be either it short circuit to ground, short to Vcc or open circuit. If a fault is found, a diagnosis is done on the hardware to fix it. On the other hand, if no fault is found, the program proceeds to the next stage. D31 ~ D18 are the thermocouple output bits in the form of analogue voltage. These 14-bit are digitally converted with the minimum value in decimal as 15384, corresponding to a temperature of -250 oC and a maximum value of 6400, corresponding to a temperature value of +1600 o C . The digital temperature value and the corresponding relationship with the resolution are: uTemperature = 0.25 * the converted digital value.

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1.3.1 Experime ntation The experimental setup consists of a node connected to K-type thermocouple, with the node connected to a computer through RS232 connector. SSCOM3.2 serial port tool to view the data on a PC. The temperature wireless sensor node was used in series of tests in the laboratory. The tests include placing the thermocouple probe into boiling water, hot flame, at room temperature and in a deep freezer. The results are shown in figures 7. 1.3.2 Results and Discussion The final WSN node is shown in figure 6. The node has been tested in terms of accuracy and stability in the laboratory and the results are shown in figures 7.

Fig. 6: WSN sensor node with MAX31855

Fig. 7a: Readings from boiling water

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Fig. 7b: Node and Thermometer readings compared

Fig. 7c: Readings from deep freezer

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Fig.7d: Node and Thermometer readings compared

Fig.7e: Readings from hot flame

Fig.7f: Node and Thermometer readings compared

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Temperature measurement by the node (Sensed Temp), as shown in figures 7a, 7c and 7e, was compared to that of a standard thermometer (Real Temp) as shown in figures 7b, 7d and 7f. Readings were taken every 10 minutes. A. Accuracy Measurement The results show that accuracy of node data compared with actual te mperature was high for temperatures between 25 and 100. Those of temperatures below zero and above 100 were less accurate. However, the overall node data accuracy was over 95%. On the other hand, the nodes gave consistent temperature reading at every given temperature. This means the nodes were stable with little fluctuations which occur in the first few data when the node is powered on and when there is a sudden change in the ambient temperature around the node. B. Power consumption Due to the application nature of the node, the node was programmed to function unattended for at least 5 years. Hence each node has specific time for data processing and transmission after which it goes to sleep. Solar cell is used to compliment the battery for constant power supply. The power consumption of the node is ~110mJ per cycle. C. Trans mission Range The node is capable of transmitting data over a distance of 300m within line of sight with no data loss. However, in the presence of obstacles and bad weather conditions, there is a significant loss of data. Therefore the transmission range that withstood obstacles was 50m. 2. CONCLUSIONS This paper described the development of a wireless sensor node that is suitable for coalfields fire application. We presented JN5139 microcontroller interfaced with MAX31855 and K-type thermocouple wireless sensor network node, designed to fill the gap created by available off-the-shelf WSN nodes in the market. The scope of the paper was to expand the range of temperature that can be monitored and transmitted by a wireless sensor network node. The use of Max31855 enables the node to read very low (-40o C) and very high (~1200o C) temperature in real-time data monitoring for coalfield fire. The design of the signal acquisition board which is made up of the sensor chip and the power management unit provides constant voltage to the node. Solar cell is use to back up the battery for constant power supply to the node. The node works stably and gives reliable data with ±2 o C error margin. Applications that need to monitor very high Margaret Richardson Ansah et al IJSRE Volume 2 Issue 3 March 2014

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temperatures such as coalfields and other application that needs to monitor very low temperature such as frozen or very cold habitat can easily be done with the node presented in this paper. MAX31855S and MAX31855R can be used to achieve wider temperature range of -50o C ~ 1768oC when used with S-type and R-type thermocouple respectively. Extension of this work includes transmitting the data to the internet to make it accessible remotely. ACKNOWLEDGEMENT This research is supported by the Science and Technology Assistance in Xinjiang Projects of Xinjiang Uygur Autonomous Region, China (201191210) REFERENCES [1]

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[3]

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[5]

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[6]

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[8]

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[9]

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[10]

Q.-H. C. Cao, Zu-Jue; Li, Shan-Rong; Yan, Shu, “Wireless sensor network monitoring node and method for 130o ~ 1000oC high temperature of fire area in coalfield,” 12-10-2011, 2011.

[11]

N. L. U. Ltd, “Data Sheet: JN5139-001 and JN5139-Z01 - IEEE802.15.4 and ZigBee Wireless Microcontrollers,” no. JN-DS-JN5139 1v9 2010.

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