Water Leaks Detection: Assessment of Wireless Communication through Water and Sand Media in Buried Supply Pipes.

S.Mekid, A.Khalifa, R.Mansour Mechanical Engineering Department

King Fahd University Petroleum & Minerals, KFUPM Dhahran, Kingdom of Saudi Arabia

smekid@kfupm.edu.sa

S.Ho, S.Sarma Mechanical Engineering Department

Massachusetts Institute of Technology, MIT Cambridge, United States of America

Abstract—The reliable detection of water leaks is becoming very important as many parts of the world are concerned with water shortages. Leaks detection is traditionally performed with sensors placed outside the pipes network. Our research groups are assessing detection techniques using sensors placed inside the pipe. Although communication with such sensors is difficult, this paper addresses wireless communication through the media typically encountered between a sensor inside a pipe and a receiver outside.

A typical application is discussed for the inspection of a buried water pipe where a mobile sensor board communicates with a receiver outside through water, PVC and sand. The key challenge in such communications is propagation loss through the media. This affects the received signal strength on the outside, as well as the ability to maintain continuous communication. We report results including received signal strength in various configurations, the impact of factors such as salinity, and the implications on the power required at the transmitter. Initial results show limitations in the range of wireless communication. Amongst the commonly used UHF ISM band, the 433 MHz band is most effective when salinity is present (in the Kingdom of Saudi Arabia, for example). However, the range from which the signal can be received is in the order of meters. This implies that the in-pipe sensor will not have an opportunity for continuous or high-bandwidth communication. Instead, the in-pipe sensor will need to perform signal processing on-board, and upload pre-computed diagnostics rather than raw data to the outside. Our results therefore inform about the design of an in-pipe sensor design considering several aspects: power, computation, data storage, and communication protocol.

Keywords-component; water leaks; leak detection; wireless; buried pipes

I. INTRODUCTION Wireless communication through a medium has received

greater attention over the last decade. The most frequent medium is air [1-3] (to cite a few) but recent interests are converging towards underwater [4-8], rocks [9], and through other materials e.g. PVC. Common applications include data communication. Applications include leak detection inspection in buried pipes, coastal surveillance systems, environmental research, autonomous underwater vehicle (AUV) operation, and communication from caves to outside world to name a few.

The speed of sound is much lower than the speed of light with a bandwidth of communication systems rather small. Acoustics waves could have better performance but in practice the related cost is high in terms of power.

The current application is related to water leak detection in buried pipes. An innovative procedure using mobile platform within the pipe network looking for cracks initiated in the pipes. The project involves the design of a floating platform housing a sensor board. The latter may host pressure, hydrophone, and speed sensors.

Depending on some locations in Saudi Arabia, sand is a little salty, hence a certain level of salinity of a few ppt. This may incur possible effects on the signal strength. The propagation speed of electro micro waves in sea water, for example, is proportional to the square root of the frequency while the absorption loss is high [10] and it is proportional to the square root of the frequency, the magnetic permeability, and the electric conductivity. It is better to use lower frequencies in highly conductive media.

A. Signal strength reliability According to the literature [11] and based on various

measurements done using low and high frequency wireless communication up to 2.4 GHz, the received signal strength indicator (RSSI) is a bad estimator of the link quality. This belief is due to the existence of many asymmetry links in older radios such as CC1000 and TR1000 (found in MICA2 for example). Newer radios that are based on IEEE 802.15.4 standard such as CC2420 e.g. in Telos, implement another parameter called link quality indicator (LQI) which is believed to be a better indicator than RSSI. Media where the radio frequency RF is transported might have an effect on the strength of the signal, a couple of papers are published to discuss wireless signal quality of sensor put in water vases [13], but nothing in the public domain for large thick materials, or buried in the ground.

II. CHARACTERISATION OF THE COMMUNICATION

A. Signal characterisation The current sensor platform MICA2 from crossbow uses

ZigBee as protocol of communication where only RSSI is measurable to characterise the signal. According to IEEE 802.16, the RSSI (mWatt) at the antenna connection can be written as in (1):

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2011 2nd International Conference on Environmental Science and Technology IPCBEE vol.6 (2011) © (2011) IACSIT Press, Singapore

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CONCLUSION

ommunicationMHz have show

ength but also n that the sig

Signal lost

rs within the

signal is mainsensor board ae secured suchrd data analysThis will specin terms of mpossibly rede

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on top of the burie

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mobile

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