Water Journal : Water Journal July 2011
asset management water JULY 2011 103 Abstract The University of Bradford, UK, has developed a technique for rapid inspection of sewers for blockages and defects, using acoustic reflectance, similar to sonar, from a speaker and a microphone array that is lowered into a manhole. It was first introduced to an Australian audience at the IWA Sewer Processes Conference, Gold Coast, November 2010. It is now being commercialised under the name 'SewerBatt'. Introduction In the current water industry climate, sewer assets have to be frequently maintained or replaced. Water companies worldwide are investing in pipeline surveys that are quite detailed and can provide visual data on the pipe condition. However, these technologies are expensive and time consuming as it takes a long time to complete the site survey, subsequent data analysis and CCTV reporting. Furthermore, commonly used technologies are unable to estimate objectively the hydraulic parameters and performance of the pipe. Water companies need enhanced survey information that can be obtained as frequently as required to manage the sewers' performance efficiently on a daily basis. Hence, there is a need for quick, reliable and low-cost sewer inspection technology that can provide information on pipe condition and estimate its effect on pipe flow capacity. Acoustical Equipment Acoustic survey equipment, which was developed at the University of Bradford, consists of an acoustic sensor that contains a speaker, microphone array and a thermocouple (Figure 1). The sensor is connected to a small electronic block (Figure 2) via an adapted 12-pin cable. The electronic block is connected to a 9-in Panasonic 'Toughbook' via a USB cable. The electronic block is used to generate a sound waveform, collect signals from the microphone array and communicate these data with the PC. This technology uses the principle of sound reflectometry, which is similar to that adopted by bats in wild. The signal emitted from the speaker is a sinusoidal chirp sound that covers the frequency ranges from 10Hz to 20000Hz. Once the reflected signal is recorded, a special signal analysis is performed to determine the pipe condition. The hardware is controlled by a specially developed Matlab code that is user friendly (Figure 3). Field Procedures The equipment has to be regularly calibrated to ensure that all the microphones are working properly and that their relative sensitivities are accurately known. One calibration per day is required, which takes around 10 seconds. The technology provides a rapid and objective inspection method for a sewer pipe between two adjacent manholes. The acoustic equipment (by the use of an extendable pole) is inserted into a sewer pipe inlet through the manhole for a short period of time. The equipment does not traverse through the pipe and it takes less than 60 seconds to complete the survey. Acoustic surveys can be carried out by a single operator from either the upstream or downstream end of the pipe. The equipment is small and light so that the operator does not need to enter the sewer and all the activity can be carried out from ground level. The recorded data is saved on the hard disk of the laptop. A Romanova, MT Bin Ali, KV Horoshenkov A novel, inexpensive and rapid primary survey technique A NON-INTRUSIVE ACOUSTIC METHOD OF SEWER PIPE SURVEY Figure 1. The acoustic sensor and Toughbook laptop. Figure 2. The electronic block.
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