Flow, level & control
Vibration sensors to pinpoint leaks in mains water pipes
Accelerometers are a well known means for monitoring the health of rotating machinery. However, these sensors have a far broader range of applications, as exemplified by their use in locating leaks in water pipelines, as Andy Anthony, Monitran, explains
V
ibration monitoring using accelerometers is an established tool in a wide range of applications, from real time monitoring of drivetrain components in a hovercraft to checking the impact of construction work on nearby buildings. However, a less common application is the use being made of these sensors by Echologics, who specialise in non-invasive leak detection. Echologics’ flagship LeakFinder-ST correlator
is an advanced acoustic leak detection system designed to work with plastic as well as metallic water distribution pipes. A result of extensive research, it uses two Monitran accelerometers to help locate the leaks. A leaking water pipe generates acoustic
noise which depends on the water pressure, pipe characteristics and the size and shape of the leak. This leak noise can be detected using accelerometers, and a correlation signal processing technique then used to locate and characterise the leaks.
The noise generation is very efficient for
metallic pipes, but for plastic pipes the sound attenuation is much greater, and the leak signals have lower frequency and narrow bandwidths. However, with its enhanced correlation function that uses advanced filtering and amplification technology, the LeakFinder-ST can reliably detect such leaks with good accuracy. This ability to identify narrow-band leak
noise also makes the instrument particularly useful for finding small leaks, and in environments where there are multiple leaks or a high level of background noise.
SiMple operAtion In operation, the accelerometers are placed in good acoustic contact at two locations on the pipe, typically at existing access points such as stop cocks. Having picked up the sound generated from the leak, and after filtering out spurious noise, the units wirelessly transmit the
leak noise data from each accelerometer back to the correlator’s central processing unit, which uses advanced signal processing to calculate the time taken for the noise to reach each sensor. As the system can accurately estimate the speed of sound in the pipe, it is able to determine the distance to the leak. The system is easy to operate and detects
leaks faster and with greater accuracy than other devices, greatly reducing the time to find and fix leaks and leading to a considerable reduction in the number of false excavations.
10V/g SenSitiVity “We chose sensors from Monitran as they provided a full solution for us, including customised design and manufacturing,” says a spokesperson at Echologics. “We also appreciate Monitran’s professional approach and customer service.” The Monitran piezoelectric accelerometer
used with the LeakFinder-ST correlator is the DF10 A4, which has a built-in amplifier with automatic gain control. It has a 10V/g sensitivity and a frequency range from 3Hz to 850Hz. With an IP67 rated stainless steel casing and an operating temperature from -25°C to +140°C, it has been fitted with a strong base magnet that makes it easy to quickly obtain good acoustic contact. Monitran designs, develops and
manufactures sensors and systems for vibration and displacement measurement. Its products include general and special purpose accelerometers, velocity sensors, displacement sensors, eddy current probes and LVDTs. Its bespoke design capabilities can be called on to provide almost any combination of sensor style, operating environment and output.
Monitran 20
www.monitran.com October 2019 Instrumentation Monthly
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