| |
管道滲漏分析及定位
Leak Noise Correlation (LNC)
Objective
This survey is to locate leakage from any pressurized pipework system by detection using equipment at exposed pipework fittings or along the pipeline route.
Correlation Theory
The conventional technique for leak detection requires identification of water fittings on which a high leak noise may be acoustically detected. From this information it is possible to use surface listening devices to detect the position of maximum sound intensity above the pipe to locate the leak position.
The technique demands a high level of operating skills and is frequently restricted by significant ambient noise levels making nighttime work is necessary.
Furthermore, the above ground maximum sound position frequently does not occur over the leak location with the sound propagating to the surface by the acoustic path of least resistance.
The correlation technique is the most cost effective means of locating underground leakage and has the ability to isolate leak noise from the background noise which prevents conventional listening techniques being applied. The novel measurement procedure realizes objective results rather than operator dependent conclusions.
The sound created by the pressurized fluid escaping from the pipe propagates in both directions along the pipe away from the leak location. Referring to the diagram below, if the leak was exactly midway between the two valves then the noise pattern at each fitting would be identical at any moment in time. When the leak is closer to one fitting then there is a time delay (of any a fraction of a second) for the noise to reach the furthest monitoring point.
A mathematical analysis of the system derives the equation:
D = (L – v.td) / 2
Two high sensitivity sensors are placed either side of the suspect leak position with a typical spacing of 10 – 800 meters. The distance the sound travels is determined by pipe diameter, pipe material, pressure, type of fracture and soil conditions.
The signal from sensor B is automatically applied and transmitted by radio telemetry to the correlator unit. The correlator compares this signal with the noise measured by the Sensor A. The leak position is automatically indicated once the operator has entered the type of pipe material, pipe diameter and measurement length.
Leak Noise Correlator (LNC)
The LNC comprises a transmitter and acoustic sensor, which is linked to a valve stem or other metal element at one end of the suspect length of pipe and a combined processor, and sensor at the other end of the pipe. Sound propagates from the leak to each sensor that measures the time delay taken for the noise to reach the sensor. The two sets of information are processed and the display indicates the distance of the leak from the sensors at each end of the pipe.
The correlator can also be used to make measurements of leak noise propagation velocity with an exceptional degree of accuracy once pipe diameters and material information has been fed into the processor. This information also enables the LNC to automatically calculate and apply the most suitable filter for each application.
The digital signal processor in the LNC greatly speeds up calculation and the correlator displays more data/second than conventional units. This high speed processing also has the advantage of reducing interference from unwanted noise and eliminates the need for a zoom feature.
Electronic Listening Device/Mechanical Listening Device (ELD/MLD)
Different types of electronic and mechanical listening devices will be utilized which will provide an audio response using headphones and/or a visual response indicated on a liquid crystal display.
The sound level in the headphones can be manually adjusted for user comfort, whilst not affecting the liquid crystal display which measures absolute leak noise.
ELD/MLD is an effective and most simple instrument for locating leaks and is standard equipment for each service van.
A./ Ground Microphone Leak Locator
One of the most commonly used ELD is Ground Microphone Leak Locator. Forwin will utilize the most advanced ground microphone that searches for the position of maximum leak noise by splitting the noise into eight frequency bands. It selects the optimum bandwidth and automatically adjusts noise gain whilst rejecting external interference, enabling position of maximum leak noise to be easily located.
Ground Microphone is a simple and speedy instrument for locating leaks over suspect lengths of pipe or for verifying information found with the Leak Noise Correlator.
B./ Mechanical Listening Strick
This is applied to find the leak point by human ear by means of noise conduction.
| |
 |
|
 |
| Leak Noise Correlation Theory |
|
Electronic Listening Device |
| |
|
 |
|
 |
| Mechanical Listening Device |
|
用locator確定喉管位置 |
| |
|
|
 |
|
 |
| LNC探測喉管 |
|
MLD檢測懷疑漏水位置 |
| |
|
|
 |
|
 |
| 管道滲透分析儀器 |
|
管道滲透分析儀器 |
|
FORWIN Site Investigation Engineering Ltd.
