FROST NICHOLAS JAMES
| US5127267A | 1992-07-07 |
PATENT ABSTRACTS OF JAPAN vol. 013, no. 488 (P - 954) 7 November 1989 (1989-11-07)
| 1. | A method of detecting a concealed pipe or cable comprising; generated sound wave in the pipe or cable at a first point; positioning a detector proximate a second point along the pipe or cable, the second point being spaced from the first point along the pipe or cable; and detecting the sound wave using the detector; wherein the detector is a ground penetrating radar. |
| 2. | A method according to claim 1 wherein the ground penetrating radar is a doppler radar. |
| 3. | A method according to either claim 1 or claim 2 wherein said sound wave is generated by the passage of an electric current through the cable. |
| 4. | A method according to claim 3 wherein said current is mains current. |
| 5. | A method according to any one of the proceeding claims, wherein the detector generates an output corresponding to the sound detected by the detector, and the output is filtered by band pass filter tuned to the frequency of the sound wave. |
| 6. | An apparatus for detecting a concealed pipe or cable comprising: means for generating a sound wave at a predetermined frequency in the pipe and cable; a portable ground penetrating radar positionable proximate the pipe or cable and arranged to generate an output corresponding to the sound detected by the radar; and; a band pass filter tuned to said predetermined frequency for filtering said output. |
| 7. | An apparatus according to claim 6, wherein the radar is a doppler radar. |
| 8. | An apparatus for detecting a connected pipe or cable substantially as herein described with reference to and as illustrated in Fig. 2 of the accompanying drawings. |
| 9. | A method of detecting a concealed pipe or cable substantially as herein described with reference to Fig. 2 of the accompanying drawings. |
SUMMARY OF THE PRIOR ART It is already known to detect the path of a buried pipe by transmitting sound through the pipe, and detecting sound by a suitable detector, such as a microphone. An example of such an arrangement is shown in US-A-5127267. As shown in Fig. 1 of the accompanying drawings, an audio speaker 3 is connected to a standpipe 7 which itself is connected to an underground pipe 2.
When the speaker 3 generates sound, it passes through the standpipe 7, down the pipe 2 on a soundwave 6, and may be detected by one or more suitable detectors 4a to 4h at a site or sites remote from the speaker 3. In US-A- 5127267, there were multiple detectors 4a to 4h and the outputs from those detectors 4a to 4h were analysed by a suitable signal processor 5.
It should be noted that such arrangements are known both for the case where the pipe 2 contains gas, and where it contains a liquid such as water.
It has recently been proposed, as mentioned in New Scientist of 19 April 1997, to use radar to detect sounds which are generated at a leak in a pipe. When gas or water leaks from a pipe, sound is generated and this generates distinctive vibrations which a ground-
penetrating radar can detect.
SUMMARY OF THE INVENTION It has been realised that such a radar is applicable to sounds which are propagating down the pipe, as in US- A-5127267. Thus, the present invention proposes that such a radar be used to detect sounds in a pipe which have been input to the pipe at a remote site.
However, it has also been realised that a high voltage cable also generates sound (mains hum) and thus the radar can also be used to detect underground cables.
In each case, the output of the radar is passed through a band-pass filter which selectively passes signals of the desired or selected sound frequency. In the case where sounds are input to and propagate down a pipe, the band-pass filter selectively passes signals at the frequency of the sounds which have been input to the pipe. For a high voltage power cable, the band-pass filter selectively passes signals at the mains frequency.
BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a known pipe detection system and has already been described; and Fig. 2 shows a pipe detection system according to an embodiment of the present invention.
DETAILED DESCRIPTION In Fig. 2, an underground pipe 20 is excited by a
suitable signal. The excitation may be the same as has previously been described with reference to Fig. 1, in which an audio speaker generates sounds which pass down the pipe. Other known methods for generating sounds in pipes may also be used.
At a desired detection site, a detector 21 is positioned over the expected location of the pipe. The detector 21 has a doppler radar device 22 which detects sound signals. Thus, vibrations in the pipe 20 are detected by the radar 22. The output of the radar passes via line 23 to a band-pass filter 24. That band-pass filter 24 is tuned at the frequency of the signals on the pipe 20. Thus, for example, if a 275Hz pressure signal is applied to the pipe 20, the band-pass filter 24 is tuned to pass signals of that frequency. The signals from the band-pass filter 24 are amplified by an amplifier 25 and output from the detector 21. That output may be in the form of an audio or visual display.
It may be noted that the same detector 21 may be used to detect a buried high voltage cable 30. In this case, the band-pass filter 24 is tuned to the frequency of the voltage on the cable 30, which will normally be mains voltage. Thus, by suitable tuning of the band-pass filter 24, the detector 21 of this embodiment is able to detect different types of underground object in the immediate vicinity of the cable 12.