GB2038585A - Duct-tracing apparatus - Google Patents

Abstract

Apparatus for tracing the path of an underground duct and comprising a casing 10 made of a substantially inert material, which casing has an internally-threaded mounting bush 17 adapted for connection to the distal end of a drain rod 19. The casing holds a radio transmitter including an oscillator circuit arranged to supply intermittent bursts of radio frequency signals and an aerial to radiate such bursts: two ferrite rod aerials arranged at right-angles preferably are provided to obtain a broad spread of radiation. The apparatus is used with a directional receiver, which can follow the progress of the apparatus as the casing is advanced through a duct on the distal end of a drain rod. <IMAGE>

Description

SPECIFICATION Duct-tracing apparatus This invention relates to apparatus suitable for employment in tracing the path of a hidden or concealed non-metallic duct, and in particular but not exclusively is concerned with apparatus for tracing the path of an underground drain. Though the apparatus may be used for tracing various types of subterranean or other concealed ducts, the invention will hereinafter be described with reference to the tracing of drain paths.

If a serious blockage occurs in a drain and which cannot completely be cleared by the conventional technique of rodding-that is to say, forcing a flexible rod along the drain to and then through the blockagc it is necesary to excavate down to the blockage and then cut out the blocked section of the drain, for replacement by a clear section. Normally, no records at all are kept as to the precise path of a drain and especially of relatively small domestic drains, but if records are kept they are usually incomplete and somewhat sketchy.

Though the distance of a blockage from a manhole or other access point may easily be determined by inserting a rod to the blockage and then measuring the length of the rod so inserted, the actual location of the blockage ~and hence the site of excavation-may lie anywhere inside on a large arc at the measured distance from the manhole. Excavation to a blocked section may therefore involve much fruitless labour.

It is an aim of this invention to provide apparatus which enables the path of a concealed drain (or like non-metallic duct) to be traced from above the ground, so that an excavation to any point on the drain at a required distance from a manhole may accurately be made.

Accordingly, this invention provides ducttracing apparatus comprising a casing having a mounting adapted for connection to the distal end of a drain rod, and a radio transmitter mounted within the casing, which transmitter includes an oscillator circuit arranged to supply intermittent bursts of radio-frequency signals and a radiating aerial to which the radio-frequency signals are supplied for radiation therefrom.

The radio transmitter mounted within the casing preferably has two radiating aerials in order to obtain a broad spread of radiation out of the duct, irrespective of the relative angular orientation of the apparatus relative to the longitudinal axis of the duct. Advantageously, two ferrite rod aerials are provided and preferably such rod aerials are mounted within the casing with their axes extending at rightangles. Moreover, it is preferred for the mounting by means of which the casing is connectible to the distal end of a drain rod to be disposed such that the axis of a drain rod coupled to the casing extends mutually at right-angles to both of the transmitting rod aerials.

It will be appreciated that the apparatus of this invention is intended for use with a radio receiver tuned to the frequency radiation of the transmitter contained within the casing.

Reception of the transmitter signals will therefore result in an operator hearing the intermittent bursts from the transmitter, and it has been found that by arranging two transmitting aerials at right-angles as described within the casing, the pattern of radiation from the transmitter is such that the use of a relatively simple, hand-held radio receiver incorporating a directional ferrite rod aerial allows an operator to locate with relative ease the precise position of the transmitter.

For simplicity in manufacture of a preferred form of transmitter, it is convenient to include two oscillator circuits, each being associated respectively with one of the two aerials. Each oscillator circuit should be tuned roughly to the same frequency and typically to f 0.5 kHz. The transmitter should include two further oscillators, adapted respectively to key on and off the two radio frequency oscillator circuits whereby bursts of radiation intermittently are transmitted.Though the further oscillators should operate at the same frequency, so that two radio-frequency oscillators are keyed on and off together, in practice it is found that owing to the close proximity of the two aerials and the inevitable electrical coupling therebetween, the two further oscillator circuits will in fact oscillate at virtually identical frequencies, provided that both originally are tuned to oscillate at substantially the same frequency. Conveniently, the radio frequency oscillators operate at approximately 120 kHz, and are keyed on for 500 ys with rest periods of 100 ms. It is preferred for an unmodulated carrier pulse only to be transmitted, the receiver being specially adapted for reception of the radiation, to provide an audible indication whenever the unmodulated carrier frequency radiation is received from the transmitter.

The casing employed in this invention preferably comprises a moulding of a material which is substantially inert, so as to be capable of withstanding the effluent encountered in drains. For example, at least a part of the casing in which the transmitter is mounted may with advantage be moulded from highdensity polyvinyl chloride, and the other parts may similarly be moulded from a plastics material or otherwise manufactured from materials such as steel, stainless steel, or bronze. To increase the resistance of the apparatus to attack by the effluent found in drains, it is preferred for at least the transmitter circuit to be encapsulated in a suitable potting compound, such as an epoxy resin.

Drain rods conventionally employed at least in the United Kingdom have two standard types of mounting bosses at the distal ends thereof, for the attachment of various implements which are useful in clearing blockages.

It is therefore preferred for the mounting of the casing to be adapted for interconnection with one of the two conventional mounting bosses found on drain rods. One such casing mounting may therefore comprise an internal screw thread inter-engageable with corresponding threads formed on the distal end of a drain rod, and the other such mounting may also comprise an internal screw thread but inter-engageable with the threads formed on a rotatable ferrule provided at the distal end of a drain rod, the casing further defining a recess of rectangular shape co-axial with the threads formed therein, for engagement with a projection of rectangular section extending beyond the rotatable ferrule on the drain rod.

The casing must also contain a source of electrical power, for operating the transmitter.

Preferably, the transmitter employs low-power oscillator circuits, in which case the power source may comprise a dry battery, replaceable when required. Optionally, however, the power source may comprise a rechargeable battery, such as a nickel-cadmium acccumulator. A switch also may be provided, to allow the conservation of power when the apparatus of this invention is not being employed.

By way of example only, one specific embodiment of this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a perspective view of an example of drain-tracing apparatus constructed in accordance with this invention; Figure 2 is a side view of the apparatus shown in Fig. -1; Figure 3 is a partial cut-away view of the apparatus shown in Figs. 1 and 2; Figure 4 is a block diagram of the transmitter employed in the apparatus of this invention; and Figure 5 is a block diagram of a receiver for use with the drain-tracing apparatus.

Referring initially to Figs. 1 and 2, there is shown an example of drain-tracing apparatus of this invention. This apparatus comprises a casing 10 having two end caps 11 and 12, between which is a battery housing 13 and a transmitter section 14. Two bolts 15 secure together the end cap 11, transmitter section 14 and battery housing 13, whereas two further bolts 16 hold the other end cap 12 to the battery housing 13. The two end caps 11 and 12 and the battery housing 13 are made of a bronze or similar corrosion-resistant metal, and the transmitter section 14 is mounded from high-density polyvinylchloride.

End cap 11 has a bush 17 brazed thereto, which bush is formed with internal threads 18 adapted for interengagement with threads provided at the distal end of a drain rod. Such a rod is shown at 19, and includes a metal ferrule 20 which has external threads 21 engageable with threads 18 of the bush 17.

Thus, the apparatus may firmly be secured to the distal end of a drain rod.

The transmitter section 14 houses a radio transmitter (not shown) suitably encapsulated for instance in an epoxy potting compound, and the battery housing 13 is adapted to hold an electrical battery (also not shown). Beneath the other end cap 15 an on/off switch may be provided, to allow energisation of the transmitter by the battery. The switch is accessible by removing the end cap 12, after releasing the bolts 1 6. If no switch is provided, the entire battery should be removed when the transmitter is not required to operate, access to the battery being gained by removing the end cap 12.

As can be seen from Fig. 3, the transmitter section 14 is in the form of a tube 22 within which fits a generally-circular printed circuit board 23. The circuit board 23 supports and inter-connects various electrical components 24 of the transmitter, as well as two ferrite rods 25 and 26 of round section, arranged with their axes at right-angles. The axes of the rods 25 and 26 are also mutually at rightangles to the axis of the tube 22, and thus to the bush 17, when assembled.

Fig. 4 shows diagrammatically in block form the transmitter circuit. It can be seen that this comprises two distinct oscillators 27 and 28, both of which may be energised by a battery 29~which is incorporated within the battery housing 13. Each oscillator has a radio-frequency section and a keying oscillator to key the output from the radio-frequency section. The radio-frequency section includes a coil wound around its associated ferrite rod 25 or 26 respectively and thus electrically is coupled to the other oscillator through the ferrite rods. The frequency of oscillation of each oscillator need not accurately be set to be the same, and ordinary electronic components of usual tolerances may be employed in constructing the two oscillators. When however one oscillator operates and the keying oscillator in particular, the other will oscillate at a substantially identical frequency, by virtue of the electrical coupling across the aerials, ensuring that each oscillator causes a pulse of radiation at the same instant.

Each oscillator is set to operate at approximately 120 kHz, and is arranged to provide bursts of oscillation of approximately 5001is pulse length, with a gap of approximately 100 ms between such bursts. By providing a relatively short burst length with a relatively long gap therebetween, battery power can greatly be conserved, but of course different burst lengths and gaps may be employed if required, as may the frequency of oscillation itself.

Each oscillator radiates from its associated ferrite rod aerial simultaneously, so that the resultant polar curve of the radiation comprises the combination of both transmissions.

The polar curve so generated is found particularly to be suitable for tracing-that is to say, following from a remote point-by means of a radio receiver having a directional ferrite rod aerial. The block diagram of one such receiver is shown in Fig. 5, from which it can be seen that a ferrite rod aerial 30 has a coil feeding an aerial tuning stage 31. The signal from stage 31 is fed to a radio frequency pre-amplifier 32, the output of which is further amplified in stage 33 and then fed to a detector 34. The output from the detector drives a pulse amplifier 35, the output of which is shaped by pulse shaper 36 to operate a DC switch 37. The switch 37 turns on and off a pulse generator 38 driving a loudspeaker 39, whereby the generator 38 operates in sympathy to reception by the aerial 30 of a radio frequency carrier signal of the correct tuned frequency.Thus, the loudspeaker will emit a series of short sounds each of approximately 500 ys pulse length with a 100 ms gap therebetween, when the aerial of the receiver picks up a signal radiated by the transmitter of the apparatus shown in Figs. 1 to 4.

In use, the transmitter of the apparatus of Figs. 1 to 4 is energised (for example by inserting a battery into the housing 13), and then the entire casing is firmly connected to a drain rod by inter-connecting the threaded portions at the end of the drain rod and on the casing 10. Thereafter, the drain rod is fed down the drain the path of which is to be traced, through an appropriate manhole or other access point. Using the receiver described with reference to Fig. 5, the passage of the apparatus below ground in the drain can be traced from above the ground by appropriately holding the receiver and walking in whatever direction is necessary to ensure that the receiver continues to emit pulses of sound. If at any point no sound is emitted, feeding of the drain rod should stop until the receiver once more emits the sound pulses, by walking around until a signal is again received.

To allow for different drain depths below ground, or for "finding" the transmitter if the sound pulses suddenly are lost, it is advantageous to provide a sensitivity control for the receiver, to allow control of the minimum required received signal strength for the pulse generator to be switched on. The provision of such a sensitivity control is within the competence of one skilled in radio receivers, and will not be described in detail here, though it will be mentioned that such a control can be included in amplifier stage 33 of the receiver.

Then, the sensitivity will control the directionality of the receiver: if the transmitter becomes "lost" as mentioned above, increasing the receiver sensitivity will enable the transmitter to be found again, and then gradually reducing the sensitivity will allow the transmitter to be pin-pointed.

The tracing of the path of a drain as justdescribed can be used to locate a blockage, as mentioned hereinbefore. Other uses include the mapping of a drain or other duct path to avoid damage thereto in the case of building work, and if additions are to be made to the drain system-for instance if another drain is to be connected to an existing drain-to allow the finding of a suitable point to insert a T-piece.

Claims (13)

1. Duct-tracing apparatus comprising a casing having a mounting adapted for connection to the distal end of a drain rod, and a radio transmitter mounted within the casing which transmitter includes an oscillator circuit arranged to supply intermittent bursts of radio-frequency signals and a radiating aerial to which the radio-frequency signals are supplied for radiation therefrom.

2. Duct-tracing apparatus as claimed in claim 1, wherein the radio transmitter mounted within the casing has two radiating aerials disposed at an angle to one another to obtain a broad spread of radiation.

3. Duct-tracing apparatus as claimed in claim 2, wherein each radiating aerial comprises a ferrite rod, the two ferrite rods being mounted within the casing with their axes mutually at right-angles.

4. Duct-tracing apparatus as claimed in claim 3, wherein the mounting by means of which the casing is connectible to the distal end of a drain rod is disposed such that the axis of a drain rod coupled to the casing extends mutually at right-angles to both ferrite rod aerials.

5. Duct-tracing apparatus as claimed in any of claims 2 to 4, wherein the transmitter includes two oscillator circuits, each being associated respectively with one of the two aerials.

6. Duct-tracing apparatus as claimed in claim 5, wherein the resonant frequency of one oscillator is within + 0.5 kHz of the resonant frequency of the other oscillator.

7. Duct-tracing apparatus as claimed in claim 5 or claim 6, wherein the transmitter includes two further oscillators, one associated with each radio frequency oscillator circuit respectively and arranged to key on and off the associated radio frequency oscillator circuit.

8. Duct-tracing apparatus as claimed in claim 7, wherein the two radio frequency oscillators operate at substantially 120 kHz, and are keyed on for substantially 500 ys with rest periods of substantially 100 ms.

9. Duct-tracing apparatus as claimed in any of the preceding claims, wherein the transmitter is arranged to transmit an unmodulated carrier pulse.

10. Duct-tracing apparatus as claimed in any of the preceding claims, wherein the casing comprises a moulding of a material which is substantially inert.

11. Duct-tracing apparatus as claimed in any of the preceding claims, wherein the mounting of the casing includes an internal screw thread inter-engageable with corrresponding threads formed on the distal end of a drain rod, or with the threads formed on a rotatable ferrule provided at the distal end of a drain rod.

12. Duct-tracing apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

13. Duct-tracing apparatus as claimed in any of the preceding claims in combination with a directional receiver adapted to receive radio frequency signals transmitted from the transmitter within the casing.