Service lines which are buried underground may be for providing electricity, gas, water, sewage, fibre optic telephone and data links or other services. It often happens that when digging for other purposes, for example to install a new buried service line, existing service lines are broken. This incurs unnecessary expense for repair purposes, whilst also causing inconvenience and cost to persons who are without the service whilst it is being repaired.

In order to try and prevent the accidental breaking of existing buried service lines, it is standard practice to bury a length of warning tape in the ground above a service line. The warning tape is normally provided with a printed warning to indicate the type of buried service underneath the warning tape. In order to facilitate detection of the warning tape, it is known to provide the warning tape with insulated or uninsulated metallic material which can then be detected, for example by a buried service route locator. The detectable tape can then be located by the buried service route locator so that the position of the buried non-metallic service can be detected before digging commences.

It sometimes happens that contractors and other persons digging holes in the ground do not check for the presence of the warning tape or existing buried service lines which may be shown on charts or maps. The result is often that the warning tape and/or the buried service line become broken. If the service line becomes broken, then it needs to be repaired as soon as possible. For example, if the service line is a water pipe containing water or a gas pipe containing gas, then loss of the water or gas will occur until such time as the water pipe or the gas pipe is repaired. If the service line is an electrical cable or a fibre optic cable, then a repair again needs to be effected as soon as possible to restore the service and to reduce any danger resulting from the broken service line.

When a service line gets broken, it often happens that an organization able to effect a repair is not informed sufficiently quickly. It : is an aim of tne present invention to reduce this problem.

In addition to the above mentioned problem, there is a further problem of theft of the buried service lines when the service lines are made of a valuable material, for example an electrical service line containing a substantial amount of copper. This type of theft is especially prevalent in less developed countries where the value of the buried service line is high in relation to a person's wages. It is also an aim of the present invention to reduce this problem.

Accordingly, the present invention provides warning tape for a buried service line, which warning tape comprises a length of data transmission material for use in providing warning information relating to the buried service line.

The data transmission material may be insulated electrical conductor data transmission material, or it may be optical fibre data transmission material. The insulated electrical conductor data transmission material may be in the form of one, two or more insulated wires. The optical fibre data transmission material may be in the form of a single optical fibre or, more usually, a bundle of optical fibres.

The data transmission material can also be used for carrying data required by the utility service. This data may include rate of flow, teiiperature measurement along an electric cable, or data voice or video transmission of any suitable and appropriate kind. With optical fibre data transmission material, for example in the form of a fibre optic cable, there is no fire risk when the cable is broken.

The warning tape will usually be made of a plastics material. The warning tape may be foil warning tape, or mesh warning tape.

The mesh warning tape may be used if the warning tape is in contact with a buried service line that generates heat, for example an electric cable carrying a heavy current, and it is desired to ensure that the warning tape does not unduly hinder the escape of the heat. The mesh warning tape can be used for all other services if desired, examples of such services being water, gas and telephone services.

The warning tape will usually bear a visual warning. Thus, for example, the visual warning may include the word"caution". If desired, the visual warning may also give details of the type of service buried underneath the warning tape, for example"high pressure gas pipe"or"electrical cable".

The warning tape may include insulated or uninsulated metallic material which is on the warning tape and which is detectable in order to detect the location of the warning tape. The warning tape may be one in which the uninsulated metallic material is at least one stainless steel wire.'rhere may be two or more stainless steel wires. Other metallic materials may be employed if desired. Stainless steel is preferred since it does not prematurely rust away during prolonged use of the warning tape underground.

The present invention also provides warning apparatus for providing an early warning relating to a buried service line which is buried underground, which warning apparatus comprises a length of the warning tape of the present invention, sensor means which is connected to the data transmission material and which is able to sense movement of or a break in the data transmission material, and locator means for locating the position of the movement or the break and for generating transmittable data on the position of the movement or the break for transmission to a control station, the locator means being electrically operated locator means which is caused to operate by the sensor means consequent upon the sensor means sensing the movement or the break.

The warning apparatus of the present invention is able to sense a break in the data transmission material on the warning tape, to locate the position of the break, and to transmit data on the position of the break to the control station. The warning apparatus is also able to sense the position of a movement in the data transmission material. The movement may cause the data transmission material to be compressed and the position of the compression can be sensed and located. Slight movement of the data transmission material, for example due to minor and natural earth shifts, can be arranged not to be sensed.

The sensor means may be any suitable and appropriate type of sensor means for sensing movement of or a break in the data transmission material, and for causing the operation of the locator means.

Preferably, the locator means is a reflectometer means, or a pulse echo locator means. Other types of locator means may however be employed.

The length of the buried warning tape may be sub- divided into various sections, such that the sensor means can determine that a break is in between two sections or subsequent to any one section.

The reflectometer means or the pulse echo locator means may generate the transmittable data by converting digital data on the position of the break into the transmittable data.

The warning apparatus will normally include transmitter means for transmitting the data to the control station. The transmitter means may be formed as a separate transmitter means, or it may be formed as a single piece of equipment with the locator means.

The transmitter means may transmit the data so that it is received at the control station in the form of speech information and/or visual information. Thus, for example, the control station may receive a simple telephone message.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows first warning tape of the present invention in use in warning apparatus; Figure 2 shows second warning tape to that shown in Figure 1; Figure 3 shows warning apparatus of the present invention; and Figure 4 is an enlarged view of part of a length of warning tape used in the warning apparatus as shown in Figure 3.

Referring to Figure 1, there is shown warning apparatus 2 for providing an early warning of the presence of a buried service line 4 which is buried underground in ground 6. The warning apparatus 2 comprises warning tape 8 which is for being buried underground above the service line 4.

The warning tape 8 may optionally have insulated or uninsulated metallic material in the form of two or more stainless steel or other metallic wires (not shown).

These wires are for enabling the presence of the warning tape 8 to be detected above the ground 6 by a buried service route locator.

The warning tape 8 is also provided with data transmission means in the form of a fibre optic cable 12. The warning apparatus 2 includes sensor means 14 which is connected to the fibre optic cable 12 and which is able to sense a break or a movement in the cable 12.

The fibre optic cable 12 is connected to an audio and visual alarm 10.

The warning apparatus 2 further comprises a locator means 16 for locating the position of the break or movement in the fibre optic cable 12. The sensor means 14 is able to generate transmittable data for transmission to a control station via a telephone dialling device and message sender 18. The locator means 16 is electrically or data link operated and it is caused to operate by the sensor means 14 consequent upon the sensor means sensing the break or movement in the fibre optic cable 12. The locator means 16 is a reflectometer means. The reflectometer means 16 generates the transmittable data by converting digital data on the position of the break into the transmittable data.

The reflectometer means 16 has an inbuilt transmitter means for transmitting the data to the control station. The transmitter means transmits the data so that it is received at the control station in the form of speech information. Thus a duty engineer at the control station is able to receive the information of the break and the location of the break in the form of a simple telephone message. The control station will record the date and time of the operation of the sensor means 14.

As can be seen from Figure 1, the warning tape 8 is a foil tape 8. Figure 2 shows that the tape 8 can alternatively be a mesh tape 8.

Referring to Figures 3 and 4, there is shown warning apparatus 102 for providing an early warning of the presence of a buried service line 104 which is buried underground in ground 106. The warning apparatus 102 comprises warning tape 108 which is for being buried underground above the service line 104.

The warning tape 108 has uninsulated metallic material in the form of two stainless steel wires 110. These stainless steel wires 110 are for enabling the presence of the warning tape 108 to be detected above the ground 106 by a buried service route locator.

The warning tape 108 is also provided with data transmission material in the form of a pair of insulated electrically conducting wires 112. The warning apparatus 102 includes sensor means 114 which is connected to the wires 112 and which is able to sense movement of or a break in the wires 112. The wires 112 are short circuited or connected together in series with a resistor or diode at their remote end as shown in Figure 4 (left hand end). Although two insulated wires 112 are shown, there can be a number of wires from one upwards. Alternatively, the wires 112 could be replaced by a fibre optic data transmission line or some other data transmission material for sending and, if required, receiving information data. The wires 112 or a fibre optic data transmission line may be laid in any form along the tape. In Figure 4 the wires 112 are shown in sinusoidal form, but they can also be in a straight form, so that the wires 112 are running parallel to the edges of the warning tape 108.

The warning apparatus 102 further comprises a locator means 116 for locating the position of the movement of or break in the wires 112. The sensor means 114 is able to generate transmittable data for transmission to a control station 118. The locator means 116 is electrically or data link operated and it is caused to operate by the sensor means 114 consequent upon the sensor means sensing the movement or the break.

The locator means 116 is a pulse echo locator means.

The locator means 116 generates the transmittable data by converting digital data on the position of the movement or break into the transmittable data.

The pulse echo locator means 116 has an inbuilt transmitter means 120 for transmitting the data to the control station 118. The transmitter means 120 transmits the data so that it is received at the control station 118 in the form of speech information. Thus a duty engineer at the control station is able to receive the information on the movement or break and the location of the movement or break in the form of a simple telephone message. The control station 118 will record the date and time of the operation of the sensor means 114. The control station 118 may be connected to other early warning alarm sensors via lines 122.

As can be seen from Figure 4, the warning tape 108 bears the words"caution"and"high pressure gas pipe".

Thus, if the warning tape is uncovered by digging, then a clear warning is given together with the nature of the service line 104 buried underneath the warning tape 108.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, the transmitter means may be separately formed from the reflectometer means 16 and the locator means 116. The sensor means 14,114 would normally be in the substation and some distance away from the buried service. It may be connected to the early warning tape by an electrical conductor or a fibre optic link. The sensor means 14,114 could be underground. There would normally only be one connection from the sensor means 14,114 to the control station or multiplexer. The reflectometer means 16 and the reflectometer means 116 may generally be any suitable and appropriate programmable means.

The warning apparatus of the invention may be used and may operate as follows.

1. A rogue contractor digs the ground without informing anybody.

2. Unwittingly the contractor cuts through the early warning tape. The sensor means-just like a burglar alarm-detects the break, and sends a signal to the control station. This signal will hopefully take place before the rogue contractor hits the buried service which could cause fatal damage to himself and severe inconvenience to persons connected to the service. In any case the system will record the exact time and date of the early warning tape break and this information alone may be sufficient for the company owning the buried service to make a successful prosecution against the rogue contractor, so as to recover the cost of repairs from the rogue contractor.

3. The control station can be connected to a large number of alarm circuits, and their associated sensor means. For example, an electricity company may decide to place early warning systems in a large city on twenty five or more different underground cable routes with T-offs from the main cable. To avoid the necessity of having twenty five separate relatively high cost pulse echo locator means or other programmable means, a multiplexer or control switching station is used.

As an alarm is activated, so the multiplexer switches automatically to that particular alarm circuit and switches the locator means into operation, on that particular circuit. The reason for the multiplexer is that the alarm sensor means is relatively cheap (less than £100) but the reflectometer device can be £5000. A multiplexer could cost £1000.

4. As an adjunct to the locator means, the speech interrogator may read the distance in metres and convert into speech. It may then telephone the duty engineer (in the same way that a burglar alarm telephones the police automatically) to report the circuit at fault and the distance of the break from the control station or multiplexer.

The development work required to get the speech interrogator working to convert digits on a display into voice messages may be complex and a simplification may be effected by only having a telephone device.