The invention relates to a method for the wireless transmission of data through the interior of a pipeline.

It has already been proposed to transmit data, e.g. from a measuring scraper travelling through a pipeline, in wireless manner through waves propagating along said pipeline to a receiving antenna and also to transmit data in wireless manner in the reverse direction.

It is assumed that the frequency of the electromagnetic wave is tuned in such a way that the information is transmitted by means of an elementary waveguide mode. This is possible in the case of a pipeline having a constant diameter over its entire length. However, conventional pipelines do not have a constant diameter over their entire length and instead said diameter can undergo changes. Within pipelines there are also constrictions in the form of sleeve valves and the like, which impede the propagation of a wave with a frequency tuned to the pipe diameter.

The problem of the invention is to provide a method by means of which, in the case of pipelines with different diameters and constrictions, data can be transmitted along the interior of the pipeline.

According to the invention the problem is solved by a method of the afore¬ mentioned type in that transmission takes place with a transmission frequency sufficiently high for the electromagnetic waves transmitting the data to propa¬ gate along the pipeline by multiple reflection on several, preferably at least five propagation paths.

According to a preferred development, the wavelength is significantly smaller than the pipe diameter, particularly smaller than 1/2 and in highly preferred manner smaller than 1/3 of the pipe diameter. Due to the fact that, according to the invention, the frequency at which the wireless transmission takes place is chosen much higher than a frequency tuned to the pipe diameter and consequently the wavelength is much smaller than the pipe diameter, the electromagnetic wave is not propagated along the interior of the pipeline in accordance with a single propagation path, but in¬ stead through multiple reflection in several propagation paths and in several modes, differentiated on the basis of transverse electric or magnetic modes, with different wavelengths, the latter being dependent on the modes or reflec¬ tion angles on the pipe wall. Thus, the electromagnetic energy of the wave propagating along the pipeline is impaired to a lesser extent by constrictions and the like than in the case of propagation by means of a single elementary waveguide mode and a frequency tuned to the pipe diameter.

As a result of the invention test transmissions have been performed over a distance of 200 m without any measurable attenuation or fading.

According to a preferred development, the signal is received and transmitted by two spaced antennas. Thus, in each case, the receiver can evaluate the antenna signal giving the best reception result. This compensates fading ef¬ fects caused by quenching and/or amplification at specific spacings between transmitter and receiver. In a preferred development the signal is received and transmitted by at least two antennas located at a distance of 1/4 of the wavelength of the propagating waves. The two single antennas positioned with a short axial spacing with respect to the pipeline can be provided in sta¬ tionary and/or mobile manner on the scraper.

According to further preferred developments of the invention the electromag¬ netic waves are received and/or transmitted by quarter-wave antennas and the received/transmitted signal is transmitted between the antenna and transmitter/receiver by a coaxial cable. In such cases the antenna can be formed by a correspondingly insulated end of the coaxial cable. No problems arise in introducing one or more antennas into a pipeline under pressure. To the extent that a pipeline has existing connections, they can be used for this purpose in a manner to be described hereinafter. If no such connections exist, according to a preferred development of the invention, hot tabs are subsequently placed on the pipeline in order to position antennas therein.

For introducing an antenna into the pipeline, according to a preferred devel¬ opment to a pipeline hot tab is fitted an attachment holding the antenna cable and provided with a pressure-resistant passage for said cable. The antenna is then introduced by opening a valve in the pipeline. However, the antenna can also be constructed as a sacrificial or lost antenna. In such a case, ac¬ cording to the invention, an antenna-holding cable can be separated by the valve after carrying out the measurement (sacrificial antenna).

If the antenna is to be reused, according to a further development of the in¬ vention, an antenna cable can be slid backwards and forwards through the pressure-resistant passage of the attachment, so that after carrying out the measurement the antenna can be removed from the pipeline via the connec¬ tion valve and the latter can then be closed. The attachment holding the an¬ tenna can then be removed again and used at another location.

As pipelines in which the invention is used can have very considerable lengths and which are in particular such that a signal propagating over the entire length would be attenuated to such an extent that there would be no incoming signal above the noise level, according to a preferred development of the invention antennas are inserted in the pipeline over a distance of sev¬ eral kilometres.

Further advantages and features of the invention can be gathered from the following description of an embodiment of the invention with reference to the attached drawings, in which: Fig. 1 is a diagrammatic view of a pipeline scraper provided with a camera and an antenna, together with a representation of the propagation of an elec¬ tromagnetic wave by means of multiple reflection on several propagation paths; and

Figs. 2a, 2b show an antenna to be inserted in a pipeline from a connection upstream of the inlet (Fig.2a) and downstream of the inlet (Fig. 2b).

Fig. 1 very diagrammatically shows a scraper means 20 in a pipeline 10. The scraper means 20 comprises two members, whereof the first member can e.g. be a measuring member or scraper, whereas the following member 23 is a transmitting and receiving member with corresponding transmitting and re¬ ceived electronics (not shown). The scraper is passively driven by the me¬ dium flowing in the pipeline 10 and namely via elastic sleeves or collars 20a, by means of which the members of the scraper means 20 are centrally guided within the pipeline.

At the rear end of the transmitting and receiving member is provided a first scraper-mobile antenna 24, which can be surrounded by a cylinder cup- shaped, back-open focussing element 25 axially aligned with the scraper axis and therefore with the pipeline and through which is brought about a different weighting of individual modes of the wave modes building up in the pipeline.

At suitable intervals of several kilometres the pipeline has further stationary antennas 31. They are preferably in the form of double antennas with two single antennas, which are axially spaced and preferably have a spacing of 1/4 of the transmission wavelength. If the latter is e.g. 2.4 GHz, then the spacing of the individual antennas should be roughly 3.1 cm. This brings about a good reception of the transmitted signals independently of the precise position of the scraper means 20.

Fig. 1 diagrammatically shows the propagation of three wave modes 41, 42, 43 in the pipeline 10. Obviously, generally more than said three modes are propagated in the pipeline. The main advantage of working with several modes is that as a result there is a much reduced interference or attenuation by parts fitted within the pipeline, such as sleeve valves or the like than in the case of working with a single propagation mode.

Fig. 2 shows a connection 11 formed on a pipeline 10 and provided with a valve 11c, above which the connection 11 forms a connecting piece 11a, which is equipped at its free end with an annular flange 11b. Onto the annular flange 11b is flanged a passage 12, e.g. by screwing, through which is passed an antenna cable 13 for an antenna 14, so that its end remote from said an¬ tenna 14 is connected to a receiver/transmitter 15.

In the embodiment of fig. 2a the valve 11c is closed. The antenna cable 13 with antenna 14 is located above valve 11c.

In fig. 2b the valve 11c is open. The part of the antenna cable 13, together with the antenna 14 located below the passage 12 has dropped into the pipe¬ line following the opening of valve 11c and antenna 14, which is preferably a quarter-wave antenna, hangs centrally in the pipe 10.

After performing the measurement the valve 11c can be closed, in which case the antenna cable is separated and the antenna 14 remains in the pipe, or the antenna cable can be drawn upwards through the passage 12 until the an¬ tenna 14 is located above the valve 11c, which can then be closed. Subse¬ quently the passage 12 can be removed from the connection 11 again and the antenna 14 can be reused.