The invention also relates to a device according to the preamble of claim 6.

A level measuring system working with radar for a tanker's load tanks is previously known from US-A 4,665,403. In load tanks of this kind, however, at least one overfill alarm independent of the level measuring system is required. The requirement for independence means that there must not be common electrical circuits and cabling, i. e. there must not be any galvanic contact between different measuring systems. However, fixed mechanical constructions for example, which cannot normally go wrong, may be shared. Float sensors and different types of capacitive sensors, for example, mounted in separate tank bushings are used as sensors for such alarm systems. These sensors are however sensitive to linings, corrosion and other influence from the content of the load tanks or their wiring and the risk of malfunction is therefore evident.

The object of the present invention is to achieve a method of the type indicated by way of introduction which is not marred by the disadvantages described above. This object is achieved by the features stated in claim 1.

The invention also has the object of producing a device according to claim 6 which is improved compared with the prior art. This is achieved with the characterizing features stated in said claim.

A number of other advantages are obtained with the invention. By utilizing a single aerial for two or more level measuring channels, costs are saved for further aerials and fitting in the tank as well as the tank bushing for these. If two measuring channels are identical, redundant measuring results are obtained, which if they only lie within a certain tolerance range are proof that the measuring channels are functioning. Several identical measuring channels also make the stocking of spare parts easier and cheaper.

The invention is to be explained further below with reference to the enclosed drawing, in which Figures 1 and 2 show diagrammatically two alternative ways of realizing the

invention for level measurement-alarm indication for a tanker's load tanks, but it is evident that the invention can be used for all types of liquids and bulk material.

In the drawing, 1 generally designates an aerial. This can be a fixed or movable parabolic aerial, a conical aerial, a transmission line or a straight tube aerial. Connected to the aerial 1 is a radar measuring channel 2 comprising a transmitter/receiver 2a and an indicating device 2b designed to indicate the current level and generate an alarm at a predetermined level. According to the invention at least one further radar measuring channel is connected to the aerial I, in the embodiment shown in the drawing there are two further radar measuring channels 3 and 4 respectively, each comprising a transmitter/receiver 3a and 4a respectively and an indicating device 3b and 4b respectively. To prevent radar waves transmitted by a transmitter e. g. in measuring channel 2 from being received reflected by the receivers in measuring channels 3 or 4, the radar waves from each channel are distinguishable by a detectable characteristic for each wave, e. g. by means of updating time-wise, polarization and/or modulation.

It will be appreciated that several different measuring and alarm alternatives can be provided using one or more additional measuring channels. For example, a measurement can be carried out using one extra radar measuring channel 3, which measurement is redundant to a level measurement carried out using measuring channel 2. If the measuring values from both measuring channels lie within predetermined tolerance values, it can hereby be verified with a very high degree of probability that the level value measured is correct. Alternatively, a high level alarm can be obtained with the extra measuring channel 3 in the form of an alarm at a maximum permitted level or an overfill alarm.

With two further measuring channels 3,4 it is possible at the same time to execute both a redundancy measurement and produce a high level alarm. Alternatively, a level measurement can be executed using measuring channel 2, a high level alarm obtained with measuring channel 3 and an overfill alarm with measuring channel 4.

The devices according to Figures 1 and 2 differ essentially only with regard to how the measuring channels 2,3 and 4 are connected to the aerial 1. In Fig. 1, the measuring channels are connected to a supply lead 1 a to the aerial. In the alternative shown in Fig. 2, the measuring channels 2,3 and 4 are connected to the supply lead 1 a via a power divider 5 known to the expert.