METHOD AND DEVICE FOR LIQUID LEVEL MEASUREMENT BY MEANS OF RADAR RADIATION

Abstract: The invention relates to a method and a device for measuring a level in a receptacle using radar. Via an aerial (1) directed down into the receptacle, an electromagnetic wave is transmitted and a reflected and time-delayed wave is received, the level being calculated from the time delay. Via one and the same aerial (1) at least two waves are transmitted and received, which are mutually distinguishable by a detectable characteristic for each wave. The device according to the invention is characterized in that connected to the aerial (1) is at least one further radar measuring channel (3; 4), the radar waves of which are mutually distinguishable and distinguishable from the radar wave used in a first radar measuring channel.

Description: Method and device for liquid level measurement by means of radar radiation The present invention relates to a method according to the preamble of claim 1. 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 1 , in the embodiment shown in the drawing there are two further radar measuring channels 3 and 4 respectively, each comprising a transmitter / receiver 3 a 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 la 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.

Claims: Claims 1. Method of measuring a level in a receptacle using radar, an electromagnetic wave being transmitted by means of a radar measuring channel via an aerial ( 1 ) directed down into the receptacle and a reflected and time-delayed wave being received, and the level being calculated from the time delay, characterized in that related waves, which are mutually distinguishable by a detectable characteristic for each channel, are transmitted via one and the same aerial (1) by means of at least one further radar measuring channel and received by a further channel respectively. 2. Method according to claim 1, characterized in that the waves are distinguishable time- ise. 3. Method according to claim 1, characterized in that the waves are distinguishable by means of modulation and/or polarization. 4. Method according to any of claims 1 - 3, characterized in that a level measurement is executed with one wave which is redundant with respect to the level measurement executed with the other wave. 5. Method according to any of claims 1 - 3, characterized in that a level measurement is executed with one wave which produces a high level alarm, e.g. an overfill alarm. 6. Device for a level indication system working with radar, with a radar aerial (1) connected to a radar measuring channel (2) comprising a transmitter, a receiver (2a) and an indicating element (2b), characterized in that connected to the aerial (1) is at least one further such radar measuring channel (3; 4), the radar waves of which are distinguishable from the radar waves used in the first-named radar measuring channel. 7. Device according to claim 6, characterized in that a first further radar measuring channel (3) is in principle identical to, i.e. redundant with respect to, the first-named radar measuring channel (2). 8. Device according to claim 6, characterized in that a second further measuring channel (3) is arranged to measure and to indicate a maximum permitted level. 9. Device according to claim 6, characterized in that connected to the aerial (1) are two further radar measuring channels (3, 4), of which one (3) is redundant with respect to the first-named radar measuring channel (2) and the other (4) is arranged to measure a maximum permitted level. 10. Device according to claim 6, characterized in that connected to the aerial (1) are two further radar measuring channels (3, 4), which are arranged to measure a level and a maximum permitted level respectively.

Inventors: KLEMAN MIKAEL, KLEMAN, MIKAEL
Applicants: SAAB MARINE ELECTRONICS, SAAB MARINE ELECTRONICS AB
Application year: 2000
Main classification: G01F23
IPC codes: G01F23, G01S7, G01S13