FI61246C - SAETT OCH ANORDNING FOR THE PURPOSE OF THE ENVIRONMENTAL LEVEL - Google Patents

Description

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Patents and registries '' AmMcm uttogd och u «i.« KriftM puMiewsd ^ o.u ^ .oc (32) (33) (31) Requested utuolkaut — Begird priorlcet 20.11.73

Sweden-Sweden (SE) 731561 * 9-9 (71) Saab-Scania Aktiebolag, S-58I 88 Linköping, Sweden-Sweden (SE) (72) Kurt Olov Edvardsson, Linköping, Sweden-Sweden (SE) (7 * 0 This invention relates to a method for calculating the level of a liquid, preferably in a tank, by transmitting a microwave signal, the frequency of which sweeps with time, against the surface against which the part is projected and delayed. then, corresponding to the distance between the reference point and the surface, receiving and mixing with the signal currently transmitted so as to obtain a separation frequency corresponding to the distance, on the other hand so that it can be received according to a known distance delay, which is similarly converted to a distance reference frequency, and that the difference frequency is related to the reference frequency so that the calculation of the distance will be based on a known distance.

Because microwaves have a very constant rate of propagation, these waves are suitable for accurate measurement of liquid surfaces, as discussed above. In addition, measuring equipment that operates in microwaves is relatively insensitive to dirt and still has non-contact measurement, which is an advantage in many applications, especially when measuring liquid surfaces from which flammable vapors evaporate.

2 61246

However, when measuring surfaces in microwaves, there are many factors that adversely affect the measurement accuracy. Such factors include the difficulty of accurately determining the resulting separation frequency to separate out interfering reflections from, for example, support beams or the bottom of the tank, and the nonlinearity or other imperfection of the microwave source. In order to increase the accuracy of the measurement, it has been proposed, for example, in the German publication 1.935.012, that the measurement take advantage of a reference delay to which the level measurement is related.

It is an object of the present invention to provide a method and apparatus for measuring the level of a liquid with microwaves which gives good dimensional accuracy, sets reasonable requirements for the linearity of a microwave source and is insensitive to interfering reflections over a wide range, and is achieved by the appended claims.

The invention is further explained below with reference to the accompanying drawings, in which:

Figure 1 shows in diagrammatic form the basic structure of a planar meter operating in accordance with the invention.

Fig. 2 is a diagram illustrating a calculator application specific to the invention.

Fig. 3 is a time-amplitude diagram showing the flow of signals taken at the indicated points in the diagram of Fig. 1.

Figure 4 shows a number of level gauges mounted on a tanker according to the invention.

Figure 5 shows in detail and in partial section such an installation.

In Fig. 1, 1 transmitter unit is connected to the signal processing unit by three connection terminals 3, 4 and 5. The signal processing unit can be connected to several transmitter units so that a periodically operating selector connected to terminals 3 to 61246 between the units.

The transmitter unit 1 comprises a microwave generator 6, for example a capacitance gun diode, the output of which is connected via a mixer R to an antenna 10 directed against the surface 9 whose level is to be measured. The mixer 8 is further connected to the terminal 3 of the signal processing unit via the amplifier 11. The microwave generator 6 is connected to the terminal 5 of the signal processing unit and is supplied via this connection by The mixer R leaks in a controlled manner so that a part of the microwave partial generator 6 is sent out against the surface 9 via the antenna 10. Some of the microradiation against the surface 9 is reflected towards the antenna 10, from where it is fed to the mixer 8. The path of this reflected microwave signal, called d, is shown in Figure 3. As can be seen, signals a and b have the same frequency value at different times. The time difference corresponds to the travel time of the microwave, the distance from the mixer 8 to the surface 9 and back. A different expression gives, with a certain blink of an eye, a difference frequency between the signal a and b, which depends on the interval just mentioned. The mixer 8 has the task of mixing signals a and b to produce such a difference frequency signal c, the flow of which can be seen in Figure 3. The irregularity units that can be detected in signal c originate from interfering echoes above or below liquid surface 9. retaining the reference numerals in Fig. 1, an object, in this case stiffening beams 12, which generate an echo which can be varied with the liquid surface 9. The transmitter units 1 are encapsulated and connected to a signal processing unit (not shown).

In order to eliminate the effect of said interference sources in a manner known per se, a mixer 13 is connected to the output of the microwave generator 6, which in the same way as the mixer 8 is connected on the one hand to the delay line 14 and on the other hand to the signal processing unit 2. In the same way as. 61246 4 described above, a difference frequency signal d having a constant frequency determined by the delay line 14 is obtained from the mixer 13. This is shown in Figure 3. The signal d will be used in the future as a reference signal. Thus, the output signals c and d of the transmitter unit 1 contain mainly two frequencies and quotients, i.e. the division between them gives the desired liquid level. The signal d is a relatively pure blue signal and has an almost constant frequency. The signal c, on the other hand, contains, as mentioned, a number of frequencies, only one of which is due to reflections in the liquid surface, the level of which is to be measured. The function of the signal processing unit 2 is to relate the difference gas signal c to the reference frequency signal d so that the calculation of the level in the surface 9 is based on the length of the delay line 14.

The connection terminal 4, to which the signal d enters the signal processing unit 2, is connected to the counter 18 by frequency multipliers 15 and a pulse modulator 17. Similarly, the connection terminal 3, to which the signal c enters, is connected to the counter 18 by an adjustable filter 19 21 connected to the indicator member 22 and on the other hand connected to the control unit 23. The indicator member 22 and the control unit 23 are connected to the member 24 for manual control of the measurement and for directing the constants to the landing. The controller unit 23 and the output from the memory 21 are connected to a filter 19, which at the input and output is connected to an amplitude comparator 25, which in turn is connected at the output to a controller unit 23. This is further connected via a terminal 5 to a microwave generator 6.

The function of the frequency multiplier 16 is to generate a signal e from the signal d, see Fig. 3, with a constant amplitude and a frequency which is a multiple of the frequency in the signal d, which corresponds to the apparent increase in the length of the delay line 14. In order to increase this length in reality, this comprises, on the one hand, an increased attenuation with a consequent measurement problem and, on the other hand, a more space-consuming and expensive line. The pulse shaper 17 is adapted to produce a pulse train f per half cycle of the pulse signal e.

The signal c is then filtered after it has passed the amplifier 11 in the filter 19, which is a narrowband controllable bandpass filter. This is arranged so that its center frequency from the signal e is arranged to be proportional to the instantaneous frequency of the reference frequency signal d and to the value coming from the control element 24 via the control unit 23. Thus, the scanning speed of the microwave oscillator 6 can be allowed to vary slightly, since the center frequency of the filter, which is also apparent from a particular feature of the invention, is arranged to monitor changes in the scanning speed. The output signal g of the filter 19 is a pure blue signal, the frequency of which is a measure of the liquid level sought. The pulse modifier 20 provides a pulse signal h from the signal g, which contains a pulse for each half-cycle of the signal g. Continuous signal processing starts from forming a quotient between the two pulse signals f and h, in which case the time positions of the pulses are not used but only the mutual order of the pulses is relevant. A weighting factor i is used to form the quotient, the course of which during one sweep is shown as an example, as in Fig. 3. According to a particular feature of the invention, this weighting factor has the form n (Nn), where N is a number of substantially equal sub-slots which is 1 for the first and N for the last subinterval. This weighting factor can be shown to include that the quotient of the frequencies of the signals f and h is determined in terms of the least squares method and gives the accuracy of the estimate after only one sweep. The constant weight factor would include a standard pulse drop, which for high accuracy requires a pulse drop with a large number of frequency sweeps, but which is nevertheless relatively sensitive to interference echoes.

The calculation of the weighting factor and the quotient characterization of the invention takes place in a calculating element 18, the structure of which is shown by way of example in Fig. 2. In this figure there is a means 26 connected to the pulse modifier 20 for calculating the weighting factor from the signal h. each of which is connected to the quotient generator 32 via the incremental registers 30, 31. The weighting factor is derived as follows: The above-mentioned intermediate length is selected to be equal to the distance between the pulses in the signal h. number of values pulses in register 30. For each pulse in signal f, the same number of pulses is calculated in register 31. After N reference signal pulses, the quotient k is calculated between the numbers 1 and m in both registers 30, 31. To the accuracy of one scale factor, this quotient k is a measure of the level sought. Since the level is measured between the mixer 8 and the surface 9, it is suitable that a constant is derived by means of the guide member 24, by means of which the liquid level measurement is related to a suitable outer point. The result of the measurement is stored in the memory 21 and displayed on the display element 24. The stored measurement result can also be registered with a printer.

As can be seen from the above, the amplitude of the difference frequency signal c has little effect on the continuous signal processing, but if the amplitude with external properties has become so small that it can be confused with the signal amplitudes coming from the interfering echoes, there is a risk of switching. Therefore, in certain applications, for example when measuring the surface, a tanker may need amplitude monitoring, as the amplitude is affected by waves in the liquid surface. The function of the amplitude comparator 25 is to provide such comparison and monitoring by comparing a signal g containing a difference frequency corresponding to the liquid surface 9, a fixed echo of the frequency filtered from the corresponding signal c, the comparator 25 being arranged to produce a logic signal showing how the signal corresponds to the level to be calculated. has a greater or lesser amplitude than the signal corresponding to a fixed echo. This comparison also makes the level measurement independent of variations in the output power of the microwave generator 6. If the amplitude in the signal c is insufficient, the measurement is stopped by the control unit 23.

Fig. 5 shows an application example of a transmitter unit according to the invention and one shown in Fig. 4. An antenna 10 is arranged in the tubular housing 33 so that it is directed against the liquid surface 9. 34 is a microwave tube connected via a waveguide 35 to a stirrer and a microwave generator which, together with the other previously described actuators 36 of the transmitter unit, are connected to a tubular housing 37 arranged in a housing 33 and smaller in this respect. 36 are easily accessible for inspection and possible repair through hatches 38, 39 located in housings 33 and 37.

Claims (8)

1. A method of calculating the level of the liquid surface, preferably in a tank, by transmitting a microwave signal whose frequency is erased over time against the surface against which the part is projected and receiving and mixing with the signal currently transmitted after the frequency corresponding to the distance between the reference point and the surface, on the other hand, the difference frequency corresponding to the distance is reached with a delay which is similarly converted into a reference frequency corresponding to the interval and that the difference frequency is related to the reference frequencies so that the distance calculation is based on a known interval with the variable factor (i) during the sweeping time, that the results of the factor (i) and the corresponding frequencies (c, d) are each summed and that at the end of the sweeping time a quotient (k) is formed between the sums (1, m) thus obtained, which is a measure of the distance sought. A method according to claim 2, characterized in that the factor (i) for each sub-slot is equal to n (Nn), where N is a number of substantially equal sub-slots and n is a sequence number of sub-slots equal to 1 for the first sub-slot and N for the last the partial interval. A method according to claim 2, characterized in that each sub-interval is equal to half the period of the difference frequency (c). Method according to one of the preceding claims, characterized in that the reference frequency (d) is multiplied by a constant selected in such a way that the frequency (e) then obtained is cm higher than the difference frequency (c), which includes an apparent increase in delay. that the apparent length of the interval is always greater than the distance to be measured. A method according to claim 1, characterized in that the difference frequency (c) is filtered by means of a bandpass filter (1), the center frequencies of which are controlled so as to be proportional to the reference frequencies (d), thereby filtering out interfering reflections despite erasure. variation in fermentation speed. A method according to claim 1, characterized in that the amplitude of the reflected microwave signal (d) is compared with the amplitude of a known echo signal and that signals having an amplitude greater than 61246 or less than the amplitude interval near the known echo amplitude are separated. A method according to claim 1, characterized in that the difference frequency signal (c) is converted into a pulse train (f) with a pulse for each half cycle of the difference frequency, that the pulses for scanning are fed to the shift register at a reference frequency controlled rate and that the stored pulses are , which is similar to the linearity of the sweep. 7 61246 Apparatus for applying the method according to claim 1, comprising a microwave generator (6) for generating a microwave signal (a), the frequency of which is erased over time, an antenna (10) connected to the generator, directed against the surface (9), for transmitting the microwave signal (a) and a portion (b) reflected from the surface (9) of the microwave signal, and a first mixer (8) connected to the antenna (10) and the generator (6), adapted to mix the reflected and transmitted microwave signal to produce a separation frequency (c) corresponding to the distance to the generator (6) a delay line corresponding to the known delay of the connected delay line (IA), a generator (6) and a second mixer (13) connected to the delay line (14), thus adapted by mixing the delayed microwave signal and the transmitted microwave signal to produce a reference frequency corresponding to the known interval, (18) arranged so that at the difference frequencies (c) in relation to the reference frequencies n (d) calculates the searched distance, characterized in that the calculator (18) contains additional registers (30, 31) operatively connected to the multiplier (28, 29), which are arranged so that the scanning time adds up the factor (i) and the corresponding frequencies. results, and a quotient generator (32) connected to the register, the function of which is to form a quotient (k) between the sums in the register at the end of the sweep time. Patentkräv 612 4 6