Measuring and testing – Liquid level or depth gauge
Reexamination Certificate
2002-01-28
2003-06-24
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
C073S29000R, C073S592000
Reexamination Certificate
active
06581460
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for directly digitizing microwave signals reflected on a filling product surface of a filling product present in a receptacle, and to a filling level measuring device working on the transit time principle and emitting microwave signals.
BACKGROUND INFORMATION
In simplified terms, microwave signals are generated (in a pulsed or continuous manner) by a transmitting means in a filling level measuring device, and are radiated via an antenna, such as, for example, a horn, rod or microstrip antenna into the direction of the filling product surface to be measured or are guides to the filling product surface by means of a waveguide (rod, cable or also rope). The microwave signals reflected on the filling product surface—in general also designated as echo signals—may be fed to a reception circuit and scanned via a receiving means, often identical to the transmitting antenna; or by means of the aforementioned waveguide. The analog values resulting from said scanning are converted into digital values, and are then made available to an evaluation means. From the digital values, the filling level height is determined in the evaluation means.
Reference is, for example, made to the document DE 42 40 491 A1, in which such a measuring device is disclosed in general. For processing the reflected and received microwave signals, various analog circuits or components are present so as to generate a so-called envelope curve, which will then be digitized for determining the filling level height therefrom. The generation of an envelope curve is well known, and, correspondingly, there is no need for further explanations as to this technology (with respect to the generation of the envelope curve, reference is made, for example, to DE 44 07 396 C2 and M. Scholnik “Introduction to Radar Systems”, 2
nd
edition, 1980, McGraw-Hill; Peter Devine “Radar level measurement—the user's guide”, VEGA Controls Ltd., 2000, ISBN 0-9538920-0-X, which are hereby included by reference).
In the present technical field, microwave signals are worked with that have a frequency of 1 to 30 GHz or more. Due to these high frequencies, various analog circuits or components may be necessary for determining the exact filling level height from the received microwave signals. In particular, a so-called mixer has inter alia to be used, with the assistance of which a temporal “elongation” of the envelope curve is carried out, so that the scanning of the envelope curve by means of conventional A/D converter (pulse frequencies of about 25 microseconds) with a sufficient fine scanning screen is possible (for achieving a sufficient precision of the determined filling level height). This means that microwave pulses are in particular transformed into another frequency and time domain by means of the mixer and the associated oscillator. Hereby, pulses are for example temporally elongated after time transformation approximately by a factor of 160,000, whereby a pulse duration of 1-2 nanoseconds before the transformation corresponds to a pulse duration of about 160-320 microseconds after the transformation. These time-elongated pulses are then fed to the A/D converter that scans said signal in a scanning screen of about 25 microseconds. Thus, with a pulse length of 160 microseconds, six scanning values are available per pulse. With these values, accuracies of about 5 mm may be obtained in the determination of the filling level height. It has to be pointed out that the precision of the filling level determination is also dependent on the height of the scanning values per echo pulse, on the gradient of the pulse flanks, and on the accuracy of the A/D converter.
In summary, it has to be stated that devices for determining the filling level height basing on reflected microwaves, in particular microwave pulses, perform an analog processing of the received signals for being able to achieve the desired accuracy in the filling level height determination. Thus, for example, reference is made to the document U.S. Pat. No. 6,087,978 that discloses a pulsed radar-filling level measuring device, wherein the microwave signals are transformed into another frequency and time domain with the assistance of a mixer and an associated oscillator so as to be able to carry out the scanning of the signals and the digitization of the scanning values. In the document U.S. Pat. No. 5,847,567, a filling level measuring device is described that is either configured as a FMCW radar device or as a pulsed radar device. With the configuration as an FMCW radar device, a mixer of the aforementioned kind is present serving for the transformation of the frequency domain, as well as the time domain of the incoming signals. Then, an analog-digital conversion of the signals is performed. With the configuration as a pulsed radar device, a transformation is performed in the above-described manner by means of a timing circuit.
It is believed that the use of analog components or analog switching technique, however, is affected with disadvantages. Thus, with the dimensioning of the circuit, component tolerances and fabrication divergences have to be taken into consideration, and have also to be monitored during the production. Analog components moreover exhibit temperature-dependence, which have to be considered and cause a not inconsiderable test expenditure. It is believed that temperature-dependence and component tolerances in addition result in a decrease of the reproducibility and accuracy of the initial signals, and have to be minimized or compensated by an additional expenditure. It is also believed that a disadvantage has also to be seen in that modifications in the functional mode of such an analog, circuit can only be carried out at a high expenditure. Finally, it is believed that analog circuits also are sensitive to disturbing influences.
SUMMARY OF THE INVENTION
A technical problem on which an exemplary embodiment of the present invention is based, consists in providing a method and a device by means of which the number of analog circuit components in devices of the mentioned kind can be reduced, and the above-described disadvantages are therewith at least decreased.
It is believed that this technical problem may be solved according to a first aspect of the invention by an exemplary embodiment of a method for directly digitizing microwave signals reflected on a filling product surface of a filling product present in a receptacle, wherein the microwave signals reflected on the filling product surface are scanned, and the individual scanning values resulting from said scanning, are stored in an analog value storage means, stored analog values having a lower rate as compared to the scanning rate being read out from the analog value storage means and being converted into digital values made available to an evaluation means for determining the filling level height.
According to another exemplary embodiment of the method it is provided that the microwave signals are scanned either unchanged in their frequency or substantially unchanged at a high scanning rate corresponding to this frequency, and that the analog values generated by the scanning process are stored at a storage rate corresponding to the scanning rate in a so-called FISO system, and that furthermore, the analog values stored in said FISO system are read out from said FISO system at a lower read-out rate as compared to the storage rate, and are converted into digital values, and that these digital values in turn are stored in a digital value storage means at a storage rate corresponding to said read-out rate, and that finally, the evaluation means for determining the filling level height, accesses the digital value storage means for reading out the therein stored digital values.
Such circuit arrangements are designated as FISO system (Fast In Slow Out) allowing for a fast read-in of analog values—hence at a very high frequency or a high scanning rate—and outputting said values in a slower manner, so that one or several A/D converters of
Fay Kaplun & Marcin LLP
Frank Rodney
Vega Grieshaber KG
Williams Hezron
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