Communications: directive radio wave systems and devices (e.g. – Determining distance – Material level within container
Patent
1984-10-03
1987-04-28
Tubbesing, T. M.
Communications: directive radio wave systems and devices (e.g.,
Determining distance
Material level within container
73290R, G01S 1308, G01F 2328
Patent
active
046618171
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method to determine the distance to an object, particularly the level of a liquid or another flowable medium in an enclosure or container.
Further the invention relates to a device for determination of such distance and level.
The terminology used in this specification relating to microwave technology is according to the definitions in IEC Standard, Publication 615: "Terminology for microwave apparatus", Geneve, Switzerlaand, 1976.
For the purpose stated above different methods based on radiation of electromagnetic waves are used.
The signal is transmitted as short pulses. The received signal consists of a series of pulses corresponding to echos from objects at different distances. The signal handling consists of a time and amplitude determination of the echo pulses which requires very fast acting circuits. The resolution will increase with decresed pulse length. A new pulse can not be transmitted before all significant echos are returned. If the period between transmission of pulses is T, the ratio of peak gain to average gain for the radar transmitter will be T/.tau.. To avoid distortion of the pulses, the radar should have a band width of .about.1/.tau..
Chirp radar
This kind of radar differs from the pulse radar only in the generation and detection of pulses. The transmitted signal has a longer duration, but is frequency modulated, changing the frequency from the lowest to the highest or vice versa, of the pulse range. In the receiver the signal is passed to a matched filter delaying the low frequencies relatively to the high and compressing the signal to a pulse of the same length as in a pulse radar with the same requirement for solution. After the compressing, the handling of the signal is alike for the two systems. The chirp radar requires lower peak effect than the pulse radar, but a matched filter.
FM-radar
In this type of radar the transmitted signal has a constant amplitude. It is frequency modulated linearly and periodically from the lowest to the highest frequency in the band or vice versa, similarly to the chirp radar, but the frequency scanning can be more time consuming. A part of the transmitted signal is branched off and utilized as a local oscillator signal for a receiving mixer circuit, mixing it with the reflected signal. Due to the time difference of the reflected signal, a difference frequency proportional to the distance to the reflecting object is developed. Different parts of reflection show up as particular frequency components in the received signal, which can be filtered out.
Analysis of the received signal is carried out in a filter assembly or one or more tunable filters. The receiver can be designed with a low bandwidth, demanding a short scanning time to work with a mixing frequency in the low noise area of the receiver.
Reflectometer
By this method the reflection coefficient .rho.=re.sup.j.phi. for the antenna over the desired frequency range is measured. Here r is the module of the reflection coefficient (amplitude) and .phi. its phase, while e is the base of the natural logarithm and j=.sqroot.-1. The reflection coefficient .rho.(f), where f is the measuring frequency, is measured for a series of discret frequencies evenly distributed over the frequency range. The data measured are fed to a micro processor or another data processor effecting a fourier transformation of .rho.(f) from the frequency plane to the time plane. The result is a time function corresponding to the reflected signal of a pulse radar system. Systems based on this method may thus be called synthezied pulse radar systems. The signal will however not be present in true time, but in data form, which will bring great advantages for the further signal analysis.
The present invention utilizes the principle described above combined with a series of particular methods of signal generation and handling which will make the level measurement more accurate and flexible than existing methods and give other advantages to be described below.
Systems based on the reflectometer method can n
REFERENCES:
patent: 3807231 (1974-04-01), Spaw
patent: 4234882 (1980-11-01), Thompson
patent: 4458530 (1984-07-01), Bastida
Bekkadal Fritz
Schoug-Pettersen Tor
501 Autronica A/S
Barron Jr. Gilberto
Pittenger James E.
Tubbesing T. M.
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