MFPW RADAR LEVEL GAUGING WITH DISTANCE APPROXIMATION
First Claim
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1. A method of determining a distance to a surface of a product kept in a tank, said method comprising:
- forming a transmit signal as a pulse train of distinct carrier wave pulses having a duration greater than 1 microsecond and shorter than 100 milliseconds, each pulse being frequency modulated around a defined center frequency,transmitting said transmit signal towards said surface,receiving an electromagnetic return signal reflected at said surface,mixing the return signal with the transmit signal in a first channel (I-channel) and mixing the return signal with a 90°
phase shifted transmit signal in a second channel (Q-channel), to provide two IF (intermediate frequency) signals,filtering said IF signals to provide a filtered signal corresponding to a first selected harmonic of said modulation frequency,mixing the filtered signals of each channel with said first selected harmonic of said modulation frequency, to provide two primary amplitude values (I and Q),calculating (step S5) actual phase properties of each distinct pulse received in relation to each corresponding distinct pulse transmitted, based on said primary amplitude values and determining a distance measure based on said actual phase properties,filtering said IF signals to provide a filtered signal corresponding to a second selected harmonic of said modulation frequency,mixing the filtered signals of each channel with said second selected harmonic of said modulation frequency, to provide two secondary amplitude values (I and Q), andproviding an approximation of said distance based on a relationship between said primary and said secondary amplitude values.
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Abstract
Level gauging including an approxiamtion of a distance to the surface of a product kept in a tank. The approxiamtion is determined by relating an amplitude of a first harmonic of an IF signal with an amplitude of a second harmonic of the IF signal.
Basically, each harmonics represents a given distance range. By determining the received power in two or more harmonics, and correlating them to each other, the distance may be estimated. Depending on modulation and other parameters the distance dependence may be very different, and may be selected to suit the application.
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Citations
26 Claims
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1. A method of determining a distance to a surface of a product kept in a tank, said method comprising:
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forming a transmit signal as a pulse train of distinct carrier wave pulses having a duration greater than 1 microsecond and shorter than 100 milliseconds, each pulse being frequency modulated around a defined center frequency, transmitting said transmit signal towards said surface, receiving an electromagnetic return signal reflected at said surface, mixing the return signal with the transmit signal in a first channel (I-channel) and mixing the return signal with a 90°
phase shifted transmit signal in a second channel (Q-channel), to provide two IF (intermediate frequency) signals,filtering said IF signals to provide a filtered signal corresponding to a first selected harmonic of said modulation frequency, mixing the filtered signals of each channel with said first selected harmonic of said modulation frequency, to provide two primary amplitude values (I and Q), calculating (step S5) actual phase properties of each distinct pulse received in relation to each corresponding distinct pulse transmitted, based on said primary amplitude values and determining a distance measure based on said actual phase properties, filtering said IF signals to provide a filtered signal corresponding to a second selected harmonic of said modulation frequency, mixing the filtered signals of each channel with said second selected harmonic of said modulation frequency, to provide two secondary amplitude values (I and Q), and providing an approximation of said distance based on a relationship between said primary and said secondary amplitude values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A radar level gauging system, for determining a distance to a surface of a product kept in a tank, said system comprising:
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a transceiver for transmitting electromagnetic transmit signals formed by a pulse train of distinct carrier wave pulses having a duration greater than 1 microsecond and shorter than 100 milliseconds, each pulse being frequency modulated around a defined center frequency, and receiving electromagnetic return signals reflected at said surface, a set of RF mixers for mixing the return signal with the transmit signal in a first channel (I-channel) and mixing the return signal with a 90°
phase shifted transmit signal in a second channel (Q-channel), to provide two IF (intermediate frequency) signals,a first set of filters for filtering said IF signals to provide a filtered signal corresponding to a first selected harmonic of said modulation frequency, a first set of IF mixers for mixing the filtered signals of each channel with said first selected harmonic of said modulation frequency, to provide two primary amplitude values (I and Q), a second set of filters for filtering said IF signals to provide a filtered signal corresponding to a second selected harmonic of said modulation frequency, a second set of IF mixers for mixing the filtered signals of each channel with said second selected harmonic of said modulation frequency, to provide two secondary amplitude values (I and Q), and processing circuitry connected to receive outputs from said IF mixers and operable to; calculate actual phase properties of each distinct pulse received in relation to each corresponding distinct pulse transmitted, based on said primary amplitude values and determining a distance measure based on said actual phase properties, and providing an approximation of said distance based on a relationship between said primary and said secondary amplitude values. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26)
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Specification