Method and apparatus for determining the contents of a gas...

Measuring and testing – Liquid level or depth gauge

Reexamination Certificate

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Reexamination Certificate

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06247361

ABSTRACT:

The present invention relates to a method for determining the contents of a gas bottle, in particular the contents of gas bottles commonly used for camping, on boats, in caravans, in camping cars, in holiday homes but also in normal households or by craftsmen as a transportable source of energy for heating with an open flame. The invention furthermore relates to an apparatus for determining the contents of a gas bottle.
So far, users of gas bottles have been able to determine the total or residual contents of such bottles made of pressure resistant material by weighing them on a scale for example (cf. e.g. DE 195 32 378). However, this is not always possible. For this purpose, the precise empty weight of the bottle itself must be known, and the filling level will then have to be calculated from a weight difference. This entire operation is not only labor- as well as time-intensive, but also inaccurate.
It has further been known to mount temperature-sensitive strips on the shell of the gas bottles, or to provide temperature sensors on the inside of gas containers (cf. DE 296 06 594). The difference in temperature between the area of the gas bottle which still contains the liquified gas and the area which has already been emptied allows an approximate estimate of the filling level to be made. However, this solution, too, is rather inaccurate and may also be influenced by fluctuations of the outside temperature, amongst other things.
It is therefore the object of the invention to provide a method of the aforementioned kind which constitutes a simple and reliable way of determining the bottle contents, is easily feasible by anybody and may be implemented at low cost.
Such object is accomplished according to the present invention by the following steps. First of all, a gas bottle is excited by the application of a signal to a loudspeaker mounted on the gas bottle. The phase of the signal used for such excitation is compared with that of the signal from a microphone, with the frequency of the signal applied to the loudspeaker being altered continuously until a resonant frequency is established. Based on the established resonant frequency, the filling level of the gas bottle is subsequently determined.
It is a further object of the invention to provide an apparatus for determining the contents of a gas bottle which constitutes a simple and reliable way of determining the bottle contents, is easily feasible by anybody and may be implemented at low cost.
In accordance with the invention, such an apparatus comprises a loudspeaker to which a signal for exciting the gas bottle may be applied and which may be placed on the gas bottle in operation, a phase detector for comparing the phase of the signal used for excitation with that of a signal from a microphone mounted on the gas bottle, an oscillator outputting the signal used for excitation, with the frequency of said signal being continuously variable, as well as means for converting a certain frequency value into a value representing the gas bottle filling level.
Advantageously, the signal applied to the loudspeaker is generated by a voltage-controlled oscillator which is in turn controlled by a microprocessor.
The resonant frequency is determined by comparing the phase of the signal used for exciting the gas bottle via the loudspeaker with that of the signal from the microphone. To avoid acoustic feedback, one may proceed as follows: The voltage-controlled oscillator generates an alternating signal which is on the one hand used for driving the loudspeaker, and on the other hand for driving the phase detector. A phase detection, and a phase comparison of the signal transmitted to the phase detector by the voltage-controlled oscillator and the signal provided by the microphone are only performed at times when there is no signal from the loudspeaker.
The continuous alteration of the frequency of the loudspeaker drive signal is preferably obtained by sweeping the frequency from a maximum value to a minimum value or from a minimum value to a maximum value.
After a resonant frequency has been established, a phase locked loop (PLL) circuit is activated, causing a pause in the continuous alteration of the frequency of the loudspeaker drive signal, with the frequency set at this time, i.e. the resonant frequency, being maintained.
However, it is also possible to determine the precise resonant frequency by controlling the voltage-controlled oscillator by means of a PI (proportional and integral) amplifier before activating the phase-locked loop circuit.
The signal from the microphone is preferably band-pass filtered so as to filter out harmonic frequencies as well as disturbing noise. Preferably, the signal from the microphone is controlled to a constant level by an automatic gain control (AGC) circuit.
Being altered continuously, the frequency passes a frequency range of between 50 Hz and 5 kHz, preferably approx. 250 Hz and 2.5 kHz.
Moreover, it is possible to also determine the temperature of the gas bottle. This temperature may then be considered when the value of the resonant frequency is converted into a value representing the filling level. While the established resonant frequency may be converted into the filling level of the gas bottle on the basis of a calibration table stored in the microprocessor, it is also possible to determine it mathematically, by means of a formula expressing the relationship between the filling level and the resonant frequency.
Furthermore, the loudspeaker drive signal is controlled to be of a constant amplitude.
Finally, the conversion result is automatically indicated on a display.
Further advantageous embodiments are described in the subclaims.


REFERENCES:
patent: 4841256 (1989-06-01), Gastgeb
patent: 5261274 (1993-11-01), Nemirow
patent: 5264831 (1993-11-01), Pfeiffer
patent: 5886262 (1999-03-01), Sinha
patent: 296 06 594 U1 (1996-07-01), None
patent: 195 32 378 A1 (1997-03-01), None
patent: 0 119 790 A1 (1984-09-01), None
patent: 2 146 770 (1985-04-01), None
patent: 2 298 279 (1996-08-01), None
patent: WO 82/01584 (1982-05-01), None

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