Ultrasound sensor for a fumes extractor hood

Details Ultrasound sensor for a fumes extractor hood Ultrasound sensor for a fumes extractor hood

1999-11-11

2001-12-04

Williams, Hezron (Department: 2856)

Measuring and testing

Instrument proving or calibrating

Apparatus for measuring by use of vibration or apparatus for...

Reexamination Certificate

active

06324889

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an ultrasound sensor for a fumes extractor hood with automatic compensation in respect of temperature and ageing drift, wherein the ultrasound sensor comprising a transmitter and a receiver monitors the vapour rising from the cooking to the fumes extractor hood and wherein the ultrasound sensor has a system-specific resonance frequency.
2. Discussion of the Prior Art
It is known from EP 0 443 141 B1 to use ultrasound sensors for controlling the fan in fumes extractor hoods. That involves taking advantage of the realisation that the rising vapours alter the amplitude of the ultrasound signal, more specifically, the amplitude of the ultrasound signal being altered to an increasing degree in proportion to increasing vapour formation. It is known in relation to ultrasound sensors for temperature drift to be automatically compensated, but hitherto there were no indications as to how the ageing drift of the sensor is compensated during on-going operation of the ultrasound sensor. Ageing drift results in a change in the resonance frequency of the sensor and therefore has to be monitored. Hitherto the necessary compensation effect is possible only in regard to a calm-air signal section and hitherto a strict association between sensor and associated electronics was also necessary as generally compensation could not be effected in the installed condition.
SUMMARY OF THE INVENTION
The object of the present invention is now that of avoiding those disadvantages and proposing an ultrasound sensor having a monitoring circuit which permits automatic compensation in respect of ageing drift during on-going operation of the sensor.
The invention therefore essentially provides that the monitoring circuit operates the ultrasound sensor at predetermined time intervals in succession at different frequencies in a frequency range near the resonance frequency and in so doing establishes the amplitudes which occur at a maximum. A frequency of the sensor is associated with each such maximum and an average frequency f (q) is ascertained from a plurality of such individual frequencies, said average frequency being firstly used as a new resonance frequency f (o). That applies until a fresh compensating test is undertaken. Each such test is effected for a very short time in order not to interfere with on-going operation of the ultrasound sensor in regard to monitoring the vapours. The frequency of the tests is empirically established.
In a preferred further configuration of the invention it is provided that the monitoring circuit, on passing through the frequency band, establishes and stores the frequency values associated with the maximum amplitudes that occur, that the monitoring circuit calculates from the frequency distribution of the respective maximum amplitudes and therewith the frequency values in a statistical calculation procedure the standard deviation and the centre frequency f (q), and that it uses that frequency as the resonance frequency f (o) for operation of the sensor until the next established change in the centre frequency f (q). That statistically calculated centre frequency corresponds to the above-mentioned average frequency and in the best case is equal to the originally predetermined resonance frequency f (o), but is at least in the proximity thereof.
A further preferred embodiment of the invention provides that, to ascertain the standard deviation and the centre frequency f (q), only those frequency values which are at a predetermined frequency spacing relative to the resonance frequency f (o), such as for example ±1 kHz, ±2 kHz, are stored.
A particularly desirable development of the invention provides that the ultrasound sensor includes a transmitter and a receiver in a housing, that it operates alternately in the transmitting and in the receiving mode and in so doing senses the vapour in a reflection procedure.
As an essential component, the monitoring circuit has a microcontroller which on the one hand provides for control of the fan of the extractor hood and which on the other hand provides for automatic drift compensation. This automatic compensation effect also makes it possible to compensate for temperature drift in the same testing cycle so that there is no need to involve separate complication and expense for same.


REFERENCES:
patent: 3967143 (1976-06-01), Watanabe et al.
patent: 5074281 (1991-12-01), Fluhrer et al.
patent: 5991234 (1999-11-01), Sejalon et al.
patent: 19510731-A1 (1996-02-01), None
patent: 0 443 141 B1 (1991-08-01), None
patent: 603539-A1 (1994-06-01), None

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