EP0443141B1 - Switching arrangement for controlling a ventilator - Google Patents

Description

The invention relates to a circuit arrangement for controlling a fan, in particular in the case of an extractor hood above a cooker, as a function of vapors drawing to the fan.

An extractor hood with a controllable fan motor is described in DE 30 39 346 A1. A sensor element responsive to moisture and / or haze and / or smoke and / or heat is arranged on this. This sensor element is, for example, a moisture sensor, a temperature sensor or a sensor that responds to particles.

DE-AS 25 18 750 describes an extractor hood, the fan of which switches as a function of a temperature difference between the temperature of the cooking fumes and the ambient temperature.

DE-GM 76 33 882 describes an extractor hood, the fan of which is switched by a moisture sensor.

US Pat. No. 3,625,135 describes an extractor hood, the fan of which is switched as a function of particles in the cooking vapor.

It has been shown that temperature-dependent control of the fan is problematic, since the temperature in the vapors in the area of the extractor hood is not so significantly higher than the ambient temperature is that this could easily be used to control the fan. Moisture sensors or particle sensors also do not simply lead to the desired control. In addition, such sensors are expensive.

According to DE 32 45 302, the extractor hood is not controlled as a function of vapors drawing to the fan. Rather, the extractor hood is controlled by a photoelectric signal transmitter of the cooker via a photoelectric sensor.

The object of the invention is to propose a circuit arrangement of the type mentioned at the beginning with which vapors can be detected easily and safely and used for switching the fan.

According to the invention, the above object is achieved in a circuit arrangement of the type mentioned at the outset in that an ultrasound path with an ultrasound transmitter and an ultrasound receiver is arranged in front of the fan, that a receiving circuit demodulates the signal occurring at the ultrasound receiver, and that an evaluation circuit shows temporal fluctuations in the input signal due to vapors based in the ultrasonic path, evaluates it and counts it within a time base and that a comparison circuit compares the counting result with preset values and switches the fan accordingly.

It has been found that the cooking process on a cooker leads to air streaks in the area of the extractor hood due to the development of vapors, ie the formation of steam, vapor and / or heat. It has also been found that such air streaks significantly influence the propagation characteristics of ultrasound. This can be attributed to the fact that the fluctuations in air streaks representing air density at interfaces result in sound scattering according to the laws of refraction.

Air streaks in the ultrasound path thus result in rapidly fluctuating damping of the ultrasound signal received by the ultrasound receiver.

The receiving circuit demodulates the signal occurring at the ultrasonic receiver in such a way that a constant received signal is produced in the case of an undisturbed ultrasonic path. It has been shown that this received signal oscillates considerably when vapors enter the ultrasonic path, be it due to the formation of steam, vapor and / or heat, whereas other movements of the ambient air only cause slow fluctuations in the received signal. Vapors therefore form a harmonic component in the received signal.

The evaluation circuit evaluates the rapid temporal fluctuations or the harmonic component of the received signal. This generates pulses that are counted within a time base. The respective count result corresponds to the intensity of the respective vapor formation. A stronger vapor formation leads to a larger count result.

With the comparison circuit, the counting result is compared with preset values. According to the comparison result, the fan is switched on or off, in particular step by step.

An optical display can also be switched simultaneously with the fan.

• Figur 1 eine Dunstabzugshaube über einem Kochfeld schematisch,
• Figur 2 ein Blockschaltbild einer Schaltungsanordnung der Dunstabzugshaube und
• Figur 3 Signaldiagramme.

Advantageous refinements of the invention result from the subclaims and the following description of an exemplary embodiment. The drawing shows:

• FIG. 1 schematically shows an extractor hood over a hob,
• Figure 2 is a block diagram of a circuit arrangement of the extractor hood and
• Figure 3 signal diagrams.

An extractor hood (2) arranged above a hob (1) has a fan (3). A filter mat (5) is provided between an intake grille (4) of the extractor hood (2) and the fan (3). An ultrasonic path (6) is provided between the filter mat (5) and the suction grille (4). This is formed by an ultrasound transmitter (7) and an ultrasound receiver (8).

The ultrasonic transmitter (7) works, for example, at a frequency of 200 kHz. An amplifier and demodulator (9) is connected downstream of the receiver (8). The demodulated received signal (Ua) occurs at its output. This is connected to an evaluation circuit (10), which is followed by a comparison circuit (11).

The transmitter (7) does not have to work continuously. It can be operated in pulse mode. In this case, the transmitter and the receiver can be formed from the same component. Only one ultrasound element is therefore required for the circuit arrangement.

The received signal (Ua) is applied to comparators (12, 13) in the evaluation circuit (10). In addition, the received signal (Ua) is due to a timing element (14) which is formed by resistors (R1, R2) and a capacitor (C). The timing element generates a mean lag level (Un) which is delayed in relation to the received signal (Ua). Certain harmonic components of the received signal (Ua) are smoothed in the lag level (Un).

The mean lag level (Un) is applied to the one input of two differential amplifiers (15, 16), at the other inputs of which there are adjustable resistors (R3 and R4). At the output of the differential amplifier (15) there is a positive switching level (Un +), which is connected to the other input of the comparator (12). At the output of the differential amplifier (16) there is a negative switching level (Un-) which is connected to the other output of the comparator (13). FIG. 3a shows a reception signal (Ua), which results, for example, when vapors occur in the ultrasound path (6) for a short time. In addition, the positive switching level (Un +) and the negative switching level (Un-) resulting from this received signal (Ua) are shown.

The output of the comparator (12) is at a set input of a flip-flop (17). The output of the comparator (13) is connected to a reset input of the flip-flop (17).

When the received signal (Ua) intersects the positive switching level (Un +), a set pulse is generated at the flip-flop (17). When the received signal (Ua) intersects the negative switching level (Un-), a reset pulse occurs at the flip-flop (17). This results in a pulse sequence at the output of the flip-flop (17) (cf. FIG. 3b). Only two such pulses are shown in FIG. 3b. The smaller the hysteresis between the positive switching level (Un +) and the negative switching level (Un-), the finer the amplitude fluctuations of the received signal (Ua) are detected, ie lead to pulses at the output of the flip-flop (17). The size of this hysteresis is proportional to the absolute level of the received signal (Ua). This ensures a largely constant sensitivity, even if that Received signal (Ua) weakens over time due to unavoidable contamination of the transmitter (7) and the receiver (8).

The time constant of the timing element (14) is selected such that it detects the harmonic components of the received signal (Ua) that are generated by vapors. If the time constant is chosen to be significantly larger, then movements in the ambient air are also detected.

The number of pulses of the flip-flop (17) is counted in a counter (18). This is always reset after a certain time (time base) via a clock circuit (19). The time base is approximately 20 s, for example.

The counting result in the respective time base is stored in a buffer (20) of the comparison circuit (11). This is also deleted cyclically with the clock circuit (19) via a latch connection.

A comparison logic (21) takes over the respective counting result from the buffer (20). On the one hand, switch-on values are applied to the comparison logic (21) via coding switches (22) and, on the other hand, switch-off values are set via coding switches (23). With the comparison logic (21), for example, three switching stages (St1, St2, St3) of the fan (3) can be switched. By specifying the switch-on values, it is predetermined at which value of the buffer store (20) the stage (St1) or the stage (St2) or the stage (St3) should turn on. The switch-off values determine the value at which the buffer (20) the fan (3) should switch back. Through the different selection of the switch-on values and the switch-off values, a desired hysteresis of the switching behavior of the fan (3) can be achieved.

It has been shown that the described Circuit arrangement of the fans (3) with vapors that become more intensive during a cooking process automatically switches up to its three stages and switches back to standstill as the vapors decrease.

Claims (9)

1. A switching arrangement for controlling a fan, in particular in the case of an extractor hood over a cooker, as a function of vapours moving towards the fan, characterised in that an ultransonic section (6) with an ultrasound transmitter (7) and an ultrasound receiver (8) is arranged in front of the fan (3), in that a receiving circuit (9) demodulates the signal occurring at the ultrasound receiver (8), in that an evaluation circuit (10) evaluates temporal fluctuations of the reception signal (Ua) which are due to vapours in the ultrasound section (6) and counts these within a time basis and in that a comparator circuit (11) compares the counting result with preset values and switches the fan (3) accordingly.
2. A switching arrangement according to claim 1, characterised in that the ultrasonic section (6) is provided in front of a filter mat (5) of the extractor hood (2), behind which the fan (3) is arranged.
3. A switching arrangement according to claim 1 or 2, characterised in that the comparator circuit (11) switches the fan (3) in a multi-stage manner.
4. A switching arrangement according to one of the preceding claims, characterised in that the evaluation circuit (10) forms from the temporally fluctuating reception signal (Ua) a positive switching level (Un+) and a negative switching level (Un-) which are in each case delayed relative to the reception signal (Ua) and in that a first comparator (12) upon equality of the positive switching level with a harmonic content of the reception signal (Ua) gives a setting impulse to a flip-flop (17) and in that a second comparator (13) upon equality of the negative switching level (Un-) with the harmonic content of the reception signal (Ua) gives a reset impulse to the flip-flop (17).
5. A switching arrangement according to claim 4, characterised in that a counter (18) counts the impulses of the flip-flop (17) occurring within the time basis.
6. A switching arrangement according to claim 4 or 5, characterised in that a time member (14) generates from the reception signal (Ua) a delayed and with respect to the harmonic content smoothed follow-up level (Un) and in that from this by way of differential amplifiers (15, 16) the positive and the negative switching level (Un+ or respectively Un-) are formed.
7. A switching arrangement according to one of the preceding claims, characterised in that an intermediate store (20) of the comparator circuit (11) receives the counting result of the counter (18) and in that the intermediate store (20) is connected to a comparator logic (21), to which by way of coding switches (22, 23) the preset values are applied.
8. A switching arrangement according to claim 7, characterised in that by means of the coding switches (22, 23) preset values for the switching-on and the switching-off of several stages of the fan (3) are settable.
9. A switching arrangement according to claim 7 or 8, characterised in that the comparator logic (21) also controls a display of the switching state of the fan (3).

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