HK1161641A - An apparatus and a method for estimating the air humidity within an oven cavity - Google Patents

Description

Apparatus and method for estimating air humidity inside oven chamber

Technical Field

The present invention relates to a device for estimating the air humidity inside an oven compartment as claimed in claim 1. Further, the invention relates to a method for estimating the air humidity inside an oven cavity as claimed in claim 7. In particular, the present invention relates to an apparatus and a method for estimating the air humidity inside the oven compartment of an electric oven.

Background

The temperature inside the oven chamber is the most important parameter during cooking. Another important parameter is the air humidity inside the oven chamber. Conventional moisture sensors are only suitable for temperatures up to 200 ℃. However, in a conventional oven, the temperature during cooking may be 250 ℃. During pyrolysis cleaning, the temperature may be higher.

Another method for estimating the humidity in a space is to detect the velocity of sound or ultrasound waves passing through the space. The speed of the sound or ultrasound waves depends on humidity and temperature, and not on ambient pressure. Since the temperature in the oven chamber is known, the humidity can be determined by the speed of the sound or ultrasound waves.

Document US 5,689,060 discloses a humidity measuring device for heat cookers. The phase difference between the sound waves received through the reference air and the sound waves received through the air under test is measured. However, the phase difference cannot exceed 1/4 for the wavelength. Therefore, the frequency of the acoustic wave must be about 4 kHz. The sound wave with a frequency of 4kHz is audible so that the user hears the sound.

In document EP 0174627B1, a gas concentration measuring instrument using ultrasonic waves is disclosed. In particular, gas concentration measuring instruments are used to measure the concentration of carbon dioxide. The measuring instrument includes an ultrasonic transmitter and a receiver. However, such a measuring instrument is not suitable for high temperatures.

Document DE 10143841a1 discloses an oven with a device for measuring humidity. The device comprises a sound or ultrasonic transmitter, a sound or ultrasonic receiver, a temperature sensor and a device for measuring the travel time of the sound or ultrasonic. From the travel time, the speed of the sound or ultrasonic wave can be calculated. The humidity can be estimated by temperature and the speed of sound or ultrasound.

Disclosure of Invention

It is an object of the present invention to provide an apparatus and a method for estimating the air humidity inside an oven cavity with an improved accuracy, wherein the complexity of the apparatus and the method is relatively low.

The object of the invention is achieved by a device as claimed in claim 1.

According to the present invention, an apparatus for estimating air humidity inside an oven compartment by using ultrasonic waves having at least two different frequencies includes:

at least one ultrasonic transmitter for generating ultrasonic waves,

at least one ultrasonic receiver for receiving ultrasonic waves,

at least one phase detection means for detecting the phase of the ultrasonic wave at the ultrasonic receiver relative to the same ultrasonic wave having the same frequency at the ultrasonic transmitter,

at least one calculation unit for calculating the velocity of the ultrasonic waves from the phase and frequency of the ultrasonic waves having two different frequencies,

at least one temperature sensor for detecting the temperature in the oven chamber, and

at least one estimation unit for estimating humidity in the oven chamber based on the temperature in the oven chamber and the velocity of the ultrasonic waves.

The gist of the invention is to use two different frequencies. This allows the velocity of the ultrasound to be calculated by two frequencies and two corresponding phases. Humidity can be estimated from speed and temperature. The maximum error of the estimated specific humidity (specific humidity) is about 9%.

In a preferred embodiment of the invention, the ultrasonic transmitter and/or the ultrasonic receiver are arranged on or inside opposite walls of the oven chamber. This allows the distance between the ultrasound transmitter and the ultrasound receiver to be as large as possible.

In particular, the ultrasonic transmitter and/or the ultrasonic receiver are arranged at the front or rear of the oven compartment side wall. At these locations, there is always a direct connection between the ultrasound transmitter and the ultrasound receiver.

Additionally, a temperature sensor may be disposed between the ultrasonic transmitter and the ultrasonic receiver. Therefore, the temperature and the velocity of the ultrasonic wave relate to the same region.

Preferably, the calculation unit calculates the velocity from the distance between the ultrasound transmitter and the ultrasound receiver. The distance between the ultrasound transmitter and the ultrasound receiver is of a given size without measurement.

According to a preferred embodiment of the invention, the apparatus is for use in an electric oven.

The object of the invention is further achieved by a method as claimed in claim 7.

According to the invention, the method for estimating the air humidity inside an oven chamber comprises the following steps:

generating ultrasonic waves having at least two different frequencies,

receiving ultrasonic waves having at least two different frequencies,

detecting the phase of an ultrasonic wave having a first frequency at the ultrasonic receiver relative to the same ultrasonic wave having the first frequency at the ultrasonic transmitter,

detecting the phase of an ultrasonic wave having a second frequency at the ultrasonic receiver relative to the same ultrasonic wave having the second frequency at the ultrasonic transmitter,

the velocity of the ultrasonic wave is calculated from the phase and frequency of the ultrasonic wave having the two different frequencies,

sensing the temperature within the oven chamber, an

And estimating the humidity in the oven chamber according to the temperature and the speed of the ultrasonic wave.

The gist of the invention is to use two different frequencies. This allows the velocity of the ultrasound to be calculated by two frequencies and two corresponding phases. Humidity can be estimated from speed and temperature. The maximum error in the estimated specific humidity is about 9%.

In a preferred embodiment of the invention, the first frequency is slightly greater than the resonance frequency of the ultrasonic transducer formed by the ultrasonic transmitter and the ultrasonic receiver, and the second frequency is slightly less than the resonance frequency. This helps to improve the accuracy of the method of the invention.

In addition, the velocity of the ultrasonic wave can be estimated by the distance between the ultrasonic transmitter and the ultrasonic receiver. The distance between the ultrasound transmitter and the ultrasound receiver is of a given size without measurement.

In particular, the velocity of the ultrasonic waves is passedMaking an estimate, ifThenIf it is notThenTherefore, the temperature of the molten metal is controlled,the value of (c) is in any case positive. If L < [ V ]_min/(f₁-f₂+Δ(Δf))-ΔL]Then the above formula is valid, where V_min331m/s is the minimum possible speed of sound, Δ (Δ f) is f₁-f₂Δ L is the possible amount of change in L. In addition, f₁Is a first frequency, f₂Is the second frequency of the radio frequency signal,is related to the first frequency f₁The phase of the signal is correspondingly set,is related to the second frequency f₂The corresponding phase, L, is the distance between the ultrasound transmitter and the ultrasound receiver.

Preferably, the temperature is detected in the space between the ultrasonic transmitter and the ultrasonic receiver. Thus, the measured temperature and the calculated ultrasound velocity relate to the same region.

For example, the frequency is generated by dividing a predetermined clock frequency. In particular, the frequencies are generated by a common generator.

The estimated humidity may be used in a cooking program to optimize the cooking process.

Finally, a computer program product is provided. The computer program product is stored on a computer usable medium and comprises computer readable program means for causing a computer to perform the method as described above.

The novel and inventive features believed characteristic of the invention are set forth in the appended claims.

Drawings

The invention will be described in further detail below with reference to the attached drawing figures, wherein:

fig. 1 shows a schematic diagram of the frequency spectrum of an ultrasound transducer according to a preferred embodiment of the invention;

FIG. 2 shows a schematic diagram of two ultrasonic waves with different wavelengths between an ultrasonic transmitter and an ultrasonic receiver according to the preferred embodiment of the present invention;

FIG. 3 shows a schematic view of a front perspective view of an interior space of an oven compartment according to a first embodiment of the invention;

figure 4 shows a schematic view of a front perspective view of the inner space of the oven chamber according to a second embodiment of the invention; and

fig. 5 shows a schematic diagram of the ultrasonic velocity versus specific humidity according to the preferred embodiment of the present invention.

Detailed Description

Fig. 1 shows a schematic diagram of the frequency spectrum of an ultrasound transducer according to a preferred embodiment of the invention. The frequency spectrum being included at the resonance frequency f₀The peak value of (d). First frequency f₁And a second frequency f₂For measuring the velocity of the ultrasonic waves. First frequency f₁And a second frequency f₂Around the resonance frequency f₀. First frequency f₁Slightly greater than the resonant frequency f₀. Second frequency f₂Slightly less than the resonant frequency f₀。

FIG. 2 shows the difference in wavelength λ between the ultrasonic transmitter 10 and the ultrasonic receiver 12 according to the preferred embodiment of the present invention₁And λ₂Schematic representation of two ultrasound waves. The ultrasound transmitter 10 and the ultrasound receiver 12 form an ultrasound transducer.

The first ultrasonic wave has a first frequency f₁And a first wavelength lambda₁. The second ultrasonic wave has a second frequency f₂And a second wavelength lambda₂. The distance between the ultrasonic transmitter 10 and the ultrasonic receiver 12 is L.

Distance L and first wavelength λ₁The relationship between is

Wherein n is₁Is the complete first wavelength λ within the distance L₁The number of the (c) component(s),is the phase of the first ultrasonic wave at the ultrasonic receiver 12 relative to the first ultrasonic wave at the ultrasonic transmitter 10.

Likewise, the distance L and the second wavelength λ₂The relationship between is

Wherein n is₂Is the complete second wavelength λ within the distance L₂The number of the (c) component(s),is the phase of the second ultrasonic wave at the ultrasonic receiver 12 relative to the second ultrasonic wave at the ultrasonic transmitter 10.

First frequency f₁And a second frequency f₂Can be controlled by having a given clock frequency f_cIs generated by a common frequency generator. First frequency f₁And a second frequency f₂By using the clock frequency f_cDivided by divisor N respectively₁And N₂The method comprises the steps of (1) obtaining,

f₁＝f_c/N₁，f₂＝f_c/N₂

the synthesis speed of the ultrasonic wave is

Wherein the frequency difference

Δf＝f₁-f₂＝f_c/N₁-f_c/N₂＞0

Must be positive and must satisfy an additional condition (side condition)

L＜V_min/[Δf+Δ(Δf)]-ΔL

If the additional condition is satisfied, the phaseAndnever equal each other. Therefore, the temperature of the molten metal is controlled,the value is always positive. Where L is the distance between the ultrasonic transmitter 10 and the ultrasonic receiver 12, Δ L is the variation range of L,is a phase difference, V_minIs the minimum possible velocity of the ultrasonic wave, and Δ (Δ f) is the variation range of the frequency difference Δ f.

If it is notPhase differenceIs composed ofOtherwise, ifPhase differenceIs composed ofThe range of variation Δ (Δ f) of the frequency difference Δ f is

Δ(Δf)＝f_c·δf_c/N₁-f_c·δf_c/N₂

Wherein, δ f_cIs the clock frequency f_cRelative error of (2).

For a temperature T of 0 c,the minimum possible speed V of the ultrasonic waves for dry air with a pressure P of 1atm_minIs a V_min＝331.244m/s。

By taking the actual value, i.e. f_c＝20MHz，δf_c＝0.5％，ΔL＝3mm，N₁497 and N₂503, the distance L between the ultrasound transmitter 10 and the ultrasound receiver 12 must be L < 684 mm.

The velocity of the ultrasonic wave depends on temperature and humidity, and the formula is:

wherein T is temperature, M_AFor the molar amount of dry air, M_VR is the molar quantity of water vapor, R is the molar ideal gas constant, and Z is the compressibility. The value of the constant is

M_A＝0.029kg/mol，

M_V＝0.018kg/mol，

R＝8.315J/(mol·k)。

The compression factor Z depends on the temperature T and the mole fraction X_VAnd a pressure P. However, in this case, the compression factor Z is approximately 1.

Mole fraction X of water vapor in air_VDetermined by the specific humidity SH

X_V＝(M_A·SH)/[M_V+(M_A-M_V)·SH]

The specific humidity SH is defined as

SH＝(m_V·100％)/(m_A-m_V)

Wherein m is_VIs the weight of the water vapour fraction, m_AIs the weight of the dry air portion. The water vapour fraction and the drying air fraction form a true air-steam mixture filled with the same volume.

For practical accuracy Δ V. + -. 6.27m/s, Δ T. + -. 5 ℃ and Δ P. + -. 300mm/Hg, the absolute error of the specific humidity is Δ SH. + -. 9% in the worst case.

If the specific humidity SH, the temperature T and the pressure P are known, the relative humidity can be calculated as follows

RH＝(P·M_A·SH·100％)/{P_VS(T)·[M_V+(M_A-M_V)·SH]}

Wherein P is_VS(T) is the saturated vapor pressure of water at a given temperature T.

Fig. 3 shows a schematic view of a front perspective view of the interior space of the oven compartment 14 according to the first embodiment of the present invention. The oven chamber 14 is defined by a top wall 16, a bottom wall 18, a left side wall 20, a right side wall 22, and a rear wall 24. The rear wall 24 includes a fan 26 having fan blades 28.

A plurality of side grids 30 are arranged in pairs on the inner sides of the side walls 20 and 22. Each pair of side grids 30 is arranged at the same height. The side grids 30 extend horizontally along the inner sides of the side walls 20 and 22. Pairs of side grids 30 are provided to support a tray or grill.

In this embodiment, the ultrasonic transmitter 10 is disposed in front of the left sidewall 20. The ultrasound transmitter 10 is arranged between the two lowermost side grids 30. In a similar manner, the ultrasonic receiver 12 is arranged in front of the right side wall 22 between the two lowermost side grids 30, so that the ultrasonic transmitter 10 and the ultrasonic receiver 12 are arranged symmetrically.

The ultrasound transmitter 10 and the ultrasound receiver 12 are located as follows: at said position, the space between them is free of any articles. Thus, the propagation of the ultrasonic waves from the ultrasonic transmitter 10 to the ultrasonic receiver 12 is undisturbed. There is a direct geometric connection between the ultrasound transmitter 10 and the ultrasound receiver 12.

The distance L between the ultrasonic transmitter 10 and the ultrasonic receiver 12 is equal to the interior width of the oven cavity 14. A typical value for the interior width of the oven cavity 14 is L440 mm. The typical internal width L440 mm fortunately satisfies the above additional condition L < 684 mm.

Fig. 4 shows a schematic view of a front perspective view of the interior space of the oven compartment 14 according to a second embodiment of the present invention. The oven chamber 14 is defined by a top wall 16, a bottom wall 18, a left side wall 20, a right side wall 22, and a rear wall 24. The rear wall 24 includes a fan 26 having fan blades 28.

A plurality of side grids 30 are arranged in pairs on the inner sides of the side walls 20 and 22. Each pair of side grids 30 is arranged at the same height. The side grids 30 extend horizontally along the inner sides of the side walls 20 and 22. Pairs of side grids 30 are provided to support a tray or grill.

In this embodiment, the ultrasonic transmitter 10 is disposed at the rear of the left sidewall 20. The ultrasound transmitter 10 is arranged between the two upper side grids 30. In a similar manner, the ultrasonic receiver 12 is arranged between the two upper side grids 30 at the rear of the right side wall 22, so that the ultrasonic transmitter 10 and the ultrasonic receiver 12 are arranged symmetrically.

Also in this embodiment, the ultrasonic transmitter 10 and the ultrasonic receiver 12 are located at the following positions: at said position, the space between them is free of any articles. Thus, the propagation of the ultrasonic waves from the ultrasonic transmitter 10 to the ultrasonic receiver 12 is undisturbed. There is also a direct geometric connection between the ultrasound transmitter 10 and the ultrasound receiver 12.

A temperature sensor 32 is arranged at the rear wall 24. The temperature sensor 32 is located in the region between the ultrasonic transmitter 10 and the ultrasonic receiver 12. Therefore, the temperature can be detected in the same region as the region where the ultrasonic velocity is estimated. This arrangement helps to improve the accuracy of the calculation of the humidity, since the calculation of the humidity is based on the actual temperature value.

Also, in this embodiment, the distance L between the ultrasonic transmitter 10 and the ultrasonic receiver 12 is equal to the interior width of the oven cavity 14. A typical value is L440 mm, which fortunately meets the above additional condition L < 684 mm.

Fig. 5 shows a schematic diagram of the ultrasonic velocity V versus the specific humidity SH according to a preferred embodiment of the present invention.

The figure shows twelve functions for three different pressures P0.5 atm, P1.0 atm and P1.5 atm and four different temperatures T100 ℃, T200 ℃, T300 ℃ and T400 ℃. The pressure P of 0.5atm is indicated by a dotted line, the pressure P of 1.0atm is indicated by a solid line, and the pressure P of 1.5atm is indicated by a dashed line.

For high humidity values, the velocity of the ultrasonic waves increases slightly as the pressure decreases. In addition, for all humidity values, the ultrasonic velocity increases significantly with increasing temperature.

By knowing the ultrasonic velocity V and the temperature T inside the oven chamber, an accurate estimation of the humidity SH can be made, using the functional relationship shown in fig. 5.

The accuracy of the estimated humidity can be improved by calibration based on the above theoretical expression. For all possible temperatures up to 350 ℃ in the oven, the calibration should be performed over the entire humidity range of 0% to 100%. In particular, calibration is advantageous if the ultrasonic waves do not form a narrow beam, so that the ultrasonic waves may be reflected at the inner walls 16, 18, 20, 22 and 24 of the oven chamber. At this point, the ultrasonic receiver 12 will receive both the direct ultrasonic waves and the reflected ultrasonic waves from the ultrasonic transmitter 10. Reflecting the ultrasound will cause errors in estimating the ultrasound velocity. The error can be compensated for by the calibration described above.

The present invention allows the estimation of the average humidity within the entire chamber, rather than any local humidity around the sensor. The invention allows for a very fast estimation of humidity. Several repeated measurements and subsequent average calculations may improve accuracy.

Suitable ultrasonic transmitters 10 and ultrasonic receivers 12 having sufficient temperature and chemical resistance properties are available.

The ultrasonic transmitter 10 and the ultrasonic receiver 12 may be used for other purposes. For example, an open oven door may be detected. In addition, the oven cavity 14 may be checked for filling.

The present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein. Additionally, the computer program product is capable of performing these methods when loaded into a computer system.

Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments; various other changes or modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the present invention as defined in the appended claims.

List of reference numerals

10 ultrasonic transmitter

12 ultrasonic receiver

14 oven chamber

16 roof

18 bottom wall

20 left side wall

22 right side wall

24 rear wall

26 Fan

28 Fan blade

30 side grid

32 temperature sensor

f₀Resonant frequency

f₁First frequency

f₂Second frequency

f_cClock frequency

N₁First frequency f₁Divisor of

N₂Second frequency f₂Divisor of

Δf f₁And f₂Frequency difference therebetween

Amount of change in Δ (Δ f) frequency difference

λ₁A first wavelength

λ₂A second wavelength

L distance between transmitter 10 and receiver 12

Delta L amount of change in distance L

n₁Complete first wavelength lambda₁Number of (2)

n₂Full second wavelength lambda₂Number of (2)

Claims (15)

1. By using a frequency having at least two different frequencies (f)₁，f₂) The apparatus for estimating the air humidity within an oven cavity (14), wherein the apparatus comprises:

at least one ultrasound transmitter (10) for generating ultrasound waves,

at least one ultrasonic receiver (12) for receiving ultrasonic waves,

at least one phase detection device for detecting that the ultrasonic waves at the ultrasonic receiver (12) have the same frequency (f) relative to the ultrasonic transmitter (10)₁，f₂) The phase of the same ultrasonic wave

At least one computing unit for computing a frequency (f) based on a signal having two different frequencies₁，f₂) Phase of the ultrasonic waveSum frequency (f)₁，f₂) The velocity (V) of the ultrasonic wave is calculated,

at least one temperature sensor (32) for detecting a temperature (T) within the oven cavity (14), and

at least one estimation unit for estimating the humidity inside the oven chamber (14) from the temperature (T) inside the oven chamber (14) and the velocity (V) of the ultrasonic waves.

2. The apparatus according to claim 1, wherein the ultrasound transmitter (10) and/or the ultrasound receiver (12) are arranged at or inside opposite walls (20, 22) of the oven cavity (14).

3. The apparatus according to claim 1 or 2, wherein the ultrasound transmitter (10) and/or the ultrasound receiver (12) are arranged in front of or behind side walls (20, 22) of the oven cavity (14).

4. The device according to any of the preceding claims, characterized in that the temperature sensor (32) is arranged between the ultrasound transmitter (10) and the ultrasound receiver (12).

5. The apparatus according to any one of the preceding claims, characterized in that the calculation unit calculates the velocity (V) from a distance (L) between an ultrasound transmitter (10) and an ultrasound receiver (12).

6. An appliance as claimed in any preceding claim wherein the appliance is for an electric oven.

7. A method for estimating air humidity within an oven chamber, wherein the method comprises the steps of:

generating a signal having at least two different frequencies (f)₁，f₂) The ultrasonic waves of (2) are applied,

receiving the signals having at least two different frequencies (f)₁，f₂) The ultrasonic waves of (2) are applied,

detecting a first frequency (f) at an ultrasonic receiver (12)₁) Has a first frequency (f) with respect to the ultrasonic transmitter (10)₁) The phase of the same ultrasonic wave

Detecting a second frequency (f) at the ultrasonic receiver (12)₂) Has a second frequency (f) with respect to the ultrasonic transmitter (10)₂) The phase of the same ultrasonic wave

According to having these two different frequencies (f)₁，f₂) Phase of the ultrasonic waveSum frequency (f)₁，f₂) The velocity (V) of the ultrasonic wave is calculated,

sensing a temperature (T) within the oven compartment (14), an

Estimating the humidity inside the oven chamber (14) from the temperature (T) and the velocity (V) of the ultrasonic wave.

8. A method as claimed in claim 7, characterized in that the first frequency (f) is₁) Slightly larger than the resonance frequency (f) of an ultrasonic transducer formed by an ultrasonic transmitter (10) and an ultrasonic receiver (12)₀) Second, secondFrequency (f)₂) Slightly less than the resonant frequency.

9. Method according to claim 7 or 8, characterized in that the velocity (V) of the ultrasound is estimated by the distance (L) between the ultrasound transmitter (10) and the ultrasound receiver (12).

10. Method according to any of claims 7-9, characterized in that the velocity (V) of the ultrasound is passed throughMaking an estimate, ifThenIf it is notThenAnd wherein f₁Is said first frequency, f₂Is the frequency of the second frequency of the first frequency,is related to the first frequency f₁The phase of the corresponding phase is determined,is related to the second frequency f₂The corresponding phase, L, is the distance between the ultrasound transmitter (10) and the ultrasound receiver (12).

11. A method as claimed in any one of claims 7 to 10, characterized in that the temperature (T) is detected in a space between the ultrasonic transmitter (10) and the ultrasonic receiver (12).

12. Method according to any of claims 7-11, characterized in that the frequency (f) is selected from the group consisting of₁，f₂) By setting a predetermined clock frequency (f)_c) Frequency division is generated.

13. Method according to any of claims 7-12, characterized in that the frequency (f) is selected from the group consisting of₁，f₂) Generated by a common generator.

14. Method according to any of claims 7-13, wherein the estimated humidity is used in a cooking program in order to optimize the cooking process.

15. A computer program product stored on a computer usable medium, comprising computer readable program means for causing a computer to implement the method of any one of the preceding claims 7 to 14.