Method and setup for analyzing gas properties

Abstract

Method for determining the humidity of the atmosphere in a cooking chamber of a cooking appliance by measuring the speed of sound in the atmosphere, characterized by providing a sound transmitter (1) and a first sound receiver (2) and a second sound receiver (2a) such that the path of the sound provided by the transmitter (1) to the first receiver (2) differs from the path of the sound provided by the transmitter (1) to the second receiver (2a), Sending the sound from the transmitter (1) to both receivers (2, 2a), Determining gas properties, in particular the composition of the gas, the temperature and / or the humidity of the gas, from the different signals supplied by the first and the second receiver (2, 2a).

Description

[0001] The present invention relates to a method for measuring the speed of sound in a gas, suitable for determining gas properties, in particular the composition, temperature, and / or humidity of the gas, and to a gas sensor arrangement configured to measure the gas properties by measuring the speed of sound, comprising sound transmitters, sound receivers, and signal processing devices. The present invention further relates to a method for determining the humidity of the atmosphere inside the cooking chamber of a cooking appliance.

[0002] The use of the speed of sound in a gas to measure its temperature, humidity, or composition is well-established, as only temperature and composition affect the speed of sound. Therefore, by measuring the speed of sound, the temperature of a gas with a known composition, or the composition of a gas at a known temperature, can be determined. The measurement can be performed using ultrasound or sound waves other than ultrasound. The term "sound" thus encompasses both types of sound. If the temperature of the gas is known, it is also possible to determine its humidity. The speed of sound is usually measured by determining the propagation time, that is, the time an acoustic signal takes to travel the distance between a source and a receiver.This can be achieved by emitting pulsed signals and measuring the signal's transit time until it is detected at the receiver, or by emitting a continuous signal and measuring the phase angle between the transmitter's excitation and the receiver's signal. The application of sound velocity measurements is particularly suitable in cases where other measurement principles cannot be used, for example, when measuring humidity over a wide temperature range, such as from 30 to 300°C, and / or at a specific humidity between 0 and 100%.

[0003] The sensitivity of sound velocity measurements based on the phase angle between the transmitter and receiver signals is a function of L·f, where L is the distance between the transmitter and receiver and f is the transmitter's operating frequency. In some cases, the measurement range is such that the span of the measured phase angle exceeds 2·π, making the measurement result ambiguous. In cases where a sound velocity measurement across the diameter of a pipe must be performed with very high temporal resolution (for example, to measure the temperature changes of a highly dynamic process), f is determined by the required temporal resolution and cannot be reduced. L is determined either by the diameter of the pipe or by the near-field limit of the ultrasonic transmitter and cannot be reduced arbitrarily.In the case where the measurement is carried out in a cooking chamber of a cooking appliance, with the transmitter located on one side wall of the cooking chamber and the receivers located on the opposite side wall of the cooking chamber, L is the length of the cooking chamber.

[0004] DE 197 22 274 A1 discloses a method for determining the density and mass flow rate in suspensions or dispersed systems with gas as the fluid phase. For this purpose, an arrangement is used that includes a sound source located in a pipe through which the gas flows, with two sound receivers on each side of the sound source at different distances from it. By measuring the travel time of the sound, both the speed of sound and the flow velocity of the gas can be determined. From this, the density of the dispersed system can then be calculated.

[0005] German patent DE 10 2010 006 901 A1 discloses a device for determining the proportion of certain molecules (SF6, CF4) in a gas mixture. For this purpose, a loudspeaker is provided in a measuring tube, which emits a sound wave. Two sound receivers are provided at two different distances from the loudspeaker, which receive the sound. Subsequently, the phase difference of the two signals is determined using a lock-in amplifier. From this, the speed of sound and the proportion of the desired molecules in the gas can be deduced.

[0006] DE 38 36 309 A1 discloses a method for determining the temperature of a gas in a closed system, in which two measuring sections of different lengths are formed between a loudspeaker and two microphones. The temperature of the gas can be determined from the phase difference of the sound waves received by the microphones.

[0007] DE 10 2005 042 792 B3 discloses a method and a device for measuring the flow velocity and temperature of a fluid using an ultrasonic transmitter arranged on the inner wall of a fluid-carrying pipe. Two ultrasonic receivers are provided on an opposite inner wall, spaced apart from each other and equidistant from the ultrasonic transmitter. Due to the flow through the pipe, a difference in the time of flight of sound occurs between the sound source and the receivers. This difference in time of flight is used to determine the flow velocity or the temperature.

[0008] German patent DE 101 43 841 A1 discloses a cooking appliance in which the speed of sound in the cooking chamber atmosphere is measured using a combined ultrasonic transmitter and receiver. For this purpose, the ultrasonic transmitter / receiver emits a sound wave, which is reflected and then received again by the ultrasonic transmitter / receiver. Simultaneously, the travel time of the sound is measured, and from this, conclusions are drawn about the composition of the cooking chamber atmosphere, in particular its humidity.

[0009] DE 10 2011 115 691 A1 discloses a method for determining the viscosity of a medium using ultrasonic waves. The viscosity is determined by measuring the amplitude drop of sound waves along two measuring sections.

[0010] However, the devices and methods known from the prior art have various disadvantages with regard to measurement accuracy and implementability.

[0011] Therefore, one object of the invention is to propose a method and an arrangement with which gas properties can be measured, in particular the gas composition, the temperature and / or the humidity, and with which the above disadvantages are overcome and which enable a highly accurate measurement of a gas with large temperature fluctuations.

[0012] This problem is solved according to the claimed invention. In main claim 1, a method for determining the humidity of the atmosphere in a cooking chamber of a cooking appliance is claimed by measuring the speed of sound in the atmosphere, and in claims 6 and 7, gas sensor arrangements provided for measuring the speed of sound in the cooking chamber are claimed. Advantageous embodiments are claimed in the respective dependent claims.

[0013] The application of this method lies in measuring the humidity of the atmosphere in the cooking chamber of a cooking appliance, in particular a combi steamer, i.e., a cooking appliance in which food is cooked using hot air and / or steam. The heating element and the steamer are controlled by a control unit. For precise operation of the cooking appliance, i.e., to achieve satisfactory cooking results, the humidity of the atmosphere inside the cooking appliance must be determined and supplied to the control unit. In known methods, a pressure difference along an element of the cooking appliance, for example, a fan, is measured. However, this measurement is influenced and thus disturbed by external parameters such as barometric pressure. The method according to the invention is independent of such disturbances. To determine the humidity, only the temperature of the atmosphere in the cooking chamber needs to be known, for example, by measurement.The measured humidity value is then fed to the control unit.

[0014] According to the invention, the method comprises providing a sound transmitter and a first sound receiver and a second sound receiver such that the path of the sound provided by the transmitter to the first receiver differs from the path of the sound provided by the transmitter to the second receiver, sending the sound from the transmitter to both receivers and determining gas properties, in particular the composition of the gas, the temperature and / or the humidity of the gas, from the different signals supplied by the first and the second receiver.

[0015] Accordingly, the gas sensor arrangement according to the invention, which is configured to measure gas properties based on the speed of sound, in particular the gas composition, temperature and / or humidity of a gas, comprises a sound transmitter as sound sending devices and at least one first sound receiver and one second sound receiver as sound receiving devices, which are arranged such that the path of the sound provided by the transmitter to the first receiver differs from the path of the sound provided by the transmitter to the second receiver. Furthermore, the arrangement includes signal processing devices, which are connected to the transmitter and the receivers and which actuate the transmitter and determine gas properties, in particular the composition of the gas, the temperature and / or the humidity of the gas, from the different signals supplied by the at least first and the second receiver.

[0016] If, for practical reasons, neither L nor f can be reduced, one solution is to use two receivers at different distances from the transmitter, L1 and L2, and to measure the two phase angles of the receiver signals, ϕ1 and ϕ2. In the corresponding equations, where the phase angle and the distance are related to the measurement result, the phase angle ϕ is then replaced by the phase angle difference Δϕ = ϕ2 - ϕ1, and the length L is replaced by the length difference ΔL = L2 - L1.

[0017] In such a case, the use of a second microphone makes it possible to adjust ΔL so that Δϕ does not exceed 2·π over the required measurement range without limiting the temporal resolution or operating the sensor within the near field.

[0018] Preferably, according to the invention, the second receiver is arranged close to the first receiver in the same direction from the transmitter, thus providing only one measuring path for the sound excited by the transmitter. In general, it is possible to use more than two receivers, for example a third receiver, if it is necessary and expedient to acquire more accurate or detailed data.

[0019] The use of a second microphone offers a further advantage in cases where the ultrasonic transmitter itself introduces a phase shift between the drive signal and the sound output. If this phase angle, generated by the transmitter, is constant, it can be compensated for through calibration. However, in most cases, the transmitter is based on a piezoelectric ceramic and is operated at its resonant frequency for the maximum sound pressure level. This resonance introduces a phase shift, which changes with the ambient temperature, as the transmitter's resonance is determined by material properties that change with temperature.

[0020] According to a further preferred embodiment of the invention, the phase angle difference of the signals from the first and second receivers is determined to ascertain gas properties, in particular gas composition, temperature, and / or humidity. Measuring the phase angle at two receivers located at different positions relative to the transmitter means that the transmitter's phase shift affects both receivers equally, and therefore, by measuring Δϕ, the transmitter's phase shift is completely suppressed. The phase angles of the two receivers can be measured separately (i.e., by a lock-in amplifier assigned to each receiver), and the phase angle difference can be calculated by post-processing.

[0021] In an alternative embodiment of the invention, the voltage amplitude between the first and second receivers is determined to ascertain gas properties, in particular gas composition, temperature, and / or humidity. The signals from the two receivers can then be measured differentially by a lock-in amplifier. In this case, the amplitude of the measured differential signal changes depending on the phase angle difference, ranging from its minimum at zero and a phase angle difference of 2π to its maximum at a phase angle difference of π. If the amplitudes of the receiver signals are identical (i.e., both receivers have exactly the same sensitivity), the minimum of the differential signal is zero, and its maximum is twice the signal of a single receiver. The amplitude of the differential signal can therefore only cover a range of the phase angle difference of π.

[0022] If both receivers have the same sensitivity, the phase angle of the differential signal corresponds exactly to the phase angle difference over a span of 2π. If the sensitivities of the two receivers are not the same, the linear relationship between the phase of the differential signal and the phase angle difference is distorted, and the unambiguous range is restricted. With large sensitivity differences, the phase of the differential signal exhibits a sinusoidal change depending on the phase angle difference, which in turn reduces the usable measurement range to a span of the phase angle difference of π.

[0023] Both the amplitude and the phase of the differential signal depend on the respective sensitivity of the receivers, and the amplitude of the differential signal also depends on the amplitude of the emitted sound. Therefore, a reduction in the functionality of one of the transducers affects the measurement of the differential signal.

[0024] In addition, according to another embodiment of the invention, the method includes differential measurement of the signals from the receivers and calculation of gas properties, in particular the temperature and / or humidity, from the amplitude and phase angle of the differential signal.

[0025] According to another embodiment of the invention, the method comprises suppressing a phase shift of the signal phase of the transmitter due to the operating mode of the transmitter by common-mode rejection based on the signals of the first and the second receiver.

[0026] In a further embodiment of the invention, the method comprises separately measuring the phase angles of the signals from the receivers and calculating the phase angle difference in a further step.

[0027] The gas sensor arrangement according to the invention, which is configured to measure gas properties based on the speed of sound, in particular the gas composition, temperature and / or humidity of a gas, is capable of carrying out the method described above. The arrangement further comprises signal processing devices for implementing the corresponding features of the method mentioned above.

[0028] The following section describes in detail embodiments of the invention in conjunction with the drawings. However, the invention is not limited to the examples described in conjunction with the drawings and includes all embodiments covered by the claims and the description, either individually or in combination. The figures show: - Fig. 1 a gas sensor arrangement in a cooking appliance with one transmitter and two receivers on the same side of the cooking appliance, together with a block diagram of a signal processing unit comprising the signal processing facilities, and - Fig. 2 another gas sensor arrangement in a cooking appliance with transmitters and receivers on opposite sides of the cooking appliance.

[0029] The invention is explained below in connection with the arrangement in a cooking appliance such as a combi steamer, a steamer, a convection oven, or a commercial oven, for example, to measure the humidity of the atmosphere inside the cooking chamber of the appliance. However, the method and the arrangement can also be used in other applications, particularly in applications with extreme environmental conditions for the arrangement and where a wide range of measured values ​​is required.

[0030] In Fig. Figure 1 shows a gas sensor arrangement 12 with a sound transmitter 1, which is arranged in a recess 3a of the cooking chamber 3b of a cooking appliance 3. A first sound receiver 2 and a second sound receiver 2a are also provided in the recess 3a. As shown in the figure, the receivers 2, 2a are arranged close together but offset from each other. Due to the arrangement of the transmitter 1 and the receivers 2, 2a, the propagation paths 4 between the transmitter 1 and the receivers 2, 2a of the sound emitted by the transmitter 1 run through the same section of the volume of the cooking chamber 3b, i.e., the propagation paths 4 are located close together.

[0031] However, the propagation paths 4 are of different lengths. Sound emitted from transmitter 1 must therefore travel different distances before reaching receiver 2 or 2a.

[0032] The propagation paths 4 can also include a reflection of the sound at the wall 3c of the cooking chamber 3b.

[0033] Transmitter 1 and the two receivers 2 and 2a are connected to a signal processing unit 7, which includes an acoustic function generator 8, capable of providing ultrasound, and is connected to transmitter 1. The signal processing unit 7 further includes a first preamplifier / AD converter 10, connected to the first receiver 2, and a second preamplifier / AD converter 10a, connected to the second receiver 2a. The acoustic function generator 8 and the two preamplifiers / AD converters 10 and 10a are all connected to a lock-in amplifier 11, which is connected to a microprocessor 13 that controls the operation of the entire sensor assembly. The lock-in amplifier 11 provides a signal that specifies the phase angle between the signals emitted by the first receiver 2 and the second receiver 2a.Using these signals, the microprocessor 13 can determine the speed of sound based on the received signals. Reference numeral 14 indicates the output of the result for further processing of the measured property of the gas in the cooking chamber 3b. In a further advantageous embodiment, the lock-in amplifier 11 can be digitally integrated into the microprocessor 13. It is clear that, for the purpose of independent phase measurement, the lock-in amplifier 11 has two separate input and output channels and an input for the reference signal.

[0034] In Fig. Figure 2 shows a further arrangement of the transmitter 1 and the first receiver 2 and the second receiver 2a, both of which are arranged opposite the transmitter 1 on the other side of the cooking chamber 3b. The transmitter 1 and the receivers 2, 2a are arranged in different recesses 3a. In this embodiment, the receivers 2, 2a are arranged such that the distance between the transmitter 1 and the two receivers 2, 2a is different. The transmitter 1 and the receivers 2, 2a are arranged in the same way as in Figure 2. Fig. 1 shown connected to the signal processing unit 7.

[0035] To measure the humidity of the atmosphere inside cooking chamber 3b, the microprocessor 13 can be equipped with a temperature signal. This temperature signal can be supplied, for example, by a temperature sensor (not shown) located inside cooking chamber 3b.

[0036] Using the temperature information, the microprocessor 13 is able to determine the humidity of the atmosphere inside the cooking chamber 3b by using the measured speed of sound.

[0037] The sound transmitter 1 and the sound receivers 2, 2a can also be located in a housing in fluidic contact with the cooking chamber 3b.

Claims

[1] Method for determining the humidity of the atmosphere in a cooking chamber of a cooking appliance by measuring the speed of sound in the atmosphere, characterized by Providing a sound transmitter (1) and a first sound receiver (2) and a second sound receiver (2a) such that the path of the sound provided by the transmitter (1) to the first receiver (2) differs from the path of the sound provided by the transmitter (1) to the second receiver (2a), Sending the sound from the transmitter (1) to both receivers (2, 2a), Determining gas properties, in particular the composition of the gas, the temperature and / or the humidity of the gas, from the different signals supplied by the first and the second receiver (2, 2a). [2] Method according to claim 1, characterized byArranging the second receiver (2a) near the first receiver (2) in the same direction from the transmitter (1), thereby providing only one measuring path of the sound excited by the transmitter (1). [3] Method according to claim 1 or 2, characterized by Determining the phase angle difference of the signals from the first and second receiver (2, 2a) to determine gas properties, in particular gas composition, temperature and / or humidity. [4] Method according to claim 1 or 2, characterized by Measuring the difference in voltage amplitude between the first and second receiver (2, 2a) to determine gas properties, in particular gas composition, temperature and / or humidity. [5] Method according to any one of the preceding claims, characterized by separately measuring the phase angles of the signals from the receivers (2, 2a) and calculating the phase angle difference in a further step. [6] Gas sensor arrangement configured to measure gas properties based on the speed of sound, in particular the gas composition, temperature and / or humidity of a gas, according to the method of any one of claims 1 to 5. [7] Gas sensor arrangement configured to measure the humidity of the atmosphere in a cooking chamber of a cooking appliance based on the speed of sound, comprising sound transmitting devices (1) and sound receiving devices (2, 2a) connected to signal processing devices (7), characterized by, that the sound transmitting devices comprise a sound transmitter (1) and the sound receiving devices comprise at least a first sound receiver (2) and a second sound receiver (2a) arranged such that the path of the sound provided by the transmitter (1) to the first receiver (2) is different from the path of the sound provided by the transmitter (1) to the second receiver (2a), and that the signal processing devices (7) actuate the transmitter (1) and determine gas properties, in particular the composition of the gas, the temperature and / or the humidity of the gas, from the different signals supplied by the at least first and the second receiver (2, 2a). [8] Gas sensor arrangement according to claim 7, characterized by, that the second receiver (2a) is located near the first receiver (2) in the same direction from the transmitter (1), thus providing only one measuring path of the sound excited by the transmitter (1). [9] Gas sensor arrangement according to claim 7 or 8, characterized by , that the signal processing devices (7) determine the phase angle difference of the signals from the first and second receivers (2, 2a) for determining gas properties, in particular the gas composition, temperature and / or humidity. [10] Gas sensor arrangement according to claim 7 or 8, characterized by , that the signal processing devices (7) for determining gas properties, in particular the gas composition, temperature and / or humidity, measure the voltage amplitude between the first and the second receiver (2, 2a). [11] Gas sensor arrangement according to any one of claims 7 to 10, characterized by, that the signal processing devices (7) measure the phase angles of the signals from the receivers (2, 2a) separately and calculate the phase angle difference in a further step. [12] Gas sensor arrangement according to any one of claims 7 to 9, characterized by , that the signal processing devices (7) measure the signals from the receivers (2, 2a) differentially and calculate gas properties, in particular the temperature and / or humidity, from the amplitude and phase angle of the differential signal.

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