Flame recognition device and method for operating flame recognition device

Abstract

The invention relates to a flame detection device and to a method for operating a flame detection device, comprising an optoelectronic sensor unit (1) suitable for flame detection and a modulator unit (2) having a first and a second input (2.1, 2.2), the sensor unit (1) is connected to a first input (2.1) of the modulator unit (2) and a carrier signal unit (3) is connected to a second input (2.2) of the modulator unit (2), and the output signal of the modulator unit (2) is a modulation product of the flame identification signal of the sensor unit (1) and the carrier signal of the carrier signal unit (3).

Description

Technical Field

[0001] The invention relates to a flame detection device according to the preamble of claim 1 and to a method for operating a flame detection device according to the preamble of claim 8 . Background Art

[0002] A flame detection device of the type mentioned at the outset and a method for operating such a flame detection device are known from document EP 3 916 693 A1. The flame detection device consists of a sensor unit (there a sensor element 16) which converts electromagnetic radiation (there a flame radiation 42 combined with a control signal 18 of a transmitting unit 40) into a sensor signal (there a sensor signal 20) and a signal preparation unit (there a signal processing step 44), wherein - expressed in terms of method - the prepared sensor signal is decomposed into a flame signal component and a control signal component (there an analysis step 46 for separating the control signal component 18') and the control signal component is evaluated (there an evaluation step 48 for evaluating the control signal component 18'). Summary of the invention

[0003] The invention is based on the object of improving a flame detection device of the type mentioned at the outset and a method for operating a flame detection device. In particular, efforts should be made to realize a flame detection device that can be tested with little effort and a method by which the functional integrity of the flame detection device can be tested particularly easily, wherein no additional transmitting elements for emitting optical or electromagnetic control signals should be required within the flame chamber.

[0004] It must be taken into account that only a false positive flame detection represents a dangerous fault state of the combustion system, while a false negative flame detection may lead to unnecessary shut-off of the flame but does not represent a dangerous fault state due to a further inflow of unignited combustion medium into the combustion chamber.

[0005] Furthermore, it should be taken into account that the sensor unit of the present flame detection device is preferably designed as a photodiode, which generates a photocurrent from incident electromagnetic radiation energy without an external operating voltage. The sensor unit is therefore intrinsically safe in the sense that, if the photodiode fails to operate, although the photocurrent may disappear despite the presence of a flame, the opposite fault situation is physically excluded due to the law of energy conservation: a photocurrent is generated despite the absence of a flame.

[0006] Therefore, only the electrical amplifier and evaluation circuit of the flame detection device need to be checked for false positive fault states.

[0007] This object is achieved with a flame detection device of the type mentioned in the introduction by the features specified in the characterizing part of claim 1. In terms of method, this object is achieved by the features specified in the characterizing part of claim 8 .

[0008] A first aspect of the present invention relates to a flame recognition device, which comprises an optoelectronic sensor unit suitable for flame recognition and a modulator unit having a first and a second input end, wherein the sensor unit is configured to be connected to the first input end of the modulator unit, and the carrier signal unit is configured to be connected to the second input end of the modulator unit, and the output signal of the modulator unit is a modulation product of the flame recognition signal of the sensor unit and the carrier signal of the carrier signal unit.

[0009] The modulator unit may also be referred to as a circuit unit for amplification, and the carrier signal unit may also be referred to as a circuit unit for modulation.

[0010] The teaching according to the invention achieves the advantage that the amplifier and the evaluation circuit of the flame detection device can be checked for false positive flame detection signals and that, when using an intrinsically safe sensor unit, the flame detection device is intrinsically safe overall with regard to positive flame detection.

[0011] According to the first exemplary embodiment, the sensor unit is designed as an intrinsically safe sensor unit, preferably as a photodiode.

[0012] This embodiment has the advantage that false positive flame detection signals can be excluded as output signals of the sensor unit. In the preferred embodiment as a photodiode, the photocurrent is generated directly from the radiation energy without an external operating voltage.

[0013] According to another exemplary configuration, the sensor unit is constructed to detect electromagnetic radiation in a wavelength range of 250-550 nanometers, preferably to detect one or more wavelengths of flame free radicals generated during the combustion process, particularly preferably to detect one or more of the 308 nanometer wavelength of the OH free radical, the 430 nanometer wavelength of the CH free radical, or the 519 nanometer wavelength of the C2 free radical.

[0014] This embodiment has the advantage that the flame detection is focused on the characteristic wavelength and the reliability is improved.

[0015] According to another exemplary configuration, the inverting input of the modulator unit is configured to be connected to the flame recognition signal of the sensor unit, and the non-inverting input of the modulator unit is configured to be connected to the negative carrier signal of the carrier signal unit, and the modulator unit is configured to modulate the carrier signal with the flame recognition signal.

[0016] This configuration has the advantage that the flame detection signal of the sensor unit is amplified and modulated onto the carrier signal at the same time. The modulation product is the carrier signal modulated with the flame detection signal. In addition to amplitude modulation, other modulation methods such as frequency modulation or pulse width modulation (PWM) can also be provided. However, amplitude modulation has the advantage that it can be realized with relatively little effort in terms of circuit technology.

[0017] Corresponding to another exemplary configuration, a switching converter is arranged between the output of the carrier signal unit and the non-inverting input of the modulator unit, the switching converter comprising an electronic switch, preferably a field effect transistor and a switching capacitor, wherein the switching converter is constructed to transform a carrier signal that is positively synchronized with respect to the ground potential into a carrier signal that is negatively synchronized with respect to the ground potential.

[0018] This embodiment has the advantage that a carrier signal which is necessary for the modulator unit and is negatively synchronized with respect to the ground potential can be provided by a single positive supply voltage. In the case of a symmetrical supply voltage, a negatively synchronized carrier signal can also be generated by means of a correspondingly designed carrier signal unit, wherein a switching converter can be omitted.

[0019] According to a further exemplary embodiment, the output of the modulator unit is designed to be connected to the input of the intermediate amplifier unit, wherein the intermediate amplifier unit is preferably designed as an active bandpass filter.

[0020] This embodiment has the advantage that the output of the modulator unit is decoupled from the subsequent stages. The embodiment as an active bandpass filter has the further advantage that only the desired carrier frequency band is processed further.

[0021] According to a further exemplary embodiment, the entire amplifier and evaluation circuit or parts thereof are arranged together with the optoelectronic sensor unit on a common circuit board, in a common assembly or as a system on a chip (SOC) on a common substrate and are protected against damaging influences by means of a seal.

[0022] This design has the following advantages: the optoelectronic sensor unit and the amplifier and evaluation circuit are protected against corrosion and contamination, and the sensor unit can be arranged close to the modulator unit, so that no long connection lines are required and distortions of the sensor signal due to electromagnetic interference and line impedances can be largely avoided. In addition, the design as a system on a chip (SOC) enables a cost-effective and integrated embodiment that is compact and mechanically insensitive and can be sealed.

[0023] A second aspect of the invention relates to a method for operating a flame detection device, in which method electromagnetic radiation is converted into a flame detection signal by means of an optoelectronic sensor unit, and the flame detection signal is supplied to a modulator unit, wherein the flame detection signal of the sensor unit is modulated onto a carrier signal of a carrier signal unit by means of the modulator unit, and the modulation product of the flame detection signal of the sensor unit and the carrier signal of the carrier signal unit is provided as an output signal of the modulator unit.

[0024] The method according to the invention achieves the advantage that a falsely positive flame detection signal is detected as faulty and rejected.

[0025] According to an exemplary first embodiment of the method, the output signal of the modulator unit is frequency-selectively filtered by means of an active bandpass filter, wherein the frequency of signal portions of the output signal of the modulator unit lies within a predetermined frequency band of a modulation product of a flame detection signal of the sensor unit and a carrier signal of the carrier signal unit, said signal portions being separated from other signal portions and provided as output signals of the active bandpass filter.

[0026] This configuration of the method has the advantage that signals with frequencies outside a predetermined carrier frequency band are filtered out. Here, erroneous flame recognition signals are also filtered out: the flame recognition signals do not have a carrier frequency or do not have a predetermined carrier frequency.

[0027] According to a further exemplary embodiment of the method, a demodulated flame identification signal is provided from the output signal of the active bandpass filter by means of a demodulator unit, and a flame identification signal is provided from the demodulated flame identification signal of the demodulator unit by means of a discriminator unit.

[0028] In other words, the solution according to the invention is characterized in that the amplifier and the evaluation circuit are not only fed with the signal of the sensor unit, but first modulate the signal onto a carrier signal, and when evaluating the amplified and prepared signal, it can be checked by means of the presence of the carrier signal whether the amplifier unit is functioning as intended. If the carrier signal is not present, the positive flame detection signal is rejected as possibly erroneous, and the flame detection is classified as negative for safety reasons. Thus, due to the solution according to the invention, a positive intrinsically safe flame detection device is realized, by means of which a false positive flame detection due to faults of the amplifier and the evaluation circuit can be prevented.

[0029] Further advantageous developments of the solution according to the invention emerge from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The solution according to the invention including its advantageous developments according to the dependent claims is explained in more detail below based on the graphical representation of various exemplary embodiments.

[0031] It shows:

[0032] Figure 1 A schematic illustration of a proposed device according to an exemplary embodiment of the invention, comprising a sensor unit and a modulator unit;

[0033] Figure 2 A schematic illustration of a proposed device according to another exemplary embodiment of the invention, comprising an intermediate amplifier or an active bandpass filter;

[0034] Figure 3 A schematic illustration of a proposed device according to another exemplary embodiment of the invention, comprising a switching converter; and

[0035] Figure 4 Graph having a schematic representation of an exemplary time profile of a flame detection signal, a carrier signal and a modulation product after modulation of the carrier signal with the flame detection signal. DETAILED DESCRIPTION

[0036] Figure 1 A schematic diagram of a flame detection device according to an exemplary embodiment of the present invention is shown. The flame detection device comprises a sensor unit 1, a modulator unit 2 with an inverting input 2.1 and a non-inverting input 2.2, a negative feedback branch with an ohmic resistor 7 and a carrier signal unit 3 with a switch relative to a ground potential 4.

[0037] If the non-inverting input 2.2 of the modulator unit 2 is constantly at ground potential, the circuit arrangement is a transimpedance amplifier with an operational amplifier 2 and a negative feedback resistor 7. Typically, the operational amplifier 2 has a very high input resistance at two differential inputs and a very small output resistance when the differential gain is very large. Therefore, under the framework of a predetermined limit, especially a supply voltage limit, the operational amplifier 2 that performs negative feedback by means of resistor 7 sets the output voltage to be such that the difference in the input voltage is almost zero. If the non-inverting input 2.2 is at ground potential here, a zero potential is also set for the non-inverting input 2.1. Therefore, the photodiode 1 operates in a virtual short-circuit state, in which no external operating voltage is applied. Here, the incident photons generate a photocurrent in the blocking direction that is almost linearly related to the luminous intensity. In terms of the circuit node on the non-inverting input 2.1, it involves a negative current flowing out of the circuit node. According to Kirchhoff's node law, the sum of the current flowing in and out of the circuit node must be zero. The inverting input terminal 2.1 does not generate significant inflow or outflow due to its high input terminal resistance. Therefore, the photocurrent I photo must flow through resistor R7, where, according to Ohm's law, a voltage drop U aus =R7*I photo , the voltage drop is also the output voltage of the transimpedance amplifier relative to ground potential.

[0038] In the present circuit, the non-inverting input terminal 2.2 of the operational amplifier 2 is not constantly at ground potential, but is instead connected to the ground potential by means of the carrier signal of the carrier signal unit 3 and the Figure 1 and 2 The switch shown only schematically in FIG. 1 is periodically switched between ground potential and the negative supply voltage potential. When ground potential is applied, the photocurrent I photo The corresponding output voltage U aus effective at the output; when a negative supply voltage potential is applied, any input voltage at the inverting input 2.1 is fully compensated, and the output voltage U aus =0, since the operational amplifier is operated only with positive operating voltages and 0 is therefore the lower limit of the adjustable output voltage range. The transimpedance amplifier thus assumes the function of a modulator unit that modulates the low-frequency flame detection signal of the photodiode onto a higher-frequency carrier signal. In the circuit arrangement described here, an amplitude modulation with a modulation level of 100% is implemented.

[0039] The carrier signal can be rectangular, but can also be trapezoidal or sinusoidal, which affects the waveform and spectrum of the modulation product. The frequency of the carrier signal must be higher than the highest relevant frequency in the spectrum of the flame identification signal and be sufficient to achieve the required reaction speed of the flame identification device.

[0040] The amplitude modulation described here is the simplest configuration of the method according to the invention in terms of circuit technology and function. In addition, however, other modulation methods such as frequency modulation and pulse width modulation (PWM) can also be provided. An important feature of the invention is that the flame detection signal is modulated onto a carrier signal and the presence of the carrier signal proves the function of the amplifier and the evaluation circuit. This proof can be carried out with the aid of an active bandpass filter 8, which is Figure 2 It is schematically shown in FIG.

[0041] Figure 2 A schematic diagram of a flame recognition device according to another exemplary embodiment of the present invention is shown. Typically, the active bandpass filter 8 includes an operational amplifier, which is configured with a high-pass filter at the input and a low-pass filter at the output, so that the frequency of the modulation product of the carrier signal and the flame recognition signal can pass through the active bandpass filter 8, while the rare frequency and the non-modulated signal without a carrier signal are filtered out. Therefore, it is achieved that the false positive flame recognition signal without a carrier signal is blocked, and only a valid flame recognition signal can exist at the output of the active bandpass filter 8.

[0042] These effective flame identification signals can be used with the help of Figure 2 The demodulation is carried out by a demodulator unit (not shown) and is compared with a threshold value by means of a discriminator unit (also not shown).

[0043] The invention therefore provides a positive intrinsically safe flame detection device and a method for operating such a flame detection device, which is based on positive intrinsically safe sensors and monitors the positive error-free function of amplifiers and evaluation circuits during ongoing operation, wherein any erroneous flame detection is rejected.

[0044] Figure 3A schematic diagram of a flame detection device according to another exemplary embodiment of the present invention is shown. The amplifier and the evaluation circuit operate with a positive supply voltage. In order to control the non-inverting input 2.2 of the modulator unit 2, a negative carrier signal relative to the circuit ground potential is required. The carrier signal is generated by means of a switching converter, which includes a switch, preferably a field effect transistor 5, and a capacitor 6 and a carrier signal unit 3, which generates a positive carrier signal and, as long as the field effect transistor 5 is conductive to the ground potential, not only controls the gate terminal 5.2 of the field effect transistor 5 but also charges the capacitor 6 to a positive voltage relative to the ground potential. With the falling edge of the positive carrier signal of the carrier signal unit 3, the field effect transistor 5 is blocked, and the potential of the positive charge side of the capacitor 6 moves to zero by the amount of the falling edge, thereby simultaneously moving the negative charge side of the capacitor 6 from zero to the negative range by the same amount. Subsequently, the capacitor 6 is discharged through the source-drain blocking resistor of the field effect transistor 5.

[0045] Therefore, in Figure 3 The switching converter shown in FIG. 1 provides negative control of the non-inverting input 2 . 2 of the modulator unit 2 by means of a positive supply voltage and a positive carrier signal oscillation of the carrier signal unit 3 .

[0046] Figure 4 A graph is shown with a schematic representation of an exemplary time profile of a flame detection signal B of the sensor unit 1, a carrier signal C of the carrier signal unit 3 and a modulation product D of the modulator unit 2. The negative carrier signal C', not shown, is generated by the mirroring of the carrier signal C on the time axis; depending on the dimensions of the capacitor 6 and the source-drain blocking resistor of the field effect transistor 5, it can also have other signal shapes, such as a sawtooth shape, whereby the output signal of the modulator unit also deviates accordingly. The flame detection signal B includes the flame intensity, while the signal A is a logical flame detection signal.

[0047] Reference numerals list

[0048] 1 sensor unit

[0049] 2 Modulator unit or circuit unit for amplification

[0050] 2.1 Inverting input

[0051] 2.2 Non-inverting input

[0052] 3 Carrier signal unit or circuit unit for modulation

[0053] 4 Ground potential

[0054] 5 Field Effect Transistor

[0055] 5.1 Source

[0056] 5.2 Gate

[0057] 5.3 Drain

[0058] 6. Capacitor

[0059] 7 Resistors

[0060] 8 intermediate amplifier units or active bandpass filters

Claims

1. A flame recognition device, comprising an optoelectronic sensor unit (1) suitable for flame recognition and a modulator unit (2) having a first and a second input (2.1, 2.2), wherein: The sensor unit (1) is designed to be connected to the first input (2.1) of the modulator unit (2), It is characterized in that The carrier signal unit (3) is configured to be connected to the second input end (2.2) of the modulator unit (2), and the output signal (D) of the modulator unit (2) is a modulation product of the flame recognition signal (B) of the sensor unit (1) and the carrier signal (C) of the carrier signal unit (3).

2. The flame identification device according to claim 1, characterized in that: The sensor unit (1) is designed as an intrinsically safe sensor unit, preferably as a photodiode.

3. The flame detection device according to any one of the preceding claims, characterized in that The sensor unit (1) is configured to detect electromagnetic radiation in the wavelength range of 250-550 nanometers, preferably to detect one or more wavelengths of flame free radicals generated during the combustion process, particularly preferably to detect one or more of the 308 nanometer wavelength of the OH free radical, the 430 nanometer wavelength of the CH free radical, or the 519 nanometer wavelength of the C2 free radical.

4. The flame detection device according to any one of the preceding claims, characterized in that The inverting input end (2.1) of the modulator unit (2) is configured to be connected to the flame recognition signal (B) of the sensor unit (1), and the non-inverting input end (2.2) of the modulator unit (2) is configured to be connected to the negative carrier signal (C') of the carrier signal unit (3), and the modulator unit (2) is configured to modulate the carrier signal (C') with the flame recognition signal (B).

5. The flame identification device according to claim 4, characterized in that: A switching converter (4, 5, 6) is arranged between the output of the carrier signal unit (3) and the non-inverting input (2.2) of the modulator unit (2), the switching converter comprising an electronic switch, preferably a field effect transistor (5) and a switching capacitor (6), wherein the switching converter is designed to transform a carrier signal (C) that is positively synchronized with respect to a ground potential (4) into a carrier signal (C') that is negatively synchronized with respect to the ground potential (4).

6. The flame detection device according to any one of the preceding claims, characterized in that The output of the modulator unit (2) is configured to be connected to the input of an intermediate amplifier unit (8), In this case, the intermediate amplifier unit (8) is preferably designed as an active bandpass filter.

7. The flame detection device according to any one of the preceding claims, characterized in that The entire amplifier and evaluation circuit or parts thereof are arranged together with the optoelectronic sensor unit (1) on a common circuit board, in a common assembly or as a system on a chip on a common substrate and are protected against damaging influences by means of a seal.

8. A method for operating a flame detection device, in which method electromagnetic radiation is converted into a flame detection signal (B) by means of an optoelectronic sensor unit (1), and the flame detection signal (B) is fed to a modulator unit (2), It is characterized in that modulating the flame recognition signal (B) of the sensor unit (1) onto a carrier signal (C) of a carrier signal unit (3) by means of the modulator unit (2); and A modulation product of the flame recognition signal (B) of the sensor unit (1) and the carrier signal (C) of the carrier signal unit (3) is provided as an output signal (D) of the modulator unit (2).

9. The method according to claim 8, characterized in that The output signal (D) of the modulator unit (2) is frequency selectively filtered by means of an active bandpass filter (8), wherein the frequencies of some signal parts of the output signal (D) of the modulator unit (2) are within a predetermined frequency band of a modulation product of the flame identification signal (B) of the sensor unit (1) and the carrier signal (C) of the carrier signal unit (3), the signal parts are separated from other signal parts and provided as output signals of the active bandpass filter (8).

10. The method according to claim 9, characterized in that A demodulated flame identification signal (B') is provided from the output signal of the active bandpass filter (8) by means of a demodulator unit; and a flame identification signal (A) is provided from the demodulated flame identification signal (B') of the demodulator unit by means of a discriminator unit.

Images