Flame detection device and method for operating a flame detection device

Description

[0001] The invention relates to a flame detection device and a method for operating a flame detection device. A flame detection device and a method for operating such a flame detection device of the type mentioned above are known from document EP 3 916 693 A1.This flame detection device consists – initially considered objectively – of a sensor unit (there sensor element 16) that converts electromagnetic radiation (there flame radiation 42 in combination with a control signal 18 of a transmitter unit 40) into a sensor signal (there sensor signal 20) and a signal processing unit (there signal processing step 44), wherein – expressed procedurally – the processed sensor signal is decomposed into a flame signal component and a control signal component (there analysis step 46 for separating the control signal component 18') and the control signal component is evaluated (there evaluation step 48 for evaluating the control signal component 18').

[0002] US 4 591 725 A shows a fail-safe, self-testing flame monitoring circuit without a mechanical shutter. A photodetector provides a signal corresponding to the flame intensity, which is then amplified. The amplification is controlled by a negative feedback circuit depending on the peak amplitude of the signal, so that all frequencies up to DC are amplified uniformly and passed on to further processing without threshold cutoff.

[0003] The invention is based on the objective of improving a flame detection device and a method for operating a flame detection device of the type mentioned above. In particular, a flame detection device that can be tested with minimal effort and a method with which the functional testing of the flame detection device can be carried out particularly easily are to be created, whereby no additional transmitting element for emitting an optical or electromagnetic control signal within the flame chamber is required.

[0004] It should be taken into account that only a false positive flame detection represents a dangerous fault condition of a combustion device, while a false negative flame detection may lead to an unnecessary shutdown of the flame, but does not represent a dangerous fault condition due to the further flow of non-igniting fuel into a combustion chamber.

[0005] Furthermore, it should be noted that the sensor unit of the present flame detection device is preferably designed as a photodiode, which generates a photocurrent from the incident electromagnetic radiation energy without an external operating voltage. The sensor unit is therefore intrinsically safe, in that if the photodiode fails, the photocurrent may fail even if a flame is present; however, the reverse failure scenario, in which a photocurrent is generated despite the absence of a flame, is physically impossible due to the conservation of energy.

[0006] Therefore, only a test of the electrical amplifier and evaluation circuit of the flame detection device for false positive error states is required.

[0007] This problem is solved by a flame detection device of the type mentioned above, by the features listed in claim 1. Methodologically, this problem is solved by the features listed in claim 8.

[0008] A first aspect of the invention relates to a flame detection device comprising an optoelectronic sensor unit suitable for flame detection and a modulator unit having a first and a second input, wherein the sensor unit is connected to the first input of the modulator unit, and a carrier signal unit is connected to the second input of the modulator unit, and an output signal of the modulator unit is a modulation product of a flame detection signal of the sensor unit and a carrier signal of the carrier signal unit.

[0009] The modulator unit could also be called the amplification circuit unit, and the carrier signal unit the modulation circuit unit.

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

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

[0012] This design has the advantage that a false positive flame detection signal as an output signal of the sensor unit can be ruled out. In the preferred embodiment as a photodiode, a photocurrent is generated directly from the radiation energy without an external operating voltage. According to a further exemplary embodiment, the sensor unit is configured to detect electromagnetic radiation in a wavelength range of 250–550 nm, preferably one or more wavelengths of the flame radicals occurring in a combustion process, particularly preferably one or more of the wavelengths of 308 nm of an OH radical, 430 nm of a CH radical, or 519 nm of a C₂ radical.

[0013] This design has the advantage that flame detection is focused on characteristic wavelengths and reliability is improved.

[0014] According to another exemplary embodiment, the inverting input of the modulator unit is connected to the flame detection signal of the sensor unit, and the non-inverting input of the modulator unit is connected to a negative carrier signal of a carrier signal unit, and the modulator unit is configured to modulate the carrier signal with the flame detection signal.

[0015] This design has the advantage that the flame detection signal from the sensor unit is amplified and simultaneously modulated onto the carrier signal. The modulation product is a carrier signal modulated with the flame detection signal. Besides amplitude modulation, other modulation methods such as frequency modulation or pulse-width modulation (PWM) can also be used. However, amplitude modulation has the advantage of being comparatively simpler to implement in terms of circuitry.

[0016] According to a further exemplary embodiment, a switching converter is arranged between the output of the carrier signal unit and the non-inverting input of the modulator unit, comprising an electronic switch, preferably a field-effect transistor, and a switched capacitor, wherein the switching converter is designed to convert a carrier signal clocked positively relative to ground into a carrier signal clocked negatively relative to ground.

[0017] This design has the advantage that a single positive supply voltage can provide the carrier signal required by the modulator unit, which is negatively switched relative to ground. With symmetrical supply voltages, the negatively switched carrier signal can also be generated by a suitably designed carrier signal unit, thus eliminating the need for a switching converter.

[0018] According to another exemplary embodiment, the output of the modulator unit is connected to the input of an intermediate amplifier unit, the intermediate amplifier unit preferably being designed as an active bandpass filter.

[0019] This design has the advantage that the output of the modulator unit is decoupled from subsequent stages. A design as an active bandpass filter has the further advantage that only the desired carrier frequency band is processed.

[0020] According to another exemplary embodiment, the entire amplifier and evaluation circuit or part thereof is arranged together with the optoelectronic sensor unit on a common circuit board, in a common assembly, or as a system-on-chip (SOC) on a common substrate and protected against damaging influences by means of sealing.

[0021] This design offers the advantage that the optoelectronic sensor unit and the amplifier and evaluation circuitry are protected against corrosion and contamination, and the sensor unit can be positioned close to the modulator unit, thus eliminating the need for long connecting cables and largely preventing distortion of the sensor signal due to electromagnetic interference and line impedances. Furthermore, the system-on-chip (SOC) design allows for a cost-effective and integrated implementation that is compact, mechanically robust, and can be sealed.

[0022] A second aspect of the invention relates to a method for operating a flame detection device, in which 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 a 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.

[0023] The method according to the invention achieves the advantage that a false positive flame detection is recognized as faulty and discarded.

[0024] According to a first exemplary embodiment of the method, the output signal of the modulator unit is frequency-selectively filtered by means of an active bandpass filter, whereby signal components of the output signal of the modulator unit, whose frequency lies within a predetermined frequency band of modulation products of the flame detection signal of the sensor unit and the carrier signal of the carrier signal unit, are separated from other signal components and provided as the output signal of the active bandpass filter.

[0025] This design of the method has the advantage that signals with frequencies outside the specified carrier frequency band are filtered out. This also filters out faulty flame detection signals that have no carrier frequency or do not have the specified carrier frequency.

[0026] According to a further exemplary embodiment of the method, a demodulated flame detection signal is provided from the output signal of the active bandpass filter by means of a demodulator unit, and a flame discrimination signal is provided from the demodulated flame detection signal of the demodulator unit by means of a discriminator unit.

[0027] In other words, the solution according to the invention is characterized by the fact that the amplifier and evaluation circuit not only receives the signal from the sensor unit, but that this signal is first modulated onto a carrier signal, and that the presence of the carrier signal during the evaluation of the amplified and processed signal allows verification of whether the amplifier unit is functioning correctly. If the carrier signal is not present, a positive flame detection signal is rejected as potentially erroneous, and the flame detection is classified as negative as a precautionary measure. Thanks to the approach according to the invention, a positively intrinsically safe flame detection device is thus created, which prevents false positive flame detection due to a fault in the amplifier and evaluation circuit.

[0028] Other advantageous developments of the solution according to the invention result from the dependent patent claims.

[0029] The solution according to the invention, including its advantageous further developments according to the dependent claims, is explained in more detail below with reference to the graphic representation of various exemplary embodiments.

[0030] It shows Figure 1 is a schematic representation of a proposed device according to an exemplary embodiment of the invention comprising a sensor unit and a modulator unit; Figure 2 is a schematic representation of a proposed device according to a further exemplary embodiment of the invention comprising an intermediate amplifier or an active bandpass filter; Figure 3 is a schematic representation of a proposed device according to a further exemplary embodiment of the invention comprising a switching converter; and Figure 4 is a diagram with a schematic representation of an exemplary time course of a flame detection signal, a carrier signal and a modulation product after modulation of the carrier signal with the flame detection signal.

[0031] Figure 1Figure 1 shows a schematic representation of a flame detection device according to an exemplary embodiment of the invention. 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 to ground 4.

[0032] When the non-inverting input 2.2 of the modulator unit 2 is constantly at ground potential, the circuit arrangement acts as a transimpedance amplifier with the operational amplifier 2 and the feedback resistor 7. The operational amplifier 2 typically has a very high input impedance at both differential inputs and a very low output impedance with very high differential gain. The operational amplifier 2, with feedback via the resistor 7, thus adjusts the output voltage within the given limits, in particular the supply voltage limits, so that the difference between the input voltages is close to zero. If the non-inverting input 2.2 is at ground, a zero potential is also set for the inverting input 2.1. Thus, the photodiode 1 is operated in a virtual short circuit, with no external supply voltage applied.Here, the incident photons generate a reverse-biased photocurrent that depends almost linearly on the illuminance. With respect to the circuit node at the non-inverting input 2.1, this is a negative current flowing out of the node. According to Kirchhoff's current law, the sum of the incoming and outgoing currents for this node must be zero. Due to its high input impedance, the inverting input 2.1 contributes no significant inflow or outflow. Therefore, the photocurrent Iphoto must flow through resistor R7, resulting in a voltage drop Uout = R7 * Iphoto, according to Ohm's law. This voltage drop is also the output voltage of the transimpedance amplifier to ground.

[0033] The non-inverting input 2.2 of the operational amplifier 2 is not constantly at ground potential in the present circuit, but is connected by means of a carrier signal from a carrier signal unit 3 and a signal in the Figures 1 and 2The switch, shown only schematically, is periodically switched between ground potential and a negative supply voltage potential. While ground potential is present, the output voltage Uout, corresponding to the photocurrent Iphoto, is effective at the output. While a negative supply voltage potential is present, any input voltage at the inverting input 2.1 is completely compensated, and the output voltage Uout = 0, since the operational amplifier is operated exclusively with a positive supply voltage, and 0 is therefore the lower limit of the adjustable output voltage range. Thus, the transimpedance amplifier assumes the function of a modulator unit, which modulates the low-frequency flame detection signal of the photodiode onto a higher-frequency carrier signal. In the circuit arrangement described here, amplitude modulation with a modulation depth of 100% is implemented.

[0034] The carrier signal can be rectangular, trapezoidal, or sinusoidal, each affecting the waveform and frequency spectrum of the modulation product. The frequency of the carrier signal must be higher than the highest relevant frequency in the frequency spectrum of the flame detection signal and sufficient to achieve the required response speed of the flame detection device.

[0035] Amplitude modulation as described here represents the simplest circuit design and functional implementation of the method according to the invention. However, other modulation methods, such as frequency modulation and pulse-width modulation (PWM), can also be used. A key feature of the invention is that the flame detection signal is modulated onto a carrier signal, and the presence of the carrier signal verifies the functionality of the amplifier and evaluation circuit. This verification can be achieved using an active bandpass filter 8, which is implemented in Figure 2 is shown schematically.

[0036] Figure 2Figure 8 shows a schematic representation of a flame detection device according to a further exemplary embodiment of the invention. The active bandpass filter 8 typically comprises an operational amplifier configured with a high-pass filter at the input and a low-pass filter at the output, such that frequencies of modulation products of the carrier signal and the flame detection signal pass through the active bandpass filter 8, while extraneous frequencies and unmodulated signals without a carrier signal are filtered out. This ensures that erroneous positive flame detection signals without a carrier signal are blocked, and only valid flame detection signals can be present at the output of the active bandpass filter 8.

[0037] These valid flame detection signals can be detected using a Figure 2The signal is demodulated by a demodulator unit (not shown) and compared to a threshold value using a discriminator unit (also not shown).

[0038] Thus, the present invention provides a positive intrinsically safe flame detection device and a method for operating such a flame detection device, which is based on a positive intrinsically safe sensor and monitors the positive fault-free function of the amplifier and evaluation circuit during operation, whereby a potentially faulty flame detection is discarded.

[0039] Figure 3Figure 1 shows a schematic representation of a flame detection device according to a further exemplary embodiment of the invention. The amplifier and evaluation circuit operates with a positive supply voltage. A carrier signal negative relative to circuit ground is required to control the non-inverting input 2.2 of the modulator unit 2. This is generated by a switching converter comprising a switch, preferably a field-effect transistor 5, and a capacitor 6, as well as a carrier signal unit 3, which generates a positive carrier signal and both controls the gate terminal 5.2 of the field-effect transistor 5 and charges the capacitor 6 to a positive voltage relative to ground as long as the field-effect transistor 5 is conducting relative to ground.With the falling edge of the positive carrier signal from the carrier signal unit 3, the field-effect transistor 5 is switched off, and the potential of the positively charged side of the capacitor 6 is shifted towards zero by the amount of the falling edge. Simultaneously, the potential of the negatively charged side of the capacitor 6 is shifted from zero into the negative range by the same amount. The capacitor 6 then discharges through the source-drain blocking resistor of the field-effect transistor 5.

[0040] Thus, the in Figure 3 The switching converter shown provides a negative control of the non-inverting input 2.2 of the modulator unit 2 by means of a positive supply voltage and the positive carrier signal oscillation of the carrier signal unit 3.

[0041] Figure 4Figure 1 shows a diagram with a schematic representation of an example time course of a flame detection signal B from sensor unit 1, a carrier signal C from carrier signal unit 3, and a modulation product D from modulator unit 2. The negative carrier signal C', not shown, is generated by mirroring the carrier signal C across the time axis. Depending on the dimensions of the capacitance 6 and the source-drain blocking resistor of the field-effect transistor 5, it can also assume a different signal shape, for example, a sawtooth waveform, which also results in a corresponding deviation in the output signal of the modulator unit. While the flame detection signal B encompasses the flame intensity, signal A represents a logical flame detection signal. Reference symbol list

[0042] 1 Sensor unit 2 Modulator unit or circuit unit for amplification 2.1 Inverting input 2.2 Non-inverting input 3 Carrier signal unit or circuit unit for modulation 4 Ground 5 Field-effect transistor 5.1 Source 5.2 Gate 5.3 Drain 6 Capacitance 7 Resistor 8 Intermediate amplifier unit or active bandpass filter

Claims

1. A flame detection device, comprising an optoelectronic sensor unit (1) suitable for detecting a flame and a modulator unit (2) having a first and a second input (2.1, 2.2), wherein the sensor unit (1) is connected to the first input (2.1) of the modulator unit (2), wherein a carrier signal unit (3) is connected to the second input (2.2) of the modulator unit (2) and an output signal (D) of the modulator unit (2) is a modulation product of a flame detection signal (B) of the sensor unit (1) and of a carrier signal (C) of the carrier signal unit (3).

2. The flame detection device according to claim 1, wherein 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, wherein the sensor unit (1) is designed to detect electromagnetic radiation in a wavelength range of 250-550 nm, preferably one or more wavelengths of the flame radicals occurring in a combustion process, particularly preferably one or more of the wavelengths 308 nm of an OH radical, 430 nm of a CH radical, or 519 nm of a C2 radical.

4. The flame detection device according to any one of the preceding claims, wherein the first input (2.1) of the modulator unit (2) is an inverting input (2.1), the second input (2.2) of the modulator unit (2) is a non-inverting input (2.2), the first, inverting input (2.1) of the modulator unit (2) is connected to the flame detection signal (B) of the sensor unit (1), the second, non-inverting input (2.2) of the modulator unit (2) is connected to a negative carrier signal (C') of a carrier signal unit (3), and the modulator unit (2) is designed to modulate the carrier signal (C') with the flame detection signal (B).

5. The flame detection device according to claim 4, wherein 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), and comprises an electronic switch, preferably a field effect transistor (5), and a switched capacitor (6), wherein the switching converter is designed to convert a carrier signal (C) clocked positively with respect to ground (4) into a carrier signal (C') clocked negatively with respect to ground (4).

6. The flame detection device according to any one of the preceding claims, wherein the output of the modulator unit (2) is connected to the input of an intermediate amplifier unit (8), wherein the intermediate amplifier unit (8) is preferably designed as an active bandpass filter.

7. The flame detection device according to one of the preceding claims, wherein the entire amplifier and evaluation circuit or a part thereof is arranged together with the optoelectronic sensor unit (1) on a common printed circuit board, in a common assembly, or as a system-on-chip on a common substrate and is protected against damaging influences by means of sealing.

8. A method for operating a flame detection device, in which 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), wherein the flame detection signal (B) of the sensor unit (1) is modulated 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 detection signal (B) of the sensor unit (1) and of the carrier signal (C) of the carrier signal unit (3) is provided as output signal (D) of the modulator unit (2).

9. The method according to claim 8, wherein the output signal (D) of the modulator unit (2) is filtered in frequency-selective manner by means of an active bandpass filter (8), wherein signal components of the output signal (D) of the modulator unit (2) whose frequency lies within a predetermined frequency band of modulation products of the flame detection signal (B) of the sensor unit (1) and of the carrier signal (C) of the carrier signal unit (3) are separated from other signal components and provided as output signal of the active bandpass filter (8).

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