FLAME DETECTION DEVICE AND METHOD OF OPERATION OF A FLAME DETECTION DEVICE

Abstract

The invention relates to a flame detection device and 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), wherein the sensor unit (1) is connected to the first input (2.1) of the modulator unit (2) and a carrier signal unit (3) is connected to the second input (2.2) of the modulator unit (2) and an output signal of the modulator unit (2) is a modulation product of a flame detection signal of the sensor unit (1) and a carrier signal of the carrier signal unit (3).

Description

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

[0002] 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 viewed objectively - of a sensor unit (sensor element 16) that converts electromagnetic radiation (flame radiation 42 in combination with a control signal 18 from a transmitting unit 40) into a sensor signal (sensor signal 20) and a signal conditioning unit (signal processing step 44). In procedural terms, the prepared sensor signal is broken down into a flame signal component and a control signal component (analysis step 46 for separating the control signal component 18'), and the control signal component is evaluated (evaluation step 48 for evaluating the control signal component 18').

[0003] The invention is based on the object 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 are to be created with which the functionality test of the flame detection device can be carried out particularly easily, whereby no additional transmitting element for transmitting an optical or electromagnetic control signal within the flame chamber is required.

[0004] It should be noted 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 continued 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 external operating voltage. The sensor unit is thus intrinsically safe in the sense that if the photodiode fails, the photocurrent may fail despite the presence of a flame. However, the reverse failure scenario, in which a photocurrent is generated despite the absence of a flame, is physically impossible due to energy conservation.

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

[0007] This object is achieved with a flame detection device of the type mentioned above by the features listed in the characterizing part of patent claim 1. In terms of method, this object is achieved by the features listed in the characterizing part of patent 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 could also be called the modulation circuit unit.

[0010] The teaching according to 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 configuration has the advantage that a false-positive flame detection signal can be excluded as the output signal of the sensor unit. In the preferred configuration as a photodiode, a photocurrent is generated directly from the radiant energy without an external operating voltage. According to a further exemplary configuration, the sensor unit is designed to detect electromagnetic radiation in a wavelength range of 250-550 nm, preferably one or more wavelengths of the flame radicals occurring during 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.

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

[0014] According to a further 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 designed 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. In addition to amplitude modulation, other modulation methods such as frequency modulation or pulse width modulation (PWM) can also be used. Amplitude modulation, however, has the advantage of being relatively easy 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 with respect to ground into a carrier signal clocked negatively with respect to ground.

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

[0018] According to a further exemplary embodiment, the output of the modulator unit is connected to the input of an intermediate amplifier unit, wherein the intermediate amplifier unit is preferably 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 a further exemplary embodiment, the entire amplifier and evaluation circuit or a part thereof is arranged together with the optoelectronic sensor unit on a common printed circuit board, in a common assembly, or as a system-on-chip (SOC) on a common substrate and is 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, eliminating the need for long connecting cables and largely preventing sensor signal distortion due to electromagnetic interference and line impedances. The system-on-chip (SOC) design also allows for a cost-effective and integrated design 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 fed 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 has the advantage that a false positive flame detection is recognized as faulty and rejected.

[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, wherein 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 method configuration has the advantage that signals with frequencies outside the specified carrier frequency band are filtered out. This also filters out erroneous flame detection signals that do not have a 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 in that not only is the signal from the sensor unit fed to the amplifier and evaluation circuit, but this signal is first modulated onto a carrier signal. The presence of the carrier signal can be used to check whether the amplifier unit is functioning properly during the evaluation of the amplified and processed signal. If the carrier signal is not present, a positive flame detection signal is rejected as possibly faulty, and the flame detection is classified as negative for safety reasons. Thanks to the approach according to the invention, a positively intrinsically safe flame detection device is thus created, by means of which false positive flame detection due to a fault in the amplifier and evaluation circuit can be prevented.

[0028] Other advantageous developments of the inventive solution emerge from the dependent patent claims.

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

[0030] It shows Figure 1 shows 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 shows 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 shows a schematic representation of a proposed device according to a further exemplary embodiment of the invention, comprising a switching converter; and Figure 4 shows a diagram with a schematic representation of an exemplary temporal profile 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 1shows 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] If 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 negative feedback resistor 7. The operational amplifier 2 typically has a very high input resistance at both differential inputs and a very low output resistance with a very large differential gain. The operational amplifier 2, with negative feedback via the resistor 7, thus sets the output voltage within the specified 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 connected to ground, a zero potential is also set for the inverting input 2.1. The photodiode 1 is thus operated in a virtual short circuit, with no external operating voltage applied.The incident photons generate a reverse-biased photocurrent that is almost linearly dependent on the illuminance. With respect to the circuit node at the non-inverting input 2.1, the current flowing out of the circuit node is negative. According to Kirchhoff's node rule, the sum of the incoming and outgoing currents for this circuit node must be zero. Due to its high input resistance, the inverting input 2.1 contributes no significant inflow or outflow. Thus, the photocurrent I photo must flow in via the resistor R 7 , whereby, according to Ohm's law, a voltage drop U out = R 7 * I photo occurs, which 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 controlled by a carrier signal of a carrier signal unit 3 and a Figures 1 and 2only schematically shown switch is periodically switched between ground potential and a negative supply voltage potential. While ground potential is applied, the output voltage U out corresponding to the photocurrent I photo is effective at the output; while negative supply voltage potential is applied, any input voltage at the inverting input 2.1 is fully compensated and the output voltage U out = 0, since the operational amplifier is operated exclusively with a positive operating voltage and 0 is therefore the lower limit of the adjustable output voltage range. The transimpedance amplifier thus takes on 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 carried out.

[0034] The carrier signal can be rectangular, trapezoidal, or sinusoidal, each of which affects 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 embodiment of the method according to the invention in terms of circuitry and functionality. 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 performed using an active bandpass filter 8, which is Figure 2 is shown schematically.

[0036] Figure 2shows a schematic representation of a flame detection device according to another 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, so 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 erroneously 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 by means of a Figure 2demodulated by a demodulator unit (not shown) and compared with a threshold value by means of a discriminator unit (also not shown).

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

[0039] Figure 3shows 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. To control the non-inverting input 2.2 of the modulator unit 2, a carrier signal that is negative with respect to circuit ground is required. This is generated by means of 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 with respect to ground as long as the field-effect transistor 5 is conductive with respect to ground.With the falling edge of the positive carrier signal from the carrier signal unit 3, the field-effect transistor 5 is turned off, and the potential of the positively charged side of the capacitor 6 is shifted toward zero by the amount of the falling edge. At the same time, 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 via the source-drain blocking resistor of the field-effect transistor 5.

[0040] Thus, the 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 4shows a diagram with a schematic representation of an exemplary time profile 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 created by mirroring the carrier signal C on the time axis. Depending on the dimensioning of the capacitance 6 and the source-drain blocking resistance of the field-effect transistor 5, it can also assume a different signal shape, for example a sawtooth shape, whereby the output signal of the modulator unit also deviates accordingly. While the flame detection signal B comprises the flame intensity, signal A represents a logical flame detection signal. List of reference symbols

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

Claims

1. 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), wherein the sensor unit (1) is connected to the first input (2.1) of the modulator unit (2), characterized in that 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 a carrier signal (C) of the carrier signal unit (3).

2. Flame detection 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. Flame detection device according to one of the preceding claims, characterized in thatthe 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. Flame detection device according to one of the preceding claims, characterized in that the inverting input (2.1) of the modulator unit (2) is connected to the flame detection signal (B) of the sensor unit (1) and the 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. Flame detection device according to claim 4, characterized in thata 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), comprising 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) which is positively clocked with respect to ground (4) into a carrier signal (C') which is negatively clocked with respect to ground (4).

6. Flame detection device according to one of the preceding claims, characterized in that 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. Flame detection device according to one of the preceding claims, characterized in thatthe 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), characterized in that 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 the carrier signal (C) of the carrier signal unit (3) is provided as the output signal (D) of the modulator unit (2).

9. 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 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 the carrier signal (C) of the carrier signal unit (3) are separated from other signal components and provided as the output signal of the active bandpass filter (8).

10. Method according to claim 9, characterized in that 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.