Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-04-05
2002-12-31
Trieu, Van (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S577000
Reexamination Certificate
active
06501383
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a method of monitoring a flame such as a flame of a gas or oil burner and an apparatus for monitoring a flame.
2. Description of the Prior Art
Monitoring gas flames frequently entails the use of flame monitors which utilize the rectifier effect of the flame, that is to say which operate on the basis of what is known as the ionization principle. In that procedure an ac voltage is applied between two electrodes. The volume which is filled by the flame depends on the instantaneous output of the burner. The direct current which can be produced can be very low at a low level of burner output and if the geometry of the electrodes is not the optimum, while the alternating current can be substantially greater in dependence on the capacitance of the sensor line. The flame signal amplifier must therefore be capable of filtering off the low direct current component in the overall sensor circuit current, without the alternating current being able to simulate a flame signal as a result of the inevitable rectifier effects in the amplifier input. Therefore the magnitude of the direct current component gives a measurement in respect of the intensity of the flame, in which respect the absence of a flame corresponds to the intensity of zero, the detection of which must be established reliably and very close to real time in order to avoid unburnt gas or oil from flowing out into the burner chamber.
In principle filtering of the direct current component can be implemented by an evaluation circuit which is connected upstream of the flame signal amplifier, such as for example a low pass filter with a sufficiently low limit frequency. If however the filter capability of the low pass filter is lost, for example because of a failure of a filter capacitor, the alternating current could simulate the presence of a flame, even when the flame is not present. The flame monitoring or burner control system must recognise that malfunction. In the case of burners involving intermittent operation, that is normally not a problem because, after the fuel supply is switched off, which results in the flame being extinguished, the control system can detect a simulated flame signal as being a defect and can prevent the burner from being set in operation again. In the case of burners in continuous operation the malfunction must be detected by periodically checking the flame monitor without the burner being taken out of operation for that purpose. In the case of optical flame sensors, this is generally effected by interrupting the beam path between the flame and the sensor by means of a shutter member, that is to say flame failure is temporarily simulated during operation of the assembly, and the output of the flame signal amplifier must suitably react thereto.
In principle the method of signal interruption at the flame sensor can also be used in regard to ionization flame monitoring. The ionization circuit could be interrupted by means of a suitable switch element. However that element would have to be disposed close to the sensor electrode so that only the flame signal current is interrupted and not for example also the alternating current which flows by way of line capacitances and whose flame-simulating effect in the event of a component fault is in fact precisely to be detected by the test. It would also be possible to envisage short-circuiting of the flame signal lines whereby the flame signal current also becomes zero, and the alternating current is even increased. For both cases, it would be necessary to use a switch element which is suitable for the high sensor ac voltage and which itself cannot assume a fault mechanism which results in undetected flame simulation.
In the present state of knowledge only an electromechanical relay can be considered for that purpose. That structure however is expensive in terms of material and equipment and requires a relatively high level of control power. The possibility of interrupting the sensor current with a relay contact is mentioned in German laid-open application (DE-OS) No 29 32 129 on page 6. DE 30 26 787 describes a construction in which there is a single filter capacitor at the input of the flame signal amplifier, which on the one hand serves as an energy storage means for the ionization current and whose discharge current on the other hand is required for dynamic operation of a semiconductor circuit. Failure of that filter capacitor has the consequence that the semiconductor circuit—even in the case of an alternating current caused by sensor line capacitances—goes into a constant state so that a flame is no longer signalled. The disadvantage of that arrangement is that a given minimum level of energy and thus a given minimum current must be supplied by the flame for dynamic operation of that semiconductor circuit. Therefore certain limits are set on the response sensitivity of that circuitry principle and it no longer satisfies all present-day requirements.
EP 159 748 discloses a circuit which leads to the assumption of a high level of response sensitivity insofar as the capacitive load current caused by line capacitances, at the sensor terminals, remains low in comparison with the flame signal current. In that respect this circuit does not satisfy the demands for a high level of response sensitivity and at the same time a high level of resistance in relation to line capacitance. A further requirement which is frequently specified is the display of flame intensity as a setting aid when bringing a burner into operation and for detecting changes of the flame in operation, in good time. The circuit disclosed in EP 159 748 does not afford that option.
The arrangement in accordance with the teaching of DE 30 26 787 supplies a pulse series in dependence on the magnitude of the flame current so that in that case it would be possible to derive a signal to indicate the flame intensity, but the dynamic range between response sensitivity and saturation limit is relatively small so that the circuit principle is only suitable for establishing “flame present”.
EP 0 617 234 also discloses an ionization flame monitor with a circuit arrangement having a capacitor which is transferred by the ionization current from a condition of being charged up by the operating voltage into a discharged condition, wherein the signal “flame present” is output when the value falls below a given threshold. The function of the capacitor can be checked by means of a test signal. The disadvantage here is that the function of the capacitor has to be periodically tested, the system does not provide for continuous monitoring of the capacitor.
SUMMARY OF THE INVENTION
Therefore the object of the present invention is to provide a method and an apparatus for monitoring a flame which serves as a flame monitoring method and circuit respectively, the response sensitivity of which is substantially improved in comparison with the state of the art without detracting from compatibility for line capacitance, whose switch-off capability can be periodically checked during burner operation and also supplies an output signal representing a measurement in respect of flame intensity. The invention further seeks to provide that the method ensures continuous checking of the monitoring action.
According to a first aspect of the present invention, there is provided a method of monitoring a flame, wherein:
in dependence on the presence or intensity of the flame there is produced from a first electrical signal a second electrical signal of different magnitude,
the second electrical signal is applied to an evaluation circuit and converted into a first output signal, and
the evaluation circuit is acted upon by a monitoring signal which upon failure of the evaluation circuit leads to a second output signal.
According to a second aspect of the present invention, there is provided apparatus for monitoring a flame, comprising:
an evaluation circuit which in dependence on the presence or the intensity of the flame generates from a first electrical signal a seco
Proskauer Rose LLP
Siemens Building Technologies AG
Trieu Van
LandOfFree
Method and device for monitoring a flame does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for monitoring a flame, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for monitoring a flame will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2985311