Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-05-05
2001-12-11
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S578000, C250S339030, C250S554000
Reexamination Certificate
active
06329921
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to flame detector units and flame management systems.
Flame detector units are used to detect the presence of a flame. There are two methods of detecting the presence of flames which are in common use. The first detects light emitted from the flame in the visible and infra red wavelength bands, and this type of flame detector is known as an Infra Red or IR flame detector. The other method is to detect ultra violet light which is also emitted by flames, and a detector which utilises this technique is known as a UV flame detector.
The advantage of detecting ultra violet emissions is that it provides a direct measure of brightness in a flame and in a prescribed range of wavelengths gives excellent discrimination. It is well suited to the task of monitoring oil or gas flames, which burn brightly and generate a significant signal in the prescribed wavelengths.
Utilising the infra red detection technique, on the other hand, has the advantage that it is not as strongly susceptible to attenuation by oil mist and combustion products, or water vapour. It is also more tolerant of movement than is the UV spectral base. Thus, IR is particularly suited to the task of monitoring pulverised coal (pc) flames, which do not burn brightly within a well defined envelope but tend to coalesce in a random fashion resulting in movement, and which also generate water vapour.
Not only is the IR spectral response well suited for monitoring pulverised coal flames but it is also particularly useful for looking at the origin of oil flames right inside the oil spray or monitoring steam atomised burners.
Every flame also has a characteristic flicker associated with it, the flicker frequency of which corresponds to intensity fluctuations and these fluctuations are generated by combustion in turbulent gaseous eddies as they are convected in the flame envelope. Put another way flicker frequency refers to the dynamic frequency of “flicker” associated with the visible and Infra Red wavelength bands, and the effectiveness of UV and IR detection has been found to be improved by utilising flicker frequency filtering in conjunction therewith, a technique known as UV flicker (UVF) and IR flicker (IRF) flame detection respectively. These modified techniques provide better discrimination than is possible using solely UV or IR techniques.
Flicker frequency is selectable in the range 10 to 1200 Hz for UV or IR. The preferred dynamic frequency for discriminatory flame detection is probably in the higher end of the range 100-1000 Hertz. There is also a fundamental flicker, typically around 25 Hz, which affects IRF or UVF response because of air currents and macro turbulence. For this reason higher frequency Flicker settings will provide better discrimination as opposed, for example, to detectors that refer to fundamental flicker which yields the biggest signal. The choice of optimum dynamic frequency within the preferred range, for the purpose of discriminatory flame detection, is dependent largely on boiler conditions, but it is also influenced by fuel type, burner geometry and mixing factors.
To apply UV or IR Flicker it is fist necessary to characterize the optimum dynamic frequency for the boiler/burner situation, and then to set the processor to accept Flicker frequencies within a narrow band on either side of the optimized value. This adjustment involves two parameters, one, the flicker frequency adjustment, the other, the quality factor (Q) or bandwidth adjustment. The quality factor is normally factory set, and the flicker frequency adjusted on-site by an installation technician.
Both IR and UV detectors, whether utilising the flicker frequency filtering enhanced detection technique or the non-filtering detection technique, can, as indicated above, only detect the presence or absence of the flame—no qualitative information regarding the condition of a flame can be obtained. This problem was addressed in GB 2283094, which discloses an oil flame monitoring system which utilises two detectors to monitor a single flame—an IR detector monitoring a first region of the flame and a UV detector monitoring a second region of the same flame. The different characteristics of the two detection systems enable the results obtained from the two detectors to be used to provide information not only about the presence or absence of the flame but also the condition of that flame.
However, this system has been found to be rather inflexible and rather bulky since it requires two flame detectors units, each producing a dedicated UV or IR response, and a processing means associated with each unit to process the output signal. Also, since the flicker frequency adjustment is preset, the system is useful for only a limited range of emission from a flame.
SUMMARY OF INVENTION
According to one aspect of the present invention, there is provided a flame management system comprising at least one flame detector unit arranged to monitor at least one flame in at least two response modes, and a processor which selectively processes the output of the or each detector unit for responses appropriate to the type and/or condition of the at least one flame. In one embodiment, the system comprises two flame detector units each of which is operable in a single mode, the processor selectively processing their output signals for a response appropriate to the condition and/or type of flame present. One flame detector unit may, then, provide an IR or IRF response and the other a UV or UVF response, or both may provide a dedicated IR, IRF, UV or UVF response but with different sensitivity settings.
In another embodiment, the system comprises a single flame detector unit which has at least two different modes of operation which can be selected by the processor. In particular, the invention may comprise at least one flame detector unit, the or each unit being operable in at least two different modes to monitor at least one flame, and a processor which processes the signals from the or each unit and actively varies the operating mode of the or each unit in response to changes in the condition of the or each flame. The different modes might be a UV or UVF response mode and an IR or IRF response mode, or might be a normal and sensitive setting for a dedicated IR or UV detector or a combination of the two.
The processor can preferably effect adjustment of the flicker frequency and also vary the signal gain for the or each detector, that is adjust the amplification applied to the response signal obtained from each detector unit. Each signal is preferably amplified to lie typically in the range of 0 to 10 volts dc and is interpreted as a percentage of the nominal maximum. By enabling active control of this setting, the sensitivity of the or each detector is improved. Alternatively or in addition, the system preferably includes at least one detector unit which is operable as either an IR or a UV responsive unit to suit the particular conditions and/or type of the flame, said operational mode being controlled by the processor. The processor may also implement flame support systems and set up alarms or the like in response to transient or deteriorating combustion conditions rather than merely shutting off a burner.
The present invention requires just a single management processor for a plurality of detector units which function in parallel, each detector being connected to a different channel of the processor, and these detector units may be dedicated to one flame, analysing different regions thereof, or may be arranged to monitor separate flames produced by different burners, either at different locations or at the same location at different times. In the case of monitoring two or more different flames produced by different burners, should any burner go to flame fail, the operational burners can automatically be kept in service provided their flame condition remains acceptable.
The system has been found to be particularly effective when implemented using a two channel processor, i.e. utilising dual channel technology
Innes David
Tindall David
Kilyk & Bowersox, PLLC
Nguyen Phung T
Spectus Flame Management Limited
Wu Daniel J.
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