Fail-safe apparatus for checking the presence of flame in a burner

Abstract

A control device for monitoring the presence or absence of a flame through the use of an ionization tube sensitive to radiation of a predetermined wavelength and which is emitted by the flame. Energy storage means are employed to accumulate the signals generated by the ionization tube. The stored energy is periodically pulsed to discharge the stored energy in an intermittent manner thereby delaying the generation of a signal representing the absence of a flame. The state of the energy storage means is digitized at the aforesaid periodic rate and is restored generally to its undigitized form before controlling the delayed generation of a flame-out signal.

What is claimed is: 
     
       1. A flame control device usable with a detector head exposed to the radiation of a flame to be monitored, said detector head preferably comprising an ionization tube which develops an output signal in the presence of flame, said flame control device comprising: a chain of stages being connected in cascade fashion, each stage including at least one electrical component;   a first stage of said chain being coupled to said detector head;   a first one of all remaining stages including dynamic coupling means to stop the continuous components and to translate only energy given by the alternate components of the input signal;   a second one of said remaining stages including energy storage means for storing energy furnished by said coupling means and generating an electrical signal representative of the signal developed by said detector head;   a third one of said remaining stages including first chopper means for sampling said electrical signal;   a fourth one of said remaining stages including a threshold circuit measuring the level of the sampled signal, for developing an output signal having a first level in the presence of a flame and for developing an output signal of a second level within a predetermined period after the absence of flame.   
     
     
       2. The apparatus of claim 1 wherein said remaining stages further comprise a fifth stage comprising energy storage means coupled to said threshold circuit for converting the output state of the intermittently operated threshold circuit to a continuous signal; a sixth stage comprising a final output stage; and   a seventh stage comprising second chopper means for intermittently coupling the output of said fifth stage to said final output stage in a periodic manner.   
     
     
       3. The apparatus of claim 2 further comprising relay means coupled to the final output stage. 
     
     
       4. The apparatus of claim 2 wherein the final output stage comprises transformer means coupling the intermittent signal to said relay means. 
     
     
       5. The apparatus of claim 1 wherein said first chopper means is periodically operated by signal generator means whose operating frequency controls the sampling rate of said first chopper means. 
     
     
       6. The apparatus of claim 2 wherein said second chopper means is periodically operated by signal generator means whose operating frequency controls the sampling rate of said second chopper means. 
     
     
       7. A flame monitoring device, which receives at its input a pulse signal originating from at least one detector head exposed to the radiation of a flame, said detector head comprising at least one ionization tube activated by the presence of the flame, said flame monitoring device furnishing at its output a fail-safe signal, said flame monitoring device comprising: a chain of stages connected in cascade fashion, each stage including at least one electrical component and generating a proper output signal by the dynamic operation thereof in the event an input of that stage receives a proper signal from an output of a previous stage;   a first stage of said chain being coupled to said detector head for receiving and shaping a pulse signal from said tube;   a second stage of said chain including dynamic coupling means for translating only energy contained in a pulse signal output from said first stage and for preventing coupling of the continuous component of said first stage output;   a third stage of said chain including energy storage and dissipation means for storing the energy furnished by said second stage and generating an electric signal representative of the signal developed by said detector head;   a fourth stage of said chain including first chopper means for sampling said electrical signal from said third stage;   a fifth stage of said chain including threshold circuit means measuring the level of the sampled signal for developing an output signal having a square-wave shape in the presence of said flame and for developing an output signal having a continuous level after the absence of said flame;   a sixth stage of said chain comprising second energy storage means utilizing a first level of said square-wave signals from said fifth stage for restoring its own level of energy and utilized a second level of said square-wave signal for making said energy available for a next following stage;   a seventh stage of said chain comprising second chopper means for intermittently transferring the energy stored in said second energy storage means into an eighth stage, the energy stored being completely exhausted within a predetermined period after the absence of said flame; and   an eighth stage of said chain utilizing the energy intermittently made available by said sixth stage for developing an output signal having a square-wave shape in the presence of said flame and for developing an output signal having a continuous level within a predetermined time period after the absence of said flame.   
     
     
       8. The device of claim 7, wherein said third stage includes adjustable resistor means for calibrating the sensitivity of the device. 
     
     
       9. The device of claim 7, wherein said third stage includes switching means for selecting the sensitivity of the device. 
     
     
       10. The device of claim 7, wherein said sixth stage includes current limiting means for adjusting a delay time for response to the absence of said flame by changing the rate of energy discharge. 
     
     
       11. The device of claim 10, wherein said sixth stage includes said switching means for selecting said delay time responsive to the absence of said flame, by changing the energy discharge rate. 
     
     
       12. The device of claim 7, wherein the last stage of the chain comprises relay means whose contacts form the output signal of the device and transformer means coupled to the output of the previous stage for transferring energy to said relay means responsive to an alternation of output signal levels therefrom. 
     
     
       13. The device of claim 7, wherein a square-wave signal generator controls said first and second chopper means.