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Publication numberUS3651327 A
Publication typeGrant
Publication dateMar 21, 1972
Filing dateAug 25, 1970
Priority dateAug 25, 1970
Also published asCA996660A1, DE2142222A1, DE2142222B2
Publication numberUS 3651327 A, US 3651327A, US-A-3651327, US3651327 A, US3651327A
InventorsThomson Elihu Craig
Original AssigneeElectronics Corp America
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Radiation sensitive condition responsive system
US 3651327 A
Abstract
A condition responsive system comprises a condition sensor for producing a fluctuating output signal having a predetermined frequency component in response to sensing of the condition to be detected, an output device arranged to assume a first state indicative of the presence of the condition being sensed when the sensor senses the condition and produces the fluctuating output signal and a second state indicative of the absence of the condition when the sensor does not produce the fluctuating output signal, and means responsive to the fluctuating output signal and connected in circuit between the sensor and the output device including an inductor for blocking signals of higher frequency than the frequency of the fluctuating output signal, a capacitor connected in series with the indicator for blocking signals of lower frequency than the frequency of the fluctuating output signal and a fail safe rectification circuit connected in circuit between the series combination of the capacitor and the inductor and the output device.
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United States Patent Thomson Mar. 21, 1972 [54] RADIATION SENSITIVE CONDITION Primary ExaminerWalter Stolwein RESPONSIVE SYSTEM AttrneyWillis M. Ertman [72] Inventor: Elihu Craig Thomson, Wellesley, Mass. [57] ABSTRACT ['73] Assignee: E FZ T Corporation of America A condition responsive system comprises a condition sensor n for reducing a fluctuating output signal having a redeter- P I P [22] Filed: Aug. 25, 1970 mined frequency component in response to sensing of the condition to be detected, an output devicea'rranged to assume a [2]] Appl' 66841 first state indicative of the presence of the condition being sensed when the sensor senses the condition and produces the [52] 11.8. CI. ..250/217 F, 250/214 R, 431/79, fluctuating output signal and a second state indicative of the 34 /2282 absence of the condition when the sensor does not produce [51] InLCl. ..G08b21/00 the fluctuating output signal, and means responsive to the [58] Field of Search ..250/217 F, 214, 206; fluctuating output signal and connected in circuit between the 340/2282; 431/79; 307/233 231 sensor and the output device including an inductor for blocking signals of higher frequency than the frequency of the [56] References Cned fluctuating output signal, a capacitor connected in series with UNITED STATES PATENTS the indicator for blocking signals of lower frequency than the frequency of the fluctuating output signal and a fail safe 2,307,008 1957 ROWell X rectification circuit connected in circuit between the series I 9 1,540 1 1/1959 Powers --250/217 F combination of the capacitor and the inductor and the output 3,154,724 10/1964 Gioffrida... ...340/228.2 X device. 3,568,074 3/1971 Carroll ..307/233 X 9 Claims, 1 Drawing Figure [5K /0K 2/V5366 5 6 2/1/5232 74 l4 :0 F\ 34 39K z/vszaz l lin. //5 v 2.2% .m" m HENRY Ir 84 I2 I6 f 022 r 46 g )r I4 52/ /a0/( {j 221% 76 72 A r 44 M232 88 7 2/V5232 2/v5252 Z 32 Alf RADIATION SENSITIVE CONDITION RESPONSIVE SYSTEM SUMMARY OF INVENTION This invention relates to improved control apparatus and more particularly to condition responsive systems such as those useful in supervising fuel burning systems, and to means for insuring fail safe operation of such systems should a component thereof fail.

In condition responsive systems of the type employed for the supervision of flame in a combustion chamber, the system arrangement must reliably and accurately indicate the presence or absence of flame, the absence of flame being promptly detected so that the fuel valve may be closed quickly thus preventing an excessive amount of unburned fuel from accumulating in the combustion chamber. Malfunction of a component of such a system may cause the flame detecting system to falsely indicate the presence of flame and thus create an unsafe condition in the event of flame failure as the system would continue to react as if flame were present.

It is an object of this invention to provide a novel and improved condition responsive system in which failure of a component will not cause the system to be placed in an unsafe condition.

Another object of the invention is to provide a novel and improved combustion supervision system particularly useful with flame sensors responsive to infrared radiation.

In accordance with the invention there is provided a condition responsive system comprising a condition sensor for producing a fluctuating output signal having a predetermined frequency component in response to sensing of the condition to be detected, an output device arranged to assume a first state indicative of the presence of the condition being sensed when the sensor senses the condition and produces the fluctuating output signal and a second state indicative of the absence of the condition when the sensor does not produce the fluctuating output signal and means responsive to the fluctuating output signal and connected in circuit between the sensor and the output device including an inductor for blocking signals of higher frequency than the frequency of the fluctuating output signal, a capacitor connected in series with said inductor for blocking signals of lower frequency than the frequency of the fluctuating output signal and a fail safe rectification circuit connected in circuit between the series combination of the capacitor and the inductor and the output device.

In a preferred embodiment the system includes frequency selective means which produces a control signal only when signals applied thereto include the predetermined frequency component, and coupling means for applying output signals produced by the condition sensor to the frequency selective means. The frequency selective means produces a fluctuating control signal which alternately applies positive and negative voltages to the inductor. The resulting alternation is passed as an AC signal by the capacitor and is rectified and energizes the control device which in the preferred embodiment is a relay.

The sensed condition is fluctuating, either by nature or by electrical modulation and the system is made fail safe by passing the resulting fluctuating signal through the series inductor capacitor circuit and thereafter rectifying it. In the preferred embodiment, an amplifier is forced to preserve the fluctuating character of the signal while it amplifies it sufficiently to actuate the output device. Neither a short nor an open circuit can simulate the condition signal for either one will render the amplifier unable to pass amplify the fluctuating signal so that either type of failure is a safe failure, that is the output device will indicate the absence of the condition to be sensed. Furthermore, in this dynamic system, a static leakage condition in components cannot of itself generate a dynamic signal that can simulate the condition to be sensed. Should the capacitor in the series circuit itself develop a short circuit or leakage and pass current directly from the supply to the fail safe rectification circuit and possibly to the output device, the rectification circuit will either shunt or block that current flow. If the rectification circuit fails, by either open or short circuit or leakage, rectification will be entirely or substantially reduced so that the output device will either be partially or completely deactuated.

In particular embodiments it is preferred to provide a first shunt diode and a second diode in series between the capacitor and the output device and a second capacitor in shunt across the output device so that the charge required by the first capacitor is transferred to the second capacitor while the shunt diode is blocking and the second capacitor can then be large enough to produce a steady relay current and in addition a deactuation delay.

The series inductor in the series circuit effectively blocks power frequency signals (e.g., 60 Hertz) and signals of frequency below the pass band of the series circuit will be blocked by the capacitor. If there is sufficient signal from the condition sensor which in a particular embodiment is a lead sulfide flame sensor, the relay will be held in from the signal within the pass band despite the presence of interfering signal. If there is insufficient signal, however, the presence of an overriding spurious signal will block the response to the fluctuating condition signal and the relay will drop out in a fail safe manner.

Other objects, features and advantages of the invention will be seen as the following description of a particular embodiment progresses, in conjunction with the drawing, in which:

The single FIGURE is a schematic diagram of a system for supervising the establishment and maintenance of flame in a supervised combustion chamber.

DESCRIPTION OF PARTICULAR EMBODIMENT The circuit shown in the drawing includes a transformer 10 having a primary winding 12 which a 115 volt, 60 Hertz signal is applied at terminals 14. Its secondary winding 16 is connected to a full wave rectifier 18 which applies the rectified signal between positive bus 20 and negative bus 22. Capacitor 24 and resistor 26 are connected between buses 20 and 22. Connected to bus 20 by resistor 28 is a subsidiary bus 30 on which the voltage is maintained at plus 7 volts by Zener diode 32. Connected between buses 30 and 22 is a voltage divider network including resistor 34 and a lead sulfide photoresistive flame sensing cell 36 which is arranged to sense the existence of flame in the supervised combustion chamber. Such flame has a fluctuating characteristic within a 5 to 25 Hertz range which characteristic is sensed by photocell 36.

The fluctuating output signal from photocell 36 is applied to a first amplification stage that includes transistor 40 and a bridge T null filter in the feedback connection from the collector 42 of transistor 40 to its base electrode 44. The filter network includes capacitors 46 and 48 and resistors 50 and 52. The output of the first amplifier stage is direct coupled to a second amplification stage that includes transistors 54 and 56 and another bridge T filter that provides degenerative feedback to the emitter 58 of transistor 54. That second filter includes capacitors 60 and 62 and resistors 64 and 66. Each filter has a pass band within the 5 to 25 Hertz range of the output signal from photocell 36.

The amplified fluctuating flame signal is then coupled by capacitor 70 to a switching circuit that includes transistors 72, 74 and 76. In the quiescent condition, transistor 72 draws base current through resistor 78 from the positive supply bus 20 so that transistor 74 is cut off and transistor 76 is saturated. When the collector of transistor 56 goes positive it charges capacitor 70, drawing base current in transistor 72. On the negative swing of the collector of transistor 56, capacitor 70 couples that signal and transistors 72 and 76 are cut off and transistor 74 draws base current through resistor 80 and is switched into conductive state. The result is that the input end of inductor 82 is alternately switched between the positive bus 20 and the negative bus 22 in response to the fluctuating flame signal.

lnductor 82 and capacitor 84 form a series circuit tuned to the frequency of the fluctuating flame signal. Inductor 80 is made so that there is a fixed spacing between input and output leads and fixed turn-to-turn and layer-to-layer spacing, and therefore the inductor is as safe from short circuit failure as any two leads in the circuit wiring. lnductor 80 also has enough resistance so that it will limit the current to the shunt diode 86 in case of a short circuit in capacitor 84. Diode 86 is connected in shunt and diode 88 is connected in series between capacitor 84 and coil 90 of output relay. Capacitor 92 is connected across the coil 90. As the input end of inductor 82 is alternately switched between the positive and nega: tive buses 20 and 22 at the frequency of the sensed flame condition, typically about Hertz, the resulting alternation is passed as an AC signal by capacitor 84 and is rectified and charges capacitor 92 so that relay 90'is pulled in.

If a very large 60 Hertz signal is imposed on the detector input lead, the filters will be insufficient to block it and as a result transistors 74 and 76 will impose on inductor 82 a 60 Hertz signal whose peak to peak value is represented by the power supply voltage. With the component values shown, the inductor effectively blocks this signal and negligable current will be rectified and delivered to the relay coil. Similarly, frequencies below the pass band of the series circuit of inductor 82 and capacitor 84 will be blocked by the capacitor 84. Capacitor 92 provides a 1% second drop out time delay so that the flame flicker signal must be absent for a number of cycles before the relay will drop out.

It will be seen that this circuitry provides discrimination against single component failure and AC signals other than the desired condition signal in a simple, economical and reliable circuit arrangement. While a particular embodiment of the invention has been shown and described, various modifications will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. A condition responsive system comprising a radiation sensitive condition sensor for producing a fluctuating output signal having a predetermined frequency component in response to sensing of the condition to be detected,

an output device arranged to assume a first state indicative of the presence of the condition being sensed when said sensor senses said condition and produces said fluctuating output signal and a second state indicative of the absence of the condition when said sensor does not produce said fluctuating output signal, and

means responsive to said fluctuating output signal and connected in circuit between said sensor and said output device including an inductor for blocking signals of higher frequency than the frequency of said fluctuating output signal, a capacitor connected in series with said inductor for blocking signals of lower frequency than the frequency of said fluctuating output signal and a rectification circuit connected in fail safe cooperation between the series combination of said capacitor and said inductor and said output device.

2. The system as claimed in claim 1 wherein said rectification circuit includes a rectifier device connected in shunt with said capacitor.

3. The system as claimed in claim 2 wherein said rectification circuit further includes a second rectifier connected in series with said capacitor and a second capacitor connected in shunt across said output device.

4. The system as claimed in claim 1 and-further including frequency selective means for producing a control signal only when signals applied thereto include said predetermined frequency component, said frequency selective means including a band pass amplifier tuned to pass signals in the 5 to 25 Hertz range. and coupling means for applying output signals produced by said condition sensing means to said frequency selective means.

5. The system as claimed in claim 1 wherein said condition to be detected is flame in a combustion chamber and-said output device is the coil of a relay.

6. The system as claimed in claim 5 wherein said sensor is a lead sulfide photocell.

7. The system as claimed in claim 6 wherein said rectification circuit includes a rectifier device connected in shunt with said capacitor.

8. The system as claimed in claim 7 and wherein said rectification circuit further includes a second rectifier connected in series with said capacitor and a second capacitor connected in shunt across said output device.

9. The system as claimed in claim 8 and further including frequency selective means for producing a control signal only when signals applied thereto include said predetermined frequency component, said frequency selective means including a band pass amplifier tuned to pass signals in the 5 to 25 Hertz range, and coupling means for applying output signals produced by said condition sensing means to said frequency selective means.

IOIOZB 0689

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2807008 *May 8, 1956Sep 17, 1957Scully Signal CoFail-safe system and technique
US2911540 *Feb 14, 1955Nov 3, 1959Gen Controls CoFlame detection system
US3154724 *Oct 9, 1961Oct 27, 1964Electronics Corp AmericaCombustion control system
US3568074 *Aug 1, 1968Mar 2, 1971Gen ElectricFrequency-sensitive circuit
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3824391 *May 21, 1973Jul 16, 1974Central Electr Generat BoardMethods of and apparatus for flame monitoring
US3846061 *Mar 22, 1973Nov 5, 1974Lucas Aerospace LtdFlame-detection circuits
US3852729 *Mar 6, 1973Dec 3, 1974Electronics Corp AmericaFlame failure controls
US3947218 *Jan 23, 1975Mar 30, 1976Honeywell Inc.Safety circuit for monitoring a flickering flame
US4280184 *Jun 26, 1979Jul 21, 1981Electronic Corporation Of AmericaBurner flame detection
US4509041 *Mar 22, 1982Apr 2, 1985The Babcock & Wilcox CompanyCorrelation type flicker flamon
US5567144 *Oct 5, 1995Oct 22, 1996Desa International Inc.Hot surface ignition controller for fuel oil burner
US5899684 *Jul 11, 1997May 4, 1999Desa International, Inc.Power phase regulator circuit improvement, motor start switch, self-adjusting preheat and ignition trial improvement, and series-type voltage regulator improvement to hot surface ignition control for fuel oil burner
US6099295 *Mar 3, 1999Aug 8, 2000Desa International, Inc.Power phase regulator circuit improvement motor start switch self-adjusting preheat and ignition trial improvement and series-type voltage regulator improvement to hot surface ignition controller for fuel oil burner
EP0767344A1 *Sep 6, 1996Apr 9, 1997Desa International, Inc.Hot surface ignition controller for fuel oil burner
EP1033535A2Mar 26, 1999Sep 6, 2000Desa International, Inc.Hot surface ignition controller for fuel oil burner
Classifications
U.S. Classification250/554, 250/214.00R, 431/79, 340/578
International ClassificationF23N5/24, F23N5/08
Cooperative ClassificationF23N2029/08, F23N5/082, F23N5/242
European ClassificationF23N5/24B, F23N5/08B