US 3906474 A
A combustion products detector of the ionization chamber type comprises a reference ionization chamber and a signal chamber arranged in series for connection across a direct current source such as a dry battery. An insulated gate field effect transistor is arranged with its drain electrode for connection to the high side of the source, and with its source electrode to the law side; its gate is connected to the common junction of the chambers; a high resistance is connected across the chambers in parallel. A control amplifier supplies the signal to a circuit for producing a preliminary alarm or proximity signal upon a predetermined increase in combustion product density in the signal chamber and a full alarm upon an additional increase. The alarm may be produced as a throbbing or undulating sound.
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Description (OCR text may contain errors)
United States Patent 1191 Lehsten 14 1 Sept. 16, 1975 COMBUSTION PRODUCTS ALARM  Inventor: George S. Lehsten, Englewood,
 App]. No.: 358,111
 US. Cl. 340/237 S; 250/384  Int. Cl. G08b 17/10  Field of Search 340/237 S; 250/381, 382,
Primary Examiner--John W. Caldwell Assistant Examiner-Daniel Myer Attorney, Agent, or Firm-Wm. Griffith Edwards [5 7 ABSTRACT A combustion products detector of the ionization chamber type comprises a reference ionization chamber and a signal chamber arranged in series for connection across a direct current source such as a dry battery. An insulated gate field effect transistor is arranged with its drain electrode for connection to the high side of the source, and with its source electrode to the law side; its gate is connected to the common junction of the chambers; a high resistance is connected across the chambers in parallel. A control am- 56 References Cited 1 UNITED STATES PATENTS plifier supplies the signal to a circuit for producing a preliminary alarm or proximity signal upon a predeter- 2,l45,866 2/ 1939 Fa1lla 250/385 mined increase in combustion product density in the 3,665,441 5/1972 Suchomel 6! a]. 340/2375 signal chamber and a alarm p an additional i 3,676,680 7/1972 Sche1dwe1ler et al... 340/2375 crease The alarm ma be reduced as a throbbin or 3,737,731 6/1973 Zeewy 340 331 x d d y p 3 3,795,904 3 1974 Beyersdorf et al. 340/237 s 3,801,972 4/1974 Kim et al. 340/2375 X 3 Claims 1 Drawing Figure c TEST SWITCH CHAMBERS i L X GI J PATENIEB SEP IS 5975 COMBUSTION PRODUCTS ALARM This invention relates to combustion product detectors and particularly to an improved detector "of the ionization chamber type. I
Numerous circuits have been provided heretofore for the purpose of utilizing ionization chamber detectors for actuating fire indicators and alarms. These circuits have proved useful to varying degrees depending upon the conditions prevailing andthe nature of the applica tions of the circuits. Reliability and consistent operation of fire detectors over a wide range of ambient conditions are desired and, accordingly, it is an object of this invention to provide an improved reliable combustion product detector of the ionization chamber type. i It is another objectof this invention to provide a combustion product detector of the ion chamber type including an improved circuit for operation from an electric battery as a direct current source. I i
It is a further object of this invention to provide an improved combustion product detector including an arrangement for providing a preliminaryvvaming before the energization of an alarm.
Briefly, in carrying'out the objects of this invention in one embodiment thereof, two ion chambers, one a reference, the other a signal chamber are connected in series with a variable resistance across a DC. source. An insulated gate field effect transistor is connected across the source with its gate connectedtothe junction between the chambers. Upon increase product in the signal chamber a control transistor energizes a unijunction oscillator which actuates a light emitting diode causing it to flash periodically to warn of the proximity of alarm conditions and which upon further increase of product, glows steadily before the circuit activates the alarm. i m
The features of ovelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. The
inventionitself, however, both as to its organization and its manner of operation, together with further ob jects and advantagesthereof, will best be understood upon reference'to the following description taken in connection with the accompanying drawing, the single FIGURE of which is a schematic diagram of a'combustion products detectorernbodying the invention.
Referring 'now to thedrawings, two ionization chambers l and 11 are connected in series with a dual potentiorneter circuit 13 across a direct current source which has been illustrated as a battery comprising two units 14 and 15. A loading resistor 16 is connected in parallel with thetwo chambers. The resistance 16 may be of the order of 2 meghohms. The circuit 13 in addition to a resistance 17 includes'a fixed resistance 18 and an adjustableresistance 19. Theresistance 17 is connected to the junction of the resistances 18 and 19 by an adjustable contact 21 and the resistance 19 is connected as a potentiometer by an adjustable contact 22 which shorts out a selected portion of the resistance toward the high potential end thereof. The testswitch sphere about the detector. The junction of the two chambers is connected to the gateof a field effect transister 24, the gate being indicated at 25. Transistor 24 is of the insulated gate type'and is an N-channel depletion mode metal oxide silicon field effect transistor. The transistor is connected across the direct current supply, its drain electrode being connected to the high potential side of thesupply and its source electrode being connected to the low side through a resistance 26. When a change in combustion product density occurs in the ionized chamber 11, this changein density of the product decreases the current through the circuit of the chambers and increases the potential at the gate 25; as a result current flows through the transistor 24 and a control transistor 27 which has its base con nected to the junction between the source of the transistor 24 and the resistance 26 conducts. Thecollector of the transistor 27 is connected to a circuit including a unijunction transistor 28 connected as an oscillator having its base-two connected to the high side of the DLC. source and its base-one connected to the collector through resistances 30 and 31 in series. A light emitting diode 32 is connected across the resistor31." The emitter of the unijunction 28 is connected to the high side of the source by a resistance 33 and to the collector of the transistor 27 by a capacitance 34 thus completingthe oscillator circuit. During operationof the oscillator the light emitting diode 32 flashes and indicates that the combustion product density is'approaching alarm condition. As a predetermined further increase of the potential difference between the supply and the transistor 27, a Zener diode 35, connected in series with the winding of an alarm relay indicated at 36, conducts and the diode glows steadily. On a further increase of -voltage difference, which in the alarm condition, the wind ing 36 is energized to actuate the relay and move a switch 37 to its upper position thereby' connecting an alarm circuit'38 across the battery comprising the units 14 and 15. A unijunction transistor 40 is connected as an oscillator across the direct current source by "resistanc es 41 and 42 and with its emitter connected to the common junction of a resistance 43 and capacitance 44. The base-one terminal of the unijunction 40 is connected through a diode 45 to the base-one terminal of a unijunction 46 which is connected to the high side of the source through a resistance 47, the base-two terminal being connected to the low side through a line 48. A resistance 50 and a capacitance 51 connected in series across the source have their common junction connected to the-emitter of the unijunction 46, as indicated at 52, and complete the oscillator circuit. The unijunction transistor 46 is a lower frequency oscillator which acts as a warbler" modifying the sound effect produced by the oscillation rate of the unijunction oscillator 40. The output of the oscillator 40 is suppliedto the base of a transistor amplifier 53 through a resistance 54. The amplifier 53 when conducting energizes a winding 55 of a horn or loudspeaker 56 and the periodic output of the oscillator 40, modified at the lower rate by the oscillator 46, is reproduced as the warning sound by 'the horn 56.
In order to minimize drain on the battery 14 and 15 a diode 57 is connected in the emitter circuit of the transistor 27 which has been illustrated as connected to the common junction of the two battery sections. The
diode 57 prevents reverse flow and drain from the battery 15.
The circuit of this invention makes it possible to calibrate the detectors by means of a simple D.C. voltmeter. When the transistor 27 is not conducting, the voltage between the test points, indicated at ,60 and 61, is the same, however, when the transistor conducts the voltage increases with increase in the current through the transistor and hence through the resistances 30, 31 and 33 and the unijunction 28. This voltage varies directly with the density of the combustion product in the chamber 11 and is an indication of that density and may be used to monitor the performance of the detector. The maximum voltage between the test points 60 and 61 immediately prior to energization of the relay winding is an accurate indication of the calibration setting of the detector for alarm operation. This voltage may thus be used for calibrating the detector by adjustment of the potentiometers to obtain alarm operation at a preselected density of product in the chamber 11.
The alarmaactuating voltage across the relay winding 36 and the Zener diode 35 in series is the same for all combustion product densities. The density of product at which the voltage is attained is determined by the setting of the .potentiometer 17 which is the sensitivity control of the circuit. With no product in the chamber 11 the voltage across the test points is substantially zero. With a selected setting of the sensitivity potentiometer, the voltagebetween zero and the alarm voltage indicates the product density inthe chamber 11. A D.C. voltmeter may thus be employed to determine the state of operation of the detector and also to calibrate the detector. t
In initial calibration the potentiometers may be set for-a fractional portion of the alarm density by subjecting the chamber 11 to product of such density and setting the potentiometer to the corresponding fractional setting of the voltage across the terminals 60 and 61. The detector will then operate to produce a voltage across the test terminals proportional to whatever density of ,product is present in the sampling chamber. By following these voltage measuring procedures, a large number of like detectors may be calibrated by calibrating a first detector using product densities in the chamber 11 'to obtain the calibrations and corresponding voltages of the first detector, and then setting all other detectors accordingly and using voltages measured at the test terminals for this purpose. Thus, it is not necessary to use the samples of combustion product for calibration of the other detectors of like construction.
As an illustration of a working embodiment of the present invention and for purposes of example and not by way of limitation, a detector having a circuit connected as shown in the drawing and having the component values set forth below, operated successfully over an extended period of time and with a large number of operations due to the presence of combustion product in the test or sampling chamber 11. The chambers and 11 were cylindrical, the chamber reference having a volume of about 0.8 cubic inches and the sampling chamber being about percent larger.
The transistors were as follows: 24 field effect transistor MU-6l2, the unijunctions 28, 40 and 46 were all type 2N487l, diode 32 was a light emitting diode type NVlOB, the control transistor 27 was a type 2N3643, the transistor 53 type 2N6099, the diodes 35 and 57 were type 1N4l48, the Zener diode 35 was type IN746A, the resistances were as follows:
17 and 19 one megohm 16-2 meghorns 18-390,000 ohms 33 and 43, 10,000 ohms 2682,000 ohms 31-1 ,000 ohms 50-1 2,000 ohms 41 and 47 180 ohms 42 and 54 ohms The capacitors 35 and 51, 50 microfarads 44 one-tenth microfarad While the invention has been described in connection with a specific embodiment thereof, various modifications and applications will occur to those skilled in the art. Therefore, it is not desired that the invention be limited to the details illustrated and described and it is intended by the appended claims to cover all modifications which fall within the spirit and scope of the invention. 1
What is claimed is: i C
l. A combustion product detector of the ionization chamber type comprising:
a. a reference ionization chamber and a sampling ionization chamber connected in series,
b. means including a variable resistor for connecting said chambers-in series therewith across circuit terminals for connection to a direct current supply,
c. a field effect transistor having source and drain and gate terminals, said. gate terminal being connected to the junction between. said chambers, and said source and drainterminals being connected across said circuit terminals in series with an output resistance, said field effect transistor being responsive to potential changes across said sampling chamber for providing a signal in proportion thereto, and
d. means dependent upon a first predetermined signal at the output of said field effect transistor for indicating the approach of an alarm condition, and
e. means dependent upon a second predetermined signal at the outputof said field effect transistor for initiating an alarm indication,
saidmeans dependent on a first predetermined signal at; the output of said field effect transistor further including a light emitting element and an oscillator for repetitively energizing said element beginning upon occurance of the first predetermined signal at the output of said field effect transistor and continuing through attainment of the second predetermined signal at the output of said field effect transistor,
said detector further including means dependent upon a predetermined signal at the output of said field effect transistor for utilizing said signal to produce an alarm indication, said signal dependent means including a control amplifier comprising a transistor connected in series with a third resistance across said source and having its base connected to the output of said field effect transistor, and wherein:
the oscillator comprises a capacitor connected in series with a portion of said third resistance and said control amplifier across said supply, and a unijunction transistor connected in series with another portion of said third resistance across said first portion and said capacitor and with its emitter connected to the junction of said capacitor and said first portion, and
the light emitting source comprises a light emitting diode connected in parallel with at least a portion of said third resistance between said unijunction transistor and said control amplifier.
2. In a combustion product detector of the ionization chamber type including a sampling chamber and :1 reference chamber, means for producing an output signal proportional to the density of combustion product in the sampling chamber, means for producing an amplified voltage proportional to said output signal, and 1 means dependent upon a predetermined amplified voltage for actuating an alarm indicator, the method of calibrating the detector for determination of the density of combustion product in said sampling chamber which comprises:
introducing combustion product of a predetermined alarm density in the sampling chamber; adjusting the voltage across the sampling chamber to produce an amplified voltage sufficient to effect actuation of the alarm indicator; and, thereafter, determining the density of combustion product in the sampling chamber as the proportion of the predetermined alarm density in the ratio of the amplified voltage resulting from such product to said alarm actuation voltage. 3. The method of calibrating a plurality of like combustion product detectors each of the ionization chamber type including a sampling chamber and a reference chamber, means for producing an output signal proportional to the density of combustion product in the sam pling chamber, means for producing an amplified voltage proportional to said output signal and means dependent upon a predetermined amplified voltage for actuating an alarm indicator, comprising the steps of: providing like means for adjusting the voltage across the sampling chamber of each of said detectors; providing means for measuring the amplified voltage on each of said detectors; introducing a density of product to the sampling chamber of one of the detectors, the density being a selected fraction of the alarm density desired, while the one detector is in operation adjusting the voltage across the sampling chamber to provide an amplified voltage equal to the same fraction of the alarm voltage as the selected fraction of the alarm density, and calibrating each of the other detectors of said plurality by setting the respective means for adjusting the voltage across the sampling chamber to the same adjustment as that of said one detector.