|Publication number||US3540042 A|
|Publication date||Nov 10, 1970|
|Filing date||Jun 26, 1967|
|Priority date||Jun 26, 1967|
|Publication number||US 3540042 A, US 3540042A, US-A-3540042, US3540042 A, US3540042A|
|Inventors||Morrow John T, Rowley Walter E Jr|
|Original Assignee||Edwards Co|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (1), Referenced by (2), Classifications (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Nov. 10, 1970 J. T. MORROW ETAL INTEGRITY CHECK FOR FIRE ALARM CIRCUITS Filed June 26, 1967 #MBX) SOURCE I E ,ll
DETECTORS SUPERVISORY INDICATOR LAMP IN VENTORS BY W.
J. T. MORROW AND E. ROWLEY, JR.
THEIR ATTORNEY icut Filed June 26, 1967, Ser. No. 648,684. Int. Cl. G081) 29/00 US. Cl. 340-409 13 Claims ABSTRACT OF THE DISCLOSURE A normally inactive alarm circuit is energized by an alternating current and comprises two resistors and an alarm device in series. The alarm can be sounded by the operation of an alarm detector which shunts one of the resistors, and thereby increases current flow through the alarm device. A capacitor in a separate supervisory circuit is intermittently charged through a diode from a source of alternating current, and is subject to discharge each time a supervisory signal is generated across a diode which is connected in multiple With the other resistor in the alarm circuit. If a charge is permitted to build up on the capacitor, a supervisory alarm is activated.
BACKGROUND OF THE INVENTION This invention relates to integrity checking systems for alarm circuits, and it more particularly relates to an integrity checking system having solid state supervisory control apparatus.
An alarm circuit to be supervised is generally a closed circuit energized by a relatively low current for checking integrity of the circuit. The detection of an alarm condition increases the current in the alarm circuit materially by shunting a series resistor, and such increase either operates an audible alarm directly, or actuates a switching device such as a relay, which in turn operates the alarm. It is desirable to continuously check the integrity of the alarm circuit, including all of the elements required to be actuated in response to the detection of a condition for which an alarm should be given.
SUMMARY OF INVENTION The system according to the present invention has a supervisory system for continuously checking the integrity of an alarm circuit. Such alarm circuit is normally energized from an alternating current source and includes in series two resistors and a normally inactive audible alarm device, such as a bell. The detection of an alarm condition, such as the actuation of a fire detector, for example, shunts one of the resistors, which materially increases current in the alarm circuit and thereby actuates the bell.
The supervisory system senses current in the alarm circuit, and if the current in the alarm circuit is above a predetermined value, no supervisory alarm is given, but if current in the alarm circuit drops below this value, due to an open or ground fault in the wiring or in an alarm detector or alarm signal, a supervisory alarm is rendered active. This mode of operation is accomplished by super visory controls governed by sensing the potential across an inverse parallel arrangement of diodes connected in multiple with the other of the resistors in the alarm circuit. When current in the alarm is normal, there is sufiicient voltage drop across said another resistor to forward bias the diode to the break point for a portion of each alternate half cycle of the supervisory current, thus clamping the voltage across said another resistor to the forward 3,54%,42 Patented Nov. 10, 1970 ice voltage drop of the diode. When the alarm is active, the relatively heavy current in the alarm circuit is passed by the inverse parallel arrangement of diodes and the voltage across said another resistor is again clamped to the forward voltage drop of the diodes, thus protecting the supervisory control apparatus against damage and against improper operation in response to the high value of current in the active alarm circuit.
The supervisory signal comprises half wave pulses which operate a switch to intermittently discharge at capacitor, the capacitor having a separate circuit by which it is intermittently charged. Should this switch cease to operate, as by failure to generate a supervisory signal of sufiicient amplitude, the capacitor does not become discharged and a supervisory alarm is given. A timing circuit involving another capacitor is employed to delay actuation of the supervisory alarm so that the supervisory alarm is not given for a momentary interruption of the supervisory signal.
An object of the present invention is to provide a substantially fail-safe and economical supervisory alarm system for checking integrity of an alarm circuit using solid state switching means for control of a supervisory alarm device.
Another object of the present invention is to protect the solid state switching means when the alarm circuit is rendered active by use of at least one diode in a circuit shunting input to the solid state switching means.
Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.
In describing the invention in retail reference is made to the accompanying drawing which illustrates diagrammatically one embodiment of the present invention as applied to supervisory checking of the integrity of a fire alarm system.
With reference to the drawing, an alarm bell 10 is connected in an alarm circuit for manifesting .the detection of an alarm condition, such, for example, as the detec tion of a fire by closure of a contact of a normally open fire detector 11. A supervisory alarm bell 12 is connected in a supervisory alarm circuit for manifesting failure to check the integrity of the alarm circuit. A supervisory indicator lamp 13 is provided for also indicating failure to check integrity of the alarm circuit, and a manually operable switch 14 is provided for silencing the supervisory alarm bell.
The alarm circuit is energized from a suitable source of alternating current having its supply terminals designated as (BX) and (CX) respectively. This circuit comprises in series resistor 15, bell 10, contact 16 of switch 14 in its right hand position, and resistor 17. Thiscircuit normally has a relatively low current flow, particularly because of the relatively high resistance of resistor 15. The low level current in the alarm circuit flows through the alarm bell 10, but this bell is not actuated because of the relatively low current level. When a detector 11 is actuated to close its contacts, the resistor 15 is shunted, and the bell 10 is rendered active by the flow of relatively heavy current in the alarm circuit.
The circuit for the supervisory bell 12 is normally open because it includes in series a SCR switch 18, which is normally turned off. The circuit for the operation of the supervisory bell 12 is energized from a source of the nating current also having its supply terminals designated as (BX) and (CX). This circuit includes a half wave rectifier 19, winding of bell 12 and SCR switch 18.
The turning on of the SCR switch 18 in accordance with the application of a potential to its gate is in response to potential across a capacitor which in turn has its charge determined by a capacitor 21. The capacitor 21 has a charging circuit including diode 19 and resistor 22. Thus the capacitor 21 becomes charged by half wave pulses from the alternating current source for the supervisory circuit. This source may or may not be the same as the source for energization of the alarm circuit, and thus it is not necessary that the power supply used for the supervisory circuit organization be in phase with the power supply used for the energization of the alarm circuit.
A transistor Q1 is provided for intermittently discharging the capacitor 21 and thus normally prevents the capacitor 21 from charging to a potential sufficient to turn the SCR switch 18 on. The transistor Q1 has its collectoremitter circuit connected across the capacitor 21 and its base-emitter circuit connected through a resistor 23 across resistor 17 in the alarm circuit and across an inverse parallel arrangement including diodes 24 and 28. If the transistor Q1 and the diode 24 are of the same material, it may be desired to use two diodes in series to replace diode 24 in order to obtain the best operating characteristics of the system.
The diode 24 is forward biased by the voltage drop across the resistor 17, and when the alarm circuit is in its normal condition, with a relatively low current flowing, this voltage drop is sufficient to render the diode 24 conductive above its break point. Thus a sufiicient voltage drop appears across the base-emitter circuit of transistor Q1 during each alternate half cycle of the energization of the alarm circuit of a particular polarity to turn the tran sistor Q1 on, and thus to discharge the capacitor 21. If the capacitor 21 is discharged intermittently by this discharge circuit organization, it cannot apply any substantial charge to the capacitor 20 through resistor 25. Thus the switch 18 is normally maintained in its turned off condition. Any charge which is applied to capacitor 20, is dissipated through resistor 26.
If the current falls below a predetermined value, the voltage developed across resistor 17 will be of too low a value to turn on transistor Q1 sufliciently to cause complete discharge of capacitor 21 on each alternate halfcycle. Capacitor 21 thus becomes fully charged through the diode 19, and it in turn charges capacitor 20 through resistor 25. After capacitor 20 has had time to become charged, positive potential on the gate of switch 18 turns the switch 18 on and the supervisory bell 12 is rendered active. Also the indicator lamp 13 is illuminated because it is connected in multiple with the bell 12 through contact 27 of switch 14. The sounding of the supervisory bell 12 attracts the attention of an operator, and the operator can silence the bell but still maintain the indicator lamp 13 illuminated by operation of the switch 14 to its left hand position.
With the switch 14 in its left hand position a connection is made in the alarm circuit through contact 16 to bypass the resistor 17. Current flowing through the lamp 13, contact 27 of switch 14 in its left hand position and resistor 1'7 in the alarm circuit, provides suflicient bias for the transistor Q1 to cause transistor Q1 to be active and thus to shunt the capacitor 21 each time it is energized through the diode 19. Thus the capacitor 20 becomes discharged, and the switch 18 is turned oil to silence the supervisory bell 12. The indicator lamp 13 remains on, however, to indicate to an operator that the alarm has been sounded and that the system has not yet been restored to its normal condition by operating the switch to its right hand position.
It is thus provided that with the manual switch 14 in its normal position, current in the alarm circuit passes through resistor 17, and with the manual switch 14 in its left hand position, the current for lamp 13 passes through the resistor 17. Either current renders the transistor Q1 active to intermittently discharge the capacitor 21, and this holds gate voltage below the turn on point for the switch 18.
Should the lamp 13 become burned out, or removed, the supervisory bell 12 cannot be silenced by operating the manual switch 14 to its left hand position, thus calling attention to this condition.
Resistor 17 in the alarm circuit is shown as being variable so that the sensitivity of the supervisory circuit can be adjusted to determine the minimum current required in the alarm circuit to prevent activation of the supervisory bell 12. Diode 28 is preferably used in multiple with resistor 17 to provide a low resistance path for the other half cycle during alarm conditions as compared to the half cycle current through diode 24.
Having thus described one embodiment of an integrity checking system for alarm circuits, it is desired to be understood that this form is selected to facilitate the disclosure of the invention, rather than to limit the number of forms the invention can assume. While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than of limitation, and that changes within the purview of the appending claims can be made without departing from the true spirit and scope of the invention in its proper aspects.
What is claimed is:
1. A supervisory indication system for checking the integrity of an alarm circuit which is normally energized by alternating current and has a series an audible alarm device and a plurality of resistors wherein a low level alternating current is normally present and is shifted to a higher level current by shunting one of the resistors when an alarm is to be sounded, and wherein the improvement comprises,
(a) at least one diode connected in parallel with the other resistor for generating a pulsed direct current supervisory signal across the other resistor and diode in parallel characteristics of the presence of current in the alarm circuit when the voltage drop across said other resistor is sufficient to forward bias the diode, thus clamping the supervisor signal to the forward voltage drop of the diode,
(b) a first capacitor for storage of a control signal,
(c) means independent of the supervisory signal for intermittently charging the capacitor,
(d) means responsive to the pulsed direct current supervisory signal for intermittently discharging the capacitor, and
(e) supervisory alarm means governed by the control signal for manifesting when current in the alarm circuit is below a predetermined value.
2. The invention according to claim 1 wherein the supervisory alarm means comprises a normally inactive supervisory alarm device controlled by a solid state switching means, and means is provided for turning the switching means on to activate the supervisory alarm device in response to an abnormally high control signal stored by the first capacitor.
3. The invention according to claim 2 wherein the supervisory alarm means includes an indicator lamp that is energized in response to the turning on of the solid state switching means.
4. The invention according to claim 3 wherein control means including a manual control switch is provided for permitting operation of the supervisory alarm device and the energization of the indicator lamp when the switching means is in one position, and for energizing the indicator lamp and preventing operation of the device when the switching means is in another position.
5. The invention according to claim 4 wherein the control means permits the supervisory alarm device to be silenced by actuation of the switching means to said another position only provided there is a closed circuit through the indicator lamp.
6. The invention according to claim 5 wherein the con- F trol means is effective to activate the supervisory alarm device upon the indicator lamp becoming open circuited when the switching means is in said another position.
7. The invention according to claim 1 wherein means for discharging the first capacitor comprises a circuit through a solid state switching means, and control means is provided for turning the solid state switching means on intermittently in response to the pulsed direct current supervisory signal.
8. The invention according to claim 7 wherein the solid state switching means is a transistor having its baseemitter circuit connected in multiple with said another resistor.
9. The invention according to claim 1 wherein timing means including a second capacitor is provided for delaying the response of the supervisory alarm means to a control signal stored by the first capacitor.
10. A supervisory indication system for checking the integrity of an alarm circuit which is normally energized by alternating current and has in series an audible alarm device and a plurality of resistors wherein a low level current is normally present and is shifted to a higher level current by shunting one of the resistors when an alarm is to be sounded, and wherein the improvement comprises,
(a) a diode connected in parallel with the other resistor for generating a pulsed direct current supervisory signal across the diode characteristic of the presence of current in the alarm circuit, whereby the amplitude of the signal is limited when the diode is forward biased beyond its break point, and (b) supervisory alarm means including a normally off solid state switching means and governed by the supervisory signal for manifesting when current in the alarm circuit is below a predetermined level. 11. The invention according to claim 10 wherein gating circuit means is provided for said solid state switching means to turn the solid state switching means on when the supervisory signal is below a predetermined value.
12. The invention according to claim 11 wherein manually operable switching means is provided for normally connecting said another resistor in the alarm circuit and at other times connecting said another resistor in another circuit for lowering the gate potential on the solid state switching means to a point where the solid state switching means is maintained turned oil.
13. The invention according to claim 12 wherein said another circuit includes an indicator lamp.
References Cited UNITED STATES PATENTS 3,010,100 11/1961 Muehter 340409 THOMAS B. HABECKER, Primary Examiner U.S. Cl. X.R. 340-1 76
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3010100 *||Jun 30, 1958||Nov 21, 1961||American District Telegraph Co||Direct current operated burglar alarm system with alternating current supervision|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US4253091 *||Jan 5, 1977||Feb 24, 1981||Mobil Oil Corporation||Method and apparatus for detection of alarm conditions|
|US4529970 *||Oct 18, 1982||Jul 16, 1985||Baker Industries Inc.||Supervision system for monitoring the integrity of a transmission line|
|U.S. Classification||340/502, 340/511, 340/507, 340/512, 340/593|
|International Classification||G08B29/06, G08B29/00|