US3866194A

US3866194A - Annunciator circuit

Info

Publication number: US3866194A
Application number: US343571A
Authority: US
Inventors: Richard A Lawton
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-03-21
Filing date: 1973-03-21
Publication date: 1975-02-11
Anticipated expiration: 1992-02-11

Abstract

An annunciation circuit is provided for an alarm signalling device, which annunciator causes a continuous indication of operation of the alarm signalling device after such operation. The indication is usually from a solid state light emitting device which is triggered from an SCR. The gate or driving circuit for the SCR is in series with a switch within the alarm signalling device, and is arranged to trigger the SCR only after the switch has operated. The SCR is in series with the solid state light emitting device and latches so that the light emitting device is maintained ''''on'''' until such time as power is temporarily removed from the circuit. A plurality of alarm signalling device may be powered from a single source and may operate a single alarm; and a simple visual inspection either of the annunciator board or of the devices themselves will show which device operated because the light or other annunciation will remain on until the SCR latch circuit is disconnected from its power source.

Description

United States Patent 1 [111 3,866,194

Lawton Feb. 11, 1975 ANNUNCIATOR CIRCUIT [76] Inventor: Richard A. Lawton, 235 Cassandro 'm l Caldwell Blvd 717 Don Mills Ontario, Assistant Examiner-Richard P, Lange Canada 22 Filed: Mar. 21, 1973 [57] ABSTRACT An annunciation circuit is provided for an alarm sig- [211 Appl' 343571 nalling device, which annunciator causes a continuous indication of operation of the alarm signalling device 52 15, 3 340 213 340/2131 340/415 after such operation. The indication is usually from a 340/248 R solid state light emitting device which is triggered [51] Int. Cl. G08b 23/00 from The gate driving Circuit for the SCR 5 Fidd f Search N 340/213 R, 252 R, 25 is in series with a switch within the alarm signalling de- 340/243 R 255 415 2131; 317/9 D 36 T vice, and is arranged to trigger the SCR only after the 200/1 7 switch has operated. The SCR is in series with the solid state light emitting device and latches so that the [56] R f e Ci d light emitting device is maintained on until such UNITED STATES PATENTS time as power is temporarily removed from the circuit. A plurality of alarm signalling device may be powered 58 from a single source and may operate a single alarm; 3525988 8/I970 Under n 340/4l2 and a simple visual inspection either of the annuncia- 3:546:692 12/1970 Salzel. H 340/412 tor board or of the devices themselves Wlll show which 3.543399 12/1970 Monigal et alm 340/415 device operated because the light or other annuncia- 3,688,294 8/1972 Erpelding 340/415 tion will remain on until the SCR latch circuit is dis- 3,696,364 10/1972 Lavelle 340/213 R connected from its power source. 3,706,087 12/1972 Berns 340/213 R 3,706,088 l0/l966 Jorgenson 340/213 R 3 Clams, 2 Drawlng Flgures PMENTEBFE H915 3866,19 1

ALARM FIG I ANNUNCIATOR CIRCUIT FIELD OF THE INVENTION This invention relates to alarm signalling devices; and particularly to annunciator or indicating circuits therefor which provide a continuous indication of the operation of an alarm signalling device. The circuits provided by this invention are particularly useful in such alarm signalling devices as rate-of-rise of temperature and/or maximum or minimum temperature sensing devices; and the invention may equally be useful in other such devices as over speed sensors, flow sensors, etc.

BACKGROUND OF THE INVENTION As noted, this invention is particularly useful in such installations of alarm signalling devices as thermal devices which may signal a rate-of-rise of temperature in excess of a predetermined rate, or a temperature in excess of a predetermined temperature, etc. Such devices are very often found in large industrial or public buildings. Very often an installation of a plurality of thermal detectors of the sort usually found in such buildings may include a number [up to a dozen or more ]of like devices which are connected to a single alarm circuit. For example, all of the devices on a floor or a group of floors of a building, or in a particular area of a building, may be connected to a single alarm circuit. Operation of any one of the devices causes an alarm signal to be given, at such receiving stations as central watch stations, police or fire department headquarters etc. Likewise, a plurality of other types of sensors or alarm signalling devices may be used in buildings, industrial processes, etc., where several devices may be connected to a single alarm circuit. In all such circumstances, however, whan an alarm is given especially in response to a transitory alarm condition, or as a result of a temporary fault it is usually not possible to determine which one of the alarm signalling devices has caused the alarm signal to be activated. Thus, an individual-inspection of each alarm signalling device may be required to determine which device cause the alarmsignal.

In such installations as thermal detector installations where a plurality of like temperature and rate-of-rise devices which may, in fact, be the same devices each having the ability to trip or cause an alarm under either or both of two pre-set alarm conditions, there may be intermittent operation of one of the devices which may be false in which case, the device is faulty or which may be as a result of transitory temperature rise or maximum temperature conditions in excess of the permitted limits, but which may last for a period of only a few seconds. Nevertheless, an alarm signal would have been caused; and in such circumstances it may be very helpful to know which of the devices has operated. If the device itself is faulty or set to operate at limits which are too low, it may be very difficult to discover such device. It is therefore desireable than an annunciation or indication be given either at an annunciator board or at the device itself whenever the device operates to cause an alarm signal; and that such annunciavices on the same alarm circuit. Power for operation of the device may be derived from the alarm circuit, or independently, as discussed hereafter.

During the installation, it is helpful to be able to test the operation of an alarm signalling device; and to check the continuity of the alarm circuit. Likewise, it is helpful in two-wire alarm circuits to make each power utilization device to be polarity insensitive: i.e., so that each device, especially a solid state circuit, which may operate no matter which direction the impressed voltage across such device may be. Indeed, it may be contemplated that in certain conditions, alarm signalling devices may be desired to have annunciators associated therewith which would operate with an AC voltage impressed across them rather the the usual DC voltage. It should be noted that most such alarm signalling circuits operate at a low DC voltage, which is easier to handle than a high voltage, and which can assure better quality power than low voltage AC which might be subject to waveform or other distortion. In any event, it may happen that a technician, when installing a plurality of alarm signalling devices in a two-wire alarm circuit, might accidentally reverse the polarity of connection of one device relative to another.

It is desirable to provide an annunciator or indicator circuit which has the smallest possible physical volume, so that it may be installed easily in the base or container of an alarm signalling device, and which provides circuit reliability and assurance of operation over a long period of time. Thus, the present invention is particularly related to annunciator circuits for alarm signalling devices where the annunciator comprises a light emitting semi-conductor device usually, a light emitting diode in series with a gating and latching device. The gating and latching device which is usually employed in such circuits is a synchronous switch operable from a gate circuit which in turn is fired from a control circuit. The most common of such device is a silicon controlled rectifier (SCR). An SCR is also a device which latches; i.e., once the SCR closes so that it becomes conductive, it will not re-open until power if removed from the cathode-anode circuit of the SCR. This is especially important in such circumstances as those discussed above, where an alarm signalling device may have intermittent operation which causes the opening or closing of a single-pole switch. After such a switching operation, an SCR which is fired or turned on in response to a control circuit which in turn is responsive to the switching operation within the alarm signalling device, then provides a latching function to assure the continuing indication of the fact that a switching operation has taken place.

Several different control circuits which control the gate of an SCR are contemplated by this invention. They include a voltage dropping network to provide sufficient gating and latching voltage for an SCR, in series with a circuit having a time delay (for DC operation, a parallel RC circuit) so as to avoid inadvertent operation due to external field conditions such as transient voltages, radio frequency interference, etc., and a transistor circuit which is operative to gate the SCR to its latched condition only after the occurrence of a switching operation within the alarm signalling device.

BRIEF SUMMARY OF THE INVENTION It is an object of this invention to provide an annunciator circuit for an alarm signalling device, which may be installed either within the device or at a remote annunciator board, and which provides a continuous indication of the fact that the alarm signalling device with which the annunciator is associated has caused an alarm signal to be given by its own operation.

Another object of this invention is to provide a lowpriced, solid state annunciator for use with an alarm signalling device, where the annunciator circuitry is physically quite small.

Yet another object of this invention is to provide an annunciator device that gives a continuing like indication of the fact that a switching operation has taken place in an alarm signalling device, where such indication is continued until power to the annunciator circuit is at least temporarily interrupted.

A still further object of this invention is to provide a low power utilizing annunciator device for use with alarm signalling devices, as spoken of above.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features and objects of the present invention are more fully described hereafter in association with the accompanying drawings, in which:

FIG. 1 is a circuit of a preferred embodiment. of an annunciator device in accordance with this invention and FIG. 2 is a circuit of an alternative preferred embodiment of an annunciator device in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As noted above, an alarm signalling device such as a thermal device which causes an alarm signal to be actuated either upon the sensing by the device of a rate-ofchange of temperature faster than a predetermined rate, or upon the sensing of a temperature higher (or lower) than a predetermined temperature, may be connected to an alarm circuit together with a plurality of like devices. Each of those devices is therefore a switching device, and an alarm condition causes a change of the switch condition of at least a single pole of a switch within the device. In the usual installations, the switches within alarm sensing devices are normally open switches, so that when the devices are monitoring but not in alarm status, there is little or no current or power consumption. Normally closed switches may, however, by used to provide an indication at a power source of the continuing operation of the circuit in monitoring or standby condition.

FIG. I shows a circuit in accordance with this invention, having

input terminals

10 and 12 which are connected to the input terminals of a diode bridge indicated generally at 14. The output terminals of the diode bridge 14 are indicated at 16 and 18, being the positive and negative output terminals of the diode bridge, respectively. Obviously, the power source to which terminals l and 12 may be connected can comprise an alarm circuit where the alarm signalling device includes only a single-pole single-throw switch, as discussed hereafter. The circuit to which terminals and 12 are connected may have an AC or a DC voltage across it, and either of

terminals

10 or 12 may be connected to the positive side or the negative side of such circuit when it is DC. In any event, the output terminals of the diode bridge 14 provide a polarized DC; so that the entire circuit is insensitive to polarity of the power source at

terminals

10 and 12. For purposes of this discussion,

however, the power source for the circuit to be discussed hereafter may be considered to be the positive and

negative terminal

16 and 18, respectively of the diode bridge 14.

Likewise, a capacitor 20 may be connected between

input terminals

10 and 12, for extreme noise suppression of noise on the input power lines if necessary.

A switch 22 is shown in FIG. 1, with one side thereof connected to the power source in this case, terminal 16 of diode bridge 14. As noted, switch 22 may be a single-pole single-throw switch, leaving aside any consideration of another pole of the switch which is discussed hereafter with respect to an alternative embodiment of the circuit of FIG. 1. Switch 22 is the switch within the alarm signalling device whose switching operation causes an alarm signal to be activated. However, as noted above, the operation of the switch 22 may be transitory, as a result of alarm conditions which occur for only a very short period of time, faulty operation of the alarm signalling device per se, or for other reasons. Thus, the circuit of FIG. 1 is provided to cause an annunciation or indication of a switching operation of the switch 22, unless that switching operation is for a very short time which is less than the time constant of an RC circuit to be discussed hereafter; and even though the switch 22 may restore to its standby condition, the annunciation will continue.

The annunciator which is most commonly used is a light emitting diode 24; although other lamp means or annunciator means such as relays, etc., may be used. In series with the light emitting diode 24 is a resistor 26 whose function is to limit the operating current to the light emitting diode 24 upon activation of the annunciator operation of the circuit. An SCR 28 is also in series with the light emitting diode 24; and the cathode side of the SCR may be connected to the negative side 18 of the diode bridge 14.

A resistor 30 is in series with the switch 22, and the side of resistor 30 which is remote from the switch 22 i.e., junction 32 is connected to the gate of SCR 28. A further resistor 34 is connected in series with resistor 30 from junction 32 to terminal 18 of diode bridge 14; so that

resistors

30 and 34 may form a voltage divider string. A capacitor 36 is arranged in parallel with resistor 34 to form an RC circuit, whose time constant is determined by the values of the capacitor and resistor within the circuit.

The operation of the circuit as it has been described so far, is as follows. If switch 22 closes, capacitor 36 begins to charge, and if the switch 22 remains closed for a longer time than the time constant of the

RC circuit

34, 36 so that capacitor 36 becomes fully charged, the voltage at junction 32 between

resistors

30 and 34 become such as to fire SCR 28 to make it conductive. The values of

resistors

30 and 34 are chosen having regard to the usual operating circuit voltage, the firing voltage required for SCR 28, etc. When SCR 28 fires and becomes conductive, current flows through current limiting resistor 26 and the light emitting diode 24. Thus, the light emitting diode causes an annunciation or indication of the fact that a switching operation of switch 22 has occurred. As noted previously, the light emitting diode 24 may be replaced with other current operated devices such as relays, small lamps, etc., whose operation and indication would continue only so long as current continued to flow through such indicating devices. If, at any time after the SCR 28 has fired, switch 22 opens once again, there will be no effect on the circuit because the SCR would remain latched i.e., conducting and the light emitting diode 24 would continue to be operative. Obviously, the only way that the annunciator or indicator can become non-operative is to at least temporarily remove the circuit from the power source. This may conveniently be achieved by opening a normally closed switch such as switch 38.

If the switch 22 is ganged as one pole of a singlethrow switch having more than one pole, such as to switch 40 in FIG. I, the operation of the circuit remains essentially as discussed above, except as follows. Either switch pole 22 or switch pole 40 may be the switch within the alarm signalling device whose operation is predicated on the existence of an alarm condition. The other of the poles of the switch is ganged so that, in this case, a two-pole single-throw switch is achieved. Switch 40 may be connected to an alarm circuit 42, whose nature is not relevant to this invention. In any event, it is now seen that the power source for the alarm circuit is independent from the power source for the annunciator circuit including the light emitting diode 24, SCR 28 and the control circuitry therefor. Operation of the annunciator circuit is therefore independent of any fault condition e.g., an open circuit which may occur in the alarm circuit. Similarly, operation of the detector and annunciator circuitry maybe proven, and continuity at least of the annunciator circuitry proven, without causing an alarm signal to be given such as at a central control receiving station, by suitable manipulation at the device itself.

An alternative embodiment of an apparatus according to this invention is illustrated in FIG. 2, where like numerals indicate like circuit elements. In the circuit of FIG. 2, the collector of a transistor 44 is connected at junction 46 to the gate of SCR 28. Also connected to junction 46 is a resistor 48. Resistor 48 and a resistor 50 are each connected to terminal 16 of the diode bridge 14, and the other side of resistor 50 is connected to the base of transistor 44. Switch 22 is also connected, in this instance to the base of the transistor 44, and to terminal 18 of thediodebridge 14.

In the same manner as discussed above, the switch 22 may be one pole ofa multiple-pole single-throw switch.

In the circuit ofFIG. 2, where switch 22 is a normally open switch, the transistor 44 is maintained in its con ducting state by the voltage across it, as seen at its base from resistor 50. The voltage at junction 46, and thus at the gate of SCR 28, is such that the SCR remains open and nonconductive. However, when switch 22 closes, even temporarily, it causes a base to emitter short circuit on transistor 44, thereby turning transistor 44 off so that it become non-conductive. The voltage at junction 46 therefore tends to go upwards to the voltage at terminal 16, or at least until the firing voltage of SCR 28 is reached whereupon the SCR fires and latches. The voltage at junction 46 thereafter collapses.

If switch 22 in FIG. 2 is opened after it has been closed and SCR 28 has fired, the SCR remains latched in the same manner as discussed above, and the light emitting diode 24 or other such annunciator device as may be used continues to indicate the fact that the switch 22 has at least momentarily been closed. Restoration of the circuit of FIG. 2 to its standby i.e., nonindicating status is, once again, accomplished by such means as temporarily opening switch 38. The circuit of FIG. 2 is such that when the annunciator is in its non-indicating status, a certain but very low power consumption will occur because of the conducting status of transistor '44. If switch 22 is replaced with one which is normally closed, the operation of the circuit of FIG. 2 can be duplicated by suitably reconnecting the transistor 44.

It will be noted that the SCR 28 or other synchronous switch which may be fired by operation of the control circuit, and which latches is operable only upon the operation of a suitable control circuit which is, itself, active so as to control the firing of the SCR only after a switching operation of the switch within the alarm signalling device. Thus, switch 22 causes a control circuit which includes resistor 30 and a

parallel circuit

34, 36 to fire the SCR 28 in the circuit of FIG. 1; whereas in the circuit of FIG. 2, a switching operation by switch 22 causes transistor 44 to turn off, thereby raising the voltage at the gate of SCR 28, and causing the SCR to fire. In both circuits, once the SCR 28 has fired, the light emitting diode 24 which acts essentially as a short circuit when it is conducting remains on, because of the latching operation of the SCR, until such time as power is removed at least from that portion of the circuit which includes the light. emitting diode and the SCR in series. I

Various alternative embodiments, and additions thereto by way of complementary or electrically isolated power circuits, have been discussed. Various types of control circuitry which causes the SCR to fire only after a switching operation of the switch within the alarm signalling device which causes an alarm signal to be generated, have been discussed, as well as various alternatives of current operation annunciator devices. It has been noted that the circuits of this invention-can operate without regard to the polarity of the power source to which the circuits may be connected; and it has been noted that especially with the use of all solid state components, power consumption'and physical size as well as costs can be kept at a minimum.

Various other amendments, alterations or :substitutions may be made to the circuits taught herein, without departing from the spirit and scope of the appended claims.

What'l claim is a 1. In an alarmsignalling device having at least a single-pole single-throw switch whose operation is determined by a change of ambient conditions being monitored by said device, and where said switch is connected in series with one side of a source of electrical power; the improvement comprising annunciator means associated with said alarm signalling device and connected to said power source to provide a continuous annunciation after a switching operation of said switch in response to a change of the conditions being monitored until such time as said annunciator means is at least temporarily disconnected from said power source, including;

annunciator means operable from said power source and in series with gate means; said gate means being operable only upon operation of a control circuit therefor; said control circuit being active to control said gate means only after a switching operation of said switch;

said gate means including latch means connectedto said power source to maintain said gate means.

7 8 until said latch means is disconnected from said switch said transistor become non-conductive and power urc Said g and latch means being an said SCR is fired by the voltage then impressed on SCR, and said annunciator means being a light the gate h f Fmming dloflei 2. The circuit of claim 1 where said power source is said control circuit for sald gate means from hav ng the output terminals of a diode bridge a translsmr whose base is connected senes wnh 3. The circuit of claim 1 where said detector device said switch; resistor means connected to bias the base of said transistor so that said transistor is conhas at least a two'pole smgle'throw sw'tch whose Opel" ductive when said switch is in its normal switching is determined and Controlled at only one pole condition; and further resistor means connected at thereof, and where the Second P of said Switch is one end both to said transistor and to the gate of nne ted o an alarm Circuit. said SCR, so that after a switching operation of said

Claims

1. In an alarm signalling device having at least a single-pole single-throw switch whose operation is determined by a change of ambient conditions being monitored by said device, and where said switch is connected in series with one side of a source of electrical power; the improvement comprising annunciator means associated with said alarm signalling device and connected to said power source to provide a continuous annunciation after a switching operation of said switch in response to a change of the conditions being monitored until such time as said annunciator means is at least temporarily disconnected from said power source, including; annunciator means operable from said power source and in series with gate means; said gate means being operable only upon operation of a control circuit therefor; said control circuit being active to control said gate means only after a switching operation of said switch; said gate means including latch means connected to said power source to maintain said gate means closed and said annunciator means operative even after a further switching operation of said switch, until said latch means is disconnected from said power source; said gate and latch means being an SCR, and said annunciator means being a light emitting diode; said control circuit for said gate means from having a transistor whose base is connected series with said switch; resistor means connected to bias the base of said transistor so that said transistor is conductive when said switch is in its normal switching condition; and further resistor means connected at one end both to said transistor and to the gate of said SCR, so that after a switching operation of said switch said transistor become non-conductive and said SCR is fired by the voltage then impressed on the gate thereof.

2. The circuit of claim 1 where said power source is the output terminals of a diode bridge.

3. The circuit of claim 1 where said detector device has at least a two-pole single-throw switch whose operation is determined and controlled at only one pole thereof, and where the second pole of said switch is connected to an alarm circuit.