Alarm Device Gas Discharge Tube

Abstract

Alarm device for detecting a radiation in a given space. The device comprises a discharge tube responsive to said radiation, a pulse generator having a first frequency and connected to said tube, a counting device whose input is connected in the circuit of said tube and of said generator, a time-base circuit connected to the reset terminal of said counting device and furnishing reset pulses at a second frequence, a control device connected to said counting device, and a signal device controlled by said control device.

Description

The present invention relates to alarm devices and more particularly to a device which, by the detection of the radiation in a given space, produces a signal and sets off by means of said signal an alarm when the radiation exceeds a predetermined quantity of radiations per time unit considered to be dangerous.

The invention provides an alarm device comprising, in combination, a discharge tube responsive to said radiation, a pulse generator having a first frequency and connected to said tube, a counting device whose input is connected in the circuit of said tube and of said generator, a time-base circuit connected to the reset terminal of said counting device and furnishing reset pulses at a second frequency, a control device connected to said counting device and a signal device controlled by said control device.

By means of this alarm device it is possible to check the quantity of the radiation in a given space, this radiation being of various types, for example a nuclear or ultraviolet radiation or some other radiation, the discharge tube being responsive to these radiations. In particular, the alarm device is applicable in the detection of the presence of flames, which usually emit an ultraviolet radiation, and consequently it can be employed for indicating fires. In this field, the alarm device according to the invention has a particular advantage over known devices. Up to the present time, there have been employed in fire alarm devices detecting elements which are responsive to the infrared rays of the flames. However, such a radiation is normally present in the atmosphere in large amounts and an alarm device provided with an infrared ray detector is unsatisfactory since it can be accidentally actuated merely by the infrared radiation of the atmosphere or other harmless sources. The alarm device according to the invention avoids this drawback since ultraviolet radiation naturally present in the atmosphere is extremely small relative to that emitted by a fire.

Another object of the invention is to provide a supervising installation comprising at least two alarm devices such as those defined hereinbefore and constituting separate supervising stations in spaced relation, said pulse generator being common to both alarm devices and located in a center supervising station, each alarm device being provided with a switch controlled by its control device, said installation further comprising a supply circuit which is connected to said pulse generator and closed by a resistor, said switches being connected in series with said resistor and a center alarm control circuit responsive to the variation in the potential of one of the points of connection of said supply circuit.

The alarm devices employed in this installation can be placed in several premises of a building for example and arranged to set off the alarm in the central supervising station.

Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawing.

In the drawing:

FIG. 1 is a simplified diagram of a single-alarm device according to the invention;

FIG. 2 is a simplified diagram of an installation comprising a series of alarm devices such as that shown in FIG. 1, the pulse generator being common to all the alarm devices, and

FIG. 3 is a modification of the alarm device shown in FIG. 1.

FIG. 1 shows an alarm device whereby it is possible to actuate or set off an alarm when a given quantity of radiation per time unit is exceeded, this device being placed in a premises in which the magnitude of the radiation must be supervised. This alarm device comprises a detector discharge tube 1 responsive to radiations, such as nuclear or ultraviolet radiations. This tube is of commercially available type and becomes conductive by innisation when energy particules of these types of radiations impinge thereon. This tube 1 is connected in series with two resistors 2, 3 forming a voltage divider the assembly being connected to the terminals 4, 5 of a pulse generator 6 through a relay contact 7 which is closed in the illustrated position, the relay coil 8 being energized. The pulse generator 6 furnishes rectangular pulses having the discharge voltage of the detector tube 1, for example 240 v., and a relatively low frequency of, for example 100 Hz. Such a generator can be constructed by means of a bridge rectifier whose output is clipped by a series of Zener diodes, as will be explained hereinafter.

The resistor 3 is shunted by a Zener diode 9 whose cathode is connected to the junction point of the resistors 2 and 3 and to the control input 11a of a flip-flop 11 which is a part of a binary counter generally designated by the reference numeral 10. In the illustrated embodiment, this counter 10 has three flip-flops 11, 12, 13, each flip-flop having a control input a, a supply terminal b, a reset terminal c, a first output d at which appears a signal when the flip-flop is in the logic state "1" and a second output e which is connected to the input a of the following flip-flop and carries a signal when the flip-flop is in the logic state "0".

All the terminals b are connected to a supply line 14 which is connected to a supply battery 15, for example of 12 v., through a terminal 16.

All the reset terminals c are connected to the output 17 of a multivibrator 18 producing a series of pulses of given frequency which are preferably adjustable. This multivibrator 18 is fed by the battery 15.

The first outputs d of the flip-flops 11, 12 and 13 are connected to the respective inputs of an "AND"-gate 19. Its output is earthed through a resistor 20 and connected to the control electrode of a thyristor 21 whose cathode-anode path shunts the coil 8 which controls the contact 7. The junction point of the anode of the thyristor 21 and the coil 8 is connected to the line 14 through a resistor 22 which is shunted by a signal lamp 23.

This alarm device operates in the following manner:

When the feed voltage of 12 v. is applied to the terminals 5 and 16, the coil 8 is energized and the contact 7 closes. Thereafter, pulses of 240 v. from the generator 6 are applied to the detector tube 1. At the same time, the multivibrator 18 delivers reset pulses to the inputs c of the flip-flop 11, 12 and 13, respectively, at a predetermined frequency.

These conditions correspond to the state of supervision of the alarm device. It is possible that during the period of supervision the tube 1 receives energy particules of a radiation of one of the aforementioned types. In this case, a discharge can be produced owing to the pulse of 240 v. applied to the tube at the moment of impact. The tube therefore becomes conductive throughout the duration of the pulse and a voltage is thus generated at the terminals of the resistor 3. Upon impact of another energy particle, the following pulse at 240 v. produces another discharge and another voltage pulse at the terminals of the resistor 3. As these pulses are applied to the binary counter 10 the flip-flops 11--13 pass successively to their 1 state up a total of seven pulses. However, if before the impact of the seventh energy particle i.e. the appearance of the seventh pulse, the binary counter is reset by the multivibrator 18 the alarm is not triggered and a new counting cycle can start. The frequency of the reset pulses of the multivibrator 18 is adjustable and thus it is possible to determine at which quantity of radiation per time unit the binary counter 10 counted seven pulses.

If seven pulses arrive within the given interval, the seventh pulse energizes the AND-gate 19, all the outputs d of the flip-flops 11-13 being energized. The AND-gate triggers the thyristor 21 which short-circuits the coil 8 and energizes the signal lamp 23. The latter can if desired be connected in parallel with a bell system or other similar signal device. The contact 7 is open.

Thus it can be seen that the alarm is set off when the quantity of radiation is such as to cause the tube 1 to discharge a given number of times within a given interval of time determined by the time-base furnished by the multivibrator 18. In other words, by means of the latter circuit it is possible to determine at which quantity of radiation per time unit the alarm device becomes operative.

FIG. 2 shows a supervising installation comprising a series of alarm devices D.sub.1 -D.sub.n which are substantially identical to that shown in FIG. 1, except that the generator 6 is replaced by a common pulse generator 24 located in a central supervising station PC diagrammatically indicated by dot-dash lines in FIG. 2.

The contacts 7 of the alarm devices D.sub.1 -D.sub.n are connected in series to each other and to resistors 25 and 26, the whole of the circuit being connected to the output terminals 27 and 28 of the pulse generator 4.

The alarm devices can be arranged in various premises of a building so as to supervise therein the quantity of radiation per time unit, for example the ultraviolet radiation. In the latter case the assembly is a fire-warning system.

The alarm devices are fed with DC from a supply line 29.

The pulse generator 24 comprises a transformer 30, a rectifying bridge 31, a resistor 32 and a series layout 33 of three Zener diodes.

The central station PC also comprises a battery 34 of for example 12 v., which is earthed and connected to the supply line 29, and a central control circuit comprising two field-effect transistors 35, 36 which are interconnected with suitable polarizations through polarization resistors 37-40. The grid of the transistor 35 is connected to the negative pole of the rectifying bridge 31, that is, the junction point 41 of the system 33 of Zener diodes and resistor 26, through the resistor 38. The point 41 is also connected to the grid of the transistor 36 through a Zener diode 42. The drains of these transistors are earthed whereas their sources are connected to the coil 43 of a relay, one being connected directly and the other through the resistor 40.

The coil 43 cooperates with two contacts 44, 45 so as to constitute a relay with sequence action, that is to say, the contacts 44 and 45 are not closed for the same current intensity in the coil 43 of the relay. In the present example, it is assumed that the contact 44 closes for an intensity value I and that the contact 45 closes when the intensity is about 2 I, the contact 44 of course remaining closed at this value of intensity.

The contacts 44 and 45 are intended to actuate conventional signal devices DS, such as lamps, bell systems and other systems in the central supervising station PC.

This supervising installation operates in the following manner:

The normal situation corresponds to the closure of all the contacts 7, the alarm devices D.sub.1 -D.sub.n being unactuated. In this case, an impulse current which is clipped by the Zener diodes 33 flows through the circuit comprising the contacts 7 and the resistors 25 and 26. As the junction of these two resistors is earthed, the point 41 is at negative potential.

The transistor 35 to which this potential is applied is thus in the turned off state. On the other hand, the transistor 36 is conductive or turned on owing to the polarization produced by the resistors 39 and 40. A current therefore flows in the relay coil 43 so that the contact 44 is open, the current having the value I. This contact actuates the signal lamp or other means so as to inform the supervisor that the situation is normal.

When the radiation in the vicinity of any of the alarm devices exceeds the previously fixed magnitude, the alarm in question is set off in the manner described hereinbefore. Consequently, the circuit comprising the contact 7 and the resistors 25 and 26 is cut off so that the potential of the point 41 rises up to the potential of the earth. This turns on the transistor 35 which is then polarized solely by the resistors 37 and 38. The intensity of the current in the coil 43 thus rises to about 2 I and the contact 45 is also closed. On the control desk will therefore appear the alarm signal which for example can be accompanied by a sound or other signal.

The alarm installation described hereinbefore also furnishes another signal when a defect concerning the lines which supply current to the alarm devices occurs.

Several different cases can be considered: 1. A short circuit between the positive and negative conductors of the pulse supply circuit. In this case, the intensity of the current furnished by the rectifying bridge 31 considerably increases and this increases the voltage drop at the terminals of the resistor 26. The potential of the point 41 therefore becomes still more negative than in the normal situation so that the voltage applied to the Zener diode 42 reaches its threshold volume and this diode thus becomes conductive and turns off the transistor 36. As the two transistors are turned off in this case, the coil 43 is no longer energized and the contacts 44 and 45 are open. A signal produced in the signal device DS then indicates the short circuit in question. The same signal is produced when the line 29 is earthed or when the connections with the battery 34 are broken. 2. In the case of the cutting of any of the pulse supply lines, the alarm signal is produced since this situation is similar to that produced when one of the devices D.sub.1 -D.sub.n is actuated.

FIG. 3 shows a modification of the alarm device shown in FIG. 1. In this embodiment the AND-gate 19 is replaced by a fourth stage 46 of the binary counter 10a, this stage being directly connected to the control electrode of the thyristor 21.

Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.

Thus, the capacity of the binary counter 10 can be increased by adding thereto a number of other flip-flops.

Further, the device according to the invention and the installation described hereinbefore are particularly appropriate for use in fire-warning systems.

Claims

Having now described my invention, what I claim as new and desire to secure

1. An alarm device for detecting a radiation in a given space and producing an alarm signal when the quantity of energy particles of said radiation per time unit exceeds a predetermined value, said device comprising in combination, a discharge tube responsive to said radiation and connected so as to be conductive each time energy particles of said radiation impinges thereon, a pulse generator having a first frequency at a voltage sufficient to cause conduction of said tube by combined action of said voltage and said energy particles, a circuit connecting said generator to said tube, a counting device having a reset terminal and an input, said input being connected in said circuit, so as to be rendered operative each time said tube is conductive, a time-base circuit connected to said reset terminal and furnishing reset pulses at a second frequency, a control device connected to said counting device, and a signal device controlled

2. A device as claimed in claim 1, wherein said counting device is a binary

3. A device as claimed in claim 2, said control device having an AND gate, equivalent outputs of said flip-flops being connected to said AND gate, the alarm device further comprising a thyristor whose control electrode is connected to the output of said gate, said thyristor being connected in

4. A device as claimed in claim 2, wherein said time-base circuit is a multivibrator whose output is connected to reset inputs of said

5. A device as claimed in claim 3, wherein the control electrode of said thyristor is directly connected to an output of the last flip-flop of said

6. A supervising installation comprising a plurality of alarm devices for detecting a radiation in a given space and producing an alarm signal when the quantity of energy particles of said radiation per time unit exceeds a predetermined value, each alarm device comprising in combination a discharge tube responsive to said radiation and connected so as to be conductive each time energy particles of said radiation impinges thereon, a pulse generator having a first frequency at a voltage sufficient to cause conduction of said tube by combined action of said voltage and said energy particles, a circuit connecting said generator to said tube, a counting device having a reset terminal and an input, said input being connected in said circuit so as to be rendered operative each time said tube is conductive, a time-base circuit connected to said reset terminal and furnishing reset pulses at a second frequency, a control device connected to said counting device, and a signal device controlled by said control device, said alarm devices constituting separate supervising stations in spaced relation, said pulse generator being common to said alarm devices and located in a central supervising station, each alarm device comprising a switch controlled by the corresponding control device, said installation further comprising a supply circuit which is connected to said pulse generator and includes a resistor in series, said switches being connected in series with said resistor, and a central alarm control circuit responsive to the variation in the potential of one of the points

7. An installation as claimed in claim 6, wherein said pulse generator comprises a transformer, a rectifier bridge and a system of a plurality of Zener diodes connected in parallel with output terminals of said rectifier

8. An installation as claimed in claim 6, wherein said central control circuit comprises a system including two field-effect transistors having drain-source circuits connected in parallel, a coil of a relay with sequence action being connected in series with said system, one of said field-effect transistors having a grid connected to said point of connection of said supply circuit whereas the grid of the other of said field-effect transistors is connected to said point through a Zener diode.

9. An installation as claimed in claim 7, wherein said point of connection of said supply circuit is the negative terminal of said rectifier bridge.