AU1111001A - Portable fire alarm - Google Patents

Description

1 PORTABLE FIRE ALARM Field of the Invention The present invention is concerned with a fire alarm. In particular the invention relates to a portable fire alarm that may be incorporated into an appliance, for example an alarm clock.

Background to the Invention Fire alarms are well known in the prior art. Two commonly available types are photoreceptor fire alarms and ionisation detector alarms. The first of these types of alarm includes a light source and a light detector. The arrangement of the photoreceptor fire alarm is such that the two components are not aligned so that the light detector does not normally detect light from the light source. In the event of a fire smoke reflects light from the source to the detector. The output from the detector is sensed by an alarm circuit which generates an audible alarm in response.

In contrast ionisation detectors work on the principle of bombarding the S 20 air in a small chamber with radioactive particles. The radioactive particles Sionize the air so that it is able to carry a small electric current. When particles associated with a fire enter the chamber they reduce the current flow. Upon the current flow decreasing to a predetermined level an alarm is triggered.

It has been known to incorporate fire alarms into alarm clocks in order to 25 produce a portable fire alarm that makes common use of alarm clock circuits such as the alarm buzzer and power supply. An advantage of such a device is that a traveller may sleep secure in the knowledge that he or she will be woken S. in the event of a fire. Devices of the type described are disclosed in US Patent No. 4,186,389 to Flittie and in US Patent No. 5,309,145 to Branch et al.

A problem with firm alarms of the type known in the prior art is that they are only able to sense fire in the proximity of the device. Thus if a prior art portable fire alarm is located on a bed-side table, for example, then the alarm will only be activated upon products from the fire, such as smoke, entering the fire alarm. However, it may be that by the time smoke has entered the fire alarm the fire will be very close to it thereby affording a person sleeping nearby little time to escape.

It is an object of the present invention to provide a portable fire alarm which is a useful alternative to those known in the prior art and which addresses the above-described problem.

Summary of the Invention According to a first embodiment of the invention there is provided a portable fire alarm including: a body incorporating an electromagnetic radiation source; an electromagnetic radiation detector orientated to detect radiation from said source reflected by a remote surface; circuitry coupled to the detector and arranged to activate an alarm annunciator in the event that the radiation signal falls beneath a reference level.

In a preferred embodiment the signal conditioning circuitry includes a discriminator coupled to the detector and arranged to discriminate against components of the radiation signal due to radiation from other than said source.

Preferably the electromagnetic radiation source comprises an infra-red radiation source, for example an infra-red LED.

Preferably the electromagnetic radiation detector comprises an infra-red radiation detector, for example a PIN diode.

In a preferred embodiment the fire alarm includes an amplitude modulator coupled to the radiation source for amplitude modulating radiation 25 emitted from the source.

000 In that case the discriminator is arranged to discriminate against radiation incident on the source which is not modulated at the modulation frequency of the amplitude modulator.

Preferably the apparatus further includes a motion detector and is arranged to activate the annunciator upon the motion detector detecting movement in the locale of the apparatus. The motion detector may be of a passive infra-red type although other types would also be suitable.

In a preferred embodiment the annunciator is the alarm of an alarm clock and the body is the body of the alarm clock.

The apparatus may be battery powered.

Preferably the circuitry includes a microcomputer programmed to switch power to the radiation detector and/or motion detector on and off in order to reduce power consumption.

In a preferred embodiment the microcomputer is programmed to set the reference level as a level of infra-red radiation reflected from the remote surface at power-on of the apparatus.

The microcomputer may be further programmed to adjust the reference level over time.

It will be understood that by providing a portable alarm which monitors a signal reflected from a remote surface, the presence of smoke at a distance from the alarm may be sensed.

Brief Description of Figures In order that this invention my be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate typical preferred embodiments of the invention and wherein: Figure 1 is a perspective view of a portable fire alarm according to an embodiment of the present invention.

S:20 Figure 2 is a block diagram of the internal circuitry of the portable fire 0 alarm of Figure 1.

Figure 3 is a flowchart of a computer program of the microcomputer of Figure 2.

25 Detailed Description of Preferred Embodiment Referring now to Figure 1, there is depicted a perspective view of a combined alarm clock and fire detector 10 according to a first embodiment of the present invention. Fire detector 10 includes a case or body 11 upon which is mounted an electromagnetic radiation source in the form of an infra red emitter 4. Also included is a corresponding radiation detector in the form of an infra red receiver 6 also mounted in the upper-side 12. An LED time display 8 and audible alarm 10 are also included. Controls 2 for setting the time displayed by the alarm clock and turning the alarm off are also provided. The alarm clock may be battery powered with cover 14 covering a battery compartment.

In use emitter 4 transmits an infra-red signal to a remote reflective surface, for example the ceiling of a room in which the apparatus is located.

The infra-red signal is reflected from the remote surface back to detector 6. As will be explained, circuitry internal to the apparatus compares the level of detected signal to a reference level. In the event that the detected level is less than the reference level then an alarm is sounded as it may be that the reduced level is due to smoke reducing the level of infra-red signal detected.

Referring now to Figure 2, a block diagram of the internal configuration of alarm clock 10 is shown. Dotted line 16 surrounds circuit blocks present within a standard alarm clock. These include standard bedside alarm clock circuitry 18 associated with timekeeping, alarm setting and alarm triggering, audible alarm circuit 20 includes circuitry for driving an audible alarm such as a loudspeaker or buzzer. Power supply circuit 22 is a standard circuit including a transformer to transform a mains level AC supply to a low voltage for rectification to a DC supply suitable for driving electronic circuitry. The low voltage DC output of power supply circuit 22 supplies power to the alarm clock circuitry 18 and also supplies smoke detector circuits enclosed by dotted line 20 24. Battery 26 is provided as a backup in the event that mains power is unavailable.

The smoke detection circuitry 24 is arranged to enable discrimination between interfering sources of infra-red energy and the reflected signal emanating from infra-red emitter 4. Amplitude modulator 26 modulates the 25 power to, and hence the light output, from infra-red emitter 4. A PIN diode 6 is used as an infra-red detector. The output of diode 6 is AC coupled to amplifier circuitry 28 which amplifies the small signals from the PIN diode. A synchronous detector 30 is coupled to amplifier 30 and is responsive to a modulating signal for modulator 26. The synchronous detector includes a rectifier for converting the signal from amplifier 28 to a DC level corresponding to the intensity of infra-red light detected by PIN diode 6. The synchronous detector is arranged to respond only to received signals modulated at a frequency matching that from modulator 26. Accordingly signals from infra-red sources other than infra-red emitter 4 are disregarded by detector Output from detector 30 is converted to a digital form by analogto-digital converter 32 suitable for input to microcomputer 34. Microcomputer 34 is powered by power supply circuit 22. The microcomputer also receives data about the time of day from alarm clock circuitry 18. Outputs from the microcomputer include a control line for transmitting an on/off signal to the smoke detector circuitry in order to reduce power consumption. The microcomputer is also able to send a command signal to alarm circuit 20 in order to activate the alarm.

The apparatus further includes a standard Passive Infra Red Detector (PIRD) 40 which detects the motion of bodies which radiate Infra Red energy.

Warm blooded creatures radiate infra-red energy and are easily detected by such devices. The technology comprising PIR devices is well known and is not described in detail herein. A digital output signal from PIRD 40 is coupled to microcomputer 34.

The microcomputer is programmed to perform four main functions. Each of the functions will now be described with reference to Figure 2. The first function is implemented at box 42 wherein at power-up the microcomputer monitors the level of reflected infra-red energy received. This level is taken to be a normal, i.e. non-fire condition, level and is stored and subsequently used to S 20 compare later readings to.

S•The second function is implemented at box 44 and operates to switch the smoke and motion detector circuitry on and off in order to minimise power .ooo.i consumption.

The third function is to monitor the level of reflected signal and to 25 respond to changes in the level of reflected signal in two different ways. This function is implemented by boxes 50-56. At box 50, whenever power is o supplied to the smoke detector circuits the level of infra-red energy reflected from infra-red emitter 4 to receiver 6 is measured. At box 52 the measurement made at box 50 is compared to previous measurements and the rate of change of the level measured over a previous number of samples is calculated. If the rate of change is above a predetermined level then it is said to be "rapid" and control diverts to box 54. Alternatively, if the rate of change is equal to or less than the predetermined level then it is said to be "slow" and control diverts to box 56. At box 56 the reference level previously determined at box 42 is adjusted by setting it, for example, to the average of the last few level readings. The adjustment at box 56 ensures that the reference level is adapted to take into account small changes in the reflective properties of the ceiling or changes in gain of the infra-red transmit receive circuitry.

At box 54 the difference between the level measured at box 50 and the reference-level previously determined at box 56 or box 42 is calculated. If the difference is greater than a preset level then it is taken to be significant and microprocessor 34 then sends a command signal to alarm circuit 20 to sound an alarm. Control then diverts back to box 44.

The fourth function is concerned with operation of the passive infra-red detector circuitry 40 and is implemented at boxes 46 and 48. At box 46 the microcomputer initially checks for output from PIRD 40. Subsequently at box 48, if output from the PIRD is detected over a number of cycles then microcomputer 34 sends a command to alarm circuit 20 to activate the alarm.

While the invention has been explained with reference to a preferred embodiment it will be clear to those skilled in the art that variations and other embodiments are also possible. For example while it is preferable that the apparatus include a passive infra-red detector it is not mandatory.

It will of course be realised that the above has been given only by way of 20 illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as set forth in the .following claims.

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Claims (14)

1. A portable fire alarm including: a body incorporating an electromagnetic radiation source; an electromagnetic radiation detector orientated to detect radiation from said source reflected by a remote surface; circuitry coupled to the detector and arranged to activate an alarm annunciator in the event that a radiation signal corresponding to radiation detected by said detector falls beneath a reference level.

2. A portable fire alarm according to claim 1, wherein the circuitry includes a discriminator coupled to the detector and arranged to discriminate against components of the radiation signal due to radiation from other than said source.

3. A portable fire alarm according to claim 1 or claim 2, wherein the electromagnetic radiation source comprises an infra-red radiation source. 20 4. A portable fire alarm according to claim 3, wherein the infra-red radiation Ssource comprises an infra-red LED. A portable fire alarm according to any one of the preceding claims, wherein the electromagnetic radiation detector comprises an infra-red radiation 25 detector.

6. A portable fire alarm according to claim 5, wherein the infra-red radiation detector comprises a PIN diode.

7. A portable fire alarm according to any one of claims 2 to 6, wherein the circuitry includes an amplitude modulator coupled to the radiation source for amplitude modulating radiation emitted from the source. 8

8. A portable fire alarm according to claim 7, wherein the discriminator is arranged to discriminate against radiation incident on the source which is not modulated at the modulation frequency of the amplitude modulator.

9. A portable fire alarm according to any one of the preceding claims wherein the apparatus further includes a motion detector and is arranged to activate the annunciator upon the motion detector detecting movement in the locale of the apparatus.

10. A portable fire alarm according to claim 9, wherein the motion detector is of a passive infra-red type.

11. A portable fire alarm according to any one of the preceding claims, wherein the annunciator is the alarm of an alarm clock and the body is the body of the alarm clock.

12. A portable fire alarm according to any one of the preceding claims arranged to be battery powered. 20 13. A portable fire alarm according to any one of the preceding claims Swherein the circuitry includes a microcomputer programmed to control operation of the apparatus.

14. A portable fire alarm according claim 12, wherein the microcomputer is 25 programmed to switch power to the radiation detector and/or motion detector on and off in order to reduce power consumption.

15. A portable fire alarm according to claim 13 or 14 wherein the microcomputer is programmed to set the reference level as a level of infra-red radiation reflected from the remote surface at power-on of the apparatus.

16. A portable fire alarm according to claim 15, wherein the microcomputer is programmed to adjust the reference level over time.

17. A portable fire alarm substantially as described herein with reference to Figure 2. Dated this 9 t h day of January 2001 HARRY WILLIAM WEEGEN By my attorneys PIZZEYS PATENT AND TRADE MARK ATTORNEYS S *SSS*S S oooo S 5* S* S. S S ooooo o*o*o* *o o o oo o*