GB2551546A

GB2551546A - Improvements in or relating to beam phasing

Info

Publication number: GB2551546A
Application number: GB1610856.5A
Authority: GB
Inventors: Andelin Jacob; Perch Marcus
Original assignee: FFE Ltd
Current assignee: FFE Ltd
Priority date: 2016-06-21
Filing date: 2016-06-21
Publication date: 2017-12-27
Anticipated expiration: 2036-06-21
Also published as: GB201610856D0; EP3260844A1; ES2928982T3; EP3260844B1; GB2551546B; US20170366292A1; US10277355B2

Abstract

In an embodiment of an optical beam detector, perhaps a smoke detector, a beam of duration L is transmitted at a nominal time interval T. The time at which the beam is projected is adjusted within a time window W. If the level of a signal of a detected beam is less than a threshold for each of a number of consecutive projections, or for each consecutive projection over a time period, a warning is initiated or alarm signalled. In another embodiment, first and second optical beam detectors are arranged in opposing configuration, such that light from the transmitter of one detector may be incident on the receiver of the other detector. By adjusting the time at which a beam (or perhaps both beams) is projected within the time window W, fluctuations in signal due to such incident light are avoided. The time adjustment may be random or pseudo-random. The optical beam detector(s) may be of reflective or end-to-end type.

Description

Improvements in or Relating to Beam Phasing

The present invention relates to randomly, pseudo-randomly or otherwise adjusting the phasing of beams. In particular, the invention relates to: a method for adjusting the phasing of beams in a beam detector; a beam detector apparatus; and an associated beam detector system.

In summary, a reflective optical beam smoke detector system has a detector unit, which includes both a transmitter and a receiver, and a retro-reflector. The detector unit and the reflector are placed opposite each other at opposing ends of a volume to be protected and monitored. The transmitter projects a modulated beam, in this example a modulated Infrared (IR) beam, on to the retro-reflector which reflects the IR beam along the same axis back to the receiver. Smoke in the beam path will reduce the amount of light returning to the receiver. The receiver continuously monitors the amount of light received and, if it drops below a certain user-defined threshold, then an alarm is initiated. Typically, the beam is not continuously projected, but only once per second for a very short time ~10milliseconds (ms).

Installing two such detectors in an opposite manner comes with both advantages and disadvantages. This configuration is advantageous if the volume which is to be protected is longer than the specified protection distance of a detector. In that situation, which is not uncommon, if the distance is anything larger, an installer will install a detector on each wall, and install reflectors back-to-back at an approximate midway point between them. The advantage of this is that all of the electrical wiring to power supplies and fire panels remains at the edges of the building, rather than having to run such wiring to midpoints in a volume to be protected. Unfortunately, although there are advantages to this configuration, it is also the cause of problems, as the beam from one detector will fall upon the opposite detector unit. This scenario is exemplified in Figure 1.

Figure 1 illustrates a prior art detector system, identified generally by reference 100, which includes a first detector unit 110 and a second detector unit 120. In this example, the detector units are operating with Infrared (IR) light.

Detector unit 110 includes both a transmitter and a receiver within the unit 110 and, as for detector unit 120, it also includes a transmitter and receiver within the unit 120.

Each of the units 110; 120 is located in an opposed manner (as shown in Figure 1) and have a corresponding reflector 111; 121, respectively, located within a volume to be monitored at a location some distance from the units 110; 120 and towards which a beam is projected by the detector units 110; 120. The corresponding reflectors 111; 121 are neither provided exactly equidistant nor centrally between the two detectors units 110; 120, although this is not an unusual configuration. Each unit 110; 120 operates independently of the other, such that if obscuration of the beam occurs between detector unit 110 and corresponding reflector 111, and between detector 120 and corresponding reflector 121, a warning or alarm is independently signalled or activated. Of course, if obscuration occurs in both regions, then two alarms would be signalled or activated. There are, of course, advantages or reasons as to why it would be useful or necessary to locate detector units 110; 120 in an opposed manner, even though there is a chance, or even likelihood, that some of the beam projected from one might interfere with detection of the beam of the other unit.

Using the beam 122 from detector unit 120 as an example, and as shown in Figure 1 in particular, normal detection can occur between the unit 120 and its reflector 121, as per normal operation of the beam detector. Flowever, in relation to part 122’ of the beam 122 which projects past the reflector 121 and illuminates the environs of the detector 110, as indicated by illuminated regions 101 and 102, and a corresponding shadow region 103 caused by the reflector 121 in the beam 122, if detector unit 120 is projecting its beam 122 at a same time as detector unit 110 is expecting to receive its own projected beam (not shown), there is a strong chance that detector unit 110 will receive more light than expected, some of which from beam part 122’.

As the detector units 110; 120 only transmit for 10ms every second, this does not cause a continuous problem as the two units will often transmit at different times. However, owing to timing differences between the two detectors, they will eventually come into phase where they will transmit at the same time. Each detector will not only receive light from its own reflector but also light from the opposite transmitter.

As the beams are modulated, depending upon how the peaks and troughs of the two beams coincide, this will cause an increase or decrease in the signal strength. The effect of this is that the effective signal strength received may go up or down at random, which leads to false alarms and the signalling of faults. Further, the phasing in and phasing out again of the beam transmissions can be somewhat random also, for example, the beams could be out of phase for hours, days or even weeks but once in phase they could be in this situation for minutes, hours or days, so it is hard to predict how long the beams will be in phase.

It is also known to place a baffle between a set of back-to-back reflectors, so as to increase the size of a shadow region caused by the light of opposed detector units, such that receiving units per se are within that shadow region. Such baffles are necessarily relatively large when compared to the reflectors and rather unsightly.

The present invention is aimed at alleviating the above disadvantage(s) associated with beam detectors.

According to a first aspect, the present invention provides a method for adjusting the phasing of beams in a beam detector, the method comprising projecting a beam at a nominal transmit interval T for the purpose of detecting obscuration of the beam and, if a level of signal of the beam detected is less than a threshold for each of a number of consecutive projections or for each consecutive projection over a pre-determined time period, initiating a warning, signalling an alarm or otherwise reacting, wherein adjusting the timing of projecting the beam within a window time-period W extending from an amount before to an amount after the nominal transmit interval.

Preferably, pseudo-randomly or randomly adjusting the timing.

Preferably, the amount before and the amount after are (approximately) equal time periods.

Preferably, W < T. Preferably W = Ύ72. Most preferably, ‘W is symmetrical about T.

Preferably, if a length of time of projection of the beam is ‘L’, W > 2’L’ to W»2’L’.

As such, the projected beam may be projected at some time before the next nominal transmit interval, on the next nominal transmit interval or after the next nominal transmit interval.

Preferably, using a pseudo-random number sequence to adjust the timing of projection.

Most preferably, using an initial light intensity reading, start-up time, or A-to-D (analogue-to-digital) converter input to generate a/the pseudo-random number sequence.

Preferably, T is about 0.1 to about 10 seconds, further preferably about 0.5 to about 5 seconds and, most preferably, about 1 second. Preferably, W is about 0.05 to about 10 seconds, further preferably about 0.25 to about 5 seconds and, most preferably, about 0.5 seconds. Preferably, ‘L’ is about 1 millisecond to about 25 milliseconds, further preferably about 5 milliseconds to about 20 milliseconds and, most preferably, about 8 milliseconds to about 12 milliseconds or about 10 milliseconds. Most preferably, T is one second, W is 500 milliseconds and ‘L’ is 10 milliseconds.

Preferably, the beam detector is an optical beam smoke detector, preferably a reflective-type optical beam smoke detector.

Otherwise reacting comprises any form of audible and/or visual stimuli, and/or even the triggering of remedial fire apparatus, for example sprinklers or the like.

According to a second aspect, the present invention provides a beam detector apparatus comprising: means for projecting a beam at a nominal transmit interval T for the purpose of detecting obscuration of the beam and, if a level of signal of the beam detected is less than a threshold for each of a number of consecutive projections or for each consecutive projection over a pre-determined time period, initiating a warning, signalling an alarm or otherwise reacting; and means for adjusting the timing of projecting the beam within a window time-period W extending from an amount before to an amount after the nominal transmit interval.

Preferably, the beam detector apparatus is for providing pseudo-randomly or randomly phased beams.

Preferably, the means for adjusting comprises means for generating a random number sequence.

Preferably, the means for adjusting comprises means for taking an initial light intensity reading and generating a/the random number sequence.

Preferably, the means for projecting is a reflective-type optical beam smoke detector, comprising a transmitter and receiver in the same detector unit, and an associated reflector. Alternatively, the means for projecting is an end-to-end optical beam smoke detector, comprising separate transmitter and receiver units.

Preferably, the apparatus includes one or more features from the first aspect.

According to a third aspect, the present invention provides a beam detector system, the system comprising: a first transmitter and associated receiver; and a second transmitter and associated receiver, in which each pair of transmitter and receiver operate independently of the other pair by each projecting a beam at a nominal transmit interval T for the purpose of detecting obscuration of the beam and, if a level of signal of the beam detected is less than a threshold for each of a number of consecutive projections or for each consecutive projection over a pre-determined time period, initiating a warning, signalling an alarm or otherwise reacting; the first and second transmitters are arranged in opposing configuration such that, during normal operation, an amount of light from the transmitter of one pair may be incident on the receiver of the other pair, wherein, in order to avoid fluctuations in signal strength in use from such incident light, at least one transmitter comprises means for adjusting the timing of projecting the beam within a window time-period W extending from an amount before to an amount after the nominal transmit interval.

Preferably, each transmitter comprises means for adjusting the timing of projecting the beam within a window time-period W extending from an amount before to an amount after the nominal transmit interval.

Preferably, the means for adjusting is for providing pseudo-randomly or randomly phased beams.

Most preferably, the means for adjusting comprises means for taking an initial light intensity reading and generating a/the random number sequence.

Preferably, wherein the system comprises a multiplicity of pairs of transmitter and receiver, subject to the size of the volume to be monitored. For instance, 3 to 100 pairs of transmitter and receiver, more preferably 3 to 30 pairs, or most preferably 3 to 10 pairs.

Preferably, the apparatus includes one or more features from the first aspect.

Advantageously, the present invention adjusts the timing of the beam signal of a beam detector within a window of possible timings, so as to lower the chance of any opposed detector unit projecting a corresponding beam at the same time, whilst maintaining consistency. Consistency is important. By maintaining the nominal time interval, the overall response time for the detector is kept constant because the speed of response of the detector to smoke is, typically, defined in terms of a ‘fire delay’ - which is a number of consecutive alarm condition readings required before the detector signals an alarm. As such, for a default delay of 10 seconds, the detector must detect an alarm condition 10 times in a row (at one second intervals of the nominal time interval) before an alarm is signalled. Without linking the random or pseudo-random timing of the beam signals to a window of the nominal time interval, then ten readings in a row could take significantly less than or more than 10 seconds, which would make the timing of the triggering of the alarm somewhat random also, and consistency of the overall response time would be lost.

As a detector system will only signal an alarm after a number of consecutive positive detection readings, which can be any number from, say, 2 to 30, this, together with the randomness of timing of the signal, acts to minimise the effects of a single in-phase timing of beam projections in opposed detector units. As such, the probability of there being a number of consecutive in-phase beam projections from the two detector units which would trigger a false alarm reduces with each consecutive projection, which means that the probability of false alarms having this cause reduces as one increases the number of consecutive positive readings required for signalling an alarm.

The invention will now be disclosed, by way of example only, with reference to the following drawings, in which:

Figure 2 is a schematic drawing of a series of pulsed transmission signals of a beam in a beam detector system; and

Figure 3 is a schematic drawing of two series of pulsed transmission signals of beams from first and second opposed detector units in a beam detector system.

With respect to Figure 2, which shows a series of pulsed transmission signals 1 of a beam, as is typical with beam detectors, the beams are not active all the time and Figure 2 shows first through to third pulsed signals 1a, 1b, and 1c. Figure 2 also shows: a nominal transmit interval T, which is also indicated by reference 2; a maximum window W, which is also indicated by reference 3, being a period of possible times during which the pulsed beam signal can be projected; and a length of time ‘L’, also indicated by reference 4, being the length of time of transmission of the beam signal.

Unlike a system which projects a beam signal exactly in a regular manner on the time interval T, the invention links randomness of the projection to the nominal time interval T so as to provide randomness or pseudo-randomness whilst maintaining consistency of response, as the time to trigger an alarm is unaffected by the randomness. Owing to the window ‘W, during which the projection may occur, the projection of the beam signal 1 can occur before or after the nominal time interval T, or even at the nominal time interval T, but it would then be expected that a following projection would not be on that nominal time interval T.

In Figure 2, three windows are shown, 3a, 3b and 3c, which correspond to the pulsed signals 1a to 1c. In window 3a, signal 1a is projected before the nominal time interval T; in window 3b, signal 1b is projected after the nominal time interval T; and, in window 3c, signal 1c is projected before the nominal time interval T. These are just examples of possible timings of the beam signals 1 a through to 1 c which can occur in the windows 3a through to 3c.

The random / pseudo-random number sequence is provided by embedded software, which generates the sequence in a defined manner.

Figure 3 shows series of signals 11; 21 respectively - shown side-by side -from a first detector unit and a second detector unit (not shown) but notionally referred to as detector units 10; 20 so as to avoid confusion. Each detector unit 10; 20 is independently operating on the principles as described in relation to Figure 2.

In this worked example, each detector unit 10; 20 is operating upon a notional transmit interval T of one second, and the first five seconds of signals are shown in Figure 3. The length of each signal ‘L’ is short, for example 10 milliseconds. The windows of operation of the beams, indicated as references 13a through to 13e for detector unit 10, and 23a through to 23e for detector unit 20, are in phase and each first signal 11a; 21a are projected on the notional time interval (indicated by the vertical lines showing the middle of each of the windows 13a to 13e and 23a to 23e). However, after the projection, timing of the projections of the beams is randomly altered within respective windows 13b through to 13e and 23b through to 23e. By way of example, in window 13b, the timing of projection of signal 11b is before the nominal time interval, and yet the timing of signal 21 b in window 23b is after. In window 13c, signal 11c is after the nominal time interval and the timing of signal 21c in window 23c is before. In windows 13d and 23d, the timing of signals 11 d; 21 d are both after the nominal time interval, but still at different times within the windows 13d and 23d. In window 13e, the timing of signal 11 e is before the nominal time interval and in window 23e, the timing of signal 21 e is again (practically) on the nominal time interval.

Therefore, Figure 3 seeks to provide a graphical example of signals 11; 21 from the respective detector units being projected at different times within their respective windows 13; 23. In this manner, this reduces the likelihood of the beam from one detector unit causing a false alarm by being detected by a separate detection unit.

Claims

Claims: 1. ) A method for adjusting the phasing of beams in a beam detector, the method comprising projecting a beam at a nominal transmit interval T for the purpose of detecting obscuration of the beam and, if a level of signal of the beam detected is less than a threshold for each of a number of consecutive projections or for each consecutive projection over a pre-determined time period, initiating a warning, signalling an alarm or otherwise reacting, wherein adjusting the timing of projecting the beam within a window time-period ‘W extending from an amount before to an amount after the nominal transmit interval.
2. ) A method as claimed in claim 1, wherein pseudo-randomly or randomly adjusting the timing of the beam.
3. ) A method as claimed in claim 1 or claim 2, wherein W < T or W = T/2, and preferably W is symmetrical about T.
4. ) A method as claimed in any preceding claim, wherein, if a length of time of projection of the beam is ‘L’, ‘W > 2’L’ to W » 2’L’.
5. ) A method as claimed in any preceding claim, further comprising using a pseudo-random number sequence to adjust the timing of projection.
6. ) A method as claimed in any preceding claim, further comprising using an initial light intensity reading, start-up time, or A-to-D converter input to generate a pseudo-random number sequence.
7. ) A method as claimed in any preceding claim, wherein T is about 0.1 to about 10 seconds, preferably about 0.5 to about 5 seconds and, most preferably, about 1 second.
8. ) A method as claimed in any preceding claim, wherein W is about 0.05 to about 10 seconds, further preferably about 0.25 to about 5 seconds and, most preferably, about 0.5 seconds.
9. ) A method as claimed in any preceding claim, wherein ‘L’ is about 1 millisecond to about 25 milliseconds, preferably about 5 milliseconds to about 20 milliseconds and, most preferably, about 8 milliseconds to about 12 milliseconds or about 10 milliseconds.
10. ) A method as claimed in any preceding claim, wherein T is one second, W is 500 milliseconds and ‘L’ is 10 milliseconds.
11. ) A method as claimed in any preceding claim, wherein the beam detector is an optical beam smoke detector, preferably a reflective-type optical beam smoke detector.
12. ) A method for adjusting the phasing of beams in a beam detector, substantially as herein disclosed, with reference to the accompanying Figure 2, Figure 3 or description and/or any example described herein.
13. ) A beam detector apparatus comprising: means for projecting a beam at a nominal transmit interval T for the purpose of detecting obscuration of the beam and, if a level of signal of the beam detected is less than a threshold for each of a number of consecutive projections or for each consecutive projection over a pre-determined time period, initiating a warning, signalling an alarm or otherwise reacting; and means for adjusting the timing of projecting the beam within a window time-period W extending from an amount before to an amount after the nominal transmit interval.
14. ) An apparatus as claimed in claim 13, wherein the means for projecting is a reflective-type optical beam smoke detector, comprising a transmitter and receiver in the same detector unit, and an associated reflector.
15. ) An apparatus as claimed in claim 13, wherein the means for projecting is an end-to-end optical beam smoke detector, comprising separate transmitter and receiver units.
16. ) An apparatus as claimed in any one of claims 13 to 15, wherein the means for adjusting comprises means for generating a random number sequence.
17. ) An apparatus as claimed in any one of claims 13 to 16, wherein the means for adjusting comprises means for taking an initial light intensity reading and generating a/the random number sequence.
18. ) A beam detector apparatus, substantially as herein disclosed, with reference to Figure 2 or 3 of the accompanying drawings, and/or any example described herein.
19. ) A beam detector system, the system comprising: a first transmitter and associated receiver; and a second transmitter and associated receiver, in which each pair of transmitter and receiver operate independently of the other pair by each projecting a beam at a nominal transmit interval T for the purpose of detecting obscuration of the beam and, if a level of signal of the beam detected is less than a threshold for each of a number of consecutive projections or for each consecutive projection over a pre-determined time period, initiating a warning, signalling an alarm or otherwise reacting; the first and second transmitters are arranged in opposing configuration such that, during normal operation, an amount of light from the transmitter of one pair may be incident on the receiver of the other pair, wherein, in order to avoid fluctuations in signal strength in use from such incident light, at least one transmitter comprises means for adjusting the timing of projecting the beam within a window time-period W extending from an amount before to an amount after the nominal transmit interval.
20. ) A beam detector system as claimed in claim 19, wherein each transmitter comprises means for adjusting the timing of projecting the beam within a window time-period W extending from an amount before to an amount after the nominal transmit interval.
21. ) A beam detector system as claimed in claim 19 or claim 20, wherein the means for adjusting comprises means for generating a random number sequence.
22. ) A beam detector system as claimed in any one of claims 19 to 21, wherein the means for adjusting comprises means for taking an initial light intensity reading and generating a/the random number sequence.
23. ) A beam detector system as claimed in any one of claims 19 to 22, wherein the system comprises a multiplicity of pairs of transmitter and receiver, preferably 3 to 10 pairs.
24. ) A beam detector system as claimed in any one of claims 19 to 23, wherein the means for projecting is a reflective-type optical beam smoke detector, comprising a transmitter and receiver in the same detector unit, and an associated reflector.
25. ) A beam detector system as claimed in any one of claims 19 to 23, wherein the means for projecting is an end-to-end optical beam smoke detector, comprising separate transmitter and receiver units.
26. ) A beam detector system, substantially as herein disclosed, with reference to Figure 2 or 3 of the accompanying drawings, and/or any example described herein.