|Title of Invention||
|Abstract||The fire alarm (1) contains an optical module (5) having a light source (7), a measuring chamber (9) and an optical receiver (8), a temperature sensor (13) and an electronic evaluator (6) connected to the optical receiver (8) and the temperature sensor (13). A sensor (12) for a combustion gas, preferably for CO, is additionally provided in the alarm (1). The electronic evaluator (6) has a fuzzy controller in which a linking of the signals of the individual sensors (5, 12, 13) and a diagnosis of the respective type of fire takes place. For each type of fire a special application-specific algorithm is provided and can be selected by means of the diagnosis. A linking of the smoke concentration with the combustion gas concentration and with a parameter generated from the gradient of the temperature and the gradient of the smoke gas takes place in the fuzzy controller.|
Siemens Building Technologies AG, CH-8708 Mannedorf CB-495
The present invention concerns a fire alarm with an optical module having a light source, a measuring chamber and an optical receiver, a temperature sensor and an electronic evaluator.
In fire alarms of this type, which are termed multiple or multi-sensor fire alarms, the optical module is used for the detection of smoke and the temperature sensor for the detection of the heat occurring at the outset of a fire. The optical module can measure either the light from the light source that is scattered by smoke particles or the light from the light source that is attenuated by these smoke particles. In the first case the optical module is a scattered-light alarm and in the second case is that of a point-extinction or transmitted-light alarm. In both cases the optical module is designed so that interfering external light cannot penetrate the measuring chamber and smoke can very easily do so. The temperature sensor is used both for increasing the sensitivity and for improving the protection for the scattered light alarm against false alarms. A scattered light alarm with a temperature sensor is disclosed in EP-A-0 654 770, for example.
The scattered light alarm and the transmitted light alarm are exceptionally sensitive and can detect fires with a high degree of reliability. However, in certain cases the high sensitivity can lead to false alarms, which is undesirable for a number of reasons. Apart from the fact that false alarms at the very least tend to reduce the attentiveness of the relevant safety personnel, in most countries the fire service and/or the police demand compensation for call-outs caused by false alarms; this compensation can rise progressively with the number of false alarms. For this reason, protection against false alarms in fire alarms now gets very high priority.
As a result of the invention, false alarm protection for the alarm should now be further improved, together with a reduction in its response time and a homogeneous alarm response characteristic should also be obtained. A homogeneous alarm response characteristic means that the alarm should respond in more or less the same way to different fires and not extremely rapidly to one type of fire and extremely slowly to another, or even not at all.
This object is achieved according to the invention in that an additional sensor for at least one combustion gas is provided in the alarm and the electronic evaluator is designed to link the
signals of the individual sensors and to diagnose the respective type of fire, and that, based on-this diagnosis, a special application-specific algorithm is selected for the processing of the sensor signals.
A first preferred embodiment of the fire alarm according to the invention is characterised in that the electronic evaluator has a fuzzy controller for effecting said linking.
The following six different test fires (abbreviated to TF) are specified by European Standard EN-54:
- TF1: wood fire
- TF2: smouldering wood fire
- TF3: smouldering textile fire
- TF4: foam material fire
- TF5: heptane fire
- TF6: alcohol fire.
The optical module of the fire alarm according to the invention can be designed so that either the light from the light source that is scattered by smoke particles or the light from the light source that is attenuated by these smoke particles is measured in the measuring chamber. In the first case the detection principle is that of a scattered-light alarm and in the second case that of a transmitted-light alarm. Here the scattered-light alarm can be designed as a forward-scatter or back-scatter device or as a forward-scatter and back-scatter device. The latter has the advantage that the type of smoke that is present can be ascertained with the aid of the scatter at different scatter angles; see WO-A-84 01650.
The multi-sensor fire alarm according to the invention, which contains an optical smoke sensor, a temperature sensor, a combustion gas sensor and a fuzzy controller and in which a special application-specific algorithm is provided for each type of fire, makes it possible by linking the signals of the sensors in the fuzzy controller to detect the respective type of fire and to select the suitable algorithm. On the one hand this improves the false alarm protection (robustness) of the alarm and on the other hand a balanced alarm response characteristic can be obtained by suitable choice of the application-specific algorithm.
A type of problem diagnosis in which the fuzzy controller monitors whether certain faults frequently occur below the respective alarm thresholds, is also possible. The fuzzy controller can report such faults to the control centre or the operating personnel via a suitable
communications interface and in this way indicate potential sources of interference whose cause may possibly lie in an incorrect application of the relevant alarm.
A second preferred embodiment of the fire alarm according to the invention is characterised in that a link is effected in the fuzzy controller between the smoke concentration, the concentration of the smoke gas to be detected and a parameter generated from the gradient of the temperature and the gradient of the smoke gas.
A third preferred embodiment of the fire alarm according to the invention is characterised in that said parameter is generated from the quotient of the temperature gradient and the smoke gas gradient.
A fourth preferred embodiment of the fire alarm according to the invention is characterised in that the additional sensor for a combustion gas is a CO sensor.
A fifth preferred embodiment of the fire alarm according to the invention is characterised in that the light source of the optical module is designed to emit radiation in the wavelength range of visible light.
In a sixth preferred embodiment the wavelength of the radiation emitted by the light source is in the range of blue or red light and is preferably 460 nm and 660 nm, respectively.
A further preferred embodiment of the fire alarm according to the invention is characterised in that at least one polarisation filter is provided in the path between the light source and the optical receiver.
A further preferred embodiment is characterised in that the at least one polarisation filter is a so-called active polariserwith electrically-adjustable polarisation plane.
By preference, the active polariser is formed by a liquid crystal display whose polarisation plane can be adjusted by applying a voltage.
The invention is explained in further detail below with the aid of an exemplary embodiment and
the drawings, of which:
Fig. 1 shows a schematic sectional representation of a fire alarm according to the invention;
and Fig. 2 shows a simplified block diagram of the signal processing.
The fire alarm 1 illustrated in an axial cross-section in Fig. 1 is substantially an optical smoke alarm that is extended by additional sensors for fire parameters, and in this representation is a scattered-light alarm. Since it is assumed that such optical alarms are known, they are not
described in detail here. In this connection, reference is made to EP-A-0 616 305 and EP-A-0 821 330. The optical smoke alarm can also be formed by a so-called point-extinction or light absorption alarm, as described in EP-A-1 017 034, for example.
The fire alarm 1 as shown consists in the known manner of an alarm insert 2, that preferably can be attached to a base (not shown) fitted to the ceiling of the room to be monitored, and an alarm cover 3 placed over the alarm insert 2, that is provided with smoke inlet openings 4 in the area of its dome which in the operating state of the alarm is directed towards the room to be monitored. The alarm insert 2 substantially comprises a compartment-type basic element on whose side facing the alarm dome is arranged an optical module 5 and on whose side facing the alarm base is arranged an electronic evaluator 6.
In the case of a scattered-light alarm, the optical module 5 consists substantially of a measuring chamber 9 containing a light source 7 and an optical receiver 8, the measuring chamber being externally shielded from external light by means, not shown. The optical axes of the light source 7 formed by an infrared or a red or blue light-emitting diode (IRED or LED, respectively) and the optical receiver 8 are bent with respect to each other, so that light beams are prevented by this path and by screening from passing by a direct path from the light source 7 to the optical receiver 8. The light source 7 sends short, high-energy light pulses into the central part of the measuring chamber 9, the optical receiver 8 "seeing" this central part of the measuring chamber 9, but not of course the light source 7.
The light from the light source 7 is scattered by smoke penetrating the scattered-light space and a portion of this scattered light falls onto the optical receiver 8. The receiver signal produced by this is processed by the electronic evaluator 6. During processing the receiver signal is compared in the known manner with an alarm threshold and at least one pre-alarm threshold, and if the receiver signal exceeds the alarm threshold the electronic evaluator 6 generates an alarm signal at an output 10. In this case, intelligent signal processing ensures that the output of the alarm signal occurs at the lowest possible smoke values, but in so doing does not give rise to unacceptable false alarms.
A so-called active polariser 11, that is a polariser with a rotatable polarisation plane, can be provided in the path between the light source 7 and the optical receiver 8 so that the light scattering can be measured in both polarisation planes. This active polariser is preferably formed by an electronic polarisation plate with a liquid crystal, which rotates its polarisation plane by 90*" when a voltage is applied. The measurement of the degree of polarisation, that is
the polarised scattered light in the two polarisation planes, can reduce the response time of the alarm 1 to certain test fires and thereby produce a homogeneous response characteristic.
As can also be seen from Fig. 1, in addition to the optical module 5, the fire alarm 1 contains a further two sensors for fire parameters, actually a CO sensor (generally a combustion gas sensor) 12 and a temperature sensor 13. A suitable CO sensor is described in EP-B-0 612 408 (see also EP-A-0 803 850). NTC thermistors have proved successful as temperature sensors (see the PolyRex smoke alarm of the AlgoRex fire alarm system - PolyRex and AlgoRex are registered trade marks of Siemens Building Technologies AG, Cerberus Division, formerly Cerberus AG).
Theoretical considerations and practical fire tests have produced the correlations between the fire parameters measured with the various sensors: optical module 5, CO sensor 12 and temperature sensor 13. These are summarised in the table below. Naturally, the amount of smoke or smoke concentration is measured as a further fire parameter; that is the known function of an optical smoke alarm and thus that of the optical module 5.
The following results can be seen from the table:
• The CO concentration is better than all the other parameters for early detection of TF3 and
correlates here with the smoke concentration.
• The CO gradient/temperature gradient quotient is very suitable for early detection of TF5 and
TF6 and correlates here with the temperature rise.
• The temperature rise is very suitable for early detection of TF1, TF5 and TF6 and, with the exception of TF6 (no smoke), correlates with the degree of polarisation. This result can be interpreted in that fires which generate a lot of heat produce fairly small aerosol particles. The correlation between temperature rise and degree of polarisation can be used to confirm the alarm and thus improve the robustness of the alarm.
The table also shows that all six types of fires can be individually diagnosed with the aid of the CO concentration, CO gradient/T gradient quotient and smoke concentration parameters. This means that the signature of a fire can be unambiguously recognised by means of these parameters. On the other hand, the CO concentration, degree of polarisation and smoke concentration allow the type of fire to be determined, with the exception of TF6 of course, which cannot be detected with the aid of these parameters. The measurement of the degree of polarisation also has the advantage that the type of fire can be recognised even in cases where the temperature does not rise sufficiently fast. This case can occur in high rooms, for example.
As schematically represented in Fig. 2, the signals of the three sensors, optical module 5 for the smoke concentration and the degree of polarisation, CO sensor 12 and temperature sensor 13, are an integral part of the diagnostic stage 14 forming the electronic evaluator 6, which substantially contains a fuzzy controller. The signals of the sensors are combined and analysed in the diagnostic stage 14 and the type of fire is determined from this analysis. Finally, the appropriate algorithm for the respective type of fire is selected and used for the evaluation of the sensor signals. As already mentioned, the fuzzy controller can also be used for diagnostic purposes, for indicating problems.
With regard to its operation, the optical module 5 of the fire alarm according to the invention corresponds to a conventional scattered-light alarm with forward scatter or back scatter, or to a scattered-light alarm with forward scatter and back scatter, or a point-extinction or transmitted-light alarm. The sensor 12 for the at least one combustion-gas, which is preferably a CO sensor, is an essential part of the fire alarm according to the invention.
It should be pointed out that it can be very advantageous to additionally fit other types of fire alarms with a combustion gas sensor, in particular a CO sensor. Such fire alarms are, for example, so-called linear smoke alarms or beam alarms such as the type DL01191 from Siemens Building Technologies AG, Cerberus Division, and the flame alarms, such as the type DF1190 from Siemens Building Technologies AG, Cerberus Division.
Fire alarm according to Claim 9, characterised in that the active polariser is formed by a liquid crystal display whose polarisation plane can be adjusted by applying a voltage.
Fire alarm according to Claims 3 and 10, characterised in that during the measurement of the smoke concentration in the optical module (5), a determination of the degree of polarisation of the radiation of the light source (7) that is scattered in the measuring chamber (9) is carried out.
12. Fire alarm with an optical module, substantially as hereinabove described and illustrated with reference to the accompanying drawings.
|Indian Patent Application Number||926/MAS/2000|
|PG Journal Number||05/2007|
|Date of Filing||31-Oct-2000|
|Name of Patentee||M/S. SIEMENS BULIDING TECHNOLOGIES AG|
|Applicant Address||CERBERUS DIVISION ALTE LANDSTRASSE 411, CH-8708 MANNEDORF|
|PCT International Classification Number||G08B 17/06|
|PCT International Application Number||N/A|
|PCT International Filing date|