Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B17/00—Fire alarms; Alarms responsive to explosion
  • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
  • G08B29/18—Prevention or correction of operating errors
  • G08B29/20—Calibration, including self-calibrating arrangements
  • G08B29/24—Self-calibration, e.g. compensating for environmental drift or ageing of components

Definitions

• the present invention relates to fire detection devices comprising analog sensors.
• the invention relates to such a device comprising a fire sensor which measures a physical quantity, the variations of which indicate the existence of a fire and which transmits an analog electrical signal to an electronic central unit, this signal having a value representative of said physical quantity, the central unit comprising measuring means for measuring the value of the signal at regular time intervals, and this central unit being designed to calculate a difference between this measured value and a value of reference of the signal and to emit an alarm signal representative of a fire if this difference is greater than a first predetermined threshold.
• the analog electrical signal received by the central unit is subject to parasitic variations independent of the existence or not of a fire.
• parasitic variations may be due to variations in the ambient temperature or to variations in other ambient physical parameters.
• the fire sensor is an ion sensor
• changes in ambient pressure and humidity change the analog electrical signal sent by the fire sensor to the detector's CPU.
• the first predetermined threshold mentioned above is generally chosen to be large enough, so that these parasitic variations do not cause alarm reactions.
• this has the disadvantage that the sensitivity of the fire detection device finds diminished.
• the object of the present invention is in particular to remedy this drawback.
• a fire detection device of the kind in question is essentially characterized in that the reference value taken into account for each new measurement of the signal value depends on at least certain values of said signal previously measured by the central unit.
• the reference value taken into account for each new measurement of the signal value depends on at least certain values of said signal previously measured by the central unit.
• the first predetermined threshold is between 10% and 20% of the reference value of the signal
• the time interval between two measurements of the signal value is between 3 and 10 seconds;
• the reference value taken into account for each new measurement of the signal value is a weighted average of the n last measurements of said signal, n being an integer at least equal to 2;
• the central unit has in memory an initial reference value, said central unit being provided for calculating a difference between this initial reference value and the measured value of the signal, and for triggering fault signaling if said difference is greater than a second predetermined threshold greater than the first threshold;
• the device further comprises communication means for transmitting the alarm signal representing a fire to a remote alarm center.
• - Figure 1 is a schematic view showing an example of a fire detector according to the invention, connected to a central unit also according to the invention, and - Figure 2 represents the signals u and i received respectively by the microprocessor of the detector d and by the alarm center when the detector signals an alarm.
• a fire detector 1 is connected to an alarm center 5 via a pair 2 of conductors 3, 4 which extends between a first end 2a where the two conduc ⁇ tors 3, 4 are respectively connected to two terminals 5a, 5b of the alarm center, and a second end 2b where the two conductors 3, 4 are connected to each other by a resistor R.
• detectors 1 are connected to the pair 2 of conductors along the latter.
• pairs 2 of conductors can be connected to the alarm center 5, on several pairs of terminals 5a, 5b of this alarm center.
• each pair of terminals 5a and 5b of the alarm center are connected in series a voltage generator 11 and a resistor R0, so that a current i is generated in the pair 2 of conductors.
• the two terminals of the resistor R0 are connected to the two inputs 9a and 9b of a voltage amplifier 9, the output 9c of which is itself connected to an analog input 10a of a microprocessor 10, which thus receives a voltage representative of the current i: in other words, the microprocessor 10 can indirectly measure current i.
• the detector 1 is connected to the pair 2 of conductors by means of four terminals 3a, 3b, 4a, 4b, the conductor 3 being connected on the one hand to terminal 3a and on the other hand to terminal 3b, and the conductor 4 being connected on the one hand to the terminal 4a and on the other hand to the terminal 4b.
• terminals 3a and 3b are connected to each other in short circuit, as are terminals 4a and 4b.
• the fire detector 1 comprises a fire sensor 7, in particular an ionic smoke detection sensor, an optical smoke detection sensor, a thermal sensor, etc.
• the sensor 7 measures a physical quantity, the variations of which indicate the existence of a fire.
• the fire detector 1 also includes a microprocessor 6, which has an analog input 6a connected to the sensor 7.
• the sensor 7 transmits to this input 6a an analog electrical signal u, for example a voltage, which is representative of the physical quantity measured by the sensor 7, and which is therefore capable of indicating to the microprocessor 6 the existence of a fire in the vicinity of the fire detector.
• the microprocessor 6 also has an output 6b which is connected to the base of a transistor T, the emitter and the collector of which are connected in series with at least one resistor Ri between the conductors 3 and 4.
• the microprocessor 6 of the alarm detector 1 measures the value of the voltage u which it receives from the sensor 7, at regular time intervals. These time intervals can for example be between 3 and 10 seconds.
• the microprocessor 6 compares the measured value with a reference value uO which depends on the previously measured values, and which can be constituted for example by the last measured value, or by a function of the last measured values, for example a weighted average of the n last measured values, n being an integer at least equal to 2.
• At least some of the predetermined measured values which are taken into account for calculating the reference value uO have been measured for more than half an hour, or even more than one hour, before the comparison between u and uO.
• the microprocessor 6 activates the transistor T via its output 6b, for example for a period of one second, which constitutes an alarm signal indicating to the alarm center 5 the existence of 'a fire.
• the threshold ⁇ 3 can be relatively low, so that the fire detector 1 can have an optimal sensitivity without risking generating false alarms.
• the resistance R0 of the alarm center is traversed by an increased current i which increases for example by 5 to 20 mA compared to normal.
• This variation in the current i passing through the resistor R0 is transmitted to the analog input 10a of the microprocessor 10 of the alarm center in the form of a voltage signal, so that the microprocessor 10 can detect the switch to alarm state of detector 1, and then trigger an alarm reaction such as the operation of a siren, the transmission of an alarm message to a remote monitoring station, etc.
• the microprocessor 10 of the alarm center 5 is designed to measure at regular time intervals, for example every 3 to 10 seconds, the current i which crosses the resistance RO, via the voltage which it receives at its analog input 10a.
• the microprocessor 10 determines whether the current i indicates that one of the fire detectors 1 connected to the pair 2 of conductors is in the alarm state, by calculating the difference between the measured value of the current i and a reference value iO , and by determining if this difference is greater than or not above a predetermined threshold ⁇ l which may possibly have a different value depending on whether i is greater or less than iO, and which can be for example 10 to 20% of the reference value or which can be fixed at a determined electrical current, for example between 3 and 15 mA.
• the alarm center 5 When the alarm center 5 has determined that one of the detectors 1 is in the alarm state, it in turn emits an alarm signal which may be an audible signal, or which may consist of a telephone call, Or other.
• the microprocessor 6 of the detector 1 may have in memory an initial reference value U of the signal u, and be programmed to send a fault signal to the pair 2 of conductors if the difference between the measured value of the signal u and the initial reference value U is greater than one second predetermined threshold ⁇ 2 greater than threshold ⁇ 3.
• the second predetermined threshold ⁇ 2 may for example be 50% of the initial reference value U, and it may possibly have a first value if the measured value u is less than the initial reference value U and a second value if the measured value u is greater than the initial reference value U.
• the microprocessor 6 activates the transistor T by means of its output 6b, but by bringing the voltage of the output 6b to a value different from the voltage taken by the said output to generate a alarm signal, so that the increase in current i perceived by the microprocessor 10 of the alarm center 5 is different from the increase in current which takes place when the detector 1 has detected a fire.
• the microprocessor 10 of the alarm center 5 is then informed that one of the fire detectors 1 of the pair 2 of conductors has a fault, so that the alarm center 5 can react accordingly, for example by transmitting a fault message to a remote monitoring station, or other.
• the microprocessor 6 of the fire detector 1 detects a fault of the sensor 7 as indicated previously, it can sequentially activate and deactivate the transistor T so as to generate in the pair 2 of conductors a binary coded signal constituted by increases and successive decreases in current i, this coded binary signal being specific to detector 1.
• the alarm center 5 can identify the detector 1 which is faulty.
• the output 6b of the microprocessor 6 could be an analog output making it possible to generate a sinusoidal voltage, in which case the fault signal can consist of a frequency sent to the pair 2 of conductors and received by the microprocessor 10, this frequency preferably being specific to the fire detector 1, so that the alarm center 5 can identify the fire detector which is faulty.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Business, Economics & Management (AREA)
• Emergency Management (AREA)
• Engineering & Computer Science (AREA)
• Computer Security & Cryptography (AREA)
• Fire Alarms (AREA)

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• 1994
  • 1994-07-29 FR FR9409477A patent/FR2723237B1/fr not_active Expired - Fee Related
• 1995
  • 1995-07-27 EP EP95926439A patent/EP0772851B1/de not_active Expired - Lifetime
  • 1995-07-27 ES ES95926439T patent/ES2115390T3/es not_active Expired - Lifetime
  • 1995-07-27 JP JP8506245A patent/JPH11509340A/ja active Pending
  • 1995-07-27 WO PCT/FR1995/001012 patent/WO1996004624A1/fr active Application Filing
  • 1995-07-27 WO PCT/FR1995/001013 patent/WO1996004625A1/fr active IP Right Grant
  • 1995-07-27 DE DE69502502T patent/DE69502502T2/de not_active Expired - Fee Related

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