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 systems comprising an alarm center receiving an analog signal.
• the invention relates to such a device comprising:
• the alarm center comprising a voltage generator which supplies the pair of conductors with an electric current known as a loop current
• the fire detector being connected to the pair of conductors in bypass between the two conductors, this fire detector having a normal state in which it does not allow passage at most that a weak derivative current between the two conductors and an alarm state in which it lets pass a higher derivative current between the two conductors, so that a change of state of the fire detector causes a variation of the loop current, this loop current thus constituting an analog electrical signal whose value is representative of the detection or not of a fire by the detector
• the unit central unit comprising measuring means for measuring the value of the loop current at regular time intervals, and this central unit being designed to calculate a difference between this measured value and a reference value of the current and to trigger an alarm reaction if this difference is greater than a first predetermined threshold.
• the CPU usually
• the loop current is subject to variations independent of the existence or not of a fire, in particular on each modification of the fire detection system.
• the loop current varies when adding a fire detector to a pair of conductors, when replacing one fire detector with another, or when removing a fire detector, since each Fire detector is generally traversed by a weak current diverted between the two conductors of the pair of conductors, even when it is not in the alarm state. Consequently, to take account of these variations, the user of the fire detection system must manually adjust the reference value of the current, after each modification of the system. This adjustment is generally carried out by means of a potentiometer.
• This adjustment step is delicate and time consuming. In addition, if the adjustment is not made by the user after the modification of the fire detection system, the operation of this system will no longer be reliable in the future.
• the present invention aims in particular to remedy these drawbacks.
• a fire detection system of the kind in question is essentially characterized in that the alarm center is adapted to make the value of loop current and the value of reference equal. less each time a certain predetermined event occurs which may correspond to a modification of the fire detection system. In this way, it is no longer necessary to manually adjust the current reference value after each modification of the fire detection system.
• the central processing unit is adapted to measure and store the value of the loop current at least each time said predetermined event occurs, the stored value of the loop current then constituting the reference value;
• the voltage generator generates an adjustable voltage, the alarm center being designed to, at least each time that said predetermined event occurs, adjust the voltage generated by the voltage generator until the loop current is equal at the reference value, this reference value being fixed, and the voltage generated by the voltage generator then remaining fixed;
• the predetermined event consists of a commissioning of the alarm center after a period of shutdown of said alarm center;
• the alarm center further includes reset control means which are connected to the central unit to reset it, said predetermined event consisting of 1 * activates said reset control means.
• FIG. 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
• FIG. 2 shows the signals u and i respectively received by the microprocessor of the fire detector and by the alarm center when the detector signals an alarm.
• a 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 conductors 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.
• the two terminals of the resistor RO 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 the 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 further comprises a fire sensor 7, in particular an ionic smoke detection sensor, an optical smoke detection sensor, a thermal sensor, etc.
• Sensor 7 measures a physical quantity whose variations 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 whose emitter and collector are connected in series with at least one resistor RI between the conductors 3 and 4.
• the output 6b of the microprocessor polarizes the transistor T in its passing direction, said transistor is activated and lets pass a derivative electric current between the conductors 3 and 4, which has the effect of increasing the electric current i which crosses the resistance R0.
• 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 possibly being for example between 3 and 10 seconds, and, at each new measurement, it compares the measured value with a reference value uO.
• the microprocessor 6 activates the transistor T via its output 6b, for example for a period of one second, so as to indicate to the alarm center 5 the existence of a fire.
• the resistance R0 of the alarm center is traversed by an increased current i which increases for example from 5 to 20 mA by compared to normal.
• This variation of 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 passes through the resistor R0, 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 whether or not this difference is greater than 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.
• 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 microprocessor 10 is programmed to measure the intensity i which traverses the resistance R0 at each new powering up of the alarm center 5, the measured value of this intensity then constituting the reference value iO.
• an input 10b of the microprocessor 10 can be connected to a reset control member 12, for example a contact controlled by a key, the microprocessor 10 being designed to measure the value of the current i on each actuation of the reset control member, the thus measured value of the current i then constituting the value iO reference.
• the fire detector 1 would not include a microprocessor 6, the signal from the sensor 7 directly controlling the base of the transistor T, - the alarm center 5 would measure the loop current other than by the resistor R0 associated with the voltage amplifier 9.
• the voltage generator 11 can be designed to generate an adjustable voltage.
• the voltage generated is adjusted until the loop current i is equal to the reference value iO, this value of reference remaining fixed.
• the voltage generator 11 may include a logic input lia which triggers the operation of an internal servo 11b of said generator, the logic input lia being connected to a logic output 10c of the microprocessor 10.
• the microprocessor 10 When the microprocessor 10 detects a new powering up of the alarm center 5 or a reset, it sends a logic signal to the voltage generator 11 via the input lia of this generator, which causes the the internal servo 11b of the voltage generator in the active state. In this active state, the control 11b varies the voltage supplied to the pair 2 of conductors until the loop current i is equal to the predetermined reference value iO. Once the loop current i is equal to the predetermined reference value iO, the control 11b returns to the passive state, and no longer varies the voltage delivered to the pair 2 of conductors by the voltage generator 11, until said voltage generator receives a new signal from the microprocessor 10 through its logic input 11a.
• control which varies the voltage delivered to the pair 2 of conductors by the voltage generator 11 could be constituted by an algorithm in memory in the microprocessor 10.
• the voltage generator 11 is no longer connected to the microprocessor 10 by a logic input 11a and also no longer comprises an internal servo 11b, but may for example include an analog input 11c connected to an analog output 10d of the microprocessor 10, the voltage delivered to the pair 2 of conductors by the voltage generator 11 then being controlled directly by the microprocessor 10 by means of the analog input links of the voltage generator.
• the microprocessor 10 detects a new power-up of the alarm center 5 or a reset, it is programmed to measure the loop current i and to vary the voltage delivered to the pair 2 of conductors by the voltage generator 11 until the measured value i of the loop current is equal to the predetermined reference value iO.

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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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Citations (5)

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

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