EP0489232A1 - Brandmeldeanlage mit Ueberwachung - Google Patents

Brandmeldeanlage mit Ueberwachung Download PDF

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Publication number
EP0489232A1
EP0489232A1 EP91115061A EP91115061A EP0489232A1 EP 0489232 A1 EP0489232 A1 EP 0489232A1 EP 91115061 A EP91115061 A EP 91115061A EP 91115061 A EP91115061 A EP 91115061A EP 0489232 A1 EP0489232 A1 EP 0489232A1
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EP
European Patent Office
Prior art keywords
ionization
signal
operating voltage
output signal
measuring chamber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91115061A
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German (de)
English (en)
French (fr)
Inventor
Marc Thuillard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Cerberus AG
Original Assignee
Cerberus AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cerberus AG filed Critical Cerberus AG
Publication of EP0489232A1 publication Critical patent/EP0489232A1/de
Withdrawn legal-status Critical Current

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    • 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
    • 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
    • G08B17/11—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using an ionisation chamber for detecting smoke or gas
    • 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
    • G08B29/26—Self-calibration, e.g. compensating for environmental drift or ageing of components by updating and storing reference thresholds

Definitions

  • the invention relates to a fire alarm system according to the preamble of claim 1, in which a number of detection lines lying ionization smoke detectors, which can assume different electrical states, are connected to a fire alarm control panel.
  • Fire alarm systems of this type are increasingly used to protect human lives and property; they consist of fire detectors that are installed in the objects to be protected and fire control panels that are connected to the detectors via a network. Ionization smoke detectors occupy a special position among fire detectors because they are able to detect fires at such an early stage that suitable means, in particular to protect human lives, can be used in good time. One therefore speaks of early warning systems.
  • the functioning of the ionization smoke detectors is based on the exploitation of the physical effect that the ion current flowing in an ionization chamber is caused by the presence of smoke, i.e. is influenced by aerosols.
  • the air is ionized in a measuring chamber to which the surrounding air has access using weak radioactive preparations, so that an ion current flows between the electrodes. If smoke, or generally speaking, a fire aerosol, penetrates into the measuring chamber, the air ions accumulate on the aerosol particles, which greatly reduces their mobility. The result is a decrease in the ion current. If the current change exceeds a certain limit value, an alarm signal is generated which is transmitted to the control center.
  • a problem with all fire alarm systems is the occurrence of false alarms.
  • a particular problem with ionization smoke detectors is that the detectors are sensitive to the occurrence of increased air velocities, to condensation or to the radioactive source being covered by dust or corrosion, since these phenomena have the same effect on the ion current as the occurrence of fire aerosols . Since such a change in the ion current causes the detectors to become more and more sensitive, the tendency towards false alarms is constantly increasing. The occurrence of false alarms is particularly disruptive if automatic alarms are triggered Extinguishing systems are put into operation or external extinguishing forces are deployed.
  • EP-A1-0'070'449 it was proposed to evaluate the measured values after transmission to a signal center.
  • An idle value is formed from the individual measured values for each detector and stored in an idle value memory.
  • a current comparison value is formed from the respective detector measured value and a comparison value stored in a comparison memory and is written into the comparison memory. After comparison of the current comparison value with a limit value, either a display device is activated, or a new rest value is formed from the current detector measured value and the stored rest value and written into the rest value memory. This makes it possible to compensate for a slow change in the detector, for example due to contamination, and to keep the detector sensitivity constant over a very long time.
  • a protective ring system serves to report an insulation resistance of the ionization measuring chamber which is reduced due to condensation or dust.
  • a change in the potential difference between the guard ring system and the connection point between the measuring and reference chamber is evaluated by the control center as a fault.
  • US-A-3,964,036 describes a fire detection system in which a measuring ionization chamber serving to detect smoke and a second ionization chamber serving as a reference chamber are connected in series between two lines which simultaneously serve to supply the detector with power.
  • An amplification element is connected to the common electrode of the measuring and reference chamber, which emits an amplified signal depending on the potential of the common electrode.
  • the course of the amplified signal from the ionization smoke detector is visualized on a display device and recorded by a writing device.
  • a false alarm is distinguished from a real alarm in that the signal curve obtained is compared with known curves obtained through contamination or condensation. This type of false alarm detection is technically and personnel-intensive.
  • the fire alarm system proposed in EP-PA-90'117'759.2 makes it possible to recognize immediately, immediately and automatically whether a change in the ionization current in the ionization measuring chamber is a false alarm or a real alarm caused by a fire acts.
  • the fire alarm system described in EP-PA-90'117'759.2 still has the disadvantage that the penetration of smoke cannot be detected if the ionization has been weakened by condensation on the radioactive source.
  • the object of the present invention is to overcome this disadvantage, i.e. to improve the fire alarm system described in EP-PA-90'117'759.2 so that the occurrence of smoke caused by a fire can be detected with certainty even with a covered radioactive source.
  • a preferred embodiment of the fire alarm system according to the invention consists in that the means for periodically changing the operating voltage of the ionization smoke detectors and the means for signal evaluation are arranged in the ionization smoke detectors.
  • the means for periodically changing the operating voltage of the ionization smoke detectors and the means for signal evaluation are arranged in the signal center.
  • a particularly preferred embodiment of the fire alarm system according to the invention consists in that means are provided in the fire detectors which are the output signal of the amplifier element of the ionization smoke detectors transmit to the signaling center that means for evaluating the transmitted signals are provided in the signaling center and that the means for changing the operating voltage of the ionization smoke detectors are provided in the fire detectors.
  • the essential improvement of the fire alarm system of the present invention compared to the fire alarm system according to EP-PA-90'117'759.2 is that the operating voltage of the ionization smoke detectors is not permanently set to a higher value if the ion current in the ionization measuring chamber drops below a predetermined value. but that the output signal of the amplifier element is divided by a constant value, that the operating voltage is periodically switched between a higher and a lower value, as long as the ion current in the ionization measuring chamber remains below the stated value and that the output signals of the amplifier element constantly at low and high operating voltage be compared with each other.
  • the output signal of the amplifier element when the operating voltage is low is smaller than the output signal when the operating voltage is high and if it is simultaneously above a predetermined value, i.e. is above the alarm threshold of the fire detector, then the ion current in the measuring ionization chamber was not reduced due to the radioactive source being covered, and an alarm is triggered.
  • an operating voltage is applied to the ionization measuring chamber of the fire detector, which determines the operating point of the measuring chamber so that it is operated in an area of high sensitivity to smoke.
  • a signal is triggered which is not certain whether it is caused by the penetration of smoke into the measuring chamber or by other events which likewise reduce the ion current.
  • the operating voltage of the measuring chamber is alternately increased to a value which is so high that the measuring chamber is operated as saturated as possible and then lowered again to the normal value.
  • the continuous comparison of the ion currents measured at different chamber voltages enables an alarm to be recognized even when the radioactive source is covered.
  • FIG. 1 shows the block diagram of a fire alarm system according to EP-PA-90'117'759.2.
  • the ionization smoke detector 7 has an ionization measuring chamber 1 with smoke entry openings which allow the ambient air to enter the measuring chamber 1.
  • a radioactive source 10 for ionizing the air in the measuring chamber 1.
  • the ionization measuring chamber 1 is in series with a high-resistance resistor 2 between two detection lines 8, 9, which are used simultaneously for the voltage supply.
  • the load resistor 2 shows a linear current / voltage characteristic.
  • An amplifier element 3 is connected to the connection point between ionization measuring chamber 1 and load resistor 2.
  • the output of the amplifier element 3 is connected to an input of two comparators 15, 16.
  • the voltage Us1 which determines the alarm threshold of the ionization smoke detector 7, is present at the second input of the first comparator 15;
  • the voltage Us2, which determines the monitoring threshold for the saturation current Is, is present at the second input of the second comparator 16.
  • the output of the first comparator 15 is connected to a monoflop 5, the time constant of which is greater than the time required to monitor the saturation current; the output of the monoflop 5 is connected on the one hand to a voltage generator 11 connected to the signal line 8 which supplies the positive supply voltage + U, and on the other hand to an input of an AND gate 12.
  • the output of the second comparator 16 is connected to the other input of the AND gate 12.
  • the voltage generator 11 is used to generate two different voltages on the signaling line 8 serving for the voltage supply.
  • the output of the AND gate 12 is connected to a bistable switch 13 which is connected to the signal center 6 via a further signaling line 14.
  • the voltage generator 11 In the normal state, the voltage generator 11 generates a voltage U1 at its output, which defines the operating point of the measuring chamber 1. This value is chosen so that the measuring chamber 1 is operated in an area of high sensitivity to smoke.
  • the measuring chamber current generates a voltage drop U0 across the load resistor 2. If the ion current in the ionization measuring chamber 1 changes, the output signal of the amplifier element 3 also changes accordingly. When the ion current drops, e.g. The operating voltage is increased to the value Ia1 by the voltage generator 11, and the current at this increased voltage is measured. If an increased current Ia2 is now detected, the penetration of smoke was the reason for the current reduction and the signal is interpreted as an alarm signal.
  • the saturation current must have decreased and coverage of the radioactive source 10 by condensation or pollution must be regarded as the reason for the current reduction; the signal is therefore not interpreted as an alarm, but, if desired, displayed as a fault.
  • the fire alarm system described cannot detect the penetration of smoke if the ionization current has been reduced simultaneously or previously by covering the radioactive source 10, for example by condensation, since the second comparator 16 blocks the triggering of an alarm when a fault occurs is.
  • This blocking of a real alarm event occurring at the same time can, however, be overcome by an improved fire alarm system, which is explained in more detail below with reference to FIG. 2.
  • the ionization smoke detector 7 also has an ionization measuring chamber 1 with smoke entry openings which allow the ambient air to enter the measuring chamber 1.
  • a radioactive source 10 for ionizing the air in the measuring chamber 1.
  • the ionization measuring chamber 1 is in series with a high-resistance load resistor 2, which is a linear current / voltage Shows characteristics.
  • An amplifier element 3 is connected to the connection point between ionization measuring chamber 1 and load resistor 2.
  • the output of the amplifier element 3 is connected to a switch 23 which alternately connects the output signal of the amplifier element 3 to two division circuits 26, 27.
  • the output signal of the amplifier element 3 is divided by a constant value, specifically by a value Ua, which is fixed in the factory. This value Ua corresponds to the output signal of the amplifier element 3 at a low operating voltage Ut. This means that the output signal of the division circuit 26 is normally one.
  • the output signal of the amplifier element 3 is divided by another constant value, namely by a value Ub, which is also set in the factory and corresponds to the output signal of the amplifier element 3 at the higher operating voltage Uh.
  • a value Ub which is also set in the factory and corresponds to the output signal of the amplifier element 3 at the higher operating voltage Uh.
  • the outputs of the two division circuits 26, 27 are each connected to two instantaneous value memories 24, 25, in which the output signal of the amplifier element 3 divided by a constant value in the division circuits 26, 27 ("normalized" value) is stored until after the next switchover, a new value is placed at the input of the corresponding instantaneous memory 24, 26.
  • the voltage generator 11 controls the switch 23 so that it connects the output of the amplifier element 3 with the first division circuit 26 and the first instantaneous value switch 24 when the voltage Ut is present and with the second Division circuit 27 and the second instantaneous value memory 25 when the voltage Uh is present.
  • the exit of the first Instantaneous value memory 24 (which corresponds to the signal at the low voltage Ut) is connected to the inputs of four different comparators 15, 16, 22, 28.
  • a voltage Us1 which represents the alarm threshold of the ionization smoke detector 7, is applied to the + input of the first comparator 15 and a voltage Us2, which represents the monitoring threshold of the ionization smoke detector 7, is applied to the + input of the second comparator 16. While one input of the third comparator 22 is connected to the output of the first instantaneous value switch 24, the other input of the third comparator 22 is connected to the output of the second instantaneous value memory 25, that is to say in the third comparator 22 the two normalized output signals of the amplifier element 3 are compared with one another .
  • the normalized output signal of the amplifier element 3 is compared with a voltage Us0.
  • the value of Us0 is greater than the alarm threshold Us1 and the monitoring threshold Us2; it represents the value of the normalized output signal of the amplifier element 3, at which the voltage generator 11 switches over the operating voltage on the detection line 8. If the value of the normalized output signal of amplifier element 3 is greater than voltage Us0, then the output at fourth comparator 28 is logic ZERO.
  • the voltage generator 11 is constructed in such a way that a constant voltage Ut is generated in this case. If the value of the normalized output signal of the amplifier element 3 at a low voltage Ut is less than Us0, then the output state of the fourth comparator 28 is logic ONE.
  • This signal is forwarded to the voltage generator 11 and causes the latter to periodically switch the operating voltage U + on the message line 8 between the low voltage Ut and the high voltage Uh. Since the voltage generator 11 also controls the changeover switch 23, the output signal of the amplifier element 3 is synchronously fed alternately (at low voltage Ut) to the first and (at high voltage Uh) to the second division circuit.
  • the voltage generator 11 In the normal state, the voltage generator 11 generates at its output a voltage Ut, which determines the operating point of the measuring chamber 1. This value Ut is selected so that the measuring chamber 1 is operated in an area of high sensitivity to smoke.
  • the measuring chamber current generates a voltage drop U0 across the load resistor 2. Since the voltage generator 11 outputs the voltage Ut, the output of the amplifier element 3 is connected to the first division circuit 26, in which the signal is divided by the constant value Ua.
  • the signal normalized in this way is present at the inputs of the four comparators 15, 16, 22, 28. Since the signal is greater than the voltage Us0, the voltage on the detection line 8 remains at the value Ut and through the switch 23 the output of the amplifier element 3 remains connected to the division circuit 26.
  • the mode of operation of the fire alarm system according to the invention is best explained in more detail with reference to FIG. 4.
  • the normalized output voltage U / Ua or U / Ub of the amplifier element 3 is plotted on the ordinate axis, while the time is plotted on the abscissa axis.
  • the crosses x represent the normalized output voltage U / Ua of the amplifier element 3 at a low operating voltage Ut, and the small circles o represent the output voltage U / Ub of the amplifier element 3 at an increased operating voltage Uh.
  • the output signal of the amplifier element 3 also changes accordingly.
  • the output signal of the amplifier element 3 also decreases.
  • the voltage generator 11 switches to the second operating state, ie it switches the voltage on the detection line 8 periodically (with a switching frequency of 0 , 25 to 1 Hz) between the lower (normal) value Ut and the higher value Uh back and forth.
  • the changeover switch 23 is actuated synchronously, so that the output signal of the amplifier element 3 is alternately connected to the first 26 or the second division circuit 27.
  • the normalized output signals are there at the outputs of the instantaneous value memories 24, 25 and are compared in the third comparator 22.
  • the normalized output signal (U / Ua) of the amplifier element 3 is consequently ONE (FIG. 4a, to the left of the point P). If a fire aerosol (smoke) penetrates into the ionization measuring chamber 10 (point P), the ion current in the ionization measuring chamber 10 decreases and the normalized output signal of the amplifier element 3 decreases accordingly until the value of Us0 (switching threshold) is reached (Fig.
  • the fourth comparator 28 switches to the logic state ONE and the voltage generator switches to the second operating state, ie it constantly switches the supply voltage + U between the low value Ut and the higher value Uh. Since the normalized output signals (FIG. 4 a, curve A) of the amplifier element 3, which are present at the first instantaneous value memory 24, ie the values measured at a low supply voltage + U, are lower than the normalized output signals (FIG. 4, curve B) of the gain element 3 with increased supply voltage + U, which are present at the first instantaneous value memory 24, the logic state of the third comparator 22 is ONE.
  • the logic state is the first Comparator 15 also ONE; as a result, the logic state of the first AND gate 12 becomes ONE and an alarm signal is transmitted to the signal center 6.
  • the normalized output signal of the amplifier element 3 which is present at the first instantaneous value memory 24 (low supply voltage), is larger than the corresponding signal when the supply voltage Uh is increased; consequently, the logic state of the third comparator 22 is ZERO.
  • the logic state of the first AND gate 12 is ZERO, so that no alarm signal is transmitted to the signal center 6. If the normalized output signal of the amplifier element 3 simultaneously falls below the value for the monitoring threshold Us2, then the second comparator 16 assumes the logic state ONE. Because of the reversal of the output state of the third comparator 22 at the input of the second AND gate 17, this also assumes the logic state ONE, and an error signal is transmitted to the signal center 6.
  • the third case remains to be considered, in which the ionization smoke detector 7 is impaired in its functionality by a cover (condensation) of the radioactive source 10 in the ionization measurement chamber (10) and at the same time smoke enters the ionization measurement chamber (10).
  • the reduction in the ionization current in the ionization measurement chamber (10) reduces the normalized output signal of the amplifier element 3 to such an extent that the value of Us0 is not reached (FIG. 4c, Point Q);
  • the fourth comparator 28 switches to the logic state ONE and the voltage generator switches to the second operating state, ie it constantly switches the supply voltage + U between the low value Ut and the higher value Uh (FIG. 4c, between points Q and P). If the normalized output signal of the amplifier element 3 simultaneously falls below the value for the monitoring threshold Us2, then, as described above for the case (2), a fault signal is triggered.
  • the logic state of the third comparator 22 is ONE. If the signal at the first instantaneous value memory 24 simultaneously falls below the alarm threshold Us1, the logic state of the first comparator 15 is also ONE; as a result, the logic state of the first AND gate 12 also becomes ONE, and an alarm signal is transmitted to the signal center 6, although the functionality of the ionization smoke detector 7 is impaired by condensation and a fault signal is present in the signal center 6.
  • the means for evaluating the signals can also be accommodated in the signal center 6.
  • the ionization smoke detector 7 contains suitable transmission electronics which digitally or analogously transmit the voltage amplified by the amplifier element 3 via the load resistor 2 to the signal center 6.
  • the switching of the operating voltage can either take place from the signal center 6 or be triggered by a signal from the signal center 6 in the ionization smoke detector 7.
  • FIG. 3 A fire alarm system according to the present invention is described in FIG. 3, in which the ionization smoke detector 7 (as in the embodiment according to FIG. 2) has an ionization measuring chamber 1 with smoke entry openings which allow the ambient air to enter the measuring chamber 1.
  • a radioactive source 10 for ionizing the air in the measuring chamber 1.
  • the ionization measuring chamber 1 is in series with a high-resistance resistor 2 between two detection lines 8, 9, which are used simultaneously for the voltage supply.
  • An amplifier element 3 is connected to the connection point between ionization measuring chamber 1 and load resistor 2. In this case, however, the output of the amplifier element 3 is connected to an analog-digital converter 19 which, via the further signaling line 14, forwards an analog signal in digital form to the signal present at the output of the amplifier element 3 to the signal center 6.
  • the digital signal is converted back into an analog signal in a digital-analog converter 20 and (as in the embodiment according to FIG. 2) fed to a changeover switch 23.
  • the further signal processing now corresponds approximately to that of FIG. 2, the voltage generator 11 being located in the signal center 6.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
EP91115061A 1990-12-04 1991-09-06 Brandmeldeanlage mit Ueberwachung Withdrawn EP0489232A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH3822/90A CH681932A5 (sv) 1990-12-04 1990-12-04
CH3822/90 1990-12-04

Publications (1)

Publication Number Publication Date
EP0489232A1 true EP0489232A1 (de) 1992-06-10

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EP91115061A Withdrawn EP0489232A1 (de) 1990-12-04 1991-09-06 Brandmeldeanlage mit Ueberwachung

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US (1) US5243330A (sv)
EP (1) EP0489232A1 (sv)
CA (1) CA2056768A1 (sv)
CH (1) CH681932A5 (sv)

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CN103946703A (zh) * 2011-10-06 2014-07-23 密克罗奇普技术公司 用以确定存在漏电流时的离子电流的差动电流测量
US10748399B2 (en) 2016-07-11 2020-08-18 Autronica Fire & Security As Smoke detector dynamic range adjustment system and method

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US9257980B2 (en) 2011-10-06 2016-02-09 Microchip Technology Incorporated Measuring capacitance of a capacitive sensor with a microcontroller having digital outputs for driving a guard ring
US9467141B2 (en) 2011-10-07 2016-10-11 Microchip Technology Incorporated Measuring capacitance of a capacitive sensor with a microcontroller having an analog output for driving a guard ring
US9071264B2 (en) 2011-10-06 2015-06-30 Microchip Technology Incorporated Microcontroller with sequencer driven analog-to-digital converter
US8847802B2 (en) 2011-10-06 2014-09-30 Microchip Technology Incorporated Microcontroller ADC with a variable sample and hold capacitor
US9207209B2 (en) 2011-12-14 2015-12-08 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9176088B2 (en) 2011-12-14 2015-11-03 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9189940B2 (en) 2011-12-14 2015-11-17 Microchip Technology Incorporated Method and apparatus for detecting smoke in an ion chamber
US9823280B2 (en) 2011-12-21 2017-11-21 Microchip Technology Incorporated Current sensing with internal ADC capacitor
US8884771B2 (en) 2012-08-01 2014-11-11 Microchip Technology Incorporated Smoke detection using change in permittivity of capacitor air dielectric
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103946703A (zh) * 2011-10-06 2014-07-23 密克罗奇普技术公司 用以确定存在漏电流时的离子电流的差动电流测量
CN103946703B (zh) * 2011-10-06 2017-02-22 密克罗奇普技术公司 用以确定存在漏电流时的离子电流的差动电流测量
US10748399B2 (en) 2016-07-11 2020-08-18 Autronica Fire & Security As Smoke detector dynamic range adjustment system and method

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US5243330A (en) 1993-09-07
CA2056768A1 (en) 1992-06-05
CH681932A5 (sv) 1993-06-15

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