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
  • 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
  • G08B17/113—Constructional details

Definitions

• the invention relates to a fire detector with at least two electrodes, between which an electric field is generated by a DC voltage source, the opposite electrode surfaces delimiting a measuring space through which the air moved by convection of a room to be monitored can pass, and one of the Electrodes as the measuring electrode and the other as the counter electrode, and a current measuring arrangement and evaluation circuit is provided.
• Fire detectors of a similar type are known and used in various designs.
• US Pat. No. 2,408,051 (Donelian) shows a fire detector with two measuring rooms, small particles and small ions being "filtered out" electrically in the first measuring room and the air being ionized in the second measuring room with the aid of a radioactive preparation.
• the resulting conductivity is reduced when smoke is present because ions attach to the difficult-to-move smoke particles. If the reduction in conductivity in the ionization chamber reaches a threshold, the alarm is extinguished.
• the electrodes which delimit the measuring spaces are connected in series in the manner of a capacitive voltage divider between the positive and negative poles of a DC voltage source.
• Fire detector is practically unusable. The same applies to the fire and smoke detector according to US Pat. No. 3,470,551 (Jaffe et al).
• Ion measuring devices or measuring arrangements for determining the mobility of particles are known, as is the case e.g. from US Pat. No. 4,114,088, but so far neither the use of such measuring devices as fire detectors has been proposed, nor are they suitable for such use due to the design. Rather, fire detectors with ionization chambers dominate, especially using radioactive preparations, although the need for simplified fire detectors that are less polluting and, above all, work without radioactive substances has been constant and has existed for a long time. This is also evident from Scheidweiler's article in "Staub-Reinhalt.Luft, Vol. 32 No.11 November, 1972".
• the invention is accordingly based on the object of providing an improved, highly sensitive and substantially simplified fire detector and a dedicated electrode arrangement which can be used for ionization without radioactive preparations.
• this is primarily achieved in that at least one of the electrodes with a circula tion openings for the ambient air to be monitored and / or consists of a plurality of partial electrodes arranged with spaces in such a way that ambient air can flow into the measuring space through these spaces that the DC voltage source on the one hand directly or indirectly with the counter electrode and on the other hand with the current -Measuring arrangement is connected, and that the measuring electrode is connected to the input of the current measuring arrangement without a direct connection to the DC voltage source.
• the invention is based for the first time in an optimally simple manner on the principle that smoke particles from burns are principally strongly electrically charged. This is due to the fact that positive and negative small ions attach to the particles. These are constantly formed in the air even in normal surroundings, especially through cosmic rays and natural radioactivity.
• the concentration of the particles of radius R with p elementary charges is accordingly
• n R is the total concentration of the neutral particles with radius R
• k is the Boltzmann constant
• T is the absolute temperature.
• charge of the smoke means the average of the amount of the particle charge.
• the fire detector according to the invention measures the amount of
• Particle charge of a certain sign also works if the net charge of the smoke is zero. With such a charge distribution, there are the same number of posi tive as negative ions on the smoke particles.
• reliable detection of the smoke in the field between the measuring electrode and counterelectrode is now ensured by electrostatically separating positive and negative particles and measuring the charge of a sign or by measuring the change in conductivity caused by the smoke.
• the electric current thus generated is relatively small at field strengths which do not yet lead to glow discharge, but at least amount to 100 volts / cm, but can easily be measured with electronic amplifiers or small electroscopes.
• the electrode spacing is advantageously less than 10 mm, but more than 1 mm. It has been shown that a number of advantageous properties can be achieved through this special dimensioning: the relatively small measuring space provides a good shielding of the measuring electrode against influence by net charge; on the other hand, the distance is large enough to avoid false reports from possibly deposited dust or soot particles. In addition, it has been shown that with such an electrode spacing, it is also possible to work with voltages in an optimal range, which on the one hand ensure reliable separation and separation of charged particles and on the other hand avoid contamination by constant attraction and deposition of dust particles.
• the invention is advantageously not based on the measurement of the excess or net charge practiced in known devices, but on the charge measurement after electrostatic separation of positive and negative particles.
• an auxiliary electrode arrangement can be provided which pre-separates small and / or charged particles carried by slow flow before they can get into the measuring space. That way the sensitivity to small smoke sources that cause small particles and / or only slow convective flow (cigarettes) are reduced.
• the net charge suppression can also be achieved or further improved by providing a compensation space which is delimited on the one hand by the measuring electrode and on the other hand by a compensation electrode.
• the measuring electrode is influenced by the influence of net charge e.g. shielded in large smoke clouds on both sides and only that in a relatively small volume limited by the measuring space and / or the compensation space is measured.
• the compensation electrode can simultaneously be designed as a shield for the electrode arrangement.
• the influences described above by the net charge or by influence can even be completely compensated for if the compensation space is arranged at approximately the same distance from the measuring electrode as the measurement space and is also able to absorb approximately the same volume of ambient air flowing through. This means that the influence of gases flowing in the measuring space with a high net charge is compensated for by the influence of reversed polarity caused by gases flowing away in the compensation space.
• Compensation can also advantageously be achieved if the measuring electrode is arranged with respect to the air flow in such a way that the air flow sweeps the measuring electrode twice, but strikes it from opposite sides, respectively, or flows through the electrode, so that influence currents caused by the net charge of the passing through Ambient air or smoke clouds appear in the measuring electrode can be compensated. Influence currents are evidently counteracted by the charged smoke hitting the electrode from different sides generated opposite polarity, which is simplest
• an electrode arrangement for the fire detector according to the invention is a measuring electrode and / or compensation electrode designed as a grid; this facilitates convection and prevents the im
• the measuring electrode can also be constructed from several electrically connected partial electrodes, which are caused by air. or gas clouds are flowed through in such a way that the influence of influence is canceled out by the net charge in the partial electrodes.
• the measuring electrode is arranged between two counter electrodes, the two
• Counter electrodes are connected to the DC voltage source and the measuring electrode is provided between the counter electrodes and is connected to the input of the measuring arrangement. This ensures that the fields in the two measuring rooms between the two counter electrodes and the
• Measuring electrode run symmetrically to it, i.e. in other words, particles of the same polarity charged from both measuring rooms hit the measuring electrode. This guarantees high sensitivity in particular.
• the measuring electrode is connected to the input of the measuring arrangement and is therefore virtually at the potential of the other side of the measuring arrangement. She lets herself down partially mechanically rigidly connect by means of insulation elements with an electrode housing and / or the counter electrodes, the insulation elements being interrupted by electrically conductive parts which are connected to the other side of the measuring electrode. This prevents leakage currents from being measured on the insulation elements.
• FIG. 1 shows the basic illustration of a fire detector with the features of the invention
• FIG. 2 shows a fire detector with a modified one
• Electrode, Figure 3 shows a fire detector with a further modified
• FIG. 4 shows a fire detector according to the invention with two measuring rooms and external shielding
• Figure 5 shows a modified embodiment of a measuring electrode.
• FIG. 1 shows the basic illustration of a fire detector according to the invention with a measuring electrode 1, a counter electrode 2, a schematically illustrated measuring arrangement 3, which at the same time serves to trigger the alarm in a known manner, and a DC voltage source 4.
• Measuring electrode 1 and counter electrode 2 are connected to a holder 7 by means of insulation elements 6 attached, which in turn is connected to a base plate 8.
• the holder 7 is electrically conductive and lies on ground, so that over the insulation elements 6 can flow no leakage currents between the measuring electrode 1 and the counter electrode 2, since the measuring electrode via the measuring arrangement 3 - but only virtually - is at ground potential. This is advantageous in view of the extremely low flowing currents.
• the distance between the measuring electrode 1 and counter electrode 2 is 5 mm, the voltage of the direct voltage source 4 is 500 volts, so that there is a field strength of 1000 volts / cm between the two electrodes 1 and 2. Now charged smoke particles get into the measuring space 9 between the measuring electrode 1 and counter electrode 2 .
• Measuring electrode 1 and counter electrode 2 the electric field causes the positive and negative particles to move to the two electrodes. This charge movement (charge drift) influences a current into the measuring electrode 1, which is measured in the measuring arrangement 3.
• the measuring electrodes 1 and the counter electrode 2 are designed as approximately square plates with an area of 40 cm 2 each.
• the area of the electrodes can be changed depending on the requirement and the desired sensitivity of the measuring arrangement, as can also be seen, for example, from the exemplary embodiment according to FIG.
• the overall arrangement is surrounded by a shield 5, which is also grounded. This not only ensures mechanical protection of the arrangement, but also influences of errors caused by net charging of a schematically indicated smoke cloud 30 are compensated to the extent that influences from the charge cloud outside the shield 5 are kept away from the measuring electrode 1 and thus no influence currents can arise
• both the measuring electrode 1 and the counter electrode 2 are provided with a multiplicity of holes 11, which allow the smoke to flow through the measuring space 9 coming from the horizontal direction as well as from the vertical direction solely due to the convection.
• Figure 2 shows an arrangement in which the base plate 8 is arranged as a compensation electrode parallel and at the same distance as the counter electrode 2 to the measuring electrode 1.
• Base plate 8, measuring electrode 1 and counter electrode 2 are (in some cases not shown) each in the form of a perforated plate. Due to the arrangement, flowing gas clouds with a net charge are initially shielded from the outside by the shield 5.
• there is approximately the same amount of gas flowing through each in the measuring space 9 and in the compensation space 10 as a result of which the amount of influence by net charge is approximately the same.
• gas flowing through in the direction of the arrow moves towards the measuring electrode 1 in the measuring space 9, but moves away from the measuring electrode 1 in the compensation space 10
• the resulting influence currents each have opposite polarity, so that the effects of net charge are compensated for.
• FIG. 3 shows an exemplary embodiment in which two counter electrodes 2 enclose a measuring electrode 1 between them and thereby delimit two measuring spaces 9 and 9 '.
• the counter electrodes 2 are designed as perforated plates, lie on ground and at the same time serve to shield the arrangement from the outside.
• the measuring electrode 1 is attached to the base plate 8 by an insulator arrangement, not shown. Since both counter electrodes 2 are at the same potential with respect to the measuring electrode 1, the field distribution is symmetrical, that is to say that ions of negative polarity drift both in the measuring space 9 and in the measuring space 9 and the resulting influencing current is determined in the measuring arrangement 3 can be.
• the sensitivity of the arrangement is increased due to the two measuring rooms 9 and 9. In addition, compensation of net charge influences is ensured by the symmetry of the arrangement.
• Figure 4 shows an arrangement in which a cylindrical, symmetrical design of all parts, ie the shield 5, the measuring electrode 1 and the counter electrodes 2 is provided.
• the outer of the two counter electrodes 2 is fastened to the shield 5 by means of bolts 12 made of insulation material.
• the measuring electrode 1 and the second counter electrode 2 are mechanically connected to one another by means of insulation elements 13a, 13b, which are also bolt-shaped.
• a metal disk 14 is arranged between the insulation elements 13a and 13b, which lies on ground. Leakage currents between the counter electrodes 2 and the measuring electrode 1 are thus avoided.
• the cylindrical configuration of the counter electrode 2 with a base plate 2a which also corresponds to the configuration of the other counter electrode 2 or the measuring electrode 1 and the shield 5, is shown schematically in the upper section of FIG. 4.
• This arrangement also has the advantage that the insulation elements are not directly exposed to the air flow and are therefore protected against contamination.
• a gas cloud with charged smoke particles flowing through the arrangement in the direction of the arrow strikes the outside of the measuring electrode 1 (at A) coming from the right and the inside of the measuring electrode 1 (at B) before leaving the arrangement. Since the measuring electrode 1 is cylindrical and constitutes a closed circuit, influent currents due to net charge will accordingly have opposite polarity and will be automatically compensated.
• shield 5 which is also designed as a perforated plate
• outer counter electrode 2 thus delimit an annular compensation space 14, which, however, has a smaller field strength than the two measurement spaces 9 and 9 due to the greater distance.
• compensation space 14 small, slowly flowing charged are therefore Particles already separated before they get into the measuring room 9 or 9. This results in a size-selective pre-separation, which can be of great advantage to reduce false alarms.
• FIG. 5 shows an exemplary embodiment of a measuring electrode which consists of a plurality of stamped-out sheet metal strips 15 which are connected to one another by means of an electrically conductive rail 16.

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• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Business, Economics & Management (AREA)
• Emergency Management (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Fire-Detection Mechanisms (AREA)
• Other Investigation Or Analysis Of Materials By Electrical Means (AREA)

Priority Applications (2)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

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Citations (5)

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• 1982
  • 1982-12-03 CH CH7028/82A patent/CH666135A5/de not_active IP Right Cessation
• 1983
  • 1983-12-02 US US06/641,946 patent/US4652866A/en not_active Expired - Fee Related
  • 1983-12-02 DE DE8383903778T patent/DE3378505D1/de not_active Expired
  • 1983-12-02 JP JP58503803A patent/JPS60500073A/ja active Granted
  • 1983-12-02 EP EP83903778A patent/EP0127645B1/de not_active Expired
  • 1983-12-02 WO PCT/CH1983/000137 patent/WO1984002215A1/de active IP Right Grant
• 1984
  • 1984-06-25 AU AU29837/84A patent/AU572517B2/en not_active Ceased

Patent Citations (5)

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