DE6603864U - FIRE DETECTOR WITH PROTECTION DEVICE FOR FIELD EFFECT TRANSISTORS - Google Patents

Description

-RA.381 -555-2.7.602. juh'βββ

PATENT Attorney Munich 21 - Gotthardstr. ^ I -

Telephone 56 17 62

CERBERUS AG Männedorf

FIRE DETECTOR WITH PROTECTION DEVICE FOR

FIELD EFFECT TRANSISTORS

The invention relates to a fire alarm with at least one sensitive to the consequences of a fire Leading element, a field effect transistor for amplification an electrical one appearing above the sensing element Signals, an electronic circuit for Alarm and a cover that covers the grid electrode of the field effect transistor and the one with the grid electrode protects connected circuit parts against contact,

The desire -for fire alarms, which with a reduced Supply voltage can be operated (easier installation Effort, easier compliance with safety regulations, lower "power consumption etc.) has to an increasing transistorisation of the detectors. For a long time, however, one of the main difficulties was replacement "of the cold cathode tube or equivalent tubes and circuits, which had to be used wherever to amplify the electrical signals appearing above the sensor element Signals a particularly high-impedance amplifier element was required. Dias was ole hot one or more Ionization fire alarms from the Case in which the amplifier element must have a pin input resistance of the order of magnitude of at least 10 Ω. A suitable semiconductor element could now be found in the field effect transistor can be found, but its serial installation in fire alarms leads to certain difficulties. the Breakdown voltage between the gate electrode and one of the two other electrodes (source or drain electrode) of the Field effect transistor is only approx. 50 V; by a Pale touching of the grid electrode by hand can cause its input capacitance but can already be charged up to several 100 V. As an El> flip ssen die;,?! · LeJung is not possible, »There is a breakthrough, which, in contrast to ordinary ones

Transistors with diode properties, causing irreparable damage. The field effect transistor can be used against a suitable cover, such as the detector housing, during operation direct contact of the gate electrode or all with the gate electrode connected hero parts are protected; must have this Coverage, however, too; Removed for cleaning or repair purposes experience is based on the damage rate of the field effect transistors very large.

ZIrI dar in fire alarms, the type described at the beginning, which destroying the field effect transistor while maintaining sarbait en \ yor Preserves charges .J ~ The invention is marked by one between the grid electrode and one of the two other electrodes of the field effect transistor arranged Switch and a device actuated by the cover which, when the cover is properly applied, the switch opens and closes the switch when the cover is removed.

In the following, the invention is intended to be based on a few exemplary embodiments are explained in more detail. Show it:

1 shows an ionization fire alarm in section;

2a shows a variant of the ionization fire alarm part according to Fig. 1 to the left of the line A-A;

FIG. 2b shows a longitudinal section of the detector part of FIG. 2a the line B-B;

3 shows a modified embodiment according to FIG. 2a;

FIG. 4 is a circuit diagram for a fire alarm according to FIG.

The fire alarms shown in FIGS. 1-3 are so-called ionization fire alarms, in which the sensor element, which is sensitive to the consequences of a fire, consists of an ionization chamber provided with a radioactive preparation. According to fig. 4 is never ionization chamber 10 connected in series with a reference ionization chamber 11 and connected via feed lines 1 and 3 to a central unit (not shown). The common connection point of the two ionization chambers is to the gate electrode 14 of a field effect transistor

out which the appearing at this switching point Changes in voltage - a consequence of the penetration of fire aerosols in the fiessionisationskammer declining ion current - amplified and via the Sourceel ektrodia 2 to one not shown, known electronic circuit "for alarm leads. The SourcRR electrode 2 is in the example of FIG. 4 Connected to the feed line 1 via a resistor 9. Between the gate celect: ode 14 and the drain electrode 13 are in

. according to a short circuit switch 15, which in normal operation

ϊ is open, but closed when the detector is covered. The scarf-

ter 15 can just as well between the gate electrode 14 and the

Source electrode 2 are arranged; this variant is with 15 ' entered with dashed lines.

Fig. 1 shows the structure of a [greatly simplified) ionization fire prevention device according to Fig. 4. In an insulating ceramic plate IS is one of the missionization chamber 10 and reference incionization chamber 11 common electrode 1 / inserted. Two radioactive sources 18 and IS ionize the air molecules in chambers 10 and 11, respectively. The reference ionization chamber 11 is mounted on an insulating base 30 by means of an electrically conductive housing 20 rests on top, almost airtight; into the measuring chamber 10, soft through a perforated 22 ?. Housing 21 limited the outside hatch, on the other hand, never has practically free access. The reference chamber housing 20 also forms the second electrode the reference ionization chamber 11. the measuring chamber housing 21 the second electrode of the ionization chamber 10. The measuring chamber housing 21 is mounted on a base plate 23 so that it can be plugged or screwed and can be removed for cleaning or repair purposes will; the measuring chamber housing is connected via a contact member 29 the feed line 3 connected and mostly earthed. The ness chamber housing 21 also serves as a cover that covers the individual diaphragm parts. but above all those elements which are connected to the grid electrode 14 of the field effect transistor 12, during operation protect against direct contact.

*

So that the field effect transistor but also in the absence of coverage remains protected against excessive charges is, as in Fig. already mentioned, a switch 15 is provided, which is operated by means of a device described in more detail below in such a way that that when the measuring chamber housing 21 is removed, the switch 15 is automatically closed and thereby the gate electrode 14 of the field effect transistor 12 is short-circuited with one of the other two electrodes 2 or 13 (in the case of FIG. 1 with the drain electrode 133. The switch 15 consists in the exemplary embodiment of Fig. 1 -an. Einöm spring contact, vjRlchnr without external force duf a mating contact 24 ″ rests. With the measuring comb housing 21 A disk 25 made of electrically insulating material is firmly connected to a protruding ring 26. This ring 2S prints on one when the measuring chamber housing is properly attached in a vertical guide 27 displaceable pin 28, which in turn deflects the spring contact 15 from its rest position. The short circuit between the gate electrode 14 and the drain electrode 13 via reference chamber housing 20, spring contact 15, mating contact ? 4 and electrode 17 are thus interrupted; the field effect transistor 12 is ready for use. When removing the measuring chamber-21 however, the pin 28 by the spring action of the

spring contact Ib printed upwards and the drain 14 the field effect transistor 12 with the drain electrode pre-tied.

Lino further variant of a suitable switch and associated actuating device, Fig. 2a, which has a modified portion rubbed MtiIders left of line AA of ^F "ig. 1 represents, f ig. 2b illustrates a section through the detector of Fig. 2 along the line BB The switching 15, which in its rest position in turn short-circuits the gate to the drain electrode of the field effect transistor, is formed here by a reed relay 31 (protective gas contact arrangement) the contacts of the reed relay 31 are normally open.

a permanent magnet 32 mounted on a base 33 is provided, which closes the contacts of the reed relay 31 when the measuring chamber housing 21 is removed. With the washer 25 of the measuring chamber housing 21 is firmly connected again. a Ring 34, which consists of a magnetically shielding material and which when the measuring chamber housing is properly attached between the permanent magnet 32 and the reed relay 31 comes to rest and thereby the influence of the magnet on the Relay contacts prevented. The contacts of the reed relay are on the one hand via a line 35 to the electrode 17 and on the other: !: t: it? via line 3B with the reference chamber housing 2 0 tied together. The cover 37 only serves to protect the inner valve against the entry of outside air. Dust, etc.

Unite? Vririonte of the detector with reed relay according to Fig. 2a show-1 Finally, FIG. 3, in which the attached to the disk 25 King 38 now consists of a further permanent agent, which when the measuring chamber housing is properly attached 21 comes to rest on the first permanent magnet 32 and thus neutralizes the effect of the first permanent magnet, whereby the contacts of the reed relay 31 open. The other "Bozug numbers correspond to ienon de: rig. 2 a or 1.

So far, the invention has only been made on the beispin! of the ionization fire alarm? It is easy to see, however, that the installation of a pin short-circuit switch and a device which is actuated by the cover and determines the position of the switch is possible in those fire alarms in which a field-effect transistor is used as the amplifier element. So <can be, in Fig. I the Fühlerslement 10 as by a temperature-sensitive resistor or photocell fabric ^r and the element are replaced by a resistor or other suitable rin bridge element.

Claims (1)

1. Fire alarm with at least one sensor element that is sensitive to the consequences of a fire, a field effect transistor to amplify the electrical signal appearing above the sensor element, an electronic circuit for alarm and a cover, which f ekttransi storr the grid electrode of the field effect, and with the grid electrode connected circuit parts protects against contact, gekennzoichnet by a between the grid electrode and one of the other two electrodes of the field effect transistor arranged switch and one through the cover bRt ^ t ^ te Device which, when the cover is properly applied opens the switch and closes the switch when the cover is removed. 2. fPUKrmelder according to claim 1, characterized in that the switch contains a spring contact, and that the device for actuating the switch has a pin connected to the cover, which ^{opens the r} ederkontakl against its spring pressure when the cover is properly applied. 3. Fire alarm according to claim 2, characterized in that the device for actuating the switch one in a vertical Guide contains freely displaceable pin, which moved by a ring fixedly connected to the cover in such a way that with a properly applied cover the spring contact is opened by the pin against its spring pressure. I ■ '· / pl -ΒΑ. Fire alarm according to claim 1, characterized in that the switch consists of a reed relay, the contacts of which through § = the effect of one in the vicinity of the relay angsordnstsn permanent- ff magnets are closed against their spring pressure, and that the I cover a ring made of a magnetically shielding material I, which when the coverage is properly drawn up to lie between the reed relay and the permanent magnets ^;; comes and by preventing the magnetic flux releases the contacts of the reed relay. 5. Fire alarm according to Anp-aruch 4, characterized in that the g attached to the cover ring made of a further permanent | IJ - magnet exists, which if the i I Cover on the permanent magnet firmly attached in the Neider I 2u comes lying, which compensates for its magnetic flux I and thus the contacts of the reed relay are released. § 6. Fire alarm according to one of the preceding claims, characterized ρ is that the switch between the * grid electrode II and the source electrode of the field effect transistor arranged is. Fire alarm according to one of: Claims 1-5, characterized in that uass the switch between the grid and drain electrodes of the F-eldeffekttransistor is arranged.