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EP 0 101 172 B2 |
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NEW EUROPEAN PATENT SPECIFICATION |
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Date of publication and mentionof the opposition decision: |
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06.05.1992 Bulletin 1992/19 |
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Mention of the grant of the patent: |
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04.03.1987 Bulletin 1987/10 |
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Date of filing: 01.07.1983 |
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International Patent Classification (IPC)5: G08B 29/00 |
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Short circuit fault isolation means for electrical circuit arrangements
Kurzschluss-Fehler-Isolierungsmittel für Stromkreiseinrichtungen
Moyens d'isolation de défauts de court-circuit pour installations de circuits électriques
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Designated Contracting States: |
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AT BE CH DE FR GB IT LI LU NL SE |
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Priority: |
16.07.1982 GB 8220753
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Date of publication of application: |
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22.02.1984 Bulletin 1984/08 |
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Proprietor: APOLLO FIRE DETECTORS LIMITED |
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Havant
Hampshire PO9 1JH (GB) |
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Inventor: |
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- Payne, Roger Dennis
Horndean
Hants, P08 9PE (GB)
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Representative: Colgan, Stephen James et al |
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CARPMAELS & RANSFORD
43 Bloomsbury Square London WC1A 2RA London WC1A 2RA (GB) |
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References cited: :
EP-A- 0 042 501 GB-A- 1 567 971 US-A- 3 652 798
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GB-A- 1 383 777 US-A- 28 958
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- INTERNATIONAL CONFERENCE ON COMMUNICATIONS, vol. 1, 8th-12th June 1980, pages 14.3.1
- 14.3.5, Seattle, USA C.H. KRAFT: "A 1 MBIT/SEC data loop for security sites"
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[0001] The central control unit of a fire detection system monitoring extensive premises
may need to be connected to a large number of fire detectors sited throughout the
premises. In order to identify with some precision the location of any fire it is
state of the art practice to divide the protected premises into local areas or fire
zones each separately monitored by the control unit. If many detectors are required
to adequately protect the premises it is usually uneconomic to have as many fire zones
as detectors because of the high cost of wiring each detectors directly to the control
unit and the cost of providing a multicity of monitoring circuits. In practice precision
is usually comprised by directly interconnecting closely associated detectors to form
fewer, less localised fire zones and connecting each group of detectors to the control
unit as shown schematically in figure 1. The control unit 19 identifies in which zone
a fire has been detected but not which detector 21 has responded. In such systems
the maximum number of detectors 21 grouped together to form a zone is normally restricted
to about 25 detectors. The interconnection of a larger number of detectors is not
normally practiced, firstly because the greater area monitored by a greater number
of detectors reduces to an unacceptable level the precision with which a fire can
be located, and secondly because the occurrence of a circuit fault, such as a short
circuit, in wiring interconnecting detectors can render all the detectors in that
zone inoperative and place an unacceptably large area at risk pending repains, even
if the presence of such a fault is indicated at the control unit 19.
[0002] Recent technology developments such as the introduction of microprocessors and improved
data transmission techniques, now make it practical to manufacture detectors incorporating
circuitry means by which each detector in a fire detection system can be made responsive
to a uniquely coded address signal that may with advantage be superimposed on the
wiring supplying power from the control unit to the interconnected detectors. When
a particular detector receives its unique address signal from the control unit the
circuitry means associated with the detector responds by transmitting to the control
unit a signal containing information about the status of the detector. The control
unit may by reference to its pre-programmed memory match the address code of the detector
with a precise identification of the detector's location. Therefore, in principle
the control unit 20 is able to determine both the status and the precise location
of every addressable detector 21 in a fire detection system of the type shown schematically
in figure 2 without the need to zone detectors on separate circuits. The elimination
of a multiplicity of zone circuits and a simplification of installation wiring are
apparent potential benefits of using addressable detectors. In practice the maximum
number of addressable detectors connected on one circuit of this type is normally
restricted to about 25 detectors because the occurrence of an open and short circuit
fault in the wiring can render some or all of the detectors on the circuit inoperative
and place an unacceptablly large area at risk pending rapairs. If detectors are interconnected
on a wiring loop L, then a single open circuit fault will not render any of the detectors
inoperative. The improved reliability afforded by the use of ring circuit may in some
circumstances permit a marginal increase in the number of interconnected addressable
detectors but the vulnerability of the circuit to a short circuit fault remains a
major constraining influence.
[0003] Thus the problem to be solved is to provide means whereby circuit elements in a loop
circuit can remain in large part operational in the event of a short circuit.
[0004] EP-A-O 042 501 discloses one solution to this problem. According to this disclosure
a plurality of circuit elements, in thy form of fire detectors are connected in a
loop circuit to a bi-directionally supply circuit. The fire detectors are sequentially
interrogated in order to send back information to a central station. In the event
of a circuit malfunction, the interrogation process is interrupted on reaching a faulty
fire detector. The interrogation process then proceeds in the reverse direction until
the faulty detector is reached once more whereupon the interrogation process again
reverse its drection.
[0005] US-A-3652798 discloses a telecommunication system in which junction switches are
provided in loop for detecting the absence of signals on a primary line, due to a
fault, and for diverting the signals to a secondary line. In the event of the fault,
the junction switches all operate together to interrupt primary and secondary lines.
They then need to be sequentially actuated, by a signal from the junction switch which
first detected the absence of the signals so as to restore operation on a reconfigured
loop which includes the primary and secondary lines but not the fault.
[0006] The invention provides an alternative solution as defined in claim 1.
[0007] In the accompanying schematic drawings:-
Figure 1 illustrates a conventional fire detection system;
Figure 2 illustrates another conventional fire detection system including addressable
fire detectors;
Figure 3 illustrates an embodiment of the invention;
Figure 4 illustrates a circuit diagram of one form of bi-directional isolator according
to the invention, and
Figures 5-8 illustrate further respective embodiments of the invention.
[0008] Figure 3 illustrates an embodiment of the invention in the form of a control unit
20 connected to a loop circuit L of detectors in which groups of one or more detectors
21 are separated by devices containing a novel circuit arrangement as disclosed herein
and termed bi-directional short circuit isolators (1, 2, 3, 4). Each isolator (1,
2, 3, 4) contains a circuit arrangement (see Figs. 4 and 5 and following description)
which normally provides bi-directional low impedance circuit paths for both of the
supply wiring circuits forming the loop circuit L such that detectors 21 may receive
power and address signals from either end of the loop L and transmit data signals
in either direction to the control unit 20. The circuit arrangement also contains
sensing means (TR2, D1, D7, of Fig. 4 or 5) for detecting a short circuit of the loop
circuit wiring on either side of the circuit arrangement and switching means TR1 and
TR3 of Fig. 4 or 5) controlled by said sensing means and arranged to switch from a
low impedance path (through TR1 or TR3) to a high impedance path (TR1 and TR3 biased
off) in response to a short circuit fault in the loop circuit. If the short circuit
occurs in the type of circuit arrangement shown in Figure 3, the short circuit will
be detected by sensing means in bi-directional isolators (1, 2, 3, 4) on both sides
of the short circuit and the impedance of the isolators adjacent to the short circuit
fault will switch to a high state thus isolating the short circuit fault from the
detectors 21 and other isolators located between each high impedance isolator and
the control unit 20. Only those detectors 21 located between the adjacent bi-directional
isolators (e.g. 2 and 3) are rendered inoperative by a short circuit fault, since
the detectors 21 will still receive current (via isolator 1) which passes through
the lines which connect them on one side to unit 20 (i.e. as far as, but not beyond
isolator 2), and (via isolator 4) which passes through the lines which connect them
to the other side of unit 20 (i.e. as far as, but not beyond isolator 3).
[0009] Ideally bi-directional short circuit isolators could, with advantage, be connected
alternately with detectors such that a short circuit fault of the loop wiring or of
a detector renders only one detector inoperative. In practice this may not always
be possible because of economic considerations and because isolators may have a low
but finite impedence in the low impedence state which gives rise to a cumulative volt
drop around the loop circuit if a large number of isolators are used. Embodiments
of isolators based on semiconductor circuits can be expectd to provide a volt drop
of less than 0.8 volts in the low impedance state. Thus ten isolators may produce
up to a 7.2 volt drop from the first isolator to the 10th isolator if a short circuit
occurs between the 10th and 11th isolator in a system fitted with 11 isolators for
example. A system of this type fitted with modern detectors having a wide operating
voltage range can be expected to accommodate a 7.2 volt drop without any performance
degradation. The maximum number of detectors which may be connected between isolators
will be largely determined by the maximum tolerable number of detectors than can be
rendered inoperative in the event of a short circuit. By way of example this number
may be approximately 25 if comparable performance with that of conventional fire detection
systems using non addressable detectors is used as the criterion. It will therefore
be perceived that a loop system using say 11 bi-directional short circuit isolators
may interconnect approximately 250 addressable detectors and be no more degraded by
a short circuit fault than a conventional 10 zone system with 25 detectors per zone.
The loop system of addressable detectors also has advantages that an open circuit
fault will not render any detectors inoperative and that the location of detectors
can be identified with precision.
[0010] Figure 4 shows one form of a practical embodiment in component form of a bi-directional
circuit isolator.
[0011] When power is applied to terminals 31 and 32 transistor TR2 is driven into conduction
by virtue of base drive derived from resistor R1 and bias resistor R5. Transistor
TR2 in turn drives transistor TR1 into conduction via diode D4 steering diode D2,
resistor R3 and bias resistor R2 thus effecting a low impedance path from terminal
31 to terminal 33 via TR1 and diode D3. Similarly and by virtue of the symmetry of
the circuit it can be shown that a low impedance path can be effected between terminals
33 and 31 via transistor TR3 and diode D5 if power is applied to terminals 33 and
34. A low impedance always exists between terminals 34 and 32.
[0012] When the isolator as described above is incorporated in a loop circuit the transistor
TR1 or TR2 associated with the input terminals receiving the higher supply voltage
will be conductive and provide the low impedance path. The terminals receiving the
higher voltage are determined -by the proximity of the isolator to the control unit,
the presence or absence of short or open circuit faults and possibly the voltage level
of any superimposed data transmission signal.
[0013] If a short circuit fault occurs across the loop circuit wiring connected to terminals
33 and 34 the drive current for transistor TR2 base cannot be sourced via R6 nor can
it be sourced from terminal 31 via R1 because the now forward biasing of diode D7
does not provide sufficient bias voltage to drive transistor TR2 and diode D4 into
conduction. The short circuit fault causes TR2 to switch off which in turn ensures
that both TR1 and TR3 are both switched off thus isolating the short circuit from
that part of the loop circuit connected to terminals 31 and 32. Similarly and by virtue
of the symmetry of the circuit it can be shown that a short circuit across wiring
connected to terminals 31 and 32 will be isolated from that part of the loop circuit
connected to terminals 33 and 34.
[0014] Resistor R7 is an optional resistor normally of high value which may be necessary
to improve the switch on characteristics of the isolator when power is first applied
in circumstances where the detectors connected to the circuit have a capacitive input
or require a higher quiescent current that can initially be sourced via resistors
R1 and R6 in parallel with D7 or R6 and R1 in parallel with D1 as circumstances dictate.
[0015] A further circuit arrangement incorporating short circuit isolators is shown in Figure
5. In this arrangement the isolators are connected in a loop circuit with groups of
detectors spurred off between isolators rather than being connected to the loop circuit
directly. Those skilled in the art will recognise that this is a particularly suitable
circuit arrangement for multi-storey buildings.
[0016] It is recognised that an open circuit in the spurwir- ing could render inoperative
those detectors furthest from the loop wiring and beyond the open circuit, but this
will not result in an intolerable situation if the number of detectors per spur is
limited to about 25 as in conventional zone systems.
[0017] A further circuit arrangement is shown in Figure 6. This arrangement has the advantages
of the loop circuit and the additional advantage that more than one open circuit fault
in the wiring linking detectors does not render any detectors inoperative unless two
or more open circuits occur on the same spur.
[0018] Further circuit arrangements formed by combining all or parts of circuit arrangements
disclosed above and containing one or more isolators whether bi-directional or uni-directional
are embodiments of the invention.
[0019] The short circuit isolatons disclosed here may constructed in various forms. They
may with advantage be incorporated within control units and within detectors or they
may be'constructed as separate units which are wired into circuit arrangements as
required.
[0020] The embodiment of the invention disclosed by way of example in Figure 4 may be implemented
in complementary form semiconductors.
[0021] A further embodiment of the invention having application with circuits using an alternating
electrical supply is illustrated in schematic form in Figure 7. In this figure, a
non-polarised bi-directional short circuit isolator23 (represented by the broken line)
comprises two polarised bi-directional short circuit isolators 24a, 24b, interconnected
as shown, and connected to a.c. supply lines 25 26.
[0022] Fig. 8 illustrates an improvement in the circuitry of Fig. 4 (similar reference numerals
or letters identify similar components). In Fig. 8 transistors TR1 and TR3 are VMOS
field effect transistors. VMOS devices have the advantage that their "on state" impedance
is very low, typically 5 ohms to 0.3 ohms. This means that, in most applications,
a smaller voltage drop will be developed across the isolator, thus permitting an increase
in the number of isolators which may be introduced into a circuit. Because VMOS devices
conduct current bi-directionally in the "on state" it is possible to connect them
in series. This has enabled diodes D5 and D3 to be eliminated thus further reducing
the voltage drop across the device.
[0023] In accordance with another improvement (shown in Fig. 8) an LED indicator LED 1 is
provided which illuminates when the short circuit isolator switches to a high impedance
state in response to the presence of a short circuit. LED 1 is incorporated within
a bridge rectifer circuit, including diodes D9-D12, which produces a rectified voltage
in response to a short circuit on either side of the isolator. LED 1 is caused to
flash periodically by incorporating it in a oscillator circuit comprising a conventional
programmable unijunction transistor oscillator and associated components TR4, R9-R13,
C1. By causing LED 1 to flash, the current required to provide indication when a short
circuit is detected is reduced.
[0024] In accordance with further improvements (shown by Fig. 8), two zener diodes D13,
D14 are provided to protect the short circuit isolator from high voltage transients
and accidental polarity reversal, and a 10K ohm resistor R14 is connected to the base
of TR2 to give a degree of control over the threshold voltage of the short circuit
sensing circuitry.
1. A short circuit detection system comprising a loop circuit (L) connected to a bi-directional
unit (20), and circuitry for isolating a section of the loop circuit (L), containing
one or more circuit elements (21), from the bi-directional unit (20) in the event
of a short circuit in said section and wherein one or more of said circuit elements
(21) are connected between adjacent bi- directional isolators (1,2,3,4) in each section
of the loop circuit (L), each of said isolators (1,2,3,4) comprising switching means
(TR1, TR3) providing a low impedance path and a high impedance path, said high impedance
path isolating said circuit elements (21) from said unit (20); and sensing means (TR2,
D1, D7) for sensing a short circuit in any one of said circuit elements (21) in said
section; said switching means (TR1, TR3) being responsive to said sensing means (TR2,
D1, D7) to cause said switching means (TR1, TR3) to provide said low impedance path
in the absence of said short circuit and to cause a change in state from the low impedance
path to the high impedance path in the presence of said short circuit, characterised
in that said bidirectional unit (20) is a power supply unit, said low impedance paths
supplying current continuously from said supply unit to said circuit elements, that
said circuit elements (21) are fire detectors which are operationally dependent on
the power supplied by said unit (20), and that the short circuit sensing means in
said bi-directional isolators (1-4) are independently and simultaneously responsive
to a change of voltage level in a short circuited section of the loop (L) between
said adjacent isolators whereby only the isolators (2,3) immediately adjacent the
short circuited section autonomously and simultaneously block the supply of power
to the fire detectors (21) therebetween without preventing the other bi-directional
isolators (1, 4) from supplying current continuously from said power supply unit (20)
to the non-isolated fire detectors (21).
2. A system according to claim 1, characterised in that a plurality of said circuit
elements (21) are connected in series between each pair of said bidirectional isolators
(1, 2, 3, 4).
3. A sytem according to claim 1, characterised in that a plurality of said circuit
elements (21) are connected in respective spurs (S) between each pair of said isolators
(1, 2, 3, 4).
4. A system according to claim 1, characterised in that a plurality of said circuit
elements (21) are interconnected in respective loops between each pair of said isolators
(1, 2, 3, 4) and that each pair of isolators (1, 2, 3, 4) are also interconnected
(Figure 6).
5. A system according to any one of the preceding claims and adapted for the supply
of alternating current characterised in that each of said isolators is of a non-polarised
form and comprises polarised isolators (1, 2) connected to respective lines (25, 26)
supplying said alternating current, opposite poles of said isolators (1, 2) being
interconnected (Figure 7).
6. A system according to any one of the preceding claims, characterised in that, in
each of said isolators (1, 2, 3, 4), said switching means comprises transistors (TR1,
TR3, of Fig. 4) connected to respective diodes (D3, D5) for conducting currents in
respective forward and reverse directions in said impedance path.
7. A sytem according to claim 6, characterised in that an impedance (R7) is connected
in a shunt path, across said switching means (TR1, TR3) in order to improve the switch-on
characteristics of the isolator (1, 2, 3, 4) when power is first applied.
8. A sytem according to any one of the claims 1 to 5, characterised in that, in each
of said isolators (1, 2, 3, 4), said switching means comprises VMOS devices (TR1,
TR3 of Fig. 8) which conduct currents bi-directionally in said low impedance path.
9. A sytem according to claim 8, characterised in that an oscillating circuit (TR4,
R9-R13, C1) is connected across a bridge rectifier circuit (D9, D10, D11, D12) in
order to operate an indicator (LED 1) intermittently on detaching a short circuit
on either side of isolator (1, 2, 3, 4).
10. A system according to claim 6, 7, 8 or 9 characterised in that said sensing means
comprises a transistor (TR2) for biasing the transistors (TR1, TR3) of said switching
means to provide respective low impendance paths, the transistor (TR2) of said sensing
means being biased by current derived from respective circuits (D1, R1, D7, R6) which
diode circuits become respectively forward, or reverse biased in response to a short
circuit in one of said current elements (21 ) whereby the transistor (TR2) of said
sensing means is biased into a non-conducting state, thereby biasing the transistors
(TR1, TR3) into a non-conducting state to provide respective high impedance paths.
1. Kurzschluß-Detektorsystem mit einer Schleifenschaltung (L), die mit einer bidirektionalen
Einheit verbunden ist, und einer Schaltungsanordnung zum Abtrennen eines ein oder
mehrere Schaltungselemente (21) enthaltenden Abschnitts der Schleifenschaltung (L)
von der bidirektionalen Einheit (20) bei Auftreten eines Kurzschlusses in diesem Abschnitt,
wobei in jedem Abschnitt der Schleifenschaltung (L) eines oder mehrere der genannten
Schaltungselemente (21) zwischen benachbarten bidirektionalen Trennvorrichtungen (1,
2, 3, 4) angeordnet sind, die jeweils Schaltmittel (TR1, TR3) mit einem niederohmigen
und einem hochohmigen Strompfad enthalten, wobei der hochohmige Strompfad die Schaltungselemente
(21) von der genannten Einheit (20) abtrennt, ferner mit Sensormitteln (TR2, D1, D7)
zur Erfassung eines Kurzschlusses in einem der genannten Schaltungselemente in dem
genannten Abschnitt, wobei die Schaltmittel (TR1, TR3) auf die Sensormittel (TR2,
D1, D7) ansprechen und von diesen derart steuerbar sind, daß sie den genannten niederohmigen
Strompfad bilden, wenn kein Kurzschluß vorliegt, und hingegen eine Zustandsänderung
von dem niederohmigen Strompfad in den hochohmigen Strompfad Impedanz bewirken, wenn
ein Kurzschluß voranden ist, dadurch gekennzeichnet, daß die bidirektionale Einheit
(20) eine Stromversorgungseinheit ist und die niederohmigen Strompfade den Schaltungselementen
kontinuierlich Strom von der Stromversorgungseinheit zuführen, daß die Schaltungselemente
(21) Feuerdetektoren sind, die wirkungsmäßig von der von der Stromversorgungseinheit
(20) gelieferten Leistung abhängig sind, und daß die Kurzschluß-Sensormittel in den
bidirektionalen Trennvorrichtungen (1-4) unabhängig und gleichzeitig auf eine Anderung
des Spanungspegels in einem kurzgeschlossenen Abschnitt der Schleife (L) zwischen
den benachbarten Trennvorrichtungen ansprechen, derart daß nur diejenigen Trennvorrichtungen
(1, 3), die unmittelbar an den kurzgeschlossenen Abschnitt angrenzen, autonom und
gleichzeitig die Stromversorgung für die dazwischen liegenden Feuerdetektoren (21)
unterbrechen, ohne daß die anderen bidirektionalen Trennvorrichtungen (1, 4) daran
gehindert sind, den nicht abgetrennten Feuerdetektoren (21) kontinuierlich Strom von
der Stromversorgungseinheit (20) zuzuführen.
2. System nach Anspruch 1, dadurch gekennzeichnet, daß zwischen jedem Paar von Trennvorrichtungen
(1, 2, 3, 4) mehrere der genannten Schaltungselemente (21) in Reihe geschaltet sind.
3. System nach Anspruch 1, dadurch gekennzeichnet, daß zwischen jedem Paar von Trennvorrichtungen
(1, 2, 3, 4) mehrere der genannten Schaltungselemente (21) in entsprechenden Abzweigungen
(S) angeordnet sind.
4. System nach Anspruch 1, dadurch gekennzeichnet, daß mehrere der genannten Schaltungselemente
(21) in entsprechenden Schleifen zwischen jedem Paar von Trennvorrichtungen (1, 2,
3, 4) angeordnet sind und daß die Trennvorrichtungen (1, 2, 3, 4) jedes Paars ebenfalls
miteinander verbunden sind (Fig. 6).
5. System nach einem der vorhergehenden Ansprüche, das für Wechselstromversorgung
ausgelegt ist, dadurch gekennzeichnet, daß die einzelnen Trennvorrichtungen stromrichtungsunabhängig
sind und stromrichtungsabhängige Trennvorrichtungen (1, 2) beinhalten, die mit zugeordneten,
Wechselstrom führenden Leitungen (25, 26) verbunden sind, wobei entgegengesetzte Pole
dieser stromrichtungsabhängigen Trennvorrichtungen (1, 2) miteinander verbunden sind
(Fig. 7).
6. System nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die
Schaltmittel in den einzelnen Trennvorrichtungen (1, 2, 3, 4) Transistoren (TR1, TR2;
Fig. 4) umfassen, die jeweils mit Dioden (D3, D5) verbunden sind, welche in dem genannten
niederohmigen Strompfad zur Stromleitung in Vorwärts- bzw. Rückwärtsrichtung dienen.
7. System nach Anspruch 6, dadurch gekennzeichnet, daß eine Impedanz (R7) vorgesehen
ist, die die genannten Schaltmittel (TR1, TR3) überbrückt und das Einschaltverhalten
der Trennvorrichtungen (1, 2, 3, 4) bei erstmaligem Anlegen der Versorgungsspannung
verbessert.
8. System nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die
in den Trennvorrichtungen (1, 2, 3, 4) vorgesehenen Schaltmittel VMOS-Elemente (TR1,
TR3; Fig. 8) umfassen, die in dem genannten niederohmigen Strompfad in beiden Richtungen
stromleitend sind.
9. System nach Anspruch 8, dadurch gekennzeichnet, daßeine im Diagonalzweig einerGleichrichterbrückenschaltung
(D9, D10, D11, D12) angeordnete Oszillatorschaltung (TR4, R9-R13, C1) vorgesehen ist,
die bei Erfassung eines Kurzschlusses eine Anzeigeeinrichtung (LED 1) intermittierend
betätigt.
10. System nach Anspruch 6, 7, 8 oder 9, dadurch gekennzeichnet, daß die genannten
Sensormittel einen Transistor (TR2) umfassen, durch den die Transistoren (TR1, TR3)
der Schaltmittel derart vorgespannt werden können, daß sie jeweils einen niederohmigen
Strompfad bilden, daß der Transistor (TR2) der Sensormittel durch einen von den jeweiligen
Diodenschaltungen (D1, R1, D7, R6) abgeleiteten Strom vorgespannt ist, und daß die
Diodenschaltungen ihrerseits bei Auftreten eines Kurzschlusses in einem der Schaltungselemente
(21) in Durchlaß- bzw. in Sperrichtung vorgespannt werden, derart daß der Transistor
(TR2) der Sensormittel in den nichtleitenden Zustand vorgespannt wird, wobei er die
Transistoren (TR1, TR3) in den nichtleitenden Zustand vorspannt, so daß sie hochohmige
Strompfade bilden.
1. Un système de détection de court-circuit comprenant un circuit en boucle (L) connecté
à un élément bidirectionnel (20) et un circuit pour isoler une partie d'un circuit
en boucle (L), contenant un ou plusieurs éléments de circuit (21) par rapport à un
élément d'alimentation bidirectionnelle (20) dans le cas d'un court-circuit dans ladite
partie et dans lequel un ou plusieurs desdits éléments de court-circuit (21) sont
connectés entre des isolateurs bidirectionnels (1,2,3,4) dans chaque partie du circuit
en boucle (L), chacun desdits isolateurs (1, 2, 3, 4) comprenant des moyens de commutation
(TR1, TR3) assurant un trajet à basse impédance et un trajet à haute impédance, ledit
trajet à haute impédance isolant lesdits éléments de circuit (21) dudit élément (20)
; et des moyens de détection (TR2, D1, D7) pour détecter un court-circuit dans l'un
quelconque desdits éléments de circuit (21) dans ladite partie ; lesdits moyens de
commutation (TR1, TR3) agissant en réponse auxdits moyens de détection (TR2, D1, D7)
pour amener lesdits moyens de commutation (TR1, TR3) à fournir ledit trajet à basse
impédance en l'absence de court-circuit et à provoquer un changement d'état du trajet
à basse impédance au trajet à haute impédance en présence dudit court-circuit, caractérisé
en ce que ledit élément bidirectionnel (20) est un élément d'alimentation en énergie,
lesdits trajets à basse impédance fournissant un courant de manière continue depuis
ledit élément d'alimentation auxdits éléments de circuit, en ce que lesdits éléments
de circuit (21), sont des détecteurs d'incendie qui sont actionnés en fonction de
l'énergie fournie par ledit élément (20), et en ce que les moyens de détection de
court-circuit dans lesdits isolateurs bidirectionnels (1-4) agissent indépendamment
et simultanément à la variation du niveau de tension dans une partie court-circuitée
de la boucle (L) entre lesdits isolateurs adjacents, grâce à quoi seuls les isolateurs
(2, 3) immédiatement adjacents à la partie court-circuitée bloquent de manière autonome
et simultanée l'alimentation en énergie des détecteurs d'incendie (21) disposés entre
eux sans empêcher les autres isolateurs bidirectionnels (1, 4) de fournir un courant
de manière continue dudit élément d'alimentation en énergie (20) aux détecteurs d'incendie
non isolés (21).
2. Un système selon la revendication 1, caractérisé en ce qu'une pluralité des éléments
de circuit (21) est connectée en série entre chaque paire d'isolateurs bidirectionnels
(1, 2, 3, 4).
3. Un système selon la revendication 1, caractérisé en ce qu'une pluralité des éléments
de circuit (21) est connectée dans des prolongements respectifs (S) compris entre
chaque paire d'isolateurs (1, 2, 3, 4).
4. Un système selon la revendication 1, caractérisé en ce qu'une pluralité des éléments
de circuit (21) est interconnectée dans des boucles respectives entre chaque paire
d'isolateurs (1,2,3,4) et en ce que chaque paire d'isolateurs (1, 2, 3, 4) est également
interconnectée (figure 6).
5. Un système selon l'une quelconque des revendications précédentes et adapté à une
alimentation en courant alternatif caractérisé en ce que chacun des isolateurs est
de type non polarisé et comprend des isolateurs polarisés (1, 2) connectés aux lignes
respectives (25, 26) fournissant ledit courant alternatif, les pôles opposés des isolateurs
(1, 2) étant inter- connectés (figure 7).
6. Un système selon l'une quelconque des revendications précédentes, caractérisé en
ce que, dans chacun des isolateurs (1, 2, 3, 4), les moyens de commutation comprennent
des transistors (TR1, TR3, figure 4) connectés à des diodes respectives (D3, D5) pour
transmettre des courants dans les directions respectives directe et inverse dans ledittra-
jet à basse impédance.
7. Un système selon la revendication 6, caractérisé en ce qu'une impédance (R7) est
connectée selon un trajet de dérivation aux bornes des moyens de commutation (TR1,
TR3) pour améliorer les caractéristiques de fermeture de l'isolateur (1, 2, 3, 4)
quand l'alimentation est initialement appliquée.
8. Un système selon l'une quelconque des revendications 1 à 5, caractérisé en ce que,
dans chacun des isolateurs (1,2,3,4), les moyens de commutation comprennent des dispositifs
de type VMOS (TR1, TR3 figure 8) qui transmettent des courants bidirectionnels dans
ledit trajet à basse impédance.
9. Un système selon la revendication 8, caractérisé en ce qu'un circuit oscillant
(TR4, R9-R13, C1 ) est connecté aux bornes d'un circuit redresseur en pont (D9, D10,
D11, D12) pour actionner un indicateur (LED 1) de façon intermittente par suite de
la détection d'un court-circuit d'un côté ou de l'autre de l'isolateur (1, 2, 3, 4).
10. Un système selon la revendication 6, 7, 8 ou 9, caractérisé en ce que les moyens
de détection comprennent un transistor (TR2) pour polariser les transistors (TR1,
TR3) des moyens de commutation pour fournir des trajets respectifs à basse impédance,
le transistor (TR2) des moyens de détection étant polarisé par un courant provenant
de circuits à diodes respectifs (D1, R1, D7, R6), ces circuits à diodes devenant polarisés
respectivement en direct ou en inverse en réponse à un court-circuit dans l'un des
éléments de circuit (21), d'où il résulte que le transistor (TR2) des moyens de détection
est polarisé à un état non conducteur, polarisant ainsi les transistors (TR1, TR3)
à un état non conducteur pour fournir les trajets respectifs à haute impédance.