Cerberus Ag

Andreas Scheidweiler

Jurg Muggli

Otto Meier

Eugen G Schibli

Bernhard Durrer

Marc P Thuillard

Peter Muller

Alfred Wuthrich

Kurt Hess

Peter Mueller

Richard Buehler

In a scattered-light smoke detector, for preventing false alarms due to extraneous matter in a measurement chamber (1), a radiation source (2) and two radiation detectors (7, 8) are included. An evaluation circuit is provided for comparing the two detector signals, and an alarm signal is triggered if at least one of the detector signals exceeds a predetermined threshold, and if the two detector signals are at least approximately equal. In another embodiment, a scattered-light smoke detector includes two radiation sources (2, 22), a radiation detector (7), and circuitry for alternatively activating one (2) or the other (22) radiation source. For comparison, corresponding detector signals are stored in sample-and-hold circuits, and an alarm signal can be triggered depending on the same tests. Furthermore, in both cases, a trouble signal can be produced if the two signals are significantly different.

Optical smoke detector with active self-monitoring

In an alarm system with a number of alarm devices such as fire intrusion alarm devices connected to a signal center, upper and a lower thresholds are defined in the alarm devices, with the inactive value of the sensor output signal located between the threshold limits. The alarm devices transmit one of three indication signals to the signal center depending on whether an alarm sensor output is above an upper limit, below a lower limit or between the upper and lower limits, with these alarm state signals being produced by threshold detectors. Also, it is possible to adjust the two threshold limits of the alarms to compensate for changing ambient conditions over extended periods of time. When the sensor output signal reaches one of the upper or lower thresholds both the upper and lower threshold limits either move up or down, respectively, so that the sensor output signal is once again located between the upper and lower threshold limits. The signal center receives the outputs of the threshold detectors and differentiates between five different states, namely the alarm states 'normal,' 'warning,' 'alarm,' 'maintenance' and 'malfunction', on the basis of the frequency and the type of these signals.

Alarm system

Measuring stations or locations are connected in cascade to signal lines and transmit measured or measuring values to a central signal station at which the measured values are linked or appropriately processed so as to obtain distinct malfunction or alarm signals. Upon activation of the monitoring system all measuring stations are disconnected by a change in voltage appearing on the signal line. Then, the measuring stations are reconnected to the signal line in a timewise staggered fashion by means of switching elements present at each measuring station in such a manner that each measuring station additionally reconnects a subsequent measuring station to the line voltage after a predetermined time-delay. Address storages are present at the measuring stations and are charged or occupied in a predetermined sequence by the central signal station with addresses associated with the individual measuring stations. The address storages are thereafter locked prior to the time that the next following measuring station at the same signal line is connected to the signal voltage by the switching element.

Method of transmitting measuring values in a monitoring system

Due to aging of the insulating materials arranged between the electrodes in ionization fire alarms or detectors the insulating efficiency of these thus formed so-called insulating paths or spans deteriorates in the course of time despite, or maybe even due to the cleaning operations performed upon such ionization fire alarms. To ensure that the insulating capacity does not fall below a critical value the insulating path or span is formed by at least two different insulating materials. The materials are arranged in such a manner that the creepage path between the electrodes extends across all the different insulating materials. This principle also may be applied to other measuring devices which require a high input resistance of an amplifier stage.

Electrode insulating member for ionization fire alarm

In the apparatus for signalling an alarm, for example, in a gas or fire detecting installation, a detector is reset after a first response and the time duration until the next-following detector response is determined and classified with respect to three classes of time periods. When the time duration until the further detector response is beyond a predetermined upper or outer time limit, no alarm signal is released and the apparatus returns into its original state. When the further detector response occurs between two time limits, the alarm is immediately signalled. When the further detector response occurs prior to a lower one of the two time limits, there is carried out still one further test during which the detector is once again reset. The alarm signal will only be released if an additional further detector response is still observed prior to the upper time limit. In this manner the reliability of alarm signalling can be enhanced and the frequency of the occurrence of false alarms, particularly due to the occurrence of short-time or brief spurious conditions, can be significantly reduced.

Method of and apparatus for signalling an alarm

A smoke detector containing at least one smoke measuring chamber which possesses a mounting or socket plate having an upper surface intended to be mounted at the ceiling of a room or other appropriate area to be monitored and a housing enclosing the smoke measuring chamber and suspendingly secured at the socket plate. The housing possesses openings for the entry of the ambient air into the smoke measuring chamber. The smoke detector comprises a manually adjustable device by means of which it is possible to change the air entry opening in a manner such that the smoke detector can be accommodated to different environmental or ambient conditions, especially those containing different quantities of dust and other contaminants. A hood ring member, movably supported at the inside of a sleeve member of the smoke detector, can be selectively displaced in order to change the air entry openings.

Smoke detector

A fire alarm installation possessing increased intelligence which enables differentiating between smoldering fires and fires having open or licking flames. This capability is obtained in that the fire alarm installation possesses two sensor elements working according to different functional principles and an evaluation circuit contains circuit elements which form the quotient of the signals received from both sensor elements. The different sensor elements can be united in a single fire alarm housing which simultaneously contains the evaluation circuit.

Method of fire detection and fire detection installation

In a fire alarm system individual fire alarms are connected in series by reporting lines with a central signal station. In order to be able to connect a greater number of fire alarms with the individual reporting or signaling lines and/or in order to be able to dispatch an increased amount of current through the reporting lines, the reporting or signaling lines from the last fire alarm of a line are returned back to the central signal station in the form of a ring circuit or loop. Upon the absence of signals at a reporting line an interrogation device is reversed, so that there can be ensured that in the event of a line disturbance or breakdown of a fire alarm the remainder of the fire alarms still can be utilized for giving a signal. The individual fire alarms are structured such that during assembly the inputs and outputs can be mutually interchanged.

Method for transmitting measuring values in a fire alarm system and

A smoke detector containing at least one smoke measuring chamber which possesses a mounting or socket plate having an upper surface intended to be mounted at the ceiling of a room or other appropriate area to be monitored and a housing enclosing the smoke measuring chamber and suspendingly secured at the socket plate. The housing possesses openings for the entry of the ambient air into the smoke measuring chamber. The smoke detector comprises a manually adjustable device by means of which it is possible to change the air entry openings in a manner such that the smoke detector can be accommodated to different environmental or ambient conditions, especially those containing different quantities of dust and other contaminants.

An ionization smoke detector containing at least one ionization chamber operated at an extra low voltage or potential. The ionization chamber contains a sensor employing a measuring electrode and a counter electrode. Ambient air has practically free access to the ionization chamber and there are provided one or more radioactive sources for generating ions, a supply voltage source and an electrical circuit for triggering an alarm. The smoke detector possesses increased operational reliability since circuit elements are provided which enable signal reporting to a central station by means of a low-voltage of about 200 volts, however the sensor is operated at an extra low voltage.

Ionization smoke detector with increased operational reliability

An ionization chamber with two electrodes having a variable spacing and with a radioactive source for the ionization of the electrode gap therebetween includes an adjusting mechanism for the positional adjustment of one of the electrodes relative to the other. The mechanism is such that a spring element presses the adjustable electrode against at least one point of the adjusting mechanism. Several arrangements are disclosed for adjustably mounting a cup-shaped electrode in the housing of the chamber in such a manner that it is readily adjustable and will not undergo spurious readjustment as a result of vibration of shock.

Adjustable ionization chamber

At least two sensors are used, providing electrical output signals to indicate alarm conditions, one of the sensors being a bipolar ion sensor having a shielded ion chamber formed to slow or brake atmospheric currents therethrough, and a second sensor which operates essentially in unipolar mode having an ion chamber freely accessible to atmospheric flow therethrough.

Fire and smoke sensing system

An ionization chamber is exposed to the atmosphere to be supervised, the ionization chamber being so constructed that the electrical resistance thereof changes in the presence of fire particles or aerosols upon occurrence of a fire; to improve reliability of detection, the ionization chamber is connected as a resistance element in a free-running multivibrator oscillator circuit, which includes a pair of cross-coupled field effect transistors (FET's) so that, upon change of the atmosphere to which the ionization chamber is exposed, the pulse frequency of the oscillator changes, which change is detected by a pulse rate detector. If the detector has upper and lower threshold levels, deviation of pulse rate in one direction may be used to sense presence of a fire, and in the other direction may be used to sense incipient trouble in the circuit itself.

Ionization-type fire sensing system

Two ionization chambers are formed on the sensor, one including a pair of electrodes and ionizing substance, which are relatively so located that, in the space between the electrodes, the air will be ionized with both positive and negative ions so that the current flowing between the electrodes will be generated by ions of both polarities to form a bipolar ionization chamber; the other has the electrodes and the ionizing substance so located that at least in a portion, preferably a major portion of the space between the electrodes, ions of only a single polarity will occur. The bipolar chamber is shielded from air flow therethrough, the unipolar chamber, however, being exposed to free air flow. Preferably, a third or reference chamber may be combined with the sensor. The unipolar and bipolar chambers are connected to an evaluation circuit which responds when the current between the electrodes in at least one of the unipolar or bipolar chambers drops below a certain threshold value.

Duplex ionization-type fire sensor

To render an ionization-type sensing element essentially immune to changes in ambient conditions, principally temperature or operating voltage, while still using low-current draining circuits to sense response of the ionization chamber of the sensor, the threshold response level of a field effect transistor (FET) is arranged to have approximately the same temperature response characteristic, within the range of ambient temperature considered, as the ionization cell so that the overall circuit or system combination of the cell and FET amplifier will have a response which is essentially independent of ambient temperature or similar conditions. The source path of the FET is connected to a voltage divider which is so dimensioned that the voltage division ratio (R.sub.2 /R.sub.1) is related to the temperature coefficient (.alpha.) of the base-emitter voltage of the FET and the temperature coefficient (.beta.) of the measuring ionization cell chamber:

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Uerikon, Switzerland

Andreas Scheidweiler