Cerberus Ag

Peter Muller

Andreas Scheidweiler

Jurg Muggli

Peter Christen

A gas sensing signaling system is provided in which a plurality of gas sensing units are connected over cables with a central station. To permit establishment of threshold levels such that false alarms are rejected while the system still remains sensitive to dangerous conditions and to permit ready supervision and testing of said system, a central station is provided in which timing circuits are included which start the time interval upon sensing of an alarm condition above a lower, or warning threshold level. If the lower warning level signal persists for the timing interval--for example for about one-half minute, a warning signal is given. A higher level signal generates an alarm signal, either immediately or after a much shorter time delay. The circuit includes self-holding circuitry so that, once a sensing unit transmits a sensing signal which persists beyond the previous predetermined warning or alarm time duration, the central station will indicate the respective conditions until manually reset. Besides indication, corrective action, such as energization of ventilation equipment and the like can be controlled. The cabling system preferably operates with predetermined, discrete voltage levels at the respective signal lines which, upon transmission of a warning and/or alarm signal, changes under control of a voltage control circuit in the central station, to permit additionally, by connection of a termination element, to indicate malfunction within the lines or the sensing units by detecting current flow and voltage relationships in the respective lines.

Gas sensing signaling system

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

A fire alarm is provided with a temperature sensitive element formed of a shape memory alloy, which following cold working, upon heating to a critical temperature, typically for instance about 70.degree. C., returns to the original impressed shape and also retains this shape even after subsequent recooling. Due to the movement of the element there is triggered a self-holding alarm signal, either directly by closing contacts or indirectly. Resetting of the fire alarm can be accomplished by mechanically cold working the element, or by using two-way shape memory alloys through cooling to a lower temperature threshold which can be below room or ambient temperature. A further beneficial construction is realized by combining the arrangement with a different type of fire detection or sensing element, for instance by arranging a shape memory alloy element in a scattered radiation-smoke detector. Upon reaching a critical temperature, the shape memory alloy element moves into the radiation region, or when used in an ionization fire alarm, the shape memory alloy element screens the radioactive radiation source and reduces the ionic current. Suitable shape memory alloys are, by way of example, nickel 55/titanium 45, or nickel 45/titanium 45/copper 10.

Employing a shape memory alloy in a fire alarm temperature sensitive

At least two photoelectric sensors, sensitive to different spectral ranges of incident light, provide two sensed output signals; the relationship of the a-c components of the sensed output signals is evaluated, and it is determined if these a-c components fall within predetermined low frequency ranges, for example, 2 to 50 Hz, preferably 5 to 25 Hz; if so, a 'flame present' signal is provided, for example to give a fire alarm, or to indicate that a burner is operating. Preferably, the relationship of the signals is such that a different signal is provided between one of the sensed signals and a fraction of the other, and conversely, and the sensitivity of the sensors is adjusted to have the same output signals at a predetermined color temperature, for example about 1,400.degree. K. Illumination signals incident on the sensors due to other sources than flames then are reliably eliminated while still providing the 'flame present' signal upon coincidence of the appropriate difference signals, which coincidence preferably is determined by analyzing the phase relationships of the resulting difference signals in a phase comparator.

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Oetwil a. See, Switzerland

Peter Muller