Cerberus Ag

Cerberus Ltd.

Marc P Thuillard

Andreas Scheidweiler

Kurt Hess

Method for analyzing the signals of a danger alarm system and danger

A flame is detected by signal analysis for intensity variations in radiation received by a sensor. A low-frequency spectrum of the signal is analyzed for mid- and cut-off frequencies, and the signal is classified as periodic or non-periodic. Periodic signals with a mid-frequency (.omega..sub.mp) above a first frequency value (G.sub.1), and non-periodic signals with a cut-off frequency (.omega..sub.gc) above a second frequency value (G.sub.2) are classified as interfering signals. The first frequency value is determined by the flicker frequency of a stationary flame having a magnitude corresponding to a flame of minimum magnitude to be detected. The second frequency value is selected greater than the first frequency value (G.sub.1).

Method and detector for detecting a flame

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

A fire detector system including ionization smoke detectors (7) is provided with improved false-alarm protection. The system includes an ionization chamber (1) with a radioactive source (10), connected in series with a resistor (2) between power supply lines (8, 9), and circuitry (11, 28) for switching the operating voltage of the ionization chamber between a normal operating value (Ut) chosen for maximized detector sensitivity, and an elevated value (Uh) for operation at current saturation. Comparisons involving the ionization currents through the ionization chamber at the two operating voltages are used not only to recognize a condition of partial shielding of the radio-active source (due to condensation, for example), but also to detect smoke under such conditions.

Fire detector system and method

A fire alarm system having increased immunity to false alarms comprises control and indicating means (6) and a plurality of ionization smoke detectors (7) connected through signal lines (8, 9, 14) with the control and indicating means (6), each ionization smoke detector (7) comprising an ionization measurement chamber (1) for producing an electrical signal having a characteristic indicative of a monitored condition, a radioactive source (10) to ionize the air in the ionization measurement chamber (1), and an evaluation circuit comprising an amplifier element (3) to amplify the electrical signal from the ionization measurement chamber (1), threshold detection means (15, 16) for comparing the electrical signal characteristic to minimum and maximum limits and for producing an alarm or trouble signal, and electronic means (5, 11) by which the chamber voltage (UK) of the ionization measurement chamber (1) is increased as far as possible to the saturation range of the ionization chamber (1) if the ionization current in the ionization chamber (1) is reduced. From the current which flows at increased chamber voltage (UK2) it can be determined whether the saturation current (Is) of the ionization chamber (1) has fallen compared with given predetermined values. If the saturation current (Is) of the ionization chamber (1) has fallen compared with given predetermined values, a malfunction has occurred, for example, due to the covering of the radioactive source (10); if not, then an alarm signal is transmitted.

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Mannedorf, Switzerland

Marc P Thuillard