Fire detector system and method
First Claim
1. A fire detector system including an ionization smoke detector (7) connected to control and indicating means (6) and comprisingan ionization measurement chamber (1) for producing an output signal as a function of the concentration of combustion aerosols in air entering the ionization measurement chamber, connected in series with a load resistor (2) between first and second voltage supply lines (8, 9),a radioactive source (10) for ionizing air within the ionization measurement chamber,an amplifier element (3) for amplifying the output signal of the ionization measurement chamber to produce an amplified signal which is directly related to an ionic current strength in the ionization measurement chamber,a voltage generator (11) for supplying to the ionization smoke detector a first operating voltage (Ut) and a second operating voltage (Uh) which is greater than the first operating voltage, andevaluation means (12, 15, 16, 17, 18, 22) for producing an alarm signal to the control and indicating means to indicate a critical concentration of combustion aerosols in the ionization measurement chamber, comprising comparator means (15, 16, 22) for evaluating first and second amplified signals from the ionization measurement chamber at the first and second respective operating voltages, and adapted to produce the alarm signal whenthe first amplified signal divided by a predetermined first quiescent-state voltage (Ua) is less than an alarm threshold (Us1), andthe first amplified signal divided by the first quiescent-state voltage is less than the second amplified signal divided by a predetermined second quiescent-state voltage (Ub).
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Accused Products
Abstract
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.
36 Citations
11 Claims
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1. A fire detector system including an ionization smoke detector (7) connected to control and indicating means (6) and comprising
an ionization measurement chamber (1) for producing an output signal as a function of the concentration of combustion aerosols in air entering the ionization measurement chamber, connected in series with a load resistor (2) between first and second voltage supply lines (8, 9), a radioactive source (10) for ionizing air within the ionization measurement chamber, an amplifier element (3) for amplifying the output signal of the ionization measurement chamber to produce an amplified signal which is directly related to an ionic current strength in the ionization measurement chamber, a voltage generator (11) for supplying to the ionization smoke detector a first operating voltage (Ut) and a second operating voltage (Uh) which is greater than the first operating voltage, and evaluation means (12, 15, 16, 17, 18, 22) for producing an alarm signal to the control and indicating means to indicate a critical concentration of combustion aerosols in the ionization measurement chamber, comprising comparator means (15, 16, 22) for evaluating first and second amplified signals from the ionization measurement chamber at the first and second respective operating voltages, and adapted to produce the alarm signal when the first amplified signal divided by a predetermined first quiescent-state voltage (Ua) is less than an alarm threshold (Us1), and the first amplified signal divided by the first quiescent-state voltage is less than the second amplified signal divided by a predetermined second quiescent-state voltage (Ub).
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10. A method for fire detection, comprising
applying first (Ut) and second (Uh) operating voltages to an ionization measurement chamber which includes a source of ionizing radiation and which is connected, in series with a load resistor, between first and second voltage supply lines, the first operating voltage being less than the second operating voltage, amplifying output signals from the ionization measurement chamber corresponding to the first and second operating voltages, thereby defining first and second amplified signals respectively, and producing an alarm signal when the first amplified signal divided by a first quiescent-state voltage (Ua) is less than an alarm threshold voltage (Us1) and the first amplified signal divided by the first quiescent-state voltage is less than the second amplified signal divided by a second quiescent-state voltage (Ub).
Specification