US 5,212,470 A · Supervised fire alarm system

Abstract

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.

Claims12

Dependent claims

A fire alarm system comprising:

(a) control and indicating means (6);
and
(b) a plurality of ionization smoke detectors (7), being connected through signal lines (8, 9, 14) with said control and indicating means (6), each ionization smoke detector (7) comprising:
(i) an ionization measurement chamber (1) for producing an electrical signal having a characteristic indicative of a monitored condition,
(ii) a radioactive source (10) to ionize the air in the ionization measurement chamber (1), and
(iii) an evaluation circuit comprising:
(A) an amplifier element (3) to amplify the electrical signal from the ionization measurement chamber (1), and
(B) threshold detection means (15, 16) for comparing the electrical signal characteristic to minimum and maximum limits and for producing an alarm or trouble signal,
(C) electronic means (5, 11) adapted to change the supply voltage (U) of said ionization smoke detector (7) to a first supply voltage and an increased second supply voltage, and
(D) electronic control means for signal evaluation adapted to compare the corresponding two currents measured at said two different supply voltages with predetermined current values and to transmit an alarm signal to said control and indicating means (6) only if variations from the predetermined current values of the actual output signal of the amplifier element (3) caused by the increased second supply voltage demonstrates that there has been no significant reduction of the saturated current (Is) of said ionization measurement chamber (1) after the supply voltage has been increased to said second supply voltage.

7 more elements

A fire alarm system comprising:

(a) control and indicating means (6) comprising an evaluation circuit comprising
(i) threshold detection means (15, 16) for comparing an electrical signal characteristic to minimum and maximum limits and for producing an alarm or trouble signal,
(ii) electronic means (5, 11) adapted to change the supply voltage (U) of an ionization smoke detector (7) having an ionization measurement chamber (1) to a first supply voltage and an increased second supply voltage, and
(iii) electronic control means for signal evaluation adapted to compare the corresponding two currents measured at said two supply voltages with predetermined current values and to generate an alarm signal only if variations from the predetermined current values of the actual output signal of the amplifier element (3) caused by the increased second supply voltage demonstrates that there has been no significant reduction of the saturated current (Is) of said ionization measurement chamber (1) after the supply voltage has been increased to said second supply voltage;
and
(b) a plurality of ionization smoke detectors (7) being connected through signal lines (8, 9, 14) with said control and indicating means (6), each ionization smoke detector (7) comprising:
(i) said ionization measurement chamber (1) for producing an electrical signal having a characteristic indicative of a monitored condition,
(ii) a radioactive source (10) to ionize the air in the ionization measurement chamber (1), and
(iii) an evaluation circuit comprising
(A) an amplifier element (3) to amplify the electrical signal from said ionization measurement chamber (1), and
(B) converter means (19) for transmitting the amplified electrical signal to said control and indicating means (6).

8 more elements

A fire alarm system comprising:

(a) control and indicating means (6) comprising an evaluation circuit comprising
(i) threshold detection means (15, 16) for comparing an electrical signal characteristic to minimum and maximum limits and for producing an alarm or trouble signal,
(ii) first electronic means (5) adapted to change the supply voltage (U) of an ionization smoke detector (7) having an ionization measurement chamber (1) to a first supply voltage and an increased second supply voltage, and
(iii) electronic control means for the signal evaluation adapted to compare the corresponding two currents measured at said two supply voltages with predetermined current values and to generate an alarm signal only if variations from the predetermined current values of the actual output signal of the amplifier element (3) caused by the increased second supply voltage demonstrates that there has been no significant reduction of the saturated current (Is) of said ionization measurement chamber (1) after the supply voltage has been increased to said second supply voltage;
and
(b) a plurality of ionization smoke detectors (7) being connected through signal lines (8, 9, 14) with said control and indicating means (6), each ionization smoke detector (7) comprising:
(i) said ionization measurement chamber (1) for producing an electrical signal having a characteristic indicative of a monitored condition,
(ii) a radioactive source (10) to ionize the air in the ionization measurement chamber (1), and
(iii) an evaluation circuit comprising
(A) an amplifier element (3) to amplify the electrical signal from said ionization measurement chamber (1),
(B) converter means (19) for transmitting the amplified electrical signal to said control and indicating means (6), and
(C) second electronic means (11) operatively associated with first electronic means (5) of control and indicating means (6) and adapted to change the supply voltage (U) of said ionization smoke detector (7) to two different supply voltages.

9 more elements

An ionization smoke detector, comprising:

(i) an ionization measurement chamber (1) for producing an electrical signal having a characteristic indicative of a monitored condition,
(ii) a radioactive source (10) to ionize the air in the ionization measurement chamber (1), and
(iii) an evaluation circuit comprising:
(A) an amplifier element (3) to amplify the electrical signal from the ionization measurement chamber (1), and
(B) threshold detection means (15, 16) for comparing the electrical signal characteristic to minimum and maximum limits and for producing an alarm or trouble signal,
(C) electronic means (5, 11) adapted to change the supply voltage (U) of said ionization smoke detector (7) to a first supply voltage and an increased second supply voltage, and
(D) electronic control means for signal evaluation adapted to compare the corresponding two currents measured at said two different supply voltages with predetermined current values and to transmit an alarm signal only if variations from the predetermined current values of the actual output signal of the amplifier element (3) caused by the increased second supply voltage demonstrates that there has been no significant reduction of the saturated current (Is) of said ionization measurement chamber (1) after the supply voltage has been increased to said second supply voltage.

4 more elements

Dependencies are inferred from the claim text.

Supervised fire alarm system

Life of this patent

Supervised fire alarm system

Life of this patent

Abstract

Claims12