Claims
- 1. 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.
- 2. A fire alarm system according to claim 1, wherein the electronic control means for signal evaluation comprise:
- a first comparator (15) and a second comparator (16) both connected to the output of the amplifier element (3),
- a first AND gate (12) to produce an alarm signal,
- a second AND gate (17) to produce a trouble signal,
- an alarm transmission circuit consisting of a bistable switch (13) connected to the output of first AND gate (12) to transmit said alarm signal, and
- a trouble signal transmission circuit (18) connected to the output of second AND gate (17) to transmit a trouble signal, wherein said electronic control means for signal evaluation is adapted to increase the supply voltage (U) via the electronic means (5, 11) and transmit an alarm signal if at increased supply voltage a current flows which causes a voltage drop at a load resistor (2) to exceed a monitoring threshold (Us2), showing no significant reduction of the saturation current (Is) of the ionization measurement chamber (1) and transmit a trouble signal if at increased supply voltage a current flows which causes the voltage drop at said load resistor (2) to fall below the monitoring threshold (Us2), and showing a significant reduction of the saturation current (Is) of the ionization measurement chamber (1).
- 3. 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).
- 4. A fire alarm system according to claim 3, wherein the electronic control means for signal evaluation comprises:
- a first comparator (15) and a second comparator (16) both connected to the output of the amplifier element (3),
- a first AND gate (12) to produce an alarm signal,
- a second AND gate (17) to produce a trouble signal,
- an alarm transmission circuit consisting of a bistable switch (13) connected to the output of first AND gate (12) to transmit said alarm signal, and
- a trouble signal transmission circuit (18) connected to the output of second AND gate (17) to transmit a trouble signal, wherein said electronic control means for signal evaluation is adapted to increase the supply voltage (U) via the electronic means (5, 11) and transmit an alarm signal if at increased supply voltage a current flows which causes a voltage drop at a load resistor (2) to exceed a monitoring threshold (Us2), showing no significant reduction of the saturation current (Is) of the ionization measurement chamber (1) and transmit a trouble signal if at increased supply voltage a current flows which causes the voltage drop at said load resistor (2) to fall below the monitoring threshold (Us2), and showing a significant reduction of the saturation current (Is) of the ionization measurement chamber (1).
- 5. 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.
- 6. A first alarm system according to any one of claims 3-5, wherein said control and indicating means (6) comprise additional converter means (20) connected to the output of converter means (19) of ionization smoke detector (7).
- 7. 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.
- 8. An ionization smoke detector according to claim 7, wherein the electronic control means for signal evaluation comprise:
- a first comparator (15) and a second comparator (16) both connected to the output of the amplifier element (3),
- a first AND gate (12) to produce an alarm signal,
- a second AND gate (17) to produce a trouble signal,
- an alarm transmission circuit consisting of a bistable switch (13) connected to the output of first AND gate (12) to transmit said alarm signal, and
- a trouble signal transmission circuit (18) connected to the output of second AND gate (17) to transmit a trouble signal, wherein said electronic control means for signal evaluation is adapted to increase the supply voltage via the electronic means (5, 11) and transmit an alarm signal if at increased supply voltage a current flows which causes a voltage drop at a load resistor (2) to exceed a monitoring threshold (Us2), showing no significant reduction of the saturation current (Is) of the ionization measurement chamber (1) and transmit a trouble signal if at increased supply voltage a current flows which causes the voltage drop at said load resistor (2) to fall below the monitoring threshold (Us2), and showing a significant reduction of the saturation current (Is) of the ionization measurement chamber (1).
- 9. In an ionization smoke detector system, a method for determining whether a possible alarm condition from an ionization smoke detector is a true alarm or a false alarm, comprising the steps of:
- operating said ionization detector with a first supply voltage and comparing a resulting chamber current to a first predetermined value to detect a possible alarm condition,
- operating said ionization detector at a second, higher supply voltage and comparing the resulting chamber current to a second predetermined value to detect a significant change in the saturation current of said chamber, and
- signaling a true alarm condition in response to said possible alarm condition only if said predetermined change in the saturation current is not detected.
- 10. A method according to claim 9 wherein said method further comprises signaling a trouble condition in said smoke detector system in response to detection of said change in the saturation current.
- 11. A method according to claim 9 wherein said step of operating said ionization detector at a second, higher supply voltage is performed in response to detection of said possible alarm condition.
- 12. A method according to claim 9 wherein said possible alarm condition is detected when said chamber current is below said first predetermined value and said change in the saturation current is detected when said chamber current at said higher voltage is below a second predetermined value.
Priority Claims (1)
Number |
Date |
Country |
Kind |
3372/89 |
Aug 1990 |
CHX |
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Parent Case Info
This application is a continuation of application Ser. No. 07/582,620, filed on Sep. 14, 1990 now abandoned.
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3676678 |
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Continuations (1)
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Number |
Date |
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Parent |
582620 |
Sep 1990 |
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