Smoke detector with a radiation source operated in a pulse-like or intermittent mode

• US 4,559,453 A
• Filed: 05/05/1983
• Issued: 12/17/1985
• Est. Priority Date: 05/13/1982
• Status: Expired due to Fees

• Current Assignee: Cerberus ABP Investor LLC (Cerberus Capital Management LP)
• Original Assignee: Cerberus ABP Investor LLC (Cerberus Capital Management LP)
• Inventors: Labhart, Martin, Muggli, Jurg
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US06/491,707
• Time in Patent Office: 957 Days
• Field of Search: 250/564, 250/565, 250/573, 250/574, 250/575, 250/214 AG, 250/205, 356/438, 356/439, 356/336, 356/337, 340/630
• US Class Current: 250/565
• CPC Class Codes: G08B 17/103 using a light emitting and receiving device
• CPC Class Codes: G08B 29/043 of fire detection circuits

Abstract

In a line extinction detector using a pulse-operated radiation source, a radiation receiver is connected to an input amplifier of an evaluation circuit. The output pulses generated by the input amplifier are compared to a reference voltage. Circuit elements having a time constant above one minute are provided to adjust either one of the voltage of the output pulses or the reference voltage such that their difference practically becomes zero. The output pulses of the input amplifier are further compared to an alarm threshold derived from the reference voltage and an alarm is triggered when the output signal falls below the alarm threshold value. The output pulses of the input amplifier are also compared to a disturbance threshold value and a disturbance signal is generated when the output signal drops below the disturbance threshold value. A further disturbance signal value is also triggered at preset limits for the compensating adjustment between the output signal of the input amplifier and the reference voltage. A device permits to change the ratio of the alarm threshold value and the reference voltage in order to adapt the sensitivity of the smoke detector to different distances between the radiation source and the radiation receiver.

Claims

1. A smoke detector comprising:

a pulsed radiation source emitting focussed radiation pulses into a region freely accessible to environmental air;

a radiation receiver arranged at a predetermined variable distance from said radiation source in the path of said radiation pulses and generating a pulse output signal under the action of said radiation pulses;

an input amplifier series connected to said radiation receiver;

said input amplifier generating output pulses of a voltage essentially proportional to the intensity of said radiation pulses impinging upon said radiation receiver;

an evaluation circuit comprising;

a reference voltage generator for generating a reference voltage for comparison with said voltage of said output pulses generated by said input amplifier;

an alarm stage defining an alarm threshold relative to said reference voltage and comparing said voltage of said output pulses generated by said input amplifier with said alarm threshold;

said alarm stage triggering an alarm signal indicative of the presence of smoke in said path of said radiation pulses, when said output pulses generated by said input amplifier have been attenuated below said alarm threshold for more than a first predetermined period of time;

a disturbance circuit defining a disturbance threshold relative to said reference voltage and lower than said alarm threshold;

said disturbance circuit triggering a disturbance signal indicative of the presence of a disturbance other than smoke in said path of said radiation pulses, when said output pulses generated by said input amplifier have been attenuated below said disturbance threshold within a second predetermined period of time shorter than said first predetermined period of time associated with said alarm stage;

adjusting means for comparing said voltage of said output pulses generated by said input amplifier and said reference voltage and, in the case of a difference therebetween, adjusting relative to each other said voltage of said output pulses and said reference voltage at a rate corresponding to a time constant greater than one minute and within a third time period longer than said first and second predetermined periods of time, such that said difference between said voltage of said output pulses and said reference voltage is maintained at a value of substantially zero; and

a device for varying the ratio of said alarm threshold to said reference voltage as a function of said predetermined variable distance between said radiation source and said radiation receiver.

2. The smoke detector as defined in claim 1, wherein:

said adjusting means comprises digital storage means for storing said output pulses generated by said input amplifier and differing in their voltage from said reference voltage;

said digital storage means being structured to be changed by at most one unit for each nth clock pulse acting on said digital storage means, wherein n≧

1; and

the direction of said change being dependent upon whether said voltage of said output pulse is greater or smaller than said reference voltage.

3. The smoke detector as defined in claim 2, wherein:

said input amplifier has a variable gain; and

said gain being controlled by the output pulses stored in said digital storage means and differing in their voltage from said reference voltage.

4. The smoke detector as defined in claim 2, wherein:

said evaluation circuit is structured such that said reference voltage is controlled as a function of the output pulses differing in their voltage from said reference voltage and stored in said digital storage means.

5. The smoke detector as defined in claim 2, wherein:

said evaluation circuit is structured such that a further disturbance signal is transmitted whenever said output pulses generated by said input amplifier and differing in their voltage from said reference voltage exceed a predetermined upper threshold or lower threshold defined at said digital storage means.

6. The smoke detector as defined in claim 1, wherein:

said ratio of said alarm threshold and said reference voltage which ratio is automatically adjustable as a function of said distance between said radiation source and said radiation receiver, is adjusted as a function of the intensity of said radiation pulses received by said radiation receiver and which intensity is a function of said distance between said radiation source and said radiation receiver.

7. The smoke detector as defined in claim 1, wherein:

said device for varying said ratio of said alarm threshold to said reference voltage comprises a switching element for manual ajdustment of the ratio of said alarm threshold to said reference voltage.

8. The smoke detector as defined in claim 1, wherein:

said disturbance circuit contains a comparator circuit having two inputs and an output;

said inputs being supplied with said output pulses generated by said input amplifier and said disturbance threshold, respectively, and said output supplying correlation pulses as long as said voltage of said output pulses generated by said input amplifier exceed said disturbance threshold;

said output of said comparator circuit being connected to said disturbance circuit, said alarm stage, and said adjusting means; and

said comparator circuit constituting correlating means correlating said evaluation circuit containing said alarm stage, said disturbance circuit and said adjusting means to said radiation pulses emitted by said radiation source.

9. The smoke detector as defined in claim 1, further including:

a reference radiation receiver arranged in close proximity to said radiation source;

said reference radiation receiver generating a reference value related to the radiation intensity of said radiation pulses emitted by said radiation source and received by said reference radiation receiver; and

a regulation circuit operatively connected with said reference radiation receiver and regulating said radiation source such as to emit radiation pulses of a predetermined substantially constant radiation intensity.

10. The smoke detector as defined in claim 9, further including:

disturbance signalling means for generating a regulation disturbance signal when the regulation of said radiation pulses exceeds a predetermined threshold.

11. The smoke detector as defined in claim 1, further including:

a pulse generator operatively connected to said radiation source in order to produce said focussed radiation pulses; and

said pulse generator being arranged in close proximity to said radiation source.

12. The smoke detector as defined in claim 1, wherein:

said device for varying the ratio of said alarm threshold to said reference voltage as a function of said predetermined variable distance between said radiation source and said radiation receiver simultaneously varies the ratio of said disturbance threshold to said reference voltage as a function of said predetermined variable distance between said radiation source and said radiation receiver.

13. A smoke detector comprising:

a pulsed radiation source emitting focussed radiation pulses into a region freely accessible to environmental air;

a radiation receiver arranged in the path of said radiation pulses;

an input amplifier series connected to said radiation receiver;

said input amplifier generating output pulses of a voltage which is essentially proportional to the intensity of said radiation pulses impinging upon said radiation receiver;

an evaluation circuit comprising;

a reference voltage generator for generating a reference voltage for comparison with said voltage of said output pulses;

an alarm stage defining an alarm threshold relative to said reference voltage and comparing said voltage of said output pulses generated by said input amplifier with said alarm threshold;

said alarm stage triggering an alarm signal indicative of the presence of smoke in said path of said radiation pulses, when said output pulses generated by said input amplifier have been attenuated below said alarm threshold for more than a first predetermined period of time;

a disturbance circuit defining a disturbance threshold relative to said reference voltage and lower than said alarm threshold;

said disturbance circuit triggering a disturbance signal indicative of the presence of a disturbance other than smoke in said path of said radiation pulses, when said output pulses generated by said input amplifier have been attenuated below said disturbance threshold for a second predetermined period of time shorter than said first predetermined period of time associated with said alarm stage;

correlating means correlating said evaluation circuit with said radiation pulses emitted by said radiation source;

said correlating means comprising a comparator circuit having two inputs and an output;

said comparator circuit receiving at one of its two inputs said output pulses generated by said input amplifier and said disturbance threshold being applied to the other one of said two inputs of said comparator circuit;

said comparator circuit generating correlation pulses at its output as long as said voltage of said output signals generated by said input amplifier exceed said disturbance threshold; and

said output of said comparator circuit being connected to said alarm stage and to said disturbance circuit.

14. The smoke detector as defined in claim 13, wherein:

said evaluation circuit contains follow-up means;

said follow-up means determining and minimizing a difference existing between said voltage of said output pulses generated by said input amplifier and said reference voltage at a rate corresponding to a time constant exceeding one minute; and

said follow-up means containing a counter clocked by means of said correlation pulses generated at the output of said comparator circuit and counting difference pulses when said difference exists between said voltage of said output pulses and said reference voltage.

15. The smoke detector as defined in claim 13, further including:

a device for varying the ratio of said alarm threshold to said reference voltage.

16. The smoke detector as defined in claim 14, wherein:

said counter of said follow-up means constitutes digital storage means for storing said difference pulses;

said digital storage means being structured to be changed by at most one unit for each nth correlation pulse, wherein n≧

1; and

the direction of said change being dependent upon whether said voltage of an output pulse generated by said input amplifier is greater or smaller than said reference voltage.

17. The smoke detector as defined in claim 16, wherein:

said input amplifier has a variable gain; and

said gain being controlled by the difference pulses stored in said digital storage means.

18. The smoke detector as defined in claim 16, wherein:

said evaluation circuit is structured such that said reference voltage is controlled as a function of the difference pulses stored in said digital storage means.

19. The smoke detector as defined in claim 14, wherein:

said evaluation circuit is structured such that a further disturbance signal is transmitted whenever said difference pulses stored in said counter exceed a predetermined upper threshold or lower threshold.

20. The smoke detector as defined in claim 15, wherein:

said radiation source and said radiation receiver are arranged at a predetermined variable distance; and

said device automatically adjusting the ratio of said alarm threshold to said reference voltage as a function of said predetermined variable distance between said radiation source and said radiation receiver.

21. The smoke detector as defined in claim 20, wherein:

said ratio of said alarm threshold and said reference voltage which ratio is automatically adjustable as a function of said distance between said radiation source and said radiation receiver, is adjusted as a function of the intensity of said radiation pulses received by said radiation receiver and which intensity is a function of said distance between said radiation source and said radiation receiver.

22. The smoke detector as defined in claim 15, further including:

said device determining a variable distance between said radiation source and said radiation receiver; and

said device containing a switching element for manual adjustment of the ratio of said alarm threshold to said reference voltage as a function of the distance determined between said radiation source and said radiation receiver.

23. The smoke detector as defined in claim 13, further including:

a reference radiation receiver arranged in close proximity to said radiation source;

said reference radiation receiver generating a reference value related to the radiation intensity of said radiation pulses emitted by said radiation source and received by said reference radiation receiver; and

a regulation circuit operatively connected with said reference radiation receiver and regulating said radiation source such as to emit radiation pulses of a predetermined substantially constant radiation intensity.

24. The smoke detector as defined in claim 23, further including:

disturbance signalling means for generating a regulation disturbance signal when the regulation of said radiation pulses exceeds a predetermined threshold.

25. The smoke detector as defined in claim 13, further including:

a pulse generator operatively connected to said radiation source in order to produce said focused radiation pulses; and

said pulse generator being arranged in close proximity to said radiation source.

26. The smoke detector as defined in claim 20, wherein:

said device for varying the ratio of said alarm threshold to said reference voltage simultaneously varies the ratio of said disturbance threshold to said reference voltage.