Method and apparatus for detecting a hazard detector signal in the presence of interference

1. An apparatus for detecting when a hazardous condition is present inside a structure, comprising:

a transducer for converting a first pattern warning signal received from a first hazard detector and a second pattern warning signal received from a second hazard detector into a composite electronic signal;

an analog-to-digital converter for converting the composite electronic signal into a digital signal;

a memory for storing processor-executable instructions and one or more thresholds;

a transmitter for transmitting an alarm signal; and

a processor coupled to the analog-to-digital converter, the memory and the transmitter for executing the processor-executable instructions that causes the apparatus to:

determine, by the processor, that the hazardous condition is present based on the digital signal; and

transmit, by the processor via the transmitter, the alarm signal to a receiver when the hazardous condition has been determined to be present.

2. The apparatus of claim 1 , wherein the processor-executable instructions that cause the apparatus to determine that the hazardous condition is present comprise instructions that causes the apparatus to:

determine an on-time duration of the digital signal as a time that the digital signal exceeded a first voltage threshold stored in the memory; and

determine that the hazardous condition is present when the on-time duration is great than a minimum duration threshold stored in the memory, and less than a maximum duration threshold stored in the memory.

3. The apparatus of claim 2 , wherein the maximum duration threshold comprises a time that is twice the on-time of a temporal-3 signal, less a gap time.

4. The apparatus of claim 3 , wherein the gap time comprises a time period less than 10 percent of on on-time of the temporal-3 signal.

5. The apparatus of claim 2 , wherein the maximum duration threshold comprises a time that is twice the on-time of a temporal-4 signal, less a gap time.

6. The apparatus of claim 5 , wherein the gap time comprises a time period less than 10 percent of the on-time of the temporal-4 signal.

7. The apparatus of claim 2 , wherein the processor-executable instructions comprise further instructions that cause the apparatus to:

after determining the on-time of the digital signal, determine an off-time duration of the digital signal; and

determine that the hazardous condition is present when the on-time duration of the digital signal is greater than the minimum duration threshold and less than the maximum duration threshold, and the off-time duration of the digital signal is less than or equal to a maximum off-time duration threshold stored in the memory.

8. The apparatus of claim 7 , wherein the processor-executable instructions that cause the apparatus to determine the off-time duration of the digital signal comprise instructions that cause the apparatus to:

determine an off-time duration that the digital signal remains below the first voltage threshold;

compare the off-time duration with a maximum off-time duration stored in the memory; and

determine that the hazardous condition is present when the processor determines that the off-time duration of the digital signal is less than or equal to the maximum off-time duration.

9. The apparatus of claim 7 , wherein the processor-executable instructions that cause the apparatus to determine the off-time duration of the digital signal comprise instructions that cause the apparatus to:

determine an off-time duration that the digital signal remains below the first voltage threshold;

compare the off-time duration with a maximum off-time duration stored in the memory and a gap time; and

determine that the hazardous condition is present when the processor determines that the off-time duration of the digital signal is less than or equal to the maximum off-time duration, and greater than or equal to the gap time.

10. The apparatus of claim 9 , wherein the gap time is less than 10 percent of the minimum duration threshold.

11. A method performed by a hazard detector monitor for detecting when a hazardous condition is present inside a structure, comprising:

converting, by a transducer, a first pattern warning signal received from a first hazard detector and a second pattern warning signal received from a second hazard detector into a composite electronic signal;

converting, by an analog-to-digital converter, the composite electronic signal into a digital signal;

determining, by a processor, that the hazardous condition is present based on the digital signal; and

transmitting, by the processor via a transmitter coupled to the processor, an alarm signal indicative of the hazardous condition to a receiver when the hazardous condition has been determined to be present.

12. The method of claim 11 , wherein determining that the hazardous condition is present comprises:

determining, by the processor, an on-time duration of the digital signal as a time that the digital signal exceeded a first voltage threshold stored in the memory; and

determining, by the processor, that the hazardous condition is present when the on-time duration is great than a minimum duration threshold stored in the memory, and less than a maximum duration threshold stored in the memory.

13. The method of claim 12 , wherein the maximum duration threshold comprises a time that is twice the on-time of a temporal-3 signal, less a gap time.

14. The method of claim 13 , wherein the gap time comprises a time period less than 10 percent of on on-time of the temporal-3 signal.

15. The method of claim 12 , wherein the maximum duration threshold comprises a time that is twice the on-time of a temporal-4 signal, less a gap time.

16. The method of claim 15 , wherein the gap time comprises a time period less than 10 percent of the on-time of the temporal-4 signal.

17. The method of claim 12 , further comprising:

after determining the on-time of the digital signal, determining, by the processor, an off-time duration of the digital signal; and

determining, by the processor, that the hazardous condition is present when the on-time duration of the digital signal is greater than the minimum duration threshold and less than the maximum duration threshold, and the off-time duration of the digital signal is less than or equal to a maximum off-time duration threshold stored in the memory.

18. The method of claim 17 , wherein determining the off-time duration of the digital signal comprises:

determining, by the processor, an off-time duration that the digital signal remains below the first voltage threshold;

comparing, by the processor, the off-time duration with a maximum off-time duration stored in the memory; and

determining, by the processor, that the hazardous condition is present when the processor determines that the off-time duration of the digital signal is less than or equal to the maximum off-time duration.

19. The method of claim 17 , wherein determining the off-time duration of the digital signal comprises:

determining, by the processor an off-time duration that the digital signal remains below the first voltage threshold;

comparing, by the processor, the off-time duration with a maximum off-time duration stored in the memory and a gap time; and

determining, by the processor, that the hazardous condition is present when the processor determines that the off-time duration of the digital signal is less than or equal to the maximum off-time duration, and greater than or equal to the gap time.

20. The method of claim 19 , wherein the gap time is less than 10 percent of the minimum duration threshold.