Flame detectors

1. A flame detector comprising:

a UV sensor sensitive to solar UV radiation in the UV-C and UV-B wavebands;

a secondary sensor sensitive to non-UV NIR radiation at or near 700 nanometers; and

a controller operatively connected to the UV sensor and the secondary sensor to:

signal an alarm in response to receiving input from the UV sensor indicative of a strong UV source and input from the secondary sensor indicative of a weak non-UV radiation source; and

suppress an alarm in response to receiving a signal from the UV sensor indicative of a weak UV source and a signal from the secondary sensor indicative of a strong non-UV radiation source to distinguish between flames and solar UV including UV-B radiation.

2. The flame detector as recited in claim 1 , wherein the secondary sensor is a NIR sensor sensitive to NIR radiation, and wherein the controller is operatively connected to the NIR sensor to:

signal an alarm in response to receiving input from the UV sensor indicative of a strong UV source and input from the secondary sensor indicative of a weak NIR radiation source; and

suppress an alarm in response to receiving a signal from the UV sensor indicative of a weak UV source and a signal from the secondary sensor indicative of a strong NIR radiation source.

3. The flame detector as recited in claim 2 , further comprising a visible radiation sensor sensitive to visible radiation, wherein the visible radiation sensor is operatively connected to the controller for using the ratio of signals from the visible radiation sensor and the NIR sensor to reject false alarms due to sunlight exposure or affirm presence of flame.

4. The flame detector as recited in claim 3 , wherein the UV, visible, and NIR sensors are thin film sensors stacked on top of one another with the UV sensor on top.

5. The flame detector as recited in claim 1 , wherein the secondary sensor is a visible radiation sensor sensitive to visible radiation, and wherein the controller is configured to:

signal an alarm in response to receiving input from the UV sensor indicative of a strong UV source and input from the secondary sensor indicative of a weak visible radiation source; and

suppress an alarm in response to receiving a signal from the UV sensor indicative of a weak UV source and a signal from the secondary sensor indicative of a strong visible radiation source.

6. The flame detector as recited in claim 1 , wherein the UV sensor and the secondary sensor are thin film sensors stacked on top of one another with the UV sensor on top.

7. The flame detector as recited in claim 1 , further comprising a smoke sensor operatively connected to the controller to:

signal an alarm in response to receiving input from the UV sensor indicative of a strong UV source, input from the secondary sensor indicative of a strong non-UV radiation source, and input from the smoke sensor indicative of the presence of smoke; and

suppress an alarm in response to receiving input from the UV sensor indicative of a strong UV source, input from the secondary sensor indicative of a strong non-UV radiation source, and input from the smoke sensor indicative of lack of smoke.

8. The flame detector as recited in claim 1 , wherein the controller is configured to suppress an alarm in response to receiving a signal from the UV sensor indicative of a strong UV source, a signal from the secondary sensor indicative of a strong non-UV radiation source.

9. The flame detector as recited in claim 1 , wherein the controller is configured to signal an alarm in response to receiving a signal from the UV sensor indicative of a strong UV source, a signal from the secondary sensor indicative of a strong non-UV radiation source.

10. The flame detector recited in claim 1 , further comprising an input module operatively connected to the controller to accept user input indicative of whether or not an alarm should be signaled or suppressed in response to receiving a signal from the UV sensor indicative of a strong UV source, a signal from the secondary sensor indicative of a strong non-UV radiation source.

11. A method of flame detection comprising:

signaling an alarm in response to receiving input from a UV sensor indicative of a strong UV source and input from the secondary sensor indicative of a weak non-UV radiation source emitting non-UV NIR radiation at or near 700 nanometers, wherein the UV sensor is sensitive to solar UV radiation in the UV-C and the UV-B waveband; and

suppressing an alarm in response to receiving a signal from the UV sensor indicative of a weak UV source and a signal from the secondary sensor indicative of a strong non-UV radiation source, thereby distinguishing between flames and solar UV including UV-B radiation.

12. The method recited in claim 11 , further comprising:

signaling an alarm in response to receiving input from the UV sensor indicative of a strong UV source, input from the secondary sensor indicative of a strong non-UV radiation source, and input from a smoke sensor indicative of the presence of smoke; and

suppressing an alarm in response to receiving a signal from the UV sensor indicative of a strong UV source, a signal from the secondary sensor indicative of a strong non-UV radiation source, and input from the smoke sensor indicative of lack of smoke.

13. The method recited in claim 11 , further comprising:

complying with user input indicative of whether or not an alarm should be signaled or suppressed in response to receiving a signal from the UV sensor indicative of a strong UV source and a signal from the secondary sensor indicative of a strong non-UV radiation source.

14. The method recited claim 11 , wherein signaling and suppressing include receiving input from the UV sensor indicative of both a UV-C and UV-B radiation.