A detector comprises a housing ( 1 ), a pyroelectric array sensor ( 2 ) mounted within the housing, a heater ( 4 ) associated with the pyroelectric array sensor, and control means ( 6 ) for varying the power supplied to the heater to control the temperature of the pyroelectric array sensor relative to the ambient temperature in order to minimise the rate of change of temperature of the pyroelectric array sensor and to keep a predetermined difference between the temperature of the pyroelectric array sensor and the ambient temperature.
1. A detector comprising:
a housing;
a flame detector sensor mounted within the housing and configured to detect an external flame;
a first temperature sensor configured to sense temperature of the flame detector sensor;
a second temperature senor configured to sense ambient temperature;
a heater positioned adjacent to the flame detector sensor; and
a controller in communication with the first temperature sensor and the second temperature sensor, and configured to vary power supplied to the heater;
wherein the controller is further configured to:
compare the ambient temperature as indicated by the second temperature sensor to the temperature of the flame detector sensor as indicated by the first temperature sensor, wherein the ambient temperature is varying;
in response to the comparison, determine an amount of power to the heater in order to control a rate of change of the temperature of the flame detector sensor to be within a predetermined limit;
control the power supplied to the heater at the determined amount of power to change the temperature of the flame detector sensor at the rate of change to a different temperature so that the different temperature of the flame detector sensor is within a predetermined temperature difference relative to the varying in the ambient temperature.
2. A detector as claimed in claimed 1 , wherein the predetermined temperature difference is dependent upon the largest temperature change that the detector has been designed to sustain in its intended operating environment.
3. A detector as claimed in claim 1 , wherein the controller is further configured to vary the predetermined temperature difference according to the ambient temperature.
4. A detector as claimed in claim 3 , wherein the controller is further configured to reduce the predetermined temperature difference to zero when the ambient temperature is sufficiently high so as to allow the flame detector sensor to operate with expected variations in the ambient temperature without power being supplied to the heater.
5. A detector as claimed in claim 1 , wherein the heater is fixed to one surface of the sensor.
6. A detector as claimed in claim 5 , wherein the heater is constituted by at least one thick film resistive element printed onto said surface of the flame detector sensor.
7. A detector as claimed in claim 1 , wherein the controller comprises a microcontroller which controls the supply of power to the heater via a heater drive circuit.
8. A detector as claimed in claim 7 , wherein the second temperature sensor is mounted in the housing remote from the heater.
9. A detector as claimed in claim 8 , wherein the first temperature sensing is integrated within the flame detector sensor.
10. A detector as claimed in claim 7 , wherein the microcontroller is programmed with software which permits the microcontroller to track the ambient temperature, to compare the ambient temperature with the temperature of the flame detector sensor, and to control the heater drive circuit to supply sufficient power to the heater to control the temperature of the flame detector sensor relative to the ambient temperature in order to minimize the rate of change of temperature of the flame detector sensor.
11. A detector as claimed in claim 7 , wherein the microcontroller is programmed so as to apply a nominal power level to the heater to maintain the temperature of the flame detector sensor at the predetermined temperature difference.
12. A detector as claimed in claim 7 , wherein the microcontroller is programmed so as to minimize the power required by the heater to maintain the temperature of the flame detector sensor at the predetermined temperature difference.
13. A detector as claimed in claim 5 , wherein said one surface of the flame detector sensor faces away from the window, the opposite surface of the flame detector sensor constituting means for sensing an external flame.
14. A detector as claimed in claim 1 , wherein the flame detector sensor comprises a sensor array.
15. A detector as claimed in claimed 1 , wherein the controller is configured to track the ambient temperature and to determine how the ambient temperature is changing.
16. A detector as claimed in claimed 1 , wherein the controller is configured to dynamically select the predetermined temperature difference.
17. A detector as claimed in claimed 16 , wherein the controller is configured to dynamically select the predetermined temperature difference based on the ambient temperature.
18. A detector as claimed in claimed 17 , wherein the controller is configured to reduce the predetermined temperature difference to zero when the ambient temperature is a predetermined temperature.
19. A detector as claimed in claimed 17 , wherein the predetermined temperature difference is a non-zero difference.
20. A detector as claimed in claimed 1 , wherein the controller is configured to determine the rate of change based on a sensitivity of the flame detector sensor.
21. A detector as claimed in claimed 1 , wherein the second temperature sensor is positioned within the housing.
22. A detector as claimed in claimed 1 , wherein the housing comprises a window; and
wherein the flame detector sensor is mounted within the housing relative to the window through which the flame detector sensor is configured to detect an external event.
23. A detector as claimed in claim 22 , wherein the external event comprises an external flame.