Wireless battery-powered daylight sensor

• US 8,723,447 B2
• Filed: 05/02/2013
• Issued: 05/13/2014
• Est. Priority Date: 03/27/2009
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Steiner, James P.
• Primary Examiner(s): PHILOGENE, HAISSA
• Application Number:
  US13/875,434
• Publication Number:
  US 20130234008A1
• Time in Patent Office: 376 Days
• Field of Search: 315294-297, 315/307, 315/312, 315/316, 315/308, 340/538.15, 340/539.1, 340/545.3, 340/540, 340/552, 340/555, 340/567, 340/600, 250/205
• US Class Current: 315/307
• CPC Class Codes: G01J 1/02 Details
• CPC Class Codes: G01J 1/0219 Electrical interface; User interface
• CPC Class Codes: G01J 1/0228 Control of working procedures; Failure detection; Spectral bandwidth calculation
• CPC Class Codes: G01J 1/0247 using a charging unit
• CPC Class Codes: G01J 1/16 using electric radiation detectors G01J1/20 takes precedence
• CPC Class Codes: G01J 1/32 adapted for automatic variation of the measured or reference value regulation of light intensity G05D25/00
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: H05B 47/10 Controlling the light source
• CPC Class Codes: H05B 47/11 by determining the brightness or colour temperature of ambient light
• CPC Class Codes: H05B 47/19 via wireless transmission
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

A wireless battery-powered daylight sensor for measuring a total light intensity in a space is operable to transmit wireless signals using a variable transmission rate that is dependent upon the total light intensity in the space. The sensor comprises a photosensitive circuit, a wireless transmitter for transmitting the wireless signals, a controller coupled to the photosensitive circuit and the wireless transmitter, and a battery for powering the photosensitive circuit, the wireless transmitter, and the controller. The photosensitive circuit is operable to generate a light intensity control signal in response to the total light intensity in the space. The controller transmits the wireless signals in response to the light intensity control signal using the variable transmission rate that is dependent upon the total light intensity in the space. The variable transmission rate may be dependent upon an amount of change of the total light intensity in the space. In addition, the variable transmission rate may be further dependent upon a rate of change of the total light intensity in the space.

Claims

1. A wireless battery-powered daylight sensor for measuring a total light intensity, the sensor comprising:

a photosensitive circuit operable to generate a light intensity control signal in response to the total light intensity;

a wireless transmitter for transmitting wireless signals;

a controller coupled to the photosensitive circuit and the wireless transmitter, the controller operable to transmit wireless signals in response to the light intensity control signal; and

a battery for powering the photosensitive circuit, the wireless transmitter, and the controller;

wherein the controller is operable to transmit wireless signals using a variable transmission rate that is dependent upon an amount of change of the total light intensity and dependent upon a rate of change of the total light intensity, such that the controller does not transmit a digital message if the rate of change of the total light intensity is outside of predetermined limits.

2. The daylight sensor of claim 1, wherein the controller is operable to enable the photosensitive circuit and subsequently sample the light intensity control signal at a sampling period, the controller further operable to disable the photosensitive circuit after the light intensity control signal has been sampled, such that the photosensitive circuit only draws current from the battery for a small time period during each sampling period.

3. The daylight sensor of claim 2, wherein the controller is operable determine a new light intensity for the lighting load in response to the light intensity control signal, the controller operable to transmit a digital signal if the new light intensity differs from a present light intensity of the lighting load by a predetermined increment.

4. The daylight sensor of claim 1, wherein the controller is operable to disable the photosensitive circuit, such that the photosensitive circuit does not draw current from the battery when the wireless transmitter is not transmitting a wireless signal.

5. The daylight sensor of claim 1, wherein the controller periodically samples the light intensity control signal, the daylight sensor further comprising a memory coupled to the controller for storing sampled light intensity values, the controller operable to analyze the samples stored in the memory to determine the rate of change of the total light intensity.

6. The daylight sensor of claim 1, wherein the wireless signals comprise digital messages, each digital message including a value representative of the total light intensity.

7. A wireless battery-powered daylight sensor for measuring a total light intensity, the sensor comprising:

a photosensitive circuit operable to generate a light intensity control signal in response to the total light intensity;

a wireless transmitter for transmitting wireless signals;

a controller coupled to the photosensitive circuit and the wireless transmitter, the controller operable to periodically sample the light intensity control signal and transmit wireless signals in response to the light intensity control signal, the controller operable to store sampled light intensity values in a memory and to analyze the sampled light intensity values to determine an amount of change of the total light intensity; and

a battery for powering the photosensitive circuit, the wireless transmitter, and the controller;

wherein the controller is operable to transmit the wireless signals using a variable transmission rate that is dependent upon the amount of change of the total light intensity, the controller operable to determine at least one predicted light intensity value, calculate an error between the total light intensity and the at least one predicted light intensity value, and transmit a digital message if the error is too great.

8. The daylight sensor of claim 7, wherein the controller collects a predetermined number of sampled light intensity values during consecutive non-overlapping time intervals, the controller operable to analyze the sampled light intensity values of each time interval to determine the amount of change of the total light intensity.

9. The daylight sensor of claim 8, wherein the controller determines at least one estimator during a previous time interval, and uses the at least one estimator to determine the at least one predicted light intensity value during a present time interval.

10. The daylight sensor of claim 9, wherein the controller calculates multiple predicted light intensity values during the present time interval.

11. The daylight sensor of claim 10, wherein the controller uses a linear prediction model to calculate the multiple predicted light intensity values, the estimators comprising a slope and an offset of a line that best represents the change of the total light intensity.

12. The daylight sensor of claim 11, wherein the controller transmits the slope and the offset of the line that best represents the change of the total light intensity when the error between the sampled light intensity values and the predicted light intensity values is too great.

13. The daylight sensor of claim 11, wherein the controller performs a linear least-squares fit to determine the slope and the offset of the line that best represents the change of the total light intensity.

14. The daylight sensor of claim 10, wherein the controller uses a parabolic prediction model to calculate the multiple predicted light intensity values, the estimators comprising coefficients of a parabola that best represents the change of the total light intensity.

15. The daylight sensor of claim 10, wherein the controller calculates a mean-square error between the predicted light intensity values and the sampled light intensity values, the controller operable to transmit a digital message if the mean-square error exceeds a maximum error.

16. The daylight sensor of claim 9, wherein the estimator comprises a minimum sampled light intensity value from the previous time interval, the controller operable to transmit a digital message if the difference between the estimator and a minimum sampled light intensity value from the present time interval exceeds a maximum error.

17. The daylight sensor of claim 16, wherein the controller transmits the minimum sampled light intensity value from the present time interval when the difference between the estimator and a minimum sampled light intensity value from the present time interval exceeds the maximum error.

18. The daylight sensor of claim 9, wherein the estimator comprises an average value of the sampled light intensity values from the previous time interval, the controller operable to transmit a digital message if the difference between the estimator and an average value of the sampled light intensity values from the present time interval exceeds a maximum error.

19. The daylight sensor of claim 9, wherein the estimator comprises a median value of the sampled light intensity values from the previous time interval, the controller operable to transmit a digital message if the difference between the estimator and a median value of the sampled light intensity values from the present time interval exceeds a maximum error.

20. The daylight sensor of claim 8, wherein the controller is operable to analyze the samples stored in the memory to determine if the data is misbehaving.

21. The daylight sensor of claim 20, wherein the controller calculates a behavior metric and determines if the data behavior metric is outside of one or more data behavior metric limits.

22. The daylight sensor of claim 21, wherein the data behavior metric comprises a rate of change of the total light intensity.

23. The daylight sensor of claim 22, wherein the controller is operable to transmit a digital message if the rate of change of the total light intensity is within the one or more data behavior metric limits.

24. The daylight sensor of claim 23, wherein the controller uses a maximum sampled light intensity value and a minimum sampled light intensity value from the present time interval to determine if the rate of change of the total light intensity is within the one or more data behavior metric limits.

25. The daylight sensor of claim 7, wherein the controller periodically samples the light intensity control signal and stores the samples in memory, the controller operable to analyze the samples stored in memory using a sliding window time interval to determine the amount of change of the total light intensity.

26. A method of transmitting a digital message in response to a total light intensity, the method comprising:

generating a light intensity control signal in response to the total light intensity;

periodically sampling the light intensity control signal;

storing sampled light intensity values in memory;

analyzing the sampled light intensity values stored in the memory to determine an amount of change of the total light intensity;

transmitting wireless signals by a controller using a variable transmission rate wherein the variable transmission rate is dependent upon the amount of change of the total light intensity, the wireless signals comprising digital messages, each digital message including a value representative of the total light intensity;

determining at least one predicted light intensity value; and

calculating an error between the sampled light intensity values and the at least one predicted light intensity value;

wherein the controller is operable to transmit a digital message if the error is too great.

27. The method of claim 26, further comprising:

collecting a predetermined number of sampled light intensity values during consecutive non-overlapping time intervals;

wherein the step of analyzing further comprises analyzing the sampled light intensity values of each time interval to determine the amount of change of the total light intensity.

28. The method of claim 27, further comprising:

determining at least one estimator during a previous time interval;

wherein the step of determining at least one predicted light intensity value comprises using the at least one estimator to determine the at least one predicted light intensity value during a present time interval.

29. The method of claim 28, wherein the step of determining at least one predicted light intensity value comprises calculating multiple predicted light intensity values during the present time interval.

30. The method of claim 29, wherein the step of calculating multiple predicted light intensity values comprises using a linear least-squares prediction model, the estimators comprising a slope and an offset of a line that best represents the change of the total light intensity.

31. The method of claim 30, wherein the step of transmitting wireless signals comprises transmitting the slope and the offset of the line that best represents the change of the total light intensity when the error between the sampled light intensity values and the predicted light intensity values is too great.

32. The method of claim 30, wherein the step of determining at least one estimator during a previous time interval comprises performing a linear least-squares fit to determine the slope and the offset of the line that best represents the change of the total light intensity.

33. The method of claim 29, wherein the step of calculating multiple predicted light intensity values comprises using a parabolic prediction model, the estimators comprising coefficients of a parabola that best represents the change of the total light intensity.

34. The method of claim 29, wherein the step of calculating multiple predicted light intensity values comprises using a linear predictor to calculate the predicted light intensity values.

35. The method of claim 29, further comprising:

calculating a mean-square error between the predicted light intensity values and the sampled light intensity values;

wherein the step of transmitting wireless signals comprises transmitting a digital message if the mean-square error exceeds a maximum error.

36. The method of claim 28, wherein the estimator comprises a minimum sampled light intensity value from the previous time interval, and the step of transmitting wireless signals further comprises transmitting a digital message if the difference between the estimator and a minimum sampled light intensity value from the present time interval exceeds a maximum error.

37. The method of claim 36, wherein the step of transmitting wireless signals further comprises transmitting the minimum sampled light intensity value from the present time interval when the difference between the estimator and a minimum sampled light intensity value from the present time interval exceeds the maximum error.

38. The method of claim 28, wherein the estimator comprises an average value of the sampled light intensity values from the previous time interval, and the step of transmitting wireless signals further comprises transmitting a digital message if the difference between the estimator and an average value of the sampled light intensity values from the present time interval exceeds a maximum error.

39. The method of claim 28, wherein the estimator comprises a median value of the sampled light intensity values from the previous time interval, the step of transmitting wireless signals further comprises transmitting a digital message if the difference between the estimator and a median value of the sampled light intensity values from the present time interval exceeds a maximum error.

40. The method of claim 27, further comprising:

analyzing the samples stored in the memory to determine is the data is misbehaving.

41. The method of claim 40, wherein the step of analyzing the samples stored in the memory to determine if the data is misbehaving further comprises calculating a behavior metric, and determining if the data behavior metric is outside of one or more data behavior metric limits.

42. The method of claim 41, wherein the data behavior metric comprises a rate of change of the total light intensity.

43. The method of claim 42, wherein the step of transmitting wireless signals comprises transmitting a digital message if the rate of change of the total light intensity is within the one or more data behavior metric limits.

44. The method of claim 43, wherein the step of analyzing the samples stored in the memory to determine is the data is misbehaving further comprises using a maximum sampled light intensity value and a minimum sampled light intensity value from the present time interval to determine if the rate of change of the total light intensity is within the one or more data behavior metric limits.

45. The method of claim 26, further comprising:

periodically sampling the light intensity control signal;

storing the samples in memory; and

analyzing the samples stored in memory using a sliding window time interval to determine the amount of change of the total light intensity.

46. A method of transmitting a digital message in response to a total light intensity, the method comprising:

measuring the total light intensity;

storing sampled light intensity values in response to the step of measuring;

analyzing the sampled light intensity values to determine an amount of change of the total lighting intensity and a rate of change of the total light intensity;

determining if the rate of change of the total light intensity is within predetermined limits; and

transmitting wireless signals using a variable transmission rate that is dependent upon the amount of change of the total light intensity and the rate of change of the total light intensity, the wireless signals comprising digital messages including a value representative of the total light intensity;

wherein the step of transmitting wireless signals further comprises transmitting a digital message if the amount of change of the total light intensity exceeds a predetermined amount and the rate of change of the total light intensity is within predetermined limits.

47. The method of claim 46, wherein the wireless signals comprise digital messages, each digital message including a command to control a lighting load in response to the total light intensity.

48. The method of claim 47, further comprising:

determining a new light intensity for the lighting load in response to the light intensity control signal;

wherein the step of transmitting wireless signals further comprises transmitting a digital signal if the new light intensity differs from a present light intensity of the lighting load by a predetermined increment.