Closed Loop Daylight Harvesting Light Control System Having Auto-Calibration

• US 20060278808A1
• Filed: 05/05/2006
• Published: 12/14/2006
• Est. Priority Date: 05/05/2005
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company), Leviton Manufacturing Company Incorporated
• Original Assignee: Leviton Manufacturing Company Incorporated
• Inventors: Hick, Robert L., Leinen, Richard A.
• Granted Patent: US 7,608,807 B2
• Time in Patent Office: Days
• US Class Current: 250/205
• CPC Class Codes: G01J 1/18 using comparison with a reference electric value
• CPC Class Codes: G01J 1/4204 with determination of ambient light solar light G01J2001/4266
• CPC Class Codes: H05B 39/042 by measuring the incident light
• CPC Class Codes: H05B 39/081 by measuring the incident light H05B39/083 takes precedence
• CPC Class Codes: H05B 47/11 by determining the brightness or colour temperature of ambient light
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

An apparatus and method for enabling an automatic calibration sequence for a light control system having a daylight harvesting scheme is disclosed herein. An ambient light sensor connects to a detection circuit for detecting the amount of ambient light within a given zone. A microprocessor connects between the detection circuit and a dimming circuit for providing control to initiate dimming and to start the auto-calibration sequence. Responsive to the amount of ambient light detected, the dimming circuit controls the power supplied to a plurality of electrical loads. A storage unit connects to the microprocessor for storing minimum light levels assessed during the auto-calibration sequence wherein the ambient light levels are monitored for a predetermined amount of time to determine the lowest level of ambient light generated for the purpose of setting and storing a target voltage level associated with such.

Claims

1. A method of auto-calibration for setting the target voltage level of a light sensor included within a daylight harvesting controller, comprising the steps of:

a. forcing all attached electrical loads to full illumination for a defined period of time;

b. disabling all control device inputs to each electrical load during the defined time period;

c. monitoring the light sensor during the defined time period;

d. detecting the light level sensed by the light sensor;

e. comparing each detected light level with a previously stored light level;

f. determining which light level is the lowest light level;

g. generating a target voltage level based upon the lowest light level;

h. storing the lowest light level and the target voltage level; and

i. repeating steps c through h.

2. The method as recited in claim 1, wherein the defined period of time is 24 hours.

3. A light control system for controlling the brightness of a plurality of electrical loads, comprising:

an ambient light sensor that outputs a first signal in response to being exposed to radiation for sensing the ambient light level;

a detection circuit coupled to the light sensor to generate a second signal from the first signal;

a storage unit coupled to receive the second signal;

a microprocessor, having an auto-calibration subroutine, the microprocessor coupled to receive the second signal from the detection circuit to control the plurality of electrical loads; and

a dimming circuitry unit coupled between the microprocessor and the plurality of electrical loads for increasing and decreasing the illumination of the plurality of electrical loads;

wherein, during the activation of the auto-calibration subroutine for a predetermined period of time, the microprocessor generates a third signal and sends the third signal to the dimming circuitry to force the plurality of electrical loads to full illumination and disables control of the plurality of electrical loads, the microprocessor sets a target signal level equal to the second signal at the beginning of the predetermined period of time and stores the target signal level in the storage unit, the microprocessor monitors the second signal for the predetermined period of time and compares the second signal with the stored target signal level to determine which is a lower signal, the microprocessor sets the target signal level to equal the lower signal and stores the target signal level in the storage unit.

4. The light control system as recited in claim 3, wherein the dimming circuitry comprises:

a triode alternating current switch (triac); and

a zero crossing detector coupled to the triac to employ phase regulation.

5. The light control system as recited in claim 3, further comprising:

a dip switch coupled to the microprocessor to activate the auto-calibration subroutine.

7. The light control system as recited in claim 3, wherein the dimming circuitry is configured to provide an output in the range 0-10 V.

8. The light control system as recited in claim 3, wherein the electrical loads comprise a fluorescent light source.

9. The light control system as recited in claim 8, wherein the electrical loads further comprise a ballast.

10. The light control system as recited in claim 9, wherein the dimming circuitry is configured to provide an output in the range 0-10 V for controlling the ballast.

6. A method of auto calibration for a light control system, the method comprising the steps of:

using a new target level to control electrical loads of the light control system where said new target level is generated based on a lowest light level detected during continuous monitoring of light levels for a defined period of time.