HVAC synchronization

• US 20080065926A1
• Filed: 10/31/2007
• Published: 03/13/2008
• Est. Priority Date: 08/22/2001
• Status: Active Grant

• Current Assignee: MMI Controls Ltd.
• Original Assignee: MMI Controls Ltd.
• Inventors: McDowell, Johnnie, Poth, Robert
• Granted Patent: US 7,945,799 B2
• Time in Patent Office: Days
• US Class Current: 713/500
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 11/46 Improving electric energy efficiency or saving
• CPC Class Codes: F24F 11/47 Responding to energy costs
• CPC Class Codes: F24F 11/52 Indication arrangements, e.g. displays
• CPC Class Codes: F24F 11/64 using pre-stored data
• CPC Class Codes: F24F 11/88 Electrical aspects, e.g. circuits
• CPC Class Codes: F24F 2110/10 Temperature
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G05B 19/0428 Safety, monitoring G05B19/0423 takes precedence
• CPC Class Codes: G05B 2219/24168 Identify connected programmer to allow control, program entry
• CPC Class Codes: G05B 2219/2614 HVAC, heating, ventillation, climate control
• CPC Class Codes: G05B 2219/2642 Domotique, domestic, home control, automation, smart house
• CPC Class Codes: G06F 21/31 User authentication
• CPC Class Codes: G06F 2221/2107 File encryption
• CPC Class Codes: G06F 2221/2131 Lost password, e.g. recovery of lost or forgotten passwords

Abstract

Systems and methods are described for synchronizing an HVAC control system. A method, includes: a synchronization sequence including: reading a base time from an internal clock at a first time and saving the base time; measuring an elapsed time interval, from the first time to a second time, by counting an external clock using a frequency counter; and then resetting the internal clock to the base time plus the elapsed time.

Claims

1. A method, comprising a synchronization sequence including:

reading a base time from an internal clock at a first time and saving the base time;

measuring an elapsed time interval, from the first time to a second time, by counting an external clock using a frequency counter; and

then

resetting the internal clock to the base time plus the elapsed time.

2. The method of claim 1, further comprising, before measuring the elapsed time interval, clearing the frequency counter.

3. The method of claim 1, further comprising, before measuring the elapsed time interval, setting a flag to enable commencement of the synchronization sequence.

4. The method of claim 3, wherein the flag is set to enable commencement of the synchronization sequence when the external clock transitions from an unavailable state to an available state.

5. The method of claim 3, wherein the flag is set to enable commencement of the synchronization sequence when a user exits a clock menu.

6. The method of claim 1, wherein measuring the elapsed time interval includes setting a flag to indicate that the synchronization sequence has commenced.

7. The method of claim 6, wherein resetting occurs when the flag indicates that the synchronization sequence has commenced and the frequency counter indicates that the elapsed time interval has passed.

8. The method of claim 1, wherein measuring the elapsed time interval commences at a predetermined time increment.

9. The method of claim 1, further comprising, after resetting the internal clock, repeating the synchronization sequence.

10. The method of claim 1, wherein the internal clock is derived from a direct current powered oscillator located in an integrated-circuit real-time clock.

11. The method of claim 1, wherein the external clock is derived from an alternating current power source.

12. The method of claim 11, wherein counting includes counting zero-voltage transitions of an alternating power line waveform.

13. An apparatus, comprising:

an internal clock;

an external clock; and

a microcontroller coupled to the internal clock and the external clock, the microcontroller including a frequency counter,

wherein the microcontroller reads a base time from the internal clock at a first time and saves the base time,

wherein the microcontroller measures an elapsed time interval, from the first time to a second time, using the frequency counter, and

wherein the microcontroller resets the internal clock to the base time plus the elapsed time.

14. The apparatus of claim 13, wherein the microcontroller clears the frequency counter before measuring the elapsed time interval.

15. The apparatus of claim 13, wherein the microcontroller sets a flag to enable commencement of the synchronization sequence.

16. The apparatus of claim 15, wherein the microcontroller sets the flag to enable commencement of the synchronization sequence when the external clock transitions from an unavailable state to an available state.

17. The apparatus of claim 15, wherein the microcontroller sets the flag to enable commencement of the synchronization sequence when a user exits a clock menu.

18. The apparatus of claim 13, wherein the microcontroller sets a flag to indicate that the synchronization sequence has commenced at the beginning of measuring the elapsed time interval.

19. The apparatus of claim 18, wherein the microcontroller resets the internal clock when the flag indicates that the synchronization sequence has commenced and the frequency counter indicates that the elapsed time interval has passed.

20. The apparatus of claim 13, wherein the microcontroller commences measuring the elapsed time interval at a predetermined time increment.

21. The apparatus of claim 13, wherein the microcontroller repeating a synchronization sequence after resetting the internal clock.

22. The apparatus of claim 13, wherein the internal clock includes an integrated-circuit real-time clock having a direct current powered oscillator.

23. The apparatus of claim 13, wherein the external clock includes an alternating current power line.

24. The apparatus of claim 13, wherein the frequency counter includes a zero-voltage transition counter.

25. A programmable thermostat comprising the apparatus of claim 13.