Power measurement in a two-wire load control device
A two-wire load control device may be configured to compute an accurate estimate of real-time power consumption by a load that is electrically connected to, and controlled by, the two-wire load control device. The load control device may be adapted to measure a voltage drop across the device during a first portion of a half-cycle of an AC waveform provided to the device. The device may be further configured to estimate a voltage drop across the load during the second portion of the half-cycle. The estimated voltage drop may be based on the measured voltage drop. The device may be further configured to measure a current supplied to the load during a second portion of the half-cycle. The device may be configured to estimate power consumed by the load based on the measured current and the estimated voltage drop.
1. A two-wire load control device comprising:
a communication circuit;
a controllably conductive device configured to be coupled in series electrical connection between an alternating current (AC) power source and a lighting load;
a control circuit configured to render the controllably conductive device non-conductive during a first portion of a half-cycle of an AC waveform generated by the AC power source and to render the controllably conductive device conductive during a second portion of the half-cycle of the AC waveform;
a signal generator that generates a voltage waveform that approximates a voltage across the lighting load during the second portion of the half-cycle; and
a current measuring circuit that measures a current supplied to the lighting load; and
wherein the control circuit is further configured to:
compute an estimated amount of power consumed by the lighting load based on the current supplied to the lighting load during the second portion of the half-cycle and the voltage waveform; and
communicate via the communication circuit the estimated amount of power consumed by the lighting load.
2. The two-wire load control device of claim 1 , wherein the signal generator generates the voltage waveform based on a voltage measured across the two-wire load control device during the first portion of the half-cycle.
3. The two-wire load control device of claim 1 , further comprising:
a voltage measuring circuit that measures a voltage across the two-wire load control device; and
wherein the signal generator generates the voltage waveform based on a voltage measured across the two-wire load control device by the voltage measuring circuit during the first portion of the half-cycle.
4. The two-wire load control device of claim 3 , wherein the voltage measuring circuit comprises a voltage divider.
5. The two-wire load control device of claim 1 , wherein the current measuring circuit comprises a micro-ohm resistor.
6. The two-wire load control device of claim 1 , wherein the control circuit is further configured to:
receive a request via the communication circuit; and
communicate via the communication circuit the estimated amount of power consumed by the lighting load in response to the request.
7. The two-wire load control device of claim 1 , wherein the control circuit is further configured to:
periodically communicate via the communication circuit an estimated amount of power consumed by the lighting load.
8. The two-wire load control device of claim 1 , further comprising:
a user interface having a display; and
wherein the control circuit is further configured to report the estimated amount of power consumed by the lighting load via the display.
9. The two-wire load control device of claim 1 , wherein the voltage waveform comprises one or more of a step-sine wave, a square wave, or a triangle wave.
10. The two-wire load control device of claim 1 , wherein the voltage waveform comprises a square wave having an amplitude that substantially matches an amplitude of a voltage across the two-wire load control device when the controllably conductive device is rendered between non-conductive and conductive states.
11. A two-wire load control device comprising:
a communication circuit;
a controllably conductive device configured to be coupled in series electrical connection between an alternating current (AC) power source and a lighting load; and
a control circuit configured to:
render the controllably conductive device non-conductive during a first portion of a half-cycle of an AC waveform generated by the AC power source and to render the controllably conductive device conductive during a second portion of the half-cycle of the AC waveform;
compute a voltage across the lighting load during the second portion of the half-cycle based on a voltage across the two-wire load control device during the first portion of the half-cycle;
measure a current supplied to the lighting load during the second portion of the half-cycle;
compute an estimated amount of power consumed by the lighting load based on the computed voltage and the measured current; and
communicate via the communication circuit the estimated amount of power consumed by the lighting load.
12. The two-wire load control device of claim 11 , wherein the control circuit is further configured to:
use a voltage measuring circuit to measure a voltage across the two-wire load control device during the first portion of the half-cycle; and
compute the voltage across the lighting load during the second portion of the half-cycle based on the measured voltage.
13. The two-wire load control device of claim 12 , wherein the voltage measuring circuit comprises a voltage divider.
14. The two-wire load control device of claim 11 , wherein the control circuit is further configured to:
use a current measuring circuit to measure the current supplied to the lighting load during the second portion of the half-cycle.
15. The two-wire load control device of claim 11 , wherein the control circuit is further configured to:
receive a request via the communication circuit; and
communicate via the communication circuit the estimated amount of power consumed by the lighting load in response to the request.
16. The two-wire load control device of claim 11 , further comprising:
a user interface having a display; and
wherein the control circuit is further configured to report the estimated amount of power consumed by the lighting load via the display.
17. A method performed by a control circuit of a two-wire load control device configured to control power delivered to a lighting load, the method comprising:
rendering a controllably conductive device non-conductive during a first portion of a half-cycle of an alternating current (AC) waveform generated by an AC power source;
rendering the controllably conductive device conductive during a second portion of the half-cycle of the AC waveform;
computing a voltage across the lighting load during the second portion of the half-cycle based on a voltage across the two-wire load control device during the first portion of the half-cycle;
measuring a current supplied to the lighting load during the second portion of the half-cycle;
computing an estimated amount of power consumed by the lighting load based on the computed voltage and the measured current; and
communicating via a communication circuit the estimated amount of power consumed by the lighting load.
18. The method of claim 17 , further comprising:
using a voltage measuring circuit to measure a voltage across the two-wire load control device during the first portion of the half-cycle; and
computing the voltage across the lighting load during the second portion of the half-cycle based on the measured voltage.
19. The method of claim 17 , further comprising:
receiving a request via the communication circuit; and
communicating via the communication circuit the estimated amount of power consumed by the lighting load in response to the request.
20. The method of claim 17 , further comprising:
reporting the estimated amount of power consumed by the lighting load via a display of the two-wire load control device.