Communication system for inductive power transfer system

1. A communication method for an IPT system having a primary conductive path capable of being energized by an electric current, and one or more pick-ups adapted to receive electrical energy from the current in the primary path to supply a load, the method comprising the steps of:

transmitting an instruction over the primary path to a pick-up;

the pick-up acting on to the instruction by supplying power to the load to induce a predetermined variation in the current in the primary conductive path;

detecting, at a location remote from primary path, the variation in the current in the primary path and using the detected variation to determine a response from the pick-up to the instruction.

2. A communication method as claimed in claim 1 wherein the predetermined variation in the current comprises a predetermined series of changes in the current, the changes being capable of being decoded to represent binary digits.

3. A communication method as claimed in claim 2 wherein the predetermined variation is detected as a frequency component of the current and the changes comprise the presence or absence of the detected frequency component.

4. A communication method as claimed in claim 2 wherein the predetermined variation is detected as a frequency component of the current and the changes comprise changes in the frequency of the frequency component.

5. A communication method as claimed in claim 1 wherein the response indicates whether the pick-up is operative.

6. A communication method as claimed in claim 2 wherein the response is operative.

7. A communication method as claimed in claim 3 wherein the response indicates whether the pick-up is operative.

8. A communication method as claimed in claim 4 wherein the response indicates whether the pick-up is operative.

9. A communication method as claimed in claim 1 , wherein the response provides an indication of a parameter being measured by the pickup.

10. A communication method as claimed in claim 2 wherein the response provides an indication of a parameter being measured by the pickup.

11. A communication method as claimed in claim 3 wherein the response provides an indication of a parameter being measured by the pickup.

12. A communication method as claimed in claim 4 wherein the response provides an indication of a parameter being measured by the pickup.

13. A communication method as claimed in claim 9 wherein the parameter comprises temperature.

14. A communication method as claimed in claim 9 wherein the parameter comprises ambient light.

15. An IPT system pick-up including a control means for receiving an instruction transmitted over a primary conductive path of the IPT system and adapted to act on the instruction by supplying power to a load to cause a predetermined variation in the current on the primary conductive path such that the variation may be detected at a remote location on the primary conductive path to determine a response from the pick-up to the instruction.

16. Communication apparatus for an IPT system, the apparatus comprising:

a first communication means for communicable connection to the primary conductive path of an IPT system;

a second communication means provided on a pick-up of the IPT system, the second communication means being capable of receiving an instruction communicated by the first communication means, and control means provided on the pick-up, the control means being adapted to control the supply of power to a load dependent on the second communication means such that a predetermined variation in the current of the primary conductive path occurs which may be detected by the first communication means at a location remote from the pick-up and on the primary conductive path to determine a response to the instruction.

17. A communication method as claimed in claim 1 wherein said detecting is performed within a cabinet housing the power source used to energize the primary conductive path.