Method and apparatus for power management of asset tracking system
A technique for controlling the state of a power supply in a mobile asset such as a cargo trailer. The technique detects motion status such as may be provided by a vibration sensor. The motion status signal is filtered by other signals, such as with inputs from a global positioning system sensor, and is then further used to select a power consumption mode. The power consumption mode may be further controlled based on configuration information that may indicate that a vibration source such as a refrigeration unit is present on the trailer.
1. An apparatus for use in controlling the state of a power supply in a mobile asset comprising:
a motion sensor for sensing vibration or motion, the motion sensor outputting one or more in-motion signals;
a memory for storing a last known stationary location of the asset;
a location device for identifying a current location of the asset; and
a power controller for:
determining whether said asset is in an In_Motion state based on said in-motion signals, causing said location device to identify a current location of the asset if it is determined that said asset is in an In_Motion state; and
determining, if it is determined that said asset is in an In_Motion state, whether the asset is in an In_Transit state by comparing the current location of the asset and the last known stationary location, and selecting a power consumption mode for the power supply based on the determination.
2. An apparatus as claimed in claim 1 , further comprising:
a filtering module for filtering the motion sensor in-motion signals,
wherein determining whether the asset is in an In_Motion state comprises determining that a predetermined number of filtered in-motion signals are detected in a predetermined period of time.
3. An apparatus as claimed in claim 2 , wherein said filtering module:
receives the motion sensor output as an interrupt signal; and
applies blanking intervals to the interrupt signal, thereby creating a filtered motion sensor output.
4. An apparatus as claimed in claim 1 , wherein the power controller determines the asset is in transit if the difference between the current location and the last known stationary location exceeds a predetermined threshold.
5. An apparatus as claimed in claim 1 , further comprising, if the controller determines that said asset is in an In_Motion state and determines that said asset is not in an In_Transit state:
said power controller determines whether a refrigeration unit is operating or present; and
said power controller disables the motion sensor if the power controller determines that a refrigeration unit is operating or present.
6. An apparatus as claimed in claim 4 , wherein the power controller determines whether a refrigeration unit is operating by checking a refrigerator unit status output signal or determines whether a refrigerator is present by checking a configuration data bit that indicates whether a refrigerator unit is present on the asset.
7. An apparatus as claimed in claim 1 , wherein the power controller re-enables the motion sensor after a predetermined period of time or if a tractor is connected to said asset.
8. An apparatus as claimed in claim 1 , further comprising, if said power controller determines that a refrigeration unit is not operating or not present, said power controller disabling the motion sensor after a predetermined number of determinations have been made that the asset is in an In_Motion state but not in an In_Transit state.
9. An apparatus as claimed in claim 6 , wherein said power controller selects a predetermined power consumption mode if a tractor is connected to the asset, regardless of the determinations of whether the asset is in an In_Motion state or in an In_Transit state.
10. A method for use in controlling the state of a power supply in a mobile asset comprising:
storing a last known stationary location of the asset;
enabling a motion sensor on the asset;
monitoring the motion sensor output;
determining whether the asset is in an In_Motion state based on the motion sensor output;
if it is determined that said asset is in an In_Motion state,
identifying a current location of the asset using a location device, and
determining whether the asset is in an In_Transit state by comparing the current location of the asset with the last known stationary location; and
selecting a power consumption power consumption mode for the power supply based on the in-transit determination.
11. The method as claimed in claim 10 ,
further comprising filtering the motion sensor output;
wherein determining if the asset is in an In_Motion state is based on the filtered motions sensor output.
12. The method as claimed in claim 11 , wherein determining whether the asset is in an In_Motion state based on the filtered motion sensor output comprises:
determining if a predetermined number of filtered in-motion signals are detected in the filtered motion sensor output in a predetermined period of time.
13. The method as claimed in claim 11 , wherein filtering the motion sensor output comprises:
receiving the motion sensor output as an interrupt signal; and
applying blanking intervals to the interrupt signal, thereby creating a filtered motion sensor output.
14. The method as claimed in claim 10 , wherein determining whether the asset is in an In_Transit state by comparing the current location of the asset with the last known stationary location comprises determining if the difference between the current location and the last known stationary location exceeds a predetermined threshold.
15. The method as claimed in claim 10 , further comprising, if it is determined that said asset is in an In_Motion state and determined that said asset is not in an In_Transit state:
determining whether a refrigeration unit is in operation or present on the asset; and
disabling the motion sensor if it is determined that a refrigeration unit is in operation or present.
16. The method as claimed in claim 15 , wherein determining whether a refrigeration unit is operating comprises checking a refrigerator unit status output signal and wherein determining whether a refrigerator is present comprises checking a configuration data bit that indicates whether a refrigerator unit is present on the asset.
17. The method as claimed in claim 15 , further comprising:
re-enabling the motion sensor after a predetermined period of time or upon the occurrence of an external trigger event.
18. The method as claimed in claim 17 , wherein said external trigger event is the connection of a tractor to the asset.
19. The method as claimed in claim 15 , further comprising, if it is determined that a refrigeration unit is not operating or not present, disabling the motion sensor after a predetermined number of determinations have been made that the asset is in an In_Motion state but not in an In_Transit state.
20. The method as claimed in claim 10 , further comprising:
determining whether a tractor is connected to the asset;
selecting a predetermined power consumption mode if a tractor is connected to the asset, regardless of the determinations of whether the asset is in an In_Motion state or in an In_Transit state.