Tamper detection methods and apparatus for load management terminals
First Claim
1. Apparatus for detecting tampering with a load management terminal, said terminal being connected to a power line and to a load, said terminal having a load control relay coupled in series to the power line wherein the load is selectably decoupled from the power line by opening the load control relay, said apparatus comprising:
- a voltage sensor coupled to the load control relay for sensing whether voltage is present across said load control relay when said load control relay is open;
a timer for measuring elapsed time during which no voltage is sensed across said load control relay when said load control relay is open; and
an indicator for indicating tampering when the elapsed time measured by said timer exceeds a pre-determined time limit.
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Accused Products
Abstract
Apparatus and methods are claimed for detecting tampering with a load management terminal, wherein the terminal has a load control relay coupled to a power line for selectably decoupling the load from the power line. One embodiment of the claimed apparatus for detecting tampering comprises a current sensor coupled to the load control relay for sensing whether load current is flowing through the load control relay contacts when the contacts are closed. A timer is provided for measuring elapsed time during which no current is sensed flowing through the closed contacts. An indicator provides an indication of tampering when the elapsed time measured by the timer exceeds a pre-determined time limit. Preferably, in this embodiment, the current sensor comprises a voltage detector coupled to the control coil of the relay for detecting whether an AC voltage has been induced in the control coil by the load current. In another embodiment, a voltage sensor is provided for sensing whether voltage is present across the contacts of the relay when the contacts are open. In yet another embodiment, a suitable resistance is connected to the power line in parallel with the load thermostat to ensure at least a nominal current flow through the load control relay at all times. Tampering is indicated when an interruption in the continuous current flow is detected.
94 Citations
14 Claims
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1. Apparatus for detecting tampering with a load management terminal, said terminal being connected to a power line and to a load, said terminal having a load control relay coupled in series to the power line wherein the load is selectably decoupled from the power line by opening the load control relay, said apparatus comprising:
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a voltage sensor coupled to the load control relay for sensing whether voltage is present across said load control relay when said load control relay is open; a timer for measuring elapsed time during which no voltage is sensed across said load control relay when said load control relay is open; and an indicator for indicating tampering when the elapsed time measured by said timer exceeds a pre-determined time limit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. In a load management terminal having a load control relay coupled to a power line and to a load wherein the load is selectably decoupled from the power line by opening the load control relay, a method of detecting tampering with said terminal comprising the steps of:
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opening said load control relay; sensing whether voltage is present across said load control relay when said load control relay is open; maintaining a measure of elapsed time during which no voltage is sensed across said load control relay when said load control relay is open; and generating a tamper indication when the measure of elapsed time exceeds a pre-determined time limit. - View Dependent Claims (11, 12, 13, 14)
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Specification