Tamper protection for an automatic remote meter reading unit
First Claim
1. A tamper protection arrangement comprising a resistance element (132), a resistance sensing circuit (101) for detecting changes in the value of the resistance element and providing an alarm signal in respect to the changes in the value of the resistance element characterized in thatthe resistance sensing circuit comprises a first transistor (109) connected directly to the resistance element and a second transistor also connected directly to the resistance element, the first transistor being turned on responsive to an increase in the value of the resistance element and the second transistor being turned on responsive to a decrease in the value of the resistance element.
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Accused Products
Abstract
In an automatic remote meter reading system, a tamper protection circuit (101) provides an alarm signal at a central station upon the disconnecting or tampering with a remote utility meter (100). Tamper protection is provided for the meter and for the transmission line carrying energy usage information to a transponder (500) such that any interruptions of the circuit path causes an alarm to be generated. The circuitry includes a remote resistance (132) associated with each meter to be protected. The value of the remote resistance is continually compared with a resistance (110) having a given value within the tamper protection circuit such that for any changes in the value of the remote resistance, an imbalance in the tamper circuit occurs and the alarm signal is generated.
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Citations
8 Claims
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1. A tamper protection arrangement comprising a resistance element (132), a resistance sensing circuit (101) for detecting changes in the value of the resistance element and providing an alarm signal in respect to the changes in the value of the resistance element characterized in that
the resistance sensing circuit comprises a first transistor (109) connected directly to the resistance element and a second transistor also connected directly to the resistance element, the first transistor being turned on responsive to an increase in the value of the resistance element and the second transistor being turned on responsive to a decrease in the value of the resistance element.
Specification