Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
1998-12-01
2001-07-03
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C307S112000, C307S131000, C340S644000, C377S021000
Reexamination Certificate
active
06255748
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a switch status sensor and more particularly, but not exclusively, to a switch status sensor for use in a water meter to reliably measure the consumption of water, or in any other type of meter which is responsive to the status changes of a switch.
BACKGROUND OF THE INVENTION
When a switch changes its state the voltages and currents in connections made to the switch are changed and the changes can be sensed by suitable apparatus to determine the status of the switch. Errors can occur in areas of high electromagnetic noise when current or voltage changes may be induced in the connections which are sensed by the apparatus and give a false indication of the status of the switch. Such errors are particularly undesirable in water meters, as they would result in a consumer being over or undercharged.
Conventionally, because switch status sensors which count the number of pulses received from a switch-type water meter are subject to electromagnetic radiation, which can cause miscounting of switching events, the signals received from the switch are heavily filtered. However, this has the negative effect of slowing down the responsiveness, with the ultimate effect of missing real switch closures. The requirements for achieving fast response and electromagnetic noise immunity are irreconcilable using filtering alone.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention aims to provide a sensor which can discriminate between signals received following a change of status of a switch and noise signals and/or which has a fast response time.
According to a first aspect of the present invention there is provided a switch status sensor for connection to a switch, the switch status sensor comprising current responsive means responsive to a current which apparently indicates a given switch status, means for applying a signal distinguishable from electromagnetic noise to said switch, and means for detecting the passage of said signal through said switch to determine the status of said switch, and wherein the means for applying said signal applies said signal to said switch in response to an indication from said current responsive means.
According to a second aspect of the invention there is provided a switch status sensor circuit adapted for connection to an electrical switch, means responsive to an electrical current flowing through said connection from the switch to determine changes in the status of the switch and means responsive to a current which apparently indicates a given switch status for supplying a special signal to the switch and sensing a passage of that signal through the switch to test whether the indicated status is correct said special signal being distinguishable from electromagnetic noise.
The signal supply and current testing is preferably performed by a microcontroller. A filter may be provided for filtering the current received through said connection, and means may be provided for disabling said filter during the testing of said given signal.
In one embodiment, the switch to be monitored changes its state in response to various events, for example the passage of a given volume of water through a water meter. By counting the number of times the switch opens and closes, a count of the water flow is obtained. If the circuit which monitors the state of the switch is subject to electromagnetic noise, then the count obtained from the switch may be inaccurate. The switch status sensor applies a signal distinguishable from electromagnetic noise to the switch, and means is provided for detecting the passage of the signal through the switch in order that the true status of the switch can be determined even if electromagnetic noise is present.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
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Collen Law Associates PC
Fleming Fritz
Fusion Meters Limited
McDermott Robert M.
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