Electrical transmission or interconnection systems – Switching systems – Condition responsive
Patent
1998-06-26
2000-09-12
Ballato, Josie
Electrical transmission or interconnection systems
Switching systems
Condition responsive
307127, H01H 4700
Patent
active
061181900
ABSTRACT:
A circuit for controlling a fail-safe operation of measurement and control apparatus for detecting the presence or absence of water by making a measurement of the impedance experienced in a gap between an insulated tip of the electrode and a surface held at a reference voltage or else connected to ground. The apparatus may be configured to provide an alarm when water is present and should not be, or vice versa. The circuit comprises comparators IC1 and IC2, a phase detector IC3 and a triple-redundant drive circuit 12 which drives a relay 14. The function of IC1 is to ensure that when operating with water as the normal condition, an electrode fault, such as could be caused by excessive contamination, will cause the system output to indicate an abnormal condition. The main function of IC2 is to discriminate between the water condition and the steam condition. The function of IC3 is to ensure that there is no output if there exists an abnormal condition or any fault condition. It follows that there will only be an output if the sensor is in the normal condition. This is then shown to operate a relay using a secure triple redundancy drive circuit so that the relay contacts may be used to indicate a normal or an abnormal/fault condition.
REFERENCES:
patent: 4001654 (1977-01-01), Davis et al.
patent: 4467386 (1984-08-01), Wasson
patent: 5438323 (1995-08-01), Shea
Ballato Josie
DeBeradinis Robert L.
Solartron Group Limited
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