Universal single point liquid level sensor

Details Universal single point liquid level sensor Universal single point liquid level sensor

1990-10-16

1992-10-27

Ng, Jin F.

Communications: electrical

Condition responsive indicating system

Specific condition

340618, 73295, G08B 2100

Patent

active

051593181

ABSTRACT:
A liquid level detector comprises a thermistor and circuitry for determining electrically if the thermistor is wet or dry and additionally, and continuously, if the thermistor is open or shorted. The voltage across the thermistor is filtered to remove low frequency electrical noise, then compared with a reference low voltage to determine if shorted and to a transition voltage chosen to be between the thermistor's normal wet and dry voltages to determine if the thermistor is wet or dry. The voltage is also compared to the supply voltage using a CMOS gate circuit element to determine if the thermistor is open. The gate passes both faults on to an LED to signal that a fault condition exists or indicates by another LED the wet or dry condition of the thermistor. A pump may be activated through a relay if the thermistor tests wet or dry, as desired.

REFERENCES:
patent: 3757317 (1973-09-01), Kahn et al.
patent: 3878541 (1975-04-01), Dodson, III
patent: 4656464 (1987-04-01), Cliffgard
patent: 4818976 (1989-04-01), Schmitt et al.

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