Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1985-08-26
1987-04-07
Rowland, James L.
Communications: electrical
Condition responsive indicating system
Specific condition
73295, 340 59, G08B 2100, B60Q 100
Patent
active
046564640
ABSTRACT:
A liquid level detector comprising a voltage-divider network, including a thermistor, connected between the terminals of a battery so that the potential at the voltage-divider output varies as a function of the resistance of the thermistor. The voltage-divider output is connected to the input of a voltage-sensitive switching circuit. The voltage-sensitive switching circuit has two stable states and is either in one state or the other depending upon whether the potential at the voltage-divider output is above or below a reference level. When the potential at the voltage-divider output indicates that the thermistor is out of a good heat conductor such as a liquid, the switching circuit closes a series circuit between the battery and an LED provide a visual indication of the low liquid level condition. The thermistor is supplied by means of a constant current source to prevent destruction of the thermistor in the event of a sharp battery voltage increase. Self-testing circuitry is included to test the operation of the circuit without requiring a separate connection to the ignition.
REFERENCES:
patent: 3631440 (1971-12-01), Cliffgard
patent: 3740740 (1973-06-01), Milo
patent: 4361037 (1982-11-01), Hauschild et al.
Myer Daniel
Rowland James L.
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