Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1979-08-07
1981-08-11
Yusko, Donald J.
Communications: electrical
Condition responsive indicating system
Specific condition
73304R, G08B 2100
Patent
active
042837197
ABSTRACT:
A liquid level sensing apparatus includes a probe having a high positive temperature coefficient of resistivity. The probe is connected in a circuit including an operational amplifier and a series transistor which maintains the voltage across the probe constant for a fixed period following switching on of the apparatus and which produces a voltage signal related to the current flowing in the probe. This voltage signal is differentiated by a differentiating circuit to provide a signal indicating the rate of change of the voltage signal from which it is determined whether or not the probe is immersed in a cooling liquid. A warning lamp is actuated by a latching switch circuit when the probe is not immersed. A second example is described in which the probe current is maintained at a fixed level and the rate of change of the voltage across it is monitored.
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Harris Paul A.
Williams David G.
Lucas Industries Limited
Myer Daniel
Yusko Donald J.
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