Liquid level sensor for corrosive baths

Claim 2

A THERMISTOR ASSEMBLY FOR LIQUID LEVEL SENSING APPLICATIONS INVOLVING CORROSIVE WHICH IS EASILY MANUFACTURED AND WHICH HAS A RESPONSE TIME THAT IS READILY SET DURING SAID MANUFACTURE, SAID ASSEMBLY COMPRISING: A THEMISTOR ELEMENT, AT LEAST TWO ELECTRICALLY WIRES ATTACHED TO SAID THERMISTOR ELEMENT, A CORROSION RESITANT TUBE HAVING A CLOSED END PORTION WITH A WALL THICKNESS OF ABOUT 0.5 - 3 MM WHEREIN SAID TUBE PROVIDES PROTECTION FOR SAID THEMISTOR FROM CORROSIVE SOLUTION WHOSE LIQUID LEVEL IS TO BE SENSED WHILE SERVING AS A THERMINAL CONDUCTOR THEREBETWEEN, A LEAD ALLOY HEAT EXCHANGE MEMBER IN THE CLOSED END PORTION OF SAID TUBE AND DIRECTLY CONTACTING THE INNER WALLS THEREOF, A COATING OF SINTERED POLYTERAFUORLETYLENE PARTICLES BETWEEN ABOUT 0.0025 - 0.25 MM THICK ON SAID THERMISTOR ELEMENT AND SAID CONDUCTOR WIRES EXTENDING FROM SAID THERMISTOR ELEMENT, THEREBY FORMING A POLYTERAFLUOROETHYLENE COATED THERMISTOR SUBASSEMBLY, AND

Claim 3

A thermistor assembly for liquid level sensing applications involving acid solutions which is easily manufactured and which has a response time that is readily set during said manufacture, said assembly comprising: a thermistor element; at least two electrically conductive wires attached to said thermistor element; a fused silica tube having a closed end portion with a wall thickness of about 0.5 - 3 mm and an inside diameter of about 8 mm wherein said fused silica tube is corrosion resistant to acid solutions whose liquid level is to be sensed; a lead alloy heat exchange member having a predetermined volume of about 0.2 - 2.0 cm3 in the closed end portion of said fused silica tube and directly contacting the inner walls thereof; a sprayed coating of sintered polytetrafluoroethylene particles between about 0.025 - 0.25 mm thick on said thermistor element and said conductor wires extending from said thermistor element, thereby forming a polytetrafluoroethylene coated thermistor subassembly; and said polytetrafluoroethylene coated thermistor subassembly being immersed in said lead alloy heat exchange member at a predetermined spacing relative to the walls of said fused silica tube wherein the spacing therebetween determines the response of said thermistor element, said polytetrafluoroethylene coating providing an impervious barrier to said lead alloy heat exchange member and electrically insulating said conductor wires from said lead alloy heat exchange member.

Claim 4

A thermistor assembly for liquid level sensing applications involving acid solutions which is easily manufactured and which has a response time that is readily set during said manufacture, said assembly comprising: a thermistor element; at least two electrically conductive wires attached to said thermistor element; a fused silica tube having a closed end portion with a wall thickness of about 0.5 - 3 mm and an inside diameter of about 8 mm wherein said fused silica tube is corrosion resistant to acid solutions whose liquid level is to be sensed; a lead alloy heat exchange member having a predetermined volume of about 0.2 - 2.0 cm3 in the closed end portion of said fused silica tube and directly contacting the inner walls thereof; a sprayed coating of sintered polytetrafluoroethylene particles between about 0.025 - 0.25 mm thick on said thermistor element and said conductor wires extending from said thermistor element, thereby forming a polytetrafluoroethylene coated thermistor subassembly; and said polytetrafluoroethylene coated thermistor subassembly being immersed in said lead alloy heat exchange member at a predetermined spacing relative to the walls of said fused silica tube wherein the spacing therebetween determines the response of said thermistor element, said polytetrafluoroethylene coating providing an impervious barrier to said lead alloy heat exchange member and electrically insulating said conductor wires from said lead alloy heat exchange member.

Claim 5

A thermistor assembly for liquid level sensing applications involving alkaline solutions which is easily manufactured and which has a response time that is readily set during said manufacture, said assembly comprising: a disc-shaped thermistor element having metallic electrodes on its major faces; at least two electrically conductive wires bonded to said electrodes on said thermistor element; a magnesia tube having a closed end portion with a wall thickness of about 0.5 - 3 mm and an inside diameter of about 8 mm wherein said magnesia tube is corrosion resistant to alkaline solutions whose liquid level is to be sensed; a lead alloy heat exchange member having predetermined volume of about 0.2 - 2.0 cm3 in the closed end portion of said magnesia tube and directly contacting the inner walls thereof; a sprayed coating of sintered polytetrafluoroethylene particles between about 0.025 - 0.25 mm thick on said thermistor element and said conductor wires extending from said thermistor element, thereby forming a polytetrafluoroethylene coated thermistor subassembly; and said polytetrafluoroethylene coated thermistor subassembly being immersed in said lead alloy heat exchange member at a predetermined spacing relative to the walls of said magnesia tube wherein the spacing therebetween determines the response of said thermistor element, said polytetrafluoroethylene coating providing an impervious barrier to said lead alloy heat exchange member and electrically insulating said conductor wires from said lead alloy heat exchange member.

Claim 6

A thermistor assembly for liquid level sensing applications involving alkaline solutions which is easily manufactured and which has a response time that is readily set during said manufacture, said assembly comprising: a disc-shaped thermistor element having metallic electrodes on its major faces; at least two electrically conductive wires bonded to said electrodes on said thermistor element; a magnesia tube having a closed end portion with a wall thickness of about 0.5 - 3 mm and an inside diameter of about 8 mm wherein said magnesia tube is corrosion resistant to alkaline solutions whose liquid level is to be sensed; a lead alloy heat exchange member having predetermined volume of about 0.2 - 2.0 cm3 in the closed end portion of said magnesia tube and directly contacting the inner walls thereof; a sprayed coating of sintered polytetrafluoroethylene particles between about 0.025 - 0.25 mm thick on said thermistor element and said conductor wires extending from said thermistor element, thereby forming a polytetrafluoroethylene coated thermistor subassembly; and said polytetrafluoroethylene coated thermistor subassembly being immersed in said lead alloy heat exchange member at a predetermined spacing relative to the walls of said magnesia tube wherein the spacing therebetween determines the response of said thermistor element, said polytetrafluoroethylene coating providing an impervious barrier to said lead alloy heat exchange member and electrically insulating said conductor wires from said lead alloy heat exchange member.