Liquid level sensor having an integral ptc and ntc thermistor

Claim 2

A composite thermally responsive resistor device for automotive liquid level sensing applications, said device comprising a barium titanate first body member, said first body member having a positive temperature coefficient of electrical resistance which dominates total device resistance at low temperatures, said first body member having two major faces, a second body member of a material having a negative temperature coefficient of electrical resistance which dominates total device resistance at high temperatures, said second body member having two major faces, a thin metallic electrode layer on each of said faces of said body members, at least one of said layers serving as a common electrode for both of said body members, said electrodes on said first and second body member major faces providing means for passing electrical current therethrough and generating heat within at least one of said body members, said first body member being connected electrically in parallel with said second body member through said common electrode, and an intimate thermal association between said first and second body members whereby heat generated in one body member is conductively transferred to the other body member to produce a device having an effective total resistance which gradually decreases with increasing temperature except for a narrow predetermined temperature range in which the resistance increases to inhibit undesirable regenerative reduction of device resistance.

Claim 3

An integral composite thermally responsive resistor device for automotive liquid level sensing application, said device comprising a solid, cylindrical barium titanate core having two major parallel faces, said barium titanate core having a positive temperature coefficient of electrical resistance which dominates total device resistance at low temperatures, a tubular outer sleeve of iron vanadium borophosphate glass surrounding and in physical contact with the periphery of said barium titanate core and having two major parallel faces coplanar with said barium titanate core faces, said iron vanadium borophosphate glass outer sleeve having a negative temperature coefficient of electrical resistance which dominates total device resistance at high temperatures, two spaced thin metallic layers serving as electrodes, said electrodes being coextensive and contiguous said major faces of said farium titanate core and said outer sleeve for passing electrical current therethrough and generating heat therein, said electrodes connecting said core and said outer sleeve electrically in parallel, said barium titanate core and iron vanadium borophoSphate glass sleeve being in intimate thermal association whereby heat generated in said barium titanate core at low temperatures is conductively transferred to said iron vanadium borophosphate glass outer sleeve to produce a device having an effective total resistance which gradually decreases with increasing temperature except for a narrow predetermined temperature range in which the resistance increases to inhibit undesirable regenerative reduction of device resistance.

Claim 4

An integral composite thermally responsive resistor device for automotive liquid level sensing application, said device comprising a solid, cylindrical barium titanate core having two major parallel faces, said barium titanate core having a positive temperature coefficient of electrical resistance which dominates total device resistance at low temperatures, a tubular outer sleeve of iron vanadium borophosphate glass surrounding and in physical contact with the periphery of said barium titanate core and having two major parallel faces coplanar with said barium titanate core faces, said iron vanadium borophosphate glass outer sleeve having a negative temperature coefficient of electrical resistance which dominates total device resistance at high temperatures, two spaced thin metallic layers serving as electrodes, said electrodes being coextensive and contiguous said major faces of said farium titanate core and said outer sleeve for passing electrical current therethrough and generating heat therein, said electrodes connecting said core and said outer sleeve electrically in parallel, said barium titanate core and iron vanadium borophoSphate glass sleeve being in intimate thermal association whereby heat generated in said barium titanate core at low temperatures is conductively transferred to said iron vanadium borophosphate glass outer sleeve to produce a device having an effective total resistance which gradually decreases with increasing temperature except for a narrow predetermined temperature range in which the resistance increases to inhibit undesirable regenerative reduction of device resistance.

Claim 5

A liquid level sensing system for automotive applications which is effective over a wide temperature range and which includes a distinctive composite thermally responsive resistor device, said system comprising an integral thermally responsive resistor device having a barium titanate first body member, said first body member having a positive temperature coefficient of electrical resistance which dominates total device resistance at low temperatures, said first body member having two major faces, a second body member of a negative temperature coefficient material which dominates total device resistance at high temperatures, said second body member having two major faces, a thin metallic electrode layer on each of said body member faces, at least one of said layers serving as a common electrode for both of said body members, said electrodes on said body member major faces providing means for electrical connection to external circuitry, said first body member being connected electrically in parallel with said second body member through said common electrode and being in intimate thermal association therewith, a vessel containing liquid whose level is to be sensed, said device being insulatingly mounted at a predetermined level within said vessel and in physical contact with said liquid, a series circuit containing a voltage source and a warning indicator means electrically connected to said device through said electrodes which passes current therethrough and generates heat within at least one of said body members, said first body member having a relatively low resistance at low temperatures whereby heat generated within said first body member is conductively transferred to said second body member to produce a responsive decrease in electrical resistance and create a regenerative action within said circuit so that said warning means will be activated if said liquid has fallen below said predetermined level at said low temperatures, said device having an effective total resistance which decreases with increasing temperature except for a narrow temperature range in which the resistance thereof increases thereover to inhibit false activation of said warning means when said liquid remains in physical contact with said device at high temperatures.

Claim 6

A liquid level sensing system for automotive applications which is effective over a wide temperature range and which includes a distinctive composite thermally responsive resistor device, said system comprising an integral thermally responsive resistor device having a barium titanate first body member, said first body member having a positive temperature coefficient of electrical resistance which dominates total device resistance at low temperatures, said first body member having two major faces, a second body member of a negative temperature coefficient material which dominates total device resistance at high temperatures, said second body member having two major faces, a thin metallic electrode layer on each of said body member faces, at least one of said layers serving as a common electrode for both of said body members, said electrodes on said body member major faces providing means for electrical connection to external circuitry, said first body member being connected electrically in parallel with said second body member through said common electrode and being in intimate thermal association therewith, a vessel containing liquid whose level is to be sensed, said device being insulatingly mounted at a predetermined level within said vessel and in physical contact with said liquid, a series circuit containing a voltage source and a warning indicator means electrically connected to said device through said electrodes which passes current therethrough and generates heat within at least one of said body members, said first body member having a relatively low resistance at low temperatures whereby heat generated within said first body member is conductively transferred to said second body member to produce a responsive decrease in electrical resistance and create a regenerative action within said circuit so that said warning means will be activated if said liquid has fallen below said predetermined level at said low temperatures, said device having an effective total resistance which decreases with increasing temperature except for a narrow temperature range in which the resistance thereof increases thereover to inhibit false activation of said warning means when said liquid remains in physical contact with said device at high temperatures.