Level sensor and method of making the same

Claim 2

A liquid level sensor adapted for connection to an electrical circuit comprising a bulbous-shaped housing having one open end and having therein an electrical isolator soldered on one side to an inside surface of the housing, a temperature sensor pill having a low electrical resistance mode and a high electrical resistance mode, the switch-over between the two modes occuring at temperatures above a predetermined anomaly temperature, a pair of leads soldered at one end to opposite sides of the sensor pill, one side of the sensor pill being soldered to the other side of the electrical isolator away from the side which is adhered to the inside surface of the housing, sandwiching the end of one lead therebetween, and cover means hermetically sealing the open end of the housing and having the other ends of the lEads extending therethrough and adapted for connection to the circuit whereby when the level sensor is immersed in one ambient it is cooled thereby and operates in one resistance mode and when the level sensor is exposed to another ambient it self-heats to temperatures above the anomaly temperature and operates in the other resistance mode.

Claim 3

The level sensor of claim 1 further comprising a sleeve within the housing surrounding the electrical isolator, sensor pill and leads for insulating the sides of the housing.

Claim 4

The level sensor of claim 2 further comprising a rear insulator material between the cover means and the sensor pill.

Claim 5

The level sensor of claim 3 wherein the cover means for hermetically sealing the open end of the housing comprises a washer portion soldered to and covering the open end of the housing and having a central aperture, a bushing portion having a central aperture and an open end, a hollow stem portion sealingly connecting the washer and bushing portions, an insulating compound sealingly closing the open end of the bushing portion, the leads extending through the central apertures, and the hollow stem and into the insulating compound and being adapted for connection to the circuit.

Claim 6

The level sensor of claim 4 further comprising a sealant material plugging the central aperture of the bushing.

Claim 7

The level sensor of claim 5 further comprising connector pins secured to the ends of the leads for connection to the circuit.

Claim 8

The level sensor of claim 1 wherein the bulbous-shaped housing is a metal can.

Claim 9

The level sensor of claim 1 wherein the electrical isolator is a thin alumina wafer and the solder comprises 95 percent Tin and 5 percent Silver.

Claim 10

The level sensor of claim 8 wherein the solder layer is thin and wide.

Claim 11

The level sensor of claim 1 wherein the temperature sensor pill is a sensor having a positive temperature coefficient.

Claim 12

The level sensor of claim 1 wherein the leads are made from a copper-nickel alloy and the end of the lead sandwiched between the sensor pill and the isolator is flattened.

Claim 13

The level sensor of claim 11 wherein the leads are each covered with an insulating sleeve.

Claim 14

The level sensor of claim 3 wherein the said sleeve and the said rear insulator material are made of kapton material.

Claim 15

The level sensor of claim 4 wherein the stem portion in relation to the housing is a long, thin, hollow, stainless steel tube of small diameter.

Claim 16

The level sensor of claim 4 wherein the washer portion is made of kovar material.

Claim 17

The level sensor of claim 4 wherein the sealing connections between the stem and washer portions and between the stem and bushing portions are a silver solder.

Claim 18

The level sensor of claim 4 wherein the bushing portion is a bushing adapted for mounting the level sensor to a structure containing the ambient.

Claim 19

The level sensor of claim 4 having a time constant of about 7 seconds.

Claim 20

A level sensor for the liquid coolant system of an internal combustion engine comprising a bulbous-shaped can having an open end, an electrically isolating wafer soldered to an inside surface of the can, a PTC pill having a predetermined anomaly temperature, a pair of insulated wire leads one end of each of which is soldered to opposite sides of the pill, the pill being soldered to a side of the wafer away from the side which is soldered to the inside surface of the can and sandwiching one end of one lead therebetween, a side insulating sleeve within the can, a centrally apertured rear insulating washer adjacent the open end of the can, a metal washer the periphery of which is soldered to the open end of the can sealingly closing said open end, a hollow, stainless steel stem sealingly secured to the metal washer, a centrally apertured, bushing having a base portion sealingly secured to the stem and an outer end portion, a mass of insulating mAterial sealingly closing the portion of the bushing, the leads passing from the can through the central apertures of the washers, the hollow stem, the central aperture of the bushing and the insulating mass, and being adapted for connection to an electrical circuit, the sensor having a high heat flow path and a low heat flow path to the ambient system, the can, wafer, PTC pill, and conjoining solder defining the high heat flow path, the sleeve, rear insulating washer, leads, metal washer, stem, bushing and insulating mass defining the low heat flow path, whereby when the sensor is immersed in a liquid coolant there is high heat dissipation through the high heat flow path and the PTC pill is cooled, operating in a low resistance mode, and when the sensor is exposed to air there is low heat dissipation through the high heat flow path and the PTC pill self-heats above the anomaly temperature, operating in the high resistance mode.

Claim 21

A level sensor for the liquid coolant system of an internal combustion engine comprising a bulbous-shaped can having an open end, an electrically isolating wafer soldered to an inside surface of the can, a PTC pill having a predetermined anomaly temperature, a pair of insulated wire leads one end of each of which is soldered to opposite sides of the pill, the pill being soldered to a side of the wafer away from the side which is soldered to the inside surface of the can and sandwiching one end of one lead therebetween, a side insulating sleeve within the can, a centrally apertured rear insulating washer adjacent the open end of the can, a metal washer the periphery of which is soldered to the open end of the can sealingly closing said open end, a hollow, stainless steel stem sealingly secured to the metal washer, a centrally apertured, bushing having a base portion sealingly secured to the stem and an outer end portion, a mass of insulating mAterial sealingly closing the portion of the bushing, the leads passing from the can through the central apertures of the washers, the hollow stem, the central aperture of the bushing and the insulating mass, and being adapted for connection to an electrical circuit, the sensor having a high heat flow path and a low heat flow path to the ambient system, the can, wafer, PTC pill, and conjoining solder defining the high heat flow path, the sleeve, rear insulating washer, leads, metal washer, stem, bushing and insulating mass defining the low heat flow path, whereby when the sensor is immersed in a liquid coolant there is high heat dissipation through the high heat flow path and the PTC pill is cooled, operating in a low resistance mode, and when the sensor is exposed to air there is low heat dissipation through the high heat flow path and the PTC pill self-heats above the anomaly temperature, operating in the high resistance mode.