Temperature sensor

A thermistor positioned within a tubular probe adjacent its closed distal end has lead wires connected with terminals by both crimp and weld connections that are independent of one another. A non-rigid heat transfer medium fills the distal end portion of the probe in surrounding relationship to the thermistor. An opening in the sensor housing leads to the interior of the probe and receives a dielectric sleeve in which tail end portions of the terminals are positioned.

BACKGROUND OF THE INVENTION 
This application relates to the art of sensors and, more particularly, to 
sensors of the type having a thermistor positioned within a tubular probe. 
The invention is particularly applicable to temperature sensors for 
sensing the temperature of a fluid and will be described with specific 
reference thereto. However, it will be appreciated that the invention has 
broader aspects and can be used for other purposes such as sensing liquid 
levels by supplying sufficient current to the thermistor to cause 
self-heating. 
Temperature sensors commonly include a thermistor positioned within a 
tubular probe. It is common to pot the thermistor in a rigid heat transfer 
medium such as epoxy. Damage to the thermistor, and to the lead wires and 
their connections to plug-in terminals, may occur due to thermal expansion 
and contraction during use of the device or by curing of the potting 
medium. It would be desirable to improve the integrity of the connections 
between the lead wires and the terminals, and to minimize damage or 
failure caused by expansion and contraction during use of the device. 
SUMMARY OF THE INVENTION 
A temperature sensor of the type described has the thermistor lead wires 
connected to the terminals with both crimp connections and weld 
connections. This redundant connection arrangement between the thermistor 
lead wires and the terminals provides very high reliability of the 
temperature sensor. 
In a preferred arrangement, the crimp connection is located closer to the 
thermistor than the weld connection. 
In accordance with another aspect of the application, a non-rigid heat 
transfer medium such as silicon grease completely fills the distal end 
portion of the probe in surrounding and encapsulating relationship to the 
thermistor. 
The terminals are shaped with grooves and embossed depressions for 
enhancing the crimp connection to the lead wires. The terminals are also 
shaped to minimize leakage of air or liquid therepast, and to securely 
lock same in a molded plastic connector. 
An opening in the sensor housing communicates with the interior of the 
tubular probe. The opening is enlarged and receives a dielectric sleeve in 
which the lead wire-to-terminal connections are positioned. 
The cylindrical bore in the probe has two different diameters intersecting 
at a shoulder and the dielectric sleeve has one end abutting the shoulder. 
It is principal object of the present invention to provide an improved 
sensor having redundant connections between terminals and lead wires. 
It is also an object of the invention to provide a sensor having improved 
terminals. 
It is another object of the invention to provide a sensor with a non-rigid 
heat transfer medium surrounding the thermistor.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawing, wherein the showings are for purposes of 
illustrating a preferred embodiment of the invention only and not for 
purposes of limiting same, the figures show a metal housing A assembled to 
a plastic connector B. 
Housing A includes an elongated tubular probe 10 having a closed distal end 
12 and an enlarged head 14 that is externally shaped for cooperation with 
a tool to facilitate installation and removal of the sensor. Tubular probe 
10 has external threads 16 thereon beneath enlarged head portion 14 along 
about one-half of the length of the probe for reception in a tapped hole. 
When installed, the unthreaded portion of tubular probe 10 and its closed 
distal end 12 are immersed in the fluid whose temperature is to be sensed. 
Housing A has an enlarged entrance opening 20 in enlarged head portion 14 
opposite from closed distal end 12 for providing access to the hollow 
interior of probe 10. Opening 20 is of generally inverted frustol-conical 
shape to facilitate insertion of components into the probe. 
Referring to FIG. 5, the interior of tubular probe 10 has first and second 
different diameter cylindrical portions 30, 32 that intersect at a 
shoulder 34. The first and larger diameter cylindrical portion 30 has a 
length substantially less than the second smaller diameter cylindrical 
portion 32. Preferably, the smaller diameter portion is at least about 
three times the length of the larger diameter portion. A thin deformable 
attaching ring 40 extends upwardly from the flat upper end 42 of enlarged 
head portion 14. 
Referring to FIG. 4, an elastomeric gasket 46 is positioned on flat upper 
end 42 of housing enlarged head portion 14. A flat end of connector B is 
positioned against gasket 46 and pressure is applied thereto for 
compressing the gasket. Deformable housing ring 40 is then deformed 
inwardly over a circular flange 50 on connector B to seal opening 20 and 
the interior of probe 10. A locking projection 52 on connector B adjacent 
flange 50 thereof interlocks with inwardly deformed ring 40 on housing A 
to prevent relative rotation between connector B and housing A. 
Connector B has opposite side projections 56, 58 for cooperation with 
latches on a socket in a known manner. Connector B also has a longitudinal 
projection 60 for properly orienting connector B with a socket and guiding 
same into the socket. Connector B has a cavity 62 surrounding portions of 
terminals C, D that are molded into connector B. The portions of terminals 
C, D within cavity 62 are receivable in sockets in a known manner. 
A thermistor E having a negative temperature coefficient of electrical 
resistance is positioned within tubular probe 10 adjacent closed distal 
end 12 thereof. The inner end portion of probe 10 adjacent distal end 12 
thereof is completely filled with a non-rigid heat transfer medium 70 such 
as silicon grease. The amount of heat transfer medium 70 is preferably 
just sufficient to insure complete encapsulation of thermistor E therein 
so that the major length of the interior of probe 10 remains free of heat 
transfer medium to minimize transfer of heat toward enlarged head 14. The 
wall thickness of the unthreaded portion of probe 10 and distal end 12 is 
preferably not greater than about 0.032 inch to insure rapid transfer of 
heat to thermistor E. 
Lead wires attached to thermistor E are connected with tail end portions of 
terminals C, D by both crimp connections 76, 78 and weld connections 80, 
82. The crimp and weld connections are longitudinally spaced-apart from 
one another along the longitudinal axes of terminals C, D. Crimp 
connections 76, 78 are located closer to thermistor E than weld 
connections 80, 82. A dielectric sleeve 84 is received in enlarged opening 
20 and closely received within the first larger diameter inner cylindrical 
portion of the probe. The bottom end of dielectric sleeve 78 abuts 
shoulder 34 formed by the intersection of the first and second large and 
smaller inner cylindrical portions of the probe. 
FIGS. 6 and 7 show terminal C having a flat blade portion 90 with a 
longitudinal axis 92 and parallel opposite sides 94, 96. Blade portion 90 
intersects a flat tail portion 98 having a reduced width and being 
laterally offset relative to longitudinal axis 92. Opposite sides 102, 104 
of tail portion 98 are laterally offset from sides 94, 96 of blade portion 
90. The shoulder 106 formed by the intersection of blade side 94 with tail 
side 102 provides a tortuous path to inhibit leakage of fluid along the 
terminal. A rectangular notch 107 in side 96 of blade 90 adjacent tail 
portion 104 serves the same purpose. These irregularities in the sides of 
the terminal also enhance interlocking of the terminals with the molded 
plastic connector. 
Tail portion 98 is formed with a curved transversely extending embossment 
110 on which a wire lead is positioned to form a weld connection. A crimp 
connection portion 112 is shown in its flat configuration in FIG. 6 prior 
to lateral bending of same into a generally U-shaped configuration. A 
plurality of spaced- apart longitudinal generally V-shaped grooves 120-122 
are formed on the surface of crimp connection portion 112 to facilitate 
bending of same into a generally U-shaped configuration and to enhance 
flattening of the generally U-shaped portion when it is crimped closed 
with a wire received therein. A generally rectangular recess 130 is 
embossed in crimp connection portion 112 in alignment with weld embossment 
110. The fine wire lead extends across embossed depression 130 and makes 
good contact with the upper and lower edges thereof when the crimp 
connection is crimped closed. FIG. 8 shows the crimp connection portion 
112 after it has been formed into a generally U-shaped configuration for 
receiving a wire therein. Grooves 120-122 and embossed recess 130 are 
located within the interior surface of the generally U-shaped crimp 
portion. After a wire is inserted within the generally U-shaped portion of 
FIG. 8, it is crimped closed to securely lock the wire therein. The same 
wire is also welded to transverse embossment 110. 
FIG. 9 shows terminal D having a flat blade portion 140 with a longitudinal 
axis 142 and opposite sides 144, 146. A narrower width tail portion 148 is 
laterally offset from longitudinal axis 142 so that its opposite sides 
150, 152 are offset laterally from blade sides 144, 146. A shoulder and 
notch 154, 156 serve the same purposes as shoulder and notch 106, 107 of 
terminal C. A transverse weld embossment 160 is formed in tail portion 148 
and a crimp connection portion 162 is provided at the lower end thereof. A 
plurality of spaced-apart longitudinally extending generally V-shaped 
grooves 163-165 are provided in crimp connection portion 162 to facilitate 
the bending and closing of same. A generally rectangular depression 170 is 
embossed in crimp connection portion 162 in alignment with weld embossment 
160. FIG. 10 shows crimp connection portion 162 after it has been bent 
into a generally U-shaped configuration for receiving a wire lead. Grooves 
163-165 and depression 170 are located Within the interior surface of the 
generally U-shaped portion. The crimp connection portions are curved into 
generally U-shaped configurations such that the pocket in the U-shaped 
portion is on the same side of the terminal as the outwardly curved 
portion of weld embossment 160. The generally U-shaped pocket and the weld 
embossment are also longitudinally aligned. 
Thermistor E and wire leads 72, 74 are preferably coated with a dielectric 
material that is removed from the end portions of the wire leads that are 
crimp and weld connected to the terminals. The wire leads are crimped and 
welded to the terminals of a connector and a dielectric sleeve is 
positioned over the connections. This assembly is then mated with a metal 
housing by extending the thermistor attached to the wire leads down into 
the tubular probe. With the parts positioned as shown in FIG. 4, 
deformable ring portion 40 on housing A is then deformed inwardly to lock 
the assembly together. 
Although the invention has been shown and described with respect to a 
preferred embodiment, it is obvious that equivalent alterations and 
modification will occur to others skilled in the art upon the reading and 
understanding of this specification. The present invention includes all 
such equivalent alterations and modifications, and is limited only by the 
scope of the claims.