Thermocouple assembly

A thermocouple assembly wherein the transition fitting has a separable nose piece which may be brazed to the probe casing before the transition fitting is coupled thereto, thus avoiding the previous occuring spread of brazing heat through the body of the fitting such as might damage contained wires and their soldered connections.

BACKGROUND OF THE INVENTION 
For many years snub nose transition fittings were attached to a 
thermocouple probe casing or sheath by the process of brazing. However the 
brazing heat necessarily spread through the fitting and frequently damaged 
the contained thermocouple wires and/or their soldered connections. 
Accordingly, this process was superceded by use of a transition fitting 
having a short crimping nose which by use of a specialized tool was 
crimped or swaged onto the probe casing (U.S. Pat. No. 3,811,958 to 
Maurer). But this has not proven entirely satisfactory and brazing would 
still be preferred if the concurrent heat spread through the fitting could 
be avoided. 
STATEMENT OF THE INVENTION 
It has now been found possible to provide such a two-piece transition 
fitting which has a severable nose piece which can be brazed to the probe 
casing by itself (with the thermocouple wirings extending therethru) and 
the body of the fitting then coupled thereto, as by screw threads, after 
the heat has dissipated. Alternately, the body may be press fit onto the 
nose piece in the absence of screw threads. The body of encapsulation 
material forms a permanent union with the individual wires and the two 
pieces of the transition fitting.

DETAILED DESCRIPTION 
The present assembly is formed by a heat-transmitting (metallic) casing or 
probe 10 having a distal closed end 11 which houses a thermocouple 
junction 12 from which a pair of thermocouple wires 14, 15 extend 
lengthwise, spaced apart, emerging through an open end 16 and extending 
therebeyond. The casing is typically filled with mineral insulation 18 
which provides support for the thermocouple wires, with sealing material 
19 forming a plug for the initially open end. Beyond the casing end 16, 
the thermocouple wires are soldered to extension wires 20, 22 which 
continue to remote utilization or monitoring device (not shown), the 
soldered unions 21, 23 and wires continuing to be held apart by insulating 
material. 
The wire lengths for which the unions 21, 23 form a more or less midpoint 
is housed in a tubular, open-ended transition fitting 25 of which the 
distal end is internally threaded 26 for threaded engagement with a short 
tubular nose piece 27. The latter has an internal diameter which will 
slidingly receive the proximate end of the probe casing 10 inserted 
lengthwise therethrough, such end 16 then conveniently projecting a short 
distance beyond--that is, into the transition fitting when assembled. The 
nose piece 27 is formed with a terminal neck 28 of reduced diameter. This 
reduced neck 28, before coupling of the transition fitting 25 thereto, is 
brazed (by torch 30 and brazing solder 32) to the probe casing 10 and, if 
desired, the joint is subsequently anodized. 
Following brazing of the nose piece 27 to the probe casing 10, the 
transition fitting 25 (with the wires 20, 22 extending therethrough) is 
coupled to the threads 29 of the nose piece. The enclosure of the fitting 
25 can be filled then by encapsulation material 38 as through an injection 
nozzle 40. The proximate end of the transition fitting 25 may also be 
formed with a series of adjacent external grooves 24 for retention of the 
lead end of a flexible wire coil 34 through the center of which the wires 
20, 22 extend within a support collar 36. Such coil serves to guard the 
emerging wires against injury by being abruptly bent or broken in handling 
the apparatus. 
The two pieces of the modified transition fitting of FIG. 6 lack screw 
threads and are formed with a relief bore 42 in the nose piece 27a. Upon 
assembly, an annular abutment face 44 registers with a press fit shoulder 
46 of the nose piece and the encapsulation material 38 further aids in 
holding the two pieces together, as permanent union. Suitable 
encapsulation material is Emerson-Cummings epoxy resin for low temperature 
thermocouples (up to 250.degree. F.) and sauereisen cement for temperatures 
up to 1000.degree. F. 
The body of the transition fitting 25 may be color coded in accordance with 
American National Standards Institute (ANSI) to signify the pair of 
dissimilar metals which are used as thermocouple conductors 12: yellow for 
Chromel/Alumel; black for Iron/Constantan; blue for Copper/Constantan; 
violet for Chromel/Constantan; green for Platinum/Rhodium.