US 3638303 A
Resistance temperature probes having novel sensing elements are disclosed. The resistance element is not wound on a rigid support but is supported in a body of particulate, dielectric refractory material. The disclosure includes methods of fabricating the probes including calibration of the resistance in situ.
Claims available in
Description (OCR text may contain errors)
United States Patent Mochizuki  METHOD OF MAKING SENSING ELEMENTS FOR RESISTANCE- TEMPERATURE PROBES  Inventor: Mitsuaki Mochizuki, Kobe, Japan  Assignee: Okazaki Manufacturing Company, Kobe,
Japan [221 Filed: Sept. 2, 1969 21 Appl.No.: 854,415
 Foreign Application Priority Data Sept. 6, 1968 Japan ..43/064097  US. Cl ..29/614, 29/619, 338/238, 338/247  lnt. Cl. ..H0lc 7/00, HOlc 17/00  FieldofSearch ..29/610,6l1,6l3,614,619; 338/28, 30, 238, 229, 240, 241, 243, 247, 273
 References Cited UNITED STATES PATENTS 579,459 3/1897 Whittingham ..338/241 1,432,064 10/1922 Hadaway, Jr. ..338/241 X 2,091,839 8/1937 Tangeman ..29/619 X 2,491,688 12/1949 Pickels ..29/613 2,508,512 5/1950 Grinde ..338/229 2,635,163 4/1953 Temple ..29/619 X [4 1 Feb. 1, 1972 2,643,317 6/1953 Tuttle ..29/613 X 3,267,733 8/1966 Chambers. ..338/238 X 3,434,207 3/1969 Frachon ..29/619 X FOREIGN PATENTS OR APPLICATIONS 1,000,463 8/1965 Great Britain ..338/240 Primary Examiner-John F. Campbell Assistant Examiner-Victor A. DiPalma Attorney-Leonard S. Knox  ABSTRACT Resistance temperature probes having novel sensing elements are disclosed. The resistance element is not wound on a rigid support but is supported in a body of particulate, dielectric refractory material. The disclosure includes methods of fabricating the probes including calibration of the resistance in situ.
- An important feature resides in the method of incorporating 1 Claims, 11 Drawing Figures PATENTED FEB] 1972 Fla? FIGS Era/l F1015 F166 I FIG. 5 F1119 FIG, i0
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O'fly METHOD OF MAKING SENSING ELEMENTS FOR RESISTANCE-TEMPERATURE PROBES BACKGROUND OF THE INVENTION Heretofore, in the manufacture of resistance-temperature probes it has been the practice to wind the resistance wire around a mica or glass mandrel and, optionally, to insert the same in a glass tube so that the wire, which is of fine gauge, has adequate support. Sometimes the element is fused to the mandrel and/or tube. However, these techniques have the follow- SUMMARY OF THE INVENTION The present invention overcomes the foregoing shortcomings by eliminating the rigid support, whereby the probe may be useful at temperatures substantially higher than the maximum heretofore possible.
The invention probe includes a rigid sheath to contain the resistance wire element and to protect the same. A particulate refractory surrounds the resistance wire. This refractory is not compacted, as has been prior practice, but is merely densely deposited around the element and within the confines of the sheath, in such a way as to avoid pressure forces on the wire, i.e., deposition is controlled so as to avoid the formation of a rocklike mass restricting expansion and contraction of the resistance wire. However, the wire is given sufficient support to preclude short-circuiting or grounding of its turns or convolutions. The invention probe has primary utility in applications where high accuracy but low resistance to shock and vibration are factors.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a metallic sheath portion and compacted refractory, dielectric material together with the lead wires, but with the resistance element not yet joined thereto;
FIG. 2 shows the element joined to the lead wires;
FIG. 3 shows a section of sheath united to the sheath portion in a butt joint;
FIG. 4 shows the element and surrounding refractory and the end of the sheath section closed;
FIG. 5 shows an alternative embodiment wherein the sheath section is united with the sheath portion by means of a telescoping joint;
FIG. 6 shows an alternative form in which the resistance wire is housed in a capsule of glassy material together with relatively uncompacted refractory,
FIG. 7 is a cross section on the line 7-7 of FIG. 6;
FIG. 8 is similar to FIG. 4 but includes the capsule of FIG. 6;
FIG. 9 shows an alternative mode of supporting the resistance wire in a rigid tube;
FIG. 10 shows the subassembly of FIG. 9 formed into a U- shape for compactness; and
FIG. 11 is a cross section taken on the line IlII of FIG. 10.
DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS Adverting first to FIGS. 1 to 5, there is shown a sheath portion 10 of any desired length, depending upon the application, and of any suitable metal, e.g., stainless steel. The lead wires 12-12 are housed within the sheath portion 10 and are securely positioned by compacted refractory, dielectric material, e.g., powdered M 0, whereby the wires are insulated from each other and from the sheath portion.
The sensing element 14 is shown in the form of unannealed resistance wire of the gauge and length required to provide the desired ohmic resistance and is wound into a helix. Since the element is to be subsequently calibrated by trimming, excess turns may be allowed. The helix is bent on itself to form a loop and the free ends are welded or otherwise secured to the ends of the leads l2l2 (FIG. 2). At this point, the element 14 is essentially self-supporting. It will be understood that the element may be of geometrical form other than that shown.
A sheath section 21 of essentially the same diameter as the sheath portion 10 is butted to the end of the latter and welded (FIG. 3). The voids within the sheath section 21 are densely filled with powdered M 0 or equivalent refractory, which operation may be facilitated by vibrating the assembly. The time and intensity of vibration will be controlled in such a way that the element is adequately supported but not restricted against expansion and contraction, as was the case with the rocklike mass characteristic of prior probes. The degree of denseness of the refractory will take into account acceptable conduction and convection of heat between the element and the environment of the probe. A closure 23 is welded to the upper end of the sheath section 10.
The embodiment of FIG. 5 is similar to that of FIG. 4 except that, in this case, the sheath section 2111 is larger and telescoped over the sheath portion, and is then welded.
In either fonn of the invention shown in FIGS. 4 and 5 swaging of the assembly may be resorted to in order to obtain a more dense matrix of insulation. It is to be noted that, within the framework of the disclosure, undue compaction is avoided. This means that when the refractory is initially deposited within the sheath, there will be enough looseness to accommodate for this later swaging. The usual annealing is performed. Following such optional step the closure 23 is removed in order to calibrate the resistance element 14 to the proper value. This is accomplished by removing a portion of the insulation to expose the bight 26 of the loop, which may then be cut and trimmed until the selected ohmic resistance is obtained. The cut ends are then rejoined, the refractory replaced, if desired, and a new closure 23 welded on.
In FIG. 6 the sensing element 14a is encapsulated in a piece of tubing of quartz or other fusible glassy material which is closed at one end, the powdered refractory deposited in a dense but not rocklike matrix and the other end of the capsule 31 closed by heat while leaving the ends of the loop protruding for juncture with the leads l2l2. Since the glassy material is an insulator it is immaterial if the element touches the sides of the capsule. The sensing element subassembly of FIG. 6 is located in a sheath section and the several steps described in connection with FIGS. I to 4 or FIGS. I, 2 and 5 follow. In the case of FIG. 6 it will be clear that the refractory surrounding the capsule 31 need only be dense enough to center and support the capsule. Further, since swaging of the sheath section 21 and sheath portion 10 may fracture the quartz envelope of the capsule, this step is desirably eliminated.
FIGS. 9, l0 and 11 illustrate an alternative in which a helix 4] of resistance wire is threaded into a quartz tube 42. The voids are then filled with powdered insulation, e.g., M 0. In this case also the helix may contact the interior of the tube. After the ohmic resistance of the element is adjusted by trimming, the ends of the tube are fused to embed the leads 4444. Then the center region of the tube is heated and the same bent into the U-form of FIG. 10. The subassembly of FIG. 10 may now be incorporated in the probe as described in connection'with FIGS. 1 to 4.
From the foregoing it will have become apparent that the only restraint on the sensing element is the surrounding body of powdered refractory, dielectric material, for example, M,,0. When the latter is selected to have a very high degree of purity, it will be found that the insulation resistance is very high, even at high temperatures, the thermal conductivity is excellent and the element is not subject to degradation by contaminating gases.
device which includes a metallic sheath within which the sensing element is housed, comprising the steps of:
a. providing a tubular sheath portion having spaced lead wires therein and dielectric material intermediate the lead wires and sheath, an end portion of the lead wires protrudingfrom one end of the sheath,
b. providing a sensing element of resistance wire,
c. uniting the ends of the wire to respective ones of the lead wires,
d. locating a tubular sheath section of a length greater than the length of the element around the element and contiguous to that end of the sheath portion at which the lead wires protrude,
e. joining the contiguous ends of the sheath section and sheath portion,
f. filling the space between the element and sheath section with dielectric, refractory material,
g. securing closure means to the outer end of the sheath section,
h. swaging at least said sheath section to a smaller diameter following securement of the closure means,
i. removing said closure means,
j. removing some of the refractory material to expose a part of the element,
k. severing the element and trimming at least one of the cut ends thereof to provide a selected ohmic resistance for the element,
1. rejoining the ends of the element,
m. refilling the sheath section with refractory material to cover the element, and
n. reclosing the outer end of the sheath section.