US2654818A - Resistance thermometer - Google Patents

Description

Oct. 6, 1953 c. c. WHITEHEAD RESISTANCE THERMOMETER 2 Sheets-Sheet 1 Filed Feb. 15, 1952 FIG. 4

FIG. 2

' INVENTOR.

CYRIL C. WHlTEHEAD B g/Win40.

ORNEY Oct. 6, 1953 c. c. WHITEHEAD RESISTANCE THERMOMETER 2 Sheets-Sheet 2 Filed Feb. 15, 1952 INVENTOR. CYRIL '0 WHITEHEAD Patented Oct. 6, 1953 RESISTANCE THERMOMETER Cyril C. Whitehead, Croydon, England, assignor to Bailey Meter Company, Cleveland, Ohio, a

corporation of Delaware Application February 15, 1952, Serial No. 271,714 In Great Britain February 20, 1951 8 Claims. 1

This invention relates to resistance thermometers, an object being the provision of improved resistance thermometer resistance elements capable of responding rapidly to changes in temperature.

The present invention includes a resistance thermometer resistance element comprising a metal sheath in the form of a tube longitudinally split or apertured and having spaced inner and outer walls and a winding formed of a wire resistance extending between a radially inner sheet and a radially outer sheet of insulating material which are sandwiched between the walls and of which the radially outer sheet is in good thermal conduction relationship with the outer wall of the tube.

The invention also includes a resistance thermometer with a tubular pocket having in the pocket a resistance element as mentioned in the preceding paragraph of which the sheath is in stressed condition tending to Dress the outer face of the sheath against the inner face of the pocket.

The invention moreover includes the method of forming a resistance thermometer resistance element for engagement with the inner surface of a tubular pocket which comprises forming an elongated resistance into a windin supported by a sheet of insulating material, applying covering metal over each side of the sheet with the interposition of insulating material between the resistance and. the covering metal, bending the said sheet of insulating material and the covering metal into arcuate form, and forming of the covering metal a sheath of metal in the form of a tube longitudinally split or apertured.

The invention also includes the method of forming a resistance thermometer resistance element for engagement with the inner surface of a tubular pocket which comprises serrating opposite edges of a sheet of insulating material, winding a wire resistance to and fro across one face of the sheet with the return bends looped over the serrations, covering the said face with a second sheet of insulating material, covering the parts of the resistance behind the serrations with insulating material, covering the sheets of insulating material with sheets of metal, bending the sheets of insulating material and the sheets of metal into arcuate form, and forming of the sheets of metal a sheath of metal in the form of a tube longitudinally split or apertured.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a a flat mica sheet wound with resistance wire;

Figures 2 and 3 show an assembly of a wound mica sheet, an insulating mica sheet on either side thereof, and metal sheets adapted for forming a metal sheath therearound, Figure 3 being a sectional view on the line III-III of Figure 2;

Figure 4 is a sectional view through the pocket of a resistance thermometer showing the completed resistance element in the form of a tube longitudinally split or apertured, in place in the pocket;

Figure 5 is a perspective view of an end of the resistance element and adjacent part of a ceramic tube housing electric leads for the resistance element, part of the metal sheath and of an insulating mica sheet being removed to show the internal arrangement; and

Figure 6 shows a resistance thermometer, the pocket thereof being shown in section on the longitudinal axis thereof, but the resistance element therein being shown in outside view.

Referring to the drawings, the resistance element of a resistance thermometer consists of a length of platinum wire I supported in looped lay-out on a mica sheet 2 largely enclosed in a metal sheath 3, the wire being separated from the sheath by further mica sheets 4 and 5, one on each side of the mica sheet 2.

The mica sheet 2 is rectangular. The end edges are serrated by forming triangular notches 6 therein and the wire I is wound on the mica sheet 2 so that it extends to and fro over one face of the sheet longitudinally thereof between the serrated edges of the sheet, with the return bends looped over serrations so as to extend from the apex of one notch to the apex of an adjacent notch. Extending along each longitudinal edge of the sheet is a terminal member for leading current to or from the wire, consisting of a copper strip 1 or 8 bent to embrace the edge portion of the sheet and secured to the sheet by piercing at a number of locations through the two arms of the strip and intermediate mica sheet so that the metal of the strip is slightly displaced in the direction of piercing. The copper strips 1 and 8 extend at their one ends 9 and I0 respectively beyond the mica sheet 2. The winding can be effected so as to accommodate different lengths of wire by winding the wire on more or fewer serrations and by leading the wire from the apex of the last notch to any desired position along the length of the appropriate terminal strip 1 or 8, to which the end of the Wire is secured in good electrical contact, e. g. by welding.

Each of the further mica sheets 4 and 5 is both longer and wider than the mica sheet 2.

In forming the resistance element, the mica sheets 4 and 5 are placed covering the faces of the mica sheet 2 and extending beyond the edges of the sheet, and metal sheets II and i2, formed of an alloy which retains elasticity at elevated temperatures, e. g. that known as Inconel, or Monel, or certain nickel steel alloys, are placed covering the mica sheets 4 and 5 respectively; the metal sheets II and I2 are in turn longer and wider than the mica sheets 4 and 5 and are placed so as to overlap the edges of the latter. Thus the assembly shown in Figures 2 and 3 is provided. The metal sheets II and I2 are of the same size and are adapted to form the inner and outer walls of the metal sheath 3. At one end of each of the metal sheets l2 and II the edge portion is cut back at [3 adjacent one side edge and at l4 adjacent the other side edge so that the ends 9 and H) of the copper strips '1 and 8 respectively may project beyond the metal sheets in a manner facilitating the attachment of leads thereto; the mica sheets d and 5 adjacent the positions 13 and I4 project, beyond the metal sheets H and IE to preserve the insulation between the copper strips 1 and 8 and the metal sheets.

The assembly of the wound mica sheet 2, mica sheets 4 and 5, and metal sheets i and H is bent on a former into the form of a tube of axis parallel to the longitudinal edges of the metal sheets, the sense of the bending being such that the face of the mica sheet 2 over which the wire I extends becomes the outer face of the mica sheet 2.

Thus the resistance wire now extends between the mica sheet 2 on its radially inner side and the mica sheet 4 on its radially outer side, which are sandwiched between the metal sheet ll on the radially outer side and the metal sheet 12 on the radially inner side, the interposed mica sheet acting to insulate the return bends of the wire from the metal sheet I2.

The side edge portions iii of the metal sheet I l and the adjacent side edge portions l6 of the metal sheet l2 are bent inwardly of the tube, and the end edge ll of the metal sheet H between the positions 13 and M is secured preferably by hard-soldering, e. g. by silver-soldering to the corresponding portion of the adjacent end edge 58 of the metal sheet I2, while the other 7 end edge is of the metal sheet I! except adjacent the side edge portions [5 is similarly secured to the corresponding portion of the adjacent other end edge of the metal sheet l2, to form the metal sheath 3, the sheet II forming the outer, and, the sheet I2 the inner wall thereof.

Preferably the bending of the metal sheets during the formation of the sheath is such that the circumferentially extending parts of the sheath tend to give the outer face of the sheath a curvature less than the curvature of the inner face of the resistance thermometer pocket for which the resistance element is intended, so that the said outer face, when the resistance element is in position is pressed against the said inner face by the stressed condition of the sheath. The inwardly bent side edge portions of the sheath, consisting of the side edge portions 15 and I6, are arranged to press upon one another when the resistance element is in position in the pocket of the resistance thermometer for which it is designed, so that insertion of the resistance element in the pocket stresses the sheath by pressing the said edge portions against one an- 4 other so that the outer face of the sheath is pressed against the inner face of the pocket.

The resistance element for insertion within the flange pocket 25 (also known as the well or bulb) of the resistance thermometer shown in Figure 6, is attached to a ceramic tube 26 by means of three arms 2! of which the one ends are secured, e. g. by hard-soldering to the inner metal sheet E2 of the metallic sheath while the other ends are gripped between the ceramic tube 26 and'a tightenable collar 28. The ceramic tube 26 is the end section adjacent the resistance element of sectionalised ceramic tubing 29 extending from the head 30 of the resistance thermometer through an extension piece 3| and alon the pocket 25 to the resistance element at the end of the pocket; the ceramic tubing is formed with three longitudinal passages for electric leads to the resistance element, of which the ends of two leads are connected to one of the contact strips 8 (the connection of two leads to' one terminal being a known measure employed for purposes of compensation) while the end of the third lead is connected to the other end of the contact strips 1. Mica discs 32 threaded on the leads at the junctions of sections of the ceramic tubing keep the tubing spaced from the walls of the pocket, extension piece, and head. In Figure 6 the showing at 33 of part of the wall of a pipe containing a stream of flowing fluid of which the temperature is to be ascertained illustrates the projection of the pocket containing the resistance element into the said stream.

The resistance element shown in the drawings is adapted for a resistance thermometer of which the pocket is of internal diameter. The thicknesses of the mica sheets 2, 4, and 5 and of the metal plates H and I2, which latter may be of the order of .005", and the diameter of the resistance wire I are shown much exaggerated to improve the representation of these items in the various figures.

During operation, rapid response to temperature changes is obtained, since the heat absorbing capacity of the resistance element is small, the Whole of the radially outer surface of the tubular sheath is maintained in effective heatconducting relationship with the inner surface of the pocket and the platinum wire resistance is located in close proximity to the wall of the pocket.

The ballast resistance, separate from the element, often provided in a resistance thermometer to compensate for differences between the desired and the actual resistance of the resistance wire may not be necessary, since the elongated termina1 members i and 8 permit of the accommodation on the mica sheet 2 of resistance wire of which the length is adjusted to a sufficient degree of nicety.

What I claim as my invention and desire to secure by Letters Patent of the United States, is:

1. The method of forming a resistance thermometer resistance element for engagement with the inner surface of a tubular pocket which comprises, serrating opposite edges of a first sheet of insulating material, winding a wire resistance to and fro across one face of the first sheet with the return bends looped over the serrations, providing an elongated terminal member along an unserrated edge of the first sheet, adjusting the length of wire at an end thereof to give a desired resistance, connecting the end of the wire to the terminal member at an appropriate point in the length thereof, covering the face of the first sheet with a second sheet of insulating material, covering the parts of the resistance behind the serrations with insulating material, covering the sheets of insulating material with sheets of metal, bending the sheets of insulating material and the sheets of metal into arcuate form, and forming of the sheets of metal a sheath of metal in the form of a tube longitudinally split or apertured.

2. The method of forming a resistance thermometer resistance element as claimed in claim 1, which comprises providing an elongated ter minal member along each unserrated edge of the first sheet and bending the sheets and sheath so that the terminal members extend longitudinally of the tube.

3. A resistance thermometer element including, a sheet of non-conducting material serrated on two opposite edges, a resistance wire looped over the serrations for its support on one face of the sheet, a sheet of insulating material on each side of the sheet supporting the resistance wire, an elongated terminal member secured to an unserrated edge of the sheet of non-conducting material and connected to the resistance wire at a point which will give a desired resistance value to the active length of the wire, and a sheet of metal on each of the outsides of the two sheets of insulating material, the metal sheets being bent into arcuate form to give a sheath of metal in the form of a tube longitudinally split or apertured.

4. The resistance thermometer element of claim 3 including, an elongated terminal member along each unserrated edge of the first sheet.

5. A resistance thermometer element including; a tubular body formed of a series of sheets including; a central insulating sheet supporting a resistance wire sensitive to temperature by reason of the wire being looped in serrations at opposite sides of the sheets, each of a pair of insulating sheets on either side of the supporting sheet, a pair of metallic sheets external to the insulating sheets bent to the tubular body form in a stressed condition; elongated terminal members along opposite unserrated sides of the central insulating sheet for connection to the ends of the resistance wire; and a base structure for supporting the tubular body in association with a variable temperature condition.

6. The element of claim 5 wherein the pair of insulating sheets are large enough to cover the wire supporting sheet and its terminals and the pair of metallic sheets are large enough to cover the pair of insulating sheets and longitudinal edges of the metallic sheets are bent inwardly of the tubular body so they will bear upon one another.

7. The element of claim 6 wherein the base structure includes a protecting metallic well in which the tubular body is retained in a stressed condition so the outer metallic sheet will press against the inner wall of the well.

8. A resistance thermometer element assembly comprising in combination, a rectangular fiat strip of insulating material, a resistance wire supported upon said strip, protecting strips of insulating material covering the flat sides of the supporting strip, and metallic strips on the outside of the protecting strips of insulating material secured to each other at their elongated edges which are bent inwardly of the tubular body into which they are formed to an arcuate crosssection, the bent longitudinal edges bearing upon one another.

CYRIL C. WHITEHEAD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,282,441 Whitlock May 12, 1942 2,540,963 Rutherford Aug. 6, 1951 2,588,014 Knudsen Mar. 4, 1952

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