US1728810A

US1728810A - Adjustable resistor unit for thermocouple circuits

Info

Publication number: US1728810A
Application number: US212350A
Authority: US
Inventors: Fernald S Stickney
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1927-08-11
Filing date: 1927-08-11
Publication date: 1929-09-17
Anticipated expiration: 1946-09-17

Description

2 Sheets-Sheet l F. S. STICKNEY Filed Aug. 11, 1927 ADJUSTABLE RESISTOR UNIT FOR THERMOCOUPLE CIRCUITS Sept. 17, 1929.

INVENTOR l rno/as. Sf/bKDQy ATTORNEY Sept. 17, 1929. F. s. STICKNEY 1,728,810 ADJUSTABLE RESISTOR UNIT FOR THERMOCOUPIJE cmcun's Filed Aug. 11, 1927 2 Sheets-Sheer.

INVENTOR r0 0/0 3 sflb/fney BY Z,

ATTORNEY Patented Sept. 17, 1929 UNITED STATES PATENT OFFICE FEBNALD HOUSE VANIA S. STICKNEY, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTING- ELECTRIC 8c MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- ADJ'USTABLE RESISTOR UNIT FOR THERMOCOUPLE CIRCUITS Application filed August 11,

My invention relates to adjustable resistor units and particularly to adjustable resistor units for thermo-couple circuits.

An object of my invention is to provide an adjustable resistor unit that shall be simple in construction, economical and easily-manufactured.

A further object of my invention is to provide an adjustable resistor unit for adjusting the resistance of a. plurality of thermocouple circuits that shall be compact and rugged.

In practicing my invention, I provide a plurality of thermo-couples, and an adjustable resistor unit for adjusting the resistance of the thermo-couple circuits. The resistor unit comprises a plurality of adjustable resistor elements for adjusting the resistance of each individual thermo-couple circuit to substantially equal values and a resistor element that is common to all of the thermofor adjusting the resistance of circuits to a predetermined fuller understanding of my couple circuits the respectlve value. For a invent-ion, reference may be had to the following description taken in conjunction with the accompanying drawings, in which Figure 1 is a schematic illustration of circuits and apparatus embodying my invention.

Fig. 2 is a top plan view of an adjustable resistor unit assembly comprising my in vention.

Fi 3 is a view in section taken on line IIIiIII of the same unit.

Fig. 4 is a top plan view of a movable contact member for the device illustrated in Figs. 2 and 3.

Fig. 5 is a view in side elevation of the contact member.

Fig. 6 is a view in section taken on line VI-VI of Fig. 2.

Fig. 7 is a view of a resistor element embodied in the device illustrated in Figs. 2 and 3, and

Fig. 8 is a partial View in section taken on line VII- VII of Fig. 2.

In Fig.1 of the drawings, a base 10 is illustrated thatiis provided with a plurality of terminals 11 and a plurality of terminals 1927. Serial No. 212,350.

12 to which

metallic conductors

13 and 14 may be connected. The

conductors

13 and 14 may be joined together in any well-known manner at 15 and 16 to thereby constitute the hot unctions of a plurality of thermo-couple circuits to be hereinafter set forth.

It is to be understood that the

conductors

13 and 14 may consist either of different metals or of different alloys, but for purposes of illustration, the conductors 13 may be considered as consisting of alloy A material and the conductors 14 of alloy B material. Likewise, the terminals 11 and 12 may be considered as consisting of alloys A and B, respectively.

In order that a single cold junction may be provided to accommodate all of the thermocouple circuits, the terminals 12 may each be connected to a single conductor 18 of alloy A material.

Each of the terminals 12 may be connected to one of a plurality of terminals 21 for a plurality of resistor elements 22 by conductors 23 of alloy B material. The other ends of the resistor elements 22 are each provided with terminals 24 that are connected one to each of a plurality of stationary contacts 25 to 30, inclusive, of a selector switch that is provided with a movable contact arm 31, one end of which is pivoted at 32 in order that the other end may selectively engage the contacts 25 to 30, inclusive.

The contact arm 32 is connected by a conductor 33 of alloy B material to a terminal 34 of an indicating instrument 35, and another terminal 36 of the instrument is connected by a conductor 37 of alloy B material to a terminal 38 of a resistor element 39. The other end of the resistor 39- is connected by a conductor 41 to a terminal 42 for a resistor element 43, the other end of the resistor element 43 being connected to a termilnal 44 therefor.

A conductor 45 of alloy B material is connected to the terminal 44 and to the conductor 18, of alloy A material, at 46, the jointure between the

conductors

45 and 18 46 constiquired, the contact 48 for be maintained either at a constant base temperature or that variations in cold junction temperature be compensated for. The latter may be accomplished by the device shown in my copending application, Serial No. 181,317, filed April 6, 192

In practice, the

conductors

13 and 14, leading from the hot junctions to the terminals 11 and 12, may be of unequal lengths because of the fact that the hot junction 15 may be located at a greater distance from the terminals than the hot junction 16. In order, therefore, that the resistance of each thermocouple circuit measured between the

terminals

34 and 36 of the instrument 35 may be adjusted to equal values, an adjustable contact member 48 is provided for each of the resistor elements 22. The resistance between these terminals may be determined by a potentiometer (not shown).

In order that the temperature of the hot junction of the respective thermo-eouples may be indicated directly, the instrument 35 is calibrated in terms of thermo-couple circuit having a resistance of a predetermined value. The instrument having been thus calibrated, the resistance of each thermocouple circuit is adjusted to the value for which the instrument is calibrated. This may be accomplished by providing the

resistor elements

39 and 43 with adjustable contact members 48 also. Since the

resistor elements

39 and 43 are connected in series between the

terminals

38 and 44, and since they are common to all of the thermo-couple circuits, the resistance of each of the thermocouple circuits may be adjusted to the clesired value simultaneously by adjusting the contact member 48 for the resistor 43 until the resistance as measured between the terminals of the instrument 35 is substantially equal to the desired value. It is to be understood that the resistor 43 is provided with relatively large resistance steps and that the

resistor elements

22 and 39 are provided with relatively small resistance steps.

For example, if the movable pointer 31 is in the position shown in Fig. 1 of the drawings, in which position the. temperature of the hot junction 15 may be determined, the contact 48 is adjusted until the resistance between the

terminals

34 and 36 is of substantially the value for which the instrument 35 is calibrated. If a finer adjustment is rethe resistor 39 is adjusted until the correct value of resistance is obtained, the resistor 39 being provided with relatively fine resistance steps as hereinbefore mentioned. Since the resistance of each of the thermo-couple circuits has first been adjusted to equal values, and since the

resistors

39 and 43 are common to all of the thermo-couple circuits, the resistance of each thermo-couple circuit Will be equal to that value for which the instrument is calibrated when the resistance of the thermo-couple circuit, in which the hot unction 15 is included, for example, has been adjusted to the above value.

In Figs. 2 to 8, inclusive, a preferred embodiment of an encased adjustable resistor unit, comprising the

resistor elements

22, 39 and 43, the

terminals

21, 24, 38, 42 and 44 and the contacts 48, as illustrated in detail.

The

terminals

21, 24, 38, 42 and 44 are mounted on a base 51 of electric insulating material and extend therethrough from the top to the bottom sides thereof in order that electrical connections may be made thereto from the upper and lower sides of the base.

A supporting member 52 of substantially rectangular shape is provided for the

resistor elements

22, 39 and 43 that is supported on the base in spaced relation therewith by'tubular bushings 53 located in close proximity to the corners of the support The support and the bushings may be held firmly in place by bolts 54, that extend through the bushings and the base, and. nuts 55.

The support 52 may be enclosed by an open-ended casing member 57 of insulating material having side and

end walls

58 and 59, respectively. i

The support 52 is provided with a plurality of spaced slots 61 that extend transversely of the support. Each of the slots are substantially bounded by a plurality of spaced openings 62 through which the resistor elements 22 may be threaded or woven, the ends of the resistor elements being electrically connected to terminal screws 63 and 64, respectively. The screws 63 and 64 are connected to the

terminals

21 and 24, respec tivcly, by conductors 65 and 66, of alloy A material, the

terminals

21 and 24 being located at opposite sides of the base 51 substantially as shown in Fig. 1.

As shown in Fig. 2. each successive pair of openings 62 are bridged by portions 68 oi the resistor elements 22. The elements 22 each comprise an uncoilcd conductor (see Fig. '7.) of alloy B material having relatively high ohmic resistance per unit length. But as the length of the conductor included between the portions 68 is relatively short, the resistance thereof is relatively small. Thus, the resistance between the terminals to which the screws 63 and, 64 are connected may be varied in relatively small steps by means of the contact 48. I

As illustrated in Fig. 2, the contact 48 is adapted to selectively engage one portion 68 of the resistor element and the portion 71 thereof that extends along the top edge of the support 52 from the openings 61 at 72 to the screws 64. It is to be seen from the drawings that the closer the contact 48 is to the point 72 of the resistor elements, the greater is the resistance included between the

terminals

21 and 24.

The resistor element 39 is substantially similar to the resistor elements 22 and is threaded through the openings 62 in the base in substantially the same manner. One end of the resistor 39 is connected to a screw 73, which, in turn, is connected to the terminal 38. The other end of the resistor 39 is connected to a screw 74, which, in turn, is connected to a terminal screw for the resistor element 43 by a conductor 76.

The resistor element 43 (see Figs. 3 and 8) consists preferably of a continuous coiled conductor of alloy B material. One end of this resistor is connected to the screw 75 and the other end to a return conductor 77 at 78, the opposite end of he return conductor being connected to a terminal screw 7 9. The terminal screw 75 for the resistor element 43 is connected to the terminal 42 bv a conductor 81 of alloy B material and the terini nal 79 is connected to the terminal 44 by a conductor 82 also of alloy B material.

In order that the coiled resistor element 43 may be divided into a plurality of resistance steps, portions thereof are uncoiled and twisted around a conductor 84 to form a pig-tail connection therewith. The conductors 84 extend downwardly through the openings 62 in the support 52 (see Fig. 8) and the ends thereof are twisted together on the bottom side of the support. Each electrical connection thus made may be soldered or brazed to ensure that the connection will be strong and rugged.

Since the portion between the pig-tail connections are relatively long, the resistance between the

terminals

42 and 44 may be varied in relatively large steps by means of the contact 48.

The contact 48 is illustrated more particularly in detail in Figs. 4 and 5. The contact 48 comprises a member 86, made in the form of a cross from a blank of suitable metallic material. portions 87 theerof being bent downwardly at 88.

When the contact 48 is located in the slots 61, the portions 87 extend below the support 52 and portions 89 thereof extend transversely of the slot in order that electrical connection may be made between the

portions

68 and 71 of the resistor elements 22 simultaneously. It is evident that the portions 87 prevent the contacts 48 from turning in the slots 61.

If the contact member 48 has been moved to such a position that the resistance of the thermo-couple circuit to be adjusted thereby is of the desired value, the contact may be secured or fastened in place by means of a screw 91 and a nut 92 located on the bottom side of the support 52. The nut 92 extends transversely of the slots 61.

lVhen the resistance of the thermo-couple circuits, in which the hot junctions 1.5 and 16 are included, have been adjusted to equal values by the resistor elements 22, the contacts 48 are fastened in place as hereinbefore set forth. The resistance adjustment accomplished by the elements 22 may be designated as the fine resistance adjustment. When this adjustment has been completed, the resistance of the thermo-couple circuits must be adjusted tothe value for which the instrument 35 is calibrated. This value is substantially approximated. by adjusting the resistor elements 43 until the resistance of one thermocouple circuit, exclusive of the resistance of the instrument, for example, the circuit comprising the hot junction 15, the contact 25 of the selector switch, the

terminals

35 and 36, and the cold junction 46, is approximately the resistance for which the instrument is calibrated. he exact value of resistance may then be adjusted by moving the contact 43 to such a position that the desired resistance of the element 39 is included in the thermocouple circuit. Since the resistors and 39 are common to all of the thermo-couple circuits, the resistance adjustments herein described will adjust all of the thermo-couple circuits to the desired value simultaneously.

When all of the thermo-couple circuits have been adjusted to the proper value, a cover 94 may be secured to the top edge of the casing 57 by means of the bolts 54 and nuts 95, thereby totally enclosing the resistor elements and the contacts associated therewith.

Various modifications may be made in the device embodying my invention without departing from the spirit and the scope thereof. I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and the appended claims.

I claim as my invention:

1. An adjustable resistor unit comprising plate of electric-insulating material having a plurality of spaced and parallel-extending slots therein, and a plurality of spaced openings closely adjacent to, and parallel with, each of said slots at one side thereof, a resistor supported by, and secured to, the plate by means of said openings, a contact member slidably disposed in each of said slots for engaging portions of the resistor, and means con'iprising conductors supported. by said plate and located at the other sides of the respective slots for connecting said resistor to said contact member independently of the position of said contact member.

2. An adjustable resistor unit comprising a plate having an elongated slot therein, a plurality of spaced openings closely adjecent to, and extending parallel with, the slot at one side thereof, a resistor supported by the plate and having portions extending through adjacent pairs of openings to constitute contact portions on one side of the plate, a conductor supported. by the plate closely adjacent to the other side of the slot, a contact