US355281A - Metallic thermometer - Google Patents

Description

(NbModeL) I a. B. ST.-JOHN METALLIC THERMOME TER. 7

No. 355,281; Patented Dec. 28, 188

UNITED STATES PATENT OFFI E.

GEORGE B. ST. JOHN, OF BOSTON, MASSACHUSETTS.

METALLIC THERMOMETER.

I SPECIFICATION forming part of Letters Patent No. 355,281, dated December 28, 1886.

(No model.)

' To all whom it may concerrt:

Be it known that I, GEORGE B. ST. JOHN, of Boston, county of Suffolk, State of Massachusetts, have invented an Improvement in Thermometers, of which the following description, in connection with the accompanying drawings, is a specification, like letters on the drawings representing like parts.

My invention relates to'a thermometer of that class in which a hand or pointer is rotated by the movement caused by the unequal expansion of the different parts of a helix composed of metals having different rates of expansionby heat.

The invention has for its object to enable the parts to be readily adjusted to give the correct indications of temperature; and it consists in the combination and arrangement of parts, substantially as hereinafter particularly set forthand claimed. I

In the accompanying drawings, illustrating the invention, Figure l is a front elevation; Fig. 2, a side elevation on a larger scale, the dial being broken off at each end. Fig. 3 is a top plan View of parts at the left-hand end of Fig. 2; and Fig. atis a rear elevation of the' parts at the right-hand end-of Fig. 2.

The operative parts are supported in a frameplate, a, connected with the dial I), graduated to co-operate with a hand or pointer, 0, fastened upon an arbor, cl, which passes through the plate a, and has a pivotal bearing on an arm or bracket, 6, connected with the said plate- The said arbor d is provided with a pinion, f, meshing with a segmental gear, 9, the arbor g of which has pivotal bearings in the bracket 6 and another bracket, 0, mounted on the frame a. The segmental gear 9 is provided with an arm or projection, h, which has securely attached to it one end of the spiral ribbon or expansion-helix t, composed of outer and inner layers of metals, alloys, or their known equivalents, having different ratesof expansion by heat, so that the expansion or contraction of the said materials produced by a change in their temperature will produce a rotary movement of one end of the coil relative to the other in the Well-known manner. In order that such rotary movement may produce a movement of the pointer c, it is necessary that the opposite end of the helix 2' to the one connected with the arm hand gear 9 should be rigidly held with relation to the frame-work a.

In order to enable the position of the helix ito be varied and adjusted quickly, as well as 5 5 the length of the effective portion between the two points of attachment of its ends, it is adjustably connected with an attachingarm, it, having a stud, k, fitted to move freely in a socket of a post, m, fixed upon the plate a, the 5 saidstud and attaching-arm being rigidly held in any desired position in the post at by means of a setscrew, 0, or equivalent, preferably operated from the face of the dial.

In putting together the thermometer, which 5 is intended to be manufactured in quantities, the end of the helixt is passed through a slot in the arm is, and made fast by a locking device or set-screw, p. The thermometer is then permitted to come to a definite known tem- 73 perature-as, for example, by immersing it in melting snow or iceand the hand a is then. turned to the proper graduation of the dial for instance, 32, if the graduation is in accordance with the Fahrenheit scale. The setscrew 0 is left loose while this operation is taking place, so as to permit the arm to turn freely, keeping the helix 4. perfectly free or without strain while the pointer is being thus set, after which the set-screw 0 is tightened, thus locking the arm is and fixing the point of attachment of the stationary end of the helix The thermometer will next be subjected to another known temperature, and the rotary movement of the end of the helix attached to the arm h, with relation to the stationaryend fastened to the arm It, will cause the pointer to turn. If the pointer arrives at the proper graduation for the known temperature, it will be understood that the thermometer is in adjustment; but if the said pointer does not move exactly the proper distance, it will be understood that the helix is too long or too short, and the proper adjustment will be made by loosening the set-screw p and taking up or lengthening the said helix, as may be required. This change in length of the helix will necessitate the readjustment of its position, which may be readily effected by loosening the setscrew 0 and turning the pointer to the proper place, after which the set-screw 0 is again tightened and the thermometer tested by another change in temperature'to see if the helix has been made of the proper length.

ICO

It is immaterial at which end of the helix the adjustment of its length is made, and by the said adjustment it is possible to make the dials of a series' of instruments all uniform, and the helices and other parts as nearly uniform as possible, the said adjustment in length of the helix being sufficient to compensate for the unavoidable inequality in the said helices, which has heretofore necessitated an especial graduation for the dial of each individual thermometer.

By having the entire helix movable before its end is finally locked or made stationary with relation to the plate, the inconvenience of disengaging the gearingf and g, or of moving the pointer on its arbor, is avoided, and the thermometers, the parts of which are made in quantities, can be readily and quickly assembled and adjusted with great accuracy.

By arranging the helix longitudinally parallel with the dial, there is an economy of space, and the parts are made very accessible.

I claim- 1. The graduated scale, the pointertherefor, a pinion on the arbor of such pointer, and a segmental gear meshing with said pinion,

and provided with an arm supported on a rock-shaft, combined with an expansion-helix attached to said arm at one end, and supported in adjustable bearings at its other end to vary 3o itsefi'ective length and, axial position, substantially as described.

2. The expansion-helix, and pointer actuated thereby, combined with the dial and the attaching-arm for the said helix, provided 5 with a stud having a pivotal movement, and a set-screw therefor operated from the face of the dial, substantially as described.

3. The combination, with the graduated dial and its pointer, of the helix longitudio nally parallel with the dial, the adjustable hearing at one end, and the gearing connect ing the helix and pointer at the other, substant-ially as shown and described.

' In testimony whereof I have signed my 5 name to this specification in the presence of two subscribing witnesses.

GEORGE E. ST. JOHN.

Witnesses:

J os. P. LIVERMORE, W. H. Sresrron.

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