US2720187A

US2720187A - Zero corrector for sealed instruments

Info

Publication number: US2720187A
Application number: US346473A
Authority: US
Inventors: Francis X Lamb
Original assignee: Weston Electric Instrument Corp
Current assignee: Weston Electric Instrument Corp
Priority date: 1953-04-02
Filing date: 1953-04-02
Publication date: 1955-10-11
Anticipated expiration: 1972-10-11

Description

Oct. 11, 1955 F. x. LAMB 2,720,187

ZERO CORRECTOR FOR SEALED INSTRUMENTS Filed April 2, 1953 FHA/V05 X. LAMB INVENTOR.

United States Patent ZERO CORRECTOR FOR SEALED INSTRUMENTS Francis X. Lamb, East Orange, N. 1., assignor to Weston Electrical Instrument Corporation, Newark, N. J., a corporation of New Jersey Application April 2, 1953, Serial No. 346,473

10 Claims. (Cl. 116129) This application is a continuation-in-part of my pending United States application Serial No. 213,433, filed March 1, 1951, and entitled Zero Corrector For Sealed Instruments.

Although the invention described herein is adapted to numerous specific applications wherein mechanical motion must be introduced from an external source into a sealed mechanism without impairing the seal, I shall limit the description to a zero adjuster used on an electrical indicating instrument.

It is desirable that electrical instruments, especially those in which the mechanism is quite delicate, be sealed effectively so that the mechanism is not affected adversely by humidity changes, deleterious chemicals, gases or dust, or etc. At the same time it is desirable and, in fact, often necessary, that some means be provided to permit adjustment of the mechanical zero position of the indicating pointer, by the user, without destroying the sealed character of the instrument case.

Various proposals, have been made for providing a zero-adjuster arrangement on sealed instruments. While such prior proposals accomplish the desired purpose they are,,in general, costly to produce and/or require the use of a special tool for the zero-adjusting operation. In either case, such prior constructions have not found wide use in the electrical instrument class.

An object of this invention is the provision of a simple motion transmitter for sealed instruments, which transmitter does not require the use of a special tool and which is effective to prevent the passage of air, dust and moisture into the instrument.

An object of this invention is the provision of a sealed motion transmitter for electrical instruments, or the like, wherein the sealing member comprises a pressure-loaded element of resilient material.

An object of this invention is the provision of a zero adjuster for sealed instruments and comprising a rotatable head accessible from the exterior of the instrument case, an insulating member within the case, a compressible member disposedbetween the insulating member and the case wall, and means securing together the said head and the insulating member in such manner that the compres sible member is subjected to pressure-deformation.

An object of this invention is the provision of a sealed zero adjuster for electrical instruments comprising a rotatable member extending through a wall of the instrument, an insulator member abutting against the opposite surface of the wall and having an axial shaft extending at least partially through such wall, a recess in the wall, a resilient washer disposed Within the recess, and means securing the rotatable member to the shaft in such manner that the washer issubjected to compressive pressure within the recess.

These and otherobjects and advantages will be apparent from the following description when taken with the accompanying drawings illustrating several embodiments of the invention. The drawings are for purposes of illustration and are not to be construed as defining the 2,720,187 Patented Oct. 11, 1955 scope or limits of the invention, reference being bad for the latter purpose to the appended claims.

In the drawings wherein like reference characters denote like parts in the several views:

Figure l is a top plan view of one type of instrument embodying the invention;

Figure 2 is essentially a cross sectional view taken through the zero adjuster and drawn to an enlarged scale;

Figure 3 is an exploded view of the Figure 2 assembly;

Figure 4 is similar to Figure 2 and showing another embodiment of the invention.

Figure 5 is a similar view of another embodiment of the invention;

Figure 6 is a front view of the rotary member shown in Figure 5 which member is disposed-against the inner surface of the instrument cover;

Figure 7 is a cross-sectional view showing another embodiment of the invention; and

Figure 8 is a similar view of still another embodiment of the invention.

Referring now ot Figure 1, there is shown a conventional electrical instrument of the permanent magnetmovable coil type that includes a magnet .10 having pole pieces 11, 12 between which is mounted a movable coil 13 that rotates through an angle which varies with the magnitude of current flowing in the coil. The coil is carried by axially-aligned shafts rotatable in adjustable jewel bearings. In the interest of simplifying the drawing, only the upper bearing 14 is shown. A pointer 15, affixed to the movable coil, moves over a calibrated scale 16 on the scale plate 17. Spiral springs, such as the spring 18, provide the mechanical torque to return the pointer to its zero position relative to the scale when current is not flowing in the coil, as is well known in this art.

The above-described mechanism is conventional and is mounted within an enclosing casing 20, made of metal or plastic, that is closed at the upper end by a transparent cover 21 hermetically sealed to the rim of the casing. It may here be pointed out that studs by which current is conducted to the movable coil, generally pass through the bottom of the casing, such studs likewise being of approved hermetically-sealed construction.

For numerous reasons, understood by those skilled in this art, it is sometimes necessary or desirable to correct the normal zero position of the instrument pointer. This is done by rotating a slotted screw 25 that is part of an assembly having a pin passing within the abutment 26 that is rotatable about the movable coil axis and connected to one end of the return spring 18.

Figure 2, which is a central cross sectional view through the zero-adjusting device, illustrates my novel pressure sealed construction, whereby the position of the pointer may be altered, externally of the instrument, without disturbing the hermetical sealing of the casing. The transparent cover 21, shown as a plastic, preferable is provided with a circular bore, or recess, in the inner surface, such recess having sections of two different diameters, as shown more clearly in Figure 3. The small diameter recess accommodates the axial shaft 30 of the metallic member 31 and the large diameter recess accommodates a resilient washer 32, made of rubber or other pressuredeformable material. The dimensions of the member 32 are such that it is freely insertable within the cover recess prior to the final assembly of the zero adjuster mechanism. It will be noted the member 31 has an integral, headed extension 33. Part, or all, of the surfaces of this extension are roughened, as by knurling, so that when it is molded directly into the plastic disc 34 such disc and the metal member 31 will form a strong unit.

In assembling the components of my zero adjuster the resilient disc 32 is placed into the recess of the cover 3 21 and the shaft 30 of the metallic member 31 is inserted through the disc opening and into the small diameter recess. The slotted member 25' is provided with a longitudinally-knurled, rather than threaded, shank which is forced into the axial bore 35 in the shaft 30. By means of a suitable tool, suchas an arbor press, opposed pressures are applied to the head of the member 25' and to the plastic disc 34 to deform the resilient washer 32 a predetermined amount. Such resilient washer, having its flat surface confined by the recess base and the member 31, will be deformed such that it will come into surface contact with all walls defining the resulting cavity between the member 31 (and its shank 30) and the plastic cover 21. When once assembled the resilient washer remains pressure loaded by reason of the gripping action between the knurled shank of the slotted member and the inner wall of the bore in the shank 30.

I have found that such pressure loading of the resilient. washer serves asan effective and entirely satisfactory hermetical seal while permitting rotation of the entire assembly by a screwdriver inserted into the slot of the external head. As is apparent, the insulator member 34 includes an integral pin 39 which is adapted. to. fit within the abutment 26, shown in Figure 1, whereby rotation of the slottedhead imparts a corresponding rotation tosuch abutment to alter'the position of. the pointer.

Figure 4' illustrates another embodiment of the invention wherein; the shank of the metallic member 31 extends through the cover 21'. In this case the slotted head 36 is provided with an axial bore 37 to receive the shank end of the member 31. It will be seen that the insulator member 34' and the head 36 can be. pressed together to apply a predetermined perssurev on the resilient washer 32" andthe parts locked in such position by a pin 38 that passes through aligned, transverse holes in the shank of the member 31" and' the head 36. In order to obviate the need for maintaining close tolerances, the transverse holes through the head 36 and the shank of the member 31 may be drilled as a single operation while the parts are restrained under proper pressure.

To facilitate rotation of the zero adjuster mechanism some or all of those surfaces subject to relative movement during rotation ofthe slotted screw, or head, may be given a light coating of a suitable lubricant.

In the Figure embodiment of the invention the internal member of the device comprises a single disc 40, made of a suitable insulating material having good mechanical strength, having an integral extension that includes an axial bore therein. The longitudinally-knurled shank of the headed member 25' is force fitted into such bore a proper distance to subject the resilient, washer, 32 to a predetermined pressure, deformation. As. shown in Figure 6', the member 40 includes radial slots 41. extending from a central recess, 42, such slots. adapted to. en-

gage, the. abutments. of the instrument mechanism, as is.

well known in. the instrument art,

Figure 7 illustrates. another embodiment of my inventi'on which is somewhat similar to the construction illustrated' in Figures. 2 and 3.. Here the hole in the cover member 21' terminates in a single, enlarged-diameter bore in the inner surface of the. cover. The body of the. metallic member 45 is encased, substantially, inthe insulator mem: ber 46', as by molding, said metallic member including the knurled portions 47 to form a strong unit. The. slotted stud 48 has a shank passing through the hole in the cover member and into an axial. hole in the, shank of the metallic member 45. The diameter of the, stud shank is. somewhat larger than that of, the. associated hole in. the shank of the member 45 whereby these parts must be forced together and when once assembled the resilient washer 32 will remain, pressure-loaded within the. bore in, the cover.

Figure 8. illustrates a modification. of theFigure 7 constructi'on, Herethemetallicmember 451' does. not include a. shank andv the, shank of the slotted stud 4.8,." is forced.

directly into a hole in the body of the member 45. It will beapparent that in this construction the hole in the cover member 21 can be of a smaller diameter than that required in the construction shown in Figure 7.

While the constructions illustrated in Figures 7 and 8 show an eccentric, integral pin 49 for transmitting rotary motion of the zero adjuster to. the instrument movable coil, or other member, disposed within the instrument casing, it will be apparent that such pin may be replaced by a slotted type of coupling arrangement as described with reference to Figures 5. and; 6.

Aside from the simple construction of the parts and the assembly thereof and the retention of the hermetical sealing of the instrument, an important feature of my invention is the complete electrical isolation of the externally-accessible zero adjuster head from the instrument mechanism by means of the insulator members. There is no difliculty in providing such assembly to meet. an A C. voltage breakdown test of several thousand volts.

Having now described my invention in detail in accordance with the patent statutes, various changes and modifications will suggest themselves to those skilled in this art. It will be apparent the member disposed inside the instrument casing, and rotatable upon rotation of the external, slotted head, may take a variety of specific forms to provide a proper engagement between such member and the part to be rotated or adjusted. For example, such member may carry a suitable arm for engaging the movable contact of a magnetic contact type relay whereby the relay contacts may be separated externally of the relay casing; Also, the specific form of the external portion of the headed member is a matter of design choice and may take the form of a hexagonal head, a knurled knob for finger operation or etc. It is intended that such changes andmodifications shall fall within the spirit and scope of the invention as recited in the following claims.

I claim:

1'. An arrangement for' adjusting the position of a movable element disposed within a casing said arrangement comprising a cover having a hole therein which terminates in an enlarged-diameter bore in the inner surface of the cover, a resilient washer disposed within the said bore and in full surface contact with the wall defining the base of the bore, a clamping member in fiush contact with the washer said member including an axial bore and engaging means for mechanically coupling the member to the movable element, and a stud having a head abutting the outer surface of the cover and a shank passing into the axial bore in the clamping member.

2. The invention as recited in claim 1, wherein the stud shank is force fitted into the axial bore in the clamping member, and the said engaging means comprises an eccentricv pin extending from the clamping member.

3'. An arrangement for adjusting the position of a movable element disposed within a casing said arrangement comprising a cover having a hole therein which terminates in an enlarged-diameter bore in the inner surface of the cover, a resilient washer disposed within the said bore, a metallic member including a shoulder abutting the washer and a shank having an axial bore therein and passing through the washer, an insulator member secured to the metallic member and including engaging means for mechanically coupling the insulator member to the movable element, and a stud having a head abutting the outer surface. of the cover and a shank passing through the cover hole and into the axial bore in. the: shank of the metallic member.

4. The invention as recited in claim 3, wherein the said insulator member is molded on to the said metallicmember and includes a fiat portion abutting the said. Washer.

5. The invention as recited in claim 4, wherein the said engaging means comprises an eccentric pin extending from. the said insulator member.

6. An. arrangement. for adjusting the position. of a movable element disposed within a casingsaid arrangement.

comprising a cover having a hole therein which terminates in an enlarged-diameter bore in the inner surface of the cover; a resilient washer disposed within the said bore; a clamping member comprising a metallic member molded in an insulator member, said metallic and insulator members including contiguous, mono-planar surfaces abutting the washer and said insulator member including engaging means for mechanically coupling such member to the movable element; and a metallic stud having a head abutting the outer surface of the cover and a shank passing through the cover hole and the washer and into a bore in the said metallic member.

7. An arrangement for adjusting the position of a movable element disposed within a casing, said arrangement comprising a cover having a small diameter hole extending in from the outer surface of the cover, an intermediatediameter bore communicating with the said hole and with an enlarged-diameter bore formed in the inner surface of the cover, a resilient washer disposed within the enlargeddiameter bore, a metallic member including a shoulder abutting the washer and a shank having an axial bore therein and passing through the washer, an insulator member secured to the metallic member and including engaging means for mechanically coupling the insulator member to the movable element, and a stud having a head abutting the outer surface of the cover and a shank forcefitted into the axial hole in the metallic member.

8. The invention as recited in claim 7 wherein the said engaging means comprises a radially-extending slot in the outer surface of the insulator member.

9. The invention as recited in claim 7 wherein the said engaging means comprises an eccentric pin extending from the insulator member. 1,

10. The invention as recited in claim 7 wherein the shank of the said metallic member extends into the intermediate-diameter bore of the cover.

References Cited in the file of this patent UNITED STATES PATENTS 1,661,214 Carpenter Mar. 6, 1928 2,413,414 Obermaier Dec. 31, 1946 2,440,392 Butler Apr. 27, 1948 2,513,184 Lamb June 27, 1950 2,560,879 Lamb July 17, 1951 2,654,070 Lamb Sept. 29, 1953