US3088084A - Potentiometer - Google Patents

Description

April 30, 1963 T. LOCK POTENTIOMETER Filed Jan. 2s, 1961 United States Patent O This invention relates to potentiometers.

According to the present invention a potentiometer comprises an annular casing, a helically wound resistance wire supported by the inner surface of the casing, a rotatable screw-threaded spindle extending axially within the casing, and a carriage mounted on said spindle which ymoves axially in response vto rotation of said spindle and carries an electrical contact connecting the spindle and resistance wire.

The casing can be of any cross-section, including rectangular, square and circular cross-sections.

In order that the invention may be more fully understood reference will now be made to the drawing accompanying this specification in which:

FIG. 1 is a cross-sectional view of an embodiment of the invention; and

FIG. 2 is a view of FIG. 1 along the lines Il-IL Referring now to the drawing a potentiometer comprises an annular casing 1 of insulating material which has a square cross-section and which supports a helically wound resistance wire 2 secured to the inner surface of the casing.

One method of securing resistance wire 2 to casing 1 comprises providing a former of low melting point material, such as candle wax, Woods metal or Cerrobend of external dimensions just slightly less than the internal dimensions of casing 1 and winding resistance wire 2 in helical fashion on the external surface. The surface of the wire wound former and/or the internal surface of casing 1 is then coated with a suitable adhesive such as Araldite and the lfor-rner is inserted within casing 1. Alternatively casing 1 can be moulded round the former. The turns of resistance wire 2 can thus be made to adhere to the internal surface of casing 1 and the former can be thereafter removed by raising the temperature sufficiently to cause it to melt. This leaves casing 1 having resistance wire 2 helically wound around its inner surfaces.

An alternative method is to use a former of P.T.F.E. which has a slight taper. The resistance wire 2 is Wound round the external surface of the former secured to the internal surface of the casing as before. The P.T.F.E. former can then be withdrawn from within the casing without interfering with the winding.

Electrical contact with the ends of resistance wire 2 is provided by narrow brass rings 14 and 15 which are a good fit on the former and are slipped over the former at either end to make contact with the ends of the resistance wires. External terminal leads 11 and 12 can then be soldered or welded to rings 14 and 15.

A rotatable screw-threaded spindle 3 extends axially within the casing and can be rotated by means of an insulating screw head 4 projecting beyond one end of the casing. The other end of spindle 3 is supported by a spring-loaded ball bearing 5 which bears against a metal bearing surface 6 in the lower end of the casing. A carriage 7 of insulating material such as nylon is mounted on spindle 3 and engages the thread thereof so that rotation of spindle 3 causes carriage 7 to move axially of the casing. Carriage 7 can be provided with a slit at one end to enable the threads to jump the threads of spindle Patented Apr. 30, 1963 ice 3 when at either end of its run and thus prevent distortion of the threads or casing.

Carriage 7 is provided with means for making electrical contact between resistance wire 2 and spindle 3. This means may comprise a hole drilled within carriage 7 extending radially of spindle 3 and carrying two ball bearings or metal caps 8 and 9 which are respectively held pressed against spindle 3 and resistance wire 2 by means of a spring 10 lying between them.

The terminal leads 11 and 12 are brought out at one end of the casing and an external connection 13 is made to metal plate 6 and thus to spindle 3.

If an electrical potential difference is applied between terminals 11 and 12 it will be appreciated that the potential on terminal 13 will depend on the position of carriage 7 which can be varied by rotation of screw head 4.

While casing 1 is illustrated as being square it should be appreciated that it can be of any cross-section, although a square or rectangular cross-section allows a plurality of such potentiometers to be positioned side-by-side with a given range of resistance wire taking the least room. Furthermore the turns of winding 2 need not necessarily entirely conform to the internal dimensions of casing 1. The casing can be enclosed in a metal can, which can be provided during moulding of the casing.

What I claim is:

1. An electrical potentiometer comprising a casing formed of insulating ducting of polygonal section, a resistance wire wound helically around the inner surface of the ducting, a rotatable conducting threaded spindle extending longitudinally within the wire, an insulating carriage in screw threaded engagement with said spindle and locked against rotation by engagement with said inner surface, whereby rotation of the spindle is effective axially to move the carriage, a spring pressed electrical contact mounted on the carriage and engaging adjacent turns of the resistance wire, and means for electrically connecting the contact with the spindle.

2. An electrical potentiometer comprising a casing formed of insulating ducting of rectangular section, a resistance wire wound helically around the inner surface of the ducting, a rotatable conducting threaded spindle extending longitudinally within the wire, an insulating carriage in screw threaded engagement with said spindle and `locked against rotation by engagement with said inner surface, whereby rotation of the spindle is effective axially to rnove the carriage, a spring pressed electrical contact mounted on the carriage and engaging adjacent turns of the resistance wire, and means for electrically connecting the contact with the spindle.

3. An electrical potentiometer comprising a hollow member of electrically linsulating material having a bore, a helically wound wire coil ixedly mounted in the wall of said bore, a threaded conductor rod rotatably mounted to extend longitudinally through the bore out of contact with said coil, a radially extending carriage of insulating material mounted in threaded engagement with said bore, and spring biased contact means extending through said carriage from the coil to the rod, whereby rotation of said rod displaces said carriage axially of said bore to determine the portion of said coil connected in electrical series with the rod.

References Cited in the le of this patent UNITED STATES PATENTS

Claims (1)

1. AN ELECTRICAL POTENTIOMETER COMPRISING A CASING FORMED OF INSULATING DUCTING OF POLYGONAL SECTION, A RESISTANCE WIRE WOUND HELICALLY AROUND THE INNER SURFACE OF THE DUCTING, A ROTATABLE CONDUCTING THREADED SPINDLE EXTENDING LONGITUDINALLY WITHIN THE WIRE, AN INSULATING CARRIAGE IN SCREW THREADED ENGAGEMENT WITH SAID SPINDLE AND LOCKED AGAINST ROTATION BY ENGAGEMENT WITH SAID INNER SURFACE, WHEREBY ROTATION OF THE SPINDLE IS EFFECTIVE AXIALLY TO MOVE THE CARRIAGE, A SPRING PRESSED ELECTRICAL CONTACT MOUNTED ON THE CARRIAGE AND ENGAGING ADJACENT TURNS OF THE RESISTANCE WIRE, AND MEANS FOR ELECTRICALLY CONNECTING THE CONTACT WITH THE SPINDLE.

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