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Патент USA US3088093

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April 30, 1963
3,088,084
T. LOCK
POTENTIOMETER
Filed Jan. 2s, 1961
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United States Patent O " ice
3,088,084
Patented Apr. 30, 1963
2
1
3 when at either end of its run and thus prevent distor
tion of the threads or casing.
3,088,084
POTENTIÜMETER
Carriage 7 is provided with means for making electrical
contact between resistance wire 2 and spindle 3. This
Tom Lock, Northampton, England, assigner to Asso
ciated Electrical Industrigs Limited, London, England,
means may comprise a hole drilled within carriage 7
extending radially of spindle 3 and carrying two ball bear
ings or metal caps 8 and 9 which are respectively held
a British company
Filed Jan. 23, 1961, Ser. No. 84,032`
Claims priority, application Great Britain June 23, 1960
3 Claims. (Cl. 338-14S)
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
This invention relates to potentiometers.
According to the present invention a potentiometer
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 poten
tial on terminal 13 will depend on the position of carriage
comprises an annular casing, a helically wound resistance
wire supported by the inner surface of the casing, a
rotatable screw-threaded spindle extending axially with~
in 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
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
spindle and resistance wire.
The casing can be of any cross-section, including rec
tangular, square and circular cross-sections.
20 of such potentiometers to be positioned side-by-side with
a given range of resistance wire taking the least room.
In order that the invention may be more fully under
stood reference will now be made to the drawing accom
Furthermore the turns of winding 2 need not necessarily
entirely conform to the internal dimensions of casing 1.
panying this specification in which:
The casing can be enclosed in a metal can, which can be
FIG. 1 is a cross-sectional view of an embodiment of 25 provided during moulding of the casing.
What I claim is:
the invention; and
FIG. 2 is a view of FIG. 1 along the lines Il-IL
1. An electrical potentiometer comprising a casing
Referring now to the drawing a potentiometer com
formed of insulating ducting of polygonal section, a
prises an annular casing 1 of insulating material which
resistance wire wound helically around the inner surface
has a square cross-section and which supports a helically 30 of the ducting, a rotatable conducting threaded spindle
wound resistance wire 2 secured to the inner surface of
extending longitudinally within the wire, an insulating
the casing.
carriage in screw threaded engagement with said spindle
One method of securing resistance wire 2 to casing 1
and locked against rotation by engagement with said
comprises providing a former of low melting point mate
inner surface, whereby rotation of the spindle is effective
rial, such as candle wax, Woods metal or “Cerrobend” 35 axially to move the carriage, a spring pressed electrical
of external dimensions just slightly less than the internal
contact mounted on the carriage and engaging adjacent
dimensions of casing 1 and winding resistance wire 2
turns of the resistance wire, and means for electrically
in helical fashion on the external surface. The surface of
connecting the contact with the spindle.
the wire wound former and/or the internal surface of
2. An electrical potentiometer comprising a casing
casing 1 is then coated with a suitable adhesive such as 40 formed of insulating ducting of rectangular section, a
“Araldite” and the lfor-rner is inserted within casing 1.
resistance wire wound helically around the inner surface
Alternatively casing 1 can be moulded round the former.
of the ducting, a rotatable conducting threaded spindle
The turns of resistance wire 2 can thus be made to adhere
extending longitudinally within the wire, an insulating
to the internal surface of casing 1 and the former can
carriage in screw threaded engagement with said spindle
be thereafter removed by raising the temperature suffi 45 and `locked against rotation by engagement with said inner
ciently to cause it to melt. This leaves casing 1 having
surface, whereby rotation of the spindle is effective axially
resistance wire 2 helically wound around its inner
to rnove the carriage, a spring pressed electrical contact
mounted on the carriage and engaging adjacent turns of
surfaces.
An alternative method is to use a former of P.T.F.E.
the resistance wire, and means for electrically connecting
50
which has a slight taper. The resistance wire 2 is Wound
the contact with the spindle.
round the external surface of the former secured to the
3. An electrical potentiometer comprising a hollow
internal surface of the casing as before. The P.T.F.E.
member of electrically linsulating material having a bore,
former can then be withdrawn from within the casing
a helically wound wire coil íixedly mounted in the wall
of said bore, a threaded conductor rod rotatably mounted
without interfering with the winding.
55
to extend longitudinally through the bore out of contact
Electrical contact with the ends of resistance wire 2 is
with said coil, a radially extending carriage of insulating
provided by narrow brass rings 14 and 15 which are a
material mounted in threaded engagement with said bore,
good fit on the former and are slipped over the former
and spring biased contact means extending through said
at either end to make contact with the ends of the resist
ance wires. External terminal leads 11 and 12 can then 60 carriage from the coil to the rod, whereby rotation of said
rod displaces said carriage axially of said bore to deter
be soldered or welded to rings 14 and 15.
'
mine the portion of said coil connected in electrical series
A rotatable screw-threaded spindle 3 extends axially
with the rod.
within the casing and can be rotated by means of an in
sulating screw head 4 projecting beyond one end of the
References Cited in the ñle of this patent
casing. The other end >of spindle 3 is supported by a
UNITED STATES PATENTS
spring-loaded ball bearing 5 which bears against a metal
1,561,137
Burns _______________ „_ Nov. 10, 1925
bearing surface 6 in the lower end of the casing. A
2,815,422
Lock ________________ __ Dec. 3, 1957
carriage 7 of insulating material such as nylon is mounted
on spindle 3 and engages the thread thereof so that rota
tion 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
2,870,303
2,873,339
2,936,516
2,985,951
O’Brian ______________ __ Jan. 20,
Bourns et al __________ __ Feb'. 10,
Adair ________________ __ May 17,
Solow _______________ __ May 30,
1959
1959
1960
1961
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