[0001] This invention relates to pressure-operated electrical switches of the type having
a static contact co-operable with a moving contact which is operated by a flexible
diaphragm.
[0002] Such switches are known in the art, and typical examples are to be found in GB-A-1537858
and GB-A-2020908.
[0003] GB-A-1537858 shows the use of a metal diaphragm to actuate the moving contact, and
while it is stated to be a compact device, it is apparently intended for use in vehicle
brake systems, where pressures are high and tolerances are not particularly tight.
Also, the contact arrangements do not seem to lend themselves to direct application
to printed circuit boards.
[0004] GB-A-2020908 shows an arrangement in which the diaphragm operates through a snap
disc and a switch bumper onto the moving contact. Such an arrangement is not particularly
suitable for sub miniature circuitry, and the pressure to which the switch is snesitive
is determined by the ratings of the snap disc and the diaphragm. The moving contact
is spot welded onto a terminal, and its flexing is controlled to some extent by the
provision of an arcuate cut out partially encircling the spot weld.
[0005] It is an object of the invention to provide a pressure switch which is particularly
compact and which can be readily adapted to operate over any of a wide spectrum of
pressure ranges, by ready adaptation of the spring rate of the moving contact.
[0006] In accordance with the invention, there is provided a sub-miniature pressure switch
for use with a printed circuit board, comprising a pressure chamber having one wall
defined by a flexible diaphragm bearing upon a flexible and resilient moving contact
electrically connected to a first conductor leg, and a static contact co-operable
with the said moving contact and connected to a second conductor leg, characterised
in that the said moving contact is arranged to flex about a hinge line at least partially
defined by at least one elongate cutout in the contact material, the section and width
of the said cutout(s) being chosen to impart a desired spring rate to the moving contact.
[0007] The moving contact may be manufactured in a number of models, giving a'choice of
cutout pattern, and the required cutout pattern is chosen in accordance with the intended
use of the switch, and particularly the range of pressures it will meet in operation.
[0008] The moving and static contacts are preferably integrally formed with the first and
second conductor legs respectively, and the diaphragm should bear directly upon the
moving contact for compactness.
[0009] The cutout will normally be rectilinear.
[0010] The effective position of the static contact may be adjustable by means of a setting
screw adapted resiliently to deform a portion of the static contact towards the moving
contact.
[0011] The switch conveniently comprises a two part housing, in which the parts of the housing
are crimped together with a periphery of the diaphragm trapped between them by means
of a marginal bead received in a matching recess in one of the housing parts.
[0012] The invention will be further described with reference to the accompanying drawings
of preferred embodiments of pressure switches in accordance with the invention, and
in which:
Figure 1 is an exploded sectional view of one form of switch in accordance with the
invention;
Figure 2 is an assembled sectional view of the switch of figure 1;
Figure 3 is a view similar to figure 2 and showing an alternative;
Figure 4 is a plan view of a blank for a moving contact, prior to bending to shape;
Figure 5 is a plan view of a blank for a static contact, prior to bending to shape;
Figure 6 is a bottom plan view of one part of a housing; and
Figure 7 is a plan view of another part of the housing.
[0013] Turning first to figures 1 and 2, these show a housing having a base part 1 and a
cover part 2, both of suitable insulating plastics material. A diaphragm 3 is trapped
between the housing parts 1 and 2 by means of a marginal annular bead 4 received in
a conforming recess 5 in the part 2 (see also figure 7). The housing part 2 defines,
with the diaphragm 3, a pressure chamber 6 connected to a duct 7 (the entrance to
which is shown offset by 90° in figures 2 and 3). The housing part 1 defines, also
with the diaphragm 3, a contact chamber 8 (see also figure 6), which may also have
a pressure conduit 9. Within the contact chamber 8 there are located static and moving
contacts 11 and 12 respectively, each of slow moving spring metal, which may be gold
or otherwise plated as required. An adjusting screw 13 for the static contact 11 is
also illustrated.
[0014] In the arrangement of figures 1 and 2, the contacts 11 and 12 are integral with conductor
legs 14 and 15 respectively, and reference to figures 4 and 5 will show more detail
of the constructions. The conductor legs are designed for compatibility with modern
printed circuit boards so as to be soldered or fitted thereto. In particular, a dual-in-line
arrangement is envisaged.
[0015] The blank of figure 4 is permanently bent along the line shown dotted at 15b to form
the angles 15a. An intermediate portion 16 is used to mount the component in the housing,
and the moving contact 12 itself is connected to the intermediate portion 16 by a
neck 17 which is provided with elongate rectilinear cutouts 18 which define a hinging
or pivot line, and the location and dimensions of the cutouts' 18 are so chosen that
a predetermined spring rate is given to the moving contact 12. It is envisaged that
movong contacts with a number of different configurations of cutouts 18 will be manufactured,
and the mbving contact with the particular configuration required for a given application
will be incorporated during assembly.
[0016] The blank of figure 5 is permanently bent along the lines shown dotted at 21, 22
and 23 to form the angles 21a, 22a and 23a respectively. An anchoring intermediate
portion is shown at 24, and the static contact itself is shown as having a centre
zone 25 which acts as the contact zone and is displaceable by means of the adjusting
screw 13 (see figure 2). The centre zone is defined by an elongate arcuate cut out
26 leaving a short hinging zone 27.
[0017] The intermediate zones 16 and 24 are provided with apertures 16a and 24a which are
engaged by contact posts 16b and 24b on the housing part 1 when the switch is assembled.
The contact posts 16b and 24b are received in holes 16c and 24c respectively in the
housing part 2. In the arrangement illustrated, there are a total of four contact
posts, but in some cases, for use with lower pressures, two may be sufficient.
[0018] In use, the two housing parts 1 and 2 are crimped together by any suitable means,
with the diaphragm trapped sealingly between them. An excess pressure in chamber 6
will urge the diaphragm 3 upwards against the moving contact 12, which will flex,
against the resilient resistance to hinging, about its hinging line defined by the
cutouts 18 and move towards the static contact 11, and particularly the zone 25 thereof,
as may be best seen in figure 2. The actual position of the zone 25 may be varied
by the adjusting screw 13 to set the amount of hinging of the moving contact 12 required
to make the switch. The minimum pressure differential required to achieve this movement
is determined by the spring rate of the moving contact 12, which itself depends on
the arrangement of the cutout(s) 18.
[0019] In the description above, the contacts 11 and 12 have been shown and described as
integral with their corresponding conductor legs 14 and 15. Figure 3 shows an arrangement
in which the contacts co-operate with separate conductor legs 31 which pass through
and crimp the housing. Figure 3 is partially in section through one of these conductor
legs, and shows another of them in elevation.
[0020] The exact pressure ranges of operation will be determined by commercial requirements.
The switching point will be chosen somewhere 0 and 100% of the range. Typical ranges
which could be used are as follows:

[0021] A maximum range would be about 0 to 150 pounds per square inch (10130mb).
[0022] Various modifications may be made within the scope of the invention as defined in
the appended claims.
1. A sub-miniature pressure switch for use with a printed circuit board, comprising
a pressure chamber (6) having one wall defined by a flexible diaphragm (3) bearing
upon a flexible and resilient moving contact (12) electrically connected to a first
conductor leg (15), and a static contact (11) co-operable with the said moving contact
(12) and connected to a second conductor leg (14), characterised in that the said
moving contact (12) is arranged to flex about a hinge line at least partially defined
by at least one elongate cutout (18) in the contact material, the section and width
of the said cutout(s) (18) being chosen to impart a desired spring rate to the moving
contact (12).
2. A pressure switch according to claim 1, characterised in that the moving and static
contacts (12,11) are integrally formed with the first and second conductor legs (14,15)
respectively.
3. A pressure switch according to claim 1 or 2, in which the diaphragm (3) bears directly
upon the moving contact (12).
4. A pressure switch according to claim 1, 2 or 3, in which the effective position
of the static contact (11) is adjustable by means of a setting screw (13) adapted
resiliently to deform a portion of the static contact (11) towards the moving contact
(12).
5. A pressure switch according to claim 1, 2, 3 or 4, comprising a two part housing,
in which the parts (1,2) of the housing are crimped together with a periphery of the
diaphragm (3) trapped between them.
6. A pressure switch according to claim 5, in which the diaphragm (3) has a marginal
bead (4) which is received in a matching recess (5) in one of the housing parts (2).
7. A pressure switch according to claim 6, in which the marginal bead (4) is annular.
8. A pressure switch according to any of the preceding claims, characterised in that
the said at least one cutout (18) is rectilinear.