GB2204449A - Reed relay contacts - Google Patents

Abstract

A miniature or subminiature reed relay comprises in a sealed casing first and second reeds, each as shown in Fig. 1, having an inclined contact area (4) in the form of a raised land so that when two such reeds are in overlapping relationship in a reed relay insert, the permissable longitudinal and lateral misalignment is increased because a constant area of overlap (7) is maintained. Preferably each reed has a corresponding raised land contact area (5) on the opposite side so that the reeds are not "handed" but can be used either way up. The reeds are coined and flattened from a circular cross-section wire. An e/m reed relay can be biased closed by a permanent magnet. <IMAGE>

Description

REED RELAY INSERTS This invention relates to reed relay inserts, particularly but not exclusively to miniature and subminiature-sized inserts.

A reed relay insert comprises two elongate contact members, or reeds, of paramagnetic material disposed approximately in alignment, with ends overlapping but slightly separated. These reeds nave their overlapping ends and a portion of their shanks sealed within a tubular glass housing and they have the advantage of long life owing to the sealed nature of the construction.

The arrangement of the reeds is such that when incorporated into a relay and the reeds are subjected to a magnetic field of sufficient field intensity, the magnetic attraction between the ends of the reeds is sufficient to cause them to be attracted to each other as to make contact, thereby establishing electrical connection between the two reeds.

With the ever-increasing pressure to reduce the size of electrical components, reed relays are no exception and relays in which the glass enclosure is only 20mm long (miniature reed elements) or even as small as 15mm long (subminature reed elements) are presently available.

Many techniques are available for assembling the components of a reed insert but basically the technique involves aligning the two reeds in overlapping relationship within the glass enclosure, sealing one of the reed shanks into the glass enclosure, laterally moving the glass enclosure and the one sealed reed laterally with respect to the other reed to define the desired contact gap, and then sealing the second reed into the other end of the glass enclosure. Preferably the glass enclosure is sealed in an atmosphere of inert gas such as nitrogen.

It can'be appreciated that, as the reed inserts become smaller and smaller, it is more and more difficult to accurately align the overlapping ends of the reeds.

If the ends of the reeds are slightly misaligned then two problems arise, firstly the contact resistance may increase and secondly, and more importantly, the attractive force between the overlapping ends when the magnetic field of the relay winding is applied, will vary considerably dependent on the area of overlap. Thus if the area of overlap is less than that intended, then the current required in the relay winding to operate the contacts will be larger; if the area of overlap is larger then the closing force decreases and separation is likely to occur earlier than intended separating when the magnetic field is switched off. In normal reed switches the natural resilience of the reeds themselves is relied upon solely to separate the reeds when the magnetic field is switched off.

It is an object of the present invention to provide a reed insert and reed relay embodying the insert, which is easier to make having regard to the problems discussed above.

According to the present invention a reed insert comprises first and second reeds having overlapping ends sealed within a gas tight enclosure, each reed having an elongated mating contact area cooperating with and crossing that of the other reed.

The crossing contact areas are preferably provided by coining the overlapping end portions of the reeds to provide a raised land forming a contact area integral with the reed. Preferably the reed is formed of circular metal wire which is flattened over a portion of its length, the flattened portion being coined at its end to produce the raised land.

Conveniently the two reeds can be identical i.e.

not handed and to this end it is proposed that each reed has two contact surfaces which cross substantially at right angles with each other, only one of said contact surfaces being used for each particular reed, it being immaterial which contact surface is used.

In order that the invention can be clearly understood, reference will now be made to the accompanying drawings in which: Fig. 1 shows an end portion of a reed for a reed switch according to an embodiment of the present invention, Fig. 2 shows a side view of the reed of Fig. 1, Fig. 3 shows an alternative embodiment of the invention, Fig. 4 shows a side view of the embodiment of Fig. 3, Fig. 5 shows a complete reed insert embodying the reeds of Figs. 1 and 2 and Figs. 3 and 4, and Fig. 6 shows an embodiment of the invention using handed reeds.

Referring to Figs. 1 and 2, the reed comprises a metal wire of, for example, 50% nickel and 50% iron. It has a circular cross section at 1 and an end portion 2 has been flattened. A tip portion 3 has been coined to provide an oblique raised contact land 4 on the upper side as shown in Fig. 2 and as indicated in plan view in Fig. 1 and in the same process on the underside as viewed in Fig. 2 there is a corresponding oblique raised contact land 5 which crosses the land 4 substantially at right angles. In Fig. 1 this is indicated generally by the dotted line 5.

The contact portion of the the reed would be plated, preferably with gold, and the extent of the gold plating is indicated by the line 6 in Figs. 1 and 2.

As indicated in Fig. 1, the lands 4 and 5 cross substantially at right angles so it can be seen that if two reeds are placed on a common axis and each as shown in Figs. 1 and 2 so that the coined raised contact lands 4 and 5 overlap one another then there will be an area of overlap which is substantially square in configuration and it will not matter if the degree of overlap of the reeds varies slightly in the manufacturing mass production process, neither will it matter if the two reeds are slightly offset in relation to one another, since the common area of overlap of the coined lands will remain substantially constant, defined substantially as a square area of overlap. This area is indicated by the shaded area 7 in Fig. 1.

In Fig. 5 is shown a completed reed insert comprising two reeds each as shown in Figs. 1 and 2, but they could alternatively be made as will now be described with reference to Figs. 3 and 4, and a winding W is shown to form a relay to actuate the reeds of the insert.

Referring to Figs. 3 and 4 the reed there shown is similar in most respects to that of Figs. 1 and 2 in that it is made from the same material, and from round wire and the reed is round at the shank portion 10. A flattened portion 11 extends up to the end contact area 12. This portion has been coined to make it thicker than the portion 11 and narrower than the portion 11 and to provide two crossing contact lands 13 and 14. As explained earlier, only one of the lands is used to make contact with the other reed, but the provision of the two raised lands on opposite sides of the reed enable identical reeds to be used for a pair of reeds in a reed contact unit as shown in Fig. 5, without it mattering which land is actually used as the contact.

Thus the effect is the same as described with reference to Figs. 1 and 2 in that the crossing area which is common to both the raised lands of the two reeds in the reed contact unit is substantially square in shape (reference numeral 15 in Fig. 3) and this will remain substantially constant even though the length of overlap of the two reeds within the contact unit is slightly greater or slightly less during the manufacturing mass production process of the reed units.

Once again the end portion of the reeds will be plated to provide long-life contacts.

Although reeds described in Figs. 1 and 2 and Figs. 3 and 4 enable identical reeds to be used in the same contact unit, it is also possible to design reeds 0 which are cranked at 45 at their ends, but it is then necessary in manufacture to ensure that the reeds are the correct way round relative to one another. This is shown in Fig. 6.

In the embodiment of Figs. 1 to 4, the portions 3 (Fig. 1) and 12 (Fig. 3) would be about 2.Omm long and the flattened portion of the shank (11 in Fig. 3 and 2 less 3 in Fig. 1) would be about 5.Omm long. The width of the mating contact areas such as 4 and 5 and 13 and 14 would be about 0.45mm so that the area of overlap would be about 0.45mm square, giving a longitudinal and lateral tolerance of +0.2mm each.

Other arrangements are possible, for example the reeds could be dissimilar, one having a straight end, the 0 other having a cranked end, e.g. cranked at 90 , so as to still achieve the crossing contact areas.

Also the relay could have a permanent magnet associated with the reeds to keep them normally closed, the winding acting to open the reeds when energised.

Claims (7)

CLAIMS:

1. A reed insert comprising first and second reeds having overlapping ends sealed within a gas tight enclosure, each reed having an elongated mating contact area cooperating with and crossing that of the other reed.

2. A reed insert as claimed in claim 1, wherein a mating contact area is provided by coining an end portion of the reed to provide a raised land forming the contact area integral with the reed.

3. A reed insert as claimed in claim 1 or claim 2, wherein each reed has a second contact area extending transverse in relation to the mating contact area and on the side of the reed away from the mating contact areas, whereby in manufacture either one of two contact areas of a reed can be used as the mating contact area.

4. A reed insert as claimed in any preceding claim, wherein a reed is formed from circular metal wire which is flattened over a portion of its length, and the flattened portion is coined at its free end to produce the or each contact area.

5. A reed insert substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

6. A reed relay comprising a reed insert as claimed in any preceding claim and an electrical winding arranged to operate the insert on energisation thereof.

7. A relay as claimed in Claim 6, comprising a permanent magnet providing a normally closed contact condition.