US3584173A

US3584173A - Reed switch with improved contact isolation

Info

Publication number: US3584173A
Application number: US849761A
Authority: US
Inventors: Larry L Launt; Gary E Northrup
Original assignee: CUNNINGHAM CORP
Current assignee: CUNNINGHAM CORP
Priority date: 1969-08-13
Filing date: 1969-08-13
Publication date: 1971-06-08
Anticipated expiration: 1988-06-08
Also published as: DE2039946B2; BE754803A; FR2057964A5; DE2039946A1; JPS4929372B1; DE2039946C3; GB1258685A; NL7011925A

Abstract

The contact tips of the reeds in a reed switch are rounded and all sharp corners removed. The result is a significant improvement in contact isolation characteristics at high frequencies when the switch is open.

Description

United States Patent Inventors Appl. No. Filed Patented Assignee REED SWITCH WITH IMPROVED CONTACT ISOLATION 3 Claims, 7 Drawing Figs.

11.5. C1 200/166J Int. Cl 1101b 1/06 Field of Search 200/ 1 66 References Cited UNITED STATES PATENTS 7/1956 Fisher H 200/166(B8) 7/1967 Adams et al. 200/166(C) 12/1966 Belic et al. 335/154 1/1970 Barlow et al 200/166(C) Primary ExaminerH. 0. Jones Attorney-Morton A. Polster ABSTRACT: The contact tips of the reeds in a reed switch are rounded and all sharp corners removed. The result is a significant improvement in contact isolation characteristics at high frequencies when the switch is open.

-?/ /l//ll//l/l//l/ REED SWITCH WITH IMPROVED CONTACT ISOLATION This invention relates to reed switches and, more particularly to the switch contact portion of reeds used therein.

Reed switches are well known and in widespread use. They generally include a pair of thin reedlike contacts cantilever supported and hermetically sealed through opposite respective ends of an elongated glass envelope with their tips in fairly close spaced opposition. The reeds are of a magnetically permeable material, and their tips are brought together to close the switch by the application of a magnetic field. When the field is removed, the switch opens.

Such switches have found great utility in a wide number of applications because they are compact, dependable in any atmosphere, very sensitive, fast acting, and have a relatively rapid cycling rate. However, concomitant with these advantages, the physical closeness and configuration of the reeds is such that they appear to have an interelement capacitance which must be considered when they are being used in switch matrices to isolate circuits carrying alternating current signals, the degree of isolation provided by such reed switches becoming less effective at a logarithmic rate as signal frequency increases.

ln prior art reed relays, the tips of the switch contact ends of the reeds either have sheared, sharply edged contours, or else have such sheared edges broken by a slight chamfer, and heretofore the best contact isolation levels that could be achieved in reed switch matrices handling signals of about 50 to 60 Megal-lertz have been approximately 55 to 60 db. below the level of the signal. For high quality systems, further reduction is highly desirable.

The invention herein is based upon the discovery that circuit isolation provided by reed switches can be improved if the end contours of the switch contact portions of individual reeds are given a full radius. Briefly, in accordance with the present invention, it has now been found that simply rounding off the tips of the reeds in reed switches, to avoid sharp corners in their overlapping portions enables the achievement of contact isolation levels approximately 65 to 75 db. down when dealing with signals in the range of about 50 to 60 MegaHertz. The reason for the improved results is not understood, although it is thought that they may be related to the well-known edge effect in electrostatics.

According to the subject invention, a reed for use in a reed switch capsule comprises a terminal portion adapted for attachment to a support by said capsule and a switch portion with a tip having full radius curvatures for height and width end contours.

The invention will now be described with greater particularity, reference being made to the accompanying drawings in which:

FlG. l is a side elevational view of a reed switch according to the invention herein;

FIGS. 2A and 2B are side and plan views, respectively, of the switch contact portions, greatly enlarged, of a pair of the most common type of prior art reed;

FIGS. 3A and 3B are views similar to FlGS. 2A and 2B of a pair of another type of prior art reed; and

FlGS. 4A and 4B are greatly enlarged views of the switch contact portions of a pair of reeds according to the invention herein.

In FIG. 1, a pair of reeds have cantilevered switch contact portions 13 adjoining and extending from terminal portions 12. The cantilevered portions 13 have rounded tips 14, and the reeds 10 are hermetically sealed within elongated glass capsule l6. Respective terminal portions 12 are attached to the ends of capsule 16 so that switch contact portions 13 are cantilever supported in overlapping relation near the center of the capsule.

Referring now to FIGS. 2A and 2B, the switch contact portions 24 of a pair of prior art reeds are shown greatly enlarged. As can be seen, the sheared ends of contact portions 24 have straight-line height contours 26 and straight-line width contours 28 which form sharp edges and corners.

The switch contact portions 34 of a second type of prior art reed are illustrated in FIGS. 3A and 3B. In this second type of reed, the sharp edges and corners formed by straight-line height contours 36 and straight-line width contours 38 are broken by chamfers 40.

In analyzing the contact isolation characteristics of the two prior art types of reed switches illustrated in FIGS. 2A, 2B and 3A, 38, it is found that reed switches having chamfered edges and corners seem to provide a greater amount of circuit isolation at high frequencies than switches using sheared reeds without chamfer. However, switches according to the invention herein, with fully rounded tips for the switch contact por tions of the reeds, have significantly greater circuit isolation characteristics than any known prior art reeds.

FlGS. 4A and 4B illustrate the switch contact portions 44 of a pair of reeds made according to the invention herein. It can be seen that the height contours 46 and width contours 48 of the tips all have full radius curvatures 50. It is essential, in order to obtain maximum contact isolation characteristics, that no sharp edges or corners appear at the tip of the switch contact ends, and to accomplish this one or more different radii of curvature may be employed. This rounding may be done by any desired means, and one satisfactory method has been to grind the contact tips by immersing them in an ultrasonic switches Of course, if the reeds are plated, as is often done to protect against corrosion and erosion and to enhance their electrical conductivity, the rounding of the end contours should precede such plating.

Switches in accordance with the invention have been extensively tested in comparison with switches of the prior art, which were identical in all respects to the switches of the invention except for the tip shape of the overlapping contact portions of the reeds. Most of the testing was carried out at signal frequencies of about 50 to 60 MegaHertz. In all cases, switches in accordance with the invention, with the rounded contact tips, were superior by a margin of 5 to 15 db. in respect of crosstalk relative to the switches of the prior art.

What we claim is:

l. A reed for use in a reed switch capsule, comprising a terminal end portion and a cantilever portion adjoining and extending from said terminal end portion and including a switch contact end, said cantilever portion being characterized by the absence of sharp corners and edges and having full radius curvatures for the height and width contours of said switch contact end.

2. A reed according to claim 1 wherein said end contours each comprise at least one radius of curvature.

3. In a magnetic reed switch with a pair of reeds hermetically sealed in an elongated capsule, said reeds having respective terminal portions attached to respective ends of said capsule and respective cantilever portions adjoining and extending from said terminal portions and including switch contact ends supported in overlapping relation intermediate said capsule ends, the improvement wherein the cantilever portion of each said reed is characterized by the absence of sharp corners and edges and by full-radius contours along the height and width of the switch contact end.

Claims

1. A reed for use in a reed switch capsule, comprising a terminal end portion and a cantilever portion adjoining and extending from said terminal end portion and including a switch contact end, said cantilever portion being characterized by the absence of sharp corners and edges and having full radius curvatures for the height and width contours of said switch contact end.