US3541483A - Reed switch - Google Patents

Description

1970 TOSHITO HARA 5%L 3 REED "swn'cn Filed Dec. 27, 1968 3 Sheets-Sheet 1 CONTACT RESISTANCE (ma) 6 1O INITIAL VALUE 10 10 NUMBER OF OPERATIONS CONTACI RESISTANCE (ma) 0 1o INlTIAL VALUE 10 o 10 10 1 NUMBER OF OPERATIONS United States Patent i US. Cl. 335-154 6 Claims ABSTRACT OF THE DISCLOSURE A reed switch comprising a sealed capsule and contact blades which may be coated with titanium, aluminum or magnesium sealed in the capsule. The atmosphere in said capsule is a contact reducing atmosphere.

This invention relates to an improvement of a reed switch characterized in that a contact blade or a contact material consisting of a magnetic material is sealed in a sealed capsule, such as, for example, a glass tube. The contact is opened or closed by impressing or removing the magnetic flux from the exterior of said sealed capsule. In the invention the reed switch is characterized in that the atmosphere in the sealed capsule is made a contact reducing atmosphere with the purpose of improving the reliability of the reed switch and elongate the life of the switch.

The invention will be described with reference to the drawings in which:

FIGS. 1 and 2 show the structure of well known representative reed switches;

FIG. 3 shows the contact resistance characteristic of a reed switch in the atmosphere of the conventional reed switch;

FIG. 4 shows the contact resistance characteristic of a reed switch under a reducing atmosphere;

FIGS. 5 to 9 show the structure of various embodiments of the reed switches according to the invention; and

FIG. shows oxidation and reduction regions of various kinds of metals.

FIGS. 1 and 2 show the representative structure of well known reed switches. As is seen, for example, from FIG. 1, in the conventional reed switch, two contact blades 1 and 2 consisting of a magnetic material (52% Ni and 48% Fe alloy) are sealed in a capsule 3. A vacuum or an inactive gas, such as nitrogen or helium, is used as atmosphere 4 in the sealed capsule 3 to prevent the deleterious influence on the contact of corrosive gas, organic vapor or dust. 3 to 5% hydrogen is sometimes mixed in the sealed capsule with the purpose of preventing to some extent blackening of the sealed part by oxidation. If a reducing atmosphere that can completely prevent oxidation is used and, for example, a glass tube is used as the sealed capsule, there is a danger that the glass tube cannot be well attached to the contact blade. For this reason, only several percent hydrogen at the most are added so that the attachment of the glass tube with the contact blade may not be prevented. However, it is generally technically difiicult to make an atmosphere of an inactive gas of a high purity or of a high vacuum that can prevent the magnetic material itself from corroding completely. In industrial products, a high vacuum of only about 10 mm. Hg at most can be realized. Therefore, in many ordinary reed switches, such as shown in FIG. 2, corrosion-resisting metals 7 and 8 are attached to contact parts of two contact blades 5 and 6 consisting of a magnetic material by welding, plating or diffusion treatment or in bulky form. The contact blades Patented Nov. 17, 1970 are then sealed in atmosphere 10 of vacuum or an inactive gas, as described above, in sealed capsule 9. However, providing a contact treatment, as described above, on the reed switch increases the number of manufacturing steps and raises the manufacturing cost. Furthermore, in a reed switch on which such contact treatment has been provided, only the thin films 7 and 8 formed on the contact parts contact each other and therefore after a long use, the thin films are transferred and worn. Consequently, the magnetic materials that are the base metals are exposed and oxidized by oxygen remaining in the tube. This has the result that the contact resistance is increased and faults are found in the contacts.

This invention eliminates these defects by providing a novel and advantageous reed switch of a high reliability and of a long life which is different from the conventional reed switch shown in FIG. 2 using corrosion-resisting contact materials at the contact parts. The invention is characterized in that a reducing atmosphere that can cause the magnetic material contact blades themselves to become corrosion-resisting is formed by inserting a reducing gas into the environment sealed capsule.

The reed switch of this invention will be described in further detail. An iron-nickel alloy (in which the percentage of nickel is about 52% by weight and which will be hereafter referred to as the 52 alloy) is presently most preferably used as contact blades of reed switches. In order to ensure that the surface of a contact may not be oxidized at an ambient temperature of above normal temperature (25 C.) when using, for example, hydrogen as the reducing gas, it is necessary to maintain the ratio of partial pressures of hydrogen and steam (F /P in the sealed capsule less than about 10- It is necessary to make this less than about 10- at about 200 C., at which values the oxidation rate bcomes high. Further more, when carbon monoxide is used as the reducing gas, the ratio of partial pressures of carbon monoxide and carbon dioxide gas (P /P in the atmosphere must be less than about l0 at room temperature (25 C.) and lower than 1 at 200 C.

FIG. 3 shows the contact resistance characteristic of a reed switch under the atmosphere of the conventional reed switch. FIG. 4 shows the contact resistance characteristic of a reed switch under the reducing atmosphere according to this invention. These characteristics were exhibited when direct current of 30 v. and ma. was applied interruptedly 50 times in a second under the same resistance load on reed switches using contact blades consisting of 52 alloy, on which no contact treatment has been provided, as the contacts. Usefulness of the reed switch according to this invention becomes evident from comparison of these two drawings.

In the above-mentioned example, magnetic materials constituting reed elements were used as the contacts without modification, but the adhesiveness can be improved or welding can be better accomplished and a reed switch of better characteristic can be obtained by making the atmosphere a magnetic material reducing atmosphere and further effecting contact treatment by the use of a precious metal in accord with the conventional method as shown in FIG. 2.

As described above, if the atmosphere in the sealed capsule of a reed switch is made a reducing atmosphere to prevent completely oxidation of the contacts and, for example, a glass tube is used as the sealed capsule, there is a danger that reed elements cannot be well attached and therefore it is necessary to devise some means so that the reed elements may be well attached to the sealing operation.

This problem is solved by constituting a reed switch as shown in FIG. 5. Namely, the atmosphere in the sealed capsule can be made a reducing atmosphere without damaging the attachment of reed elements by inserting a contact blade '1 consisting of a magnetic material such as, for example, 52 alloy, and a pipe 3' consisting of a similar magnetic material into seal capsule 2, attaching the contact blade 1' and pipe 3 to the glass tube; arbitrarily controlling the atmosphere 6 in the capsule from the exterior through pipe 3 to make the atmosphere a reducing atmosphere and then welding part 4 of pipe 3 to completely separate the air from the atmosphere in the capsule. Namely, in this method, as in the conventional method of sealing in a reed switch, a cylindrical sealed capsule 2 such as a glass tube is first held by a clamp and a contact blade 1' and a pipe 3 are inserted into the glass tube 2 by holding them at the appointed positions with chucks and further the sealing positions at the two end parts of the glass tube 2. are inserted into heaters. Here, needless to say, chucks firmly holding the contact blade 1 and the pipe 3' are adjusted so that there may be an appropriate overlap and gap necessary for performing the switching action in that part, at which contact blade 1 is opposed to pipe 3. Under such a condition, a heater is heated and either one of contact blade 1 or pipe 3 is attached to glass tube 2. Then, as is well known, the atmosphere in the glass tube is made oxidizing to the extent that the attaching part can wet the glass to attach well the conact blade or pipe to the glass. For example, as is well known, while blowing an inactive gas into the glass tube from the exterior, the heater at the other end part of the glass tubeis heated, and the contact blade 1' or pipe 3', 'which had not been attached, is sealed. In the foregoing sealing process, the sealing method itself is completely the same as in the conventional sealing method shown in FIGS. 1 and 2. The two contact blades 1 and 2 or and 6 in the conventional reed switch have been replaced by a single contact blade 1' and a pipe 3', and therefore, in the foregoing sealing method, the conventional sealing method can be applied without modification. And after contact blade 1' and pipe 3 are sealed into glass tube 2, a gas such as an inactive gas within the glass tube 2 is removed from the exterior by utilizing the hole penetrating said pipe 3' and making the capsule 2 nearly vacuum. And after evacuation, a reducing gas such as hydrogen H or carbon monoxide CO is blown in through said pipe 3. The atmosphere in the capsule is, as described above, made a contact reducing atmosphere. Then part 4' of pipe 3 located at the exterior of capsule 2' is sealed by a suitable method such as welding whereby the atmosphere in the sealed capsule is completely separated from the air. By this technique, a reed switch as shown in FIG. 5 can be completed.

And if suitable contact treatment is effected in advance, as is well known, on the contact parts of the contact blade -1' and pipe 3 before sealing them in glass tube 2, when a magnetic field is impressed on the reed switch from the exterior by the well known method, contact blade 1' and pipe 3' attract one another by the magnetic attractive force operating between them and contact parts at the end of the contact blade 1' and pipe 3 come into contact. When the external magnetic field is removed, the contact parts are disconnected as in the conventional reed switch and contact blade 1 and pipe 3' are restored to the original positions by their own resting force. In this case, if pipe 3' is stiff, pipe 3" becomes a fixed contact blade and contact blade 1 becomes a movable contact blade. Thus when the external magnetic field is impressed or removed, contact blade 1 is connected to or disconnected from pipe 3'. Therefore, if external terminals of contact blade 1' and pipe 3' are connected to a suitable electric circuit, opening and closing of said circuit can be controlled by this switch. It is also possible, where occasion demands, to process external terminal part 4 of pipe 3' into a shape that will facilitate its use as an electric terminal by crushing it or welding other suitable terminal material on it.

It will be evident from FIGS. 3 and 4 that the reed switch of this invention has the advantage that a satisfactory contact characteristic can be obtained without effecting a special contact treatment as was required in contact blades in the conventional reed switch on the contact parts at the ends of contact blade 1 and pipe 3' in the sealed capsule, since the atmosphere in the sealed capsule is kept a reducing atmosphere in the reed switch of this invention.

The form of the section of pipe 3 is not limited to a specific form and sections of various forms such as circular, rectangular and square sections can be used if they are capable of performing gas supply action and contact action for controlling the atmosphere in capsule 2 arbitrarily. In the example described above, pipe 3 used as a contact was used to make the atmosphere in sealed capsule 2 a reducing atmosphere but this pipe 3' can be used not only for this object but can be used, in general, for the purpose of controlling the atmosphere in the capsule arbitrarily.

In addition to the switch of FIG. 5 as described above, one can make a switch as shown in FIG. 6. In this figure, a contact blade 1' and another contact blade 3" inserted in a pipe 4" are placed in a sealing glass tube 2' and are sealed in as is shown in FIG. 5. Then atmosphere 6' in glass tube 2' is changed to a reducing atmosphere through the gap between 3 and pipe 4". Thereafter, part 5" of pipe 4" is sealed by welding.

The device and method shown iin FIG. 7 is characterized in that a contact blade 7' and another contact blade 9' attached to the end of pipe 10' by caulking or welding, are placed in glass tube 8' and are sealed in as in the method of FIG. 5. The atmosphere 12 in the capsule is then changed to a reducing atmosphere. Part 11 of pipe 10 is then sealed by welding.

In the method shown in FIG. 8, the contact blades 18 and 22 are provided in advance with parts 1-9 and 2.1 for attaching the contact blades to glass tube 20. Materials which can be attached to the glass tube excellently, such as glass beads, are placed in glass tube 20 and then contact blades 18 and 22 are sealed in glass tube 20. A reducing gas is blovm into the glass tube directly from the exterior, changing the atmosphere in the glass tube to a reducing atmosphere.

There is also a method which is characterized in that a metal having a wider oxidation region than 52 alloy is plated on the parts of the contact blades attached to the glass case to improve the attachment of the contact blades with the glass tube. Oxygen remaining in the glass tube is removed by these metals to improve the performance of the contacts. In general, oxidation and reduction regions of a metal M are determined by the following formulas where ,uO (A) is chemical potential of oxygen in atmosphere A and is balancing chemical potential of oxygen in oxide MmOn, wherein m and n are integers to balance the valences:

oxidation= O (A) ,u.O (MmOn) reduction: ,uO (A) .O (MmOn) M FIG. 10 shows quantitatively the oxidation and reduction regions of 52 alloy which is a constituent of contact blades, sodium, Na, and silicon, Si, which are the chief constituents of glass, and titanuim, Ti, aluminum, Al, and magnesium, Mg, as representative examples of metals having wider oxidation and reduction regions than 52 alloy in an atmosphere formed when hydrogen (H or carbon monoxide (CO) is used as the reducing gas. It can be seen from FIG. 10 that in an atmosphere of H or CO, at a temperature lower than the fusing point of glass (about 650 C.), where the condition of or P /P 1O is satisfied, only 52 alloy (52% Ni and 48% Fe) belong to the reduction region. Sodium and silicon, which are the chief constituents of glass, and Ti, Al and Mg all belong to the oxidation region. Therefore, taking notice of the above fact, if a metal having a wider oxidation region than 52 alloy such as, for example, Ti, Al or Mg, is plated on the parts of contact blades 12 and 15 attached to glass tube 14 and the surrounding parts 13 and 16 as shown in FIG. 9 and these contact blades 12 and 15 are inserted into glass tube 14 and are then sealed in an atmosphere of H or CO satisfying the aforementioned condition, while blowing a reducing gas into the glass tube from the exterior, attachment of the contact blades with the glass can be improved by plating TiO, A1 or MgO, which is an oxide of metal Ti, Al or Mg, on contact blades 12 and 15 without decomposing Si0 and Na O which are the chief constituents of the glass. The oxygen remaining in the glass tube is eliminated by being absorbed by these metals after the sealing and consequently atmosphere 17 in the tube is further transferred to a reducing atmosphere and the performance of the contacts can be further improved.

In the sealing method of FIGS. 6 and 7 described above, a pipe 4" or is required in addition to two line materials 1' and 3" or 7' and 9. Therefore the fabricated reed switch becomes more expensive than the conventional reed switch and moreover the manufacture is made troublesome since a process of changing the atmosphere in the glass tube to a reducing gas is required after the sealing. The methods shown in FIGS. 8 and 9 have an advantage that the reed switch can be readily manufactured without the use of the pipe but by sealing a reducing gas by the use of the sealing method used in the conventional method of manufacturing reed switches wherein an inactive gas is sealed in the capsule.

As described above, the reed switch of this invention in which a contact reducing gas is sealed has an extremely stable contact resistance compared with the conventional reed switch, in which an inactive gas is sealed, and moreover has an advantage that 52 alloy itself ordinarily used as a contact blade can be used as the contact without eifecting any contact treatment on it.

I claim:

1. A reed switch comprising a sealed capsule and contact blades of a magnetic material sealed therein, said capsule containing a reducing atmosphere of hydrogen and water vapor with a partial pressure ratio of P /P of less than 10 2. A reed switch comprising a sealed capsule and contact blades of a magnetic material sealed therein, said capsule containing a reducing atmosphere of carbon monoxide and carbon dioxide and the partial pressure ratio of P /P is less than 1.

3. A reed switch, comprising a sealed envelope, two overlapping reed contact blades through said envelope into said housing and means to operate said contact blades. wherein said contact blades, except for the contact end portions, are plated with titanium.

4. A reed switch, comprising a sealed envelope, two overlapping reed contact blades through said envelope into said housing and means to operate said contact blades, wherein said contact blades, except for the contact end portions, are plated with aluminum.

5. A reed switch, comprising a sealed envelope, two overlapping reed contact blades through said envelope into said housing and means to operate said contact blades, wherein said contact blades, except for the contact end portions, are plated with magnesium.

6. A reed switch, comprising a sealed envelope, two overlapping reed contact blades through said envelope into said housing and means to operate said contact blades, wherein the contact blades are coated with a metal of a gigher oxidation region than the metal of said contact lades.

References Cited UNITED STATES PATENTS 2,925,510 2/1960 Morgan 313-478 X 3,242,557 3/1966 Ellwood 335-154 X 3,275,776 9/1966 DeLucia 335154 X 3,292,122 12/1966 Belic et al 335-154 BERNARD A. GILHEANY, Primary Examiner R. ENVALL, JR., Assistant Examiner UNITED STATES PATENT OFFICE (slss) CERTIFICATE OF CORRECTION Patent No- BHSIUUUBK Dated November 17, 1970 Inventor(s) TOSHITO HARA It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading the German priority number should read as follows: h2/84,190--.

Signed and sealed this 27th day or April 1971.

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents

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