DE1125509B - Contact arrangement which is housed in a hermetically sealed space under reduced pressure - Google Patents

Description

The so-called protective tube or protective gas contacts consist of magnetizable contact springs, ijie in a glass tube that is fused at its ends are housed. In order to protect the contacts, such a glass tube can, as is well known, be Protective gas, such as B. a mixture of nitrogen and hydrogen, filling, causing corrosion of the Contacts is prevented. A filling with an inert gas, e.g. B. Argon. ίο

Β, εί such contacts are in the Principle of contact arrangements, which in a herjaefisch enclosed space are housed, which is filled with a protective or noble gas.

It has already been used with thermostat switches that are housed in a gas-tight container are provided, a gas filling which enables heat transfer. As a particularly suitable one Gas, in particular, hydrogen has been proposed. With these switches the aim was to have one at Suppression occurring gas discharge in the case of to avoid opening the contact point as far as possible, because this results in undesired heating of the contact point on the one hand and cracks on the other the contact point by transporting electrical thread material causes. On the other hand, a glow discharge has a significant advantage, when it comes to switching off an inductive load. In this case, the Switching off the inductive load will form a glow discharge, which automatically reduces the induced voltages limited to the ignition voltage of the glow discharge. Without the limiting effect, the voltage take on significantly higher values at the opened contact point, which is detrimental to the I $ olation of the inductive load. So under certain conditions it is quite desirable to accommodate the contact point of a switch in an atmosphere under negative pressure.

The invention described below relates to such a contact arrangement and enables it to significantly increase the service life of such contacts. This is achieved according to the invention by filling with a pressure that is so low compared to atmospheric pressure, that a glow discharge which forms in the event of a contact actuation with its cathode cover extends over an area which is substantially larger than the contact area belonging to the contact point is, so that the cathode sputtering caused by the glow discharge for the most part Contact arrangement in a hermetically sealed space under degraded

Drock is housed

Applicant:

Siemens & Halske Aktiengesellschaft,

Berlin and Munich, Munich 2, Wittelsbacherplatz 2

Dipl.-Ing. Dr. rer. nat. Karl Ludwig Rau, Munich, has been named as the inventor

is shifted to areas that are not actually involved in making contact; are.

The invention is based on the following findings:

An open contact is provided that it is in a gas atmosphere under negative pressure is comparable to a gas discharge tube. As a result, it ignites during the opening process a glow discharge between its electrodes if one above the ignition voltage lying tension arises. This is the case inbespndere when using such contacts an inductive load, e.g. a relay, is switched off. In such a case it causes the spontaneous Current interruption the induction, a voltage spike, which occurs directly at the contact gap and thus ignites the glow discharge.

The result is sputtering of the contact part forming the cathode, the so-called cathode sputtering. This manifests itself in a destruction of the surface piece in question and a material migration, which have an extremely unfavorable effect on the properties of the contact point.

The cathode cover and thus the destruction zone of the glow discharge are now in their expansion depending on the pressure in the discharge vessel. As is well known, they stretch with falling pressure over a larger area. This The effect is now in a very specific manner in the case of the contact applications described above applied, foolishly, that it was caused by a glow discharge caused inevitable catho

209 519/334

Claims (4)

Exercise now mainly extends to cathode areas that are not involved in the actual contact involved. By increasing the cathode coverage it is achieved that the specific current load is opposite during the switching process the previously usual filling pressures and thus weakened the cathode sputtering on the one hand and on the other hand is largely shifted away from the area of the actual contact point. This or tantalum, the cathode sputtering that occurs during glow discharge has a very high resistance oppose. Such metals are therefore already available as so-called pure metal cathodes in cathode tubes used. However, these metals have heretofore appeared for use as a contact material relatively unsuitable as experience with such air actuated contacts, e.g. B. Tungsten Con- resulting in a corresponding increase in the service life of the contact. The above-described measure of setting a very specific pressure in the her-5 Metically closed space can be reinforced in their effect according to the further invention, if the area of the contacts over which the glow discharge essentially extends, with a Surface that consists of a high melting point the latter effect is therefore of particular importance, io metal, e.g. B. molybdenum, tantalum or tungsten, according to because this largely results in the deposition of Zer type of a so-called pure metal cathode, Dusting products and the migration of material. The refractory metal is expediently in the actual contact point can be avoided. Plated in the form of a foil on the contacts. Due to the above-described invention, this measure is based on the knowledge according to measures one achieves a long life 15 that certain metals, namely those with a relatively duration of the contacts, since the undesired changes high melting point, such. B. molybdenum, tungsten tion of the contacts due to glow discharge is largely eliminated. This in turn has an improvement in the temporal constancy of the electrical
and magnetic parameters result. Given a certain load, one can reduce the pressure in the hermetically sealed Lower the space so that there is just one over the entire surface of the cathode Cathode coverings extending to form the contact part showed that these materials in particular result. In this case one achieves the lowest possible with a lower load for the formation of the highest possible cathode sputtering, since the glow-ohmic and even insulating layers tend to discharge as a cathode, the entire surface of the man therefore has mostly protective tube contacts with relevant contact part is exploited. a noble metal layer, e.g. B. made of gold, the In Fig. 1, a known protective tube 30 is shown, however, relatively little resistant to the or protective gas contact, consisting of the aforementioned cathode sputtering. In contrast, protective tube 1 and the contact springs 2 and 3. The above mentioned high-melting Me-Kontaktfedern2 and 3 are fused into the glass-made talle, as a surface material of Kontaktanordnun protective tube 1 at its ends. genes that are in a hermetically sealed, with your contact giving parts are thus housed in a space filled with protective or inert gas, a hermetically sealed space. The inside are that the harmful sputtering is prakdes protective tube 1 with some protection or
Noble gas filled. FIG. 1 also shows the way in which a protective 40 is known. pipe contacts with previously customary filling pressures - In Fig. 3 a protective pipe contact is shown, forming glow discharge expands. Through the dashed lines the cathode covering 4 of a developing glow discharge is indicated. As can be seen concentrates this cathode covering 45 surface, which in this case is in the form is completely plated onto the actual contact point of a film on the contacts. As hearing contact surface. As a result, it can be seen that the film 5 is made of flat sheet metal Area of the unavoidable cathode sputtering strips existing contact springs 2 and 3 so far Exercise extends over a relatively small area, thereby dragging around that a relatively large area entin this zone has a correspondingly high current density 50, which is present in the case of a glow discharge during the switching process and, as a result, high resulting cathode sputtering a correspondingly Material migration is recorded. The cathode can oppose high resistance. Self-atomization is therefore exclusively on the switching position, it is also possible to use the plating 5 focus. to pull the entire area of contacts 2 and 3, In contrast, FIG. 2 shows the effect of the 55 with which this measures in the interior of the protective device according to the invention. In this figure, the tube 1 protrudes when a correspondingly large cathode coverage corresponding to the arrangement according to FIG. 1 is to be expected. Protective tube contact shown, in which, however, through the above-described setting of the pressure in the protective design of protective tube contacts, it is possible that the cathode cover 60 has the effect of setting a certain pressure of a glow discharge over a significantly greater one in the tube to increase substantially hermetically enclosed space area as belonging to the contact point contact, extending area, namely, in this case, over the entire surface of the cathode-forming contact CLAIMS: spring 2, as far as these befin- in the protective tube 1 65 det. As a result, with this arrangement only 1. Contact arrangement, which is hermetically sealed a very low current density and, as a result, a closed space is housed with rings of cathode sputtering occur, which entails a protective or noble gas under negative pressure table is eliminated, with the otherwise observed inclination prevents such metals from forming high-resistance layers by the protective or noble gas whose contacts in the area over which the glow discharge essentially extends, with a made of a refractory metal is filled, characterized by a filling with a pressure so low compared to the atmospheric pressure that a glow discharge which forms in the event of a contact actuation extends with its cathode covering over an area which is significantly larger than the contact area belonging to the contact point, so that the through the cathode sputtering caused by the glow discharge is predominantly shifted to areas that are not involved in the actual contacting. 2. Contact arrangement according to claim 1, characterized in that for a predetermined Load the pressure in the hermetically sealed space is so low that a cathode covering extending over the entire surface of the contact part forming the cathode results. 3. Contact arrangement according to claim 1 or 2, characterized in that the area of the Contacts over which the glow discharge essentially extends, one made of high-melting point Metal (e.g. molybdenum, tantalum, tungsten) in the manner of a so-called pure metal cathode owns existing surface. 4. Contact arrangement according to claim 3, characterized in that the high-melting point Metal is plated in the form of a foil on the contacts. Considered publications:
German patent specifications No. 705 358, 966 816. 1 sheet of drawings ® 209 519/334 3.