US2251923A - Ionic discharge tube - Google Patents

Description

Aug. 12, 1941. M. J. DRUYVESTEYN 3 IONIC DISCHARGE TUBE Filed Nov. 7, 1959 I Jinan/7'01? M JDrzgue's-Zeyz Patented Aug. 12, 1941 Iomc mscnaaoa TUBE Marl Johan Druyvesteyn, Eindhoven, Netherlands, assignor, by meane assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application November 7, 1939, Serial No. 303,297

' 3 Claims.

This invention relates to an ionic discharge tube having a separate supply of mercury communicating with the discharge space proper via a separating member. This supply serves in well-known manner for makingup for losses of the vapour filling in the tube and by its temperature to maintain a given vapour pressure therein.

Particularly with discharge tubes for very high anode voltages the maintenance of constant conditions in the discharge vessel when in use is of substantial importance. The risk that consequential disturbances may occur which may lead, for example, to back ignitions in the non-conducting phase is very great particularly when the tube has been cut out of circuit for comparatively long time so that its various parts have assumed the surrounding temperature and is then connected into circuit again so that the aggregate is heated again and assumes the operating temperature within a certain time of retardation, for example from minutes to one hour and more.

In the above described heating process an excessive quantity of mercury vapour received from the liquid mercury at a temporarily warmer spot may be deposited on a temporarily colder spot, e. g. on a thermally more inert electrode and cause back ignition. This is due to the fact that the electrodes generally have a. higher thermal capacity than the corresponding part of the wall of the vessel and a rapid equalization of the temperatures of the electrodes and the wall of the vessel is prevented by the resistance to the flow of heat from these electrodes to the medium which serves to cool the tube. Thus, during th heating-up of the tube the risk of harmful mercury deposit is particularly high.

It is already known to. arrange a supply of mercury in a separate vessel which is preferably provided at the coldest spot of the tube and which is in communication with the discharge space proper in such manner that flowing about of the supply of mercury in the latter is avoided and as far as possible only the mercury vapour can pass into the discharge space. Particularly two forms of construction were proposed for this purpose, one of which has a constriction, for example in the form of acapillary tube, whereas with the other the shape of .the comparatively wide connecting channel is such that due to its having suitably shaped perforated partitions, for example, there is apassage for the vapour, but the mercury cannot flow from the separate container even if the vessel is turned upside down.

Germany November 11, 1938 The above solutions have, however, the disadvantage that, particularly in the case of shocks of the vessel, the mercury can still pass through it or that there is only an extremely narrow aperture for the passage of the mercury vapour.

The object of the invention is to insert, in the connecting channel, a separating member which on the one hand fully avoids the discharge of liquid mercury and on the other hand permits of altering the resistance to the passage of vapour to accord as far as possible with practical requirements without the perfect fulfillment of the first-mentioned condition being impaired even to the slightest extent.

According to the invention, use is made for this purpose of a separating member-having a large number of fine passages or apertures each of which is small enough to prevent the liquid mercury from passing through the apertures under the conditions prevailing in the tube, the sum of the latter apertures enabling equalisation of the mercury vapour, existing on both sides, to the extent required in the circumstances.

In view of the above-described difliculties during heating-up of the tube after an interval of operation it is preferable that the flowing resistance of the filter should be such that the quantity of mercury vapour necessary for obtaining the operative vapour pressure in the tube requires an amount of time for its passage into the discharge space which exceeds that in which the tube assumes its operative temperature. Thus the premature passage of an excessive quantity of mercury vapour is avoided in the heating-up period.

The term flowing capacity as used herein and in the claims is to be understood to-mean the number of milligrams of mercury in its vaporized state which will pass through the filter in one minute with a differential pressure of 1 mm. of Hg.

For this reason it is preferable, particularly in the case of high voltage current converting tubes having intermediate electrodes arranged between the anode and the cathode for the purpose of regulating the voltage that the flowing resistance of the filter should be such that during the heating-up period of the tube the deposit of liquid mercury on the said intermediate electrodes is avoided.

It is preferable that. the porous separating body should be sintered together from a powder terial.

In order that the invention maybe clearly understood and readily carried into eflect it will now be described more fully with reference to the accompanying drawing.

The single figure of the drawing shows an incandescent cathode rectifier tube having a mercury vapour filling for very high voltages up to about 180 kilovolts peak voltage in the non-conducting direction. The discharge vessel of this tube is constituted by a glass member I carrying the stem 2 of the helical incandescent cathpde 3 which is activated by means of barium oxide and is provided with a screen 4. The said glass part has connected to it in alternative order the wall'parts of metal 5, 6, 1, 8, 9 and I and also the wall parts of glass H, l2, l3, H, II and it, of which the latter one constitutes the lower closure of the vertically arranged rectifier tube. This part It is provided with acomparatively narrow cylindrical extension l1 the lower end of which contains a small supply of mercury l8 which, due to correct proportioning of the extension, assumes, the temperature necessary for maintaining the desired vapour pressure of about 1 to 6 microns, viz, 20 to 40 C. The supply of mercury I! is separated from the discharge space proper by a so-called glass filter I9, that is to say, a porous member which is made of glass finely pulverized and then sintered together, or in some cases of ceramic material, and which has such a cross-sectional area that irrespective of the conditions the passage of mercury vapour through the filter is practically precluded from being interfered with by the liquid mercury. Even if in themost unfavourable case the total supply of liquid mercury would exist on the upper surface of the filter the equalization of the mercury vapour would nevertheless by effected towards below in an almost unhampered manner in view of the favourable condi-- tions of the free filter surface and of the part of the surface that may be covered by mercury.

In the construction according to the invention it has been found possible to confine the liquid mercury under all operating conditions to the supply container provided for it and in contradistinction to the greater part of well-known con structions the liquid mercury is prevented from passing through the filter even in the case of most violent shaking.

The construction according to the invention permits of the flowing resistance of'the separating member being proportioned to the optimum extent; this results from view points which may be explained most efiiciently with reference to a practical example:

It may occur in practice that the rectifier tube is out of use by night, it being possible for the temperature in unfavourable cases (portable systems in open air) to assume even values of minus 10 C. In this case an increase in temperature of 25 C. is required for putting the tube into use at the lowest admissible temperature of C.

During the heating-up process a temperaturelag of the metal electrodes or the screens may occur since their thermal contact with the heat transmitting surfaces is often unsatisfactory and their thermal capacity is high. The temperature, for example, of the metal rings of the tube,

described is consequently temporarily lower than that of the glass so that condensed mercury becomes deposited on the rings which in turn entails the risk of back-ignitions.

\ In this case it is necessary for the resistance of the glass filter to be maintained at such a value that the rate of the mercury vapour flow in the direction of the discharge vessel is limited to such a value that any excessive quantity of mercury vapour that may become deposited in the manner described does not become available.

The factors decisive in view. thereof, that is to say the thermal capacity of the tube parts, the thermal contact resistances on the contacting surfaces and also the energy and arrangement of the source of heat are so different in practice that itis impossible to give a general rule for proportioning.v On the other hand there is, however, not the leastdifiiculty in each separate case to ascertain, by practical experiments, the value the flowing resistance of the filter must have to avoid condensation on the electrodes during heating-up and on the other hand, however, to obtain the value 01' the vapour pressure necessary for the use of the tube within a time period which may not be too long for practice, for example 01' 15 minutes.

The requisite supply of mercury is distilled into the tube during pumping through a suction tubule 23 and, after the tube has been scaled oi! the'pump, is distilled thence into the lower part of the extension I! by heating the tube in a furnace. For this purpose it is necessary for the lower part of I! to protrude from the furnace so as to assume a lower temperature.

It is advisable to avoid contamination oi the filter surface adjacent the discharge space due, for example to electrode particles that have sprung off, by suitable screens. In the construction described this result is obtained due tothe fact that the metal cylinder 20 which represents the main anode of the tube and is arranged within the metal wall part III also constitutes a closure of the lower part of the tube so that this special part which surrounds the supply of mer-' cury I8 and the filter I9 only communicates freely with the discharge tube proper through lateral apertures 2|. Since the tube is used in the vertical position shown particles falling from the cathode 3 will fall on to the anode bottom 22 and cannot contaminate the filter l9.

It is an advantage of the separating body according to the invention that it can be arranged at any spot of the discharge vessel when the latter is the coldest spot. of the tube and that in this case the supply of mercury can also be arranged above the separating body without there being any risk that liquid mercury'may pass into the discharge space.

What I claim is: p

1. An ionic discharge tube comprising an envelope having a reservoir portion and a connecting portion connecting said reservoir portion to the main discharge space of the tube, a sup,- ply of liquid mercury in' said reservoir portion, an anode and cathode within said envelope and spaced apart to form a discharge path, and means in said connecting portion to prevent passage of the liquid mercury to the main discharge.

space under any condition while allowing equalization of the pressure of the mercury vapor in said reservoir portion and the discharge space, said means comprising a porous member having a flowing capacity not greater than that value at which the time required to obtain the operative vapor'pressure in the tube is equal to thetime required for the tube to reach its operating temperature. v

2. An ionic discharge tube comprising an en'- velope having a reservoir portion and a connecting portion connecting said reservoir portion to and in the discharge space, said means comprising a porous member having a flowing capacity less than that value at which mercury deposits on said intermediate electrode during the heating-up of the tube.

3. An ionic discharge tube comprising an envelope having a reservoir portion and a connecting portion connecting said reservoir portion to the main discharge space of the tube, a supply of liquid mercury in said reservoir portion, an anode and cathode within said envelope and spaced apart to form a discharge path, and means in said connecting portion to prevent passage of the liquid mercury to the main discharge space under any condition while allowing equalization of the pressure of the mercury vapor in said reservoir portion and the discharge space, said means comprising a porous member of sintered material having a flowing capacity not greater than that value at which the time required to obtain the operative vapor pressure in the tube is equal to the time required for the tube to reach its operating temperature.

MARI JOHAN DRUYVESTEYN/

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