US2170034A - Rectifier tube - Google Patents

Description

g- 22, 1939' j E, H. REERINK ET AL RECTIFIER TUBE 2 shet -sheec 1 Filed June 19, 1937 6 W M V A E 1% FEE M0171? KIA/A W lead Patented Aug. 22, 1939 UNITED STATES wag PATENT OFFICE RECTIFIER TUBE Engbert Harmon Reerink and Mari Johan Druyvesteyn, Eindhoven,

Netherlands, assignors to N. V. Philips Gloeilampenfabrieken, Eindhoven,

Netherlands Application June 19, 1937, Serial No. 149,234 In Germany June 29, 1936 '7 Claims.

and for other gaseous fillings lies between maximum and minimum values which result in a free path of the atoms of identical order of magnitude, and having an incandescible cathode of metal wire which is loaded with an emissive current whose value is at least amps. per sq. cm. of active cathode surface..

The term "active cathode surface as used herein and in the claims is to be understood to mean the contour surface of the cathode wire; i. e. a surface of circular section surrounding the oathode wire in the form of a tube and having a diameter equal to the outside diameter of the completed cathode wire. The comparatively small irregularities in the surface of the cathode wire, which may be formed by a number of individual wires, are of no importance as regards the present invention, and therefore are not taken into consideration. The term gaseous filling is to be understood to include a filling of one or more gases or vapors, or a mixture thereof.

The main object of our invention is to increase the life of such tubes.

A further object of the invention is to decrease the arc voltage of the discharge.

Another object is to decrease disintegration of the cathode.

In accordance with the invention, we obtain the above objects by properly spacing the parts of the cathode, for instance by stretching a helical cathode wire so that there is considerable distance between adjacent turns.

More particularly, in the case of a helical cathode, we make the distance between the surfaces of adjacent turns of the wire at least equal to the largest diameter of the wire, or we make this distance at least twice that distance required in order that the entire periphery of the wire may participate in the emission.

We have found that with the above zone oi pressures and current loads a proper interspacing of the cathode results in a substantial increase in tube life. Furthermore, simultaneously with this increase in life, there is a decrease inthe are voltage of the discharge which, probably because of the resulting decrease in cathode disintegration, is to be considered as the cause of the increased life.

The same ratio between maximum and minimum values applies to other rare gases and to mercury vapor, in which cases the maximum values pmaxare for example:

Millimeters of mercury Helium 0.100 Neon 0.070 Argon 0.020 Krypton 0.012 Xenon 0.010 Mercury vapor 0.008

The values of the free path of the atoms which correspond to the pmax. values for rare gases and mercury vapor indicated above are all of the same order of magnitude. The surface load of the cathode when using any of the fillings should be at least amp. per sq. cm. of active cathode surface, as for lower loads a more perforated form of the cathode no longer yields any appreciable advantages.

We are aware that in so-called gas-free discharge tubes, it has been proposed to stretch a helical cathode wire so that adjacent turns were not too close together; however, this was done in order that the negative space charge of the electrons on the cathode would not prevent emission by the less accessible parts. Although similar constructions were also used with tubes having a gas filling of very low pressure in which a larger zone of the negative spacial charge is adjacent the cathode, for example at a gaseous pressure of about 0.004 mm. for argon, in such cases the current density was substantially below the load values with which the invention is concerned, i. e. below 0.050 amp. per sq. cm. of active cathode surface.

Such cathode constructions, however, are rarely used in incandescible cathode tubes having a higher operating pressure, and in which the voltage drop between the anode and the cathode is limited to a very thin space charge layer on the incandescible cathode (arc discharge), but the cathode wire is wound in a compact helical form to avoid unnecessary heat losses to the surrounding gaseous filling. Positive ions for neutralizing the space charge are in this case also available to a suflicient extent in the clefts and recesses of the cathode.

We are also aware that it is known to form the cathode in a gas-filled tube as a hollow cathode, i. e., to arrange the cathode windings with such a relative spacing, or to give them such a diameter that also the inner surface of the cathode participates in the emission. The phenomenon on which the present invention is based is, however, quite different because a cathode which satisfies the above requirements, will give new and advantageous results when used with the range of current loads and gas pressures with which the present invention is concerned.

Tests on discharge tubes according to the invention having identical pressure and helical cathodes of identical nature, but with the windings drawn apart to a greater or less extent, have shown that for the purpose of obtaining the desired increase in life, it is necessary to make the relative spacing between adjacent wireshaped cathode parts, e. g. twists or windings, at least about double that value at which the entire periphery of the cathode wire participates in the emission.

In order that our invention may be clearly understood and readily carried into effect, we shall describe the same in more detail with reference to the accompanying drawings, in which:

Figure l is a, partly sectionized view of a rectifier tube according to the invention;

Figs. 2a and 2b are enlarged views of a portion of Figure 1,

Figs. 3 to 6 are graphs showing the currentvoltage curves of the tube shown in Fig. 1 for different filling pressures, and

Fig. '7 shows a switching device in which a discharge tube according to the invention is used.

The rectifier tube illustrated in Figure 1 com prises a spherical glass envelope 1 forming a press 4. Centrally arranged within envelope l and supported from press 4 by lead-supports 5 is an incandescible oxide cathode 2 in the shape of a helix. Arranged symmetrically with respect to cathode 2 with their surfaces parallel to the axis thereof are two disc-shaped nickel anodes 3.

Measurements were taken upon the tube shown in Figure 1 with direct current and with anodes 3 connected in parallel to one side of a load, whereas the tube was connected to a suitable direct current supply as indicated in Figure 1. The measurements were taken upon tubes having dimensions as given below and indicated in Figures 2a and 2b:

Diameter of envelope 1 mms Distance of anodes 3 from center of the cathode 2 g mms 15 Diameter of anodes 3 (W) mms 30 Number of turns of cathode 2 6 Diameter of covered cathode wire (L) mm. 0.6 Internal diameter of cathode 2 (H) mms. 3.3 Length of cathode helix (K) (5 different Values) mms 5.5, 9, 14, 19 and 34 Distance between turns of cathode helix ((1) mms 0.2, 0.8, 1.6, 2.5 and 5.0 Active cathode surface sq. cms 1.6 Black temperature of the non-emitting cathode deg. K 1200 Real temperature of the non-emitting cathode deg. K 1350 Cathode-supply voltage approximately volts 2 Heating current of the cathode approximately amps. 8.5 Gas filling used Argon The adjustment of the incandescible cathode to the temperature value given above was effected with an unloaded anode circuit; that is to say free from any influence of variations in the load condition of the anode circuit.

The curves of Figures 3 to 6 were taken with an argon filling of 0.004, 0.006, 0.018 and 0.060 mms. of mercury respectively, whereas the four curves of each figure were taken for distances d of 0.2, 0.8, 1.6, and 2.5 mms. It may be assumed that at a distance d of 0.2 mm. the entire periphery of the cathode wire participated in the emission.

Inspection of Figures 3 to 5 shows that at current loads of amp. per sq. cm. of active cathode surface, i. e. from 0.16 to 0.44 amp. (which, for the purpose of the invention, constitute minimum values) and at a small winding distance, i. e. 0.2 mm., the arc voltage is substantially higher than for greater distances cl, 1. e. distances that exceed the wire diameter of the cathode, i. e. 0.8 mm. or over.

In contradistinction to this, Figure 6 shows that the difierence between the arc voltage values for the various distances (1 is but very small at a pressure of 0.060 mm.

At the gas pressures according to the invention, 1. e. as shown in Figures 3 to 5, the abovementioned difference in arc voltages exists even up to the highest current values; the difi'erence at the lower pressures of 0.004 and 0.006 being particularly remarkable. At 0.018 mm. pressure, as shown in Figure 5, there is still a reduction of the arc voltage of the order of 50 volts, whereas at 0.060 mm. pressure, as shown in Figure 6, no effect can be ascertained at all for the highest current values.

It will be noted that the above effect ceases as soon as the curves have a decidedly negative character. On the other hand it should be noted that the characteristic curves of Figures 3 to 5 at the small current values obviously tend, for all the distances d respectively, to reach a common voltage value, which indicates that the eifect according to the invention is no longer present for currents lying substantially below the minimum limit of per sq. cm. of active cathode surface, or 0.096.

We have found that there is a certain relation between the arc voltage and the length of life of a discharge tube, i. e. that a comparatively small reduction in the arc voltage, under certain conditions, brings about a substantial increase in the life. For this reason the reduction of the arc voltage obtained in accordance with the invention is of decisive importance in connection with the length of life of the tube.

For example, from Figure 3 it may seem that for a discharge current of 1 amp. and d equal to 0.2 mm., the arc voltage has a practically unserviceable value, whereas when d=0.8 mm. it falls to about 30 volts, and when (i=5 mms. it falls to about 20 volts. This is extremely favorable in view of the low pressure of 0.004 mm. of mercury, because the length of life of the tube, which was previously practically unserviceable, is greatly increased.

This same eiTect is shown in Figure 4, in which the arc voltage, for the same current value of 1 amp. and the distances d of 0.8 and 5 mms.,

decreased from above 50 volts to 23 volts and about 17 volts respectively. Also in Figure 5,

for the same current value of 1 amp. the initial potential loss of 23 volts for (i=0.8 can still be reduced to the very favorable values of 16 and 14 volts respectively.

The variations of the arc voltage between 12 and 14 volts, as shown in Figure 6, at 1 amp. discharge current, will have only an immaterial eifect upon the length of life of the tube.

From Figures 3 to 5 it will be noted that for current loads below the limit of amp. per sq. cm. of active cathode surface, the effect is strongly decreased, and that the values for the life and the arc voltage of the tube approach, with decreasing current strength, more and more to those values which can be obtained by means of a cathode which is not drawn apart. However, by increasing the peak-value of the discharge current to at least are coordinated parallel to each other and the surface parts of which turned to each other have largely been annihilated by the coordination. It is also clear without further explanation that on a band-shaped cathode an emitting point has available a substantially smaller solid angle within which it can derive the requisite ions from the gas filling than on a round wire-shaped cathode.

Although vention may be filled with rare gases, and have been described in this connection, equally good results can be obtained with mercury vapor or a mixture'thereof, Furthermore, mercury vapor has the advantage that the correct vapor pressure in the tube can be maintained at all times byproviding within the envelope a mercury drop serving for permanent renewal of the vapor. Our invention is particularly advantageous when applied to switch devices for high currents in which instantaneous currents are conducted via the main discharge path of amercuryvapor-filled discharge tube. Because of instantaneous switching operations taking place in such devices, there is insufficient time for the mercury vapor pressure to reach a high value due to the heating up of the tube, and as a result of the low pressure, an intense cathode disintegration resulting in a shortened tube life takes place. By applying the present invention to such devices a greatly increased life is obtained, which is particularly valuable.

In Fig. 7 a switching device of this kind is shown in a diagrammatical manner. A grid controlled discharge tube 1 and a load are connected in series to an A. C. supply. Tube 1 is provided with a filling of mercury vapour prodischarge tubes according to the in amp. per sq.

duced by a liquid mercury supply 8 situated in a projection 9 of the discharge vessel of the tube. Moreover a filling of 30 microns of argon is provided in order to facilitate starting of the discharge. The incandescible cathode I0 is connected to the secondary winding ll of a step down transformer the primary winding l2 of which is connected to the same supply. A control circuit has been shown in a schematical manner, by means of which the flow of a discharge current through tube I may be initiated or stopped at will suitable potentials being applied to the control grid l3 of the tube. Thus the latter may perform the function of a switching member interposed between the load and the supply. This permits the same to provide pulsating direct current to the load as if it were controlled by means of a switch.

The spacing of the helical windings of the incandescible cathode I0 and the intensity of the load current are chosen to fulfill the requirements of the invention in connection with the pressure of the argon filling. Thus an appreciable gain is obtained in cathode life and consequently in the useful life of the switching tube 1.

Although we have described our invention in connection with specific examples and applications, we do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What we claim is;

1. An ionic discharge tube having an arc-like discharge comprising an anode, an envelope and a gaseous filling within said envelope having during operation a pressure between a maximum value pmax. and a minimum value 9 equal to 1/25 pmax pnm. being equal to 0.02 mm. of mercury in the case of argon and for other gaseous fillings being values which result in a free path of the atoms of identical order of magnitude, and an incandescible cathode having a plurality of parts spaced apart by a distance at least twice the distance at which the entire cathode participates in the emission, said cathode having an electronemitting current capacity whose value is greater than cm. of active cathode surface and below the value at which unsatisfactory tube life is obtained.

2. An ionic discharge tube operation with an arc-like discharge and comprising an anode, an envelope, a gaseous filling within said envelope and having during operation a pressure between a maximum value pmax. and a minimum value p equal to 1/25 pm, jUmax. being in the case of argon equal to 0.02 mm. of mercuryand fore other gaseous filling being values which result in a free path of the atoms of identical order of magnitude, and an incandescible cathode having a plurality of parts spaced apart by a distance which is at least twice the distance at which the entire surface of the cathode would participate in the emission, said cathode being designed to have a current carrying capacity whose value is greater than amp. per sq. cm. of active cathode surface and less than the value at which the tube has an unsatisfactory life.

3. A rectifying device comprising an ionic discharge tube with an arc-like discharge and having an anode, an envelope and a gaseous filling within said envelope and having during operation a pressure between a maximum value pmax. and a minimum value 19 equal to 1/25 pmax, pmax. being equal to 0.02 mm. of mercury in the case of argon and for other gaseous filling being values which result in a free path of the atoms of identical order of magnitude, an incandescible cathode having a plurality of parts spaced apart by a distance at least twice the distance at which the entire cathode participates in the emission, means to heat said cathode, and means to apply a voltage across said anode and cathode to load said cathode with an emission current having a value greater than F .08 0.4 pinax.

amp. per sq. cm. of active cathode surface and below the value at which unsatisfactory tube life is obtained.

4. A rectifying device comprising an ionic discharge tube having an anode, an envelope and a gaseous filling within said envelope and having during operation a pressure between a maximum max amp. per sq. cm. of active cathode surface and below the value at which unsatisfactory tube life is obtained.

5. A rectifying device comprising an ionic discharge tube with an arc-like discharge and having an anode, an envelope and a gaseous filling within said envelope and having during operation a pressure between a maximum value pmax. and a minimum value p equal to 1/25 171mm,, pmax. being equal to 0.02 mm. of mercury in the case of argon and for other gaseous filling being values which result in a free path of the atoms of identical order of magnitude, an incandescible cathode wire having a plurality of portions spaced apart a distance at least twice the distance at which the entire cathode participates in the emission, means to heat said cathode, and means to apply a voltage across said anode and cathode to load said cathode with an emission current having a value greater than amp. per sq. cm. of active cathode surface and below the value at which unsatisfactory tube life is obtained.

6. A rectifying device comprising an ionic discharge tube with an arc-like discharge and having an anode, an envelope and a filling of saturated mercury vapor within said envelope and having during operation a pressure between 0.008 and 0.003 mms. of mercury, an incandescible cathode comprising a wire helix, the distance between the turns of said helix being at least the outside diameter of the wire, means to heat said wire, and means to apply a voltage across said anode and cathode to load said cathode with. an emission current having a value greater than 0.095 amp. per sq. cm. of active cathode surface and below the value at which unsatisfactory tube life is obtained.

7. A circuit arrangement for the switching of high current intensities, said circuit arrangement comprising a current supply, a load, a control circuit and an ionic discharge tube with an arclike discharge and having an anode, a control grid, an envelope and a gaseous filling within said envelope having during operation. a pressure between a maximum value pmax. and a minimum value q al to 1/25 pmasn, pmax. being equal to 0.02 mm. of mercury in the case of argon and for other gaseous fillings being values which result in a mean free path of the atoms of identical order of magnitude, an incandescible cathode having a plurality of parts spaced apart by a distance at least twice the distance at which the entire cathode participates in the emission, said cathode having an electron-emitting current capacity whose value is greater than from said current supply to said load through said discharge tube, the flow of said load current being controlled by means of said control circuit in connection with said tube.

ENGBERT HARMEN REERINK. MARI JOHAN DRUYVES'I'EYN.

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