US 2445782 A
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July 27, 1948. J. KRUITHOF ETAL ELECTRONIC DISCHARGE TUBES AND CIRCUITS THEREFOR Filed April 1, 1943 2 Sheets-Sheet 1 hllmlw JHCOB KP T OF L. CflBES July 27, 1948. J. KRUITHOF ETAL 2,445,782
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gww/wbo'm JHCOB KPU/THOF' L. CHBES Patented July 27, 1948 "U l TED S TATES ELECTRONIC'DISCHARGE TUBE AND CIRCUITS THEREFOR Jacob Kruithof and Lucien Alfrcd Benoit Cabes, Antwerp, Belgium, assignors to International Standard Electric Corporation,
N. Y., a corporation of Delaware Application April 1, 1943, Serial No. 481,510 In the Netherlands February 24, 1941 'Section 1, Public Law 690, August 8,1946 Patent expires February 24, 1961 3 Claims.
. 1 This invention relates to a gaseous discharge tube having a closed envelope in which electrodes are provided, which according to the purpose and the use of the tube, may be arranged as cathode;
the invention also relates to control circuit arrangements in which such discharge tube is used.
'Itis already known to provide in a gaseous discharge tube a controlling electrode between cathode and anode, whereby the starting of the discharge between cathode and anode is determined by the value of the potential applied to the controlling electrode. It is also already known to provide additional grids in the tube, by
which a shifting of the point of starting of the paratus connected in series with the discharge tube. The disadvantage of these known circuits is that a certain quantity of energy is always taken from the control circuit, the control electrode being (during the discharge time) in conductive contact with the other electrodes by way of the ionized gas of the tube.
The purpose of the invention is to provide means to control directly the starting and stopping of the main discharge and to use this control also to operate a consuming apparatus connected in series with the'discharge tube, withoutenergy being taken from the control circuit during the discharge time.
According to the invention one or more con- "trol electrodes are mounted outside the envelope of the tube, the control electrodes being made in 'the'form of a metallic layer, band, ring, cover or any arbitrary form, each control electrode serving as a direct controlling electrode for the starting and stopping of the main discharge to the anode.
As the control electrode or control electrodes is or are outside the envelope of the tube, conductive contact with the other electrodes through the ionized gaseous inner space of the tube is avoided and no decrease of energy of the control circuit takes place during thedischarge condition of the tube.
#Accor'ding tonne of thercirouit arrangements of the invention, two electrodes, one of which or both may serve as cathodes, are mounted at equal distance from the anode, and an alternating potential of sufficient magnitude is applied between the two first-named electrodes to cause a glOW discharge between them.
This glow discharge may be considered as a fictive filament, which causes an emission of electrons. The maximum value of the alternating potential and the magnitude of the positive potential applied to the anode, are, when added algebraically, not sufficient to initiate an independent discharge between the fictive filament and the anode; however, this discharge does take place as soonas a potential is applied to the control electrode (or to one of the control electrodes) of such a value that will sufiiciently a'cthe two cathodes and the anode, and the discharge will be extinguished when the algebraical 'sumof these potentials becomes less than required for the maintenance of the discharge.
Between the D. C. source and the anode, or at another point in series with the discharge space between anode and cathode, a consuming apparatus, e. g. a relay, may be provided which responds to the changes of the potential applied to a control electrode.
The advantage thereof is that the energy, required for the operation of the consuming apparatus, is only taken from the sources of potential connected in series to the tube, and no energy is taken from the control electrode.
A second circuit according to the invention is arranged in such a way that a rectified A. C. potential is connected to the anode, and the oathode (or more than one cathode connected in parallel) is connected to the negative terminal of a D. C. source through a consuming apparatus, which is either shunted or not by a capacity, and the sum of this D. C. potential and the maximum value of the rectified A. C. potential at the anode is less than the potential required to change the invisible discharge to the anode into an independent visual discharge; the
starting of the visual discharge is controlled by a potential of sufiicient value applied to the control electrode or to one of the control electrodes, while the extinguishing of the discharge takes place after the decrease of the potential applied to the control electrode, as soon as the sum of the rectified A. C. potential and the D. C. potential becomes less than that required for maintaining the discharge.
Two embodiments of the invention are shown in the accompanying drawings.
Figure 1 shows a circuit arrangement in which an A. C. potential is applied between two electrodes within the tube and in this way a fictive filament is formed by the glow discharge between these electrodes. The consuming apparatus to be controlled is connected in the anode circuit of the tube.
In Figure 2 two electrodes serving as cathodes are connected in parallel, and the consuming apparatus to be controlled is connected in the cathode circuit of the tube. Curves illustrating the operation of the circuit arrangement of Figure 1 are shown in Figures 3a and 31), while Figures 4a and 4b are curves which relate to the circuit arrangement of Figure 2.
In Figure 1 three electrodes C, C" and A are arranged within an envelope filled with gas at low pressure.
An A. C. source is connected to a transformer T from which a potential Vl is applied between the ends of the secondary winding to the electrodes C and C", over which a glow discharge is established, bringing about an emission of electrons.
This glow discharge forms a fictive filament or a source of electrons.
' Practically equidistant from electrodes C and C the anode A is arranged, a positive potential V being applied to the anode from source B. The potentials VI and V are connected therefore in this circuit arrangement in series with electrodes C and A of the tube. A load device, such as relay R, is also connected in the anode circuit.
In Figure 1 four potentials are of practical interest:
(1) A lighting potential Va, required to cause the starting of a glow discharge between the electrodes C and C;
(2) A potential Vb, which is just suificient to maintain such a glow discharge between the electrodes C and C";
(3) A lighting potential Vc, required to cause the starting of a glow discharge between C or C" and A;
(4) A potential Vd, which is just suflicient to maintain this last named discharge.
The values of V and VI are selected such that the maximum potential of VI is equal to or larger than Va; further than the V+VI max. is lower than V0, and V is lower than Vd.
From the last named condition it follows that the field ACC" is of too small value to cause the Townsend discharge to change into an independent visual discharge; in other words, the electrons emitted by the fictive filament C'C" will not be sufficiently accelerated on their way to the anode to energize the anode circuit through the main discharge space of the tube.
Outside the tube a control electrode H is arranged and may have an arbitrary form, for example, it may be formed as a cap, a ring or a band. An appropriate form, however, consists in a metallized layer on the glass of the tube.
Normally such a potential is applied to the electrode H that the electro-static field between H and C, C" is opposite to the field C'C"A, so that the electrons from the fictive filament encounter still more resistance in order to reach the anode.
The situation is completely changed as soon as apositive potential is applied to the electrode H, as now the two fields are supporting each other, and therefore the ionization is (at a predetermined value of the positive potential of H) increased to such an extent that the invisible discharge of Townsend changes into a visual discharge, the discharge takes place in the tube and a current flows through the anode circuit, in which the consuming apparatus R is inserted. As soon as the potential of H is made negative again, the accelerated movement of electrons to the anode is decreased and a moment comes at which the tube will extinguish, i. e. when the potential VI passes the point at which this potential, together with the D. 0. potential V, becomes less than the value Vd. The above is illustrated by Figure 3a.
This figure shows that the A. C. potential VI superposed on the D. C. potential will, in the normal condition of the tube, (that is to say when no positive potential is connected to a control electrode) never reach the value Vc, i. e. the potential which in the normal condition of the tube causes the main discharge. By connecting the control potential to H an amplification of the electrostatic field is obtained, which has the same effect as if the value Vc were decreased to Vcl, as shown in Figure 3b. This discharge is established as soon as the potential curve reaches the value Vcl, and is extinguished when the potential curve decreases to the value Vd. During the following cycle of the A. C. potential, if the potential of the controlelectrode H is still present, the discharge takes place again as described above. The discharge is definitely extinguished when, after decrease of the potential of H, the decreasing potential curve intersects again the line Vd; or when, at a time when the control potential is taken away from H, no discharge takes place. Current flows in the anode circuit during the periods shown by shaded areas of Figure 3b.
The consuming apparatus R receives rectified current pulses as long as a potential of sufilcient value is present on the control electrode, and the consuming apparatus may be supplied with constant current in one of the different known ways during the entire duration of connecting the potential to H, for example, by connecting a capacity in parallel to R.
From the above it appears that control electrode H provides very simple means to control the action of the tube so that the consuming apparatus responds in accordance with the polarity and value of the potential applied to the control electrode. I V
Figure 2 shows a second embodiment of the invention. Here the electrodes C and C are connected in parallel, so that there is no question any more of a fictive filament. They are biased by source B to a negative potential V with respect to ground G, which potential is lower than Vd, i. e.,the potential whichis just sufficient to maintain the discharge between C, C" and A.
A pulsating DC. potential V2 originating from a rectified A. C. potential is applied to the anode. As shown in Figure 2, the rectified potential is supplied by a rectifier consisting of a transformer Tathe primary of which is conhected to a suitable source of alternating current. The mid-point of the secondary is grounded, and the ends of the secondary winding areconnected through rectifier elements Ru and Rb to one terminal of a load resistance Re, the other terminal of this resistance being connected to the grounded mid-point connection. The anode A is connected to the common connection between rectifier elements Ra and Rb and resistance Re. The arrangement produces full-wave rectification, and the rectified potential V2 developed across resistance Re is applied to the anode A.
This rectified potential is selected in such a way that V+V2 max. is lower than the lighting potential Vc for a discharge between '0" and A and the sum is greater than Vd.
If a negative potential is applied to the control electrode H, then 'an insufficient number of electrons are freed to convert the Townsend discharge into an independent ionized discharge.
If, however, a positive potential of sumcient magnitude is connected to the control electrode, then the independent discharge will take place, since both fields aid each other in giving sufficient acceleration to the electrons.
The discharge extinguishes as soon as the potential of the rectified alternating current, together with the direct current V, becomes smaller than the value Vd.
The above is illustrated in Figures 4a and 412. Figure 40. represents the condition when no positive potential is present on H. The rectified A. C. potential V2 is superposed on the D. C. potential V in the main discharge space, but the maximal sum of the values of these potentials does not normally reach the starting potential V0. The connecting of a positive potential of sufiicient value to H has the same result as if the value Vc were reduced to Vcl, as shown in Figure 4b. The discharge now takes place at the moment the potential curve reaches at least the value Vcl and continues until, by the decrease of the potential, the line Vd is reached. Then at a following increase of potential, the potential on H being still present, the discharge takes place again as described above. The discharge is definitely extinguished when, after the decrease of the potential of H, the potential curve reaches the line Vd; when the rectified A. C. potential V2 decreases, or when the potential is removed from H, no discharge occurs. Rectified current pulses pass through the main discharge space of the tube and through the consuming apparatus R, which is now connected in series between the electrodes C, C and the negative terminal of the direct current source B.
The condenser 0 parallel to the consuming appar'atus '(relay R) serves to smooth the rectified alternating current flowing through R; moreover, this condenser promotes the extinguishing of the main discharge.
In order to shorten the periods of no current for the consuming apparatus as much as possibio, and also with the aim to make the time during which the consuming apparatus responds equal, as accurately as possible, to the time during which potential is connected to H, it is advisable to select the frequency of the potentials VI and V2 as high as possible. This frequency is, however, limited to an upper limit by the deionization time of the tube.
When during the discharge condition the potential decreases to the value Vd, the discharge will stop immediately, but the gas in the tube still remains in an ionized condition for a short time.
During this time the potential curve may again reach the value Vd, and the discharge condition would again occur, even if the potential on H be removed.
In order to prevent this, it is necessary to select the frequency of VI or V2 such that de-ionization can take place between two consecutive discharge periods.
The time of de-ionization of the tube causes a certain delay in the operation of the consuming apparatus in response to the potentials applied to H.
Instead of connecting a rectified A. C. potential to the anode as in Figure 2, an A. C. potential may be used if desired. In this case the operation will be as shown in Figures 3a and 319. Here the relative time available for de-ionization is greater than with a rectified A. C. potential, so that the frequency may be increased.
Instead of only one control electrode H, a larger number of control electrodes may be provided, by which operation with more control potentials is possible. Moreover the shape and arrangement of the control electrodes may differ from each other.
It is clear that in the arrangements described, operation of the consuming apparatus requires energy to be taken only from the potential sources V and VI, and no energy is taken from the control electrode.
1. Control apparatus comprising a discharge tube containing an anode, a cathode and a third electrode, an external control electrode on the envelope of the tube, said cathode and said third electrode being spaced substantially equal distances from said anode, and including means for applying a direct current potential between said anode and said cathode and means for applying an alternating potential between said cathode and said third electrode to establish an ionized discharge between said electrodes, said discharge forming an electron emitting fictive filament, the algebraic sum of said alternating potential and of the potential applied to said anode being insufiicient normally to initiate an independent discharge between said fictive filament and the anode, but being efiective to establish said independent discharge when a positive potential is applied to said control electrode.
2. Control apparatus comprising, in combination, a gaseous discharge tube having a closed envelope with an external control electrode and containing three spaced electrodes comprising a cathode, an anode and a third electrode, said cathode and said third electrode being spaced substantially equal distances from said anode, a source of alternating current potential connected between said cathode and said third electrode to establish an ionized discharge between said electrodes, said discharge forming an electron emitting fictive filament, a work circuit including a source of direct current connected between said anode and one of the electrodes of said fictive filament, said direct current potential being insufiicient normally to establish an independent discharge between said fictive filament and the anode, and control means for successively accelerating the electrons supplied from said fictive filament to said anode to a value sufiicient to establish an independent discharge between said anode and said fictive filament.
3. Control apparatus comprising, in combination, a gaseous discharge tube having a closed envelope containing an anode and two spaced cathode electrodes, means for applying an alternating potential between said two cathode electrodes for establishing a glow discharge between the cathode electrodes, a control electrode arranged outside of said envelope, a Work circuit including a source of direct current potential connected between said anode and said cathode electrodes, the algebraic sum of said direct and alternating potentials being insufficient normally to establish an ionized discharge between said anode and cathode electrodes, and a control circuit for selectively applying a sufiicient positive potential to said control electrode to establish an ionized discharge between said anode and cathode electrodes, said work circuit including a consuming device.
JACOB KRUITHOF. LUCIEN ALFRED BENOIT CABES.
REFERENCES CITED The following references are of record in the file of this patent:
UNITEDSTATES PATENTS Number Name Date Re. 20,345 Schaberle Apr, 27, 1937 1,410,702 Meyer Mar. 28, 1922 1,661,579 Rollinson Mar. 6, 1928 1,863,702 Smith June 21, 1932 1,938,742 Demarest Dec. 12, 1933 1,984,877 Jobst et al Dec. 18, 1934 2,001,836 Craig May 21, 1935 2,103,439 Swart Dec. 28, 1937