US2475197A

US2475197A - High-tension switching means

Info

Publication number: US2475197A
Application number: US781378A
Authority: US
Inventors: Quittner Victor
Original assignee: GEN RADIOLOGICAL Ltd
Current assignee: GEN RADIOLOGICAL Ltd; GENERAL RADIOLOGICAL Ltd
Priority date: 1946-02-01
Filing date: 1947-10-21
Publication date: 1949-07-05
Anticipated expiration: 1966-07-05

Description

y 1949. v. QUITTNER 2,475,197

HIGH-TENSION SWI'ECHING MEANS Filed Oct. 21, 1947 M VEN'rcn Vwron Gun-mu:

Patented July 5, 1949 UNITED STATES PATENT OFFICE HIGH-TENSION SWITCHING MEANS Application October 21, 1947, Serial No. 781,378 In Great Britain February 1, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires February 1, 1966 8 Claims.

This invention relates to the control of high tension electric circuits.

Its purpose is to make it possible to control such circuits with a high degree of precision of timing by the aid of low tension control means.

In particular, but not exclusively, the invention is concerned with the control of the high tension supply circuits of Xray tubes, more especially in X-ray photography, to make possible short exposures of the order, say, of one fiftieth of a second, or a rapid succession of short exposures such as are required for kinematography with X-rays.

To control the heavy currents which necessarily flow in the primary circuit of an X-ray tube supply network necessitates the use of robust contactors or like switching apparatus which cannot readily be operated with great precision. For this reason it has been proposed to control the high tension circuit of the X-ray tube by means of a grid-controlled thermionic valve, or by means of a grid in the X-ray tube itself. Moreover when the X-ray tube is supplied from high tension condensers-e method which diminishes the surge of current drawn from the mains by the transformer supplying the tube on switching on-interruption of the supply must necessarily be cfiected on the high tension side. But the manual means, or, where used, the automatic means, employed for switching the X-ray tube on and off should preferably be at a low voltage relatively to earth for reasons of safety and to save expense in insulation.

The problem therefore arises of operating a switch tube in a high tension circuit from low voltage control means; the term switch tube is to be understood hereinafter as including the X-ray tube itself where the operation of an X- tube is controlled by its own grid, as well as any other grid-controlled tube controlling a high tension circuit.

With this problem in view one object of the present invention is a control apparatus for high tension circuits which includes besides the switch tube a gas-filled tube governing the rid circuit of the switch tube, and itself governed by impulses conveyed to it from a low tension circuit thoroughly insulated from it.

A further object of the invention is a control apparatus for high tension circuits in which. each operation upon the high tension circuit, whether of closing it or opening it, is effected by rendering conductive a gas-filled tube by means of an impulse conveyed to it from a low tension circuit.

Yet another object of the invention is a con- 2 trol apparatus for high tension circuits comprisin a switch tube and a grid-controlled gas-filled tube governing the grid circuit of the switch tube.

These and other objects of the invention will be more fully understood from the following description of embodiments of the invention illustrated, by way of example, in the accompanying drawings.

In. these drawings,

Figure 1 is a diagram of connections of a switch tube controlled by a gas-filled diode;

Figure 2 is a-diagram of connections of a switch tube controlled by a gas-filled triode;

Figure 3 is a modification of the scheme of i ure 2;

Figure 4 is a dia am of connections of a switch tube which is switched on by rendering conductive a gas-filled tube, and is switched off by rendering conductive nother gas-filled tube;

Figure 5 is a diagram of connections enerally similar to Figure 4 utilising capacitative coupling to convey control impulses from a low tension circuit to gas-filled valves;

Figure 6 is a diagram of connections generally similar to Figure, i showing the use of automatic timing means in t e low tension control circuit.

In all these figures I is a grid-controlled switch tube Which may itself be an X-ray tube which it is the purpose of the circuit to control, or may have an X-ray tube or other high tension apparatus included in its anode circuit. Its cathode and anode are connected directly or through other apparatus to be controlled to the negative and positive terminals marked and of a high tension source of supply. The grid circuit of tube I includes the usual protective resistance 2 a sourc of negative bias 3 and a substantial resistance 4. The source of bias is indicated for simplicity as a battery, but the bias may be obtainedin any well-known way; it is sufilcient in amount to render the tube I non-conductive notwithstanding the high tension supplied to its cathode-anode circuit.

The resistance 4 is included with a source of voltage 5, also indicated as a battery but which can be any convenient source, in the circuit of a gas-filled diode 6. This circuit also includes the secondary winding 1 of a cored or coreless transformer I, 8.

As is well known a gas-filled tube requires the application of a certain voltage to render its substantially conductive; but when it has been rendered conductive a less voltage is sufficient to maintain the current through it; the least voltage necessary to, produce substantial conductivity may be distinguished as the striking voltage, and the least voltage sufiicient to maintain the flow of current as the extinction voltage. The source of anode voltage has a voltage intermediate between the extinction voltage and the striking voltage of tube 6.

In the primary circuit of the transformer i, 8 there is a switch 9, which may be operated manually or mechanically, as by the mechanism of a kinematographic camera; and there is a source of current i I. The circuit controlling part of the switch will usually be a thermionic tube, with a grid circuit controlled manually or mechanically or by electronic timing means such as described hereinafter with reference to Figure 6.

The source H, and the transformer 1, 8 are so designed that the closing of the switch 9 produces in the secondary winding 1 a pulse of voltage in a direction assisting the source 5 and of a magnitude exceeding the difference between the voltage of source 5 and the striking voltage of tube 5. The tube 6 therefore becomes con ductive and current from the source 5 flows through it and the resistance 4, and continues to flow notwithstanding the cessation of the pulse of voltage in the secondary winding 1 since the voltage of source 5 exceeds the extinction voltage of the tube 6.

The circuit 4, 5, 6, 1 is so designed that the current flow in the resistance 4 produces across the resistance a voltage opposing the bias voltage of 3 and of sufficient magnitude to make the tube l conduct.

When the switch 9 is opened a reverse pulse of E. M. F. is generated in the secondary Winding I of suiiicient magnitude to reduce momentarily to zero the current through the diode 5. The diode does not again become conductive when this reverse pulse ceases because the voltage of the source 5 is less than the striking voltage of the tube.

Thus the high tension circuit is closed and opened as if it were under the immediate control of the switch 9.

Figure 2 shows the use of a gas-filled triode It in place of the diode 6. Its anode circuit contains a source of voltage l3 sufficient. when the triode is rendered conductive, to pass through the resistance 4 such a current as will make the voltage drop across 4 adequate to overcome the cut-on bias 3 upon the switch tube I. Its grid circuit contains a source of bias M sufiicient to prevent current flowing through the triode I? under the voltage applied to its anode.

In some gas-filled tubes the flow of current once started cannot be, or cannot readily be, influenced by the grid alone. For this reason the secondary winding 1 is placed in the cathode circuit of the tube 2. that is to say it is common to both the grid circuit and the anode circuit. If the tube i2 is of a kind in which a moderate negative grid voltage will suffice to interrupt the curent flow, the secondary winding 1 may be in the rid circuit alone.

The impulse of E. M. F. generated in the winding 1 upon the closing of the switch. 9 opposes the bias M and makes tube l2 conduct; the impulse generated upon the opening of switch 9 adds to the bias I4 and opposes the anode voltage l3 and brings the tube current to zero.

It is likely that a switch tube suitable for the control of a high tension circuit will need a high negative bias to bring it to cut-off. and will have a considerable grid current when anode current is flowing. For such a tube it is desirable to modify the circuit shown in Figure 2 by putting the high cut-off bias voltage l5 in series with a high resistance It in the anode circuit of the gas-filled tube l2, leaving only a relatively low resistance i! in the grid circuit of l and not in the anode circuit of I2. The source I 5 now serves as, or as part of, the anode voltage for tube 12 while the voltage produced across resistance Hi When tube l2 conducts opposes as before the grid bias due to i 5 and causes the tube l to conduct.

To make the gas-filled tube conduct the transformer l, 8 has only to supply a pulse of voltage. To bring to zero the current in the gas-filled tube the transformer must supply a substantial amount of energy, especially if the switch tube is one that needs a somewhat large positive bias to make it conduct and carried considerable grid current when conducting. It is therefore preferable so to arrange the control circuit that the extinction of the discharge through the switch tube, like the striking of the discharge, is brought about by the striking and not by the extinction, of a discharge through a gas-filled tube. This is readily done by use of two gas-filled tubes connected in series or in parallel.

Figure 4 is an example of such an arrange ment. So far as switching on the switch tube l is concerned the circuit is substantially like that of Figure 2. The grid circuit of the gas-filled triode receives impulses from the low tension primary circuit 8. 9, l I through the transformer I, 8, and its anode circuit contains the resistance 4, flow of current through which modifies the bias on tube 1 causing it to conduct. But in addition to the triode l8 there is a second triode l8a connected in series with the triode i8 and in parallel with the resistance 4. A source of anode current l9 and a resistance 20 are common to both the tubes l8 and Mia. The tube [8a may be controlled by a

primary circuit

8a, 9a, H operating through the transformer 10:, 80..

On closing the switch 9 tube i8 is made con ductive and tube is switched on substantially as explained with reference to Figure 2. On closing the switch 9:; tube I8a is made conductive, and as its anode-cathode impedance is small compared with the resistance 4 it, in effect, shortcircuits the resistance restoring the bias on tube l to substantially its initial cut-off value.

The circuit may be modified to require only one switch, and indeed only one primary winding, the two secondary windings being put upon a common core; or there may be only a single secondary also.

In all the circuits so far described the low tension control circuit is insulated from the high tension circuit by the use of a well-insulated transformer I, 8 or 1a, 8a. It is equally possible to separate the circuits by the insulation of a suitably designed condenser; in other words to use capacitative coupling in lieu of inductive coupling between the low tension circuit and the rest of the apparatus. trated in Figure 5 in a circuit otherwise corresponding with Figure 4. In lieu of the

transformer

1, 8, 1a, 8a, three high tension impulse condensers 2!, Z2, Z3 couple the two primary circuits to the grid circuits of the tubes l8 and HM respectively, the connection of the grid circuit of tube Iiia being completed by a connecting condenser 24. The grid circuit of tube l8 contains a high frequency choke 25, and the grid circuit of tube [8a a high frequency choke 25. The condensers 2|, 22 and 23 are designed to afford the desired insulation and to pass an impulse of the By way of example this is illus- AJWAQ des ed magn tude; h operation at t e circui is substantially, thev Same as that of the circuit of Fi ure In any of these circuits, an amplifier stage may be inserted between the gas-filled tube and the switch. tube, it is to control, to diminish the voltage that the gas-filled tube is to deal with and to, provide considerable grid current for the switch ube- When the, action is v required to be automatic, the primary circuit may be governed by a timin device, which may be electronic and dependent either directly on time or on the passage of a given quantity of electricity through the X-ray tube circuit. Many such timing devices are already well known. The application. of, the inven tion to an automatically controlled high tension circuit will be understood from the instance illustrated in Figure 6. In main this figure 1s similar to Figure 4 and its part are correspondingly: numbered. Closing of the switch 9 effects the switching on of the switch; tube I in the manner already explained. In lieu of the switch 9a of Figure. 4 there is provided an additional gas-filled triode 21 the grid circuit of which contains, a source of cut-off bias 28 and a back contact, 29, on the switch 9. There bridged across the source 28 a condenser 3i shunted by a high resistance 32.

So long as the switch 9 is open, and the contact 29 therefore closed, the tube El is biassed to cut-off, and the condenser M is charged to the voltage of the source 28. When the switch 9 is closed an impulse is transmitted through transformer I, 8 which switches on the X-ray tube in the manner explained with reference to Figure 4. The tube 21 remains biassed to cut-off by the voltage across the condenser 3|, although the contact 29 is opened and the condenser is now disconnected from the source 28. But be cause of this disconnection the condenser 3| begins to discharge through the resistance 32, and when its voltage has fallen to a value which permits the tube 2! to conduct, the tube strikes and transmits a voltage pulse through the transformer la, 8a to the grid circuit of tube Hid, thereby causing the switching off of the high tension circuit as before explained.

I claim:

1. Apparatus for switching on and oil a high tension circuit by means of a low tension control device. comprising a grid-controlled tube in the high tension circuit, a source of cut-off bias and an impedance in the grid circuit thereof, a gasfilled tube circuit including the said impedance, a gas-filled tube, and a source of voltage sufficient to maintain and insufficient to start a discharge through said gas-filled tube, and a low tension control circuit, including switching means and a non-conductive coupling to said gas-filled tube circuit, for injecting into said gas-filled tube circuit an impulse adequate in conjunction with said source of voltage to start a discharge through said gas-filled tube and an impulse adequate to interrupt a discharge through said gasfilled tube.

2. Apparatus for switching on a high tension circuit by means of a low tension control device, comprising a grid-controlled tube in the high tension circuit, a source of cut-ofi bias and an impedance in the grid circuit thereof, a gas-filled tube circuit including the said impedance, a gasfilled tube, and a source of voltage sufiicient to maintain and insufficient to start a discharge through said gas-filled tube, and a low tension 6 cotr i ircuit, includin sw chin mea d oneccnduc ive c up ing t said. sed tube ircui or: i jecting i toa d -fi ed tube rcuit, an impulse adequate in; conjunction with said source of; voltage tov start a discharge through, said gas-filled tube.

3. Apparatus for switching off a hightension circuit by means, ofi a low tension control device, comprising a grid-controlled tube in the high tension circuit, a source of cut-off bias and an impedance in the; grid circuit, thereof, a gas-filled tube circuit including the said impedance, a gasfilled tube, and a sou-roe of voltage suflicient to maintain andinsufiicient to start a discharge through said gas-filled tube, and a low tension control; circuit including switching means and a non-conductive coupling to. said gas-filled tube circuit, for injecting into said gas-filled tube circuit, an impulse adequate to interrupt a discharge through said gas-filled tube.

4. Apparatus for; switching on and oii a high tension circuit by means of a low tension control device, comprising a grid-controlled tube in the high tension circuit, a source of cut-off bias and impedance the grid circuit thereof, a gasfilled tube having at least an anode and cathode and capable of assuming; conductive and nonconductive states, an anode-cathode circuit for said gas-filled tube including said impedance and a source of voltage sufficient to maintain and insufficient to start a discharge through said gas-filled tube, and a low tension control circuit comprising a source of voltage, switching means and a non-conductive coupling to at least one circuit of said gas-filled tube for injecting an imulse into at least one circuit of said gas-filled tube of suificient magnitude to change its state.

5. Apparatus for switching on and off the high tension circuit of an X-ray tube by means of a low tension control device, comprising a gridcontrolled tube in the high tension circuit, a source of cut-off bias and an impedance in the grid circuit thereof, a gas-filled tube having at least an anode and cathode and capable of assuming conductive and non-conductive states, an anode-cathode circuit for said gas-filled tube including said impedance, and a source of voltage sufiicient to maintain and insufficient to start a discharge through said gas-filled tube, and a low tension control circuit comprising a source of voltage, switching means and a non-conductive coupling to at least one circuit of said gas-filled tube for injecting an impulse into at least one circuit of said gas-filled tube of sufiicient magnitude to change its state.

6. Apparatus for switching on and off a high tension circuit by means of a low tension control device, comprising a grid-controlled tube in the high tension circuit, a source of cut-off bias and an impedance in the grid circuit thereof, a gridcontrolled gas-filled tube, a cathode-anode circuit for said gas-filled tube including said impedance and a source of voltage sufficient to maintain and insufficient to start a discharge through said gas-filled tube, a grid circuit for said gas-filled tube including a source of cut-off voltage, and a low tension control circuit including switching means, a source of voltage and a non-conductive coupling to at least the grid circuit of said gas-filled tube for injecting into at least the grid circuit of said gas-filled tube an impulse adequate to overcome the grid cut-01f bias and to start a discharge and an impulse adequate to interrupt the flow of current through said gas-filled tube.

'7. Apparatus for switching on and off a high tension circuit by means of a low tension control device, comprising a grid-controlled tube in the high tension circuit, a source of cut-ofi bias, a grid resistance and an impedance in the grid circuit thereof, a grid-controlled gas-filled tube, a cathode-anode circuit for said gas-filled tube including said impedance, said source of cut-01f bias and a source of voltage suflicient in conjunction with said source of cut-ofi bias to maintain and insufficient to start a discharge through said gas-filled tube, a grid circuit for said gasfilled tube including a source of cut-off voltage, and a low tension control circuit including switching means, a source of voltage and a nonconductive coupling to at least the grid circuit of said gas-filled tube for injecting into at least the grid circuit of said gas-filled tube an impulse adequate to overcome the grid cut-off bias and to start a discharge and an impulse adequate to interrupt the flow of current through said gas-filled tube.

8. Apparatus for switching on and off a high tension circuit by means of a low tension control device, comprising a grid-controlled tube in the high tension circuit, a source of cut-01f bias and an impedance in the grid circuit thereof, two

8 grid-controlled gas-filled tubes connected in series with each other, and one of them in shunt with said impedance, the cathode-anode circuit of said gas-filled tubes including a source of voltage suficient to maintain and insufficient to start a discharge through either of said tubes, grid circuits for said gas-filled tubes each including a source of cut-01f bias, and low tension control means for injecting into the grid circuit of each gas-filled tube in turn a sufiicient voltage to start a discharge through the tube.

VICTOR QUIT'I'NER.

REFERENCES CITED The following referenices are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,693,685 Weaver Dec. 4, 1928 1,956,416 Elder Apr. 24, 1934 1,971,855 Millar Aug. 28, 1934 2,110,433 Cummings et al. Mar. 8, 1938 2,124,848 Powell July 26, 1938 2,240,478 Bischoff et a1 May 6, 1941 2,320,916 Dawson June 1, 1943 2,348,555 Mathes May 9, 1944