US2810861A - Electrical circuits using multi-gap cold cathode gas filled tubes - Google Patents

Description

Oct. 22, 1957 JACKSON ETAL 2,810,861

ELECTRICAL CIRCUITS USING MULTI-GAP COLD CATHODE GAS FILLED TUBES Filed March 14, 1955 R5 g R2 Inventors M. JAC KSO N AD 00 u. By

Attorney 2,810,861 Patented Oct. 22, 1957 art (IRCUE'SS USsElG MULTI-GAP COLD CATHQBDE GA FRIED TUBES Thomas P/i'eirion .laclrson and Alexander Douglas Odell, London, England, assiguors to International Standard Electric corporaticn, New York, N. Y.

Application March 14, 1955, Serial No. 494,112

Claims priority, application Great Britain March 19, 1954 7 flairns. (Cl. 315S4.6)

The present invention relates to electrical circuits using multi-gap gas-filled discharge tubes of the type having an array of inter-electrode gaps. In such tubes, suitablyapplied electrical pulses cause the discharge in the tube to be moved from gap to gap along the array of gaps in a predetermined direction.

It has been found that when those tubes are used in circuits wherein the discharge is allowed to remain at one gap for a relatively long period, there is a risk that the next pulse will not cause the correct movement of the discharge.

it is believed that this phenomenon is due to a leak discharge current which flows in a gap ahead of the discharging gap, and it is an object of the present invention to provide circuits wherein the adverse effect of this phenomenon is overcome.

According to the invention, therefore, We provide circuits for a multi-gap gas-filled discharge tube of the type referred to above wherein the adverse effect of this is overcome by applying to the gaps electrical potentials which are such that during the intervals between the pulses a substantial current is caused to flow in a gap ahead of the discharging gap in the predetermined direction. This substantial current is less than the normal discharge current.

The invention will now be described with reference to the single accompanying drawing, in which the commoned transfer cathodes of a tube having alternate transfer cathodes and storage cathodes are connected to a biasing potential of such a value that during the intervals between pulses a substantial current which is less than the normal discharge current is caused to flow in a transfer gap ahead of the discharging storage gap in the intended direction of movement of the discharge.

The circuits described herein were developed for tubes such as are described and claimed in United States Patent No. 2,553,585 (G. H. Hough). An example of such a tube is the GIG/241E tube, such as is sold under the registered trademark Nomotron. These tubes have alternate storage cathodes and transfer cathodes of which all transfer cathodes are internally commoned. The Gl/241E also has additional electrodes known as control plates whose function is to control the area of the cathode glow, and to screen the discharge gaps from external influences. The invention is, of course, applicable to circuits using other tubes of generally similar type, for instance, tubes without the control plates.

In the circuit shown, the transfer cathodes are biassed to a voltage near to that of the discharging storage cathode. This has the result that when a storage cathode is discharging, a discharge exists between the anode and the end of the transfer cathode immediately ahead of that storage cathode. This discharge is a substantial dis charge, i. e. of the order of hundreds of microamperes, but is less than the normal discharge current.

In the normal driving circuits used hitherto, the transfer cathodes are biassed to a value between the voltages of the positive and negative supply terminals. Under these conditions a leak current flows from the end of a. transfer cathode ahead of the discharging storage cathode, and it is this leak current which causes the faulty operation referred to above. The result of this 'operation is that in tubes of the type shown in the circuits when the Stepping pulse ends, the discharge may still be on the same storage cathode as it was before the pulse occurred. The substantial current which has been mentioned as flowing in our modified circuit which is less than the normal discharge current, overcomes this sticking of the discharge. Typical current values are 2.5-3.5 milliamperes for the normal discharge currents, and 2G0500 microamperes for this substantial current.

The tube MCT has its storage cathodes, four only of which are shown, each connected to earth via a resistorcapacitor circuit such as R1-C1, and its anode connected to a high positive voltage (e. g. 310 to 350 volts) via two resistors in series R2. and R3. A capacitor C2 is connected in parallel with R3. The commoned transfer cathodes are connected to earth via a resistor R4 and via rectifiers MR1 and MR2 to a point on a bleeder formed by resistors R5 and R6. The control plates (or control plate where only one is provided) are connected to earth via a resistor R7.

The principle of the input circuit to the transfer cathodes is that the transfer cathodes are biassed to a voltage near to the voltage of a discharging storage cathode. This has the result that when a storage cathode is discharging, a discharge exists between the anode and the transfer cathode immediately ahead of that storage cathode. This discharge, which is between the end of the aforementioned transfer cathode adjacent the discharging storage cathode, is a substantial current discharge which is of the order of 200500 microamperes, but is less than the normal discharge current.

At this point it is desirable to mention that although the conventional symbol adopted for the tube has an arrow-head for each transfer cathode, in the GIG/241E the storage cathodes are shaped to give directional transfer of the discharge, while the transfer cathodes are partially shaped to give directional transfer. Certain other forms of tube have all cathodes shaped, while still others have none of the cathodes shaped and rely on external circuitry to ensure directional transfer.

Returning to the circuit shown the junction between rectifiers MR1 and MR2 is connected via a high value resistor to the positive supply. The end of MR1 connected to the transfer cathodes is designated its anode and the other end thereof its cathode. Hence the direction of how of conventional current in which a rectifier such as Milli is in its low resistance state is from anode to cathode. The bleeder resistors R5 and R6 are so proportioned that normally current flows through R8 and MR2. Normally MR1 is biassed to its high resistance condition by the current flow just mentioned, so that the transfer cathodes are virtually isolated from the rest of the circuit. in this condition, the discharge mentioned above from the end of the transfer cathode ahead of the discharging storage cathode causes current flow through R4. The value of R4 is such that the bias on the transfer cathodes is within a few volts of the voltage of a discharging storage cathode.

The anode circuit of the tube t lCT includes, as men tioned above, a capacitor C2 which while the discharge is stationary on a storage cathode becomes charged to the voltage across R3. This arrangement has been described and claimed in co-pending U. S. application No. 463,450 filed October 2-3, 1954, T. M. Jackson-i. H. Fraser, now Patent No. 2,749,479.

When a negative pulse (in one specific circuit of volts and having a pulse width of 16 micro-seconds) is applied to the input terminal P, it reaches the junction of cause the correct movement of the discharge.

.vvill clearly vary' with theparticular gap arrangement.

3 MR1 and MR2 via capacitor C3. This pulse is eifectively applied to the transfer cathodes of MCT via MR1,'which is in its low. resistance state for a negative pulse. At the sflrne time MR2 is 'biassed to its: high resistance state.-

Since MR1 is in its high resistance state in'th e absence of V a negativepulse, these rectifiers serve to isolate the transfer cathodes until a'negative'pulse occurs. The negativepulse on the transfer cathode causes, on its leading edge, the transfer cathodeahead of thedischarging storage cathode (whichalre ady passes a-lowcurrent discharge) to discharge fully. The capacitor C2 discharges through the discharge path of this transfer cathode, thereby providing an increased current flow during the transfer'cathode dis- 7 charge; The discharge so produced from the transfer cathode'causes an increased voltage drop across the anodeload formed byresistors-R2 and R3. Since the capacitor in the cathode circuitofthe storage cathode cannot immediately discharge, this reduces the potential across the previously-discharging storage cathode-anode gap to below thereto; a

flt will beremembered that the control plates are con- "nected tolearth via a resistor R7. The portion of the control'plate near the discharging cathode also passes current, when it is acting as a cathode, the discharge being,

' of course, to the common anode. This discharge is a low current discharge of the order of hundreds of microamperesh It is employed, as is that of the transfer cathode,

to provide automatic bias for the electrode in question. Resistor R7 is so proportioned as to hold theipotential of the control plate to a voltage of the order of 70 volts. '--By' using this method of biassing the control plate'sinstead of the hitherto-used bleeder, a considerable improvement in operation has been obtained. 7

It should be'noted that MR1 and MR2 can'be replaced by other forms of diodes such as gas diodes or vacuum diodes.

It will be remembered that in the early part of the specification'it was stated that when tubes of the type to which this invention is applicable are used in circuits wherein the discharge is allowed to remain at one gap for a relatively long period there is a risk thatthe next pulse will not it was further stated in the opening paragraphs of the specification that this phenomenon is believed to be caused by a leak discharge current flowing in a gap ahead of a dis charging gap. Such a low current discharge has the eifect of alteringthe discharge characteristics of-the gap in such a Way that the maintaining voltage of the gap is reduced, 'Where the tube has transfer gaps interspersed with storage gaps the result of this alteration of'the maintaining voltage is that when the pulse which should causetransfer away from the transfer gap ends, the discharge may fail to transfer'from that gap in the desired direction. 'This It has been noted that a discharge current of the same.

order of magnitude as the normal discharge current in a gap does not reduce the maintaining voltage of that gap. The reason why this is so although a much lower current does have this eifect is not understood. However, it has been found that if a current which is comparable in mag nitude with, but of a noticeably lower value than, the

normal discharge current is allowed to flow in the gap immediately ahead of the discharging gap, then the troubles due to sticking are overcome. The reasons for'the success of this solution 'to the problem are, as already men- IPA-circuit for a multi-cathode gas-filled electric dis- 7 charge {tube of the type having a common anode and alternate storage cathodes and. transfer cathodes, which with'said anodes define an array of alternate storage gaps and transfer gaps, means for applying negative potential pulses to said transfer cathodes in common for causing'the di'sch'a'rge'to be moved from one storage gap to the next storage gap in'a'predetermined direction, means for ina suring the. stepping of the discharge from a fired storage gap to a contiguous gap in said'predetermined direction 7 cathodes from said pulse application means, and means i for. normally maintaining said isolating means efiective' until application of a pulse from said source, whereby the transfer gap contiguous to said fired gap is caused to fire. 2. A. circuit for a multi-cathode gas-filled electric discharge tube as claimed in claim 1, wherein said isolating means comprises a first two-pole unidirectional current carrying device having one pole coupled to said transfer cathodes andjpoledj to conduct current away frornsaid transfer cathodes. i r

3.. A circuit for a multi-cathode gas-filled. electric discharge tube as claimed in claim 2, wherein said means for normally maintaining .said isolating means efiective comprises a'sour'ce of anode potential for said tube, voltage dividing means connected across said potential source, said dividing means comprising a second two-pole unidirectional current carrying device, the other pole of said firstunisdirectional device connected to the oppositepole of said secondlunidirectionaldevice. a if 4. A circuit for a multi-cathode gas-filled electric discharge tubeasclaimed in claim 3, wherein said uni-direc tional devices comprise metal rectifiers. V V i -5. A circuit for a multi-cathode gas-filled electric discharge-tube as claimed in claim 1, Whereinsaid biassing eans comprises aresistor connected between said transfer cathodes and ground. 1 .6; A circuit for a multi-cathode gas-filled electric discharge tubeasclairned in claimli wherein said means for insuring thestepping of thedischarge from a fired storage gap to a contiguous gap further comprises a source of anode potential for said tube, an anode load resistance coupled bctweenthepositive. terminal: of said potential' source'andsaid anode, and a capacitor connected in par allel with jalportion of said load resistance remote from said anode, said capacitor. adapted to be normally charged to avoltageequal to thevoltage dropsacross said resistor portion, charge in s aid capacitoradapted.to increase he tta fersjansu upon fi iys su sap 5 7. A circuit for a multi-cathode gas-filled electric discharge tube as claimed in claim 1, wherein said array further comprises control electrode means for limiting the discharge area of a fired cathode, and means for biassing said control electrode means.

References Cited in the file of this patent

Images