US2519535A - Control circuit for high surge currents - Google Patents

Description

Aug. 22, 1950 c. E. ATWOOD 2,519,535

CONTROL CIRCUIT FOR HIGH SURGE CURRENTS Filed Aug. 15, 1948 IN V EN TOR.

'larelzc'eci'. Jizwod Patented Aug. 22, 1950 UNITED STATES T OF' F-I CE CONTROL CIRCUIT FDR HIGH SURGE CURRENTS OlarenceE. Atwood, MountProspect, IlL, assignor,

bymesne assignments, to Hubcr Manufacturing 00., Chicago, 111., a corporation oftIllinois Application August 13, 1948; SerialN-o. 44,127

.agent-.has ,a working voltageof 2000 and yields a,.practica1ly pure white light of high intensity .andof approximately /10000 second duration when subjected tothe. discharge of a condenser of approximately 125 .microi-arads. Various circuits .forapplying the charge of the condenser to'the ,lamp have been evolved, but in all of these prior arrangements known tame, the circuit has'been .closedlby means ofarelay actuated by a push button .or equivalent device under the control of the operator. The high voltage at the instant the contarbts'begin to close is sufficient to form an arc therebetween, and the relatively 1 heavy .currentthen flowing combined with the blow of contact frequently Welds the relay contacts together.

.I havefound-that it is unnecessary to closeLthe relay contacts completely since the glow discharge occurseven before the contacts are actually closed, and that ionization voltagemay be impressed on the tube without a solid conductiiingpath. I attain this object by an arrangement which will permit the contacts to approach but nottouch physically, and rely upon the arcthus initiated across the contacts to form'a currentconducting path.

Accordingly the principal object ofmy invention is 'the provisionoi a system foractuating a glow discharge tube which does not utilizephysically"contacting'members for completing the circuit to the tube.

.Another'object is'to-provi'de a'system as aforesaid in which'the circuit 'closing-membersare included in a relay.

A further object-is'to provide in the rel'ay as aforesaid means for adjusting thecontacts in accordance with the operating characteristics of the tube.

An additional object contemplates la-systeminsource as heretofore pointed out.

eluding arelayeasaaforesaid and a network in shuntvwith 'ithe 'tube for facilitating ionization thereof.

Generally speaking the invention consists in providing a system including a relay having a ,pair of 'hemispherical-vcontactsand means eifeotive .upon senergizationxof the. relay for. permitting the contacts :to .approachaeach 013116124. predetermined iamount; but'not to touch,.in order to effect a ",COl'ldGDSlVG z=action within: the contacts proper andiso towcontrol thepotential availableifromthe lmainicharging condenser-and the efiect thereof in initiating and maintaining glow discharge in :the flash lamp.

In the drawing which shows-several modes in which the invention :may ibe "embodied in practice:

-'Fig. 1' is a circuit diagram of a preferred form "of the invention; and

Figs; 2,1-3-and:4:ar.e circuit'diagrams of alternative. embodiments thereof.

In all ofithe figuresthe means for charging the main'con'denser andfor completing th circuit ithroughi-therelay operating coil have been omitted :as'capable'of wide variation depending upon thefdesigner and the purpose-and as forming :nmpartof the invention'per se. vIn each of the figures the reference letters S-S will identify the leads going .to :a sourcefor impressing a charge on the vmain: condenserll]; and the letters A--A the leads'connectingthe relay'coil- I I to a suitable circuit forenergizing the same.

Turning first to Fig. 1 .there'is shown a glow lamp-l2 of 'the photoflash type, for example, a

glass envelope serving asnprotector for a tubular glass 'helixcontaining xenon or other suitable ionizablergas yielding the desired spectrum when subjected to a predetermined voltage, -.the leads i3 and i4 being connected to the anode and cathode respectively of the helix -as-is understood in the art.

Condenser lflt'may be of anysuitable capacity,

sayL125 microiarads, and is charged toia potentialof approximately 2000 volts by connecting the same for a sufficient period of time to a charging Relay I! is provided with the armature [8 bearing a substantially. hemispherical contact l9 adapted to cooperateWithiasSimi-Iar fixedcontact 2|. telore: preiera'bly of V silverv for good conductivity.

These lat- 3 Armature I8 is provided with a motion-limiting screw 22 and locknut 23, the tip of the screw being adapted to abut some fixed part of the relay,

here shown for convenience as the core Z. Ar-

mature I8 is shown in its back position and the amount of movement thereof to front position is indicated by dimension a, this being variable by means of the screw 22 and nut 23. However, the gap 13 between the contacts l9 and 2| is greater than a by a predetermined amount predicated upon the parameters of the system.

Operation of the system just described is as follows. Assuming condenser ID has been fully charged and that the relay I1 is deenergized, a potential exists across the condenser Ill, and by leakage, across the contacts 19 and 2! and the elements of the lamp l3. At this time the poten tial across l9 and 2! is insufiicient to cause current to flow across the gap b and similarly the voltage across the elements of the lamp !3 is inadequate to trigger the same. However upon closure of the circuit through coil II the armature I8 is actuated to bring contacts l9 and 2| closely adjacent, i. e. defining a gap b minus a.

The electrostatic capacity of the condenser formed between I9 and 2| as electrodes, and the air gap therebetween as the dielectric, changes rapidly as the relay operates, resulting in a sudden decrease of potential across the gap and a sudden increase of potential across the lamp !2.

By initially establishing across condenser It a potential which is well above the ionization potential of the lamp, the sudden application of additional potential due to closing movement of the contacts 19 and 2! is sufficient to start ioniza tion of the lamp. With the lamp in an ionized state, and therefore conducting, substantially the entire potential of the capacitor I0 is imposed upon the gap b minus a causing an arc discharge thereacross which efiectively closes the circuit including the condenser l0 and the lamp l2 for ignition of the lamp.

It will have been concluded from the foregoing that the objectionable welding of the relay contacts inherent in prior systems has been avoided by my invention, and with no loss of efficiency, since the whole charge of the condenser ID is effective in actuating the lamp [2. Moreover, in such prior devices the heat generated at the relay contacts was accompanied by the force of closing resulting in a forging action which intensified the sticking due'to the welding action alone. a

In the invention system contacts [9 and 2| are hemispherical to provide a concentrated electrostatically stressed region therebetween, and are preferably large as compared to similar contacts in prior relays to provide wider distribution of the arc and hence less pitting of the contact surfaces. By employing silver the conducting oxides thereof formed by the are do not result in any diminution of the effective arcing area. Moreover, the low melting point of silver and its consequent vaporization under the heat of the arc contributes appreciably to conductivity across the gap b minus a by migration of silver ions.

In Fig. 2 is shown an alternative arrangement like that of Fig. 1 except that a resistor 26 of relatively high value, as on the order of 2 megoiims, has been shunted across the conductors l3 and i t. Thus an additional leakage path is provided to augment the accrual of potential across the contacts l9 and 2|. This form of the invention system provides more positive action when the leakage current'is low or when the di rellq 4 between the ionization voltage of the lamp and its glow discharge voltage is of low order.

Fig. 3 shows still another form similar to that of Fig. 2 except that a capacitor 21 replaces the resistor 26. lhe capacitor is preferably of small capacity, say 6.6005 microfarad and necessarily of high voltage. Capacitor 2i serves to transfer a charge from condenser It to the contacts [9 and 2!.

The modification of Fig. 4 is similar to that of Fig. 1 except for the addition of a second armature 29 including contact 3%, and a fixed contact Moreover a capacitor 33 of the same order as that of Fig. 3 is bridged across armatures I8 and 29. Contacts 3! and 32 are adapted to close before contacts I9 and 2! approach arcing distance and thus to shunt capacitor 33 across the iatter. Thus a small initial charge is transferred to the lamp l2 sufficient to initiate ionization.

It will be understood that in general any suitable network may be shunted across the lamp, the resistor 2:3 or condenser 2'! being only typical arrangements. The characteristics of the network generally are such as to facilitate ionization of the tube when used in conjunction with the invention system.

While I have shown particular embodiments of my invention, it will be understood, of course, that I do not Wish to be limited thereto since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A system for controlling the ignition of a glow discharge tube comprising a capacitor for storing a charge capable of causing the discharge, circuit means connecting said capacitor and the tube, said circuit including a pair or" juxtaposed electrodes in electrically condensive relation, means supporting said electrodes for movement from a predetermined spaced relation to a more closely spaced relation, and a device for moving said electrodes from one said relation to the other for varying the capacity between said electrodes.

2. A system as in claim 1 in which said electrodes are substantially hemispherical and positioned with their convex faces opposed.

3. A system as in claim 1 in which said device includes means for adjusting the minimum spacing between said electrodes.

4. A system as in claim 1 in which said device is a relay including a movable armature, said armature supporting one of said electrodes and the other electrode being stationary.

5. A system for controlling the ignition of a glow discharge tube comprising a capacitor for storing a charge capable of causing th discharge, and a pair of electrodes providing a second capacitor, said two capacitors being connected in series circuit relation with the tube, and means for varying the spacing of said electrodes from a finite spacing to zero for transferring a part of the charge to the tube by electrostatic coupling, and for transferring substantially the balance of said charge to the tube by conduction.

6. A system as in claim 5 in which said spacing varying means includes a relay means for actuating at least one of said electrodes.

7. A system as in claim 6 in which said relay is provided with an armature for supporting one of said electrQdes and the other said electrode being fixed.

8. A system as in claim 5 in which said spacing varying means comprises a relay having one armature for supporting one of said electrodes, the other said electrode being fixed, and a second armature and fixed contact cooperative therewith, a condenser connected across said armatures, and said fixed contacts being connected together.

9. A system as in claim 5 characterized by a resistor in shunt with the tube.

10. A system as in claim 5 characterized by a third capacitor in shunt with the tube.

11. A system as in claim 5 characterized by an impedance network in shunt with the tube.

CLARENCE E. ATWOOD.

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

UNITED STATES PATENTS Number Name Date 2,269,338 Edgerton Jan. 6, 1942 10 2,465,131 Sundt Mar. 22, 1949

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