US2977509A - Electric-discharge system - Google Patents

Description

March 28, 1961 F. E. BARsTow ETAL 2,977,509

ELECTRIC-DISCHARGE SYSTEM 2 Sheets-Sheet 1 Filed Sept. 17. 1959 INVENTORS FREDERICK F. BARsTaw BYIRVING. F. ASTMAN ,47am/@Ys March Z8, 1961 F. E. BARsTow ETAL 2,977,509

ELECTRIC-DISCHARGE SYSTEM 2 Sheets-Sheet 2 Filed Sept. 17. 1959 Nmo 'mM/m /WTORNEYS United States Patent() ELECTRIC-DISCHARGE SYSTEM Frederick E. Barstow, Needham, and Irv-ing F. Eastman, Natick, Mass., assignors to Edgerton, Germeshausen & Grier, Inc., Boston, Mass., a corporation of Massachusetts Filed Sept. 17, l1^,9.59\S1e11.,15km-840,591

7 claims. (m5315441) The present invention yrelates to electric-.discharge systems and, 'though it is useful, also, rin more general fields, it is particularly adapted for lsystems 'in which one or more flash condensers or capacitors is or Yare discharged through the gaseous medium of a gaseous-discharge `device for such purposes as the production of a single ash of light or a repetition of flashes, as inash photography, stroboscopic applications and the like.

For purposes of illustration, the klight-.flash-producing systems to which the present invention is applied are of the type disclosed in United States Letters Patent No. 2,722,629 and 2,756,365, issued, respectively, on November 1, 1955, and July 24, 1956, to Kenneth J. Germeshausen, embodying normally ineffective voltage-.adding mechanisms, operative substantially simultaneously with the application of a triggering impulse `to a ash device, to boost the value of the voltage available for :discharging through .the flash device. AIt will `be evident, however, that the invention is also adaptable vto other types of electric-discharge circuits, as well, such as those described in United States VLetters Patent Nos. 2,478,901 through 2,478,907., issued August 16 1949, to Harold E. Edgerton.

In summary, the present invention is directed to safety, hold-olf, and voltage-level-regulating systems land circuits, particularly ,adapted for apparatus of the above-described character, wherein protection is afforded for variations in voltage of the rflashing capacitor or capacitors or failures in the same, and control is provided over the capacitor char-ging rate and the tendency for the ilashing device to hold-'over its discharging following a flash.

An object `of the present invention, accordingly, is to provide a new yand improved electric system embodying such safety, 'hold-olf and voltage-level-regulating circuits that automatically insure the proper performance characteristics of the system.

Other and further objects will be explained hereinafter and will be more particularly pointed out in connection with thc yappended claims.

The invention lwill now be described in connection with the accompanying drawings, Figs. 1 and 2 of which are schematic circuit diagrams of a preferred flashing apparatus, particularly emphasizing safety and hold-off features thereof, respectively.

In the drawings, positive and negative banks of parallel-connected ashing storage capacitors C1 and C, are shown connected in a series discharge circuit between the anode 1 and cathode 2 of a three-electrode preferably gaseous-discharge flash-tube device 3. The voltage lstored in the-capacitor banks C1 and C7 is normally insuiiicient to produce breakdown and hence a discharge between the anode 1 and cathode 2 of the tube 3 in the absence vof a triggering stimulus applied to the trigger Velectrode 4. The device 3 may, for example, be of the various types described in the'said Letters Patent. A satisfactory deviceof this nature, is, for example, thetype FX-29 xenon ash'tube marketed'by Edgerton, Germeshausen & Grier, Inc.

The capacitor banks C1 and C7 arecharged from upper l 380-800 cycle per second generator, having phase lines f A, B and C and a ground Vline D. The phase lines of the source A, Band C, are, in turn, connected to respective pairs ofupower-leg windings A1-A2, B1-B2 and C1-C2 of a conventional magnetic amplifier switching circuit T1. Threevcontrol windings C3, C 4 and C 5 `are provided, with the winding C3v connected at its lower end to the ground terminal D and at its upper end, by conductorrS. to a terminal 5. l The control winding .C1V is connected by conductor 6 to the lower terminal of the capacitor bank C7, and by conductor 7, through a rectifier CR27 and a .resistanceR17, to the B- conductor line. Control winding C5 is connected by conductor 8 to a terminal 8 and by conductor 9 to a terminal 9.

As an example, kthe 'power-legrwindings A1-A2, B1-B2,` C1.C2 may have 330 turns each. T-wo control windings may each have 500 turns, a resistance Vof ohms and a current requirement, for full control, of 7 milliamperes; whereas the third control winding, for a purpose later described, may be 1000 turns, and have resistance of 360 ohms, and a lesser full control-current requirement of 3.5 milliarnperes. Connected to the right-hand ends of each .pair of the power-leg windings A1-A'2, B1-B2, C1C2, are oppositely-poled rectifers CR3-CR4, CRS-CR@ .andCR7-CR8, as is well known, to control the current path through the windings during each half cycle. See, for example, Transactions of the American Institute of Electrical Engineers; Part I, September 195,2, Since the oper-ation of such `ampliiiers is widely understood, it will not be explained herein in great detail other than to Ystate that the rectiiiersr CRS-C114, CRS-CR and CR7-CR8, such as Type 303C Westinghouse diodes, are respectively connected to Y-connected primary windings Pl, P2, P3 of a power transformer T2. The cooperative step-up secondary windings S1, S2 and S3 of the power transformer T2, connect to terminals III, IV and V, with va common terminal connection VI. such as Type '1Nl127 Texas Instrument rectiiers, in series banks CR-9 through CR14 connect the terminals III, IV and V to terminals I and II in order to provide full-wave rectification for the B+, B- lines. As an example, a 420-volt alternating-current output from the transformer T2 will produce, at terminals I and II a 900-volt directcurrent voltage for charging capacitor banks C1 'and Cr; `along the B+, B- lines. The capacitor banks, indeed,

may, for example, each comprise six parallel capacitors,

as shown of total capacitance value of about1750 microfarads.

Diodes CRS to CRS permit current to llow during the positive half of each cycle only through the upper windings A1, B1 and C1. During the negative half of cach cycle, the diodes pass current through the lower windings A2, B2, C2. In this mode of operation, the special cores in each winding are kept completely saturated, andy there is no restriction to the rate of current flow. However, a small D.C. current applied to one of the three control windings C3, C4 and C5 will control directly the ow of A.C. current in the power windings by driving the cores out of saturation. Current in the power windings will be restricted as it Vtries to drive the cores back into saturation. By regulating ypower input to the stepup transformer T2, the control windings C3, C4 and C5 establish the rate at which charging current flows into the `capacitor'banks C1.C7. The degree of A. C. control is directly proportional to the amount of,D.-C..c urrent-which tlows. At 7 ma., inthe above example, there" Diodes,

is maximum restriction to current flow in the power windings A1-A2, B1-B2, Cl-Cg. When current ows in the positive direction, say downward in the control winding C3, positive control is exerted. However, if current in one of the control windings reverses, it will oppose the controlling effect of the other windings, prevented by series diodes such as CR2 at terminal 5', and diode CR27, before mentioned.

As explained in the said Letters Patent, a gaseousdischarge switch VI is preferred, for triggering the ashtube 3, the tube VI having an anode 9, a control electrode 10, a cathode 11 and a keep-alive electrode 12, connected through a resistance R11 to the terminal Vl. A plate Y transformer winding L, is connected between the anode 9 and terminal VI and the cathode 11 is returned through a resistance R10 to the B- line. A capacitor C14, normally charged from terminals VI and II, through cathode resistance R10, will discharge through the primaryrwinding L1 and the tube V1, upon grounding of the control electrode 10. This may take place by closing switch S, or any other initiating device or circuit, connecting the electrode 10 through capacitor C15 to the ground terminal D. The secondary winding L2 then applies a negative pulse, say 15,000 volts for several microseconds, to the trigger electrode 4' of the ilashtube 3. This reduces the firing voltage to approximately the potential across the capacitor banks C1, C7. The discharge of capacitor C14, as explained in the said Germeshausen Letters Patent, causes the normally ineffective secondary winding L3, the upper terminal of which is connected to the flashtube cathode 2, to reinforce, supplement or add to the negative potential already at the cathode 2, further increasing the potential between the flashtube anode 1 and cathode 2, and causing the ashtube 3 to fire. A light flash of, say, one millisecond duration, more or less, will thus emanate from the tube 3. The network R14- C16 connected between the upper terminal of L2 and the terminal VI acts as an isolation circuit at the grounded end of the high-voltage winding and is designed to prevent external arc-over from either electrode of the flashtube to the trigger winding. The before-mentioned cathode resistor R10 prevents the negative capacitor bank C7 from discharging through the trigger tube V1.

A voltage regulating and level control circuit is also employed comprising the rectifier CR1, such as a Zener diode, connected to terminal 9 and thus to the control winding C5 by conductor 9", and thence by conductor 8 to terminal 8 and the slider S of a potentiometer R5 (connected in -a bleeder network R4-R5R6 between terminals VI and B+), back through resistor R6. The heavy-shaded components CR1, C5, R4, R5, R5 and R2 thus serve to provide for control of the winding C5, thus to adjust the voltage applied to the capacitor banks C1, C7 by the slider S. ln addition, at some point of B+ voltage, the diode CRI exercises controlling or regulating action, keeping the lower terminal of winding C5 more negative than the upper terminal-such negative current flow in C5 having a lessened elect upon the charging current control. If polarity reversal occurs, as the B- voltage approaches a limit, current Hows in the opposite direction in C5, regulating the bleeder current at R5.

The action just described is essentially that of a bridge circuit. By varying the tap-off S' at R5, the point at which the bridge balances can be altered. Shifting the quiescent point changes the value of the -B voltage. Conversely, if the line voltage changes, the resultant change in -B voltage causes the magnetic amplifier T1 to reinforce or oppose the A.C. current as necessary to return the -B (and +B) voltages to normal.

As before stated, one of the important features of the invention resides in a hold-off or quenching circuit that prevents continuous arcing after the flash tube 3 has fired, caused by suiciently high continued current in the discharge circuit. This circuit is shown'in heavy lines in Fig. 2. `With the capacitor banks C5C7 fully charged,

the terminals of the control winding C4 are both at the same potential. When, however, the flashtube 3 fires, the B capacitor bank C7 discharges rapidly (in, say, one millisecond) and the upper terminal of C4 returns to a near-zero potential. The long time constant of the network, consisting of C13, R7, and the control winding C4 combined with the isolating action of CR27, before-mentioned, result in holding the lower terminal of C4 at a negative potential. With a difference in potential across its terminals, current ows through the control winding C4 from the upper to the lower terminal 3. As described earlier, positive D.`C. current ow in the winding limits the rate at which A.C. current ows, thus electively causing the magnetic amplifier T2 to isolate and thus, in effect, to disconnect power source A, B, C. The reduced current, thus, will not sustain arcing in the flashtube.

As the capacitor C13 discharges through R7, the control-winding negative current will decrease, resulting in an increase charging current once more to the capacitor banks C7, C7-but at a time when there is no longer danger of flashing hold-over in the tube 3, in view of the hold-off period, say of the order of tenths of a second, more or less, that permits the tube 3 to de-ionize.

The capacitor charging rate of the banks C7, C7 is controlled by a current-limiting circuit. In the normal mode of operation with the Form-Run switch S" in the Run position, shorting out resistor R15 in the B- line, the voltage drop across R16, in series therewith, which is proportional to the charging current, places a positive potential on the upper terminal of control winding C4 in relation to the lower terminal. The potential difference produces a positive D.C. current in the control winding C4 (from the upper to the lower terminal) which is lim-` ited by before-described resistance R17. The control current causes the charging current to be limited to the desired charging rate. Y

If the Form-Run switch is moved to the Form position, the larger voltage drop creates a higher potential difference; considerably more current ows from the upper to the lower terminal of C4; maximum restriction is placed on the charging current; and the voltage forms very slowly on the capacitors C1-C7.

Because the before-described voltage-regulator circuit is only connected across the negative bank C7, a shortcircuit or other malfunction in the negative circuit will produce an overvoltage on the positive bank C1. One of the circuits shown in heavy lines in Fig. l prevents this condition, as follows. Any decrease in voltage on the negative bank C7 without a corresponding decrease in the positive bank C1 will cause the upper terminal of the control winding C4 to go positive in relation to its lower terminal. Positive current will ow through the control winding C4, thereby reducing the rate of voltage buildup on the capacitors to zero.

An unbalance in the B+ bank C7 does not endanger the B- bank C7 because of the protection afforded by the previously ldescribed voltage regulator across the B- bank, C7.` Because a B+ unbalance might reverse the current in the control winding and aggravate the unbalance condition, the diode CR2 is inserted in circuit with the control winding C3 to prevent the reversal of current.

If, for any reason, the voltage on both banks C1, C7 becomes excessive, neon tubes V3--V10, indicated in heavy lines in Fig. l, and connected between terminals I and 5', will ash over. The upper terminal of control winding C3 then becomes positive. A positive D.C. current will thus flow through the control winding C3 and the regulatory action will reduce the voltage. The circuit may, for example, be designed to operate at 950-1000 v.

Further modifications will occur to those skilled in the art and all such are considered to fall within thepspirit and scope of the Vinvention as deiined inthe appended claims.

What is claimed is:

l. An electric flash-producing system having, in combination, an electric flash device having a pair of principal electrodes and a trigger electrode, a source of energy, energy storage means, a charging circuit including switching means for storing voltage from the source in the energy-storage means, a discharge circuit for the energy-storage means connected to the principal electrodes and including normally ineiective means for supplying voltage, when effective, in the discharge circuit along with the voltage of the energy-storage means, means for supplying a trigger impulse to the trigger electrode and substantially simultaneously rendering the normally ineiective means effective, thereby to enable the energy-storage means to discharge through the discharge circuit in order to produce a Hash of energy between the principal electrodes of the Hash device, and means operable upon a component failure in the energy-storage means for controlling the switching means to disconnect the said source from the energy-storage means.

2. An electric hash-producing system having, in combination, an electric tlash device having a pair of principal electrodes and a trigger electrode, a source of energy, energy storage means, a charging circuit including switching means for storing voltage from the source in the energy-storage means, a discharge circuit for the enorgy-storage means connected to the principal electrodes and including normally ineiective means for supplying voltage, when eifective, in the discharge circuit along with the voltage of the energy-storage means, means for supplying a trigger impulse to the trigger electrode and substantially simultaneously rendering the normally ineifective means eifeotive, thereby to enable the energy-storage means to discharge through the discharge circuit in order to produce a ash of energy between the principal electrodes of the ash device, and means responsive afterthe production of the ash of energy to current in the controlling the switching means to disconnect the said Y source from the energy-storage means. l

3. Apparatus as claimed in claim 2 and inwhich means cooperative with the said switchingmeans is provided for regulating the voltage supplied from the said source to the energy storage means.

4. Apparatus as claimed in claim 2 and in which the last-named means comprises further energy-storage means, means operable upon the production of a dis-l charge through the ash device for discharging the fur-r ther energy-storage means, and means for controlling the switching means in response to the discharging of vthe further energy-storage means to elect the said discon-A source of energy and the energy-discharge device, magnetic amplifier means connected between the source and the energy-storing circuit, and means responsive to suiciently high current discharged through the discharge device and connected to the magnetic amplier means to control the same to isolate the said source from the energy-storage circuit. Y Y

7. Apparatus as claimed in claim 6 and in which the magnetic amplifier means is provided with control windfor continued current flow through the ash device for ing means and the isolating means comprises further energy-storage means connected with the magnetic amplitierv control winding means in order to discharge therethrough. t f

References Cited inthe file` of this patent UNITED STATES PATENTS Parker Aug. 5, 1952l Y Edgerton Feb. 3, 1959

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