US3195014A - Electronically controlled spectro scopic low voltage spark source and interrupted arc source - Google Patents

Description

July 13, 1965 A. BARDOCZ 3,195,014

ELECTRONICALLY CONTROLLED SPECTROSCOR-IC LOW VOLTAGE SPARK SOURCE AND INTERRUPTED ARC SOURCE Y Filed June 28, 1961 INVENTOR. A RPAD BA Rpocz Attorneys f United States Patent 3,195,014 ELECTRGNICALLY CUNTROLLED SPECTRO- SCGPIC LOW VOLTAGE SPARK SOURCE AND INTERRUPTED ARC SOURCE Arpad Bardez, 4 Orlay Utca, Budapest, Hungary Filed June 28, 1961, Ser. No. 146,023 5 Claims. ((31. 315232) This is a continuation-in-part of application Serial No. 688,694, filed October 7, 1957, now abandoned.

In spectroscopic research work and spectrochemical analysis, the separately ignited spark or low voltage spark and the interrupted arc are frequently employed as light sources. The igniter spark generator is an important component for the separately ignited spark as well as for the interrupted arc sources.

In the spectroscopic art, the term separately ignited spark means a spark discharge across a gap between two electrodes spaced several millimeters apart, the gap being an electric circuit connection with a condenser which is charged to a relatively low voltage which is insufficient to break down the gap, or effect ionization thereof, upon discharge of the condenser. In a separately ignited spark the breakdown of the spark gap, or ionization thereof, is elfected by a high voltage, high frequency discharge between the electrodes of the gap. The term interrupted arc is understood to mean a circuit including a gap between two electrodes spaced several millimeters apart and across which there is applied a relatively low A.C. voltage which is not high enough to ionize the gap. In this case, also, the ionization of the gap is ef' fected by a high voltage high frequency discharge be tween the electrodes.

The production of sparks is carried out, in case of spectroscopic light sources, in such a manner that condensers (Working condensers) are charged from the A.C. mains and then discharged through the analytical spark gap. Igniting sparks are discharged in general, through a controlling spark gap or controlling tube. To obtain correct operation of the spark source, the charging and discharging processes of the condenser should be separated from one another. This is necessary because if, during the spark discharge and immediately after it, the supply voltage remains on the analytical and controlling spark gaps, in case of higher excitation energies and greatcr spark frequencies the deionization of the spark gaps is incomplete. Consequently the network will be short circuited through them and a regular controlling of the spark discharges cannot be maintained. In other words, the spark source has to be formed in such a manner that, during charging of the condenser, no discharge shall occur, while during the discharge the condenser shall be completely isolated electrically from the charging network.

Recently a further requirement consists in that in spark sources the start of spark discharges shall take place with a small time scattering (jitter) of the order of magnitude of a microsecond relative to the moment of a given control signal, so that, consequently, spark sources may be applied for the production of time resolved spark spectra. This can be realized by means of electronically controlled spark sources operating with high precision in time. In connection with the problem following should also be noted.

In order to perform spectroscopic analysis or investigations, and primarily spectrochemical analysis, a single spark discharge is not sufiicient to produce a satisfactory spectrum on a photographic plate. To produce a satis factory spectrum, many hundreds or even many thousands of successive discharges are necessary. These successive discharges must be resolved in time. That is, the particu 3,195,014 Patented July 13, 1965 lar time, during each discharge, in which a given spectrum occurs must be the same for each successive discharge. Thus, if it is desiredto use that portion of the discharge occurring between 0.0 and 0.1 microsecond of a given sparkdischarge, thesuccessive discharges must also be analyzed within the 0.0 to 0.1 microsecond range of the discharge. Thereby, the successive discharges being analyzed will always be coincident in time with respect to the portion of the period of a single discharge during which they occur. The procedure by which corresponding time periods of successive discharges appear at the same position on the photographic plate is known as time resolution. One manner in which the time resolution, may be eifected is by using a rotating mirror to direct the image of theatre or spark discharge to the admission slit of the spectrograph; With such an' arrangement, each respective position along the slit will be illuminated with light originating from the same respective time periods during the radiation of each successive discharge. correspondingly, every particular position on the spectrum line of a spectrum plate will be indicative ,of,detection of the radiation arising from the same particular period during the discharge of each successive spark or are. It is thus imperative that a high time resolution must be effected so that corresponding time-portions of successive discharges will always appear at the same position on the spectrum line as photographed,

on a spectrum plate. In other words, to obtain a high time resolution, the superposition of the spectrum from successive discharges must be effected with a very high precision timewi se. If this is done, corresponding increments of successive sparks or are discharges will appear exactly on the same place on the slit of the spectrograph, and every successive corresponding spectrum will appear exactly on the same place on the photographic plate, It will therefore be apparent that a high time resolution is necessary when using a multitude of successive spark or are discharges to produce a photographic spectrum on the photographic plate of a spectrometer. H

The production of time resolved interrupted arcs, as well as the investigation of processes taking place in them are of equal importance. A high precision ignition is needed for the time resolution, which might be ensured by an igniter spark operating with high precision.

The above mentioned requirement,namely,' that chargingand discharging processes be separated from one another, can be relatively easily met if a number of sparks per second equal to the frequency of the network has to be produced. In this case, by inserting a rectifier before the working condenser, the charging of the condenser takes place during one of the helf cycles of the A.C. network whereas the discharge takes place during the other half cycle when thechargedcondenser is completely electrically isolated from the mains by the rectifier; Hitherto the sepcration of charging and discharging processes was solved in this manner in the case of some spark sources. 3

In practical and scientific spectroscopic practice, however, in general a higher spark frequency than the frequency of the network is desirable. A higher spark frequency results in shorter exposition times and in a higher analytical precision; Moreover, it is experimentally proved that the higher the sparking frequency, the higher is the stability of the discharge, and consequently, the smaller is the time scattering in the production of time resolved spectra. It should be noted further that the timeresolved spectroscopy for routine operation can be,.in general, only possible by a spark frequency higher than the mains frequency. In the majority of cases it is su'fiicient if the frequency of the spark discharges is twice the frequency of the A.C. mains.

The subject of the invention consists in such separately ignited spark and are source which is also suitable for the production of time-resolved spectra, with the aid of which the realization of spark frequencies higher than the mains frequency is feasible in such a manner that the charging and discharging processes of the condenser supplying the excitation energy are completely separated from one another.

The appended drawings diagrammatically illustrate some embodiments of, and best Ways for, carrying out the invention, to which the invention is not limited to such embodiments. In the drawing FIG. 1 illustrates the application of the principle of the invention to separately ignited spark sources and interrupted are sources.

FIG. 2 shows the voltage, current, and magnetic induction relations of the transformer T in FIG. 1.

An example'of the invention for the production of separately ignited sparks and interruped arcs is illustrated in FIG. 1. The upper part of FIG. 1, consisting of components T, G, L L C A and F, is the low voltage spark circuit or working circuit. The lower part of FIG. 1,

consisting of components R C V, IG, L R C A and S, is the high voltage, high frequency igniter circuit. The common component of both of the circuit parts is the coupling means A which, in the present case, is an aircored transformer. The part of the figure to the left of condenser C is the charging circuit of the low voltage spark part of the source, and the part to the right is the discharge circuit. C is the working condenser storing the excitation energy. Condenser C is charged from the A.C. network through a suitable transformer T. and the rectifier G. F denotes the analytical gap. The discharging of the working condenser C is carried out by means of the high voltage, high frequency currents induced by the igniter circuit into the circuit C A-F, through the air-cored transformer A. L and L are filter coils, their function being to prevent thehigh frequency currents circulating in circuit C AF from flowing into the mains.

The operation of the charging circuit of the spark source illustrated in FIG. 1 is as follows: the core of the secondary coil of transformer T'is possibly of a material ofl-ow magnetic saturation, and moreover its cross section is relatively small, so that the saturation point is already attained with small field intensities. The further increase of the magnetic induction is absorbed by a shunt magnetic circuit which may or may not include an air gap.

The voltage, current and magnetic induction relations of transformer T are illustrated in FIG. 2.

Curve a illustrates the course, in time, of the primary voltage, curve b the primary current, c the magnetic induction appearing in the core of the secondary coil,'and d the voltage on the secondary terminals of the transformer.

The working condenser C of FIG. 1 is charged by the voltage impulses d in FIG. 2. It should be-kept in mind that owing to the presence of the rectifier G, all the voltage impulses d in FIG. 2 are unidirectional as applied to condenser C The igniter circuit of FIG. 1 operates as follows. The igniter circuit illustrated in FIG. 1 is coupled with the low voltage spark circuit of FIG. 1 by the air-cored transformer A. C is the working condenser of the igniter circuit, which latter supplies the excitation energy. S is a controlling spark gap. If condenser C 'is charged to such a high voltage that spark gap S breaks down, condenser C discharges in the circuit C S-primary of air-cored transformer A, and induces the ignition energy in the circuit C F'secondary of the air-cored transformer A, in FIG. 1. The working condenser C obtains its charge from the storage condenser C through the controllable gas-filled electron tube V, inductor L and resistor R Tube V is ordinarily cut off or blocked by a negative bias. If condenser C is charged, and a positive voltage signal is applied to the grid of tube V, tube V is triggered conductive and condenser C begins to charge from condenser C As a consequence of the presence of L the circuit C L R C -V is an oscillatory one- Condenser C will be charged by the first quater wave of the oscillatory current initiated by triggering the tube V. When gap S breaks down in the circuit C L R C -V, a transient equalizing process starts, the starting voltage of which is equal in value, but of opposite polarity, to the voltage on the terminals of C just before the breakdown of gap S. As a consequence of this equalizing process, an opposite current flow starts in the circuit C L R C V, which extinguishes tube V. After extinguishing of tube V, there is practically no voltage on the terminals of condenser C in consequence of which gap S may deionize. The role of resistor R in FIG. 1 is to limit the current. Condenser C may be charged by DC. or AC. voltage through current limiting resistor R Since FIG. 2 illustrates, to a fairly good approximation, the effective conditions, the objective of separating. the charging and discharging phases of Working condenser C from one another is practically attain-ed even with a spark frequency corresponding to only twice the frequency of the network.

Condensed C should be discharged in the neighborhood of the zero value of the descending voltage pulses, so that for a time no voltage will be present on the terminals of condenser C Thus the conditions will be favourable for the deionization of the spark gap F.

If the aim set is that the voltage pulses illustrated by curve d in FIG. 2 be as perfect as possible, this can be realized, for instance, by using controllable rectifiers, which are somewhat biased, instead of the rectifying elements G. No current will then flow through the controllable rectifiers except after a certain voltage threshold is reached, which is, however, higher than the eventually remaining voltage between the voltage pulses. The situation is more simple if, in the circuit of FIG. 1, instead of the bridge rectification, a full wave rectification is present, because in the latter case only two controlled rectifiers have to be used. Another possibility for producing the more perfect voltage pauses between the voltage pulses with a very small residual voltage consists in using forthe transformers one or more auxiliary coils. The auxiliary coil in question may be short-circuited, connected in series with the primary, or fed separately from a separate supply.

Applying the saturated core transformers described, the reactive (wattless) current uptake from the network may be high with respect to the effective consumption. This might be reduced by applying, in the usual way, a power factor condenser on the network part of the system.

The application of polyphase transformers for the production of the voltage pulses in question is considered as self-evident and will not be dealt with here.

In spectrochemical analysis and other spectroscopic investigations, interrupted arcs of a very short duration are often desirable. The shorter the arcs, the smaller is the cratering in the samples, so that the possibility of reproduction is greater and the precision is higher. In case of a sine wave voltage, if not too high voltages are used, the difficulty encountered in producing individual arcs of very short duration is that the arc has to be ignited at the end of the sine wave, where the voltage is already very low, so that the ignition is rather cumbersome. Interrupted arcs of a very short duration may be produced with the aid of the circuit illustrated in FIG. 1 by their self-ignitionin this case, condenser C becomes a bypass condenser and its capacity is only so large as to readily pass the high frequency and high voltage currents induced into the circuit C A-F. In this case the excitation energy is applied directly to analytical gap F through transformer T, rectifier G and filter coils L and L Thus the higher ignition voltage and short arcing time is provided directly.

If the circuit illustrated is used for producing interrupted arcs, unidirectionally polarized arcs are obtained.

Omitting the rectifying element G the polarization of the arcs to be produced becomes bidirectional.

The pulse generator illustrated may be constructed so, that the repetition rate per second of the control voltage pulses delivered by said generator is variable. In this way, the discharge repetition rate per second can be varied at will, which is advantageous in all cases when the electrode samples to be analysed must be protected against excessive heating.

it is understood from what has been set forth above that this invention is not limited to the arrangements, devices, operations, conditions and other details specifically described and illustrated, and can be carried out with various modifications without departing from the scope of the invention as defined in the appended claims.

What I claim is:

l. A low voltage spectroscopic spark and arc source comprising, in combination, a source of low frequency A.C. potential; a device having an input connected to said potential source, an output, and means producing, at its output, relatively sharp output voltage pulses in one-to-one correspondence with half cycle voltage surges of said source and respectively of duration which is short in comparison with the duration of the half cycle of said potential source; rectifying means connected to the output of said device; a low voltage energy storage means; a charging circuit including said energy storage means and connected to the output of said rectifying means; said rectifying means charging said energy storage means to peak voltage during each pulse and interrupting the charging current at the end of each pulse while maintaining said energy storage means charged to peak voltage; an analytical spark gap; a power circuit connecting said gap in series across said energy storage means; the peak voltage of said energy storage means being incapable of breaking down said spark gap; an igniter circuit including a control spark gap; a high voltage condenser; a discharge circuit including said high voltage condenser across said control spark gap and operable upon charging of said high voltage condenser for the voltage thereof to break down said control spark gap and for said high voltage condenser to discharge across said control spark gap; and means coupling said discharge circuit and said power circuit for transfer of energy from said high voltage condenser discharge to said power circuit whereby said transferred energy breaks down said analytical spark gap for discharge of said energy storage means through said power circuit and across said analytical spark gap; said igniter circuit further comprising circuit means for charging said high voltage condenser including a source of direct voltage; an inductance; a controllable electron tube which is normally current blocking and which is triggerable into conductivity and which then remains conductive when the current therethrough is above a specified value; and means for triggering said controllable electron tube operable at the conclusion of the charging pulse on said energy storage means to trigger said controllable electron tube for current flow therethrough; said control spark gap shunting said high voltage condenser in the charging circuit thereof and the inductance opposition to the current resulting from the control spark gap breakdown being sufficient to cause said controllable electron tube to cease passing current prior to the beginning of recharging of said energy storage means.

2. A low voltage spectroscopic spark and arc source, as claimed in claim 1, in which said output pulse producing device is an electromagnetic device.

3. A low voltage spectroscopic spark and are source, as claimed in claim it, in which said output pulse producing device is a saturated core transformer having a primary winding connected to said source of AC. potential and a secondary winding connected to said rectifying means.

4-. A low voltage spectroscopic spark and are source comprising, in combination, a source of low frequency A.C. potential; a device having an input connected to said potential source and producing relatively sharp output voltage pulses responsive to each half cycle of input potential and each having a duration which is short in comparison with the duration of the half cycle of said potential source; rectifying means connected to the output of said device; a low voltage energy storage means; a charging circuit including said energy storage means and connected to the output of said rectifying means; said rectifying means charging said energy storage means to peak voltage during each pulse and interrupting the charging current at the end of each pulse while maintaining said energy storage means charged to peak voltage; an analytical spark gap; a power circuit connecting said gap in series across said energy storage means; the peak voltage of said energy storage means being incapable of breaking down said spark gap; an igniter circuit including a control spark gap; a high voltage condenser; a discharge circuit including said high voltage condenser across said control spark gap and operable upon charging of said high voltage condenser for the voltage thereof to break down said control spark gap and for said high voltage condenser to discharge across said control spark gap; an air core transformer having a primary winding in said discharge circuit and a secondary winding in said power circuit for transfer of energy from said high voltage condenser discharge to said power circuit whereby said tranferred energy breaks down said analytical spark gap for discharge of said energy storage means through said power circuit and across said analytical spark gap; said igniter circuit further comprising circuit means for charging said high voltage condenser including a source of direct voltage; an inductance; a con-' trollable electron tube which is normally current blocking and which is triggerable into conductivity and which then remains conductive when the current therethrough is above a specified value; and means for triggering said controllable electron tube operable at the conclusion of the charging pulse on said energy storage means to trigger said controllable electron tube for current flow therethrough; said control spark gap shunting said high voltage condenser in the charging circuit thereof and the inductance opposition to the current resulting from the control spark gap breakdown being sufficientt to cause said controllable electron tube to cease passing current prior to the beginning of recharging of said energy storage means.

5. A low voltage spectroscopic spark and arc source as claimed in claim 4-, in which said output pulse producing device is a saturated core transformer having a primary winding connected to said source of AC. potential and a secondary Winding connected to said rectifying means.

References Cited by the Examiner UNITED STATES PATENTS 2,391,225 12/45 Clark 3l5l74 X 2,480,681 8/49 Stiefel 315-237 X DAVID J. GALVIN, Primary Examiner.

GEORGE N. WESTBY, Examiner.

Claims (1)

1. A LOW VOLTAGE SPECTROSCOPIC SPARK AND ARC SOURCE COMPRISING, IN COMBINATION, A SOURCE OF LOW FREQUENCY A.C. POTENTIAL; A DEVICE HAVING AN INPUT CONNECTED TO SAID POTENTIAL SOURCE, AN OUTPUT, AND MEANS PRODUCING, AT ITS OUTPUT, RELATIVELY SHARP OUTPUT VOLTAGE PULSES IN ONE-TO-ONE CORRESPONDENCE WITH HALF CYCLE VOLTAGE SURGES OF SAID SOURCE AND RESPONSIVELY OF DURATION WHICH IS SHORT IN COMPARISON WITH THE DURATION OF HALF CYCLE OF SAID POTENTIAL SOURCE; RECTIFYING MEANS CONNECTED TO THE OUTPUT OF SAID DEVICE; A LOW VOLTAGE ENERGY STORAGE MEANS; A CHARGING CIRCUIT INCLUDING SAID ENERGY STORAGE MEANS AND CONNECTED TO THE OUTPUT OF SAID RECTIFYING MEANS; SAID RECTIFYING MEANS CHARGING SAID ENERGY STORAGE MEANS TO PEAK VOLTAGE DURING EACH PULSE AND INTERRUPTING THE CHARGING CURRENT AT THE END OF EACH PULSE WHILE MAINTAINING SAID ENERGY STORAGE MEANS CHARGED TO PEAK VOLTAGE; AN ANALYTICAL SPARK GAP; A POWER CIRCUIT CONNECTING SAID GAP IN SERIES ACROSS SAID ENERGY STORAGE MEANS; THE PEAK VOLTAGE OF SAID ENERGY STORAGE MEANS BEING INCAPABLE OF BREAKING DOWN SAID SPARK GAP; AN IGNITER CIRCUIT INCLUDING A CONTROL SPARK GAP; A HIGH VOLTAGE CONDENSER; A DISCHARGE CIRCUIT INCLUDING SAID HIGH VOLTAGE CONDENSER ACROSS SAID CONTROL SPARK GAP AND OPERABLE UPON CHARGING OF SAID HIGH VOLTAGE CONDENSER FOR THE VOLTAGE THEREOF TO BREAK DOWN SAID CONTROL SPARK GAP AND FOR SAID HIGH VOLTAGE CONDENSER TO DISCHARGE ACROSS SAID CONTROL SPARK GAP; AND MEANS COUPLING SAID DISCHARGE CIRCUIT AND SAID POWER CIRCUIT FOR TRANSFER OF ENERGY FROM SAID HIGH VOLTAGE CONDENSER DISCHARGE TO SAID POWER

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