US2480681A - Electrical circuits - Google Patents

Description

ELECTRICAL CIRCUITS Filed Aug. 14, 1946 nc. SOURCE /6 ET: W m

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MULTIVIBRATOR AND 7 SHARDENER INVENTOR' KARL J. .ST/EFEL.

Patented Aug. 30, 1949 rKarl J aStiefel; Waltham, theon Manufacturing 0 a corporation. ofiDelaware Mass., assignor to Ray- 11 1 3,

Newton, Mass,,

Application. August 14, 1946, Serial No. 690,455 Claims. Cl. 315207) This invention-relatesto electrical circuits, and more particularly to a novel spectroscopic arc source,

An object of. this inventionisto provide-a highvoltage are source, whereby a high ionization, andtherefore a goodspeotrum, may be. obtained.

Another-object is to devise an arc source for use in spectroscopy, which utilizes a polarized voltage andcurren-t. impulse which can-bedefined and which, therefore, ,canrbe reproduced by'diiferent experimenters who can, therefore, obtain uniform results .from their spectrographic work.

A further object is to devise an adjustable arc source by an adjustment of which materials with lowimel-ting points can be exposed to .high excitation voltageswithout danger-of. melting.

A stil-l'further object'isto devise a-high-voltage are source which is1relativelylsafeto personnel operating the same.

Theforegoing. and other-objects of thecinvcntion will be best understood from the following description of an exemplification. thereof, reference being had tame-accompanying drawing, wherein the single figureiisqa diagrammatic-representation of one means :iorcarrying out the invention.

Referring tothe drawing, a source of direct current-L'which. may beairectifier supplied from an A. C. 1ine,has one :of itsoutput terminals 2 connectedto groundat-2I .and the other terminal 3 connected to :the anode 4 ofa-dioderectifier 5. Cathode 5 of therectifier or blocking tube 5 is connected through a-choke T to'the anode ii of a gaseous triode 9, preferably a hydrogen-filled thyratron. Anode 8 'isconnected, through a pulse-forming line or equivalent wave-shaping network 23 comprising a series-connected inductance l9 and a capacitance or condenser H, to one end of a charging inductance :12 and also to one of the -.arc electrodes l3. The other end of the inductance I2 is connected toground, as is cathod l l of-the thyratron or modulator'tube 9, while the-other arcelectrode 15 is connected through a resistor l6 to-ground.

A multivibrator and sharpener circuit H, which produces unidirectional pulses repetitively at a variable-rate and thereforemay be termed a variable repetition 'rate pulser,-has its output terminals .laand l9connected, respectively, to grid ZUoftube-ll and to ground at 22. The repetition rate of pulser I! may be varied over a range'of the order ofzerotofifiOO-cycles per second.

Theenergv-necessaryito produce an are betweenspaced electrodes-t3 @ndtlti is adapted to be supplied tov said electrodesfrom the pulseforming line :or Wave-shaping network 23, the capacitance 14- thereof .providing a means for storing-energy. Capacitance H functionsas an energy-storing capacity and also functions in conjunction with the inductance lflsfor generatin a substantially -rectangular wave. The energy-storing capacitance .of the wave-shaping networkis isadapted torbe charged from-source 5 "through the anode-cathodepathA-t of blocking tube 5,choke '1', inductance "Land charging inductance 1 2-.

The discharge of-the capacitance of waveshaping network 23 through thelarc path l?i5 'is timed by the controlled gaseous discharge de- Vice 9, which has its anode .8- connected to the positive side of the capacitance of the waveshaping network 23-and its cathode Hiconnected through the arcpath l:5--l-3-.to the negative side of said capacitance; The control gridZQ-of tube 5 is driven positive relative to the cathode 14 of said tube periodically'by the repetitive pulse output of pulser l 'b ataperiodicity determined by the manually-adjustable. setting-of the repetitionrateof said pulser. Thecharging inductance l2 has a high value of inductance and therefore does i not. interfere with the discharging of the-capacitance throughthelarc path %3 a5 through tube 9.

Tube 5 acts asa blockingtube to prevent pulses of current from beinglsent back to the rectifier: source l andto holdthe voltage: onthe capacitance H constant until discharging of said capacitance occurs'asaresult of firing of tube .9.-

The values of the inductances of choked, in ductance ill, andinductanceJZ- are so correlated tov the maximum frequency of pulser I! 'as to give resonance charging a of the condenser =1 l in accordance with the expression where f is the maximum frequency of pulser l'l,

L is the combined. inductances of chokes 1, l0,

- and i2, and C is the capacitance of the condenser.

By this arrangement-the voltage across the con- 7 denser whencharged is substantially double the voltage of source I. "Blockingtube 5 also functions to prevent an oscillatory discharge of the condenser through the source when said con denser has become chargedto substantially'dou bleth'e source voltage. As aresult of this voltage doubling effect-pulsesiof high voltage are applied to are electrodes l- 3 and l5 The resistor i6 is, of the type-having negative, I

resistance-current characteristics; that is to say, the resistor i6 is of the type whose resistance falls as the current therethrough increases. Preferably, the resistor I6 is a device of the yp the resistance of which varies as a negative nonlinear function of the current therethrough, so that as the current increases from zero the resistance decreases very sharply. Devices having resistance-current characteristics suitable for the purpose of this invention are known per se; for example, the device may be of the type known as Thyrite, formed of a mass of silicon carbide crystals or similar material suitably bound together.

If the characteristics of the circuit are such that then the discharge of the condenser is non-oscillatory. If it be attempted to avoid oscillations by increasing the resistance of the circuit so that the above inequality is achieved, then the energy available for the desired pulse would be greatly decreased, for, since the resistance of the arc during conduction would be low relative to the resistance of the circuit, much of the energy of the impulse would be lost in the resistance of the external circuit. In order to avoid oscillations and still preserve the character of the desired rectangular pulse and maintain this pulse at a high energy level, the resistor 15, having negative resistance-current characteristics, is provided in the discharge circuit of the condenser. During the period of the initial substantially rectangular pulse, the resistance It offers but small resistance to the current flow in the arc circuit since the current therethrou h is high Maximum energy is therefore supplied to the arc. When the cur ent t rough the arc path falls to a low value, as the volta e on the condenser i I reverses, the resistance of the resistor I6 becomes great. thus matching the resistance of the arc ath which ofiers great resistance as the voltage thereacross drops to a level below which the arc will no longer conduct. 7

As is well known, an arc in air does not conduct at low voltages. and during the period that the vo tage thereacross isr sing to such a. value that the arc path is conductive. its resistance is hi h: after the arc oath becomes conductive. its resistance is relatively low until the voltage again dro s to a value below which it is no longer conductive. at which time the, resistance is again high. The resistor I6 matches these cond tions, since its resistance ishigh when the current therethrough is low, and its resistance becomes low when the current therethrou h is high. The high resistance of the circuit to the low current thus prevents a sharp reversal of the voltage across the arc path I3-l5 so thatthe reverse voltage does not rise to a high level. The reverse voltage rises gradually and then dies away substantially exponentially since the resistance of the resistor I6 increases substantially exponentially as the current therethrough decreases. Accordingly, the current does not again reverse and there is no further impulse in the direction of the original rectangular impulse, so that oscillations after the main pulses are non-existent. Therefore, re-' sistor It serves to damp the pulses. Also, the impulses supplied to the'electrodes are substantially unidirectional, because the reverse voltage rises only to a level which is extremely small as compared to the level of the initial or main rectangular pulses.

By utilizing the capacitance of a wave-shaping network as the source of the stored energy for the arc impulses, substantially rectangular pulses may be obtained. Therefore, a series of high voltage unidirectional impulses of substantially rectangular wave shape, having a repetition rate determined by the setting of the variable pulser H, are applied to the arc electrodes. Each individual pulse is of equal magnitude and is a definite multiple of the applied D. C. voltage,

In a practical embodiment of this invention, with an input to rectifier l of one it. v. a. at sixty cycles, pulses having a width of 0.05 microsecond, at 14 kilovolts and 1,000 amperes, were obtained.

Since the pulses are substantially rectangular, are unidirectional, and can be produced at a readily determinable repetition rate, they could be defined as a standard and could be readily reproduced by different equipments for uniform results.

Since the pulses are of high voltage, high ionization of the arc, and therefore also a good spectrum, may be obtained by the use of this invention. Also, since the voltage of the source i is not dangerously high and since the high-voltage output of the circuit is not steady but is only in the form of pulses, the arc source of this invention is relatively safe to personnel operating the same.

By reducing the repetition rate of the pulses, giving a proportionately longer cooling time between successive pulses, materials with low melting points can be exposed to high excitation voltages without danger of melting.

In the use of this invention as a spectroscopic arc source, the material to be spectroscopically analyzed is utilized as the negative arc electrode l5. Since substantially unidirectional highvoltage pulses are applied to the arc electrodes, this negative electrode emits from its surface a large number of particles of vapor, while the positive electrode 13 emits few particles, so that the vapor between the electrodes is composed mainly of particles of the material whose spectrum is desired. Both electrodes remain relatively cool during operation, so that they contrib- 51.) ute little background to the spectrum, most of the spectrum being obtained from the highlyexcited analytical vapor between the electrodes.

Of course, it is tobe understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art,

What is claimed is:

1. A spectroscopic arc source, comprising a pair of spaced electrodes one of which is comprised of a material whose spectrum is desired, a source of current, a pulse-forming network including an inductance and a capacitance between said source and said electrodes for storing electrical energy from said source, circuit means for repetitively discharging said stored energy through said electrodes, said inductance and capacitance being arranged to deliver said stored energy in the form of a series of substantially rectangular impulses.

2. A spectroscopic arc source, comprising a pair of spaced electrodes one of which is comprised of a material whose spectrum is desired, a source of current, a pulse-forming network including energy, means for charging the storage capacity of said network from said source through a circuit in shunt with said electrodes, an intermit-' tently-operable discharge circuit for discharging said stored energy through said electrodes, said inductance and capacitance being arranged to deliver said stored energy in the form of substantially rectangular impulses, said discharge circuit through said electrodes including a series resistor having a negative resistance-current characteristic, said resistor having a zero current value at least equal to that required for critical damping of said discharge circuit.

3. A spectroscopic arc source, comprising a pair of spaced electrodes one of which is comprised of a material whose spectrum is desired, a source of current, a pulse-forming network including an inductance and a capacitance between said source and said electrodes for storing electrical energy from said source, an intermittently-operable discharge circuit for discharging said stored energy thorugh said electrodes, said inductance and capacitance being arranged to deliver said stored energy in the form of substantially rectangular impulses, whereby the duration of discharge of said energy through said electrodes is maintained at a constant value.

KARL J. STIEFEL.

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

UNITED STATES PATENTS preface dated Jan, 1946.

Radar System Fundamentals (Navships 900,- 017), page 180, (Bureau of Ships, Navy Dept, Wash., D. 0.), released July 5, 1946.

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