US2560165A - Carbon arc feed - Google Patents

Description

July 10, 1951 R. L. GARMAN ET Ax. 2,550,155

CARBON ARC FEED Filed OCT,- 26, 1950 Non Y MW

Parental July 1o, i951 CARBON ARC FEED Raymond L. Garman and John K. McKendry, Pleasantville, N. Y., assignors to General Precision Laboratory Incorporated, a corporation of New York Applicationctober 26, 1950, Serial No. 192,214

1o claims. l

This invention relates to an improved carbon arc control and more especially to a control for automatically regulating the position in space of the luminous crater of the positive electrode of a direct-current arc lamp. The invention is applicable to automatically-controlled arc lamps employed in searchlights and for use in the projection of mctionpictures or in the illumination of studios, and to automatically-controlled arc heaters.

In direct-current arc lamps and arc heaters the major portion of the emitted light and heat is generated at or closely adjacent to the positive carbon crater. and the generated heat or light is applied to the desired location by means of some form of optical concentrating system.

As the positive carbon is consumed it must be v fed or advanced, not only to maintain the arc at its desired length but also to keep the positive crater at its optimum optical position. It is well recognized that this advancement of the positive carbon is accomplished with greater accuracy and ease by automatic means than by manual means, with the radiation from the luminous crater itself made to actuate such automatic positioning means through a light-sensitive or heat-sensitive device.

The use-of light-sensitive devices for the automatic control of the position of the positive carbon crater of an'arc has usually required the use of a sensitive and relatively expensive ampliiier. The instant invention, however, employs simple means for accomplishing this object. The light from the luminous positive crater of the are is directed upon a dual photoconductive cell which controls a gas discharge tube. The internal resistance of this` tube is thereby varied and the variation is made to control the speed of an electric motor geared to advance the positive carbon. The speed of this advance is thus simply controlled by the position of the positive arc crater.

The general objective of this invention is to provide improved means for controlling the position of the positive carbon of a direct-current arc lamp, including photosensitive means and discharge tube ampliiication means.

More speciiically the objective of this invention is to provide means for automatically keeping the crater of Ythe positive carbon of a directcurrent arc lamp in the proper operative position, the light of the positive crater of the arc being employed through photosensitive means to control the position-regulating means.

A further understanding of the invention may 2 be secured from the following detailed description together with the accompanying drawings. in which:

Figure 1 illustrates a circuit embodying the invention.

Figure 2 illustrates an alternative circuit employing a hot-cathode amplifying tube.

Referring now to Fig. 1 an electric arc lamp is represented by a positive electrode I I and a negative electrode I2, between which an arc is maintained supplied from direct-current terminals I 3-I3. Due to the action of the arc, a crater I4 is hollowed in the end of the positive electrode II, and most of the light and heat emitted by the lamp originates at this point by the arc action. The positive crater is automatically and precisely held in a iixed position. counteracting consumption of the positive carbon,.by the apparatus of this invention, and the negative carbon I2 is advanced to maintain a constant arc length by any conventional means which is not shown, but which may be manual or may be controlled by the current flow through the arc.

A portion of the light emitted at the positive crater I4 is directed by means of a simple system, consisting of a slit I6 between the opposed parallel edges of two plates I1 and I 8, upon a photoconductive cell represented by the symbol I3. This cell may be of any type but as van example a lead sulphide cell is here illustrated. This cell is constructed by applying a very thin coating or film of lead sulphide to the interior surface of a transparent glass tube. Two conductors 2I and 22 are secured to the glass and conductively connected to the film at diametrically opposed locations, and a third conductor 23 is secured and connected to a medial location of the lm. These three electrical connections to the lead sulphide film are in the form of parallel lines, represented in Fig. 1 by the terminals 24, 26 and 21, the distance separating terminals 24 and 28 being the same as that separating terminals 26 and 21. The lead sulphide iilm resistance is inversely related to the in-l tensity of the light falling upon it, and it is this property that is here employed.

The terminals 24 and 21 are connected through amorce be employed to accomplish the saine results as are accomplished by this circuit. lit is preferred, however., to employ a gas discharge tube ampliiler because or its simplicity and high amplidcation, the cold cathode type being depicted in Fig. l at I3.

Alternating potential is applied to the gas triode anode circuit from till-cycle supply terminals 34-34 and a transformer 3G, so that anode current ilows during the positive halt of each cycle,under control of the starting time thereof by the grid 34, and the current is inrrupted during negative haii-cycles. l limiting resistor 3l is placed in series with the anode circuit to limit the maximum current ilow and a coupling resistor 38 is also included in series.

This resistor 36 is common to another circuit including direct-current power terminals ill-39a motor held 4 i, a neld rheostat i2 and a nxed field resistor 43. The direct-current terminals are also connected to a motor armature and rotor @d associated with the iieid di. A double-pole single-throw switch @d is arranged so that when in the "manual position it is open and when in the automatic position it is closed, one pole short-circuiting the resistor lli) and the other 'pole closing the circuit to the primary winding oi the transformer tb. In operation oi the circuit, light from the positive crater M oi the burning arc lamp falls through aperture l@ upon an area ci the surface oi the photoconductive cell lil. lf egual areas on opposite sides oi the medial connection represented by the terminal 2o are equally illuminated, the resistance between terminals il and 26 equals the resistance between terminals 2G and 2l and the potential or the terminal 2G is half-way between the potential at the terminal 2d and the potential at the terminal 2l. But since the terminals 24, 25 and 2l are connected t@ the anode 3i, control grid lit, and cathode 32 respectively oi the gas tube 33, the potential oi the grid iid is, under this condition, halt-way between the apodo and cathode potentials. The characteristie or the cold-cathode tube is such that its current dow is then or an intermediate amount. Component circuit magnitudes are such that this current is secured almost entirely by self-rectilication oi' the alternating current output of the transiormer so, when its primary switch is closed. This alternating current is prevented from nowing through the circuit including the motor iield @l because oi its inductance.

The direct-current news from o9-3@ oi the power supply through the armature lill, energizing it, and through a relatively low resistance circuit including the held li and the resistors 36, di and d3 in series, when switch at is open. Circuit magnitudes are selected to be such that when the switch GG is open, the held rheostat di may be adjusted to operate the motor di at a speed that moves the positive carbon il at a rate that approximately compensates its rate ci consumption. 'llhus the crater ld will remain. at about the same point in relation to the aperture i6.

lin order to control position ci the crater ld automatically., the switch d6 is closed, energizing the gas triode 33 and short-circuiting the resistor d3. The latter action increases the field current, slowing the motor Gd. Consumption of the positive carbon then causes the crater ld to move to the right in. the ligure, causing more light to fall upon the area of the photoconductive cell lil between terminals 2G and 2l and less to iall lil between terminals 24 and 26. Consequently the resistance between terminals 26 and 2l falls because oi' the photosensitivity of the cell, while that between terminals 24 and 26 rises, and as a result the potential of the control grid 34 appreaches that of the cathode 32. The gas triode 33 consequently res later in each positive half cycle and its average anode current becomes less. This reduces the current drawn through the resistor 38 by the gas triode 33. However, this tube current flow is in the opposite direction to the larger current ow in the same resistor due to the direct-current source 39-39 so that the net current increases. Therefore, the voltage drop in the resistor 38 increases, leaving less of the direct-current voltage available for the motor field 4i which accordingly is reduced in strength. 'lihis of course speeds up the motor 44 and iucreases the rate of advance ofthe positive carbon li, tending to restore the crater i4 to its correct position. This action continues until the crater l@ is fully restored to the correct position, when the two halves of the cell I9 are again equally illuminated and the grid 34 is brought to its medial potential. On the other hand, any deviation of the crater I4 to the left from its correct position causes the opposite action, again resulting in restoration of the crater to its correct position and maintenance of it there.

in Fig. 2 there is depicted an embodiment of the invention employing a hot cathode gas discharge tube. This circuit has the advantage of being somewhat more sensitive to light variations and, in addition, the grid current requirement is so low that the photoconductive cell can if desired be replaced by a phototube. The circuit is intended to replace a portion of the circuit oi Fig. l, electrical connection points 4l and 48 and resistor 38 being similarly numbered. A hot cathode gas triode 49 is connected for energizetion by the section 5i of the secondary windingv of a transformer 52, the anode 53 being connected to terminal il and through resistors 38 and 5U to the end terminal 54 of the winding 5i. The secondary midterminal 56 is connected to the cathode 5l. The heater 58 is heated by current from a heater winding 59. Operation of the control grid of a hot cathode gas tube is at about the voltage level of the cathode, therefore it is necessary to employ a second section of secondary winding (il connected to one diametral terminal of a photoconductive cell 63, with the other diametral terminal 64 connected to the anode terminal lil. The medial terminal 66 is then at approximately the cathode potential level, and is connected to the control grid 6l;

ln operation, when both halves of the cell 63 are equally illuminated a normal current iiows in the anode circuit of tube 49, when that half oi the cell included between the terminals tti and @il is illuminated more than that included between the terminals 62 and Bil the grid 6l is made more positive and more anode current iiows; while when that portion between 62 and il@ is illuminated more than the portion between 64 and @d the grid 6l ls made more negative and less anode current flows. The action through the coupling resistor 36 to control the motor dfi, Fig. l, is exactly as before described.

What is claimed is:

i. A control system for maintaining the electrode crater of an arc lamp at a fixed position in space comprising, a pair of photosensitive elements, means lor varying the relative illumination oi` salti photosensitive elements in accordance with the position of said electrode crater, a gas discharge tube, means interconnecting said pair of photosensitive elements and the electrodes of said gas discharge tube for varying the grid cathode potential thereof in response to the relative illumination of said pair of photosensitive elements, a motor including a direct current iield connected to advance said arc electrode, an alternating current circuit energizing the anode of said gas discharge tube, a direct current circuit energizing said motor field, said alternating current and direct current circuits including a common series resistor.

2. A control system for maintaining the electrode crater of an arc lamp at a fixed position in space comprising, a motor including a direct current winding connected to adjust' the position of said arc electrode, a pair of photosensitive elements positioned for illumination by said arc crater, means interposed between said arc crater and said pair of photosensitive elements for varying the relative illumination thereof 'in accordance with the position o! said arc crater, a gas discharge tube including at least anode, cathode and grid electrodes, said photosensitive elements being connected in series between said anode and cathode, and said grid electrode being connected to a common terminal of said photosensitive elements, an alternating current circuit energizing the electrodes of said gas discharge tube, a direct current circuit energizing the direct current iield winding of said motor, and a resistor common t said alternating current and direct current circuits.

3. A control system for maintaining the electrode crater of an arc lamp at a fixed position in space comprising, a motor including a direct current winding connected to advance said arc electrode at a rate depending on the speed of said motor, a pair of photoconductive elements, means for differentially illuminating said photoconductive elements in accordance with the position of said electrode crater, a gas discharge tube, means for varying the grid potential of said gas discharge tube relative to the remainder of the electrodes thereof in accordance with the relative differential illumination of said photoconductive elements, an alternating current circuit energizing the anode of said gas discharge tube, a direct current circuit energizing said motor field, said alternating current and said direct current circuits including a series resistor in common thereto.

4. A control system for maintaining the electrode crater of an arc lamp at a iixed position in space comprising, a motor including a series direct current winding connected to advance said arc electrode at a rate depending on the speed ot said motor, a pair of photoconductive elements positioned for illumination by said arc crater, means interposed between said arc crater and said pair of photoconductive elements differentially illuminating said elements in accordance with the position of said arc crater, a gas discharge tube including at least anode, cathode and grid electrodes, said photoconductive elements being connected in series between anode and cathode electrodes, and said grid electrode being connected to a common terminal of said photoconductive elements, an alternating current energizing circuit connected between said cathode and anode electrodes, a direct current circuit connected in series with said direct current motor winding, and a resistor common to said alternating current and direct current circuit.

5. A control system for maintaining the electrode crater of an arc lamp at a iixed position in space comprising, a motor including a series direct current iield winding connected to advance said arc electrode at a rate depending on the speed of said motor, a pair of photoconductive elements, means for differentially illuminating said photoconductive elements in response to the position of said electrode crater, a gas discharge tube including at least anode. cathode and grid electrodes, means varying the potential of said grid electrode in response to the relative differential illumination of said photoconductive elements, a first circuit including a source of alternating current and a resistor connected in series between said anode and cathode, a second circuit including a source of direct current and said resistor connected in series with said motor field winding, said resistor constituting the sole element common to said lirst and second circuits.

6. A control system as dened in claim 5 in wligh said gas discharge tube is a cold cathode tu 7. A control system as defined in claim 5 in viich said gas discharge tube is a hot cathode 8. A control system for maintaining the electrode crater of an arc lamp at a iixed position in space comprising, a motor including a series direct current neld winding connected to advance said arc electrode at a rate depending on the speed of said motor, a pair of photoconductive elements positioned for illumination by said arc crater, means interposed between said arc crater and said pair of photoconductive elements dinerentially illuminating said elements in accordance with the position of said arc crater, a gas discharge tube including at least anode, cathode and grid electrodes, said photoconductive elements being connected in series between said anode and cathode electrodes, and said grid electrode being connected to a common terminal of said photoconductive elements. a iirst circuit including a source of alternating current and a resistor connected in series between said anode and cathode, a second circuit including a source of direct current and said resistor connected in series with said motor field winding, said resistor constituting the sole element common to said first and second circuits.

9. A control system as deiined in claim 8 in which said gas discharge tube is a cold cathode tube and one of said photoconductive elements is directly connected to said cathode.

10. A control system as dened in claim 8 in which said gas discharge tube is a hot cathode tube and the cathode thereof is connected to one of said photoconductive elements in seeswith a source of alternating potential.

RAYMOND L. GARMAN. JOHN K. MCKENDRY.

No references cited.

Images