US2375213A - Control system - Google Patents

Description

May 8, 1945. F. Meca. CHILTON CONTRDL SYSTEM Filed Aug. 8. 1941 than it should create.

Patentedl May 8, 1945 :CONTROL sYs'rEM n v A FrankMcG. Chilton, Arlington, Va.. t y`Application'August 8, 1941,A Serial No. 406,014

f 12 Claims.

y (Granted under the act ofMarch 3. 1883, as

" amended April 30, 1928; 3701'0. G. 757) The invention described herein may beV manufactured and used by or for the'Government Afor governmental purposes, without the payment to me of any royaltythereon.

This invention relates to control systems andv particularly tovoltage control systems. It yalso relates to a system for controlling the lbrilliancy of the lamp in a` film printing machine. The primary object of this invention is to provide means for accurately regulating the D. rC. voltage across the lamp of a photographic printing machine andinovelty resides in the regulator per-'se and in the combination of such auregulator and the other parts of the lphotographic printing machine. i

In certain typesgof photographic printing ina-V chines a rheostat is employed in series with the lamp and this rheostat is moved to various posivtions depending on the density .of the lm. Such a rheostat is accurately-calibrated and for proper operation the supply 'voltage must be maintained accuratelyat a constant value. In some installations the variation in the .rheostatadjustment,

affects the line voltage and'hence the movement of the rheostat creates a greater change in voltage ll'he present invention overcomes this disadvantage and produces a system wherein the supply voltagetremains substantially constant, whereby the accurate calibration of the rheostat is maintained.

A rheostat varies the current to the lamp .and I provide a potentiometer connected across this rheostat. The drop across this potentiometer therefore varies inversely with 'the current in the lamp, hence when the current to the lampl decreases the drop across the potentiometer' increases. This increased drop opposes and reduces the bias on a vacuum tube which has -an anode and cathode respectively connected across the incoming line. When its bias is reduced,` the tube Ibecomes more conducting and effects acurrent flow from the source of supply to and through the tube but not through the lamp. /The sum total current consumed by the lamp plus that consumed by the tube remains substantially constant, hence the voltage of the source of electricity remains constant notwithstanding the poor regulation of the current source. Hence the rheostat and lamp are operated from a constant supply voltage and the'calibrations made thereof at the factory are not affected by changes in local line voltage.

In the drawing there isshown a system including seven main parts respectively indicated by reference letters. The voltage regulator A is connected across the incoming 115 volt A. C. sixty s cycle line. The purpose of. this regulatoris to maintainy the input voltage constant. In addi- .tionto the voltage regulator A, there is a rectifier B which converts the incoming voltage to a direct i current voltage. Following the rectier B in the circuit is a second regulator C which compensates-forchanges inthe rectified D. C. voltage. vThe printer D has a lamp I (for printing the i nlm) connected to the output of regulator C. The

printer D includes an accurately calibrated rheostat Il which is operated to different positions of adjustment by a notch-responsive means E, the latter being controlled by notches in the film F v to be printed. The motor G is connected to the v `stat arm Adoilvllllvard one tap in response to act Vation by a notch. For example, the first not `h 7causes the arm 23 to move from the uppermost tap into engagement with the tap 24. The rheostat arm 2,3 remains on tap 24, which gives the correct brilliancy for lamp ill to print scene #l of the lm F, until the second notch reaches the notch-responsive means E whereupon the arm 23 moves to tap 25. The tap 25 is adjusted sowhen the rheostat arm 23 moves to it, lamp vlil has correct brilliancy for printing scene #2. .The third notch is-located at the beginning of scene #3 and when it reaches the-means E the arm 23 moves to tap 26. This latter tap is positioned to give correct brilliancy for scene #3. Therefore the functional purposel of notch-responsive means E is vto move the rheostat arm 23 to notches so positioned'as t'o give such resistance inlthe lamp circuit that a proper brilliancy for pprlinting the different scenes of the lm will always be'obtained. kHence the brilliancy ofv the liampf- I0 is varied depending on the density of the/film F. So far as this feature yis concerned the idea disclosed is well known to the art and needs no more than a simple schematic illustration to convey the same to those skilled in the art. The rheostat il as normally produced and sold is very expensive and is accurately calibrated. It is calibrated to operate with aLlampsuch as i0 and at constant line voltages. However, I have found that when rheostat I i is moved, the current is changed, and since the rectifier B-has appreciable resistance there is anIR drop in the rectifier B that changes proportionately to the current to the lamp. If no means is provided to correct for this IR drop, the calibration of the rheostat Il would then be in- TheV notch-responsingy correct. In other words the change in position of rheostat II, would cause a greater change in current at the lamp than contemplated if and when a rectifier B (or lother current source) is used that has an IR drop varying proportionally to the current. While itlwould be possible to provide a rheostat II calibrated for each particular installation, I find it desirable to incorporate a regulator C to control the voltage and maintain a constant voltage on the input of printer D.' l

The regulator C comprises an adjustable resistor I6 which may be used for purposes of ad# justing .the voltage on the-printer D manually to a predetermined value. The remaining parts of regulator C interact to hold the voltage at: printer D to that value. A vacuum tube I4 ,(or;f when necessary to carry the current 'a plurality of such tubes connected in parallel) has itsplate I1 connected to the positive side of the D. C. line and its indirectly heated cathode I8 to the negative side of the D. C. line. A resistor I2 of Ilow resistance value is in series with thegfD.- C. line and a potentiometer i3 of high resistance, say having a total resistance four hundred times the resistance of resistor I2, is connected `between the wire 20 and the upper end of rheostat II.

The principal current path from the .rectifier B to and from the printer lamp is-as'follows: 2I--IG--I0-II-I2-2ll. However, some current does flow through the following path: 2I--I6-III3-20. -When the rheostat Il is shifted, the current in 4potentiometer I3 varies. The vacuum tube I4 has agrld I9 connected to the movable arm 22' of potentiometer I3. Hence a voltage is impressed between the grid I9 of the tube I4 .and the cathode IB. This voltage varies with the current fed to the lamp. As will appear later, the voltage across the resistor I2 remains substantially constant at all times. The positive end of this resistor is connected to one end of potentiometer I3. The potentiometer I3 therefore, would effect a constant negative bias on grid I9 except for the opposing effect of the potential across potentiometer I3. The effective biasing potential on grid I9 equals the drop acrossA resistor I2 less the opposing drop that occurs between wire 20 and arm 22 of potentiometer I3. This latter opposing drop varies with and depends on the current in potentiometer I3. The current in potentiometer I3 in turn depends on the position of arm 23 of rheostat II. As the arm 23 moves to connect higher taps and increase the value of resistance in the lamp circuit, the current through potentiometer I3 increases hence the drop between 20 and 22 increases thereupon reducing the negative bias on grid I9, whereupon the current through tube I4 increases. When the arm 23 of rheostat II moves downward, the drop across potentiometer I3 decreases (the drop across potentiometer I3 is substantially equal to the drop from wire 20 to arm 23, since the resistance of I3 is large as compared to the re `sistarlce vof rheostat II). Hence as arm 23 moves downward, the potential across I3' de-u creases its opposition to the negative bias of resistor I2 and therefore, the tube I4 becomes less conducting and the shunting current through the tube is reduced.

By proper adustment of potentiometer I3 the totalcurrent consumed by the lamp I8 plus that consumed by the tube i4 thereafter automatically is held constant. In other words [L4-Ir equals a constant, where IL is the current in the lamp and Ir the current flowing from the cathode to the plate of the tube. Hence the voltage drop across the rectifier B as well as across resistors .I2 and I6 remains constant for any given setting of variable resistor I6. Moreover, the voltage across the voltmeter I5 remains constant and the effect of a change in setting of of arm 23 does not create a greater change in current than that for which it is calibrated to create. E I' claim toV have'jiented:

LA .devicegiorfprinting film comprising in combinatic'urfwitlji the film to be printed; a lamp kfor efieetinggprinting of the film; a sourcegrgof ,electriabspplw a rheostat in series with 'the `'source vof electrical supply and the lamp; control means responsive to the densities of different scenes of the lm for adjusting said rheostat to control the brilliancy of said lamp to effect thereby different printing brilliancies for the different scenes respectively; and means responsive to the control means for shunting current across the source of electrical supply; the last-named means including means whereby the sum of the current thus shunted plus that consumed by said lamp remains substantially constant when the rheostat is operated to change the current to the lamp.

2. In a device for printing film, the combination with a source of electrical supply, of a lamp operated from such source for printing the film, control means responsive to different densities of portions of the film for controlling the current to said lamp, and means operated by said control means for` shunting current across said source to such degree that the sum of the shunted current plus the lamp curent remains constant when said control means varies the lamp current.

3. In a device for printing nlm, the combination with a direct current source of electrical supply of poor regulation whereby the voltage output therefrom varies when the load varies, of a lamp operated from said source, accurately calibrated rheostat means accurately controlled by the density of the film for varying the current through the lamp, and means associated with said rheostat means and affected by changes thereof for shunting current across said source in such quantity that the current drawn from said source remains substantially constant when the current through said lamp is varied.

4. In a device for printing film, a source of alternating current supply, a voltage regulator across said supply, a rectier connected to the output of said supply, said receiver having characteristic of poor voltage regulation under varying load conditions. a lamp for printing a film connected to the output of' said rectifier, rheostat means controlled by the density of the film for accurately controlling the brillancy of said lamp Vwhen the film density varies, and means associated with and operated by the rheostat means to hold the current from the rectifier conetant when the current to the lamp is varied by said rheostat means. i

5. In a direct current voltage regulator, a two wire input; a discharge tube comprising a plate connected to one of said wires, a cathode conn nested to the other of said wiresand a grid controlling the currentJ through the tube; a two wire output4 respectively connected to the two wire input; a load; a rhecstat in series with the load; a constant source of bias connected between the cathode and the grid of said tube to bias said grid negatively; and control means to oppose the negative bias including means cocnected to said rheostat and responsive to the drop across the rheostat to increase the opposition to said negative bias when the drop across the rheostat increases and to decrease such opposition when the drop across the rheostat decreases; said tube and control means being so constructed and arranged that the sum of the current passed by the rheostat plus that passed by the tube remains substantally constant.

6. In a device for varying the current at a load without varying the current at the source of supply, the combination with the load and the source of a rheostat connected between the load and source for varying the current to the load to such an extent as to have very marked effect upon the operation of the load, current shuntlng means connected across said source, said current shunting means including control means thereof adapted for connection to a source of control potential for controlling the quantity of current shunted and means connected to said rheostatI and responsive to the drop across the same and also connected to said control means to vary said control potential and thereby control the quantity of shunting current in such degree as to hold the current from the source constant when the load current is varied by said rheostat.

7. In a control' device, a source of electricity of poor regulation, a load, a rst wire leading from one side of the source to the load, a rheostat having two end connections and a movable arm connection, a'second wire connecting thev ing said cathode to said first wire; means con movable arm of the rheostat to the other side of the load, a resistor, a third wire connecting one end of said rheostat to one side of said resistor, a fourth wire connecting the other side of said resistor to the other side of said source, an electron discharge device having a grid, cathode and an anode, said electron discharge device constituting the only electron discharge device in or about said control device means connecting .the cathode to said third wire, means' connecting said anode to said first wire, a potentiometer having a movable tap, said potentiometer being connected from the fourth wire to the remaining end of said rheostat, and means connecting the movable tap of said potentiometer to said grid; the above named parts all being so. constructed and arranged as ,to control the bias on said grid and effect a current shunted through said discharge device which eiects a constant drain from said source when the rheo stat arm connection is moved.

8. In a device for printing film, the combina tion with the nlm of a lamp operatively related with such nlm, means responsive to the density of the nlm for controlling the brilliancy oi the lamp comprising a rheostat in series with the necting the plate to the said remaining terminali of said lamp; and means, comprising a potenn tiometer having its respective ends connected to the remaining terminal of said rheostat and to the second side of said resistor and including a movable tap connected to said grid, for ccntrolling the .quantity of current shunted by the tube to reduce the variation in current from said source when the rheostat tap is moved.

9. A voltage regulator as dened in claim 'i in which the rheostat functions to eiectuate wide variations in load current.

10. The device deiined in claim 5 in which said tube constitutes the only tube in the device.

1l. 'I'he device defined by claim S in which the last-named means includes; wires connected directly to opposite ends of said rheostat and subject only to the drop across said rheostat, whereby the potential across said wires increases whenlthe potential across the load decreases, and current shunting means for shunting cur rent across said source to effect increased shunting when the potential across said Wires inn creases and to effect decreased current shuntn ing when the potential across said wires decreases.

12. In a direct current regulator, a two wire input; a discharge tube comprising a plate connected to one of said wires, a cathode connected to the other of said Wires and a grid controlling the current through the tube; a two wire output respectively connected to the two wire input; a load; a rheostat in series with the load, said rheostat having wires connected to diierent points of same whereby to develop a potential across the wires depending on the setting of said rheostat;' a constant source of bias connected between the cathode and the grid of said tube to bias said grid negatively; and control means to oppose the negative bias including means com nected to said rheostat and responsive to the potential across said wires to increase the opposition to said negative bias when the drop across the rheostat increases and to decrease such opposition when the drop across the rheostat decreases; the last-named means includ ing means to hold the sum of the current through said tube and rheostat substantially constant.

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