US2347015A - Means of compensating for drift of photoelectric devices and associated circuits - Google Patents

Description

April 18, 1944. n WOLOSCHAK MEANS OF GOMPENSATIHG FOR DRIFT OF PliCHl'OIEiLnEGERIC DEVICES AND ASSOCIATED CIRCUITS Filed Sept. 1-1

1942 5 Sheets-Shani 1 )umvme. H ffonsfanfin mamm- April 18, 1944.

5 Shuts-Shut 2 K. WOLOSCHAK MEANS OF COMPENSATING FOR DRIFT OF PHOTOELECI'RIC DEVICES AND ASSOCIATED CIRCUITS Filed Sept. 1'7. 1942 2 vi -Eon IN VEN TOR.

l" M M M m i m M V Q "mu Ai-gys.

Aim-i118, 1944.

K. WOLOSCHAK 2,347,015

MEANS OF COMPENSATING FOR DRIFT OE PHOTOELECTRIC DEVICES AND ASSOCIATED CIRCUITS Filed Sept. 17 1942 5 Sheets-Sheet 3 JNVENTOR. Konafanhn Wa/osoha Affyli 8 1944- K. WOLOSCHAK 2,3 7,0 5

MEANS OF COMPENSATING FOR DRIFT 0F IHOTOELECTRIC DEVICES AND ASSOCIATED CIRCUITS Filed Sept. 17, 1942 5 Sheets-Sheet 4 x INVENTOR. E 2 Kansfanf-m wolaaohak Q 5 BY E u: a i

18,1944. K. WOLOSCHAK 2,347,015

MEANS OF COMPENSATING FOR DRIFT 0F PHO'I'OELECTRIC DEVICES AND ASSOCIATED CIRCUITS Filed Sept. 17, 1942 5 Sheets-Sheet 5 'Aw 's.

Patented Apr. 18, 1944 i 7, OF COMBATING FOR DRIFT F 'PHO'IOELEGTBIO DEVICES AND ASSOCI- Konstantin we... rm Chester, s. m, as-

signer to Press Association, Inc, New York. N. Y., a corporation of New York Application September 17. 1942, Serial No. 458,842

14 Claims. (Cl. 178-6.!)

} This invention relates to means for compensating for the gradual .drift of the signal output voltage of an electron amplifleror a photoelectric cell, and the gradual change in the overall gain oftransmission circuits." In accordance with some applications of this invention com'- pensation for the drift of. either transmission circuits, the photoelectric device or its associated circuits, or the two in combination, may be accomplished.

A specific oblect of this invention is the ap plication thereof for use with facsimile picture transmission systems.

The detailed objects of the invention and details of various circuit arrangements for accomplishing those objects are set forth below in corn nection with the attached drawings in which the same or similar reference numerals are used throughout to indicate the same or similar parts.

This invention resides substantially in the combination, construction, arrangement, relative system.

Figure 2 is a left hand end elevational view of the rotatabie cylindrical support for the picture to be transmitted.

Figure 3 is a schematic circuit arrangement showing amodinc'ation which may be applied to the circuit arrangement of Figure i.

Figure 4 is a diagrammatic view of a modified form of the portion of the apparatus of Figure 1 involving the picture support and scanning head.

Figure 5 is a left hand end elevational view of the rotatable picture support of the structure of Figure 4.

l lgureoisaviewsimilartoi'iguredofafurther modified construction.

Figure 7 is a complete diagrammatic and circuit schematic arrangement involving a still further modified form of transmission equipment of this type embodyin the invention with further modifications.

Figure ii is a diagrammatic illustration of the application of this invention in the correction of gradual variations in a, transmission line or other. communication channel.

Figure 9 is a diagrammaticillustraticn oi the application of the subicctmatter of this invention to a system wherein the gradual drlitln the signal output voltage oi a photoelectric device and the gradual varlationsin the connected transmission line or other communication channel are compensated for.

In the use of photoelectric cells and electron multipliers of the photoelectric type. as for example when used in connection with facsimile picture transmission systems, there is inherent therein, as well as in the circuits associated therewith, a tendency for the signal v itage to change gradually due to the drifting of he output voltage of the photoelectric devices and to a gradual over-all change or drift in the gain 0! the circuits associated therewith. It is the prime object of this invention to provide means for automatically compensatingior either of these drift components, or for both of them.

In accordance with this invention the voltage drift of the photoelectric devices and associated equipment at the transmitting station may be compensated for by association of the herein disclosed invention with the equipment at the transmitter. Similar results can be secured by the appropriate application of this invention to the transmitter and receiver to accomplish correction of the gradual variations in the transmission line or other communication channel therebetween. As a finalapplicatlon of this invention, portions thereof may be associated with the transmitting and receiving equipment to compensate both for the drift of the photoelectric devices and for the associated and interconnecting circuits. These various applications oi the invention will be separately described hereinafter.

Referring to Figure l of the drawings, a rotatable cylinder I of the type usually employed in iacsimile picture transmission is dia rammatically illustrated to include a shaft 8 for supporting it for rotation on its longitudinal central axis. The picture such as a photograph to be transmitted, is diagrammatically illustrated at 2 applied around the periphery of the cylinder 1 and attached thereto at its top and bottom edges by means of a wedge bar I which clamps the top and bottom edges of the photograph into a longitudinal slot in the cylinder i and holds the photograph in intimate contact with the cylinder l throughout its area. Clamping bars of this type are commonly used in such systems. As a part of this invention a special contact 5 is mounted on the end of the cylinder I and aligned with the end of the clampi'i bar 4 in a radial direction (or cooperation with contacts which will be referred to later.

Only so much of the scanning head has been diagrammatically illustrated herein as is necessary to an understanding of the invention. The parts illustrated are enclosed within a dash line box for the purpose of indicating that the scanning head 8 is a structural unit which. as is well known in this art. is driven in synchronism with the rotation of the cylinder I. so that it slowly moves longitudinally thereof. As illustrated, this to unit includes a light source I the light from which is focused by a lens system 8 to a point P on the surface of the photograph 2 along an axis at an angle so that the light reflected from the point P is refocused by a lens system 8 onto the pickup photoelectric cell It or electron multiplier having a photoelectric cathode.

with this arrangement, as is well known, when the transmitter is in operation the point P has a helical path of relative travel with respect to the photograph I. so that the point gradually traverses the entire surface of the photograph 2 and thereby scans each elemental area thereof. The output of the photoelectric device it varies in accordance with the reflective characteristics of the elemental areas scanned. The output of the photoelectric device It has been diagrammatically illustrated as being supplied by means of the circuit wires II to an amplifier l2, preferably of the vacuum tube type. and associated equipment. Circuits of this type are well known in the prior art and one form of this circuit is illustrated in the co-pending application of James C. Barnes. Serial No. 426,813, filed January 15, 1942.

The amplified signal currents are supplied from the amplifier I: by circuit wires I3 and II to the primary of the input transformer ll of the multistage vacuum tube signal amplifier, as illustrated.

The secondary of transformer II is connected in the input circuit of a triode vacuum amplifier ill whose output circuit is connected by the coupling transformer 11 to the input circuit of a second triode vacuum tube amplifier l8. As a further aid in the application of this invention it maybe noted that these triodes may be the commercially known 7H7 tubes connected so as to be used as triodes. The output circuit of this ampliher is connected by the coupling transformer it to the ton line. Anode voltage supply is connected to the lead 28 in accordance with well known practice.

In accordance with this invention, the compensating device is associated with this amplifier in the following manner. The output leads I! of the amplifier II are also connected to the primary of a coupling transformer 20 whose secondary is connected in the input circuit of a diode vacuum tube detector It. This input circuit includes a pair of contacts 22 arranged to be interconnected by means of the contact I mounted on the cylinder l. n Contacts 22 are connected by the wires Ii in the input circuit of the diode. The output circuit of the diode includes a network 24 comprisingaoondensercandaresistorlt. This network 23 has a relatively high time constant due to the fact that the capacitance and the resistance of which it is composed are large.

(:ommon lead 2| extends from the network It to the cathodes of the triodes II and It. An adjustable connection 26 from the resistor R is connected to the input circuits of the triodes it and "through the resistors 26 and fl. By-pass condensers are connected between the points of connection of the cathodes of the triodes it and I I to the lead 2! and the points of connection of the resistors 20 and 21 to the input circuits of those triodes.

In the operation of this system it will be seen that the input circuit to the diode 23 will be completed once for each-revolution of the cylinder 1.

that is. at the time the contacts 22 are interconnected by the contact I. At this time the light point P will be projected pon the surface of the clamping bar I. This clamping bar should be made to have uniform reflective characteristics and should preferably be white although a gray or other tonal value would be suitable. It thus provides a reflection standard of uniform reflecting power throughout its length so that the light reaching the photoelectric device I I provides a standard reference signal. Since the contact I and strip I are radially aligned, the signal voltage output of the electron device HI is a maximum once for each revolution of the cylinder i at the time that the input circuit for the diode is complete at the contact 8.

At this time the voltage developed across the resistor R is determined solely by the signal voltage generated by the light reflected from the strip 4. If the output signal voltage of the photoelectric device lt drifts or changes gradually, due to the drifting of the operating voltage of the electron device, or to a gradual change in the over-all circuits connected between it and the detector 28, the voltage across the resistor R'will likewise change slowly. -This rectified voltage across the resistor R can be used as illustrated in Figureltovarythegridbiasvoltageofoneor more of the trlodcs of the amplifier (in the case illustrated this bias control is shown for both stages of the amplifier) to compensate for the original signal voltage change resulting from the drift components mentioned. The average value of this compensating voltage can be controlled by adjustment of the connection of line 26 to the resistor R as illustrated.

In order to increase the sensitivity of this arrangement, the modification of Figure 3 may be employed, which consists solely of inserting in the connection between the resistor R. and the lead a a battery or other source of constant voltage 8|! so that it is in opposition in polarity to the compensating bias voltage generated in the resistor R.

The voltage value of the' source Ill should be almost equal to the compensating bias voltage drop in the resistor It. From an examination of Figure 3 it will be obvious by reason of the use of the same reference numerals how to apply thefeatureoi.l 'igureiltothecircuitoi'il lirurel.

By this use of the biasing voltage source ll it will be apparent to those skilled in the art that the effect of the voltage variations across the network Rwillbemoredlrectlyproportionaltothevarlations inthe energy l t from the circuit II thaninthecaseoftheofllgure 1 wherethesourc lliisnotemployed. Thereasonsforthlssreatonceapparenttothoseskilled incirouit operations.

Themangementofi 'lguresiandficontainsa variation of a portion of the vention heretofore disclosed wherein theuse of th ping-bar I is withasasourceofmaximum reflection and a special white target, moving in timed relation with the cylinder, is employed. In this case the light from the source I is focused upon a white target it which is connected to a shaft on which is mounted a bevel gear ii for rotation therewith. The bevel gear If in turn meshes with a bevel gear I! which is spllned to the shaft 83 so that itsmay progress therealong as it revalves with the shaft. The target and gears are mountedonandforma partofthescannlng head i so that they may move with the other parts of the scanning head longitudinally of the cylinderiinaccordancewlthcommonpraetioe. Shaft It isprovided with a gear It which meshes with a gear ill mounted upon the shaft 3 for retation with it and the cylinder. These various partsareproportionedsothatssthepowerdrlvterconnec'ting the transmitter and receivr of such a system. Thu is a good point to note. that the application of this invention to facsimile picture transmission systems does not represent the only use to which the subject matter of the invention may be put. Particularly it is to be noted in connection with the application of the invention as illustrated by Figure 8, that the subiect matter of this invention may be used for improving transmission line characteristics generally. Only sufiicient of the transmitter and receiver of a facsimile picture system is illustrated in Figure 8 to make the subject matter of the invention clear. The transmitting cylindo:- or support I, rotatably mounted on the shaft 3 and provided with the cam 5', is like that previously described in connection. for example, with the description of Figure 1. In this arrangement, however, the receiving support for the receiving negative is illustratedas likewise comprising a rotatable support It! provided with a shaft upon which a cam I similar to the cam 5' is mounted. The scanning and recording heads have not been shown as unnecessary to an understanding of the invention. The signal to be transmitted, such as the picture signal, is fed by the circuit it into the transformer 42 and may come directly'from the scanning head or an amplifier fed by the scanning head. The cam 6 operates a single pole double throw switch 4! whose movable blade is operated by the cam. One of the fixed contacts thereof is connected to one terminal of the secondary of transformer 42. The other terminal of this secondary is connected to one terminal of the secondary of a transformer 45 and to one of the transmission circuit lines 48. The movable contact of switch ll is connected to the other transmission circuit line 8. The other terminal of the secondary of transformer i is connected to the other fixed contact of switch 43. The primary of the transformer ii is fed by a suitable signal source ll, preferably an alternating current generator of constant amplitude. The broken line box 41 represents the transmission line or communication channel between the transmitter and the receiver with its usual adjuncts and in the various known suitable forms.

The incoming signal from the transmission line is fed to a transformer l3 whose secondary is connected at one terminal to the movable contact of a switch ll operated by the cam 4| on the receiver. Hie fixed contact of this switch is connected to the cathode oi a diode rectifier 51. The plate circuit of the diode is connected to the other terminal of the secondary of transformer {I through a network Ii comprising a potentiometer shunted by a capacitor. shunted across the incoming end of the transmission line is a transformer 52 whose secondary is connected to the input of a triode 55 forming part of the compensating amplifier indicated by the broken line box. This input circuit includes the bypass condenser 58. The output circuit of the triode It feeds a transformer 66 whose secondary is connected in a known manner, not shown, to the rdcordinghead of the receiver of which the cylinder II is a pert. The signal current in this secondary circuit represents the compensated signal from the transmitter, that is. the signal from the transmitter compensates for any variations introduced by changes in the transmission einciency of the channel 01. This compensation is effected by reason of the connections i'romthenetwortli ecroestheterminaleofthe condenser II in the input of the triode ll. The resistor-flisprovidedfortheobviouspurpose of creating the proper circuit conditions in conjunction with the adjustment of the potentiometer of the network ll.

It will be seen that the compensating amplifier audits manner of connection with the diode rectifier and other portions of the circuit is similar to that previously described and only difiers in that the compensating amplifier is shown as having one stage, it being understood, of course. that the required number of stages may be employed as previously indicated in connection with Figure 1. It is, of course, apparent that the operation of this system depends upon suitable synchronism, the requirement for which is indicated by the relative positions of the cams 5' and ti. In other words. when the reference signal source 44 is in circuit at switch 43. switch 4! must be closed so that the compensating signal circuit is in operation.

In the actual application of this invention these conditions will preferably exist at the interval between scanning strokes. For example in the case of the rotatable support type of facsimile system, these conditions would be maintained at the time the scanning head and re cording heads are aligned with the clamping bars of the supports. In the case of the reciproeating type of supports, this condition would exist during the return stroke of the supports at which time scanning and rebordingnoes not take place. To summarise. the receiving end of the line is periodically connected to the rectifier ,circuit for controlling the gain of the amplifier at the time the reference signal source is connected in circuit. all of which shouldoccur at the interval between what may be termed the scanning strokes. This application of the invention will be seen to differ from those previously described in that the reference signal is. in the former case. produced by a separate reierence signal generator ll as distinguished from the case of the latter where this signalis gotten 4:. by the use of a target in one form or another of uniform reflection characteristics. p

The arrangement of Figure 9 will be described,

wherein is mustrated the application of this invention to a facsimile picture transmission eye Mteminordertocompensatenotonlyi'oradrlft m use. 'lhepositiveorotherformofscenelto in the signal output voltage of the electronic device. but also for variations in the transmission efilcieney of the channel connecting the transmitter to the receiver.

1n the system illustrated diagrammatically in Figure 9, both the transmitter and receiver have been shown. As illustrated. the transmitter includes a suitable support such as a drum I, mountedupontheshafttsoastoberotatablein transmittedismountedonthedrum I and held thereon by meansof the clamping bar reflected from the photograph is a focusing lens system 9 arranged to focus the reflected light on a suitable photoelectric device III. The scanning head unit 8 of course movesin timed relation with the support I so as to slowly travel in an axial direction from one end to the other during scanning.

At this point it may be noted, as those skilled in the art will appreciate. that the subject matter of this invention in all of its various forms, may be equally well applied to a facsimile picture transmission system where the scene to be transmitted is in the form of a transparency and the scanning head of a type employing 30 makes one complete revolution for each revolution of the drum I and hence is interposed between the light source I and photoelectric cell III once for each rotation thereof.

The output of the photoelectric cell is applied by the circuit wires II to the input of a transmission amplifler I2 whose output terminals are connected to the transmission line channel or network 41 connecting the transmitting station with the receiving station. In this system the signal voltage is amplified and compensation is applied to the amplifier at the receiving station. The channel I1 is coupled to the signal amplifier by means of aztransformer I5 which corresponds to the similarly numbered transformer at the transmitter in the system of Figure l. A multistage signal amplifier is employed, as before, including the trlode amplifiers I8 and Ill. The compensating detector in the form of a diode 23 has its input circuit coupled to the receiving station'tcrminals of the channel ll by,means oi the leads II and the transformer 20. In this case the input circuit oi the diode 23 is connected by the leads 2I through a switch 220. which is operated by means of a cam II on the shaft ll so that the switch 221: closes once for each revolution of the support II. The compensating detector circuit and its manner of connection to the received signal amplifier is the same as that of the arrangement of Figure 1.' 'In this case, however, the anode circuit of the triode I8 includes the signal operated recording lamp 200 in the recording head of the receiver.

In the operation oi this system, once for each revolution of the transmitter the target 38 is interposed to cause excitation of the photoelectrio device II at a uniform value to provide a reference signal which is amplified, sent over the transmission line, and applied to the compensating detector 23. As before, the output of this detector is applied to the received signal amplifier to bias it to a value which will compensate in this arrangement not only for any drift or variation in the signal output voltage of the photoelectric device I0, but for any variation or change in the ton line characteristics. As illustrated, this reference or compensating signal is preferably applied at the time the scanning head and the transmitter would be scanning the clamping bar l, which is also the time when the light from the recording lamp 200 is impinged upon the clamping bar 4a of the receiver. Thus the visible light variation due to the compensating signal will not aiIect the sensitized negative 2'.

For the purpose oi orienting the reader's viewpoint, it may be noticed that the systems of Figures 2 and 9 are quite similar in the equipment used, and they really only dlifer in two main respects. Firstly, the switch 22 01' the system of Figure 1 which has been designated switch 22a 01 the system of Figure 9, has been moved from the transmitter to the receiver. Secondly, the compensating detector has likewise been shifted irom the transmitting end to the receiving end of the line. The received signal amplifier is equivalent to the amplifier at the transmitting end of the system oi Figure l but in actual use may not really be the same amplifier because it is common to employ a signal amplifier at the receiving station so that in applying the system of Figure 9 the biasing detector 23 and its associated circuits are simply applied to the receiving amplifier.

It will be apparent from the above description that the subject matter of this invention can be widely varied as suggested by the modifications herein disclosed, and I do not, therefore, desire to bestrictly limited to the disclosure as given for purposes 0! illustration. but rather to the scope of the appended claims.

What is claimed is:

1. The combination with a facsimile picture transmitter having a seaming head including 9.

- photoelectric device, and an amplifier fed by said device, of means operated periodically by said transmitter for applying a bias voltage to said amplifier to correct for the signal drift of said photoelectric device.

2. The combination with a facsimile picture transmitter having a scanning head and a transmission circuit connected to said scanning head. oi means operated periodically by said transmitter for applying a compensating voltage to said transmission circuit at the transmitting end to compensate for inherent signal drlft therein.

3. In a system oi the type described the combination including a facsimile picture transmitter composed of a rotatable support for a picture to be transmitted, a scanning head including a light source and a photoelectric device, means for causing timed relative movement between said support and scanning head, a transmission network connected to said photoelectric device, and means operated in timed relation with said support to apply a compensating voltage to said network at its transmitting end once for each rotation of said support.

4. In an apparatus of the type described. the combination comprising a movable support for a picture to be transmitted. a reflecting member moving in timed relation with said support. a scanning head including a light source and a photoelectric cell, means for causing a desired relative movement between said support and scanning head, a transmission circuit connected to said photoelectric cell, and means controlled by said relative movement for applying a biasing voltage to said network at its transmitting and to picture to be transmitted. a reflecting member, a

scanning head including a light source and a photoelectric cell, means for causing a desired relative movement between said suplm t, scanuingheadandreilectingmembenatrammissiorf circuit connected to said photoelectric cell. and means controlled by said relative movement for applying a biasing voltage to said network to compensate ior inherent signal drift in said network and in said photoelectric cell.

8. In a transmitting apparatus or the type described. the combination comprising a movable support for apicture to be transmitted, a reiiecting member driven in timed relation with said a scanning headincluding a light source and a photoelectric cell, means for causing a desired relative movement between said support and scanning head, a transmission circuit connected to said photoelectric cell. and vacuum tube repeating means including a network having a predetermined time constant operated as a result of said relative movement each time said reflecting member is exposed to said light source to apply a compensating voltage to the network at the transmitting end to compensate for inherent signal drift therein.

7. In a transmitting apparatus of the type described, the combination comprising a facsimile picture transmitter having a rotatable support for a picture to be transmitted, a reflective member synchronized with said support, a scanning head having a light source and a photoelectric device, means for causing relative longitudinal movement between said support and scanning head as the support rotates. a transmission network connected to said photoelectric device, and meansconnected to said transmission circuit and operated each time said reflective member is a scanned by said light source to apply a compensating biasing voltage to the network at its transmitting end.

B. In a facsimile picture ton system. the combination including a rotatable support forapicturetobetransmitted.ascanning head including a light source, a photoelectric cell, and a movable reflective target, means for causing relative longitudinal movement between said scanning head and support as the support rotates, and for causing said target to move between said light source and support once for each rotation thereof, a on network connected to said photoelectric device, and means energised each time said target intercepts the lightiromsaidsourceiorap wi acompensating biasing voltage to said network at its transmitting end.

9. In a combination as disclosed, a facsimile Picture transmitter including a support for a scenetobetransmitted.ascanningheadhaving a light source and photoelectric device, means ior causing relative movement between said scanningheadandsupportsoastosuccessivclr scanelementalareagoiasceneonsaidsupport. a transmission network connected to said photoelectric device, and mean connected to said photoelectric device and energised intermittently thereby during'relative movcnent between saidsupportandscanningheadior applyinga compensating voltage to said network at its transmitting end.

10. In a combination as disclosed, a facsimile picture transmitter including a support for a scenetobetransmittemaheadhaw lngalightsourc'eandphotoelactricdevicameans for causing relativemcvement between said scannin'gheadandsupportsoas'tosuccessivem scanelementalareaeciasceneonsaidsupport.

electric device. and means connected to said photoelectric device and energised intermittently thereby during relative movement between said support and scanning head for applying a compensating voltage to said network. said last means including an impedance network having a large time constant,

11. In a combination as disclosed. a iacsimile picture transmitter including a support for a scene to be transmitted, a scanning head having a light source and photoelectric device, means for causing relative movement between said scanning head and support so as to successively scan elemental areas of a scene on said support, a transmission network connected to said photoelectric device, means connected to said photoelectric device and energized intermittently thereby during relative movement between said support and scanning head for applying .a coinpensating voltage to said network, said last means including an impedance network having a large time constant, and means for applying a bucking voltage to said network to increase its seniitivity.

12. In a combination as disclosed. a facsimile picture transmitter including a support for a scene to be transmitted, a scanning head having a light source and photoelectric device, means for causing relative movement between said scanning head and support so as to successively scan elemental areas oi a scene on said support. a transmission network connected to said photoelectric device, means connected to said photoelectric device and energized intermittently thereby during relative movement between said support and scanning head for applying a compensating voltage to said network, said last means including an impedance network having a large time constant. a second impedance network having an equal-or a smaller time constant connected to said first network, and means for applying a bucking voltage to said second network.

13. In a system of the type described, a lacslmile picture transmitter including'a movable support for a scene to be transmitted. a scanning head operating in conjunction therewith to produce picturesignals in accordance with the variations in the tonal value of the scene, a iacsimile picture receiver including a support for a sensitized negative on which the original scene is toberecordemareceiverincludinganamplii'ier l'or converting said signals into light variations and for applying them to the sensitised negative, a signal transmission network interconnecting the transmitter and the receivm means operated by the transmitter for a 8 acompensatingsignaltoaaidnetworkatte transmitting end at regular intervals.

14. In aiacsimilepicturetransmittlngandreceiving system, the combination comprising a facsimile picture transmitter including a scanning head employing a photoelectric device, a

facsimile picturerecorder including arecording lamp, a transmission network interconnecting thetransmitterwiththerecorderandinchrdmg asignalamplifleratthetransmittingenmmeam for periodically eacitingsaidphotoelectrio device to produce a compensating signal, and means for intermittently applying said compensating signaltosaidampliilertobiastheampliflersc astocompensateiorsignalvoltagedrlitoithe photoelectric device.

KORBTANTIR WOIOBCHAK.

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