US1794222A

US1794222A - Photo-electric system

Info

Publication number: US1794222A
Application number: US38377A
Authority: US
Inventors: Willis R Whitney
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1925-06-19
Filing date: 1925-06-19
Publication date: 1931-02-24
Anticipated expiration: 1948-02-24
Also published as: GB253916A

Description

Patented Feb. 24, 1931 UNITED STATES PATENT OFFICE I WILLIS R. WHITNEY, OF NISKAYUNA, NEW YORK, ASSIGNQR TO GENERAL ELECTRIC COMPANY, A CORPORATION F NEW YORK PHOTO-ELECTRIC SYSTEM Application Ied June 19, 1925.

Mypresent invention relates to light sensitive apparatus such as photo-electric cells, and more particularly to the use of such cells as a means for comparing the light conductivity of a fixed or known light filter with a variable light filter, such as paper pulp, or any turbid or colored solution.

In the use of photo-electric cells as a means for comparing light intensities, it has been 3e dit'icult to procure a substantially constant potential for both circuits of the cell, i. e. a steady potential for the source of light employed and a steady potential for the cell it self. As a consequence of my invention, an le easily available electric source, such as a lighting or power circuit, can be used for operating photo-electric apparatus, without introducing errors in the photo-electric currents due to the unavoidable variations in voltage 2o of such a circuit.

ln the present instance, instead ot using a sin gle photo-electric cell I have employed two such cells having a common source of energy to supply the potential across the cells. By using two cells in this manner l employ but one source of light which may or may not be connected in circuit with the common source of supply for the two cells. One cell receives light from the light source after passing through a fixed or known filter, while the other receives light through the filter which is the substance to be measured. The cells are so connected that the'currents produced in them by the action of light, oppose each other, and

any difference in the currents produced by the two cells is indicated on a galvanometer or other suitable device. Since a single lamp is used to illuminate both cells any slight change in voltage across the lamp does not 4@ produce any serious defect as both cells are equally affected by any change in the intensity of the light source. y

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims.`

My invention itself, however, both as to its organization and method of operation will best be understood byy reference to the following description taken in connection with 5 the accompanying drawing in which Fig. 1

Serial No. 38,377.

shows a circuit organization whereby my inventlon may be carried into eect, the invention in the instance shown being applied to means for maintaining paper pulp at a substantially constant density. Fig. 2 shows a modilied motor control system.

Referring to the drawing I have indicated at 1 a pulp tank having a water supply pipe line 2 and a. pulp supply pipe line 3. The pulp from the tank l may be supplied directly to a paper machine through a pipe line 4l or, if desired, the line a may simply constitute means whereby a sample of the pulp may be obtainedV in which latter case pipe linee would be returned to the tank 1.

In the supply pipe l l have inserted a motor driven pump 5 and a transparent window portion 6. ln order to maintain the density of the pulp supply to the paper machine substantially constant, l associate with the window portion 6 of the supply pipe 4.., means to control the action of a valve connected with the water supply line 2. The means employed includes a TWheatstone bridge having variable resistors 8 and 9 respectively in two arms of the bridge, while the other two arms include resistors which in the present instance constitute photoelec tric cells 10 and 11. The bridge is supplied from a source of energy 12, and any variation in current in the arms of the bridge is indicated by the usual galvanometer 13.

A common source of light 14, which may be energized from any suitable source of power 15 cooperates with both photo-electric cells. A known iilter or light controlling means 16, which may be of paper or any suitable material, is placed between the source 14 and cell 10, while the transparent portion 6 of the supply line l is placed between the source 14 and the cell 11. The cells are connected so that the currents produced in them oppose each other. The resistors 8 and 9 are then adjusted so that when the pulp is -of the desired density, no current will flow through galvanometer 13.

In the operation of the device, when there is any variation/ini the physical or optical as color, opacity or pulp density, the curcharacteristicsyof the pulp such for example l rent roduced by cell 11 will vary proportionally to the variations in the physical characteristics of the pulp and the needle of galvanometer 13 will move to the right or left of the zero or normal position and close a circuit from a source of energy 17 through

relay

18 or 19 depending on the nature of the change in the pulp solution.

Relays

18 and 19 control the energization of

coils

20 and 21 which operate

reversing switches

22 and 23 respectively. When one of the reversing switches` 23 for instance, 1s operated, current is supplied from mains 24 to motor 25 to further open valve 7 and increase the supply of: water to the pulp tank 1 to thereby reduce the density of the pulp solution. Operation of switch 22 supplies current in the opposite direction to the armature of motor 25 causing reverse operation of the motor to close the valve 7 and thereby decrease the supply of water to the tank 1. A winding 26 is connected across the armature of motor 25. The Winding controls the operation of a switch 27 which governs a dynamic braking resistor 28. Deenergization of'switches 22 and 23 enables switch 27 Y to close and complete a dynamic braking ciry32 if desired.

cuit for motor 25 through the braking resistor 28 and thereby promptly stop the motor. Pump 5'may be mechanically connected wlth a driving motor 29 in any manner desired. Instead of the direct current motor 29, an'y substantially constant speed driving device may be employed.

In Fig. 2 I have shown a modified form of motor control for the valve motor 25. In this figure galvanometer 11 controls relays r18 and 19 as in Fig. 1. rIhe relays control 'resistors 30 and 31 respectively in the shunt field circuit of motor 25, one of the resistors 30 being normally short circuitcd by relay 18.

In the operation of the device as shown in Fig. 2 when the galvanometer needle moves to the left, relay 18 is energized to insert resistor 30 in the shunt field circuit to thereby increase the speed of motor 25. Likewise, energization of relay 19 short circuits resistor 31 to decrease the speed of motor 25. Each of

switches

18 and 19 may be'maintained in normal position by means of springs Although I'have illustrated myV invention as applied to paper making it is obviously not restricted to use in that art alone. While I have shown the motor 25 controlling the supply of the water to the pulp tank obvi-y ously the water supply might be maintained constant and a valve in the pulp supply line 3 be controlled by motor 24 to vary lthe amount 'of pulp supplied to tank 1. It is alsol obvious that the arrangement shown can be used for reflected, instead of transmitted light, so that opaque surfaces can be quantitatively compared or controlled as to theiry reecting powers or colors. Various modifications of my invention will readily suggest themselves to persons skilled in the art without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. In combination, a plurality of photoelectric cells, said cells being so connected that the currents produced by them are in opposition, a source of energy, connections between said source of energy and said cells, a single source of light cooperating with said cells, independent means interposed between each of said cells and said source of light for controlling the amount of light delivered to the cells, and electro-responsive means operated by the difference in current in said cells.

2. Means for determining the light reflected from or transmitted by a` given medium, said means comprising a circuit including a plurality of photo-electric cells, said cells being so connected that the currents produced by them are in opposition, a single source of light adapted to control the operation of said cells, independent light controlling mediums interposed between said source of light and each of said cells, and electroresponsive means operated by the difference in current in said two cells.

3. In a device of the class described, a Wheatstone bridge, a source of energy eonnected to said bridge, a light sensitive cell in each of two arms of the bridge, a source of light adapted to control the operation of said cells, a fixed or known light filter interposed between said source and one of said cells, a variable light ilter interposed between the source and said other photo-electric cell, and

electro-responsive means operated by the difference in current in said two cells.

4. In a device of the class described, a Wheatstone bridge, a source of energy connected to the bridge, a light sensitive cell in each of two arms of said bridge, said cells being connected so that the currents produced by them are in opposition, a source of light cooperating with each of said cells, the light directed onto one cell being substantially constant, a light controlling means .interposed between the other of said cells and said source `of light, and an electro-responsive means associated with said bridge and operated by v variations in the physical characteristics of tween its associated cell and said source of light, and electromagnetic means associated .with said bridge and responsive to variations in the currents in said cells.

i 6. Means for indicating variations in the density of paper pulp supplied to a paper making machine, said means comprising a Wheatstone bridge, a source of ener `con- A nected to said bridge, a light sensitlve cell connected in each of two arms of said bridge, a source of li ht cooperating with each of said cells, the 'ght directed onto one cell being substantially constant, means for passin light from said source to the other of sai 1; cells through'a portion of the pulp supplied to said machine, whereby changes in pulp density produce proportional changes in the current produced by the latter cell, and vmeans for indicating variations in the current produced in said latter ce 7. In combination, a Wheatstone bridge, a.

, source of energy connected to the bridge, a light-sensitive cell in one of the arms of said bridge, a source of light cooperating'l withl said cell, a light'controlling means inter osed between said source of light and said ce and means comprising an electro-responsive device for indicating variations in the physical characteristics 'of said li ht `controlling ao means and for controlling sai light controlling means. v

8. Apparatus responsive to an 4optical characteristic of a medium, said apparatus Ycomprising a Wheatstone bridge, a lightsensitive cell electrically connected in one of the arms of said bridge, a light-sensitivelcell electrically connected in another arm of said bridge, and means for va g the resistance of one of said cells in accorldilce with changes 40 in the optical characteristics of said medium while maintaining the resistance of the other cell substantially constant.

In witness whereof, I have hereunto set my hand this 17th day of June, 1925. WILLIS R. WHITNEY.