US3262356A - Line voltage compensating timer - Google Patents

Description

July 26, 1966 I F. F. FORBES Q LINE VOLTAGE COMPENSATING TIMER Filed April 10, 1963 5 Sheets$heet l INVENTOR FRED EFoRBEs W WM ATraRwEYs' July 26, 1966 F. F. FORBES LINE VOLTAGE COMPENSATING TIMER Filed April 10, 1963 5 Sheets-Sheet 2 INVENTOR. FRED F. F'0RBE6 WIM Arron/vs? United States Patent 3,262,356 LINE VOLTAGE COMPENSATING TIMER Fred F. Forbes, Moundsview, Minn., assignor to The Regents of the University of Minnesota, Minneapolis,

Minn., a corporation of Minnesota Filed Apr. 10, 1963, Ser. No. 272,143 Claims. (CI. 8824) The present invention relates to timing devices and more particularly to an electronic timing apparatus for controlling the operation of an appliance such as a photographic enlarger by regulating the period of time that the appliance operates as a function of the integral of the line voltage.

It is common practice in most photographic printing and enlarging procedures to utilize a light source which is operated from a commercial power line. For a given exposure time, small fluctuations in line voltage are found to produce relatively large fluctuations in the light source intensity which causes the resulting prints to be nonuniform. It is therefore one objective of the present invention to provide a timer for photographic use which will compensate for line voltage fluctuations by integrating the fluctuating light intensity and will turn ofi a photographic enlarger after a preset amount of light has been collected.

Numerous automatic timing devices of the type described have been previously proposed for photographic enlarging. These prior timing devices have not however been entirely satisfactory. One prior device of the type described includes a photoelectric cell or other light sensitive unit for receiving light transmitted through the printing paper. The cell functions to control the duration of exposure as a function of the light thus collected. The prior devices of this type have, however, been found susceptible to error due to a variation in light-transmitting qualities of localized areas from sample to sample.

Another previously proposed device of the type described employs a photoelectric cell or the like positioned above the printing paper and including a lens system for focusing the light reflected by the printing paper onto the cathode of a photocell. The system has a relatively high cost due to the fact that an optical system, casing and supporting stand is required in addition to the stand supporting the illuminating lamp. A further disadvantage of many of the previously proposed devices is that the electric circuitry required is relatively complicated in construction. It is therefore expensive to manufacture and is more frequently subject-to malfunction.

-In still other prior devices of the type described, a fnaction of the light produced by the enlarging lamp must be deflected to the light sensing means.

In view of these and other defects in the prior art, it is thus one object of the present invention to provide an improved line voltage compensating timer of the class described which is relatively simple in construction, reliable in operation and can be manufactured at a relatively low cost.

It is yet another object of the present invention to provide an improved line voltage compensating timer of the class described which does not require the use of a light emitting load to illuminate the light sensing means.

Still another object of the present invention is the provision of an improved line voltage compensating timer which requires no incandescent lamp as an integral part thereof and can be used for timing the operation of various devices whether or not they include illuminating lamps.

A still further object of the present invention is the provision of an improved line voltage compensating timer which is light in weight, compact in construction and can "ice be used for timing the operation of an appliance simply by making a single electrical connection between the timer and the appliance.

Other objects of the invention will become apparent as the description proceeds.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Y

The invention is illustrated by the accompanying drawings in which the same numerals refer to corresponding parts and in which:

FIGURE 1 is a side elevational view partly broken away of one form of apparatus embodying the present invention;

FIGURE 2 is a schematic wiring diagram of an apparatus embodying the present invention;

FIGURE 3 is a diagrammatic side elevational view a modified form of my invention;

FIGURE 4 is a diagrammatic side elevational view of another modification of my invention;

FIGURE 5 is a chart illustrating uncompensated changes in light intensity as a function of changes in the line voltage;

FIGURE 6 is a chart illustrating a current characteristic of the light sensing means employed in the present invention as a function of the voltage at three different light intensities;

FIGURE 7 is a chart illustrating the exposure time established by the present invention as a function of the line voltage when connectedv to a photographic enlarger; and

(FIGURE 8 is a chart illustrating compensated and uncompensated exposure values plotted against line voltage.

The present invention will be best understood by reference to the following detailed description and to the accompanying figures wherein the same numerals refer to corresponding parts of the several views.

Referring now particularly to FIGURES l and 2 there is shown a line voltage compensating timer according to the present invention. The apparatus includes a chassis 10 of any conventional and well known type on which is mounted a light-tight enclosure 12. Current is supplied to the apparatus through conductors 14 and 16, which are connected to a suitable wall plug 18. Connected across the conductors 14 and 16 is the primary winding 19 of a transformer 20.

In line 14 is provided a switch 24 which can be used for turning the apparatus on and off. Connected across the conductors 14 and 16 is a current controlling device such as a thyratro'n 26. The thyratron 26 includes an anode 28, a cathode 30, a control element or grid '32 and a filament 34 which receives current through conductors 36 and 38, the latter being connected to the secondary winding 22 of the transformer 20. The cathode 30 is connected by means of a conductor 40 through a selector switch 42 to the conductor 16. The holding coil 44 of a relay 46 is connected in the line 14 between the plug 18 and the anode 28 by means of lines 47 and 48. A condenser 50 is connected between the lines 47 and 48 and across the coil 44. A condenser 52 is connected between the anode 28 and the cathode 30 A resistor 54 is connected in line 14 between the coil 44 and the plug 18.

The relay 46 includes an armature 60 which is yieldably biased toward the right in FIGURE 2 by a spring 62 and is held thereby in contact with a terminal 64, the latter being connected to a conductor 66. When the holding coil 44 of the relay 46 is energized the armature 60 will move to a second position shown by the dotted lines in FIG- URE 2, in contact with a terminal 68 which is connected to a line 70. A safe light or load off indicator 72 of any suitable known construction is connected between line 70 and the conductor 16. The load off indicator 72 will only be energized when the current is supplied to the holding coil 44. Connected to the line 66 is a terminal 74. Another terminal 76 is connected to line 16. Between the terminals 74 and 76 is connected the load or appliance which is, to be operated such as an enlarger lamp 78.

Connected between the conductor 66 and line 16 is the coil of a potentiometer 80. The potentiometer 80 includes a contact arm 82 which is wired to a condenser charging circuit 84. The condenser charging circuit 84 includes a selector switch 86 wired to connect one of a pair of condensers 88 and 90 across a light responsive means such as a photocell 92 or other light sensitive device. A conductor 94 is connected to the plates of the capacitors 88 and 90 opposite from those connected to the potentiometer 80. The conductor 94.is connected to a terminal 96 of the selector switch 42 for purposes hereinafter explained. A conductor 98 is connected between the condenser charging circuit 94 and the grid 32.

A resistor 100 is provided in the conductor 98.

The switch 42 includes a first terminal 96 connected to line 94 as described hereinabove. A second terminal 102 connected to line 16 and a third terminal 104 connected to line 40. A contact element 106 is secured to an arm 107 which is mounted on a pivot pin 108. The contact element 106 will normally be retained in the solid line position of FIGURE 2 and in this position will contact both of the terminals 102 and 104 so as to complete a circuit between conductors 16 and 40. When it is desired to begin a cycle of operation, the switch contact element 106 is moved to the dotted line position 110 thereby disconnecting terminal 104 from the terminal 102. A spring 112 is connected between the arm 107 for yieldably hiasing the element 106 toward the solid line position of FIG- URE 2. The arm 107 includes a lobe 114 at its lower end which is adapted to engage -a resilient member such as a leaf spring 116 for normally preventing a counterclockwise movement of the contact element 106 beyond the solid line position of FIGURE 2. When it is desired to connect terminals 96 and 102, contact element 106 is moved against the tension of the spring 116 to the dotted line position 118 of FIGURE 2. The contact element 106 will remain in the dotted line position 118 until it is returned manually to the solid line position of FIGURE 2.

As can be seen by reference to FIGURE 1, I position the photoelectric cell 92 a short distance from the thyratron '26 so that it will receive light radiation emitted from the filament 34. Thus, during operation, the impedance of the cell 92 will vary as a function of the intensity of the light incident thereon from the tube 26. I have found that the cell 92 need not he placed immediately adjacent to the tube 26 in order to operate satisfactorily. The cell 92 can, in fact, be placed on the opposite side of the enclosure 12 from the tube 26 so long as it will receive light directly or indirectly from the tube 26. I have also found that the light sensitive surface of cell 92 can be facing in the opposite direction from the tube 26 under some conditions as, for example, when the enclosure 12 is coated on the inside with a light reflective material such as White paint.

There are many advantages of employing the tube 26 as the light source for the cell 92. One advantage is that a separate light source such as an incandescent lamp need not be provided, thereby reducing the cost of the apparatus. Another advantage of the system described is that an electronic vacuum tube such as the tube 26 will considerably outlast an incandescent lamp as the light source. In this way I achieve a substantial increase in the reliability of the system.

Another advantage of the apparatus of FIGURES 1 and 2 is that it can beused for regulating operation of any appliance whether or not the appliance includes an incandescent light. The apparatus of FIGURES 1 and 2 can be, for example, used for timing the operation of an electric 'bread toaster.

Refer now to FIGURES 3 and 4 which illustrate a modified form of my invention. In FIGURE 3, the lamp 78 is positioned above a photographic transparency such as a negative 130. The light passing through the negative is focused by means of a vertically adjustable lens 132 onto the upper surface of a sheet of commercially available photographic paper 134, resting on a sheet of glass 136 afiixed to the top 'of a box 138. The box 138 is provided with a highly reflective inside surface and to this end can be formed from highly polished metal or the like. In the alternative, the box 138 can be formed from wood or plastic and lined with a reflective material such as a metal foil. On one side of the upper surface of the box is a light shield 140. Mounted beneath the light shield 140 is a photoelectric cell 142, in all respects similar to the cell 92. The cell 142 is wired in the circuit of FIGURE 2 in the place of the cell 92. The impedance of the cell 142 will change responsive to the light passing from the enlarger lamp 78 through the photographic paper 134 rather than in response to the light emitted from the tube 26 as in the case of cell 92. The reflection of light onto cell 142 from the entire inside surface of box 138 has the advantage of reducing light variations at cell 142 due to localized differences in thickness of the paper 134.

A generally similar arrangement to that illustrated in FIGURE 3 is shown in FIGURE 4 to demonstrate the manner in which a modified form of the present invention can be employed for producing contact prints. Thus, in FIGURE 4, the lamp 78 is mounted above a sheet of opal glass 146 which is placed over a negative 148. Beneath the negative 148 is a sheet of photographic paper 150 which itself rests upon a sheet of glass 152 affixed to the open end of a box 154. A photoelectric cell 156 is mounted at one end of the box 154. The box 154 and the cell 156 are in all respects similar to those of FIG- URE 3. A light shield 158 is mounted above the cell 156. Again, as in FIGURE 3, the duration of exposure of the paper 150 when employed as shown in FIGURE 4, will depend upon the intensity of the light emitting from the lamp 78 and passing into the enclosure 154. v

As mentioned hereinabove, for a given exposure time, small fluctuations in line voltage produce relatively large fluctuations in the intensity of light emitted from the illuminating lamp which in turn causes a non-uniformity in the density of the emulsion of onepicture to another. The effect of line voltage changes is graphically presented in FIGURE 5, which illustrates the uncompensated variation in light intensity as a function of the line voltage in the case of two enlarger lamps as, for example, a 60 watt lamp at the left and a 150 watt lamp at the right.

FIGURE 6 illustrates the current characteristics of any of the photoelectric cells 92, 142 or 156 at three light intensities of 1/2L L and 3/ 2L To explain the operation of the cell, it will be assumed that the cell is operating at point A where 1:1 E=E and L=L The resistance, R of the cell will then be given by the equation R =E /I. Therefore, for a given voltage E, the resistance of the cell will provide a resistance R in the capacitor charging circuit 84. Therefore, during operation, the voltage or potential across one of capacitors 88 or 90 will decrease as the function of the time capacitor C discharges through cell 92, 142 or 156 depending upon which cell is used. If the voltage on the capacitor 88 at the time of the starting cycle is E Max (point B of FIGURE 6), and at the end of the cycle when the thyratron Voltage has reached E the voltage is at point C, the resistance of the cell 92 will have decreased exponentially from a first resistance value to a second value.

- ergizing the safe light 72.

Before a cycle of operation is initiated, the selector switch 86 is adjusted so as to choose whichever of capacitors 88 or 90 will provide the appropriate time range for which operation is desired. The potentiometer 80 is then adjusted to select the exact duration of exposure. Since the grid voltage is increased by elevating the contact 82 of the potentiometer 80 in FIGURE 2, the time required to charge the condenser 88 will be increased and the cycle time will accordinglyincrease. If the grid voltage is lowered, on the other hand, the time required to charge the condenser 88 will be reduced.

To start one cycle of operation, the lever 107 is pivoted in a clockwise direction as seen in FIGURE 2 about the pin 108 so that the contact element 106 moves to the dotted line position 110. The circuit through coil 44 is thus temporarily interrupted causing the element 60 to engage contact 64. It should be understood that the spring 112 will return the contact element 106 to the solid line position of FIGURE 2 as soon as manual pressure thereon is released. When the element 60 of the relay 46 has contacted terminal64, current will flow through the terminals 74 and 76, through the enlarger lamp 78 and also through the potentiometer 80 to line 16. Only a very low current will flow through the coil 44 and this will be insuflicient to withdraw the contact 60 from terminal 64. In the tube 26, a relatively small intermittent direct current will flow between the cathode 30 and grid 32 thereby charging whicheverof capacitors 88 or 90 is connected across the cell 92. The condenser 88, for example, will of the light collected in the cell 92 until the charge on the grid 32 has reached a value sufficient to trigger tube 26 at which time the impedance of tube 26 will drop to a very low value and in turn cause a surge of current between the cathode 30 and the plate 28 and through the coil 44. Current in coil 44 will in turn disconnect the condenser charging circuit 84 and enlarger lamp 78'from the circuit and again establish a circuit through the safe light 72.

When it is desired-to focus the enlarger lens 132, the element 106 of switch 42 is moved to the dotted line position 118, thereby providing a sufiicient potential at the grid 32 to reliably maintain tube 26 in the conductive condition. The tube 26 will remain conducting until element 106 of switch 42 is again moved to the dotted line position 110, at which time a second cycle of operation can be initiated in the same manner as described above. While various circuit components can be employed in the present invention, by way of Example I set forth below several of the most important components of the circuit shown in FIGURE 2. It is assumed that a 60 cycle 110 volt alternating current supply is employed:

Resistor 54 3.3K ohms, 1 watt.

Condenser 50 16 ,ufd. 150 volts.

Condenser 52 .01 afd.

Resistor 100 10K ohms.

Condenser 88 4 ,ufd.

Capacitor 90 20 ,ufd.

Photocell 92 La Fayette MS 895, cadmium sulfide photocell.

Potentiometer 80 100K ohms.

Tube 26 6D4 thyratron tube.

' then become charged at a rate which varies as a function With the apparatus according. to the present invention connected to the enlarger lamp 78, changes in the line voltage will be compensated as best shown in curve E of FIGURE 7. Uncompensated changes in light intensity is a function of line voltage are shown by way of contrast in curve F in :order to emphasize the results achieved.

It is apparent that many modifications and variations of this invention as hereinbefore set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only and the invention is limited only by the terms of the appended claims.

What is claimed is:

1. An apparatus for controlling the time interval that electrical power is available to a load by monitoring the line voltage by means of generating light directly from the line voltage source and coupling that light to a light responsive means whose impedance is a-function of the variation in line voltage, said apparatus comprising in combination; a current controlling device having a control element therein, a voltage impressed upon said control element being adapted to vary the impedance of said current controlling device; a light source operatively connected to said current controlling device; a source of electric current connected to said current controlling device; said light source generating light directly from the line voltage source; a condenser charging circuit including a timing condenser and a light responsive means conductively connected to said timing condenser, conductor means between said condenser charging circuit and said control element, said light responsive means being positionedto receive light from said light source, the impedance of said light responsive means being dependent upon the intensity of the light incident thereto from said light source and a function of variation in line voltage, a source of electrical current connected to said condenser charging circuit to facilitate the charging of said timing condenser, whereby the time of charging said condenser varies with the change of impedance of said light responsive means as a function of the amount of light received thereby from said light source.

2. A line voltage compensating timer comprising in combination, a current controlling device including a control element adapted to regulate the impedance of said current controlling device, said current controlling device including an incandescent element therein, a source of electric current connected to said current controlling de vice, a condenser charging circuit operatively connected to said control element, said charging circuit including a timing condenser and a light sensitive means positioned in light receiving relationship with said incandescent element, the impedance of said light sensitive means being dependent upon the intensity of light impinging thereon from said incandescent element.

3. A line voltage compensating timer comprising in combination, a current controlling device having a light value being thereby regulated by the light emitted from said filament.

4. A line voltage compensating timer for supplying current to a load.by monitoring the line voltage by means of generating light directly from the line voltage source and coupling that light to a photoelectric cell whose impedance is a function of the variation in line voltage, said apparatus comprising in combination, a condenser charging circuit including a timing condenser and a photo- 7 electric cell connected in parallel therewith, a current controlling electronic tube having a grid conductively connected to one side of said condenser, said electron tube also having a cathode, means for connecting a source of current across the cathode and the condenser charging circuit whereby said condenser will become charged responsive to the current between said cathode -and said grid, a light source operatively connected to said current controlling tube and connected to said current source to generate light directly from the line voltage source, said light source being positioned to direct light on said cell, switch means for interrupting the current between the cathode andthe grid so that the tube becomes nonconducting, means wired to said tube for energizing said load when the current through said tube is interrupted, the impedance of said cell being a function of variation in line voltage and controlled by means of the intensity of illumination of said cell by said light source, the charging of said condenser being controlled responsive to the change in impedance of said cell and the increase of potential on the grid being adapted to initiate a current through said tube to said means for energizing said load.

5. The apparatus according to claim 4 wherein said means for engaging. said load comprises a relay having a holding coil connected in series with said tube and said source of current.

6. The apparatus according to claim 4 wherein said electronic tube comprises a thyrat-ron.

7. The apparatus according to claim 5 wherein a potentiometer is connected between said condenser char ing circuit in said source of current for regulating the current between said cathode and said grid.

8. The apparatus according to claim 7 wherein said condenser charging circuit includes a first and second condenser and a selector switch means for selectively connecting said first and second condensers across said cell.

9. A timing apparatus for a photographic enlarger lamp comprising in combination, a source of current, a thyratron including a grid and an incandescent element therein, a condenser charging circuit including a timing condenser and a photoelectric cell, said cell being posisaid apparatus comprising in combination, a source of current, a current controlling vacuum discharge device including a grid, said enlarger lamp :being operatively connected to said current controlling device and generating light directly from the line voltage source, a condenser charging circuit including a timing condenser and a photoelectric cell, saidcell being positioned to receive light from said enlarger lamp and operatively connected to said grid for controlling the impedance of said device and relay means conductively connected with said device for turning off said enlarger lamp when said device is conductive, the impedance of said cell being function of variation in line voltage and controlled by means of the intensity of illumination of said cell by said enlarger lamp, a photograph supporting box positioned in spaced relationship from said enlarger lamp, said box having a reflective interior and said cell being mounted within said box.

References Cited by the Examiner UNITED STATES PATENTS 2,293,425 8/ 1942 Dam-mond 8824 2,481,667 9/ 1949 Holden.

2,749,799 6/1956 Strem 88'24 2,965,814 IQ/r1960 Gartner 8824 X 3,165,988 1/1965 Wick et al. 8824 X 3,178,999 4/ 1965 Clapp 8824 NORTON ANSHER, Primary Examiner.

RICHARD A. WINTERCORN, Assistant Examiner.

Claims (1)

1. AN APPARATUS FOR CONTROLLING THE TIME INTERVAL THAT ELECTRICAL POWER IS AVAILABLE TO A LOAD BY MONITORING THE LINE VOLTAGE BY MEANS OF GENERATING LIGHT DIRECTLY FROM THE LINE VOLTAGE SOURCE AND COUPLING THAT LIGHT TO A LIGHT RESPONSIVE MEANS WHOSE IMPEDANCE IS A FUNCTION OF THE VARIATION IN LINE VOLTAGE, SAID APPARATUS COMPRISING IN COMBINATION; A CURRENT CONTROLLING DEVICE HAVING A CONTROL ELEMENT THEREIN, A VOLTAGE IMPRESSED UPON SAID CONTROL ELEMENT BEING ADAPTED TO VARY THE IMPEDANCE OF SAID CURRENT CONTROLLING DEVICE; A LIGHT SOURCE OPERATIVELY CONNECTED TO SAID CURRENT CONTROLLING DEVICE; A SOURCE OF ELECTRIC CURRENT CONNECTED TO SAID CURRENT CONTROLLING DEVICE; SAID LIGHT SOURCE GENERATING LIGHT DIRECTLY FROM THE LINE VOLTAGE SOURCE; A CONDENSER CHARGING CIRCUIT INCLUDING A TIMING CONDENSER AND A LIGHT RESPONSIVE MEANS CONDUCTIVELY CONNECTED TO SAID TIMING CONDENSER, CONDUCTOR MEANS BETWEEN SAID CONDENSER CHARGING CIRCUIT AND SAID CONTROL ELEMENT, SAID LIGHT RESPONSIVE MEANS BEING POSITIONED TO RECEIVE LIGHT FROM SAID LIGHT SOURCE, THE IMPEDANCE OF SAID LIGHT RESPONSIVE MEANS BEING DEPENDENT UPON THE ITENSITY OF THE LIGHT INCIDENT THERETO FROM SAID LIGHT SOURCE AND A FUNCTION OF VARIATION IN LINE VOLTAGE, A SOURCE OF ELECTRICAL CURRENT CONNECTED TO SAID CONDENSER CHANGING CIRCUIT TO FACILITATE THE CHARGING OF SAID TIMING CONDENSER, WHEREBY THE TIME OF CHARGING SAID CONDENSER VARIES WITH THE CHANGE OF IMPEDANCE OF SAID LIGHT RESPONSIVE MEANS AS A FUNCTION OF THE AMOUNT OF LIGHT RECEIVED THEREBY FROM SAID LIGHT SOURCE.

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