US2274992A - Electrical timing circuit - Google Patents

Description

March 3, 1942. M. G. NELSEN I 2,214,992

ELECTRICAL TIMING v CIRCUIT Filed Feb. 26, 1940 2 Sheets-Sheet 2 56 90 Z--d|- A I! 2 1 3 5P g 56 W; 48 5O 5 6O Patented Mar. 3, 1942 ELECTRICAL TIMING CIRCUIT Marvin G. Nelsen, Chicago, Ill., assignm- Guardlan Electric Manufacturing Company, Chicago, 11]., a corporation of Illinois Application February 20; 1940, Serial No. 320,982

10 Claims.

The present invention relates to an electrical control circuit of the class commonly referred to as "timer circuits. The function of such circuits is to cause current flow, or cessation of current flow, in some part of the circuit for a definite and predetermined length of time. Any current or voltage actuated device, as, for example, an electromagnetic relay, may be inserted in the con trolled part of the circuit, to perform switching or other mechanical or electrical operations, responsive to current flow or cessation .of current flow in that part of the circuit.

Some of the previous devices employed to give timed control of electrical circuits have used clockwork or similar mechanisms. Such mechanisms require winding or require an electric motor, and are subject, as is well known, to wide variations in accuracy due to temperature, dirt, faulty workmanship, improper maintenance, etc.

Timer circuits employing electron tubes have also been devised, but have required auxiliary apparatus for supplying direct current. Such auxiliary apparatus obviously entails greater expense in first cost and upkeep, as well as adding to the space and weight requirements.

An object of my invention is to provide a circuit of this character which shall'be operable from an alternating current source and which does not require any auxiliary apparatus to provide a direct current supply.

Another object is to provide a timing circuit whereby the time interval can be conveniently selected or varied by a simple control means.

Still another object is to provide a control circuit which shall have a high degree of consistency in operation, that is, a circuit in which the timed period shall have substantially the same duration in consecutive operationsof the'device, for the same setting of the control means.

A further object is to provide a circuit which is readily adaptable to being made up in commercial form, and having adjustment means whereby the commercial variations in the elements of the circuit can be conveniently com pensated for.

Another object is to provide a circuit whereby a wide range of selection in the duration of the timed interval may be had.-

With these and other objects in view, my invention with respect to its features which I believe to be novel and patentable will be pointed out in the claims appended'hereto. For a better detailed understanding of the invention, and further objects and advantages thereof, reference is made to the following description and to 55 the accompanying drawings, wherein such further objects will definitely appear, and in which- Figure l is a symbolic representation of an electrical circuit embodying my invention.

Figure 2 shows a modified and somewhat simplified form.

Figure 3 is a graphical representation of the time variation of potential diiference between certain points in the circuit.

In the accompanying drawings, I have used the reference numeral ID to illustrate an electron tube having a cathode, a grid l4 and an anode or plate IS. The cathode I2 may be of the filament type or may be of the indirectly heated type. In the drawings, I have shown a cathode of the filament type which is heated by being connected in circuit with the secondary winding I8 of a step-down transformer. The primary 20 of the step-down transformer is connected to the supply wires 22 and 24. When a transformer is used in this manner for heating the cathode, it

will be understood that the supply must be alternating current. The circuit is operable from a direct current supply, but in that case the stepdown transformer cannot be used, and suitable resistance means must be interposed between the supply wires and the filament to limit the filament current, as is well known in the art.

My circuit is adapted for use with electron tubes of several types. The common high vacuum or hard" tube may be employed, but I have found that more consistent and satisfactory results are obtained with the gaseous tubes of the general class represented by the so-called Thyratron and grid-glow tubes. Of the common tubes of this class, either the triode or three element type, or the four element or shield-grid type can be employed in my circuit.

In the form of my circuit shown in Figure 1, the cathode I2 is connected by a wire 25 to the resistor 21, the condenser 29, the condenser 52, and the resistor 42. The other terminal of the condenser 52 leads to the common terminal 3| of a single pole, double throw switch. A wire 40 connects the grid I4 and the resistor 42 to one terminal of the switch.

The resistor 21 is preferably of the potentiometer type, having a tap or slider which is adjustable along the resistance. This tap is connected by a wire 35 tothe condenser 29 and to a terminal 31 of the switch. The switch may conveniently be of the push button or spring biased type, in which the common terminal 3| normally engages the terminal 33, but. disengages terminal 33 and moves into contact with terminal 31 when the button is pressed.

The resistor 21 is connected to supply line 22, and supply line 24 is connected by a wire 23 to the coil of a relay 30. A wire 35 leads from the coil of the relay to the plate I oLthe tube Ill. It will usually be found desirable to provide a condenser 32 in shunt across the relay coil.

Practical operation In explaining the operation of the form of my circuit shown in Figure 1, it may be well to start with the condition of operation in which the switch terminals 3| and 33 are in contact. Assuming this to have been the case for some appreciable time, it may then be further assumed that the grid [4 is at substantially the same potential as the cathode l2. In this situation, electron current will flow from the cathode l2 to the plate 16 during the portions of the voltage cycle in the supply lines 22 and 24 during which the line 22 is sufiiciently negative with respect to the line 24 to cause conduction through the tube. During the parts of the cycle when an opposite potential exists, the rectifier action of the tube will prevent any flow of current. Consequently there will pass through the wires 23 and 35 a pulstating, unidirectional current. This current will pass through the relay coil 30 and will cause attraction of the armature 54. The condenser 32 is shunted across the relay coil 30 in order to smooth out the pulsations, and thus to reduce chattering and heating of the relay. This condenser may be of the electrolytic type.

The pulsating unidirectional current which flows through the wires 28 and 35 flows also through the wire and the resistor 21, the latter elements being a part of the same series circuit. The current flowing through the resistor 21 will result in a potential difierence or 9. voltage drop between the terminals 01' the resistor which are connected to the wires 25 and 22, respectively. The value of the voltage appearing between the wire 25 and wire 35 will depend upon the location of the tap or slider on the resistor 21. Between the two latter points, the condenser 23 is provided. It may be an electrolytic condenser, and is preferably of large capacity, its function being to maintain a relatively uniform voltage across its terminals throughout the supply voltage cycle.

To actuate my timer circuit, the element 3| of the switch is thrown to contact the switch terminal 31. This places the condenser 52 in shunt with the condenser 29 and a portion of the resistor 21. The condenser 52 will then be charged to the potential existing across the terminals of the condenser 29, and the terminal of the condenser 52 which is connected to the switch element 3i will be at a negative potential with respect to the terminal that is connected to the wire 25.

The switch is then released, to bring the moving element 31 into contact with the terminal 33, thus placing the charged condenser 52 in shunt with the resistor 42.

The potential diiierence between the terminals of the charged condenser will result in a flow of current from the condenser through the resistor 42. Because of the voltage drop across the resistance while this current flows, the grid [4 will no longer be at the same potential as the cathode l2, as initially assumed, but will be negative with respect thereto.

, would give a timed interval of ten seconds.

The negative bias on the grid at the instant the 7 switch is thrown to place condenser 52 in shunt with resistance 42 will be the same as the voltage to which the condenser 52 was charged. This grid bias must be suiiicient to reduce the plate current in the wire 36 to a' value at which the relay 30 will drop out, i. e., will release the armature 54. In the case of gaseous tubes, this means a bias voltage at which the tube will be non-conducting.

Throwing the charged condenser 52 in shunt with the resistance 42 thus causes release of the armature 54 and initiates the timed interval. Any suitable contact-making means may be operated by the armature, for controlling an electrical circuit or other apparatus as desired. In Figure l, for example, a single pole, double throw arrangement is shown. The circuit including terminals and 53 will be closed when the rea lay is energized, open when it is de-energized. The circuit including terminals and 50 will be open when the relay is energized, closed when the relay is de-energized.

As current flows from the condenser 52 through the resistor 42, the charge of the condenser will gradually be dissipated, and the terminal voltage of the condenser will decrease. Since the grid I4 is at the same potential as one terminal of the condenser, and the cathode I2 is at the same potential as the other terminal of the condenser, the diil'erence of potential between the grid and cathode, i. e., the grid bias, will similarly decrease.

The nature of the decrease in voltage is shown in Figure 3, where the curve R indicates the time variation in grid bias for a given value R of the resistance. The value of voltage to which condenser 52 is charged may be indicated as E, and the initial bias applied to the grid at the beginning 01' the interval will therefore be E.

As the grid bias decreases, it will fall ultimately below some value A at which the electron tube Ill will pass suflicient plate current to actuate the relay 30. Actuation oi the relay consists of attraction of the armature 54 and operation of the associated contact means. This action terminates the timed interval. Where a Thyratron type tube is used, the value A represents the grid bias at which the tube would become conductive.

The value of grid bias A at which actuation of the relay will occur is represented in Figure 3 by the dotted horizontal line. When the resistance 42 has the value R, for example, the timed interval will be 2 seconds-the time elapsing between the instant of application of the negative grid bias E, and the instant when the grid bias has decreased to the value A.

If the value of the resistance 42 be increased, the charge of condenser 52 will be dissipated less rapidly, and the duration of the timed interval will be increased. If the value of the resistance be doubled, for example, then the time variation of grid potential will be as represented by the curve 2R, from which it may be seen that the timed interval will be four seconds. As indicated by the curve 5R, a resistance of five times R If the resistor 42 be variable and suitably calibrated, therefore, the user can quickly and conveniently make the adjustment necessary for any desired time interval.

The duration of the timed interval can also be varied by changing the voltage to which the condenser 52 is charged. This voltage must always be greater than the value A, but with that limitation it may be varied throughout the range available bychanging the location oi the tap on the resistor 21. If the tap is moved toward the end of resistor-21 which is connected to the wire 25, the voltage will be reduced. 1 For this new voltage, which may be designated as E, the variation of grid-cathode potentials when the charged condenser 32 is shunted across the resistor 42 will have new values. 1 I

For example, it was indicated above that when the charging value isE; with the resistance-52 having a value-of R, the grid-cathode potential would fall below A in about ten seconds, as represented in Figure 3. With a charging voltage of E, and a resistance value oi'iR, the grid-cathode potential would vary as indicated by the curve bolic manner. In actual practice, it is preferably a spring actuated switch in which the moving elements 48 and 50 normally engage the terminals 44 and 28, respectively, but can be momentarily moved to a position engaging the terminals 33 and 34, respectively. When released, the moving elements will .then return immediately to the 'normalposition in contact with the terminals and 23. The particular type of switch, however,does not constitute a partof my invention, as any suitable type may/be used, and I v have merely described .a form which is most convenient in operation.

- plained for Figure 1 above.

'in the wires 23 andii, a diflerence of potential IR-E', resulting in a timed interval of approximately eight seconds.-

If the resistor 42 is variable, its control and that of the slider on the resistor 2'! can be madeavailable to the operator, making possible a very wide range in the durationof the timed intervals. On the other hand, it may be desirable to make only one of the controls accessible to the ordinary user of the device. A knob for the var iable resistor .42 may be brought out on a control panel, whereas the tap adjustment on the resistor 21 is only made at the factory. The tap adi'ustment in such a case-would constitute convenient means for adjusting the operation of the circuit to specified standard conditions, thus compensating for commercial variations in the elements employed'in the circuit, as for example, in the resistors used as element 42, or in the condensers used as element 52.

The condenser 52 is preferably one having mica or paper dielectric, because a very low leakage characteristic is desirable, and it is important that the amount of charge absorbed by the condenserv for a given applied voltage shall be consistent to a high degree. The relay can be of any type which will actuate the armature 54 when the normal plate current of the electron tube III flows in the wires 28 and 36. By normal plate current is meant the current which flows when the grid is at cathode potential.

The winding of the relay 3!! necessarily has some resistance, and, hence when current flows through it there will be 'apotential difference between the terminals. This fact constitutesthe basis for the form of my circuit shown in Figure 2. Where the resistance of the relay is such that the voltage drop across it is greater than the value A, it is possible to eliminate the resistor 21 and the condenser 28 shown in Figure 1.

As will be seen in Figure 2, the cathode I2 is connected to the supply wire 22, to one terminal of the variable resistor 42, and to one terminal 26 of a double pole, double 'throw switch. The supply wire 24 is connected by a wire 28 to the relay coil 30, the condenser 32 and to a terminal 34 of the double pole double throw switch.

The plate l6 of the electron tube is connected by a wire 36 to the other terminal of the relay coil 30 and the condenser 32, and also to a terminal 33 of the double pole double throw switch.

The grid l4 of the electron tube I0 is con- The principle of operation of the circuit in Figure 2 is substantially the same as that ex- When current flows exists across the terminals-of the relay 30, and hence across terminals 34 and "of the switch. The condenser 32 maintains this potential substantially uniform during the supply voltage cycle. Operating the double throw switch shunts thecondenser 52 across the terminals 34 and,

' If the relay is connected into the circuit in place of the resistor 21, Figure 1, then a singlepole and charges the condenser to the potential existing across those terminals. Release of the switch then shunts the charged condenser across the grid resistor 42, and the result is the same as above described in connection with Figure 1'." T

A double pole switch is necessary only when the relay is located in the line from the plate 18- to the supply wire 24 as shown in the drawings.

switch can be used, as that figure shows.

The time control circuit which I have described has many'useful applications: 'It maybe used, for example, in photographic work, for controlling exposure times- The relay contacts may close the circuit which actuates an electrically operated shutter, as on a camera, or may close the circuit which supplies the light source,'as' in printing'or enlarging equipment.

The control, thus provided is flexible, convenient, readily adjustable throughout a wide range, and capable of reproducing consistently the same timed interval for a given setting of the adjustable elements. It has no moving parts in the ordinary sense, and requires a minimum of care and attentio Although I have above described the element 42 as a resistance, an imp nce having characteristics othergthan those of afpure resistance can be employed at this point in the circuit, and the timed interval can be varied by changing the value or the character of the impedance.

[For example," the element 42 may be an inductnected by a wire 40 to a terminal of the variable resistor 42 and to another terminal 44 of the double pole double throw switch, which includes movable switch elements 43 and 50. Connected across the moving elements 48 and 50 of the switch is the'condenser 52. A

The double pole double throw switch has been shown in the drawings in the customary sym- 75 1. In a time control circuit, an electron tube a ance, or may be a series or parallel combination of inductance and resistance. The curves shown in Figure 2' would no longer apply, but the circuit would still have utility as a timing control.

Similarly, I havedescribed the element 52 as a a condenser, but any desired combination of circuit elements having a capacitive impedance may be employed in lieu of the single condenser shown.

Although I have herein shown and described a preferred embodiment of my invention, manifestly it is capable of modification and rearrangement without departing from the spirit and scope thereof. I do not, therefore, wish to be understood as limiting this invention to the precise embodiment herein disclosed, except as I may be so limited by the appended claims.

I claim as my invention:

having a cathode, anode and grid, a source of potential, a current actuated device, a resistor, said cathode, anode, current actuated device and resistor being connected in series with said source of potential, a condenser, discharge means connected between said grid and said cathode, said discharge means being adapted to discharge said condenser when placed in shunt therewith, and manually operable means consecutively shunting said condenser across a portion of said resistor and then across said discharge means.

2. In a time control circuit, an electron tube having a cathode, anode and grid, a resistance connected between said grid and said cathode, a source of potential, impedance means including a current actuated device, said cathode, anode and impedance means being connected in series with said source of potential, a condenser shunted across at least a portion of said impedance means, a second condenser, and means operable to charge said second condenser by shunting it across said portion of said impedance means and further operable to discharge said second condenser by shunting'it across said resistance.

3. In an electrical circuit, an electron tube having a cathode, an anode and a grid, a resistor connected between said grid and said cathode, a source of potential, a current actuated device, said cathode, anode and current actuated device being connected in series with said source of potential, a capacitive'impedance, and means whereby said capacitive impedance may be selectively shunted across said current actuated device or across said resistor.

4. In an electrical circuit, an electron tube having a cathode, an anode and a grid, a resistor connected between said grid and said cathode, a source of potential, a current actuated device, said cathode, anode and current actuated device being connected in series with said source of potential, a capacitive impedance, a condenser in shunt with said current actuated device, and means whereby said capacitive impedance may be selectively shunted across said current actuated device or across said resistor.

5. In an electrical circuit, an electron tube having a cathode, an anode and a grid, a resistor connected between said grid and said cathode, a source of potential, a current actuated device, said cathode, anode and current actuated device being connected in series with said source of potential, a capacitive impedance, and means for sequentially shunting said capacitive impedance across said current actuated device and said resistor, whereby said capacitive impedance first becomes charged to the potential existing across the terminals of the current actuated device, so that upon subsequently being shunted across the resistor current flows from the capacitive impedance through said resistor for imposing negative bias on the grid, to reduce current flow through the current actuated device to render said current actuated device inoperative for a predetermined period of time.

6. In an electrical circuit, an electron tube having a cathode, an anode and a grid, a resistor connected between said grid and said cathode, a source of potential, a current actuated device, said cathode, anode and current actuated device being connected in series with said source of potential, a capacitive impedance, and means for sequentially shunting said capacitive impedance across said current actuated device and said resistor, whereby said capacitive impedance nrst becomes charged to the potential existing across the terminals of the current actuated device, so that upon subsequently being shunted across the resistor current flows from the capacitive impedance through said resistor for imposing negative bias on the grid, to reduce current flow through the current actuated device to render said current actuated device inoperative tor a predetermined period of time, said resistor being manually adjustable for varying the predetermined time interval during which said current actuated device is inoperative.

7. In an electrical circuit, an electron tube having a cathode, an anode and a grid, a source or potential, a current actuateddevice, said cathode, anode and current actuated device being connected in series with said source oi potential, a capacitive impedance, means whereby said capacitive impedance may be selectively shunted across said current actuated device or across said cathode and grid, and a variable impedance connected between said grid and said cathode whereby the time rate of discharge of said capacitive impedance may be selectively controlled.

8. A control circuit including an electron tube, cathode, grid and anode elements in said tube, an impedance connected between said grid and said cathode, a relay, a connection between said anode and one terminal of said relay, a source of potential, a connection between said cathode and one terminal of said source of potential, a connection between the other terminal of said source of potential and the other terminal 0! said relay, a condenser, and means for shunting said condenser across said relay, and subsequently disconnecting said condenser from said relay and shunting said condenser across said impedance.

9. A control circuit including an electron tube, cathode, grid and anode elements in said tube, an impedance connected between said grid and said cathode, a relay, a connection between said anode and one terminal of said relay, a source of potenial, a transformer connected to said source of potential and to said cathode for heating said cathode, a connection between said cathode and one terminal of said source of potential, a connection between the other terminal of said source of potential and the other terminal of said relay, a condenser, and means for shunting s'aid condenser across said relay, and subsequently disconnecting said condenser from said relay and shunting said condenser across said impedance.

10. In a time control circuit, a rectifier, a source of potential, a current actuated device and a resistance connected in series, control means in said rectifier, terminals for said control means, said control means effecting a reduction in current flow through said rectifier when a potential exceeding a given'value is applied to said terminals, a condenser shunted across at least a portion of said resistance, a second condenser, a second resistance, connected across said terminals of said control means, and means operable to charge said second condenser by shunting it across said portion of said first mentioned resistance and further operable to discharge said second condenser by shunting it across said second resistance.

MARVIN G. NELSEN.

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