US2232694A - Timing device - Google Patents

Description

1941. D. M. DUINKER 2,232,694

TIMING DEVICE Filed Oct. 4, 1938 Grid I bliaye (I?) INVENTOR. DANIEL MARIE DUlNKER ATTORNEY.

Patented Feb. 25, 1941 UNITED STATES TIllflNG DEVICE Daniel Marie Duinker, Eindhoven, Netherlands,- assignor, by .mesne assignments, to Hartford National Bank and Trust Company, Hartford,

Conn.', as trustee Application October 4, 1938, Serial No. 233,314

In G

5 Claims.

My invention relates to timing devices using a grid-controlled gaseous discharge tube which is supplied with direct current.

The term gaseous discharge tube as used herein and in the claims is to be understood to mean a tube Whose filling comprises one or more gases, or one or more vapors, or a mixture of gases and vapors.

Timing devices of this type are often used to obtain current impulses which must be accurate and frequently of very short duration, for instance in timing the welding period in spot or seam-welding machines or in timing X-ray exposures. Such devices, however, have the drawback that the duration of the voltage impulses produced, which duration may control the discharge path of a second gaseous discharge tube, depends upon the supply voltage used and also upon the electrical characteristics of the discharge tubes used. Thus, provided those elements of the delay circuit which substantially determine the duration of the voltage impulse, e. g. a resistance and a condenser, remain the same, replacement of one of the discharge tubes by a similar discharge tube may cause a variation in the duration of the impulse due to the always present differences in similar discharge tubes as regards vapor-pressure, etc. Similar difiiculties arise if the supply voltage is changed. This of course is a serious disadvantage as it makes the device inaccurate or makes it necessary to recalibrate the device when a tube is replaced.

The main object of my invention is to eliminate the above difficulties and to provide a timing device in which the duration of the produced voltage impulse is substantially independent of the supply voltage used and of the electrical characteristics of the discharge tubes.

In accordance with the invention, I connect the control grid of the discharge tube through a resistance to the anode thereof, and also through a condenser to the cathode of the tube, and so arrange the circuit that the ratio between the anode voltage and the grid bias is independent of the value of the supply voltage. The resistance is preferably adjustable, and if desired the condenser can also be adjustable.

The arrangement preferably comprises a resistance which is connected in parallel with the discharge path of the tube and in series with a second resistance which is connected between the cathode .and one of the electrodes of the condenser and which serves to produce the negative grid bias. The rectangular voltage impulses produced across the former resistance are used to control the discharge path of another discharge tube, which is preferably of the gaseous type and is supplied with alternating current.

According to a further embodiment of the invention, I connect in series with the discharge ermany September 29, 1937 path of the first-mentioned gaseous discharge tube, an auxiliary discharge tube whose grid circuit comprises further means for switching-in the D. C. feed voltage at a preferably adjustable instant, which is determined with respect to the phase position of an alternating voltage.

A further advantage of the arrangement according to the invention is that the duration of the produced voltage impulse is rectilinearly proportional to the value of the resistance connected to the control grid.

In order that the invention may be clearly understood and readily carried into effect, I shall describe the same in more detail with reference to the accompanying drawing, in which:

Figure 1 is a schematic wiring diagram of a timing device according to the invention,

Fig. 2 is a graph giving the ignition characteristic curve of a grid-controlled discharge tube, and

Fig. 3 is a schematic wiring diagram of a timing device according to another embodiment of the invention.

The arrangement illustrated in Fig. 1 comprises a gaseous discharge tube 2' having an anode 3, a control grid 4 and a cathode 5. Tube 2 is supplied with direct voltage from a battery I which has a voltage E and has its positive terminal connected through a switch 4i and a conductor 42 to anode 3, and its negative terminal connected through a conductor 43 and a resistance 60 to cathode 5.

Control grid 4 is connected through a currentlimiting resistance 6 to a point 44 connected through a preferably variable resistance GI and conductor 42 to anode 3. Point 44 is. also connected to cathode 5 through .a condenser 62, which if desired may be variable, and a resistance 60 which serves to produce a negative grid bias. A resistance 63 is connected in parallel with the discharge path. The two resistances 80 and 63 form a potentiometer so that the ratio between the anode voltage (Va) and the grid bias (V0) is independent of the value of the supply voltage E.

In operation, closure of switch 4! connects the discharge path of tube 2 to the direct voltage of source I. However, the ignition does not take place at once because the current 2'1 which starts flowing through resistances 63 and 60 applies to grid 4, a potential which is negative with respect to the cathode and which prevents ignition. The ignition does not take place until condenser 62 has been charged through resistance 6| by the current is to such an extent that the grid potential exceeds the ignition voltage of the tube.

I will now show that the time T,i. e. the time between closure of switch 4! and ignition of the.

discharge path of tube '2, is substantially indedimensioned tubes of the same type.

pendent of the supply voltage E and of the electrical characteristic of the tube 2.

As indicated in Fig. 1, E is the supply voltage,

Va. is the anode voltage, i. e. the voltage between anode 3 and cathode 5. I

Vg is the grid voltage, 1. e. the voltage between grid 4 and cathode 5.

Va is the voltage across condenser 62.

R, R1 and R2 are the values of resistances 61, 66,

and 63 respectively.

C is the capacity of condenser 62.

Immediately upon closure of switch 4! we find In the Equation 2 the grid current has been neglected. By integrating Equation 2 I obtain:

wherein it is assumed that, at the time of closure of the switch M, the time i= and Vc=0. The grid voltage Vg is equal to the sum of the voltage across condenser 62 and the voltage across resistance 66 and consequently is equal to:

By substitution of Equations 1 and 3 in Equation 4 I obtain:

1 V,=E-(1e t l 2 an 5 RI+RJ R,+R2 e U The anode voltage Va. of the discharge path is equal to the voltage across resistance 63 and consequently is:

R VG=i1-RZ= By logarithming we obtain the time T, i. e. the time interval which elapses between the closure of switch 4| and the ignition of the discharge path of tube 2 g RI+R2 A suitable value of the tube constant g, which can easily be obtained in practice, is 1Il0. By introducing this value into the Equation 11 we obtain 1 Since the value V0, for example 200 volts, may be equal to the value of E, e. g. 250 volts, these valuesmay be practically neglected with respect to the small value of the factor l V -100 so that we obtain the equation:

As is shown in Equation 13, the characteristic magnitudes have in this case substantially no influence on the switching time T, particularly when R1 is not taken excessively large with respect to R2.

For Equation 13 we may approximately write:

1 T: C.R.ln R2 R1+R2 T= C.R.Zn(1 15 Equation 15 shows that the switching time T is independent of the supply voltage E if the arrangement is such that the ratio between the grid voltage and the anode voltage is independent of the value of the supply voltage.

Fig. 3 illustrates an arrangement according to the invention in which means are provided to efiect switching-in independently of the phase position of an alternating voltage.

In Fig. 3, in which the elements of Fig. 1 are indicated by the same reference numerals, switch 4| is replaced by a circuit arrangement comprising a gaseous discharge tube I having an anode 8, a control grid I0 and a cathode 9. A direct current produced by battery I passes through a resistance II, which serves to produce a negative bias on grid Ill. Resistance II has one end 41 connected through a resistance 28 to the positive terminal of battery I and has its other end 48 connected directly to the negative terminal of battery I. The end 48 is connected to grid I0 through a current-limiting resistance I2, and I the secondary winding I3 of a transformer I4 whose primary winding I 5 is connected to an A. C. supply.

The values of the resistances I I and 23 and the voltage of the battery I are so selected that the voltage across resistance II is sufficiently high to prevent ignition of the discharge path of tube 1. However, when resistance II is short circuited an alternating voltage is applied to grid I0 and the discharge path is ignited, depending upon the phase position of the alternating voltage.

For the above purpose a' two-position switch I6 having two arms 64 and ESis provided. Point 41 is connected to the heel 5B of arm 64 'and point 48 is connected to a fixed contact 49. The function of arm will be described later.

A condenser I] connected between cathode 9 and a point 54 between resistanceIZ and winding I3 serves for the adjustment of the phase position. When arm 64 engages contact 49, re-

sistance II is short-circuited, grid Ill acquires an alternating voltage, and the discharge path of tube 1 ignites at a moment which depends upon the phase position of the alternating voltage as adjusted by condenser H.

The timing arrangement described above is used for controlling the welding current between two welding electrodes 58 which are connected to the secondary winding of a step-down transformer 29 whose primary winding 10 has one end connected to one terminal of an A. C. supply 30. The other end of winding 16 is connected to the other terminal of supply 30 through the primary winding of a series transformer 23 having a secondary winding 22 provided with a mid-tap 54.

For the above purpose two main grid-controlled discharge tubes l8 and I9 are used and are supplied with alternating current. Tube I8 ha an anode 20, a grid 26, and a cathode 24, and tube I9 has an anode 2|, a grid 21, and a cathode 25. Anodes 26 and 2! are connected one to each end of winding 22, and cathodes 24 and 25 are connected together and to cathode 5 through a conductor 55 which is connected by a conductor 56 to tap 54. Grids 26 and 21 are connected together and through a conductor 51 to a tap 46 on the potentiometer 28, through which passes direct current supplied by battery 5.

Thus, if the discharge path of tube 1 is nonconductive, grids 26 and 21 will receive a potential which is negative with respect to the cathodes Z4 and 25. However, when this discharge path is ignited, the potentials of grids 26 and 21 with respect to the cathodes will be changed, due to the voltage drop in resistance 63, to such an extent that the discharge paths of tubes l8 and I9 will be ignited. As a result the resistance of the transformer 23 will be reduced and current will start to flow between the electrodes 5.

However, the duration of this current flow is limited, because when the discharge path of tube 2 becomes ignited it short-circuits resistance 63, and as a result grids 26 and 21 are negatively biased as before and the discharge paths of tubes 18 and [9 are blocked.

After the termination of the passage of current between electrodes 58, the device must be restored to its initial state and for this purpose tube 1 must be extinguished. This is affected in known manner by means of an extinguishing grid or a switch in the anode circuit. As shown, anode 1 is connected to point 45 through a switch 66. The condenser 52 must be discharged and this is effected by placing switch 16 in the position shown whereby condenser 62 discharges through resistance 32 and arm 65.

The restoration of the device may, of course be effected automatically by using an additional time switch arrangement, such arrangements being useful for example in seam-welding machines.

While I have described my invention with reference to specific examples I do not wish to be limited thereto, but desire the appended claims to be construed as broadly as is permissible in view of the prior art.

What I claim is:

1. A'timing device comprising a gaseous discharge tube having an anode, a cathode and a grid, a resistance connected between the grid and anode, a condenser and a second resistance connected in series between the cathode and grid with one terminal of the condenser connected to the grid, 2. source of direct voltage connected between the anode and a point between said condenserand second resistance, and a third resistance connected between said anode and cathode.

2. A timing device comprising a gaseous dis.- charge tube having an anode, a cathode and a grid, a resistance connected between the grid and anode, a condenser and a second resistance connected in series between the grid and cathode with one terminal of the condenser connected to the grid, a source of direct current connected between the anode and the other terminal of the condenser, a third resistance connected between the anode and cathode and a discharge tube associated with said third resistance and controlled by rectangular voltages taken therefrom.

3. A timing device comprising a gaseous discharge tube having an anode, a cathode and a grid, a resistance connected between the grid and anode, a condenser having one terminal connected to the grid and a second terminal, a second resistance connected between said second terminal and said cathode, a third resistance con nected between said anode and cathode, a supply of direct voltage, and means for connecting said supply between said anode and the second terminal of the condenser at a predetermined moment, said means including an auxiliary discharge tube having a grid, and a grid circuit for said latter tube including a source of alternating current supply.

4. A timing device comprising a gaseous discharge tube having an anode, a cathode and a grid, a resistance connected between the grid and anode, a condenser having one terminal connected to the grid and a second terminal, a second resistance connected between said second terminal and said cathode, a third resistance connected between said anode and cathode, a supply of direct voltage, and means for connecting said supply between said anode and the second terminal of the condenser, said means comprising an auxiliary discharge tube having a control grid, 2. grid circuit for said latter tube including a source of alternating voltage and a biasing resistance, and switching means for short circuiting said latter resistance to thereby reduce the negative bias on the grid and permit the ignition to the tube.

5. A timing device comprising a gaseous discharge tube having an anode, a cathode and a grid, a resistance connected between the grid and anode and having a value (R), a condenser having a capacity (C) and a second resistance having a value (R1), said condenser and second resistance being connected in series between the oathode and grid with one terminal of the condenser connected to the grid, a source of direct voltage having a value (E) connected between the anode and a point between said condenser and second resistance, and. a third resistance having a value (R2) connected between said anode and cathode, said gaseous discharge tube having an electrical characteristic (9') Whose absolute value is large in comparison with unity and an electrical value (V0), the values (V0) and (E) being such that the fraction is negligible with respect to the value of the remainder of the denominator.

DANIEL MARIE DUINKER.

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