US2248929A - Welding timer - Google Patents

Description

July 15, 1941. H. ADLER 2,248,929

' WELDING TIMER.

Filed Dec. 14, 19:58

lAAllA 7 6'95 or vapor filled 22 Pea #07 0 F a/rafting WITNESSES: INVENTOR f2. C I Hans f7d/er:

ATTORNE Patented July 15, 1941 'WELDING TIMER Hans Adler, Berlin-Haseihorst, Germany, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 14, 1938, Serial No. 245,650 In Germany March 5, 1938 19 Claims.

The invention relates to a short time circuit breaker through which a load is connected for a predetermined number of alternating current periods to an alternating current network. As circuit interrupter, gas or vapor filled paths, preferably grid controlled mercury vapor discharge paths with are type discharge, serve. The invention consists of a novel construction of the control circuit determining the ignition of the discharge paths; the circuit differs from the known short time switches advantageously by the fact that the operating requirements put on such a circuit breaker may he fulfilled with simple and inexpensive switching means. One of the essential characteristics of the invention consists in the fact that in the control circuit determining the ignition time-point of the discharge paths, two potentials differing from each other are effective. One of the potentials has a peaked wave form; accordingly rises steeply and remains positive only during a comparatively short time. This potential determines the ignition time-point when the discharge path is first connectedin. The second potential which is effective in the same control circuit has, in contrast to the first potential, an essentially wider wave form. Accordingly, it maintains its positive value during a relatively long time. This potential is only brought into action after the ignition of the dis-'- charge paths is initiated by the first potential of peaked wave form, and if the discharge paths are to remain conducting during a number of half waves of the feeding alternating current potential.

The manner of. operation of a short time circuit breaker functioning in this manner with different control potentials will be explained more in detail with reference to the exemplary embodiment shown in the figure.

A welding transformer l, the secondary winding of which is connected to welding electrodes 2, is connected through two grid controlled discharge vessels 3 and i with mercury cathodes to an alternating current network. In the grid circuit of the discharge vessel 3, there are a blocking potential source 5 and an impedance 6 which may be connected in a circuit through a grid controlled arc discharge vessel 1, preferably a hot cathode discharge vessel. The potential for the circuit of the impedance 6 is supplied by a transformer 8 which is connected to the same alternating current source as the welding transformer. The impedance 6 and the auxiliary discharge vessel 1 are so connected that on the ig nition of the discharge vessel 1, a potential difference exists across the impedance 6 which counter-acts the blocking potential 5 in the grid circuit of the discharge vessel 3 and thereby ignites the vessel.

The second discharge vessel 4 which is connected in the primary circuit of the welding circuit in antiparallel to the discharge vessel 3 is ignited by a transformer 9, the primary winding ill of which is connected to the primary terminals of the welding transformer I. The transformer 9, accordingly, obtains potential as soon as the welding transformer is connected through the discharge vessel 3 to the alternating current source. A secondary Winding 92 of the transformer 9 is connected in the grid circuit of the discharge vessel 4 and ignites the latter discharge vessel after the current during the previous half cycle of the feeding alternating current potential is extinguished in the previously ignited discharge vessel 3. By the two discharge vessels 3 and 4, at least two successive half waves of the feeding alternating current potential are thus supplied by means of the transformer I at any time.

A measure for the time during which the Welding transformer I remains connected through the two discharge vessels 3 and 4 is the control circuit of the auxiliary discharge vessel 1. In this control circuit, there act, in accordance with the invention, in addition to a negative blocking potential l0, two alternating potentials which are supplied to the two impedances (resistances) H and I2 connected between the grid and the cathode of the discharge vessel 1. The potential diiference across impedance H is supplied by a transformer [3, the primary winding of which is connected to the transformer 8 and thereby to the feeding alternating source. The transformer [3 produces across the impedance II, a potential difference of peaked wave form, 1. e., a potential which becomes positive only during a comparatively short time compared to the half wave of the feeding alternating potential. For converting the sinusoidal potential into a potential of peaked wave form, means are used which, in .the technical art of controllable discharge vessels, are, in general, known. It is essential that the potential supplied by the transformer I3 shall have such a phase position that when the welding transformer l is first connected in, the passage of non-permissible high current impulse through the main discharge vessel 3 shall as far as possible be precluded. In accordance with the inductance of the welding transformer or any other load connected through the short time circuit breaker to the feeding network, the ignition potential of the transformer [3 must lag the feeding alternating current potential by a smaller or greater phase angle which, for welding transformers of substantial power, amounts to approximately 60-70 electrical degrees, for example.

The second control potential in the grid circuit of the discharge vessel 1, which is supplied to the impedance E2, is also an alternating potential. It is not derived from the feeding network directly but through a secondary winding 43 of the transformer 3. The potential difference across impedance it may thus first appear after the first half wave of the alternating current potential has been connected in through the main discharge vessel 3. In contrast to the potential difference across the impedance H, the potential difference across impedance I2 has a wide curve shape. It accordingly, remains, positive during a substantially longer time. It may, for example, be sinusoidal or rectangular shape. A further characteristic which is essential for the potential difference across impedance [2 consists in the fact that this potential shall lead the potential difference across impedance H in phase. It is preferably at least so far displaced ahead that it is in phase with the feeding alternating potential. It is, preferable, however, to provide additional means to cause the potential difference across impedance E2 to lead the alternating current potential. In the exemplary embodiment, a capacitor, i is provided for this purpose. In lieu of this capacitor, other known means, for example, bridge circuits or the like, may naturally be used for the purpose of attaining the desired phase lead.

The two control potentials for the auxiliary discharge vessel 1 impressed on the impedances H and i2, are so dimensioned that the potential difference across impedance l2 determines the ignition time-point of the discharge vessel 1 as soon as both potentials are simultaneously effective. The potential difference across impedance l2 alone, accordingly, determines the ignition time-point after the discharge vessel 3 becomes conductive by the operation of the potential of peaked wave form impressed on the impedance ii at the beginning of the total on time of the short time circuit breaker. The potential difference across impedance l2 has the same eifect as is attained in the present short time circuit breakers by causing a practically invariable direct current potential to act in the grid circuit of the main discharge paths after the discharge paths are first rendered conductive. The advantage of the invention as compared to these known circuits consists in the fact that special auxiliary potentials are not necessary but that all control potentials may be derived from the feeding alternating current source. The phase lead of the control potential acting on the impedance i2 provided in accordance with the invention assures that the discharge vessel 3 will, with certainty, receive a positive grid potential at the instant at which the current in the parallel connected discharge vessel 4 becomes extinguished, This time-point is not fixed but depends on the effective inductance of the welding transformer which, as is known, may fluctuate in accordance with the magnitude of the charge in the arms of the welding machine.

In addition to the negative blocking potential source it] and the two impedances H and I2, there is, in the circuit of the discharge vessel 1, a condenser E5. The latter supplies, in itself, in

til

known manner, a potential which, measured from the time-point of the connecting in, gradually rises, and after the passage of a predetermined number of half waves, removes the ignition effect of the potential difference across impedance 12. The condenser i5 is, for this purpose, charged through a rectifier l6 and a regulating impedance H from the secondary winding 94 of the transformer 9. Because of the derivation of this potential from the transformer 9, the charging starts only as soon as the welding transformer is connected in through the discharge vessels 3 and 4. The condenser It may be short circuited by a switch l8 so that it may be discharged to t prepare for a new operation.

At the terminals of condenser l5, there is connected, in accordance with the invention, still another potential which is derived through a rectifier l9 from the transformer 20, The transformer 20 is connected to the secondary winding of transformer 3 and thereby to the feeding alternating current potential source. Through the transformer 20, the condenser i5 is thus permanently charged, nevertheless, in contrast to the above described charging circuit, with such a small charging current that only the characteristic losses of the condenser I5 are equalized. In the charging circuit of the transformer 20, an impedance 2| is connected for limiting the charging current and it is considerably larger than the regulating impedance H which measures the charging from the transformer 9. The additional charging from the transformer 20 should prevent he blocking potential of condenser is from disappearing after the end of a time switching process, if, for any reason, the switch [8 short circuiting the condenser 15 is not closed; accordingly, if, for example, the operator of the welding machine permits the foot switch of the welding machine to remain actuated for a substantial time and thereby holds the welding electrodes on the workpiece although the welding process has already been terminated.

t has already been mentioned that potential difference across impedance 12 in the grid circuit of the auxiliary discharge vessel 1 should be so dimensioned that this potential alone determines the ignition time-point even if the potential difference of peaked wave form is at the same time effective across impedance II. If the potential difference across impedance 1! leads, by a sufficient angle, the potential difference of peaked wave form on impedance I l, the potential peak of impedance ll lies behind the maximum of a sinusoial alternating current potential effective on impedance l2. The potential peak does not act (even after the potential difference across condenser [5 has become sufficient to prevent ignition of valve 1 by the potential difference across impedance l2) if it is so dimensioned that it does not jut out over the maximum value of the potential difference across impedance l2. A further means of attaining the same result consists in introducing means in the grid circuit of the discharge vessel 1, which provide that all the potentials effective in this circuit together do not exceed a predetermined maximum value. For this purpose, a discharge path 22 may be connected in parallel to the two impedances H and [2, as is indicated in the figure. The total potential difference across the impedances and thus the total potential measuring the ignition of the discharge vessel 1, may then, even if both potentials are simultaneously effective, not exceed a predetermined value. Regardless of the relative phase position of the two alternating potentials on the impedances II and I2, the discharge vessel 1 and with it also the discharge vessel 3, is always ignited at the instant at which the potential difference of wide wave shape across impedance l2 exceeds the blocking limit of discharge vessel 1. In lieu of the glow discharge path 22, other potential limiting means may be used, such as, for example, a grid leak resistance which may be so dimensioned that the potential drop manifested on it for large grid potentials prevents a further rise in the potential. Also by it, the upper part of the total potential acting on the grid may be cut oil.

A switching process of the time switch illustrated in the figure and described in detail above develops as follows: When the welding electrodes on the welding machine are engaged with the work-piece, the switch 18 in the grid circuit of the auxiliary discharge vessel 1 is opened by a foot switch or by a similar switching apparatus, under certain circumstances, with an auxiliary relay interposed. One of the two contacts of this switch lifts a short circuit path parallel to the two impedances ii and I2 so that the potential differences across on these impedances become cfiective and the discharge vessel 1 may ignite. In addition, the short circuit on the condenser i is also opened by the switch I 8. As soon after the opening of the switch [8 as the positive potential peak is manifested for the first time on impedance Ii, the vessel 1 ignites, supplies the impedance 5 and thereby at the same instant ignites the discharge vessel 3 in the primary circuit of welding transformer l. Thereby the transformer 9 obtains potential which, on the one hand, through its secondary winding 92 ignites the discharge vessel 4 in the following half wave and, on the other hand, through a secondary winding 93 supplies leading potential to the impedance ill in the grid circuit of the discharge vessel T. This potential renders the peaked potential difference across impedance H ineffective and supplies the ignition of the discharge vessel 1 in the succeeding half wave. This continues until the condenser is charged up through 3e secondary winding 94 of transformer 9 to a point such that its potential counteracts the potential difference across impedance iii. The discharge vessel 7 then is not ignited in the succeeding half wave. correspondingly, the ignition potential difference across impedance 6 disappears and the two discharge vessels 3 and 4 also extinguish. If the foot or control switch !8 is closed after this time switching process, the condenser i5 may discharge. In addition the two impedances H and I 2 are short circuited. The next switchini process may take place in the above-described manner only if the contacts of the switch 18 are opened. If, for any reason, the switch 18 is maintained open for a substantial time, the discharge vessel l is, in spite of this, not ignited because the discharge taking place through the characteristic losses of condenser I5 are equalized by the permanent charging from the transformer 20.

I claim as my invention:

1. Time switching apparatus for spot welding machines, comprising two gas, or vapor, discharge valves connected in anti-parallel between a load and an alternating current source, said discharge valves having a control circuit, means for impressing a plurality of potentials in said control circuit, said means including means for impressing a first potential of peaked wave form pressing a to initiate the ignition of said discharge valves, and means for impressing a second potential of wider wave form effective to maintain said discharge valves conducting only after the ignition of the discharge valves.

2. Time switching apparatus according to claim 1, characterized by the fact that the first and second potentials are de ived from the alternating current source.

3. Time switching apparatus for spot welding machines, comprising two gas, or vapor, dis charge valves connected in anti parallel between a load and an alternating current source, control circuit means for said discharge valves, means for impressing in said control circuit means a plurality of potentials derived from the alternating current source, said means for impressing potential including means for impressing a first potential of peaked wave form to initiate the ignition of said discharge valves, and means for impressing a second potential of wider wave form effective to render said discharge valves conduct ing only after the ignition or the discharge valves, said means for impressing a second poten tial including a transformer which is eifective only after the first ignition of the discharge valves.

4. Time switching apparatus for spot welding machines, comprising two gas, or vapor, discharge valves connected in anti parallel between a load and an alternating current source, control circuit means for said discharge valves, means for impressing in said control circuit means a 1 of potentials derived from the alternat- -nt source, said means for impressing potential including means for impressing a first potential of peaked wave form dephased relative to the potential of the alternating current source to initiate the ignition of said discharge devices, and means for impressing a second potential of wider wave form in phase with, or leading, the potential of the alternating source and effective to reinitiate the ignition of said discharge valves only after the ignition of the discharge devices by means of said 'irst potential, said means for imseccnd potential including a transformer.

5. Time switching according to claim 4, characterized by the fact that the potential of peaked wave form is so dimensioned that it does not eX- ceed the maximum value of the potential or wide wave form on simultaneous application of both potentials.

6. Time switching apparatus for spot welding machines, comprising two gas, or vapor discharge valves connected in anti-parallel between a load and alternating current source, control circuit means for said discharge valves, means for impressing a plurality of potentials in said control circuit means, said means for impressing potential including means for impressing a first potential of peaked wave form to initiate the ignition of said discharge Valves and means for inn pressing a second potential of wider wave form effective to render said discharge valves conducting only after the ignition of the discharge valves by means of said first potential, and said control circuit means including potential limiting means comprising a closed discharge path which does not permit the total potential resulting from the first and second control potentials to exceed a predetermined value.

7. Time switching apparatus for spot Welding machines, comprising two gas, or vapor, main discharge valves connected in anti-parallel between a load and an alternating current source, control circuit means for said main discharge valves, said circuit control means comprising an auxiliary discharge device having a grid circuit, two impedances and a capacitor connected in series in said grid circuit, means for impressing a plurality of potentials in said grid circuit, said means for impressing potential including means for impressing a potential of peaked wave form across one of said two impedances to initiate the ignition of said main discharge valves and means for impressing a potential of wider wave form across the other of said impedance, said last named potential being effective only after the ignition of the main discharge valves, means for gradually charging said capacitor after the initiation of the ignition of the main discharge valves, and a control device adapted to shunt the two impedances and also the capacitor at will.

8. Time switching apparatus according to claim 7, characterized by the fact that a glow discharge path is connected in parallel to the said two impedances in the grid circuit of the auxiliary discharge device.

9. Time switching apparatus according to claim '7, characterized by the fact that an auxiliary potential is impressed across said capacitor through a high ohmic resistance to compensate for the losses of said capacitor.

10. For use in controlling the supply of power from a source to a load the combination comprising in efiect a first electric discharge valve and a second electric discharge valve interposed between said source and said load, means for arbitrarily rendering said first valve conductive, means for thereafter rendering said second valve and said first valve conductive in succession in response to current flow respectively through said first valve and said second valve and means, in-

cluding means responsive to current fiow through said valves, for restraining said valves from becoming conductive after they have been rendered conductive a predetermined number of times.

11. For use in controlling the supply of power from a source to a load the combination commeans for thereafter rendering said second valve and said first valve conductive in succession in response to current flow respectively through said first valve and said second valve, means for restraining said valves from becoming conductive after they have been rendered conductive a predetermined number of times and additional means for preventing said means for arbitrarily rendering said first valve conductive from functioning after said restraining means has functioned if said arbitrary means is maintained in the condition for rendering said first valve conductive.

12. For use in controlling the supply of power from a source of alternating current to a load the combination comprising a first electric discharge valve and a second electric discharge valve connected in anti-parallel between said source and said load, means for supplying a potential to render said first valve conductive, means for thereafter deriving potentials from said load as it is supplied through said first and second valves to render said second and first valves respectively conductive in succession and means for deriving a further potential from said load as it is supplied through said first and second valves for restraining said valves from being rendered conductive after a predetermined number of half periods of said source.

13. For use in controlling the supply of power from a source of alternating current to a load the combination comprising a first electric discharge valve and a second electric discharge valve conheated in anti-parallel between said source and said load, means for supplying a first potential to render said first valve conductive, means for thereafter deriving second and third potentials from said load as it is supplied through said first and second valves respectively to render said second and first valves respectively conductive in succession, said third potential being superimposed on said first potential and said first potential having an amplitude no greater than said third potential, and means for deriving a fiuther potential from said load as it is supplied through said first and second valves for restraining said valves from being rendered conductive after a predetermined number of half periods of said source.

14. For use in controlling the supply of power from a source of alternating current to a load the combination comprising a first electric discharge valve and a second electric discharge valve connected in anti-parallel between said source and said load, means for supplying a first potential to render said first valve conductive, means for thereafter deriving second and third potentials from said load as it is supplied through said first and second valves respectively to render said second and first valves respectively conductive in succession said third potential being superimposed on said first potential and means for deriving a further potential from said load as it is supplied through said first and second valves and superimposing it on said first and third potentials for restraining said valves from being rendered conductive after a predetermined number of half periods of said source and means for limiting the magnitude of the sum of said first and third potentials to a value less than said further potential.

15. For use in controlling the supply of power from a source of alternating current to a load the combination comprising a first electric discharge valve and a second electric discharge valve connected in anti-parallel between said source and said load, means for deriving a first periodic potential from said source to render said first valve conductive and means for thereafter deriving second and third periodic potentials from said load as it is supplied through said first and second valves respectively to render said second and first valves respectively conductive in succession, said third potential being superimposed on said first potential and leading it in phase.

16. For use in controlling the supply of power from a source of alternating current to a load the combination comprising a first electric discharge valve and a second electric discharge valve connected in anti-parallel between said source and said load, means for deriving a first periodic potential of short duration compared to a half period of said source from said source to render said first valve conductive at a predetermined instant in a half period of said source, and means for thereafter deriving second and third periodic potentials from said load as it is supplied through said first and second valves respectively to render said second and first valves respectively conductive in succession said third potential being superimposed on said first potential and leading it in phase.

1'7. Apparatus according to claim 12 characterized by the fact that the further potential is derived by charging a capacitor through a regulating resistor.

18. Apparatus according to claim 13 characterized by the fact that the valves are controlled through an auxiliary valve in the control circuit of Which certain of the potentials for rendering the valves conductive and non-conductive are impressed.

19. For use in controlling the supply of power from a source of alternating current to a load the combination comprising a first electric discharge valve and a second electric discharge valve connected in anti-parallel between said source and said load, means for supplying a first potential to render said first valve conductive, means for thereafter deriving second and third potentials from said load as it is supplied through said first and second valves respectively to render said second and first valves respectively conductive in succession, said third potential being superimposed on said first potential and means for deriving a further potential from said load as it is supplied through said first and second valves and superimposing it on said first and third potentials for restraining said valves from being rendered conductive after a predetermined number of half periods of said source and means for limiting the magnitude of the sum of said first and third potentials to a predetermined value.

HANS ABLE-R.

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