US2825809A

US2825809A - Electronic welder pulse controlling circuit

Info

Publication number: US2825809A
Application number: US536222A
Authority: US
Inventors: David S Ferguson
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1955-09-23
Filing date: 1955-09-23
Publication date: 1958-03-04
Anticipated expiration: 1975-03-04

Description

March 4, 1958 D. s. FERGUSON ELECTRONIC WELDER PULSE CONTROLLING CIRCUIT Filed Sept. 23, 1955 INVENTOR DAVID S. FERGUSON AT'rRNEY ELECTRONIC VJELDER PULSE CIRCUIT Applicatinn September 23, 1955, Seriai No. 536,222 Claims. (Cl. ESQ-27) This invention relates to an electronically controlled A. C. pulser.

in particular the invention relates to the control of an electronic pulser whereby a definite number of A. C. pulses will be caused to flow into a load.

In a more limited sense the invention relates to a welder with means to enable the welder to operate through a number of predetermined A. C. cycles, the number being variable at will.

The invention herein is an improvement on the invention disclosed in the application of Donald B. Martin, Serial Number 482,723, filed January 19, 1955, and assigned to the same assignee as the instant application.

It is an object of this invention to provide a means settable at will whereby any predetermined number of cycles of A. C. current can be caused to flow through a welding transformer.

It is a further object of the invention to provide means whereby closure of a start switch will cause the predetermining means to operate, the mere maintaining of the switch closed being ineffective to maintain energization of the transformer after the predetermined cycling has taken place.

It is yet another object of the invention to make a control unit of this character with a minimum number of parts and without mechanical relays to make the device reliable in operation and cheaper to produce.

These and other objects will be apparent after reading the following specification and claims in conjunction with the accompanying drawing which exemplifies one embodiment of the invention.

In said drawing there is disclosed a three wire A. C. line, the outside wires being indicated as 19 and 12 and across which there is a nominal 220 volts and the neutral grounded wire being indicated as 14. Between wire 14 and either of the outside wires there is a nominal 110 volts.

' Bridging the wires and 12, in series relation, is a gas filled triode 16, a variable resistor 13, a second circuit limiting resistor 20 and a third resistor 22. The resistor 18 is paralleled by a condenser 24. Grid bias for the tube is obtained by connecting a resistor 26 between the grid of the tube and the lower end of resistor 18. This tube will conduct when the A. C. voltage on the line rises high enough on the positive half cycle to ionize the gas within the tube. After several cycles, the condenser 24 will be charged to a low value and the voltage across this condenser will establish a bias on the cathode to delay the firing of the tube until a desired point on the positive cycle of the A. C. supply is reached. This bias may be adjusted so as to vary the time of firing of the tube 16 by varying the resistor 18. After the bias is established, the tube 16 will always be conductive for the i tent flow through the tube 16 and

resistors

18, 20, and 22.

T e current flow produces a potential difference across the resistor 22, the voltage curve across the resistor following the current curve across the tube. Since at firing potential on the grid of the tube, the tube becomes instantly conductive, the voltage curve across the resistor 22 is characterized by a sharp rise. This sudden rise in voltage or positive pulse is applied to a condenser 28 connected via a grid resistor 3th to the grid of a gas filled tube 32 of large current capacity. This high current capacity tube is in the wire 10 and in series with the high voltage winding of a welding transformer 34, via a current controlling variable resistor 36. The resistance 20 and the variable resistor 18 control the current flow through the tube 16 to the condenser 28. The grid of tube 32 is biased to swing negative as the anode goes positive by providing a transformer 38, the primary of which is connected between line 14 and ground of the supply, and the secondary of which is connected between cathode and grid of the tube 32 via a current limiting resistor 39 and grid bias resistor St). The windings of the transformer are so related that the grid and plate swing in opposite phases. This prevents firing of the tube except under control of the pulses derived from the tube 16. Pulses from the tube 16 are led to the condenser 28 via a switch it To prevent inadvertent firing of the tube 32 on closure of the switch solely because of surge phenomena, a high resistance 42 bridges the switch. Upon closure of the switch, full potential, as it quickly rises across resistance 22, is applied to the condenser 28 and the grid of tube 32.

In accordance with this invention, the conduction of tube 32 is limited as a maximum to any predetermined number of positive half cycles regardless of whether or not the switch 41} is maintained closed after the predetermined number of cycles have passed therethrough.

To attain this result the following circuitry is provided. Paralleling the network involving the tube 32, resistor 36 and the primary of transformer 34 is a gas filled tube 763 having a cathode resistor 72 of low ohmage and grid bias resistor 74, said bias resistor being connected to the same point on a line as the grid bias resistor 30 of tube 32. As a consequence the tube is ionized at the same time as tube 32, resulting in flow of current through the resistor 72. Bridging the resistor 72 is a pair of series connected high ohrnage resistors 76 and 78, a tap from the juncture of the resistors leading to a capacitor iii) and the grid of a normally cut off gas filled tube 44. The tube 44 will fire only if the grid is sufficiently positive with respect to the cathode. The cathode of tube 44 is maintained at a desired variable positive potential by feeding to it a filtered D. C. voltage. This voltage is derived from a bleeder network involving a series arrangement of selenium rectifier 52, selenium cell protective resistor 5d, a further current limiting resistor 60, and potentiometers 66 and 68. The cathode bias voltage is filtered by capacitor 58, resistor 6t), potentiometer 66 and capacitor 62, and the selected cathode bias voltage is obtained by the setting of the arm of potentiometer 63. in the exemplification disclosed herein the potentiometer 68 is provided with four taps designed to enable the cathode to be raised to four ditferent potentials. The arm of the potentiometer 66 is adjusted to compensate for slight variations in tubes when a tube 44 is replaced or changes its characteristics so that a given basic potential level selected at the cathode of the tube may always ,be the same. The anode of tube 4-4 is fed with direct current from rectifier 52 via resistors 54 and 56 and switch 40, the capacitor 58 for this purpose being made large and maintaining positive potential on the anode during the negative half cycle of the alternating current.

A resistor 64 bridges'the primary of the welding transformer 34 to damp out inductive kick from the-transformer to the cathode of tube 32 and interfere with the proper functioning-of tube 32. 7

On closure of. the switch 40 and on the occurrence of apredetermined point in the positive swing of the A. C.

voltage in, the line 10, 12, as determined by the setting of variable. resistor or potentiometer 18, a pulseof current' will. flow through the tube 16, potentiometer 18, resistor zflswitch ditto capacitor 23 and a positive voltagepulsewm appear at the grids of gas'filled tubes 3 2,and. 70, causing both of them to fire. The tube 32 will. then-conduct one halft cycle pulses to the. welding transformer 34 until no further positive pulses are permitted-toappear on the grid of that "tube. The tube 70 when fired conduets current viarthe cathode resistor 72 andwhich resistor while allowing tube current how there- 7 through. provides a potential drop thereacross. The currenfthroughthe tube 70 also flows to the capacitor 80;

gradually bringing: the same up in positive'voltage, the voltage of the control grid in tube 44 following the voltage. of thecapacitor. The cathode of tube 44 is set' at a desired level by preliminary adjustment of potentiometer 66 ('s'et.at.interva1s'for the tube and reset, if necessary, on exchange of tube) and by adjusting the arm of potentiometer 68 to. the desired tap. When the voltage on the grid of tube 44 issufiiciently above the cathode voltage, tube 44' fires, shorting out pulses from tube 16 to the grids oftubes 32 and 70 thereby rendering these latter tubesinefiective:regardless of the fact that switch 40 is maintained .closedr Opening of switch 49 is then effective to cut ofl D. C. supply to the anode of tube -44 and extinguish the same. It. requires reclosure. of the. switch to initiate the cycle of. operation of the system, 7 r

. Having thus described the invention what is claimed is:

1; A welding unitcomprising a two wire, alternating,

current. supply;-.a grid controlled ionizable tube having an anode connected to one wire of said supply and a cathode conuected to one terminal of a load,the. other terminal: ofv theloadfbeing connected to. the, other wire of; the supply, a second grid controlled ionizable tube having an anode, connected to theanode of the first tube and a cathode connected to one. terminal of a voltage dropping .means,- the other terminal ofthe voltage droppingmeans being connected to' saidother wire, means across. the wires for creating positive pulses and means for applying them to the grids. of both tubes, a third grid Controlled ionizable tube having'its anode connected to the'means for creating positive pulses and its cathode connected to said-other .wire,..a capacitor, having one terminal connected to the gridof the third tube and its other terminal, connected .to s aid other wire, means for applying positive voltage created by said voltage dropping means to said'one terminal of said'capacitor to build up apositive potential therein and on the, associated grid with respect to its cathode, 'andnieans for applying a positive, potentialto the'cathode of the third tube 'with respect to its grid.

2.,A weldingunit comprising a two wire, alternating.

currentsupply; a grid controlled ionizable tube having an anodegconneeted to one wire. of said. supply and a cathodelconnected to one terminal ofa load,;the other terminaloff the load" being connected, to. theother-wire 'ofthe supply, a second grid controlled, ionizable tube having an anode connected-to the anode of th'efirst tube andf'a 'cathodejconnected, to one terminal of ;a voltage. dropping means; the other terminal of 'the voltage drop ping means being connected to said other. wire, means,

7 4 r across the wires for creating positivepulses and meaus for applying them to the grids of both tubes, a third grid controlled ionizable tube having its anode connected to the means for creating positive pulses and its cathode connected to said other wire, a capacitor having one terminal connected to the grid of the third tube and its other terminal connected to said other wire, means for applying positive voltage created by said voltage dropping means to said one terminal of said capacitor to build up a positive potential therein and on the associated grid with respect to its cathode, means for applying a positive potential to the cathode of the third tube with respect to its grid, and means for varying said positive potential.

3. A welding unit comprising a two wire, alternating;

current supply, a 'grid. controlled ionizablegtube having an anode connected to one wire of said supplyand a cathode, connected to one terminal of a load, the other' terminal of the load being connected to the" other wire of the supply, a second grid controlled ionizable tube having an anode connected to the anode of the first tube and a cathode connected to one terminal of. a voltage dropping means, the other terminal. of the voltage dropping means being connected to said other wire,.-means across thewires for creating positive pulses and means for applyinglthem to the. grids of both tubes a, third grid controlled ionizable tube having its anode connected to the' means for creating positive pulses and its cathode connected to said otherwire, a capacitor having one 1 terminal connectedto-the grid of the third-tube audits other terminal connected to said" other wire, means for" applying positive voltage created by said voltage dropping means to said'one terminaloffsaid capacitor to buildup a positive potential thereinand on the associated grid with respect to itsicathode, means for applying a variable positive potential to thecathode'of the-third tubewith respect to its grid,ssaid last means comprising a. rectifier and resistance in series across the. alternating current V supply, a point on said resistance being connected tothe cathode of said, third tube, .and means forvarying the resistance to thereby vary the potential. on the cathode. of the third tube.

4 A welding unitjcomprising, a two wire,.alternating current' supply,' a grid controlled ionizable. tube having,

an anode connected to one wire of the. suppIywand. a:

cathodeconnected to oneterminal of a load, the other terminal 'of theload being connected to the otherwire of, :the supply, a second. grid controlled. ionizable tube having an anode. connected to the anode of the firsttube and-a cathode connected to one. terminal of. a resistor, the; other terminal. of the resistor being-connected to said other wire, a tapped ,blee der shunting the resistor, means across the wires for creating phsitivepulses and operator= operated, switch .havingan input and outputlterminalfor applving themto. the grids? of both tubes,;a third grid controlled ionizable tube having an anode connected to the outputterminal of the switch anditsgtid connected to a tap on said bleeder, acapacitorhavingone terminalconnected to the third grid and its'other terminal con nection; to said. .other wire, a cathode of said thirdftube leading to said other. wireLviaa-potentiometer,.and a rectifier having its. negative/end. connected tolsaids one wire with its positive end connected. to the cathodeconnected ,end of the. potentiometer and with the input terminahoffthe. switch. v s I *5. A weldingunit com-prising, current supply/ a. first ionizable tube having. a first anode,, a first grid and a first cathode,, ,with itsia'node connected to one wireiof the line andlits cathode: connected to one terminal-of the load, as other terminalfof; the loadheing:

connected to, the other 'wire' of. the: supply,=a second ionizable tube. havingra.secondfanodaa second ltgrid and a second cathode. with. a-resistor in series withsthe tubqi the second anode beingconnected. withthe first anode,

and" the otherwise free end..of the.-resistor connected-to. 1

said other line, means responsive to voltage cycling in the alternating currentsupply to furnish positive pulses.-

a. two-wire alternating;

an operator operated switch to apply said pulses simultaneously to said first and second grids, a bleeder shunting the resistor, a tap on said bleeder, a third ionizable tube having a third anode, a third grid and a third cathode with the third anode connected to the terminal of the switch nearest the first and second grids and with the third grid connected to the tap on the bleeder, a rectifier having its positive end connected to the other terminal of said switch, an adjustable resistor, conductors connecting 6 the positive end of the rectifier via the adjustable resistor to the third cathode to apply a positive potential thereto, and a. potentiometer between the third cathode and the other wire of the supply.

References Cited in the file of this patent UNITED STATES PATENTS