Lincoln Electric SVM118-A service manual Spot Controls, Pulse Controls, Start Controls

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B-8			OPERATION						B-8
	At Maximum, the arc will be more forceful and less			Press and hold in this pushbutton to display the
	prone to sticking but will produce more spatter.			Start Current preset by the Start Current control.
	12. PREFLOW			(The Volts/Amps switch (Item 7) must be in the
				“AMPS” position to read preset current.)
	This control adjusts the amount of time the gas			Start Current Control
	and water valves are open before the arc starts. It
	is adjustable from 0 to 10 seconds.			Locked out if the Start switch is off.
	The Preflow time occurs only if the valves were			Presets the current that will be provided at the
	closed (no gas flow) when the Arc Start switch or			start of the weld. The current can be preset from
	Amptrol was pressed.	If a new weld is started		2 to 400 amps. The position of the amptrol has no
	while the gas valve is still on during the Afterflow			effect on the initial		current.	The	present Start
	time of a previous weld, the Preflow time is			Current is displayed on the Ammeter when the
	bypassed since gas shielding is already present.			pushbutton is pressed before welding.
	This allows new welds to start immediately with no			A “hot” start is used to quickly heat the tungsten
	preflow delay.
				and work, usually on DC TIG welding. Set the
	Note that since the arc cannot start during the			Start Current higher than what the welding current
	Preflow time, a long Preflow setting can cause			will be. After the time is set on the Start Time con-
	complaints about arc	starting.	In general, a	trol, the current will step down to the current set
	Preflow time of 0.5 seconds is satisfactory for			and controlled by the Peak Current control (Item 6)
	most applications.			and the Amptrol.
	13. SPOT CONTROLS			A “soft” start is used to preheat the tungsten and
	Spot Switch — A two-position toggle switch:			work, usually on AC TIG welding.				Set the Start
				Current lower than what the welding current will
	Recommended for use in the 2-step Arc Start			be. The arc will establish at the Start Current and
	Switch mode only.			then ramp up to the current set and controlled by
	ON: Spot Time control is active. Once the arc is			the Peak Current control (Item 6) and the Amptrol.
				The time to get up to welding current is set by the
	established, the Spot time begins. At the end of
				Start Time	control.	During	the	ramp	up, the
	the Spot time (or if the Arc Start switch/Amptrol is
				Amptrol will	affect	the current that the			ramp is
	released sooner), the arc stops. (If Crater Fill [Item
				going toward and therefore the rate at which the
	16] is on, downslope begins.)
				current increases.
	OFF: Locks out the Spot Time control.			Start Time Control
	Spot Time Control: Not active if the Spot switch			Locked out if the Start switch is off. Adjusts the
	is off. Adjusts weld time from 0.1 to 5 seconds.
				Start Time from approximately 0.1 to 10 seconds.
	Weld time is the time from when the arc is fully
	established until the arc is turned off (or when			15. PULSE CONTROLS
	Crater Fill downslope is started).		The Arc Start	Pulse Switch — A two-position toggle switch:
	switch or Amptrol must be held down during the
	Spot time; if it is released before the end of the			ON: Pulsing will begin as soon as an arc is estab-
	Spot time, the arc will be turned off (or Crater Fill			lished and will continue until the weld is complet-
	started).			ed. If you are using Start Controls, pulsing begins
	14. START CONTROLS			after the Start Current. If you are using Crater Fill,
				pulsing will continue during the downslope period.
	Start Switch — A two-position toggle switch:			OFF: Locks out Pulse controls.
	ON: Start Current control is active. At the begin-			Pulses per Second Control — Controls the num-
	ning of the weld, current will be the value preset by
				ber of pulses per second from approximately 0.1
	the Start Current control. Th		position of the
				to 10 pps. 0.1 pulses per second is slow pulsing
	Amptrol has no effect on this current.
				(one pulse every 10 seconds); 10 pulses per sec-
	OFF: Locks out Start Current and Time controls.			ond is fast pulsing.
	Start Current Display Pushbutton			Background % Peak Current Control —
				Controls the background (low pulse) current from
				zero to 100% of the peak current set and con-
				trolled by the Peak Current control (Item 6) and the
				Amptrol.

SQUARE WAVE TIG 355