What is a " Pilot arc" ??

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In a discussion about High frequency to stabalize the arc on a tig welder,  a friend said he would rather have a miller Pilot arc as High frequency can disturb electronic stuff in the shop....can anyone tell me what he is talking about ( needless to say i am quite new to tig)'thanksjoeLongevity LS 160 P tig/Plasma comboLincoln AC/DC 225 TombstoneMiller 170 Mig (shared with neighbor)"Life is like Ice cream...Enjoy it or it melts away" joebiplane
Reply:I don't know a thing about Pilot Arc. My Syncrowave 250 uses HF and this is my story.   A buddy wanted to fix his alum prop and wanted to try my TIG. While he was welding, I went in the house. The sprinkler system solenoids were going knutz, hammering away. Now, there is a post-it over the switch on the welder, Unplug the Sprinkler. Attached Images9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Originally Posted by Craig in DenverI don't know a thing about Pilot Arc. My Syncrowave 250 uses HF and this is my story.   A buddy wanted to fix his alum prop and wanted to try my TIG. While he was welding, I went in the house. The sprinkler system solenoids were going knutz, hammering away. Now, there is a post-it over the switch on the welder, Unplug the Sprinkler.
Reply:Duane:Maybe, but I had the circuit installed by a licensed electrician. The welder is on its own circuit from the box. The sprinkler clock is about 35' from the welder. He also drove a ground rod at the box, for this circuit. And he had that same drawing during the project (my owners manual). BTFOM (beats me). 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:He's probably talking about "touch start."  It doesn't do anything to help stabilize the arc when welding on AC though, because it shuts off after the arc is started.
Reply:No he means pilot arc. It's common on Plasma Arc Welding power supplies. It's a continious arc that stays lit even when no welding is being done. It helps initiate the plasma arc. I don't know how you could have it set up on a tig process. And if you could with a transformer machine it would only be good on DC since there is no zero voltage point. --Gol'
Reply:Originally Posted by Go1lumNo he means pilot arc. It's common on Plasma Arc Welding power supplies. It's a continious arc that stays lit even when no welding is being done. It helps initiate the plasma arc. I don't know how you could have it set up on a tig process.
Reply:you are probably right --Gol'
Reply:I think the pilot arc is a standard frequency, high voltage but extremely low amperage arc which the high current, low voltage is superposed on. It is probably AC so because of the lower frequency and loss of ionization during the zero voltage period, the voltage would need to be much higher. The HF on my welder doesn't bother anything in the house, but my Plasma cutter sets off the answering machine unless I disconnect the phone switch in the garage. As for that diagram about what is 'correct', .....it just aint always possible......Hell(o?), sometimes I can't even get five feet of clear space to work in! Forget the grounding of everything, the copper screen, etc.
Reply:Originally Posted by Go1lumNo he means pilot arc. It's common on Plasma Arc Welding power supplies. It's a continious arc that stays lit even when no welding is being done. It helps initiate the plasma arc. I don't know how you could have it set up on a tig process. And if you could with a transformer machine it would only be good on DC since there is no zero voltage point.
Reply:yes we used to use that on the ultima 150 we used at work it was argon pilot arc and 98/2 shielding gas for plasma welding of .008 stainless steel.
Reply:Originally Posted by Oldiron2I think the pilot arc is a standard frequency, high voltage but extremely low amperage arc which the high current, low voltage is superposed on. It is probably AC so because of the lower frequency and loss of ionization during the zero voltage period, the voltage would need to be much higher. The HF on my welder doesn't bother anything in the house, but my Plasma cutter sets off the answering machine unless I disconnect the phone switch in the garage. As for that diagram about what is 'correct', .....it just aint always possible......Hell(o?), sometimes I can't even get five feet of clear space to work in! Forget the grounding of everything, the copper screen, etc.
Reply:In plasma cutting...a pilot arc is an arc that is sustained (in the air) without transferring to the metal that is destined to be cut. As soon as this "pilot arc" gets close to the workpiece...which is connected via a work clamp (to the positive output of the plasma power supply)...then the arc naturally transfers to the workpiece.Over the years....and with different technologies and different manufacturers...this pilot arc was initiated and sustained using different methods. In all cases....a plasma cutting pilot arc is developed between the torch electrode (negative) and the torch nozzle (positive)....this arc is sustained between negative and positive by first ionizing (heating the plasma gas to a temperature where it becomes electrically conductive) the gas that is being used in the plasma torch....then passing this ionized , electrically conductive gas between the electrode and nozzle....which produces a limited current (limited by a pilot arc resistor or other means of limiting current flow) plasma arc....which is forced by the plasma gas flow to exit through the nozzle orifice. There are at least two methods of heating the gas to it's ionization temperature....The oldest method is by using a high voltage source such as a high frequency generator...(typically 15 killovolts at a high frequency) or a capacitive discharge circuit to create a high intensity spark between the electrode and nozzle....as the plasma gas (air.....or other gases depending on the design of the system) is forced to pass through this spark...energy in the form of heat transfers to the gas....and when the gas reaches its ionization temperature it becomes more conductive.....this conductive gas creates a short circuit between the electrode and nozzle....which superheats the gas forming a very hot plasma jet. The newer design.....which uses a moving nozzle or electrode withing the torch....eliminates the need for a high frequency generator. This design (Hypertherm's blowback electrode design as an example)..uses an electrode and nozzle that are electrically shorted.....DC (negative to the electrode and positive to the nozzle) is activated....and a few milliseconds later...plasma gas pressure arrives at the torch....this gas pressure forces the electrode to move away from the nozzle...releasing the short circuit...which causes a DC spark to ocurr. This spark takes the place of the high frequency discharge described above....and ionizes the gas....which forms a plasma jet.Some older technology plasma systems that use high frequency start....keep the high frequency active as long as the pilot arc is on.....more modern designs that use high frequency shut off the high frequency as soon as the gas ionizes....yet can maintain a pilot arc without high frequency by using the DC plasma arc to self sustain.The moving electrode design requires no high frequency.High frequency as used to start plasma systems and TIG systems can create electrical noise interference issues in sensitive electronic and computer controlled equipment. Sensitive equipment that is used around Plasma and TIG machines should be "industrially hardened" for use in these areas...meaning all inputs and outputs are filtered and optically isolated and all equipment is properly grounded.Hope this explains this a bit!Jim coltLast edited by jimcolt; 09-06-2008 at 07:04 PM.
Reply:There's only 3 ways to start an arc with TIG that I know of:1) High Frequency2) Lift arc/Touch start (same basic thing, Miller & Lincoln just have different names for it)3) Scratch start "Pilot arc" is a Plasma thing. Since you were talking about TIG, I would think he was referring to Miller's lift-arc. You just touch the tungsten to the work for a couple seconds and then lift. It's good to use if you ever have to weld near unshielded electronic equipment. Lift arc doesn't use HF, so in context what he said would make sense. He probably just got the name mixed up.Read pg. 15 here -> LINK-Matt------------------------------------------