Understanding High-Frequency EMI

(Electro-Magnetic Interference)

The primary source of EMI is radiation from your weld cables

As high-frequency sparks travel through weld cable, they dissipate energy as radio waves. The farther the sparks must travel, the more of their energy will be radiated.

Dissipation

Long cables convert HF sparks to radio noise

How serious is the HF EMI problem?

We can only tell you our experience, accrued over several years in a crowded shop working with Arc Pigs. Our experience includes early Pig prototypes that were too powerful to sell. Here is what we learned:

HF interference routinely disconnects USB computer peripherals, out to a distance of several feet.
EMI has never actually damaged any of our electronic devices (oscilloscopes, laptops, cell phones, voltmeters, cameras, clocks, radios, thermometers, and chip programmers) though we make no effort to protect them.
HF interferes with radio reception, especially AM radio, to a distance of several yards.
Under some circumstances, faint AM radio static can be discerned from 200 ft.

When you consider our experience, bear in mind that we use 8-ft output cables. Longer output cables will give more EMI (and weaker spark) and are usually pointless. To work farther from your welder, lengthen the cables between welder and Pig, and just drag the Pig around. It won't mind.

How can EMI be reduced?

Close to your torch

Reduces EMI

High-frequency EMI can be reduced by several means:

Shorter cables.
This also strengthens your HF spark, but until now it has required you to work close to your welder.

No more. The Arc Pig's revolutionary, cable-powered, 5-lb draggable body can be treated as a lump in your weld cables. Use 20-ft, 40-ft, or 2,000-ft weld cables and the HF spark will only pass through the last 8 feet.

Yeah, we know. Nobody uses 2,000-ft weld cables. But if you did, the Pig would still deliver full-power, rock & roll arc ignition and FCC-approved EMI.
Tie the cables closely together.
This low-cost measure can be used with any arc starter, and reduces the "loop area" of your HF broadcast antenna. Unfortunately it also increases cable capacitance, which reduces your spark voltage.
Ground nearby metallic objects.
This measure can also be used with any arc starter, though it is costly (especially at remote job sites) and has limited effectiveness.
Reduce the strength of the HF spark.
This is a popular option among old-style arc starters that fire continuously. Unfortunately, it reduces ignition power.

The Pig needs no "Spark Intensity" adjustment, because the Pig is intelligent and fires only as needed. If your arc is stable, the Pig does not fire at all. If your arc falters, the Pig fires at maximum power for only the time needed (typically 1-2 milliseconds) to re-ignite. Thus the Arc Pig achieves, with dramatic effect, the most powerful method of reducing EMI, which is:
Reduce the number of HF sparks.
Old-style arc starters typically feature two modes: Start Only and Continuous. In start-only mode, the HF stops when weld voltage falls below some fixed threshold (typically 50-60V) that opens a mechanical relay. In continuous mode, the HF fires whenever the trigger is pressed, or, if you did not buy a trigger, it fires all the time. This generates continuous EMI, but is necessary to prevent arc rectification, Arc rectification is extinction of half the AC cycle. (Usually the EP half.) or if your welder's voltage does not match the arc starter's threshold.

With an Arc Pig, you do not need continuous mode. In fact you do not need any modes, because the solid-state Pig is smarter and faster. It auto-adjusts to your weld voltage, and it responds to arc extinction fast enough to prevent rectification. Just press the trigger through the entire weld (the trigger is free, and you will like how it feels) and the Pig will fire only as needed. You may hear an occasional crackle as the Pig restarts your arc faster than you can see.