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Arc welder noise coupling in robotic arm controller

Short answer

Source impedance is 0.1 Ω (low), so magnetic (inductive) coupling dominates: large di/dt in welder cables induces voltage V = M di/dt in controller loops. Radiated and conductive coupling also occur. Minimize by twisting welder cables, shielding the controller, using optical isolation, separating grounds, and increasing distance.

An arc welder on the end of the robotic arm generates noise interference in the local embedded controller. The welder produces 120A at 12V. What could be the coupling mechanism for noise interference? How this can be minimized?

The welder carries a very high current (120 A) at low voltage (12 V), so the source impedance is Z = V/I = 12/120 = 0.1 ohm, far below 377 ohm. This is a low-impedance, high-current source, so the main coupling is inductive (magnetic field) coupling: V = M·dI/dt, as the cables carrying the large and rapidly changing current create strong magnetic flux linking the controller's wires. Because arc welding produces sparks and broadband RF, radiated (EM) coupling and conductive coupling via common ground/power supply are also present.

Minimising

  • Keep the welder cables twisted/coaxial (go and return together) to reduce the loop area, and route them away from controller wiring.
  • Use shielded, twisted-pair cables for the controller signals, with a magnetic shield (steel conduit) where needed.
  • Put the controller in a grounded metal enclosure; filter all its inputs/outputs and power lines (LC filters, ferrite beads, TVS).
  • Use optical isolation or fibre-optic links to the controller's I/O.
  • Separate the welder supply and controller supply; single-point ground with a proper star arrangement.
  • Increase distance, and cross cables at right angles.

✓ Answer checked by Claude Sonnet 5.5

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