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Welding Monitor

for laser and arc welding

The S+K Welding Monitor (international Patent DE 33 39 182 / EU 0 160687) produces high definition images during laser and arc welding in unprecedented detail for:

  • quality control during remote-controlled welding (in hazardous areas, such as a nuclear installation),
  • the positioning of industrial welding robots, and
  • education and training.

Laser and Arc Welding Monitor

The monitor was developed by Schäfter+Kirchhoff for the visual control of laser and arc welding, where the light intensity is too high for conventional visualization and display systems. The remote monitoring of the welding process is also particularly important for inaccessible environments, such as underwater or when potentially hazardous or contaminated. By using highly flexible and reinforced fiber-optic cables, the full and sustained mobility of the robotic welder is guaranteed.

All aspects of the welding process are fully visualized on the monochrome monitor: the weld itself, the electrode, the molten weld hotspot, the solidifying weld path and the affected margin of the welded material. Even in laser welding, the shape of the ‘keyhole’ is clearly visible. The stark contrast between the high intensity of the arc (plasma) and the surrounding dark regions is so successfully corrected that the displayed image reveals more of the welding process than that observable to an experienced welder from behind smoked glass. The novel contrast correction uses adapted illumination from an intense IR radiation source, optical filters and a tuned sensitivity camera.

The monitor image is free of blooming or streaking artifacts. The high image quality of the weld monitor encourages its use in welding applications using expensive components, as well as providing a highly accessible medium for education and training.

Operation Principle

The majority of the radiation emitted during arc welding is in the ultraviolet and adjacent visible region of the spectrum, with much lower intensities in the red and infrared. These characteristics facilitate spectral selection of the light impinging onto the image sensor without restricting its dynamic range, inherent to the use of non-selectively attenuating gray filters, which would also weaken the detection of the low light yields from the areas adjacent to the arc and weld.

Spectral analyses of various welding processes identified an optimum range of low self-emission at 800–850 nm. By utilizing a strong illumination source within this spectral range, the optical contrast of the scene can be exploited by the relevant dynamic range of the video camera. The highest image quality across these diverse contrast extremes is captured for storage in an analog or digital archive, for subsequent evaluation of weld integrity or safety concerns.


The IR beam provided by the laser radiation source SK 1100 is guided through a highly flexible IR optical fiber, coiled onto a cable drum.

The IR beam head, for effective illumination of the welding area, is very compact (outer diameter 12 mm) and has already seen exemplary service in numerous welding applications, including pipe-welding repair in nuclear power facilities (with orbital heads for external and internal pipe welding).

A fully flexible reinforcement protects the optical fiber without constraining the mobility of the welder.

The compact video camera has a specially developed lens head of small diameter. Auxiliary control of aperture or focus is unnecessary and the internals are protected when the system is exposed to extremes in environment or heat.

The objective unit is fully equipped with a close-up lens, aperture adjustment and filters, all protected behind resilient safety glass. This protective glass shield, as well as that on the illumination head, must be changed regularly to ensure the consistent quality of the imaging.


  • Repair and maintenance in nuclear facilities (especially: pipe welding with inner or outer orbital heads)
  • Remote manipulation
  • Positioning of welding robots
  • Monitoring of precision welds
  • Micro-welding
  • (Underwater) welding of pressure vessels
  • Training of welding specialists
  • Welding and safety documentation

Laser Safety

The IR laser radiation source SK 1100 Welding Monitor, produced by Schäfter+Kirchhoff, is a Class 4 laser device in accordance with DIN VDE 0837 "Radiation safety of laser products" and IEC 825.

System Details

The overall system consists of:

  • IR camera head with capture lens
  • Camera cables
  • Camera control unit
  • 9" video monitor
  • IR laser light source SK 1100
  • IR illumination head
  • Optical fiber: reinforced, standard 30 meters on a cable drum (longer lengths according to customer requirements)
Schäfter + Kirchhoff GmbH - specialists for optical sensors and measurement technology
Kieler Str. 212, D-22525 Hamburg, Tel. +49(0)40 85 39 97-0, Fax +49(0)40 85 39 97-79