Creating real-time welding video is a significant challenge for any digital camera:
- Extreme brightness. A welding arc creates intense light that is a challenge for the sensor to handle.
- Huge dynamic range. The arc is the primary light source, and the rest of the scene is lit by arc reflections. The arc can be 10000 times brighter than the metal closest to the electrode. On top of this, metal only inches away can be another 1000 times darker than the metal below the arc, which makes this dim metal a total of 10,000,000 times darker than the arc. A useful welding image must preserve good contrast and detail over this enormous brightness range.
- Functional arc-off imaging. The same camera must also provide quality imagery without an arc to enable pre-weld setup and post-weld inspection. Room light illumination levels are only a tiny fraction of the arc brightness.
- Rapid intensity changes during welding. In some welding processes the arc itself changes brightness by more than 100 times in a fraction of a second. This creates challenges to appropriately scale the displayed image contrast.
To meet these challenges, the UDR camera uses a special sensor based on non-integrating pixels with a logarithmic response. This technology can nominally deliver up to 140 dB (10,000,000:1) of dynamic range including full arc light. Rapid arc intensity fluctuations are handled electronically while high performance electric iris is programmed to react to the arc. When the arc ignites, the system automatically closes the iris to an aperture setting suitable for the arc light. Most cameras adjust the iris slowly, taking 1 or 2 seconds to reach a new level. In a welding camera this would create unusable imagery (all white or black) until the iris movement finished. To avoid this blind time we developed a custom iris system optimized for rapid computer-controlled movement. The custom iris system can be ordered to a pre-determined position in only 1/10th of a second, 10 times faster than standard iris movement. The interior of a Visible Welding UDR camera is shown below with the iris control circuits on the blue PCB on the near side of the black 10x zoom lens assembly. The sensor and image circuits are on the green PC boards partially visible behind the lens (left in the photo).
The entire package fits inside a protective case (shown below) with an air-cooled option for operation in a high temperature environment.