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Fig. 5. Transfer occurring within 1/1000 sec.
tor under investigation occur in a timd interval represented by 1 or 2 frames This change would not be evident all normal projection speeds and occurs todf rapidly for analysis at 4000 frames/seal For these special cases, even higher speed) Would be desirable.
In most photographic studies it if often necessary to correlate the filnj* frames with recorded electrical measure ments such as oscillograms. Most highj speed cameras are or can be equippec with, a flashing argon lamp which form light impressions at the film edges a intervals of 1/120 sec. The correspond^ ing electrical impulse for each flash ma\ be used as a reference timing line on tht oscillograph. A preferable system is < newly developed double-lens camert whervein the oscillograph trace and the visual conditions occurring in the welding arc are recorded on a single frame simultaneously.
At the Laboratory with which the authors are associated, high-speed pictures have been taken on black-andwhite, infrared and indoor and outdoortype color film.
Black-and-white film does not differentiate between the various light frequencies emitted and consequently the resulting pictures are masked by the glare surrounding the arc.
Infrared film tends to overemphasize some aspects of the arc at the expense oi others and consequently does not give a true picture of the arc conditions. However, in the case of specialized investigations, this distortion of conditions may prove desirable because of the overemphasis that it produces.
Daylight-type color film is the film of choice for most investigations of the welding arc. Clear, definitive pictures of the metallic arc, tungsten arc and other welding operations have been taken with this film, without the use of filters.
Indoor-type color film may also be used; however, in this case appropriate filters are necessary for optimum results.
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April 1953 Journal of the SMPTE Vol. 60