Abstract: A band-ratio radiometer is disclosed which makes use of either a bifurcated or trifurcated fiber optic bundle, over two branches of which the sample radiation is transmitted in different wavelength regions. The third branch may be used to provide illumination of the target area, for aiming purposes, by injecting light at the near end of this branch. By this means, the remote ends of all three bundles may be focussed precisely upon the target area, with no parallax problem. The system avoids the use of conventional optical filters by making use of detectors which are identical in wavelength sensitivity and optical fibers which differ in wavelength transmittance.

Abstract: Control of spot weld quality is effected by observing the progress of heat generation within the weld and initiating automatic corrective action if the heating rate is initially too high or too low. A flexible optical fiber bundle has one end located in the welding tip and the other end optically coupled to an infrared detector. Due to the excellent thermal conductivity of the copper material of the welding tip, thermal energy is conducted very rapidly for a short distance into the tip during the weld formation so that the infrared detector produces an output signal proportional to the weld temperature. This signal is sampled and compared with a previously-recorded signal corresponding to the heating rate that produced a good spot weld in the material being welded.