For process control it is necessary to construct robust feedback system against various disturbances. In CO arc welding process the top bead width is not suitable for feedback signal of the control system due to the melting electrode spreaded on the weldment.
We choose surface temperature on the weldment as the feedback signal and develop the nontactile infrared temperature sensor with the basic principle of optics. The sensor detects infrared emission from the point which has 0.8 mm of target diameter on the weldment and converts it to voltage signal. This has been calibrated with the practical situation of CO arc welding by using thermocouple at the same measuring point. The result to the calibration could be found the excellent characteristic of the high temperature. The range of measured temperature is 600 C-1200 C. Because of spatters, the practical welding process is very noizy so that the output signal of the sensor is processed through low pass filter which has the cut off frequency about 10 Hz.
The surface temperature of the weldment measured at three points, 7 mm, 9 mm and 11 mm, from seam line as changing one among three optimal input parameters.
Therefore, the relation of measured temperature and weld pool size was found from the result of experiment.
