Abstract: To solve the synchronizing problem between the fixed exposure schedule of the ordinary industrial CCD camera and the various state of welding arc during welding processes, a visual image sensor with controllable exposure was developed based on CPLD (complex programmable logic device)for arc welding.The novel sensor is composed of an ordinary industrial CCD camera, optical system, mechanical iris and an exposure controller.The exposure controller consists of the modules of detection of welding arc state detecting, exposure parameters presetting, logic control with CPLD and so on.The exposure schedule logics of different arc welding processes were described with very-high-speed integrated circuit hardware description language (VHDL) and programmed with a CPLD.Both CO₂ short circuiting transfer arc welding and pulsed gas tungsten arc welding were carried out, and the experimental results show that clear and consistent molten pool images can be acquired, and the disturbances of arc light and spatter are avoided.