A skilled welder may produce quality welds with a desired weld penetration depth based on his/her observation on weld pool surface. In a recent study the authors found that the arc voltage change during the peak current period in pulsed gas metal arc welding is a relevant measurement of the weld pool surface that can estimate the penetration depth. A system is thus developed to measure the arc voltage and control its change as output using the base current period as input and the necessity to use relatively complex sensors such as imaging systems is avoided. Analysis shows that the resultant process being controlled is time-varying, noisy, and nonlinear. After simplification into a linear system, an adaptive interval model control system has been designed. Experimental results confirmed the effectiveness of the adaptive interval model control algorithm and the developed control system. (C) 2011 Elsevier Ltd. All rights reserved.