Abstract A digital control system for distributed temperature control in a catalytic chemical reactor producing hydrogen is required. The system uses a 6809-based S/09 microcomputer from Southwest Technical Products Corp. The paper first overviews the reaction process, the reactor and its modelling, and then discusses the microcomputer and data acquisition system. The implementations of power control and energy requirement calculation are presented before a summary of the complete control algorithm; a listing of the control algorithm is supplied as an appendix. The final modified PID control algorithm adopted shows significant improvements in temperature adjustment time when compared to manual and open loop control methods.