EMI restricts in automation of the process control industries. Here is a method of solving EMI problems by using a SMPS power supply and resonating it at high frequency. At the same time use of resonance mode SMPS helps by providing advantages of higher efficiency (95%), less heat dissipation, reliability of operation and compactness. This paper is the outcome during development and maintenance of microcontroller based process control instruments for Nalco, Orissa.