Hardware failures are inevitable but random events in the useful life of any batch chemical plant. If such incidents are not efficiently diagnosed, the consequences may be very serious and sometimes even catastrophic. The present study aims to develop a systematic procedure-synthesis strategy for generating the test plans that minimize the chance of misjudgements. By modelling the components in the given system with timed automata, all possible fault propagation scenarios and their observable event traces (OETs) can be enumerated. The test procedure for every OET can then be conjectured by designing a supervisory controller to achieve the highest level of diagnostic resolution. One example is provided to show the feasibility of the proposed approach.