In order to ensure the reliability and security of the system, prior to the design of the system it is important to make certain that the conditions in which it will be installed is well understood. Basically, the stresses on the PLC system (temperature, humidity, vibrations, shocks, corrosive gases, over current , noise etc.) need to be reduced as much as possible. However, the extent to which measures need to be taken in this regard will depend upon the likelihood of problems arising, the conditions in which the system is installed, and the cost of implementing measures. By taking advanced measures to prevent problems, the reliability of the system can be im-proved, and in the long-term the operation rate can also be increased. .