?the function and usefulness of the PLC can be said is almost unlimited. But in practice can be divided in general and specific. In general, the function of PLC are as follows: 1. Control Sequential PLC processing binary input signals into outputs that are used for the purposes of processing techniques sequentially (sequential), here the PLC to maintain that all the step / steps in a sequential process takes place in the proper sequence. 2. Plant Monitoring PLC continuously monitors a system (e.g. temperature, pressure, level of altitude) and take necessary action in connection with a controlled process (for example, already exceeds the limit value) or displays a message to the operators. Advantage of the PLC 1. Flexible 2. Having a lot of contact 3. Lower costs 4. Safe 5. It can be observed visually 6. Fast operating times 7. Relatively easy in terms of programming 8. High level of reliability and low maintenance 9. Easy to order components in terms of 10. The documentation was easy to do 11. Security in terms of programming 12. Adaptive to changes in production Disadvantage of the PLC 1. Because it is a new technology, so that should require training. 2. Some applications that perform a single function, is not efficient in the use of PLC. 3. Limited usage environments, high temperatures and harsh vibrations can disrupt electronic equipment on the PLC. 4. Need extra security equipment such as really. 5. PLC is not considered necessary when applied to industrial systems that do not need to change the wiring.