Years ago, as PLCs became smarter and more powerful, there was a push to get PLCs to perform basic PID control. Shortly after, some manufacturers developed units that functioned as a PLC but also had the ability to perform eight PID control loops. In the early 1980s, this was pretty exciting stuff.
Since then, modern PLCs have become extremely powerful. Because of advances in technology, many customers want to know whether a PLC or a stand-alone temperature controller is the right choice for a process. At the same time, many processors say they are reluctant to employ PLCs to control a new process, and some say they would never use a PLC for temperature control. Common reasons for these decisions include cost as well as ease of use, adjustment and troubleshooting.