Programmable Logic Controllers (PLCs) are computer control systems with numerous inputs that allow you to monitor and control different final elements from one device. PLCs often have both digital and analog inputs that allow the user to connect either transmitters or switches, and must be programmed by the user to determine the end response of each input.
Now, with companies investing more into process efficiency and optimization, we are seeing companies using VFDs to control their application. VFDs are most commonly used within motor driven systems. The biggest difference between PLCs and VFDs is that VFDs have the ability to control the speed of a motor they are connected to, while PLCs simply send an on or off signal. As an example, you could run your motor at a low speed when around 5mA then keep increasing motor speed as the mA reading rises.
While controlling motor speed, you can increase system efficiency by optimizing speed to the exact level required by your application. This can also reduce wasted energy caused from running a motor at only either full strength or off. Besides the analog input, VFDs also include digital inputs that allow such abilities as stopping, starting, and reversing the motor. Some of the more common applications for VFDs include controlling the speed of fans, pumps, and compressors.
