VFD with PLC for motor controls

The two most important emerging technologies associated with motor control are variable frequency drives & programmable logic controllers. VFDs allow motor driven loads to operate within a wide range of speeds. Con trolling motor speeds to load requirements can increase both the efficiency & performance of a motor installation. A programmable logic controller (PLC) is a type of computer commonly used in motor control applications. The traditional motor control circuit is hard-wired while PLC control is program-based. This section deals with the unique installation requirements of these electronic control systems.

The primary function of any electronic VFD is to control the speed, torque, acceleration, deceleration, & direction of rotation of a machine. Unlike constant speed systems, the VFD permits the selection of an infinite number of speeds within its operating range.

The use of VFDs in pump & fan systems can greatly increase their efficiency. Outdated technology most often used throttles or dampers to interrupt the flow as a means to control it. The fluid or air was held back by the throttle or damper but the energy used to move the fluid or air was then dissipated uselessly. That wasted energy was still accounted for & paid for. Running a system this way is like driving a car with the accelerator pressed to the floor while con trolling speed with the brake. An electronic VFD, on the other hand, allows precise control of motor output. In the case of centrifugal fans & pumps, there is a significant savings in the power required to handle the load.