Today the VFD could very well be the most common type of result or load for a control system. As applications are more complicated the VFD has the capacity to control the rate of the electric motor, the direction the engine shaft is definitely turning, the torque the electric motor provides to lots and any other engine parameter which can be sensed. These VFDs are also available in smaller sizes that are price-effective and take up less space.
The arrival of advanced microprocessors has allowed the VFD works as an extremely versatile device that not only controls the speed of the motor, but protects against overcurrent during ramp-up and ramp-down conditions. Newer VFDs provide ways of braking, power improve during ramp-up, and a variety of handles during ramp-down. The largest financial savings that the VFD provides is that it can ensure that the electric motor doesn’t pull excessive current when it begins, therefore the overall demand factor for the entire factory can be managed to keep the utility bill as low as possible. This feature by itself can provide payback in excess of the price of the VFD in less than one year after purchase. It is essential to keep in mind that with a traditional motor starter, they’ll draw locked-rotor amperage (LRA) if they are starting. When the locked-rotor amperage takes place across many motors in a manufacturing plant, it pushes the electric demand as well high which often results in the plant paying a penalty for all of the electricity consumed through the billing period. Since the penalty may be just as much as 15% to 25%, the savings on a $30,000/month electric expenses can be utilized to justify the buy VFDs for practically every electric motor in the plant even if the application might not require operating at variable speed.
This usually limited the size of 
the motor that may be managed by a frequency and they were not commonly used. The earliest VFDs used linear amplifiers to control all areas of the VFD. Jumpers and dip switches were used provide ramp-up (acceleration) and ramp-down (deceleration) features by switching larger or smaller resistors into circuits with capacitors to make different slopes.
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