Today’s VFDs perform far more than just traditional motor controls. Some include computing, I/O handling, and even motion-control capabilities. Such intelligent drives excel in smaller and localized systems.
Case in point from material handling: Some VFDs with onboard PLCs work for motion control on infeed conveyors. In one specific case, a photoeye and tower light wired locally into the VFD I/O provide operator data and response. When the conveyor is empty and idle, the motor is stopped — and the tower light illuminates to prompt operators to load the conveyor.
When operators place product totes on the conveyor, the photoeye detects the totes and triggers the conveyor to start. Then the conveyor runs to transport totes according to a preset routine. After the cycle is complete (and no new totes are sensed) the conveyor stops. This minimizes energy consumption and system wear.
Such localized automation can be easier to setup and troubleshoot than those employing centralized controls integrated into larger systems.
Consider another process application for irrigation. Smart VFDs here can perform all local start, stop, level and pressure control using onboard logic. In this case, controls onboard the VFD can operate a pump with an alternating on and off time — and use local I/O to stop pumping when the supply tank runs low. Precise control over pump speed maintains ideal system pressure. What’s more, because a VFD is already necessary for the application, any additional control functionality is has with no additional hardware. Such a VFD might also have IoT connectivity to trigger alarms if system limits are exceeded. There are caveats: A larger water treatment skid is likely to need a standalone PLC, even if there are one or more VFDs onboard capable of executing controls. That’s because more complex applications have higher I/O counts to accommodate the signal monitoring and control of valves, level sensors, and chemical injection devices.
Technical information provided by Jeff Payne — drives and motors group product manager at AutomationDirect.
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