The combination of PLCs with VFDs in industrial automation enables accurate and effective motor control.
There are five typical methods for controlling a Variable Frequency Drive (VFD) with a Programmable Logic Controller (PLC):
1). Digital I/O Control
2). Analog Signal Control
3). Communication Protocols
4). Pulse Train Input (PTI)
5). Embedded Function Blocks
1). Digital I/O Control
Basic control functions such as start, stop, forward/reverse, & fixed-speed selection should be implemented with discrete inputs and outputs. Suitable for simple systems.
2). Analog Signal Control
Send analog signals (e.g., 4-20mA or 0-10V) to precisely adjust the speed. When precise speed adjustment is required, this is an excellent option.
3). Communication Protocols
Use protocols like as Modbus, Ethernet/IP, (or) Profibus to communicate precise data between the PLC and VFD. This enables advanced diagnostics & multi-drive control.
4). Pulse Train Input (PTI)
Send a series of high-frequency pulses to the define speed; generally employed in high-precision applications such as positioning systems.
5). Embedded Function Blocks
Many current PLCs include pre-configured function blocks for controlling VFDs, which simplifies programming and setup.
Each approach has distinct advantages and is appropriate for a variety of applications. The decision is based on considerations such as system complexity, precision requirements, and cost.
Important Note: To ensure effective and dependable control, always configure and test the parameters between the PLC and the VFD.