The following Speed Control Equipment, five types of ASDs (Adjustable Speed Device) are available.
VFD
Electronic devices to control the speed of the motor by controlling the frequency of the voltage at the motor.
Direct current ASDs
Electronic devices to control direct-current motors by changing the voltage applied to the motor.
Eddy-current drives
Electrical devices that use an electro-magnetic coil on one side of coupling to induce a magnetic field across a gap, creating an adjustable coupling.
Hydraulic Drives
Devices that operate much like an automotive hydraulic transmission.
Mechanical speed-control
Mechanical speed-control products including gearing, mechanical transmissions, and belt drivers with variable-pitch pulleys can be used.