VFDs have become so inexpensive that they are replacing __________ for many constant-speed applications.

Variable Frequency Drives (VFDs) are widely used in industrial applications to control the speed and torque of electric motors during operation. One of the main advantages of VFDs is their ability to provide variable speed control, which makes them highly versatile compared to traditional motor control methods.

In many constant-speed applications, VFDs have started replacing magnetic motor starters due to their cost-effectiveness and additional functionalities. While magnetic motor starters are effective for starting and stopping motors at a constant speed, they do not offer the same flexibility in speed control that VFDs provide. VFDs can adjust the speed of a motor to match the requirements of the application, which can lead to energy savings and improved process efficiency.

The other options, such as servo motors, relay switches, and resistive loads, serve different purposes or operate under different principles. Servo motors, for instance, are used for precise control of position and speed, which is not typically a feature in constant-speed applications. Relay switches are usually part of control circuits, and while they can be used to turn motors on and off, they do not directly influence the motor speed like a VFD. Resistive loads refer to devices that convert electrical energy into heat, which is a different application altogether.