What is a method used to control elevator speed and movement by varying strength?

The method used to control elevator speed and movement by varying strength is through hoist motor fields. This involves adjusting the field strength of the hoist motor, which directly affects the motor's torque and speed. When the field strength is varied, it allows for a more precise control of the elevator's ascent and descent, enabling smoother operation and better handling of different load conditions. This is particularly important for maintaining safety and efficiency in elevator systems.

Other options, while related to elevator technology, do not focus specifically on controlling speed and movement through strength variation. For example, dispatching elevators relates more to the scheduling and operations management of elevator systems rather than speed control. AC cycle reversal pertains to changing the direction of the motor but doesn't directly affect speed modulation. Finally, magnetic switch contact rating is important for the operation and safety of electrical circuits in elevators, but it is not a method for controlling speed itself.