There are several types of control devices, but two main types are:
Discrete control devices: These devices are used to control on/off, open/closed, or other binary states. They include switches, relays, and contactors.
Analog control devices: These devices are used to control continuous variables such as temperature, pressure, or position. They include valves, motor starters and adjustable speed drives.
Other types of control devices, such as smart devices, can be discrete or analog, have a microcontroller or microprocessor and can communicate over a network.