There are many other types of actuators including those on the brief list below.
Heaters - The are often controlled with a relay and turned on and off to maintain a temperature within a range.
Lights - Lights are used on almost all machines to indicate the machine state and provide feedback to the operator. most lights are low current and are connected directly to the PLC.
Sirens/Horns - Sirens or horns can be useful for unattended or dangerous machines to make conditions well known. These can often be connected directly to the PLC.
Computers - some computer based devices may use TTL 0/5V logic levels to trigger actions. Generally these are prone to electrical noise and should be avoided if possible.
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