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PLC wall switches and dimmers are specific form factors of what we will call "actuators." PLC-controlled electrical outlets are also an important HA actuator. Like wall switches, these devices include one PLM-1 IC, are unidirectional (receive-only) or bidirectional, are designed for 120V or 240V operation, etc.
The same basic outlet-controller may be packaged differently and becomes a plug-in PLC controller. This device plugs into standard electrical outlets along with the controlled load. A lighting-control PLC relay (installed inside a fixture or ceiling junction box) is yet another example of the same basic product re-packaged in a different form. For commercial/industrial remote control, an eight-relay output-control module might be designed and installed inside lighting control panels. Etc.
Actuators are, generally, simple devices and include a small amount of intelligence. As the basic components of HA and industrial/commercial PLC control, actuators must be low-cost. Unlike other popular PLC products, PLM-1 actuators may include analog functions. For example, line-voltage communicating thermostats use PLM-1 to convey set-point and actual room temperature information.
We define actuators as simple analog and/or digital output modules. Lighting control actuators (switches, dimmers, etc.) and general purpose actuators (relays, plug-in modules, etc.) do not include time clocks-though an essential function in lighting control-nor any complete TCP/IP stacks and modems for internet access. Yet, we want the lighting functions of a given HA system to be remotely accessed, controlled, and programmed through the Internet. Thus, actuators are generally designed as simple and low cost devices. They execute PLC commands transmitted by one or many intelligent controllers.
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