Topography (I/O)
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The primary/secondary bus can be fiber optic, Ethernet, Arcnet, RS232, RS485, wireless, depending on the system.
Most controllers are proprietary. Each company has their own controllers which meet specific applications. Some are designed with limited control, example: Package Roof Top Unit. Others are designed to be flexible. Most have a proprietary software that will work with Bacnet, Lontalk and Ashrae standards.
Inputs and outputs are either analog of digital (some companies say binary).
Analog inputs are used to read a variable measurement. Examples are temperature, humidity and pressure sensors which could be thermistors, 4-20MA, 0-10V or Platinum RTD (resistance temperature detector), or wireless sensors which usually have an IP address.
A digital input indicates if a device is turned on or not. Some examples of a digital input would be a 24VDC relay or air flow switch.
Analog outputs control the speed or position of a device, such as a variable frequency drive, a pneumatic I-P transducer, or an actuator. An example is a hot water valve opening up 25% to maintain a setpoint.
Digital outputs are used to open and close relays and switches. An example would be to turn on the parking lot lights when a photocell indicates it is dark outside.
