Main Page | See live article | Alphabetical index Fire suppression control system panel Modern computerized HVAC control systems are used for temperature, humidity, and pressure control, and often integrate fire, security, and lighting controls into one system. These systems typically use one or more central controllers to command and monitor the remote terminal unit controllers, and they communicate with one or more personal computers that are used as the operator interface. These control systems are typically used on large commercial and industrial buildings to allow central control of many HVAC units around the building(s). The latest systems use the building ethernet for communications between central controllers, and allow operator access from an Internet Web Browser. Direct Digital Control Central controllers and most terminal unit controllers are programmable, meaning the direct digital control program code may be customized for the intended use. The program features include time schedules, setpoints, controllers, logic, timers, and alarms. The unit controllers typically have analog or digital inputs, that allow measurement of the variable (temperature, humidity, or pressure) and analog or digital outputs for control of the medium (hot/cold water and/or steam). Digital inputs are typically contacts from a control device, and analog inputs are typically a voltage or current measurement from a variable (temperature, humidity, velocity, or pressure) sensing device. Digital outputs are typically relay contacts used to start and stop equipment, and analog outputs are typically voltage or current signals to control the movement of the medium (air/water/steam) control devices.(Valves/dampers/motor speed) This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.