Building automation systems control various systems within a building and use controllers, relays, and servers to do so. There are different control modes that a controller uses in order to communicate with these various devices. Binary control, floating control, sequence control, and proportional integral derivative (PID) loops.
Binary control is typically used to control devices that have two states, on or off. Depending on their state the output will provide voltage to a control device. The control device is usually used to operate a device like an actuator. With binary control a device is either on or off, it is never anywhere in between.
Floating control is similar to the above type of control but operates within the “grey” area or the in-between states of ON and OFF. This type of control requires a fast responding sensor and a slow-moving actuator. For example, if a setpoint for a water temperature sensor is 70 degrees and the setpoint is too cold at 68 degrees, the actuator slowly opens the hot water valve to heat up the water and closes once that setpoint is achieved.
This type of control uses logic to control various systems states. For example, an elevator uses logic based on a systems current state to react to a person's interaction, ie: button push, and how it handles that based on the current position of the elevator if the door is open...etc. There are two different types of sequencers, logical and physical.
Logical- these exist primarily in software. They look at data and depending on what the data says they turn ON or OFF BAS controllers.
Physical- physical sequencers are a physical control board that takes a signal and sends commands of ON and OFF. Typically the board consists of dip switches or potentiometers that allow adjustments of ON and OFF timers for each stage.
Proportional Integral Derivative Loops
PID loops are typically the main loops used to control the building automation system as a whole. They adjust the command sent to an output based on the difference between a setpoint and an input. For example, it measures the current temperature and the setpoint, it takes the difference and starts or stops an action depending on the desired outcome.