LX Series Unit Ventilator Controller User's Guide 55
Emergency Initiation
Emergency modes are initiated by:
• Setting nviEmergCmd to EMERGE_PURGE or EMERG_SHUTDOWN.
• Closing the emergency contact wired to the emergency input.
The network variable nviEmergCmd has priority over the emergency contact. The
network variable nviEmergCmd is a SNVT_hvac_emerg (103) type. Invalid value
is EMERG_NUL.
The emergency contact input can be configured as emergency purge or emergency
shutdown on the General Settings screen of the UV configuration wizard.
Otherwise, you can modify UCPTobjectOptions:
• Setting bit 54 to 0 selects emergency purge.
• Setting bit 54 to 1 selects emergency shutdown.
Normal Operation
When there is no emergency and operations are normal, nviEmergCmd is set to
EMERG_NORMAL.
The PID Loop
Proportional plus Integral plus Differential (PID) loops provide precise control
over space temperature and ventilation.
The control loop modulates its output to drive its input to a setpoint. The control
loop inputs are the sensor readings of the temperature. For example, the outputs
can be the fan speeds and the heating or cooling outputs.
The difference between the input and the setpoint is called the error. The controller
output is a function of the error.
Controller
SpaceSensor Output
Input
Output
Setpoint
Figure 20: PID Controller with Input, Setpoint, and Output
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