Application

Sequence of Operation
Electric Heat Interlock
10
Siemens Industry, Inc. Application Note, App 2032 140-1022
2015-08-07
Electric Heat Interlock
Terminal unit heat stages
The electric heat stages will be enabled as long as FLOW > EHEAT FLOW. The
electric heat stages will not be disabled (turned OFF) until FLOW < EHEAT FLOW -
5%. Once disabled, FLOW must become greater than EHEAT FLOW before the
electric heat stages will return to normal control.
CAUTION
Do not set EHEAT FLOW to less than 5%; otherwise, the electric heat interlock will be
disabled.
Calibration
Calibration of the controller’s internal air velocity sensor(s) is periodically required to
maintain accurate air velocity readings. CAL SETUP is set with the desired calibration
option during controller startup.
Depending on the value of CAL SETUP, calibration may be set to take place
automatically or manually. If CAL AIR = YES, calibration is in progress.
 For a controller used without an Autozero Module (CAL MODULE = NO), the
damper is commanded closed to get a zero airflow reading during calibration.
 For a controller used with an Autozero Module (CAL MODULE = YES), calibration
occurs without closing the damper.
NOTE:
The first time after startup or initialization, the controller will calibrate the dampers as
if not using Autozero Modules, although the Autozero Modules will be activated. All
subsequent calibrations will use the Autozero Modules only.
At the end of a calibration sequence, CAL AIR automatically returns to NO. A status of
NO indicates that the controller is not in a calibration sequence.
Fail Mode Operation
If the air velocity sensor fails, the controller determines the status of FAIL MODE and
positions the damper accordingly. If FAIL MODE = OPEN and the velocity sensor fails,
the damper will open. If FAIL MODE = CLOSED (the default) and the velocity sensor
fails, the damper will close.
If the room temperature sensor fails, the controller holds the last known temperature
value.