Application

Sequence of Operation
Application Notes
26
Siemens Industry, Inc.
Application Note, App 6751
140-1331
2015-07-07
Laboratory Room Controller – If the LCM power fails, all actuators default to their user-
defined fail-safe states. Since there is no power to the controller, no LEDs are
available.
Electronic Actuator – If the actuator fails, typically, flow control is lost and alarms are
triggered.
Upon loss of power or control signal to the actuator, it will move to its fail-safe position.
Room Temperature Sensor – If the room temperature sensor fails while CTL TEMP is
not overridden or is not being adjusted by a field panel, then ROOM TEMP and CTL
TEMP both display as “Failed” and temperature control is suspended at the current
value of TEMP LOOPOUT. If ROOM TEMP is unbundled in a field panel and defined
as alarmable, an alarm will be annunciated across the network.
If the room temperature sensor fails while CTL TEMP is overridden or is being adjusted
by a field panel, then ROOM TEMP displays as “Failed”. CTL TEMP will continue to be
overridden or adjusted by the field panel and room temperature control proceeds as
normal. CTL TEMP will continue to have a status of NORMAL. If ROOM TEMP is
unbundled in a field panel and defined as alarmable, an alarm will be annunciated
across the network.
Room Temperature Setpoint Dial – If the room temperature setpoint dial fails while CTL
STPT is not overridden or is not being adjusted by a field panel, then ROOM STPT and
CTL STPT both display as “Failed” and the last known good value of ROOM STPT is
used to determine the current value of CTL STPT. The rest of the room temperature
PID loop is unaffected by the setpoint dial failure. If ROOM STPT is unbundled in a
field panel and defined as alarmable, an alarm will be annunciated across the network.
If the room temperature sensor fails while CTL STPT is overridden or is being adjusted
by a field panel, then ROOM STPT displays as “Failed”. CTL STPT will continue to be
overridden or adjusted by the field panel and room temperature control proceeds as
normal. CTL STPT will continue to have a status of NORMAL. If ROOM STPT is
unbundled in a field panel and defined as alarmable, an alarm will be annunciated
across the network.
Application Notes
Operating Without a General Exhaust Box
This application can operate without a general exhaust box. If a general exhaust box is
not being controlled, set TRACK METHOD to FLOW and set the following points:
 TRACK MODE to 0.
A value of 0 = STE (supply tracks exhaust) Flow Tracking, should be used for both
the occupied and unoccupied modes.
 GEX FLO COEF to 0.
When GEX FLO COEF equals 0, GEX AIR VOL will always read 0, but will never
show as Failed.
 OCC GEX MIN and UOC GEX MIN to 0.
If these two points are not set to 0, GEX AIR VOL— will read 0 since GEX FLO
COEF was set to 0—will be less than the general exhaust box minimum, resulting
in a false ventilation alarm.
The application varies the supply airflow as the fume hood flow changes, in order to
maintain the proper room pressurization. The supply airflow is not varied for cooling
purposes; all temperature control is done by the reheat valve.
Because of this, START should be set to 100 to allow the reheat valve to be controlled
by the full range of TEMP LOOPOUT and to prevent the room temperature PID Loop
from winding up.