Application

Sequence of Operation
Application Notes
27
Siemens Industry, Inc.
Application Note, App 2927
140-1311
2015-07-07
Fume Hood Flow – If the LCM receives an invalid (less than 1 Vdc) fume hood flow
signal, or the fume hood controller (FHC) loses power or loses its flow sensor, HOOD
VOL will fail. If HOOD VOL fails and if VOL DIF STPT is greater than or equal to 0
(negative or neutral pressurization required), the supply and exhaust loops assume a
hood exhaust value of 0 cfm and continue to maintain user-defined pressurization. If
HOOD VOL fails and VOL DIF STPT is less than 0 (positive pressurization required),
the supply and exhaust loops assume the hood's exhaust value is equal to MAX
HOOD VOL and continue to maintain user-defined pressurization. When the LCM is
being used with fume hoods, and MAX HOOD VOL is set above its default of 0 cfm, a
failure of HOOD VOL causes TOTL EXHAUST and VOL DIFFRNC to fail in succession
(see figure). When VOL DIFFRNC fails, the pressurization alarm point, VOL DIF ALM,
turns on automatically. If any of these points have been defined as alarmable and
unbundled at the field panel, an alarm will be annunciated across the network.
NOTE:
If desired, the LCM can be used without any fume hoods attached. In this case, MAX
HOOD VOL should be set to 0 cfm to disable the alarming that would occur if the
fume hood flow input drops below 1 Vdc.
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.
Discharge Temperature Sensor – Temperature control is lost and BTU calculations
cease if the discharge temperature analog input point, DISCH TEMP fails. This is
because the temperature loop stops updating and the discharge loop stops operating.