Application

Sequence of Operation
Fail Mode Operation
38
Siemens Industry, Inc.
BACnet LCM-OAVS, Application 6754
140-1325
2015-07-07
Fume Hood Flow – If MINHOODVOLTS is 1 Volt or higher, HOOD VOL will fail when
the LCM receives an invalid (less than .4 Vdc) fume hood flow signal or when the fume
hood controller (FHC) loses power or when it loses its flow sensor. 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. 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.
If MINHOODVOLTS is set to a value less than 1 (including 0), the fail voltage sensing
at .4 Vdc as described above is disabled. However, if there is a break (open circuit) in
the wiring, both the AI 3 point and HOOD VOL point will indicate failure.
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.
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.