Application
Sequence of Operation
Application Notes
38
Siemens Industry, Inc.
Application Note, App 6752
140-1322
2015-07-07
* If MAX HOOD VOL is set to 0, a “Failed” status of HOOD VOL will not initiate a failure
in TOTL EXHAUST or VOL DIFFRNC. See
Fume Hood Flow Input
.
Air Velocity Sensors – If one or both of the LCM air sensor signals (SUP AIR VOL,
GEX AIR VOL) are out of range (for example, improper wiring to/from the Offboard Air
Module(s), tubing not connected or connected backward), then the actions of the
supply and general exhaust Venturi Air Valves will depend on the value of AVS
FAILMODE. Once GEX AIR VOL and SUP AIR VOL are normal, the supply and
general exhaust Venturi Air Valves return to normal operation.
See
Operation of AVS FAILMODE
for more information.
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.
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 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.