Application

Sequence of Operation

Fail Mode Operation

Siemens Industry, Inc.

Application Note, Application 6759

140-1335

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 Dampers will depend on the value of AVS FAILMODE.

Once GEX AIR VOL and SUP AIR VOL are normal, the supply and general exhaust

Dampers return to normal operation.

See

Operation of AVS FAILMODE

for more information.

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.