Application

Sequence of Operation

Fail Mode Operation

Siemens Industry, Inc.

Application Note, App 2927

140-1311

2015-07-07

The last two values of AVS FAILMODE do not describe specific actions; that is, when

an AVS fails, the supply and general exhaust will react differently depending on the

circumstances.

If AVS FAILMODE equals

7, the supply Damper will hold. The general exhaust

Damper will also hold if a fume hood is present (that is, if MAX HOOD VOL > 0). If a

fume hood is absent, then the general exhaust Damper will close if the room is being

positively pressurized and open if the room is neutral or negatively pressurized (that is

if VOL DIF STPT is equal to or greater than 0).

If AVS FAILMODE equals

8, the supply Damper will open if the room is being positively

pressurized and close if the room is neutral or negatively pressurized. The general

exhaust Damperwill hold if a fume hood is present. If a fume hood is absent, the

general exhaust Damper will close if the room is being positively pressurized and open

if the room is neutral or negatively pressurized.

NOTE:

If AVS FAILMODE is set greater than 8, it will default to 0.

Fail Mode Operation

If one of the controller’s accessories (inputs) fails, a failure mode sequence is initiated

that leads to the failure of VOL DIFFRNC. The following figure shows the order in

which points will fail.

* 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.