Application

Sequence of Operation
Fail Mode Operation
39
Siemens Industry, Inc.
Application Note, App 2928
140-1302
2015-07-07
The first seven values of AVS FAILMODE (0 through 6) describe specific actions taken
when an AVS fails. For example, if AVS FAILMODE equals
5, then whenever an AVS
fails, the supply Venturi Air Valve will always close and the general exhaust Venturi Air
Valve will always open.
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 Venturi Air Valve will hold. The general
exhaust Venturi Air Valve 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 Venturi Air Valve 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 Venturi Air Valve will open if the room is being
positively pressurized and close if the room is neutral or negatively pressurized. The
general exhaust Venturi Air Valvewill hold if a fume hood is present. If a fume hood is
absent, the general exhaust Venturi Air Valve 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 .