Application

Sequence of Operation
Return from Power Failure and Venturi Air Valve Action
35
Siemens Industry, Inc.
Application Note, App 6750
140-1328
2015-07-07
Return from Power Failure and Venturi Air Valve
Action
NOTE:
In this section, the phrases Normally Closed and Direct Acting are interchangeable.
Likewise, the phrases Normally Opened and Reverse Acting are interchangeable.
You notify the application whether or not a Venturi Air Valve is normally opened or
normally closed is by setting the point VENTURI ACT to the value that represents the
actions of the air valves connected to the controller.
VENTURI ACT Values.
VENTURI ACT
(value)
Description
0
All Supply and Exhaust Venturi Valves are Normally Closed (Direct
Acting)
1
(default)
Supply Venturi Normally Closed, Exhaust Venturi Normally Opened
2
Supply Venturi Normally Opened, Exhaust Venturi Normally Closed
3
All Supply and Exhaust Venturi Valves are Normally Opened (Reverse
Acting)
NOTE:
If VENTURI ACT is set greater than 3, it will default to 0.
NOTE:
On a return from power failure, the AOs remain OFF for 5 seconds. Therefore, it is
recommended that the Supply Venturi Air Valve be Normally Closed for rooms where
negative or neutral pressurization is required, and Normally Opened for positively
pressurized rooms. Likewise, it is recommended that the General Exhaust Venturi Air
Valve be Normally Opened for rooms where negative or neutral pressurization is
required, and Normally Closed for positively pressurized rooms. Setting of the Venturi
direction is via VENTURI ACT.
Operation of AVS FAILMODE
AVS FAILMODE is an enumerated point that describes how the supply Venturi Air
Valve and the general exhaust Venturi Air Valve will respond if one or both Air Velocity
Sensors (AVS) fail. It can handle both positively pressurized rooms and negatively
pressurized rooms.
The default value of AVS FAILMODE is
0. This default causes both the supply and
general exhaust to hold their current position when an AVS fails. Open Supply, Open
Exhaust and Close Supply, Close Exhaust are not defined AVS FAILMODE states.