Application
Table Of Contents
- Overview
- Sequence of Operation
- Average Face Velocity Control
- AVS Calibration
- AO2 Flow Signal
- Control Loop - Damper Application
- Venturi Application
- Minimum Exhaust Mode
- Maximum Exhaust Mode
- Warning Limits
- Alarm Limits
- Alarm Output
- Horn Disable
- Sash Area Alarms
- Table Access Feature
- Emergency Mode
- Start-up/Decommission Mode
- Fail Mode
- Wiring Diagrams
- Point Database Application 2941
- Point Database Application 2942
- Point Database Application 2900
Sequence of Operation
AVS Calibration
9
Siemens Industry, Inc. Application Note, Apps 2941/2942 140-1319
Restricted 2015-11-04
If the face velocity setpoint is overridden by the system or the controller is in
Emergency/General Failure this function does not work. The controller will remember
the current occupied face velocity setpoint even after changing from unoccupied back
to occupied.
Air Velocity Sensing
Primary sensing of the exhaust airflow is through the OAVS. Optionally, AI3 may be
used to input a Differential pressure transmitter or a Linear Flow input signal. Using AI3
for this purpose will prevent you from using the external face area functionality.
AVS Calibration
When using an OAVS sensor the following applies.
Calibration of the air velocity transducer(s) is periodically required to maintain accurate
air velocity readings. Depending on the value of CAL SETUP, calibration takes place
either at fixed time intervals or whenever the application goes into unoccupied mode.
When calibration is in progress, CAL AIR equals YES. After calibration, CAL AIR
returns to NO.
The application uses Autozero Modules connected to AUTOZERO DO8. This means
that the exhaust flow control device does not close during calibration of the
transducers.
NOTE:
The FHC does not monitor Fume Hood flow changes for 3 seconds during AVS
calibration.
AO2 Flow Signal
An analog signal of the exhaust flow is available at AO2 of the controller board and is
displayed at EXH SIG AO2. To get an output from EXH SIG AO2, you must command
AO2 RANGE to the maximum expected flow for the fume hood. Then AO2 is scaled
such that 1 Vdc is equal to 0 cfm, and 10 Vdc is equal to AO2 RANGE. If the output
drops below 1 Vdc, this indicates a GENERAL FAILURE or loss of power.
EXH SIG AO2 = (EXH VOL/AO2 RANGE x 9 volts) + 1 volt
AO2 V MIN allows the minimum AO2 output voltage to be modified.
NOTE:
If the AO2 V MIN is set to 0, failure detection is lost.
The value of AO2 is determined by the following conditions:
Operating Condition
AO2 FLOW SIG Value
Normal/warning condition inside the range of
AO2 DEADBAND
EXH STPT
Normal/warning condition outside the range of
AO2 DEADBAND
EXH VOL
Alarm and emergency condition