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
Average Face Velocity Control
8
Siemens Industry, Inc. Application Note, Apps 2941/2942 140-1319
Restricted 2015-11-04
Sequence of Operation
The following paragraphs present the sequence of operation for Fume Hood Controller
Application 2941 and Application 2942: Vertical Sash Configuration Fume Hood with
Damper or Venturi Air Valve.
Average Face Velocity Control
In face velocity mode, the Fume Hood Controller maintains the average face velocity at
the face velocity setpoint, FVEL STPT. This is accomplished as follows:
The controller uses the following points to calculate the open area of the Fume Hood:
VERT WIDTH1 VSASH HGHT1
TRACK HEIGHT VERT WIDTH2
VSASH HGHT2 BYPASS HGHT
BYPASS OPEN FACE AREA
VERT SASH1 VERT SASH2
FAIL AREA EXTERNAL A
FIXED AREA
The calculated face area is then stored in FACE AREA.
EXTERNAL FACE AREA – The controller allows an external face area to be included
in the final FACE AREA calculation. Optionally, EXTERNAL A is inputted from AI3 and
is scaled using MAX EXT AREA and MIN EXTVOLTS.
EXH STPT – The controller calculates the exhaust airflow volume setpoint, EXH STPT,
that is required to reach the face velocity setpoint, FVEL STPT, by using the following
equation:
EXH STPT = FACE AREA × FVEL STPT
Using a Proportional, Integral, and Derivative (PID) control algorithm, the controller
modulates the exhaust flow control device to adjust the actual exhaust flow so that
FVEL STPT is reached.
FVEL STPT – The controller uses the following points to determine the face velocity
setpoint: OCC DELAY, OCC.UNOCC, OCC FV STPT, and UNOCC FV STPT.
OCC.UNOCC is controlled by the DI. When it is in OCC mode, the face velocity is
controlled to OCC FV STPT; when it is in UNOCC mode, the face velocity is controlled
to UNOCC FV SET. When changing from OCC to UNOCC mode, the controller must
wait for the time specified in OCC DELAY to elapse before the face velocity is set to
UNOCC FV STPT.
ODP Face Velocity Setpoint Control – Additional face velocity setpoints can be
assigned to the lower middle buttons on the ODP.
If Table Access points OCC LOW FV and OCC HIGH FV equal 100 (default), no
control is assigned to the ODP buttons.
The left button will lower the face velocity setpoint from high to medium or medium to
low. The right button will raise the face velocity setpoint from low to medium or medium
to high. The new face velocity will display for 2 seconds.