Application

Overview
Hardware Inputs
4
Siemens Industry, Inc. Application Note, Apps 2941/2942 140-1319
Restricted 2015-11-04
Overview
Application 2941 and Application 2942 are designed for use with a wide range of fume
hood sash configurations connected to a manifold fume hood exhaust system. The
sash configurations include:
 Bench style fume hoods – single vertical sash
 Dual Bench style fume hoods – side-by-side single vertical sash
 Floor Mounted style fume hoods – two vertical sashes, one on top of the other
WARNING
The application cannot detect a broken wire to the analog input for the second sash.
An external sash aggregating device should be used to calculate the face area for all
fume hoods with more than one sash.
This application uses sash position sensors and three face velocity setpoints to limit
the air entering the hood, each fume hood has an individual exhaust damper or valve
connected to a central fan and allows face velocity setpoint changes at the ODP.
An Autozero module automatically calibrates the flow input to the FHC. The application
incorporates special functionality that changes AO2 (hard-wired to room controller) to a
value that more closely matches the exact measured airflow rather than the setpoint.
This application also modulates the normally open exhaust damper/air valve based on
inputs from the vertical sash sensor(s), external face area input, an exhaust airflow
sensor and the controller setpoints.