Application

Sequence of Operation
Table Access Feature (Mode 1, 3)
22
Siemens Industry, Inc.
BACnet LCM-OAVS, App 2924
140-1304
2015-07-07
Venturi Airflow @ 350 fpm.
Valve Size in
Inches
cfm
5
48
6
69
8
122
10
191
12
275
Dual 10
380
Dual 12
550
Triple 12
825
During calibration, voltage/flow values are automatically generated. Typically there are
8 or 9 pairs. The first pair of voltage/flow values—the low flow point—is not generated;
it must be set manually. The Venturi Valve actuator is then fed the voltages and the
application reads the resulting airflows. At the end of calibration, the airflow readings
are analyzed and the calibration is either given a PASS or a FAIL (GEX VLV STAT is
set to CAL OK or NOTCAL). To obtain a CAL OK, the airflow readings must increment
correctly (the points in the table increase as the voltage increases). For example, if one
point on the voltage/flow curve shows 5V and 500 cfm and the next point shows 6V
and 450 cfm, the second point (6V, 450 cfm) would fail. But 6V at 550 cfm would pass.
(This example assumes the actuator is direct acting, where more volts equal more
flow. Exhaust devices are usually reverse acting and have an inverse voltage/flow
relationship.) Too many failed airflow points along the voltage/flow curve will result in a
NOTCAL status for the calibration.
This application has a table statement edit feature that allows you to view and edit the
voltage/flow values in the table. This is useful for fine tuning the air valve to meet
precise room flow setpoints and for diagnosing/editing problematic voltage/flow curves
(see the Table
Venturi Air Valve Table Statement ).
Problematic Venturi Air Valve Voltage/Flow Curves.
NOTE:
Bouncy flow means that airflow through the air valve’s flow orifice is too turbulent to
be read consistently.