Application

Sequence of Operation
Venturi Table Evaluation and Editing (Mode 1, 3)
18
Siemens Industry, Inc.
Application Note, App 6750
140-1328
2015-07-07
Venturi Airflow @ 350 fpm.
Valve Size in
Inches
cfm
10
191
12
275
Dual 10
380
Dual 12
550
Triple 12
825
During calibration, up to 15 voltage/flow values are automatically generated (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, or the SUP VLV
STAT is set to PASS or FAIL). To obtain a PASS, at least 12 of 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 FAIL 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.
Venturi Table Evaluation and Editing (Mode 1, 3)
A Venturi Air Valve table statement consists of two sets of voltage/flow values—one
set is active and the other inactive. When you run the calibration, the first thing that
happens is that the inactive table values are filled in with new values generated by the
calibration. Then the application checks these new values to make sure they are good.
If they pass (that is, if enough increment correctly), these new values become the
active values, and the old active values become inactive. However, if the new values
don’t pass, then the old active values remain active.