Application

Sequence of Operation
Venturi Table Evaluation and Editing (Mode 1, 3)
19
Siemens Industry, Inc.
Application Note, App 2926
140-1308
2015-07-07
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.
Running a successful calibration sequence is one way of changing/updating the active
values. You can also edit the table manually. Normally this is not necessary, but if you
are having flow control problems you may need to edit the table.
In order to manually edit the table statement, you must first know which points in the
active table need adjusting. This is done by setting V TABLE PT
to the appropriate
active point values found in the Table
Venturi Air Valve Table Statement in order to
gather and view the active voltage/flow curve for the Venturi Air Valve and its actuator.
By gathering and analyzing the active voltage/flow values (for example, you can plot
them on a graph as in the figure Problematic Venturi Air Valve Voltage/Flow Curves ),
you can decide which one(s) need adjusting. The flow curve should be smooth and
incremental.
You can change the active values using the following steps:
1. Set V TABLE PT to a “swap” value that tells the application to exchange active
table values with inactive table values (see the Table Venturi Air Valve Table
Statement for swap value).
 This step is necessary because the application does not allow active values to
be manually overridden.
NOTE:
An exception to this rule is when active values cannot be manually overridden. The
first element in the active portion of the table—the low flow point—can be edited
directly. The Table Venturi Air Valve Table Statement explains this in more detail.