Application

Sequence of Operation

Venturi Table Evaluation and Editing (Mode 1, 3)

Siemens Industry, Inc.

BACnet LCM-OAVS, Application 6754

140-1325

2015-07-07

Venturi Airflow @ 350 fpm.

Valve Size in

Inches

cfm

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.

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.