User's Manual

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2801989 December 2006 ©2006 Fluke Corporation. All rights reserved. Printed in U.S.A. 1
922 Pitot Tube
Instruction Sheet
Introduction
Use the 922 Pitot tube with the 922 Airflow Meter to
ensure accurate pressure, velocity, and flow
measurement.
Contacting Fluke
To contact Fluke, use one of the following telephone
numbers:
USA: 1-888-99-FLUKE (1-888-993-5853)
Canada: 1-800-36-FLUKE (1-800-363-5853)
Europe: [phone]
Japan: [phone]
Singapore: [phone]
Anywhere in the world: [phone]
Or visit Fluke’s Web site at: www.fluke.com
.
Register the Meter at: http://register.fluke.com
Safety Information
WWarning
To avoid injury, or damage to the
Pitot Tube or 922 Airflow Meter,
follow these safety guidelines:
• Read the entire 922 Users
Manual before using the 922
Pitot Tube with the Meter.
• The Pitot Tube contains no
user-serviceable parts. For
service, return to Fluke. See
“Contacting Fluke”.
Measuring Air Velocity with Pitot
Tubes
Pitot tubes are commonly used to measure velocity
pressure within a duct. Velocity pressure is the
pressure resulting from moving air within a duct. As
air velocity increases, velocity pressure increases
accordingly. A Pitot tube is used to sense both total
pressure (TP) and static pressure (SP), which are used
to calculate velocity pressure (VP) according to the
following equation:
VP = TP-SP
Because airflow through a duct is turbulent and of
varying velocities, a single reading does not represent
the overall air velocity in the duct. Several readings
must be taken across a traverse plane, converted to
velocity, and then averaged. To take an accurate air
velocity measurement, the Log-Tchebycheff rule
provides the greatest uniformity because it accounts
for the friction effect of air moving near duct walls.
Figures 1 and 2 show the points along the traverse
plane where measurements should be taken, either in
rectangular or circular ducts.
Per the ASHRAE standard 111-1988, a minimum of
25 points should be measured in a rectangular duct
traverse. When traversing a duct side less than 18 in.
(450 mm), take readings from the center of equal
areas that are no more than 6 in. (150 mm) apart, with
a minimum of two points per side of the duct. See
Figures 1 and 2.
Refer to the 922 Users Manual for more information
about using the 922 Pitot Tube for measurements with
the 922 Airflow Meter.
Helpful Tips
• When performing a duct traverse, ensure the nose
of the Pitot tube is parallel to the duct wall and
facing the airflow.
• Take readings in long, straight runs of duct, where
possible. Avoid taking readings immediately
downstream of elbows or other obstructions in the
airway.