Extech Instruments AN340 User Manual page 9

AREA programming for Air Flow (Volume) CMM/CFM Measurements
To accurately measure the volume of air flow in a duct, the area of the duct must first be measured
and the result entered in the meter via the button press sequences described below. Refer to the
Appendix for more information on area measurements, calculations, and unit conversions. Area
measurements are entered as square centimeters or square inches (cm
First decide the method for programming the area information into the meter and then proceed.
The three methods are:
a. L x W: Enter the duct's Length & Width measurement values in centimeters or inches
(rectangular ducts); the meter then calculates the area in square centimeters or square
2
inches (cm or inch
b. D: Enter the duct's Diameter value in centimeters or inches (for round ducts); the meter
calculates the area automatically in square centimeters or square inches (cm
c. A: Enter the area value directly in square centimeters or square inches (cm
Appendix for tips on area measurements, calculations, and unit conversions.
Important Note: Area measurements must be entered in centimeters or inches. If
measurements are made in meters or feet please convert to centimeters or inches. See the
Appendix for more information.
 From the normal operating mode, use the MODE button to scroll to the Air Volume mode.
 Use the LW‐D‐A button to select the method: LW (LENGTH x WIDTH for rectangular ducts), D
(DIAMETER for circular ducts), or A (AREA: if the area value is known). The display icons L, D,
and A inform the user as to which mode is selected.
LENGTH x WIDTH (Area) Mode
 When the 'L' is shown at the top of the LCD, the meter is ready to accept a rectangular duct's
Length measurement in centimeters or inches.
 Use the button ONLY to change the value of the flashing digit (pressing the down arrow
will cause the screen to change from Length to Diameter). Use the ENTER button to move
from digit to digit.
 When finished entering the length, and with the right‐most digit flashing, press the ENTER
button to move to the Width (W) screen.
 When the 'W' is shown at the top of the LCD, the meter is ready to accept the Width
measurement in centimeters or inches.
 Use the button ONLY to change the value of the flashing digit (pressing the down arrow
will cause the screen to change to Diameter mode). Use the ENTER button to move from
digit to digit.
 When finished entering the width, and with the right‐most digit flashing, press the ENTER
button to return to the main operating mode.
 The meter automatically calculates the area of the duct and, when volume measurements
are taken, the LCD will show accurate air volume (flow) in CMM/CFM units.
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