7
MEASURING AIR VOLUME (CFM OR CMM) CONT.
TIMED AVERAGE AIR VOLUME
1. Press
MODE
until VOL is showing in the upper right corner of
the display
2. Enter duct dimensions using the method described on page 6
3. Extend the probe to the width of the duct or more
4. Verify that you are aiming the “Air In” into the air flow. This
is the side opposite of the inch/cm markings on the probe
extension. The grooves of the probe should be perpendicular to
the air flow direction
5. Insert probe into duct access hole (3/4” hole required)
a. See “Measurement Location and Method” for instructions on
where to measure
6. Start with the probe inserted just inside the access hole
7. Press “
START
” to begin timed average
8. Slowly move probe into the duct until it crosses the duct and
contacts the far side
9. Press “
STOP
” to interrupt timed average. The cumulative timer
will stop when the DAFM4 is not capturing data
10. Move to the next access hole and repeat steps 6~9.
11. Press
MIN/MAX AVG ( )
after capturing data on all access
holes to view average volume
a. AVG flashing and elapsed time will show when displaying
average
b. AVG flashing, elapsed time and MIN will show minimum
measured volume
c. AVG flashing, elapsed time, and MAX will show maximum
measured volume
12. Press and hold
EXIT
to end test
MEASUREMENT LOCATION AND METHOD
There are recommended methods to traverse a duct in order to collect
sufficient data for an accurate average. Using a timed average increases
the number of data points for a much more accurate result. It is still
recommended to use the approach taken by the Log-Tchebycheff Rule
for access hole spacing, but the number of data points is not needed. By
utilizing a timed average you will capture these locations, plus data from
the entire width of the duct being measured.
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