Delta OHM DO2003, Manual

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2) Moving Average
The Duct Calc function provides a space average of acquired values in order to compensate
speed differences between a point and another in the pipe section. There is also another cause of
error due to stream variations over the time: actually, a stream is not steady but, on the contrary,
it can decrease or increase even in the same point. In order to compensate this second source of
instability, a time moving average of the last
n acquired measurements can be provided: thus
n>1 (the displayed valued) will not correspond to a single acquired value, but to the current
average of the last recorded and continuously updated
n measurements.
To set the “ n ” value, use the SAMPLE TIME sub-function of the HOLD key: press PROG >>
HOLD, use the arrows to select the desired “n” value and press ENTER to confirm it. “n” can be
set between 1 (no average) and 99.
Note: grills and diffusers with reclining fins cause stream measurement errors because of
turbulences. These turbulences develop because part of the stream meets an obstacle (the fin)
and, consequently, slows down, while the rest of the stream speeds ahead. In this case, to get
correct measurements, it is suggested to temporarily insert, in front of the ventilating grill, a pipe,
having a length twice the length of the grill diagonal. Measurements have to be taken at the ends
of this pipe. The area to be considered for flow calculations will be that of the temporary pipe
positioned between the ventilating grill and the probe.
D
L = 2 x D
TEMPORARY PIPE
PROBE
AIR VENT
PIPE SECTION
PIPE
Unit Conversion Table
m/s ft/min km/h mph
1 m/s 1 196.87 3.60 2.24
1 ft/min (1 foot/minute) 0.00508 1 0.01829 0.01138
1 km/h 0.2778 54.69 1 0.6222
1 mph (1 statute mile/hour) 0.4464 87.89 1.6071 1