Retrotec DM-2 - Manual (Page 35)

Page 35 of 72
©Retrotec Inc. 2012
6 Reduce uncertainty in results by taking lots of readings
Table 8 shows tests with approximate uncertainties that can result from applying various number of
Baseline points, Baseline times, and Time Averaging when taking induced pressures. As the number of
Baseline points, the Baseline time, and Time Averaging used for induced pressure readings increase,
the uncertainties decrease. For example, repeating the test using the same fan reduces the
uncertainty by 5% in each case. Typical uncertainties would be less than half of the values shown,
however the table exaggerates the uncertainty trend assuming there are errors while testing with
different fans, gauges, and test conditions.
Table 8: Test result uncertainties vary by changing the number of baseline points, the baseline time, and Time Averaging
for induced pressures.
Gauge
error
Fan
error
Baseline
points
Baseline
time
Baseline
variation
Time Averaging for
induced pressure
Uncertainty
1% 5% 1 5 s 1.5 Pa 5 s 22%
1% 5% 30 5 s 1.5 Pa 10 s 8.6%
1% 5% 30 10 s 1.5 Pa 10 s 7.9%
1% 5% 30 10 s 1.5 Pa 100 s 6.5%
1% 5% 30 20 s 0.5 Pa 100 s 5.9%