On the gauge – Retrotec DM-2 User Manual
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©Retrotec Inc. 2012
in fact the results are way off. Particularly unusual behavior in the gauge could mean that there is
water in the end of the tube.
Water can cause either a positive or a negative pressure, based on which way the drop of water is
pulling. If a drop of water is facing downward, it pulls out of the tube, creating a negative pressure (as
displayed in Figure 16). Point the tube upward, and the water drop falls back into the tube, creating a
positive pressure.
Figure 16: Water in the reference tube (left); high fixed pressure due to water (right).
To fix this problem:
Whip the end of the tube around to remove excess water.
If this doesn’t work (in extreme cases), water can be blown out from the other end. Be sure to not
have the gauge connected when blowing water from the tube.
9.6 Check if large fixed errors are caused by sun heating the tubes
If air inside the exterior heats up due to the Sun shining on it and if the tube end is above or below the
point where it leaves the enclosure, a stack pressure will build up inside the tube that will create a
steady pressure that may increase as the tube gets hotter.
9.7 Results will be wrong if the Range and Device being used are
different than those selected on the gauge
If the results just don't make sense, check to make sure the “Range Config” and “Device” selected on
the gauge are the same as the Range and Device being used. Each Device and Range configuration has
its own individual flow curve that is used to convert Fan Pressure into flow and the other results
selected for display on the gauge.
If a test is completed with the incorrect Range selected, it is possible to salvage the data by using the
customized flow charts provided in
To determine correct flow if Range selected was different than the actual Range used:
1. Select the Fan Pressure reading for which a corrected flow value is needed.
2. Find this Fan Pressure value in the left column of the flow conversion tables in