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individual parameters that are 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 Appendix F
.
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 Appendix F
.
3. Move across the row and record the flow value beneath the column heading with the actual
Range that was used.
Note: Retrotec 1000, 2000 and 3000 series fans have the same flow curves.
8.3 Moving tubes might cause fluctuating pressure readings
If the measured values on Channel A or B are fluctuating back and forth, in a way that doesn't correspond
with any of the current testing conditions, it's possible that the pressure tube is moving. A moving tube can
cause a significant error. For instance, a tube that is attached both to the gauge and to the fan, but is in the
path of the fan's air flow, can swing back and forth. This swinging motion can easily cause fluctuations in
the measured pressure.
Outdoor pressure tubes need to be sheltered from the wind. In spite of standards that require tubes be
attached to walls, this strategy does not work particularly well for limiting wind related fluctuations. What
does seem to work is taking the outdoor pressure pickup tube 25 feet away from the building, and setting it
in a flat area. Cover the end of the tube with a heavy flat sheet of half-inch plywood or place the tube into
a box, for example, to reduce wind fluctuations.
It's never a good idea to leave a tube hanging in the air, either between two points, or out of a window.
The pressure tube should sit securely on the ground and be kept still as much as possible. The effects of a
moving tube are very similar to the effects of wind on a tube, which is described below.
To see the effect of a moving tube
1. Connect a pressure tube (10 feet or longer) to the blue port of the gauge.
2. Set Time Averaging to one second.
3. Wave the end of the tube through the air. Notice the fluctuations.
4. Hold the end of the tube still, and swing the middle of the tube. Notice the fluctuations.
8.4 Fans with a single tube have results adjusted by gauge
When the gauge is connected to a fan with only a single pressure tube connection such as the Model 1000,
2000, or 3000 fan, fan pressures are adjusted in the gauge to compensate for the back pressure on the fan
before being used to calculate flow or other results. Since this adjustment is done by the gauge, these
devices do not require reference tubing (the green tube) for accurate results. Whenever the gauge
measures a positive pressure, the fan flow is towards the greater pressure, and the gauge makes the
necessary deductions from the “B” Fan Pressure before calculating other results. When showing pressure
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