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© Retrotec 2017
Figure 67: The effect of a moving tube on pressure readings.
8.10
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
on “B”, the value shown on the gauge for “B” is
the actual measured pressure on channel B, without
deductions. See
Fans with two pressure tube connections (yellow and green) such as the Model 3000SR fans and the DU200
DucTester are self-referenced and include a connection point for the green tube, which must be connected.
Because these fans are self-referenced, the gauge does not make any adjustments to the Fan Pressure
reading before calculating the other results.
It is important that the correct Device selected on the gauge since the chosen Device determines whether
the gauge has to do any adjusting. If a self-referenced model fan such as the 3350SR series or the DU200
DucTester is in use, the gauge knows not to adjust the fan pressure before calculating other results.
8.11
Pressure can overshoot when using the Set Pressure key
When Set Pressure is used to establish 60 Pa for example, the fan can overshoot and reach up to 90 Pa for a
few seconds before it settles back to the desired 60 Pa, depending on the response time of the fan
attached to the gauge. If this is a concern, start the fan on Set Speed or set to a lower pressure and then
use the
[Jog]
key to increase the set point in smaller steps. The speed control in the gauge has been
optimized to achieve the desired pressure as quickly as possible and to remove the overshoot would force
the user to wait much longer.
Pressures can also overshoot when the range is set incorrectly. Ranges should always be selected so the
fan runs at the fastest possible speed in order to achieve the lowest desired test pressure.
To mitigate pressure overshoot when using the FanTestic software, enter the list of pressures in order of
pressure, with the lowest first. For example, set pressure range from 10 to 60 Pa, rather than 60 to 10 Pa.
To experience the overshoot and understand how to avoid it, perform the following test on the Retrotec
simulator or on a tight room where the leakage can be adjusted.
For an example using a 1000 fan, set Device to 1000, range to C1, time averaging to 10 seconds. Set the
leakage area on an enclosure by adjusting the size of the hole. When using the Retrotec simulator, use the
sliding panels to adjust the size of the hole. Optionally, measure the leakage area with a Door Fan using
EqLA10 which you can access using the [Channel B] key. Watch the gauge carefully to detect the peak
pressure reading on Channel A and the peak percent speed on the bottom right-hand of the display.
