Retrotec DM-2 - Manual (Page 47)

Page 47 of 72
©Retrotec Inc. 2012
9.2.2 Use Time Averaging feature to reduce the effects of wind
Variable readings caused by changing input pressures can be rectified by increasing the Time Averaging
to 20 seconds or more. Quadrupling the Time Averaging typically halves the pressure variation due to
the effects of wind. Be aware that if the fan is increasing or decreasing in speed, it will take 20 seconds
at least for the gauge to register its reading. For example, if during the initial 10 seconds there was no
building pressure whatsoever, and during the second 10 seconds there was 50 Pa, then the gauge will
average that to 25 Pa. The rule of thumb here is to wait for at least double the time average period
before a reading is taken.
[Time Avg] exercise to practice reducing the effects of wind
1. Use a fan to create an air stream.
1. Set Time Averaging to “1 s”.
2. Place a tube, connected to the positive port, in the path of the air stream.
3. The gauge will display a pressure that fluctuates. Adjust the "wind" speed until the gauge is
reading between 2 and 5 Pa.
4. Adjust Time Averaging to 20 seconds.
5. Notice that after 20 seconds, the gauge reading fluctuates significantly less.
9.2.3 Use Baseline feature to reduce the effects of a constant wind
The [Baseline] feature can be used to minimize the effects of Bias Pressures, including that caused by
wind if the wind is relatively constant. This will reduce remove the bias caused by constant wind from
the measurements but will not help with the fluctuating nature of wind which is the biggest issue.
[Baseline] exercise to practice minimizing the effects of wind
1. Use a fan to create an air stream that causes between 2 and 5 Pa pressure.
2. Set Time Averaging to one second.
3. Place a tube, connected to the positive port, in the path of the air stream.
4. Establish a Baseline pressure.
5. Notice that once a Baseline pressure is taken, the measured pressure drops closer to zero,
negating the effects of the wind on the actual measured pressure.
6. Stop the fan.
7. Notice now that the measure pressure is negative, even though no pressure is being
received by the gauge. With the Baseline feature still active, the gauge is compensating for
a pressure that does not exist. Clear the baseline reading to eliminate this error.
9.2.4 In extreme cases you can use a Wind Damping Kit designed to reduce
wind-related fluctuations
In extreme cases, wind damping kits split the main pressure pickup point into either two or four
directions, which will average the fluctuation across the building. Recent experience has shown that
longer time averaging on a digital gauge is almost as effective as the four tube wind damping kit.
When the time taken to set up the kit is taken into account, increasing the time averaging will actually
save time.
A wind damping system can be used to average out the wind, and get a more stable pressure reading.
In addition to a number of suggestions for obtaining better performance from a single tube system,