Retrotec DM32 User Manual download pdf (Page 66)

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©Retrotec Inc. 2014

To learn how Time Averaging can cause error

1. Create a pressure on the positive port of Channel A (Input).

2. Set Time Averaging to one minute.

3. Wait until the pressure reading becomes stable. After one minute, Channel A should display

the created pressure.

4. Remove the tube from Channel A, eliminating the pressure.

5. Notice that the gauge continues to display a pressure on Channel A, which slowly decreases.

After one minute, the gauge should display no pressure difference.

If a reading is taken from the gauge before the full time averaging period has passed, then the displayed

pressure may not be accurate.

8.15.4. 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 measured 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.

8.15.5. 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 averages out pressure fluctuations created by the wind yielding a more stable

pressure reading. In addition to a number of suggestions for obtaining better performance from a single

tube system, Retrotec offers two wind-damping kits specifically designed to reduce the pressure

fluctuations due to wind.

The basic wind-damping kit consists of a dual-tube pressure averaging system and will work in wind

conditions up to about 10 mph. The deluxe wind-damping kit (our “Wild Wind Tamer”) consists of a four-

tube engineered damping system that will provide damping results in winds up to 20 mph.

1. Set up the house/room gauge and red tube as normal.

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Retrotec DM32 User Manual Page 66