Retrotec DM-2A Instrukcja Użytkownika Pobierz pdf (Strona 47)

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©Retrotec Inc. 2012

7.2 Serial Number and Calibration Date Check

It's recommended to check the serial number and calibration date on the DM-2 regularly.

If the screen does not display a valid serial number and calibration date, please contact Retrotec tech

support since your gauge may have switched over to default calibration values. This can be checked by

connected your gauge to another gauge, port to port to ensure they read within 1%.

7.3 Moving Tubes Cause Fluctuating Pressures

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.

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 DM-2.

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.

Figure 11. The effect of a moving tube

on pressure readings.

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Retrotec DM-2A Instrukcja Użytkownika Strona 47