Retrotec DM-2 - Manual (Page 30)

Page 30 of 72
©Retrotec Inc. 2012
4 Understand the Pressure Gauge
A high-performance digital differential pressure gauge offers a number of advantages over analog
counterparts:

Easy to read

Pressure sensors have greater sensitivity

Performs calculations that would otherwise need to be done manually
A digital gauge, therefore, can save a lot of testing time with proper use of its functions.
4.1 Differential Pressure
Each gauge contains two pressure transducers, which each measure the difference in pressure
between two ports. The most common units of measurement are Pascals (Pa), but inches of water
column (in WC) and pounds per square foot (psf) are also available. Inches of water column is the
easiest to visualize because one inch water column (1 in WC) is the amount of pressure required to
suck water up a straw to a height of one inch.
One inch of water column (in WC) = 249 Pa = 5.2 psf
To measure a pressure
5. Connect a pressure tube to the blue port of the DM-2.
6. Press [On].
7. Place the end of the tube into a glass of water, slightly more than 1 inch below the surface.
8. The gauge will display around 1.00 in WC, or 249 Pa or 5.2 psf depending on the units being
displayed. Units can be easily changed using the “Setup” Menu as explained in the section
above.
Figure 3: Gauge displaying 249.5 Pa (or 1 in WC).
4.2 Positive vs. Negative Pressure
The gauge will display pressures from -1250 Pa to + 1250 Pa.