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© Retrotec 2017
Appendix A: Understanding Pressures on the 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.
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
1. Connect a pressure tube to the blue port of the gauge.
2. Press [On].
3. Place the end of the tube into a glass of water, slightly more than 1 inch below the surface.
4. 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 by tapping [Settings]>>[Result to be displayed] and tapping [Pressure] to
change pressure units between Pa, in WC, and psf.
Figure 71: Gauge displaying 250.5 Pa (or 1 in WC).
Positive vs. Negative Pressure
The gauge will display pressures from -1250 Pa to + 1250 Pa.
A higher pressure on the positive (“input”) port than on the negative (“ref”) port displays a positive
pressure on the gauge. Alternatively, a higher pressure on the negative (“ref”) port than on the positive
(“input”) port displays a negative pressure.
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