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©Retrotec Inc. 2012
A higher pressure on the positive (“Input”) port than on the negative (“Reference”) port displays a
positive pressure on the gauge. Alternatively, a higher pressure on the negative (“Reference”) port
than on the positive (“Input”) port displays a negative pressure.
Measure a negative pressure
1.
Connect a pressure tube to the red (negative, “Reference”) port of the gauge.
2.
Place the end of the tube into a glass of water, about 1 inch below the surface.
3.
The gauge will display around -1.00 in WC, or -250 Pa or -5.2 psf. Notice the negative sign.
Figure 4: The gauge displaying a negative pressure (-251.5 Pa).
4.3
Analog Magnehelic Gauges
Retrotec no longer manufactures or sells analog gauges. It is recommended that Blower Door systems
using analog gauges be upgraded with a digital gauge.
Retrotec manufactured three types of analog gauges:
A 60 Pa gauge, which displays two ranges, 0 Pa to 60 Pa and 20 Pa to 40 Pa
A 250 Pa gauge
A 500 Pa gauge
The E43 Door Fan system included an analog gauge clip which contained two 60 Pa analog gauges and
a 500 Pa analog gauge. The analog gauges are as shown in the right hand image in Figure 5. Any
Retrotec Door Fan system can be connected to an analog gauge.
Reading the pressure on an analog gauge is simply a matter of determining where the needle is
pointing on the gauge. The needle indicates the pressure differential between the two pick-up points
