A magnehelic pressure gauge is a device, similar to a manometer, used to measure positive, negative and differential pressures. These gauges are often used in the HVAC industry to measure pressure drop across air filters to determine when it is time for them to be changed.
Although magnehelic gauges are resistant to shock and vibration, they are extremely sensitive and accurate. Calibration is very easy due to the zero calibration screw located on the plastic cover. Although Dwyer makes gauges in about thirty different pressure ranges, the most common ranges are 0 to 0.5 in, w,g. (25 Pa), 0 to 1.0 in. w.g. (250 Pa), and 0 to 5.0 in. w. g. (1250 Pa). They consist of a die cast aluminum case and bezel with an acrylic cover. Magnehelic gauge accuracy is typically + or – 2%.