The PS-PAFS Differential Pressure Air Flow Sensor Probes are ideal for sensing differential pressure in the inlet section of variable air volume terminal units and fan terminal units. Units can also be used to sense differential pressure at other locations in the main or branch duct systems. The “H” port senses total pressure and the “L” port senses static pressure. The difference between these signals is the differential, or velocity pressure. Models offer up to ten sensing points and lengths of 3-5/32˝ to 23-29/32˝ (8.02 to 60.72 cm) to accommodate box sizes of 4˝ to 30˝ (10.16 to 76.20 cm).