The Series PAFS-1000 Averaging Flow Sensor is 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. For models PAFS-1002 to PAFS-1005, up to four sensing points and lengths of 3-5/32" to 9-29/32" (8.02 to 25.26 cm) to accommodate box size diameters of 4" to 16" (10.16 to 40.64 cm) are available. For models PAFS-1006 to PAFS -1011, up to 10 sensing points and lengths from 12-1/2" to 23-29/32" (31.75 to 60.72 cm) are available to accommodate appropriately sized duct dimensions.