Sonartrac GVF-100 Entrained Air Monitoring System, manufactured by Cidra, 2017. 2 inch senor assembly, standard sensor band, fiberglass cover, 1.8Hz W/5.5X Higher gain reamp, thermal barrier, ac transmitter, RS232/485. The Sonartrac GVF-100 system is a clamp on process monitoring system used to measure the volumetric flow rate and the amount of entrained air/gas contained in a fluid within process pipes on a real-time basis.