Abstract: A densitometer (10) includes a gas sample plenum (40) that is connected to a gas supply pipe (26) via a flow-restricted inlet duct (42) to at least partially isolate and damp the sample plenum (40) from shocks and noises, turbulences, and abrupt pressure changes in the gas supply. A cantilevered vane (110) is positioned in the sample plenum (40) for gas density determinations on the principle that resonant frequency of the vane (110) is a function of the density of the gas in the sample plenum (40). The resonant frequency of the vane (110) in the gas is determined by applying a magnetic field generated by a driver assembly 120 against the vane (110) and detecting the resonant frequency with a vibration detector (117), which is connected to the driver assembly 120 in a phase locked loop.