Paper VT-TuP4
Simultaneous Measurement of Pressure and Viscosity with a Resonant Sensor in a Viscous Flowing Gas

Tuesday, October 19, 2010, 6:00 pm, Room Southwest Exhibit Hall

With a quartz tuning-folk resonator vibrating at the resonant frequcny in the viscuos flowing gas, we found that the measurement of the resonator’s Δf and ΔZ enabled to derive the pressure and the viscosity of the viscous flowing gas simultaneously. The parameter of Δf is the frequency change from its vibrating frequency in high vacuum. Another parameter of ΔZ is the impedance change from the resonator impedance in high vacuum. Also the ΔZ is related to the pressure and the viscosity of the gas. We focused on the pressure dependence of Δf and of ΔZ to derive the pressure and the viscosity.

In this experiment, to achieve the precise measurements of Δf and ΔZ, we paid careful attention to the temperature control because Δf was very sensitive to the temperature. We used the constant-temperature chamber in which the resonator, the driving circuit for the resonator, mass flow controllers, and the absolute pressure gauge were installed. The temperature variation was ±0.1ºC during the experiment. In addition the driving circuit was stored in a thermostatic box which temperature was maintained at 30±0.02ºC to minimize the frequency drift. The driving circuit applied constant driving voltage(Vd) to the resonator and the driving current(Id) passing through the resonator was monitored. The impedance of the resonator (Z) was given by the ratio of Vd to Id. The resonator was a tuning-folk type quartz resonator and had a vibration frequcny of 32kHz. The measured gases were Ne, Ar, N₂, O₂, Kr. The gas was charged at 130 kPa initially, and was vacuumed at the rate of 20 Pa/sec. The pressure of the gas was measured with the capacitance manometer.

The results showed that P-ΔZ for every gas showed the same characteristics; the ΔZ has larger value for higher pressure. For the higher mass of the gas showed the larger ΔZ at atmospheric pressure except for Ne. The every P-ΔZ curve did not across each other except for Ne.

The P-Δf graph showed also the same tendency. The Δf has larger value for higher pressure, however, for the higher mass of the gas showed the larger Δf at atmospheric pressure including Ne. The every P-ΔZ curve did not intersect one another except for Ne. Then showed close but not the same characteristics.

The ΔZ-Δf plot revealed the difference between the P-ΔZ and P-Δf. The ΔZ-Δf curves did not intersect one another above 1 kPa and that the ΔZ-Δf curves were arranged in order of the viscosity of the gas. Then the pressure and the viscosity of the gas can be derived simultaneously from ΔZ-Δf curve.