Preliminary Study Of Static And Dynamic Performance Of A High Freauency Direct-current Glow Discharge Pressure Sensor

In order to capture more detailed and accurate unsteady flow information,such as clarifying the mechanisms of stability and transition to turbulence of high-speed compressible boundary layers,the unsteady flow separation bubble and instability,MHz level ultra-high frequency bandwidth is desirable with a sensor that combines robustness,high temporal resolution and spatial resolution.Nowadays,piezoresistive silicon pressure transducer is the most widely used pressure measurement instrument.Thermally based sensors,particularly the hot-wire anemometer and surface mounted hot-film,almost monopolize the whole market for mass-flux and turbulence structure measurement.However due to the effects of mass inertia and thermal inertia,the frequency response of piezoresistive silicon pressure sensors and thermally based sensors is still limited to less than 500 kHz and can become unstable due to the non-linear response to changes in overheat and cable capacitance.The field of glow discharge(GD)has the potential to break these frequency barrier.Ever since 1934 it was initially suggested by Lindvall that an electric discharge could be used in an anemometer application which was encouraged largely by the consistent interest by Dr.Theodor Von Karman,the glow has been investigated to measure the flow mass-flux as an anemometer.As a new developing measurement,it is necessary to investigate whether if the glow discharge has a monotonic response and high sensitivity to the pressure fluctuation before applying to the practical flow field.Therefore it is necessary to develop both experimental and theoretical research on the glow discharge plasma,with the aim to reveal the generation and evolution of the plasma under different pressure,thus to provide the effective and reliable principle of the sensor design.1.Design a multiplication microscope observation platformCircuit current,electrode shape and spacing are the three main parameters of influencing the plasma pressure sensor’s sensitivity to pressure.With the aim to measure the electrode spacing accurately,it is necessary to ensure a uniform spacing between the two electrodes each other,and change the electrodes conveniently(including the replacement of electrode material,size,shape,etc),a multiplication microscope was designed and refitted.Two plane parallel platinum electrodes are 0.5 mm in diameter.The electrode spacing is changed by monitoring a micro-calliper.2.Obtain the characteristics curves between the plasma sensor voltage and pressureWe found that the plasma voltage is a function of the product of air pressure and electrode spacing.When Pd is small enough,the calibrated curves between discharge voltage and pressure show a definite monotonically decreasing trend.The sensor was working in the "abnormal" GD regime When Pd is large enough,the calibrated curves between discharge voltage and pressure show an opposite monotonically increasing trend.The sensor was working in the "sub-normal" GD regime under this circumstance.3.Develop a static calibration procedure to obtain the monotonic response regularity of voltage to air pressureAs the first step of fundamental research,a calibration procedure is developed.In this paper,a direct current was applied to the electrodes.By fixing a proper clearance and changing the power supply,a series of typical current-voltage(I-U)characteristics curves between the electrodes can be obtained by varying the static pressure.It has found that to maintain the discharge in same regime is the key to guarantee the monotonic response of voltage to air pressure.The electrode spacing and circuit current are two main factors which influence the sensor discharge regime and the sensitivity to pressure fluctuation.Keeping the current constant,the sensor voltage responds quantitatively and in a reproducible manner to pressure changes with a sensitivity depending chiefly upon the electrodes spacing.For a spacing of 50μm with the current increasing from 3mA to 4.5 mA,the sensor was working in the "abnormal" GD regime.The calibrated curves between discharge voltage and pressure show a definite monotonically decreasing trend at the same time.On the contrary,the calibrated curves for a spacing of 250μm with the current increasing from 2mA to 3.5 mA,show an opposite monotonically increasing trend.The sensor was working in the "sub-normal" GD regime under this circumstance.For a spacing of 190μm the plasma was insensitive to the pressure fluctuation.These results demonstrate that maintaining the discharge in same regime is crucial to guarantee the monotonic relation between discharge voltage and pressure.4.Invesitigate the dynamic performance of the plasma sensor by a shock tubeBased on the static calibrated results,the dynamic performance of the Plasma Pressure Sensor was further investigated in this chapter.A shock tube was proposed to generate a step pressure signal.In order to guarantee the plasma would respond primarily to pressure fluctuations,a plexi-glass cap was designed to shield the induced velocity.The electrode pair is formed by the two platinum conductors,which are spaced roughly 0.25 mm apart.As a baseline comparison to a traditional sensor,the plasma sensor output was compared to data previously captured from a fast-response Kulite pressure sensor.As can be seen from the voltage amplitude,the two sensors almost simultaneously capture the shock wave.As the input-output(Kulite-Plasma)amplitude transfer function and phase transfer function characteristics shown,the plasma pressure sensor has a smooth continuous amplitude transfer function curve with respect to Kulite,which demonstrates that the plasma pressure sensor has at least the same frequency response characteristics as the Kulite.When we use the simulated shock step pressure as an input signal,the results show that Kulite has a 35 kHz frequency response,and plasma sensor has a 55 kHz frequency response.