High-pressure optical sensor

Benjamin, R.F., F.J. Mayer, and R.L. Maynard (1984), Microshell-Tipped Optical Fibers as Sensors of High-Pressure Pulses in Adverse Environments, in Eiber Optics in Adverse Environments 11, Proc. SPIE, 506 (edited by R.A. Green well),... 

The regenerated extraction gas leaves the second regeneration column at its head and is cooled down in (WT3) to a temperature of approximately 20°C. Depending on the type of extraction solvent the buffer vessel (KP) contains liquid phase in equilibrium state with gas or merely gas of high density. In the last case a pressure controlled pneumatic pump feeds fresh solvent into the circular process. If a gas/liquid equilibrium is achieved in the buffer vessel the gas pressure remains constant until a minimal amount of liquid remains there. For this purpose two optical sensors are introduced into the buffer vessel registrating the minimum and maximum extraction liquid level If the level falls below minimum, fresh liquid extraction solvent is refilled. 

An experiment with a dilute ceramic suspension was made as follows A very small quantity of silicon carbide particles (d 6 /xm) was dissolved in silicon oil ( 350mPas). The suspension was pumped at high pressure through a glass capillary (d = 0.6 mm). The experimental setup is shown in Fig. 3. The velocities of the silicon carbide particles in the capillary are detected by an optical sensor. From these data, the statistics of the particles velocities is calculated. Due to the optical properties of the sensor, the particles are only detected in a wedge-like sector of the cross-section of the capillary. The measured velocity distribution of the particles (Fig. 4) depends on the shape of this sector and, additionally, on the measuring tolerances of the sensor. 

The main developments in experimental techniques for measuring high pressure to obtain reliable pressure sensors are extensively discussed by Decker et al. [42]. These include (1) the establishment of a primary pressure scale using a free piston gauge (2) the selection and precise measurement of identifiable phase transitions as fixed pressure points and (3) the use of interpolation and extrapolation techniques for continuous-pressure calibration based on changes in resistance, volume, or optical spectra (based on an equation of state). An alternative method of estimating absolute pressure in isotropically compressed materials is based on measurements of ultrasonic velocity [43, 44]. 

Glotzl, R. Hofmann, D. Basedau, F. Habel, W.R. Geotechnical Pressure Cell Using a Long-Term Reliable High-Precision Fibre Optic Sensor Head. Int. Conf. on Smart Struct, and Mater. 2005. SPIE-Vol. 5758 (2005), pp. 248 253... 

Other technical appUcations based on the optical properties of cubic zirconia include high-temperature optic pressure sensors and components for laser optics. 

More recently, fiber-optic sensors have been developed to measure pressure in high-temperature environments (Krohn, 2000). Multivariable transmitters are available that measure several process variables (see Fig. 9.4). 

Fiber-optic sensors are attractive options (but more expensive) for acquiring measurements in harsh environments such as high temperature or pressure. The transducing technique used by these sensors is optical and does not involve electrical signals, so they are immune to electromagnetic interference. Raman spectroscopy uses fiber-optics and involves pulsed light scattering by molecules. It has a wide variety of applications in process control (Dakin and Culshaw, 1997). 

However, optical nanostructured sensors exhibit a significant color change only at relatively high partial pressures of detected vapors, while at relative vapor partial... 

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