DE2354307A1 - Pressure measurement using cholesteric mesophase - with reversibly pressure-dependent reflection colours, for accuracy and simplicity - Google Patents

Abstract

Pressure measurement is carried out by exposing a cholesteric mesophase (I), with reversibly pressure-dependent reflection colours, to the pressure to be measured and measuring the resultant spectral shift of the light reflected from this. (I) pref. consists of a mixt. of cholesteryl oleyl carbonate, cholesteryl myristate or cholesteryl nonanoate with cholesteryl chloride. The appts. used consists of a sealed housing contg. (I) with part of the walls ensuring transfer of the pressure to be measured to (I) and a window for illuminating (I) and transmission of the reflected light. No connections between the measuring cell and the display are necessary, so that measurement is possible in situation which are difficult to reach with leads. The light from the cell can be transmitted by fibre optics for analysis and display. Correlation of the pressure with colour makes the process very suitable for pressure monitoring, e.g. in autoclaves, with the possibility of automatic regulation of pressure by an optical-photoelectric system. The system is also insensitive to excessive pressures, outside the measuring range, and not damaged by these. A wide range of pressures can be accommodated by the use of a series of suitable cells. Measurement is very accurate and the cell used is small and simple.

Description

EIKENBERG 8s BRÜMMERSTEDT

PATENT LAWYERS IN HANOVER

Riedel-de Haen AG 318/3

Pressure measurement method and device to carry out this procedure

The invention relates to a method for measuring pressure and a device for carrying out this Ver ~ driving.

Organic substances are known, the mesophases form. A "mesophase" is understood to mean a phase which lies between the anisotropically solid and the isotropically liquid phase and has anisotropic properties in this liquid area having. Mesophases, which consist of chiral anisotropic molecules, are classified as cholesteric! Some of such cholesteric mesophases show in certain Temperature ranges brilliant and temperature-dependent reflective colors in the visible, i.e. when the temperature changes a reversible spectral shift occurs in the light reflected from the affected phase.

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In the well-known Meso.ptiasen with temperature-dependent In reflective colors, the spectral shift that occurs is practically independent of pressure. So own 25.B. Mixtures of cholesteryl ethyl carbonate with N- (4-methoxybenzylidene) -4'-n-butyl aniline (ICBBA), which are considered to be typical systems with temperature-dependent reflective colors can, no pressure dependence of the reflection colors in the area from O - 2000 bar. Mesophases with reversible pressure-dependent Reflective colors have not yet become known.

Surprisingly, it has now been found that there are also cholesteric mesophases, which are only slight Temperature dependence of the reflection colors a sear strong Show the dependence of the reflection colors on the static pressure acting on the phase on all sides. So it was found "that e.g. for mixtures of cholesteryl oleyl carbonate with cholesteryl chloride an increasing pressure causes a clear red shift of the reflected light, and that from the maximum the narrow-band reflection curve can clearly be deduced from the pressure.

The invention makes consistent use of this knowledge and creates a new method for measuring pressure, which is characterized by the fact that a cholesteric mesophase with reversible pressure-dependent reflection colors corresponds to the one to be measured Subject to pressure and the resulting spectral shift of the light reflected from this mesophase measured will.

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Carrying out the method according to the invention is device-wise to no "particular embodiment bound, but necessarily with a measuring cell, which is characterized by the fact that it is a cholesterol Has mesophase-tight enclosing housing, which is so formed in at least a portion of its walls is that a transfer of the pressure to be measured to the mesophase is guaranteed, and what a window for exposure the mesophase and the passage of the mesophase having reflected light.

The pressure measurement according to the invention has opposite known methods of pressure measurement have many and significant advantages. One of these advantages is that none Lines from the pressure measuring cell to a display device are required, since the retrieval of the measured values is carried out with the aid of light will. The measurement can therefore also be carried out in places that are difficult to reach with cables. Furthermore omitted but also any line feedthroughs from the interior of the pressure measuring cell to the outside, which with conventional methods, e.g. for electrical lines when measuring pressure with metal resistors or for pressure lines when measuring pressure with manometers, are required and can cause significant sealing problems. The one emerging through the window of the pressure measuring cell Rather, reflected light is completely separated from the pressure measuring cell recorded and can be guided with the help of light guides to a greater distance and analyzed there and into a Pressure indication can be converted.

Another benefit derives from the fact

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that "certain pressure values with defined reflection colors can be correlated. Therefore, the invention can be used very well for pressure control in, for example, a reaction autoclave use. Only the upper and lower ones need it Reflection colors assigned to limit pressures through filter combinations Photoelectrically indicated and the indications obtained are further processed to trigger the necessary control processes be su. Such an optisoh-photoelectric detection of limit pressures is in many cases a decrease the limit values by means of mechanical bsw. electrical switch superior.

Also the complete insensitivity to excess pressure above the measuring range is to be emphasized as an essential advantage of the invention. In contrast to other measuring methods, where there is damage when the measuring range is exceeded of the measuring instrument can occur or at least the risk of inaccuracies occurring in subsequent There is measurement processes, shifts in the inventive Measuring method (provided that the measuring cell is designed to be sufficiently strong, which does not encounter any difficulties) after exceeding of the measuring range only the color display (when using of cholesteric meosphases with redshift) into the infrared area, i.e. it occurs in the visible area no more earbanseige on. Otherwise the system remains completely unaffected, and when the overpressure subsides the display continues to work as before.

This insensitivity to excess pressure makes it also possible to expand the measuring range in the invention in that several measuring cells, each of which is different

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for a "specific print area, visible light reflecting Embedded mesophases are simultaneously exposed to the bridge to be measured, in which case the display of the most sensitive in the specific pressure range Measuring cell is removed. ' A further measuring range is therefore possible by selecting suitable mixtures of cholesteric substances with practically consistently good display sensitivity adjustable.

Further advantages of the invention reside in a great deal high measurement accuracy because of the dependence of the color shift of the reflected light from the print runs very steeply, as well as in the space-saving, small construction of the measuring point for which only a few simple components are required.

The invention is explained in more detail below in exemplary embodiments with reference to the drawings. Ask dar: ■

Pig. 1 a possible embodiment of a measuring cell in cross section,

Pig. 2 graphically shows the dependence of the maximum the reflected wavelength from the Druok for two different cholesterol ' niche mesophases.

3 for a measuring cell which can be used in the context of the invention it is necessary to embed the pressure-dependent cholesteric mesophase in a housing in such a way that a transmission

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of the su inessenden pressure on the mesophase is guaranteed and there is a possibility of exposing the mesophase through a window and receiving the emerging reflected light. In the embodiment according to FIG 4a, of which the disk 4, which can be made of metal, is provided with one or more bores 5, while the disk 4a is made of quartz glass or another optically transparent material a fixed distance of not more than 20 / .mu.m from one another, which is ensured by a spacer 6. The perforated disk 4 is covered by a membrane 3, which closes the bores 5 in the disk and allows an outer one in the area of the bores 5 To transfer pressure statically to the mesophase 8. In the installation of all parts in the frame 1, contact pressure screws 1 are used, whereby Ausglei chs washers 2 ensure tension compensation. In addition, the bores 5 with the overlying membrane 3 are not necessary if one or both of the disks 4 or 4a are so thin that they themselves can transmit the pressure to be measured to the mesophase 8.

The measuring cell according to FIG. 1 can be part of the

Form the wall of a pressure chamber (with the bores 5 facing inwards), but it can also be arranged within a pressure chamber. In each pail the pressure is measured by means of exposure the measuring unit through the quartz disk 4a and by means of Measurement of the light exiting through this disk and reflected in mesophase 8. It is useful the surface of the disk 4 facing the mesophase 8 should be designed to be non-reflective, so that the measurement is not caused by reflection

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from the surface. to disturb the disc 4.

An example of a pressure-dependent cholesteric kesophase is a mixture of cholesteryl oleyl carbonate and cholesteryl chloride ·. With this' mixture, the for a pressure measurement usable pressure range, i.e. that pressure range, in which a strong change in the reflection wavelength is noticeable per unit of pressure, clearly from Mixing ratio from, in such a way that the usable pressure range increases with increasing content of Oholesterylchlorid is shifted towards higher values. That's based on the Pig. illustrated for zv / ei special hybrids.

Curve A of the Pig. 2 was obtained with a mixture of 74.8 mol ^ cholesteryl oleyl carbonate and 25.2 Md1 # cholesteryl chloride. A sample of this mesophase was in the measuring cell according to 'Fig. 1 different pressures? and the maximum of the respectively reflected wavelength was determined with a UV YiS spectrophotometer Perkin-Elmer, model 159, by measuring the light absorption. The resulting shift in the reflection maximum as a function of pressure is shown by curve A of Pig. 2, which can thus be regarded as a "calibration curve" for this particular mesophase. In the same way, curve B became the pig. 2 earned with a mixture of 80 _? 1 mole of gholesteryl oleyl carbonate and 19.9 mole of cholesteryl chloride. It can be seen ₉ that the mesophase "B" is more sensitive than the mesophase "A" in a lower pressure range. The limit values are at a content of the mixture of about 26 mol of cholesteryl chloride as the upper limit and about 5 mol of cholesteryl chloride as the lower limit.

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Bas mixture, of cholesteryl oleyl carbonate and Cholesterylcliloriä is not the only one for the purpose of Invention useful mesophase. It has generally been found that all those mesophases show reversible pressure-dependent reflection colors in which, in addition to mixing with cholesterol Phase type still, a smectic phase type is present. These Such mixtures, for example, have properties of chiral anisotropic molecules in which at least one component in the pure state has a smectic phase type trains. That is with relatively elongated molecules the jail. Accordingly, for the purposes of the invention also use mixtures of Oholesterylmyris.tat with Gholesterylchlorid or Cholesterylnonanoat with cholesteryl chloride «, For these mixtures, too, the pressure range that can be used for the measurement can be determined by changing the mixing ratio set to different values »

Expectations -

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Claims (5)

.9- Expectations; 1Y. A method for measuring pressure, dadurc h marked that a caolesterol mesophase with reversible pressure-dependent reflection colors is exposed to the pressure to be measured and the resulting spectral shift of the light reflected by this mesophase is measured. 2. The method according to claim 1, characterized in that a mixture of cholesteryl oleyl carbonate or cholesteryl chloride is used as the cholesteric mesophase. 3. The method according to claim 1, characterized in that a mixture of cholesteryl myristate with cholesteryl chloride is used as the cholesterol mesophase. 4. The method according to claim 1, characterized in that a mixture of cholesteryl nonanoate with cholesteryl chloride is used as the cholesteric mesophase. 5. Device for performing the method according to one of the preceding claims, characterized in that a housing (4, 4a, 6) which tightly encloses _{the cholesteric mesophase is provided?} which is designed at least in a partial area (5) of its walls so that the pressure to be measured is transmitted to the mesophase (8), and which has a window (4a) for exposure of the mesophase and for the light reflected from the mesophase to pass through having. 509819/0535 Blank page