GB2061495A - Improvements In or Relating To Measurement of the Thickness of a Liquid Film - Google Patents
Improvements In or Relating To Measurement of the Thickness of a Liquid Film Download PDFInfo
- Publication number
- GB2061495A GB2061495A GB8032804A GB8032804A GB2061495A GB 2061495 A GB2061495 A GB 2061495A GB 8032804 A GB8032804 A GB 8032804A GB 8032804 A GB8032804 A GB 8032804A GB 2061495 A GB2061495 A GB 2061495A
- Authority
- GB
- United Kingdom
- Prior art keywords
- light
- liquid film
- liquid
- film
- measuring
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/024—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by means of diode-array scanning
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
- G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
- G01B11/0658—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating with measurement of emissivity or reradiation
Abstract
In a method of and apparatus for measuring the thickness of liquid film 9 upon a surface 7, collimated beam 1 of light is made incident upon the film at a known angle of incidence. Light 13 emanating from that part of the liquid through which the beam of light passes is collected and an image of the illuminated portion is formed. The length of the image is measured to derive the film thickness. <IMAGE>
Description
SPECIFICATION
Improvements in or Relating to the
Measurement of the Thickness of a Liquid Film
The present invention relates to the measurement of the thickness of a liquid film.
For purposes in connection with the study of two phase flow or process control it may be desirable to measure the thickness of a film of liquid on a wall of a duct through which a medium containing the liquid is flowing. It has been proposed to do this by measuring the intensity of fluorescence from the liquid. However this method suffers from the disadvantage that it does not provide an absolute method of measuring the thickness of the liquid film.
According to the present invention there is provided a method of measuring the thickness of a liquid film upon a surface, comprising the operations of causing a collimated beam of light to be incident upon the fluid film at a known angle of incidence, collecting light emanating from that part of the liquid through which the beam of light passes, forming an image of the illuminated portion of the liquid film, and measuring the length of that image.
Preferably, the beam of light is plane polarised, derived from a laser source, and is incident upon the liquid film at the appropriate Brewster angle so that the reflection of light from the surface of the liquid film is avoided. In order to increase the amount of light emanating from the liquid, a fluorescent compound can be added to the liquid.
If the liquid is fluorescent itself under the influence of the light, or if it contains sufficient light scattering centres then the dye can be dispensed with.
If the liquid film is associated with a medium flowing through a duct and the liquid contains sufficient scattering centres to enable a fluorescent dye to be dispensed with, then the possibility arises of measuring the velocity of the film by means of the Doppler shift of the light scattered by the scattering centres in the liquid film.
Also according to the present invention there is provided an apparatus for measuring the thickness of a film of liquid upon a surface, comprising means for generating a collimated beam of light, means for causing the beam of light to be incident upon the film of liquid at a known angle of incidence, means for receiving light from the liquid film arising from the passage of the beam of light through the liquid film and forming an image of the illuminated portions of the liquid film, and means for measuring the length of the said image and deriving therefrom an indication of the thickness of the liquid film.
Preferably, the means for generating a collimated beam of light is a laser source, the light from which is plane polarised, and the means for causing the light to be incident upon the liquid film at a known angle of incidence is arranged to cause the light to be incident at the Brewster angle required for there to be no light reflected from the surface of the liquid film.
The means for measuring the length of the image of the illuminated portion of the liquid film can comprise an array of photo-electric devices the outputs from which are scanned to produce an output signal which is indicative of the length of the image of the illuminated portion of the liquid film.
The invention will now be described, by way of example, with reference to the accompanying drawing which is a diagrammatic representation of an apparatus embodying the invention.
Referring to the drawing, a plane polarised beam of light from a helium-cadmium laser 2 is reflected from a mirror 3 onto an entrance face 4 of a prism 5 which is attached to a transparent region 6 of a wall 7 of a duct 8 on which there is a liquid film 9 which is derived from a medium flowing in the duct 8. In order to prevent any reflection of the beam of light 1 from the interface between the prism 5 and the region 6 of the wall 7 of the duct 8, a layer of refractive index matching fluid 10 is interposed between the prism 5 and the region 6 of the wall 7 of the duct 8. A suitable liquid is glycerol. A pair of lenses 11 is provided to enable the collimation of the beam of light 1 to be maintained in the liquid film 9, or for it to be brought to a focus in the liquid film 9.
The plane of polarisation of the beam of light 1, mirror 3, and the angles of the prism 5 are arranged to be such that the beam of light 1 is incident upon the surface 12 of the liquid film 9 at the Brewster angle for there to be no light reflected from the surface 12 of the liquid film 9.
The liquid which forms the liquid film 9 is caused to fluoresce under the action of the beam of light 1 by means of a dye which has been added to it. (If the liquid is fluorescent itself, or if it contains a large number of scattering centres, the addition of dye can be omitted). Light 13 emanating from the liquid film 9 is collected by an aplanatic lens combination 14 and brought to a focus via a mirror 15, another lens 1 6 and a filter 1 7, which is such as to stop light of the original wavelength, on an array of 128 photo-diodes 18 which forms part of a line scan camera 1 9. The aplanatic lens combination 14 includes a stop 20 which is arranged to restrict the range of angles over which light is gathered by the aplanatic lens combination 14.Pulses at a repetition frequency of 1 MH2 from a clock pulse generator 21 are applied to the line scan camera 19 to drive the scanning of the array of photo-diodes 1 8, and to a generator 22 of scan start pulses at a repetition frequency of 8 kHz which also are applied to the line scan camera 1 9. The output signal from the line scan camera 19 is applied to a cathode ray oscilloscope 23 and comparator 24 in which they are compared with a reference level derived from a reference source 25. The output from the comparator 24 is applied to a gate 26 to which the clock pulse generator 21 also is connected.
The gate 26 is so arranged that it is open whenever the output signal from the line scan camera 19 exceeds a predetermined level. The predetermined signal level is set by observing the line scan camera 1 9 output signal on the oscilloscope 23 and adjusting the reference level until it is half the level of the plateau region of the output signal from the line scan camera 22.
When the gate 26 is open the clock pulses are applied to a first digital counter 27. The start scan pulses also are applied to the counter 27, which is arranged to clear the clock pulses counted in one scan of the array of photo-diodes 18 into a second digital counter 28 in response to each of the start scan pulses which are applied to the counter 27. The count transferred is proportional to the number of illuminated photo-diodes 18, and hence to the length of the image of the illuminated portion of the liquid film 9; this in turn is proportional to the thickness of the liquid film 9.
The relationship between the length of the image and the thickness of the liquid film 9 is calculated from the parameters of the optical components of the apparatus. The output of the second counter 28 gives a digital measure of the liquid film thickness which is updated after each scan of the array of photo-diodes 1 8. If desired, a digital-toanalogue converter 29 can be connected to the counter 28 to provide an analogue liquid film thickness signal.
In the apparatus described, the liquid film is illuminated at an angle, and hence the focussed image also is skew. Thus if the array of photodiodes 1 8 is placed normally to the light incident upon it, both ends of the image cannot be in focus at the same time. If the magnification of the optical system is not too great, this effect can be accommodated by tilting the array of photodiodes 1 8 appropriately. If it is desired to go to higher magnifications, say above four times, then the effect must be corrected optically.
Claims (11)
1. A method of measuring the thickness of a liquid film upon a surface, comprising the operations of causing a collimated beam of light to be incident upon the fluid film at a known angle of incidence, collecting light emanating from that part of the liquid through which the beam of light passes, forming an image of the illuminated portion of the liquid film, and measuring the length of that image.
2. A method according to claim 1, wherein the light is plane polarised and is incident upon the liquid film at the appropriate Brewster angle so as to avoid deflection from the surface of the liquid film.
3. A method according to claim 1 or claim 2, wherein a compound which is fluorescent under the action of the incident light is added to the liquid.
4. A method according to any of claims 1 to 3, wherein the beam of light is monochromatic, the liquid film is moving, the light collected from that part of the film through which the beam of light passes is scattered by particles entrained in the liquid film, and the frequency of the scattered light is compared with that of the incident light thereby to derive an estimate of the velocity of the liquid film.
5. An apparatus for measuring the thickness of a film of liquid upon a surface, comprising means for generating a collimated beam of light, means for causing the beam of light to be incident upon the film of liquid at a known angle of incidence, means for receiving light from the liquid film arising from the passage of the beam of light through the liquid film and forming an image of the illuminated portions of the liquid film, and means for measuring the length of the said image and deriving therefrom an indication of the thickness of the liquid film.
6. An apparatus according to claim 5, wherein the beam of light is plane polarised and the means for causing the beam of light to be incident upon the liquid film at a known angle of incidence is arranged to cause the beam of light to be incident on the liquid film at the appropriate
Brewster angle so as to avoid reflections from the surface of the liquid film.
7. An apparatus according to claim 5 or claim 6, wherein the means for generating the collimated beam of light is a laser source.
8. Apparatus according to any of claims 5 to 7, wherein the means for measuring the length of the image of the illuminated portion of the liquid film comprises an array of photo-electric devices which are scanned to provide an output signal which is indicative of the length of the illuminated portion of the liquid film.
9. An apparatus according to claim 8, wherein the photo-electric devices are photo-votaic devices.
10. A method of measuring the thickness of a liquid film substantially as hereinbefore described and with reference to the accompanying drawing.
11. An apparatus for measuring the thickness of a liquid film substantially as hereinbefore described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8032804A GB2061495B (en) | 1979-10-17 | 1980-10-10 | Measurement of the thickness of a liquid films |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7936032 | 1979-10-17 | ||
| GB8032804A GB2061495B (en) | 1979-10-17 | 1980-10-10 | Measurement of the thickness of a liquid films |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2061495A true GB2061495A (en) | 1981-05-13 |
| GB2061495B GB2061495B (en) | 1984-03-14 |
Family
ID=26273245
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8032804A Expired GB2061495B (en) | 1979-10-17 | 1980-10-10 | Measurement of the thickness of a liquid films |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2061495B (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0119679A1 (en) * | 1983-03-18 | 1984-09-26 | ROLLS-ROYCE plc | Optical determination of clearances |
| EP0119455A2 (en) * | 1983-02-14 | 1984-09-26 | Hitachi, Ltd. | Etching method and apparatus |
| EP0211654A2 (en) * | 1985-08-06 | 1987-02-25 | Mitsubishi Denki Kabushiki Kaisha | Sheet coating thickness measuring apparatus |
| US4647219A (en) * | 1983-10-31 | 1987-03-03 | Baxter Travenol Laboratories, Inc. | Safety system for heating conduit |
| GB2254917A (en) * | 1991-02-28 | 1992-10-21 | Heidelberger Druckmasch Ag | Determining the amount of a fluid or the thickness of a fluid film |
| CN103267488A (en) * | 2013-06-03 | 2013-08-28 | 北京科技大学 | Device for measuring thickness of thin liquid film |
| CN107860322A (en) * | 2017-12-07 | 2018-03-30 | 东华大学 | A kind of thickness of liquid film measurement apparatus and method |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107084669A (en) * | 2017-05-17 | 2017-08-22 | 上海理工大学 | Pure water thickness of liquid film measuring system and measuring method |
-
1980
- 1980-10-10 GB GB8032804A patent/GB2061495B/en not_active Expired
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0119455A2 (en) * | 1983-02-14 | 1984-09-26 | Hitachi, Ltd. | Etching method and apparatus |
| EP0119455A3 (en) * | 1983-02-14 | 1986-02-05 | Hitachi, Ltd. | Etching method and apparatus |
| EP0119679A1 (en) * | 1983-03-18 | 1984-09-26 | ROLLS-ROYCE plc | Optical determination of clearances |
| US4596460A (en) * | 1983-03-18 | 1986-06-24 | Rolls-Royce Limited | Optical determination of clearances |
| US4647219A (en) * | 1983-10-31 | 1987-03-03 | Baxter Travenol Laboratories, Inc. | Safety system for heating conduit |
| EP0211654A2 (en) * | 1985-08-06 | 1987-02-25 | Mitsubishi Denki Kabushiki Kaisha | Sheet coating thickness measuring apparatus |
| EP0211654A3 (en) * | 1985-08-06 | 1988-09-28 | Mitsubishi Denki Kabushiki Kaisha | Sheet thickness measuring apparatus |
| GB2254917A (en) * | 1991-02-28 | 1992-10-21 | Heidelberger Druckmasch Ag | Determining the amount of a fluid or the thickness of a fluid film |
| CN103267488A (en) * | 2013-06-03 | 2013-08-28 | 北京科技大学 | Device for measuring thickness of thin liquid film |
| CN107860322A (en) * | 2017-12-07 | 2018-03-30 | 东华大学 | A kind of thickness of liquid film measurement apparatus and method |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2061495B (en) | 1984-03-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |