GB2192987A

GB2192987A - A device for measuring physical properties of liquids

Info

Publication number: GB2192987A
Application number: GB08717205A
Authority: GB
Inventors: Stefan Nowinski
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-07-24
Filing date: 1987-07-21
Publication date: 1988-01-27
Anticipated expiration: 2007-07-21
Also published as: GB8717205D0; GB8618084D0; GB2192987B

Abstract

The physical properties of a liquid are tested by illuminating a portion of the surface of the liquid sample with a beam of light, e.g. laser light, measuring a characteristic, e.g. intensity, distribution of the light reflected from the illuminated portion of the surface of the liquid, directing a pulse of gas at the illuminated portion of the surface of the liquid to cause local deformation therein, and measuring the change in the characteristic of the light reflected from the illuminated deformation of the surface of the liquid. The device for carrying out this method comprises a conduit 10 through which gas can be passed and which is terminated by gas outlet 7 for directing a stream of gas towards a sample of liquid 18 to be tested, means 2-7 for directing a beam of light parallel and adjacent to a stream of gas from the outlet, means 12 for causing the stream of gas to pulse from the outlet, means 11 for measuring the gas pressure in the conduit, means 15 for receiving light reflected from the surface of a liquid sample and for measuring a characteristic of the reflected light. <IMAGE>

Description

SPECIFICATION A device for measuring physical properties of liquids The invention relates to a method and device for measuring physical properties of liquids.

Known means for testing liquids usually require contact with the liquids concerned. Thus when measuring the viscosity of a liquid it is usually necessary to insert a paddle or weight into the liquid sample.

It is an object of the invention to provide a method and means for making such measurements without mechanically contacting the liquid being measured.

According to the invention there is provided a method of testing the physical properties of a liquid comprising illuminating a portion of the surface of the liquid sample with a beam of light, e.g. by laser light, measuring a characteristic, e.g. intensity or distribution, of light reflected from the illuminated portion of the surface of the liquid, directing a pulse of gas at the illuminated portion of the surface of the liquid to cause local deformation therein, and measuring the change in the characteristic of the light reflected from the illuminated deformation of the surface of the liquid.

The method may comprise sharply terminating the pulse of gas and continuing to measure the characteristic of the reflected light thereafter to determine the rate of decay of the deformation in the liquid surface, or may comprise directing a series of pulses of gas at the illuminated portion of the surface of the liquid to vibrate the liquid. Preferably the gas pulse is directed at right angles to the surface of the liquid.

If desired the illuminated portion of the liquid may be vibrated by means of a beam of sound waves, and if desired the frequency of the sound beam may be varied to maximise the sympathetic vibration of the said portion of the liquid. Preferably the sound beam will be directed at right angles to the surface of the liquid.

Preferably the light beam is directed at right angles to the surface of the liquid, and preferably the gas pulse is released at a gauge pressure in the range 1 to 5 millibars. The gas pulse may be directed at the surface of the liquid through a nozzle disposed at a distance from the surface in the range 5 to 15 mm.

The method may comprise the steps of pulsing the gas so that it rises in pressure to a predetermined level and maintaining the pressure at that level for a fixed period of time. The method may comprise measuring the rate of rise in gas pressure and measuring the steady state of the gas pressure, and may also comprise the step of continuously monitoring the gas pressure. The method may comprise measuring a characteristic of the reflected light beam during the gas pressure rise, and/or during steady state of gas pulse and/or during the gas pressure fall.

From another aspect the invention is a device for measuring physical properties of liquids comprising. a conduit through which gas can be passed and which is terminated by gas outlet for directing a stream of gas towards a sample of liquid to be tested, means for directing a beam of light parallel and adjacent to a stream of gas from the outlet, means for causing the stream of gas to pulse from the outlet, means for measuring the gas pressure in the conduit, means for receiving light reflected from the surface of a liquid sample and for measuring a characteristic of the reflected light.

The device preferably comprises an electrically controlled valve in the conduit to permit gas pulses to be released from the outlet, a source of gas under pressure, and means for controlling the gas pressure in the conduit.

Preferably the device comprises a laser light source, which may be a semiconductor laser.

A collimating lens may be provided for collimating light from the light source.

The device may comprise a photo detector arranged to receive light reflected from the liquid sample, and a pin-hole aperture may be disposed in front of the photo detector to restrict light reaching the photo detector.

Preferably the device comprises means for varying the distance between the gas outlet and the surface of the liquid sample, and means may be provided for varying the size of the gas outlet. Thus for example the gas outlet may comprise a series of interchangeable nozzles.

The method and device enable physical properties of the liquid such as density, surface tension and viscosity to be deduced from the measurements made.

The invention is diagrammatically illustrated, by way of example in the accompanying drawing which is a cross-sectional sketch of a preferred embodiment of a device for measuring physical properties of liquids.

Referring to the drawing, a device 1 for measuring physical properties of liquid comprises a generally tubular housing 3 having a laser diode light source 2 at its upper end and which is arranged to direct light from an aperture or nozzle 7 in the bottom of the housing.

Near to its bottom end the housing is formed with a gas inlet which opens into a chamber 8 bounded at its upper end by a window 6. Gas entering the chamber 8 is exhausted downwardly through the nozzle 7. The inlet 9 is connected to a source 13 of gas under pressure by means of a pipe 10 and a valve 12 is arranged in the gas pipe 10 so that a stream of gas passing down the pipe can be pulsed.

A pressure sensor 11 is disposed in the pipe downstream of the valve so that the pressure of the gas in the pulse can be continuously monitored.

A collimating assembly 4 is disposed in the housing 3 below the laser 2 to condition light from the laser and a beam splitter is -disposed in the housing below the assembly 4 so that light reflected from a liquid sample 18 is deflected substantially at right angles onto a photo detector 15. The photo detector 15, in this case a photo diode, is disposed in a tubular side limb 14 of the housing 3. A mask 16 formed with a central pinhole aperture 17 is disposed in front of the photo diode 15 to restrict the area of light impinging on the photo diode.

In operation light from the laser diode 2 is directed at the liquid surface 18 and light reflected from the liquid surface is received by the photo detector assembly 15. The detector may be arranged to measure any desired characteristic of the reflected light, for example intensity, distribution and so on.

A pulse of gas created by the valve 12 exits through the nozzle 7 and impinges on the liquid surface in the area illuminated by the optical system to distort the liquid surface.

The gas may be air which can be drawn from the atmosphere and filtered and pressurised within the instrument. Alternatively, an inert gas may be supplied from a separate source.

The pressure profile as the gas fiows through the tube to the liquid surface is preferably continuously monitored by the pressure sensor.

Thus the device can measure the intensity of the reflected light before a gas pulse is initiated, during the rise in gas pressure, during its steady state and during its decay. Thus the device can measure the. time taken for the liquid surface to recover from the deformation, which will give the viscosity of the liquid. The gas pulses may be rapid so as to vibrate the liquid surface and if desired the gas pressure pulses may be created by a sound-wave generator, Preferably the electronics of the device is such that the device is self ranging. Thus the device may at first provide a low pressure pulse of gas and depending on the results obtained will then increase the gas pressure until a satisfactory response is achieved.

Values of the physical properties of the liquid are derived from the type of gas used, the gas jet pressure, the dynamic profile and steady state value, the liquid surface curvature, from the photo detector signals during dynamic pressure rise, liquid surface curvature, from the photo detector signals in the steady state, liquid surface curvature, from the photo detector signals during the pressure fall, and the frequency of bounce of liquid sample after being subjected to the gas pulse.

Since the device described above operates without contacting the sample, it has the advantages of being aseptic, sterile, thus preventing cross-contamination between samples and is non-invasive. The device has low power requirements and works on small samples with minimal mechanical disturbance.

The device operates in real time and with a fast cycle time. It requires no cleaning and permits the monitoring of reactions. The output of the device may be fed directly to a computer. Also the device can be used to measure a pluraiity of different properties of a sample.

Claims

1. A method of testing the physical properties of a liquid comprising illuminating a portion of the surface of the liquid sample with a beam of light, measuring a characteristic of the light reflected from the illuminated portion of the surface of the liquid, directing a pulse of gas at the illuminated portion of the surface of the liquid to cause local deformation therein, and measuring the change in the characteristic of the light reflected from the illuminated deformation of the surface of the liquid.

2. A method according to claim 1, comprising measuring the intensity of the reflected light.

3. A method according to claim 1, comprising measuring the distribution of the reflected light.

4. A method according to any preceding claim, comprising sharply terminating the pulse of gas and continuing to measure the characteristic of the reflected light thereafter to determine the rate of decay of the deformation in the liquid surface.

5. A method according to any preceding claim, comprising directing a series of pulses of gas at the illuminated portion of the surface of the liquid to vibrate the liquid.

6. A method according to any preceding claim, comprising directing the gas pulse at right angles to the surface of the liquid.

7. A method according to claim 5 or claim 6, comprising vibrating the illuminated portion of the liquid by means of a beam of sound waves.

8. A method according to claim 7, comprising varying the frequency of the sound beam to maximise the sympathetic vibration of the said portion of the liquid.

9. A method according to claim 7 or claim 8, comprising directing the sound beam at right angles to the surface of the liquid.

10. A method according to any preceding claim, comprising directing a source of laser light at the portion of the liquid surface.

11. A method according to any preceding claim, wherein the light beam is directed at right angles to the surface of the liquid.

12. A method according to any one of claims 1 to 6, wherein the gas pulse is released at a gauge pressure in the range 1 to 5 millibars.

13. A method according to any one of claims 1 to 6 or 12, wherein the gas pulse is directed at the surface the liquid through a nozzle disposed at a distance from the surface in the range 5 to 15 mm.

14. A method according to any one of claims 1 to 6 or 12 or 13, comprising the steps of pulsing the gas so that it rises in pressure to a pre-determined level and maintaining the pressure at that level for a fixed period of time.

15. A method according to claim 14, comprising measuring the rate of rise in gas pressure and measuring the steady state of the gas pressure.

16. A method according to claim 14 or claim 15, comprising the step of continuously monitoring the gas pressure.

17. A method according to any one of claims 14 to 16, comprising measuring a characteristic of the reflected light beam during the gas pressure rise, and/or during steady state of gas pulse and/or during the gas pressure fall.

18. A method of testing the physical properties of a liquid substantially as hereinbefore described.

19. A device for measuring physical properties of liquids comprising a conduit through which gas can be passed and which is terminated by gas outlet for directing a stream of gas towards a sample of liquid to be tested, means for directing a beam of light parallel and adjacent to a stream of gas from the outlet, means for causing the stream of gas to pulse from the outlet, means for measuring the gas pressure in the conduit, means for receiving light reflected from the surface of a liquid sample and for measuring a characteristic of the reflected light.

20. A device according to claim 19, comprising an electrically controlled valve in the conduit to permit gas pulses to be released from the outlet.

21. A device according to claim 19 or claim 20, comprising a source of gas under pressure, and means for controlling the gas pressure in the conduit.

22. A device according to any one of claims 19 to 21 , comprising a laser light source.

23. A device according to claim 22, wherein the laser is a semiconductor laser.

24. A device according to any one of claims 19 to 23, comprising a collimating lens for collimating light from the light source.

25. A device according to any one of claims 19 to 24, comprising a photo detector arranged to receive light reflected from the liquid sample.

26. A device according to claim 25, comprising a pin-hole aperture disposed in front of the photo detector to restrict light reaching the photo detector.

27. A device according to any one of claims 19 to 26, comprising means for varying the distance between the gas outlet and the surface of the liquid sample.

28. A device according to any one of claims 19 to 27, comprising means for varying the size of the gas outlet.

29. A device for measuring the physical properties of a liquid substantially as hereinbefore described with reference to, and as iliustrated in, the accompanying drawing.