(54) METHODS AND APPARATUS FOR PREVENTINGTHE ACCUMULATION OF DEPOSITS ON SURFACES(71) We, WILLIAM BOULTON LIMITED, a British Company, of Providence EngineeringWorks, Navigation Road, Burslem, Stokesn- Trent, Staffordshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:The invention relates to methods and apparatus for preventing the accumulation of deposits on surfaces immersed in liquid.
In connection with the control of water pollution it is necessary to monitor the turbidity of water in rivers, streams and the like. For this purpose apparatus is known which comprises a light source and a detector in the form of a photoelectric cell so disposed that the water to be tested flows between them. The degree of cloudiness or turbidity of the water therefore effects the amount of light transmitted to the photoelectric cell and this information can be recorded to provide a record of changes in turbidity.
A problem arising with equipment of this kind is that the growth of algae and like deposits on the surfaces of the light source and the detector obscures the light and produces a false reading and it is an object of the present invention to provide a method and means by which this problem can be overcome, although the invention is capable of application in a much wider field.
The invention provides a method of preventing the accumulation of algae on turbidity sensing apparatus incorporating a light source and a detector having associated lenses disposed in positions facing one another comprising directing ultra-sonic waves between the light source and the detector at a frequency and power sufficient to prevent growth of algae without damaging the lenses or seriously affecting the light transmission between the light source and the detector.
The frequency of the ultrasonic waves, the manner in which they are directed relative to the lenses and the distance from the lenses at which the vibrations are introduced into the liquid may be varied considerably depending on the nature of the lenses and other factors such as the nature of the algae deposit, the accumulation of which is to be prevented.
It is necessary to ensure that the optical properties of the liquid are not affected and in such situations frequencies of the order of lkHz100 kHz have been found to be satisfactory.
It is believed that the invention functions due to the ultra-sonic waves causing cavitation in the liquid. The ultra-sonic waves may be introduced into the liquid so as to be directed at an angle to the lenses to be treated. It has been found however that satisfactory results can be attained by directing the waves in a direction parallel to the surfaces of the lenses and in this way the spaced lenses used in the turbidity recording apparatus may both be cleaned by a single ultra-sonic source positioned to direct waves between the lenses. The arrangement adopted will of course depend to a considerable extend on the nature of the lenses and of the liquid and on the frequency of vibration concerned.
The invention also provides apparatus for measuring the turbidity of a liquid including a light source and a detector having associated lenses disposed in positions facing one another and defining a passage through which the liquid may flow and means for directing ultra-sonic waves into the liquid in the vicinity of said lenses at a frequency and power sufficient to prevent growth of algae without damaging the lenses or seriously affecting the light transmission between the light source and the detector.
Said means for directing ultra-sonic waves into the liquid may be arranged to direct the waves into said passage at right angles to the common axis of the lenses.
An embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:Figure 1 is a side elevation of an apparatus for sensing the turbidity of water incorporating means for preventing the accumulation of algae deposits; and Figure 2 is an end view of the apparatus shown in Figure 1.
Referring to the drawings, the apparatus comprises a sensing unit 5 suspended by a stainless steel tube 4 in river water and having two depending portions 6 and 7 one of which incorporates a light source and the other a de-tector in the form of a photoelectric cell. The portions 6 and 7 of the sensing device are spaced from one another by a distance of about 2-3 inches to define a channel or passage 8 through which water may flow in the direction of arrow F in Figure 2 and the light source and photo electric cell have respective lenses 6A and 7A disposed facing one another at opposite side of the passage 8. In operation the turbidity of the water passing through the passage 8 affects the quantity of light reaching the photoelectric cell from the light source and the changes in light intensity thus provide a measure of changes in turbidity of the water.
The electrical connections to the unit 5 are made through the tube 4.
An ultra-sonic transducer 10 is disposed opposite the channel 8 in the device 5 and is connected thereto by support brackets 11 (seeFigure 2). The transducer incorporates a pair of piezoelectric elements 12 mounted on a bar 13 which is bonded to the external wall of the unit and faces the channel 8 in the sensing unit 5.
The outer surface of the unit 10 therefore constitutes a radiating face and in the example is spaced about two inches from the lenses 6A and 7A. A coaxial cable 14 is connected to the transducer 10 through a water-tight seal 15 and is led to an ultra-sonic generator whereby the piezoelectric elements are constrained to vibrate at ultra-sonic frequency and the vibrations are transmitted from the radiating face of the bar 13 through the surrounding water and into the channel 8 between the lenses 6A and 7A. In the example the ultra-sonic generator is an 80 watt generator powered by a single phase 240 volt, 50 HZ A.C. supply producing an ultra-sonic base frequency of 40 kHz.
It has been found that while the sensing unit 5 used on its own requires frequent cleaning of the lenses 6A and 7A, the incorporation of the ultra-sonic transducer 10 substantially reduces the extent to which cleaning of the lenses is required. It is believed that the invention functions due to the fact that the ultra-sonic waves induce cavitation in the water in the region of the passage 8 thereby producing large numbers of microscopic bubbles which result in a scrubbing effect on contacting the lenses thereby preventing the accumulation of algae. Due to the microscopic nature of the bubbles they do not interfere with the optical properties of the water and therefore do not affect the turbidity readings of the device 5. Although the ultrasonic waves are directed parallel to the surfaces of the lenses an appreciable side effect is produced which achieves the desired result.
Various modifications may be made without departing from the invention. For example the spacing apart of the lenses 6A and 7A and the distance of the ultra-sonic radiating surface 13 from the lenses may be varied considerably depending on the construction of the apparatus and on the operating frequency. Various different operating frequencies and powers may be used and the device may operate on continuous or modulated waves. The essential requirements are that the ultra-sonic waves generated must be sufficient to prevent growth of algae without in any way damaging the lenses or producing cavitation bubbles of a size which affect the light transmission between the light source and the photoelectric cell. The preferred range of operating frequencies is 1 kHz-100 kHz, but frequencies up to 1000 MHz could be used.
WHAT WE CLAIM IS:1. A method of preventing the accumulation of algae on turbidity sensing apparatus incorporating a light source and a detector having associated lenses disposed in positions facing one another comprising directing ultrasonic waves between the light source and the detector at a frequency and power sufficient to prevent growth of algae without damaging the lenses or seriously affecting the light transmission between the light source and the detector.
2. A method according to claim 1 wherein said waves are directed between and parallel to the surfaces of said lenses from a single source.
3. A method according to claim 1 or 2 wherein the frequency of said ultra-sonic waves is 1 to 100 kHz.
4. A method of preventing the accumulation of algae on turbidity sensing apparatus substantially as hereinbefore described.
5. Apparatus for measuring the turbidity of a liquid including a light source and a detector having associated lenses disposed in positions facing one another and defining a passage through which the liquid may flow and means for directing ultra-sonic waves into the liquid in the vicinity of said lenses at a frequency and power sufficient to prevent growth of algae without damaging the lenses or seriously affecting the light transmission between the light source and the detector.
6. Apparatus according to claim 5 wherein said means for directing said waves into the liquid is arranged to direct the waves into said passage at right angles to the common axis of the lenses.
7. Apparatus according to claim 5 or 6 wherein said means for directing said waves into the liquid comprises an ultra-sonic transducer having a radiating face directed towards said passage.
8. Apparatus according to claim 7 wherein said transducer is carried by a housing in which said lenses are mounted and is secured to the housing by brackets serving to space the transducer a predetermined distance from said passage.
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