Abstract:
A multisensor employs an optical system that is modified by the index of refraction of fluid passing between a light emitter and light detector to successfully distinguish between air and water (of any turbidity) and between water of different turbidity values. The optical system may employ lenses contacting the fluid to change their focal length and thus to focus and defocus light on the light detector depending on an index of refraction of the fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application 61/903,035 filed Nov. 12, 2013, and hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to optical sensors for the measurement of both of the turbidity of liquid and the presence of the liquid in a sensing volume and in particular to an optical sensor that may make both measurements using a single optical channel. 
       BACKGROUND OF THE INVENTION 
       [0003]    Optical sensors may be used to detect the presence or absence of a liquid, for example, in a washing machine or dishwasher and for determining the turbidity of that liquid when liquid is present. Such turbidity measurements may indicate the amount of dirt suspended in the water and may be used to assess how much cleaning or rinsing is required. 
         [0004]    The turbidity of a liquid in a sampling volume may be measured by assessing how much light passes between a light transmitter and light detector positioned so that the path of light between the light transmitter and light detector crosses the sampling volume. The light transmitter may be an electronic light source such as a light emitting diode and the light detector may be an electronic light sensor such as a photodiode, phototransistor, or the like. 
         [0005]    The amount of light passing between the light transmitter and light detector in a turbidity sensor will also be affected by whether the sampling volume contains air or water. Air in the sampling volume will typically reduce the amount of light passing between the light transmitter and light detector when compared to the light transmitted by a clear liquid. This is because the turbidity sensor normally includes optical elements configured to maximize light transmission in liquid to ensure sufficient light is transmitted for measurement of highly turbid water. As a result, a turbidity sensor with a single optical channel (for example, one light transmitter and one light detector) cannot reliably distinguish between air and turbid water. 
         [0006]    Multisensors which combine a liquid presence sensor and a turbidity sensor normally use two optical channels each producing independent signals. The first channel may provide a straight transmission path through the sampling volume between a first light transmitter/receiver pair to deduce turbidity. The second channel may provide a transmission path reflecting off a boundary between an optical element and material in the sampling volume between the second light transmitter/receiver pair. The optical element will provide for a greater internal reflection when air is in the sampling volume than when water is in the sampling volume thus reliably distinguishing between air and liquid. 
         [0007]    These two optical channels may share one of optical transmitters or receivers, for example, through multiplexing techniques, but generally require at least three components selected from optical transmitters and receivers and two optical paths. 
       SUMMARY OF THE INVENTION 
       [0008]    The present inventors have recognized that a single optical channel can be used to detect turbidity and to detect the presence or absence of liquid by ensuring that the attenuation of the light in this optical channel is less for air than it is for clear water. In one embodiment, this relative attenuation is enforced by focusing the light between the light transmitter and the light detector using refractive elements under the assumption that the refractive elements are in an air environment. The introduction of water into that environment upsets this assumption and de-focuses these refractive elements reducing the light intensity at the light detector. 
         [0009]    Specifically then, at least one embodiment of the invention provides a turbidity sensor having an electronic light source and electronic light detector positioned in opposition along an optical path through a channel open to receive a passage of fluid therethrough. At least one optical element is positioned along the optical path in contact with the fluid to change the transmission of light between the electronic light source and electronic light detector as a function of an index of refraction of the fluid relative to material of the optical element to produce a first level of transmission of light from the electronic light source to the electronic light detector when the fluid in the passage is air and to produce a second level of transmission of light from the electronic light source to the electronic light detector when the fluid in the passage is clear water, the first level being greater than the second level. 
         [0010]    It is thus a feature of at least one embodiment of the invention to provide a turbidity sensor that unambiguously distinguishes between air and water of different turbidities. 
         [0011]    The optical element may be a focusing lens positioned along the optical path to be in contact with fluid in the passage. 
         [0012]    It is thus a feature of at least one embodiment of the invention to employ optical elements that increase the light energy transmitted through the fluid by focusing. 
         [0013]    The turbidity sensor may employ two lenses positioned along the optical path to be in contact with fluid from the passage wherein the lenses are positioned and focused to provide the first level of transmission of light from the electronic light source to the electronic light detector when the fluid in the passage is air and the second level of transmission of light from the electronic light source to the electronic light detector when the fluid in the passage is clear water, the first level of transmission of light being greater than the second level of transmission of light. 
         [0014]    It is thus a feature of at least one embodiment of the invention to employ a defocusing to distinguish between types of fluid in contrast to fluid turbidities. 
         [0015]    The lenses may be circular lenses selected from the group consisting of circular plano-convex lenses and bi-convex lenses. 
         [0016]    It is thus a feature of at least one embodiment of the invention to permit the use of common lens structures. 
         [0017]    Alternatively, the lenses may be cylindrical or sphero-cylindrical lenses. 
         [0018]    It is thus a feature of at least one embodiment of the invention to provide a lens structure that permits wide beam shapes or that accommodates optical misalignment. 
         [0019]    The turbidity sensor may include detection circuitry for detecting at least three levels of light transmission corresponding to the fluid in the passage being air, the fluid in the passage being water of low turbidity and the fluid in the passage being water of high turbidity, higher than the low turbidity. 
         [0020]    It is thus a feature of at least one embodiment of the invention to provide a turbidity sensor that may be used for multiple control purposes within the appliance to both sense turbidity and distinguish between different fluids. 
         [0021]    The turbidity sensor may include only a single electronic light source and single electronic light detector. 
         [0022]    It is thus a feature of at least one embodiment of the invention to greatly reduced the parts count required of current turbidity sensor technologies. 
         [0023]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a simplified perspective view of a multisensor in phantom detecting both turbidity and liquid presence constructed according to one embodiment of the invention; 
           [0025]      FIG. 2  is a depiction of the optical path of the sensor of  FIG. 1  under three conditions of air, clear water, and turbid water interposed between the light transmitter and light detector and showing a relative signal strength provided by the multisensor in each situation; 
           [0026]      FIGS. 3 a -3 c    are examples of three different optical systems that may be employed in various embodiments of the present invention; 
           [0027]      FIG. 4  is a chart of light transmission in the prior art showing the overlap of light transmission levels for air and water normalized to a peak value of 100 percent and plotted against turbidity in Nephelometric Turbidity Units (NTU); 
           [0028]      FIG. 5  is a chart similar to that of  FIG. 4  showing the separation of transmission levels for air and water in the present invention; 
           [0029]      FIG. 6  is a simplified block diagram of detection circuitry suitable for use with the present invention; and 
           [0030]      FIG. 7  is a simplified diagram of a washing appliance that may use the multisensor of the present invention. 
       
    
    
       [0031]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Referring now to  FIG. 1 , a multisensor  10  per the present invention may provide a U-shaped frame  12  having opposed arms  14   a  and  14   b  extending in opposition across a fluid passage  16 . The first arm  14   a  may hold at a distal end a light transmitter  18 , for example, providing a light source, and including but not limited to a light emitting diode die or light emitting diode die plus encapsulating lens element. The light transmitter  18  directs light along optical axis  20  through the fluid passage  16  toward a distal end of the second arm  14   b.    
         [0033]    The second arm  14   b  may in turn hold at a distal end a light detector  22 , for example, a photosensor such as a photodiode, photo transistor, a photo resistor, or photocell, receiving light along the optical axis  20  through the fluid passage  16  from the first arms  14   a . The photosensor may include some integrated optical lenses or may be a die without lens. 
         [0034]    A collimating lens  24  may be positioned along the optical axis  20  between the light transmitter  18  within the arm  14   a  and an external fluid  26  in the fluid passage  16 . Likewise a focusing lens  28  may be positioned along the optical axis  20  between the external fluid  26  in the fluid passage  16  and the light detector  22  in the arm  14   b.    
         [0035]    Generally both the collimating lens  24  and focusing lens  28  will contact the external fluid  26  such as may modify the focal properties of the collimating lens  24  and the focusing lens  28  by changing the difference in index of refraction between the optical material of the lenses  24  and  28  and the surrounding medium such as changes refraction. 
         [0036]    The light transmitter  18  may communicate via leads  30  passing within the arm  14   a  to a source of electrical power and the light detector  22  may communicate via leads  32  passing within the arm  14   b  to detection circuitry for determining an amount of light received by the light detector  22 . 
         [0037]    The collimating lens  24  and the focusing lens  28  may be sealed to the respective arms  14   a  and  14   b  to prevent fluid from leaking into the arms  14  which are otherwise sealed against fluid ingress. The arms  14  may attach to a base  19  that includes a seal  17  allowing the base  19  to be attached through an opening and sealed to the opening in a channel containing a stream of liquid flow of external liquid  26  to prevent leakage therefrom so that the arms  14  extend into the liquid flow and the leads  30  and  32  are accessible outside of the channel from an opposite side of the base  19 . 
         [0038]    Referring now to  FIG. 2 , in environment  37  when the multisensor  10  is operated with air  33  within the fluid passage  16 , collimating lens  24  and focusing lens  28  transmit an image of a surface of the light transmitter  18  originating at a first focal plane  34  to a second focal plane  36  focused on the surface of the light detector  22 . In this regard, collimating lens  24 , focusing lens  28 , and the geometry of the focal planes  34  and  36  and the positions of the lenses  24  and  28  are selected according to well understood optical principles to provide this focusing with air  33  within the fluid passage  16 . 
         [0039]    It will be understood that this focusing described above is dependent on the focal length of the lenses  24  and  28 , the latter of which is generally determined by the difference between the index of refraction of the lens material and the index of refraction of the medium surrounding the lens and in particular the media in the fluid passage  16 . 
         [0040]    By placing light detector  22  at focal plane  36  of lens  28  in the environment  37 , a compact illumination spot  38  (shown displaced from light detector  22  and rotated 90 degrees for clarity) will generally conform to an image of the light transmitter  18  concentrating and maximizing the light energy from the light transmitter  18  on the active area of the light detector  22 . This will produce a detector output, for example, of 180 percent, as referenced to a detector output of 100 percent expected when clear liquid water is within the fluid passage  16  as shown in  FIG. 5  by curve  51 . This output is independent of the turbidity of water (shown in the horizontal axis of  FIG. 5 ) simply because water is not positioned between the light transmitter  18  and the light detector  22  in this environment  37 . 
         [0041]    Referring still to  FIG. 2 , in environment  40 , when the multisensor  10  is operated with clear water  41  within the fluid passage  16 , collimating lens  24  and focusing lens  28  transmit an image of a surface of the light transmitter  18  at a second focal plane  42  past the surface of the light detector  22 . In this case, the illumination spot  38 ′ on the light detector  22  will be an unfocused image of the light transmitter  18  and thus be larger to extend outside the boundaries of the light detector  22  and more diffuse within the boundaries of the light detector  22 , reducing the amount of light detected by the light detector  22  to a value of 100 percent (normalized to this water transmission path) which is, importantly, lower than that obtained when air  33  is within the fluid passage  16  as shown in environment  37 . 
         [0042]    Finally, referring to  FIG. 2 , in environment  46 , when multisensor  10  is operated with turbid water  48  within fluid passage  16 , including, for example, water holding suspended solids and bubbles, collimating lens  24  and focusing lens  28  again focus the image of the surface of the light transmitter  18  at second focal plane  42  removed from the light detector  22  providing not only a more diffuse illumination spot  38 ″ but also one that is attenuated by the scattering and absorption of the turbid water  48 . The result is a detector value, for example, of 50 percent, being below the detector values for air or clear water. Generally, a range of varying turbidity will provide a corresponding range of varying attenuation in detected light along a curve  50  in a plot of light attenuation vs. turbidity that may be used to provide a quantitative output of turbidity. 
         [0043]    The chart shown in  FIG. 5  may be contrasted with the chart in  FIG. 4  showing a prior art system without the focused optics of the present invention such as produces an overlap between curve  51 ′ corresponding to curve  51  and curve  50 ′ corresponding to curve  50 . In the chart of  FIG. 4 , the presence of air between the light transmitter  18  and light detector  22  cannot be distinguished from the presence of water between the light transmitter  18  and the light detector  22  if the water has an NTU value of approximately 200. Given that there will be some variation in the values of the signals based on normal manufacturing tolerances, the practical effect is that the presence of air or water may not be adequately distinguish over an important range of turbidity. In contrast, the chart of  FIG. 5  shows that the presence of air may be readily distinguished from the presence of water at all turbidity levels. 
         [0044]    Referring still to  FIG. 2 , it will be noted that the light transmitter  18  and light detector  22  may include optional ancillary lenses  35 , for example, incorporated into the packages of the light transmitter  18  and/or light detector  22  or other lenses may be placed along the optical path. Generally these lenses will not be in contact with fluid in the fluid passage  16 . The focusing effect of these ancillary lenses  35  is simply accommodated in the placement and focusing of the lenses  24  and  28  to provide the desired detection effect described above. 
         [0045]    Referring now to  FIG. 3 , various optical systems may be used in the present invention including circular plano-convex lenses or biconvex lenses  52  as shown in  FIG. 3 a   , cylindrical lenses  54  as shown in  FIG. 3 b    and sphero-cylindrical lenses  55  as shown in  FIG. 3 c   . A cylindrical lens  54  is one having a surface that is a portion of a cylinder. A sphero-cylindrical lens  55  is one having different portions of its surface that are portions of spheres (for example, the ends of the lens) and other portions that are portions of a cylinder. Any of these lenses may be solid surface or Fresnel versions. It is contemplated that the lenses will be injection molded but other fabrication techniques may be employed. The lenses may be integrally molded into opposed faces of the arms  14 . 
         [0046]    Each of these lenses  52 ,  54 , and  55  may be configured to provide a concentrated focusing of light from the light transmitter  18  on the light detector  22 , and thus a maximum light detected at light detector  22  in the presence of air along the optical axis  20 , and a lesser focusing and lower light detected at light detector  22  even with perfectly clear water and decreasing with increased water turbidity. 
         [0047]    Referring now to  FIG. 6 , a control circuit  49  suitable for the present sensor may provide for a biasing circuit  56  for the light transmitter  18  and a biasing circuit  57  for the light detector  22  both operating from a common power line  58 . Fluctuations in the power, for example, incident to unregulated power in a home appliance or the like may be accommodated by also providing a comparator system  59  that generates threshold voltages  61  from the power line  58 . In this way, common mode variations in the power line  88  cause the threshold voltages to rise and fall together with the biasing of the light transmitter  18  and light detector  22  to offset this effect. The generated threshold voltages may provide for two threshold voltages V 1  and V 2  provided to separate comparators  63   a  and  63   b  which also receive an output from the light detector. 
         [0048]    Referring momentarily to  FIG. 5 , these threshold voltages V 1  and V 2  may distinguish curve  51  from curve  50  at all turbidities and distinguish a high and low turbidity value on curve  50  such as may trigger a washing process. Specifically, the voltage V 1  defines above it, a first range  53  of light transmission indicative of the presence of air between the light transmitter  18  and light detector  22 , and the voltage V 1  defines below it a second range  65  associated only with the presence of water between the light transmitter  18  and light detector  22 . The voltage V 2  divides the second range  65  into a first sub range  65   a  associated with a first turbidity and the second sub range  65   b  associated with a second turbidity. These first and second sub ranges  65   a  and  65   b  may be used to control the washing cycles of the appliance selecting between light and heavy cycles while the first range  53  may be used to determine that the water is present or absent at the beginning or end of the cycles to ensure that a washing chamber is filled or emptied as the case may be. 
         [0049]    Referring now to  FIG. 7 , the multisensor  10  of the present invention may be positioned in a fluid conduit as part of a washing appliance  60  having a washing chamber  62  accessible through a lid  64 . Washing water may be circulated to the washing chamber  62  as pumped by a pump  66  through the fluid passage  16 . The appliance may include water heater  67  for heating that recirculating water, water inlet valve  68  for adding water from a public water supply to the washing chamber  62 , drain valve  70  for removing water from the washing chamber  62  into a water drain, and agitator  72  for agitating the water within the washing chamber as connected to a motor  74 . Generally each of the multisensor  10 , pump  66 , water heater  67 , valve  68 , valve  70 , and motor  74  may be read by or controlled by electronic computer  80  executing a stored program  82  to adjust washing parameters based on turbidity and the presence or absence of water within the fluid passage  16 . The computer  80  may communicate with a console control  84  providing input and output to a user of the appliance. For example, the multisensor  10  may determine how dirty is the material being washed and change the length or number of washing cycles by controlling duration of operation of the pump  66  or the temperature of the water by controlling the duration of the operation of the heater  67 . 
         [0050]    It will be appreciated that the invention may also be accomplished with a single lens system, for example, providing a lens only at the light detector so long as the same defocusing occurs in the presence of liquid between the light transmitter and light detector. In one embodiment, a single light detector and single light sensor may be used, as shown herein; however, will be appreciated that multiple light sensors and light detectors may be added in tandem for increased sensitivity while still constituting a single optical channel. The invention may also be used with completely separate optical channels yet still provide an optical system that maximizes light throughput on one channel for air over water. The path of light along the optical axis  20  within the arms  14   a  and  14   b  may travel through air, although any medium of known index of refraction may be placed in this region. 
         [0051]    While the present invention has been described with respect to a U-shaped frame  12 , it will be appreciated that the fluid passage  16  may be of arbitrary shape that allows the flow of external fluid  26  between the light transmitter  18  and the light detector  22  including, for example, a tubular structure. 
         [0052]    Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.