Patent Publication Number: US-2013235380-A1

Title: Calculating the concentration of solids in a fluid

Description:
BACKGROUND 
     Densitometers can measure the passage of light through a transparent or semitransparent material. The measured density of a measurable substance is typically determined by measuring attenuation in the intensity of light which reaches the optical detector of the densitometer after passing through the measurable substance, the measurement being related to the absorption of light of the measurable substance. 
     Most densitometers include a light source, often a laser, aimed at a photoelectric cell, arranged with a gap in between so as to allow placing the measurable substance in the gap. The electric current that is generated by the photovoltaic cell of the densitometer is typically directly proportional to the intensity of the incident light, and thus the density of the measurable substance is determined by comparing the generated current with a reference current value that corresponds to the passing of light from the light source to the photovoltaic cell when the gap is kept empty (e.g. in vacuum). 
     Densitometers can be either transmission densitometers or reflection densitometers. Transmission densitometry instruments typically measure how transparent a substance is to visible light or other electromagnetic radiation. Reflection densitometry devices measure the amount of reflected visible light or other electromagnetic radiation of a sample. Densitometers are used in many industries as tools to measure the concentration of solids in a liquid of materials, i.e., liquids, and to provide quality assurances of a particular liquid, including foodstuffs, medications, or ink for inkjet printers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples are described in the following detailed description and illustrated in the accompanying drawings in which: 
         FIG. 1   a  is a schematic illustration of a device for calculating the optical density, and in some examples, the concentration of solids in a fluid, according to an example; 
         FIG. 2  is a flow chart of a method for calculating the concentration of solids in a liquid of a fluid, according to an example; and, 
         FIG. 3  is flow chart of a method for calculating the concentration of solids in a liquid of a fluid, according to an example. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the methods and apparatus. However, it will be understood by those skilled in the art that the present methods and apparatus may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present methods and apparatus. 
     Although the examples disclosed and discussed herein are not limited in this regard, the terms “plurality” and “a plurality” as used herein may include, for example, “multiple” or “two or more”. The terms “plurality” or “a plurality” may be used throughout the specification to describe two or more components, devices, elements, units, parameters, or the like. Unless explicitly stated, the method examples described herein are not constrained to a particular order or sequence. Additionally, some of the described method examples or elements thereof can occur or be performed at the same point in time. 
     Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification, discussions utilizing terms such as “adding”, “associating” “selecting,” “evaluating,” “processing,” “computing,” “calculating,” “determining,” “designating,” “allocating” or the like, refer to the actions and/or processes of a computer, computer processor or computing system, or similar electronic computing device, that manipulate, execute and/or transform data represented as physical, such as electronic, quantities within the computing system&#39;s registers and/or memories into other data similarly represented as physical quantities within the computing system&#39;s memories, registers or other such information storage, transmission or display devices. 
       FIG. 1   a  is a schematic illustration of a device for, in some examples, calculating the concentration of solids in a fluid, according to an example. 
     A densitometer  100  may typically include a light source  10 , a collimating lens  20 , a focusing lens  30 , and a detector  40 . Other lenses as are known in the art may also be employed in addition to, or instead of, lenses  30  and  40 , in some examples. 
     In some examples, detector  40  may be a photodiode. Other detectors that are known in the art may also be employed. 
     Densitometer  100  may typically be configured to determine the optical density of a fluid  60  passing through a gap  50  between lens  20  and lens  30 . Typically, densitometer  100  measures the concentration of solids in a fluid. In some examples, densitometer  100  measures other characteristics of fluids as are known in the art. 
     In some examples gap  50  may be between light source  10  and detector  40 . In some examples, gap  50  may have a set width, the width maintained by a support structure, the support structure configured to maintain the width of the gap to a high degree of tolerance. 
     In some examples, light source  10  may be configured to transmit a signal  5  through fluid  60  and gap  50 . Typically, signal  5  may be a light beam. In some examples, the light beam may be produced by a laser. Other signals known in the art may also be employed by densitometer  100 . 
     In some examples, gap  50  may have a width of a few hundred microns (e.g. about 300 microns, for example, with a tolerance of +/−10 microns). In some examples, gap  50  may have a width less than 300 microns. In some examples, gap  50  may have a width greater than 300 microns. 
     In some examples, gap  50  may be configured to be positioned between an inlet  70 , and an outlet  80 , such that the pathway of fluid  60  flowing through gap  50  is substantially perpendicular to the pathway of signal  5  traveling from light source  10  to detector  40 . Fluid  60  traveling from inlet  70 , through densitometer  100  and continuing, in some examples, through outlet  80 . 
     In some examples, inlet  70  is part of a pathway of ink in a printer; inlet  70  may be connected to an ink reservoir. In some examples, outlet  80  is part of the pathway in a printer, the pathway ending at a printing element of a printer. A hydraulic system  130  may provide a constant ink flow through gap  50  in some examples. 
     In some examples, inlet  70  and outlet  80  are part of a pathway of a quality assurance system. In further examples, inlet  70  and outlet  80  are part of a pathway in a production line. 
     In some examples, densitometer  100  may be configured to determine the optical density of fluid  60 . In some examples, densitometer  100  may be configured to measure characteristics of fluid  60  that affect the propagation and/or attenuation of light through a fluid, the characteristics, as are known in the art. 
     In some examples, densitometer  100  may be configured to determine the percentage of solids in a fluid. In some examples, densitometer  100  may be configured to determine the amount of solid particles within fluid  60 . In some examples densitometer may be configured to determine the percentage of non-volatile substances (% NVS) in the fluid, such as, for example, % NVS, where the NVS are pigments of a colorant of ink for a printer. 
     In some examples, densitometer  100  may be configured to determine the % NVS of a range of colorants of ink for a printer with a high dynamic range of optical densities ranging from 0% NVS to 8% NVS, as described below. 
     In some examples, densitometer  100  may be configured to measure a dynamic range of % NVS from 0% to 8% with a resolution of +/−0.0005% NVS as described below. 
     In some examples, densitometer  100  may be configured to measure a dynamic range of electronic signals, typically a range of 90 decibel milliwatts (dBm). 
     Typically, signal  5  may include measurable and/or determinable characteristics and/or properties. These include the frequency of signal  5 , the shape of signal  5  and the amplitude of signal  5 . In some examples, signal  5  may be describable as a wave function. In some examples, signal  5  may be describable as a sinusoid, i.e., a mathematical function describing a smooth, and in some examples, repetitive oscillation. Other characteristics and/or properties of signals are known in the art and may also be measurable and/or determinable. 
     In some examples, the detection and analysis of the generated signal  5  through fluid  60  in gap  50  may provide a measurement of the absorbance of signal  5  by fluid  60 . In some examples, the detection and analysis of the transmission of light may provide a measurement of the attenuation of signal  5  from light source  10  by traveling through fluid  60 . 
     The attenuation of signal  5  traveling through liquid  60 , as signal  5  propagates through the fluid, can provide information regarding the concentration, and in some examples the % NVS value of fluid  60 , according to the following equation: 
         P ( x )= P   τ   ·b·e   [−L·a·x]   
     where: P(x) is the received power detect by detector  40 ; 
     x is, in some examples, % NVS; 
     L is, in some examples, the width of gap  50  between lens  30  and  40 ; 
     a is, in some examples, an empirical value calculated experimentally with relation to a particular pigment; 
     P T  is, in some examples, the emitted power emitted by light source  10 ; and, 
     b is, in some examples, an experimental proportional value. 
     Typically a look-up table  110  may be provided, to store measured or calculated values of some or all of the above mentioned parameters to be used as reference. 
     In some examples the attenuation of light may be exponential. In some examples, the light from light source  10  may be attenuated by at least about 10 −4 . In some examples, light from light source  10  may be attenuated as it passes through fluid  60  by as much as about 10 −19  or more, as is known in the art. 
     In some examples, light source  10  may be a laser. Typically, the power of the light source  10  may be limited due to limitations inherent in densitometer  100  and, in some examples, limitations inherent in a device to which densitometer  100  is coupled. In some examples, laser power may be limited by nature of the materials used to construct densitometer  100 . In some examples, laser power may be limited by the size of the area in which densitometer is configured to placed. In some examples where densitometer is a component of a printing system, laser power may be limited by the materials employed in construction of the printer and the location of densitometer  100  within the printing system. 
     In some examples, light source  10  may include a laser with a power of between 65 mw to 85 mW, e.g., 70 mW. For example, light source may include a 780 nm 70 mW laser. Other lasers known in the art may also be used. 
     In some examples, light source  10  may be a laser with a near built-in power detector  140 , such that the laser may shift a transmitted signal away from a noisy frequency band in response to a data signal, typically in response to a data signal from a processor  90  as described below. 
     In some examples there may be one or a plurality of processors  90 . Typically, one or more processors  90  are in communication with each other as is known in the art. 
     In some examples, light source  10  may be a laser configured to maintain a constant optical power. In some examples light source  10  may be able to generate a modulated signal, the properties of said modulated signal may be communicated to processor  90 . 
     In some examples, light source  10  may be configured to provide a signal in the form of a wave. In some examples, light source  10  may be configured to powered on less than 100% of the time that densitometer  100  is powered on. In some examples, the ability of light source  10  to be powered on less than 100% of the time allows light source  10  to have a longer life span. 
     In some examples, light source  10  may be able to generate a signal that may be locked-in with relation to some properties of the signal, the locked-in the properties of said signal may be communicated to processor  90 . 
     Other light sources that are known in the art may also be employed as well. 
     In some examples, light source  10  may be a laser more powerful than 70 mW. In some examples, light source  10  may be a laser less powerful than 70 mW. 
     In some examples, the environment for the transmission of signal  5  from a typically, low powered light source through fluid  60  in gap  50  may be noisy. Typically, noisy refers to signal extraneous to light source  10 . In some examples, noise refers to electrical noise, as is known in the art. 
     In some examples the noise in the environment may be the result of unstable transistors. In some examples the noise in the environment may be the result components in the densitometer. In some examples the noise in the environment may be the result other components coupled to the densitometer. In some examples the noise in the environment may be the result components within a device that also contains densitometer  100 . In some examples the noise in the environment may be the result devices external to the device that may contain densitometer  100 . In some examples the noise in the environment may be the result of other sources of noise that are known in the art. 
     In some examples, signal  5  is assimilated in the noisy background and attenuated by fluid  60  such that while initially light source  10  may produce a signal at 70 mW, the detected signal  5  from light source  10  may be only measurable in picowatts by detector  40 . 
     In some examples, densitometer may include a processor  90 , e.g., a computer processing unit (CPU). In some examples, processor  90  may be mounted on a circuit board  160 . 
     In some examples, circuit board  160  may be configured to reside between inlet  70  and outlet  80 . 
     Typically, processor  90  may be configured to be in communication with light source  10 . In some examples, processor  90  may be configured to control light source  10 , such that light source  10  produces signal  5  with predefined characteristics. In some examples, predefined characteristics may include a known wave function or know wave shape with know frequency and amplitude. In some examples, processor  90  may be configured to control light source  10  such that light source  10  produces signal  5  definable as a sine wave with a predefined frequency of one kilohertz. 
     Typically processor  90  may be in communication with detector  40 . In some examples, processor  90  may receive a detected signal form detector  40 . Typically, processor  90  may determine the concentration of fluid  60  by analyzing the detected signal from detector  40  and comparing detected signal with the generated signal  5  from light source  10 . 
     In some examples, processor  90  may be configured to determine the predefined wave of signal  5  to be a wave function as known in the art. Typically, processor  90  may be configured to determine the predefined wave of signal  5  to be a sine wave. 
     Typically, processor  90  may be in communication with detector  40  such that detector  40  is configured to specifically filter out a signal not definable by the sine wave with the known frequency produced by light source  10  from other noise in densitometer  100 . 
     In some examples, processor  90  may be in communication with detector  40  such that detector  40  is configured to specifically filter out a signal not definable by a sine wave with a frequency of one kilohertz, wherein light source  10  produces signal  5  describable as a sine wave with a frequency of one kilohertz. 
     In some examples, processor  90  may be in communication with detector  40 , such that detector  40  is configured to detect signal  5  with a particular sine wave with know frequency and, in some examples, detect changes in amplitude of signal  5 . 
     In some examples, processor  90  may optimize and/or modulate the frequency of signal  5  from light source  10 , such that a ratio of signal to noise is changed. 
     In some examples, detector  40  may include or, in some examples, detector  40  may be in communication with an analog to digital converter  120 . Typically, analog digital converter  120  may be coupled to processor  90 . The analog to digital converter  120  may be configured such that a dynamic range of attenuated signal from light source  10  may be detected by detector  40  as is known in the art. 
     Typically, analog to digital converter  120  may have of resolution of 24 bits. Other analog to digital converters as are known in the art may also be used. 
     Typically, as a generated signal  5  travels through fluid  60  from light source  10  to detector  40 , the amplitude of signal  5 , signal  5  defined by a particular sine wave at a particular frequency, may change, but typically, the frequency and shape of the sine wave does not. 
     In some examples, processor  90  may employ an empirically defined look-up table  110  to determine the density of and/or concentration of solids within fluid  60  from the detected signal by detector  40 . 
     Typically, look-up table  110  may contain data relating to the amplitude, frequency and shape of a received signal  7  by detector  40  given the characteristics of fluid  60 . In some examples, look-up table contains empirically derived data given the parameters of densitometer  100 , the parameters of fluid  60  and/or the parameters of signal  5 . 
     Typically, characteristics of fluid  60  included in look-up table  110  may include the color of fluid  60 . 
     In some examples, a generated signal from light source  10  through fluid  60  may be propagated through fluid  60  and gap  50  and received by detector  40 . Typically detector  40  is in a powered on stage wherein some or all signals are detected. 
     Received signal  7  may be converted into a current by a current to voltage converter  150 , in some examples, a transimpedance amplifier. Current to voltage converter  150  may have a selectable gain, the gain selected typically by processor  90 , and in some examples, according to data from look-up table  110 . 
     Typically, voltage from current to voltage converter  150  may be filtered by detector  40  such that received signal  7 , an attenuated form of signal  5  with known and in some examples, predefined characterizes from light source  10  is detected amongst the noise. 
     Typically, received signal  7  is sampled by analog to digital converter  120 . In some examples, analog to digital converter may have a built-in digital filter configured to improve the dynamic range of detector  40 . 
     In some examples, one manufactory calibration of densitometer  100  may be employed to allow for a wide dynamic range of signal, large signal to noise ratios, and weak signal. In some examples, one or a plurality of manufactory calibrations may be employed. In some examples, the user may be able to calibrate densitometer  100 . 
     In some examples, densitometer  100  is configured to communicate to another system if the detected % NVS of fluid  60  is higher or lower than anticipated or expected. In some examples, densitometer  100  may be configured to communicate to another system if the % NVS of fluid  60  is out of a particular predefined range. 
     In some examples, densitometer  100  may be configured to communicate to another system if the % NVS of fluid  60  is trending toward an undesired level. In some examples, when the % NVS of fluid  60  is trending toward an undesired level, densitometer  100  may signal another system to change the constitution, e.g., the concentration of solids, of fluid  60  passing through gap  50 . 
       FIG. 2  is a flow diagram of a method for calculating the concentration of solids in a liquid of a fluid, according to an example. 
     Fluid  60  may typically be passed through gap  50  as depicted by box  200 . 
     A signal  5 , typically light, configured to be defined as a sine wave at a predefined frequency, is generated by light source  10  as depicted by box  210 . 
     Signal  5  from light source  10  is propagated through any fluid  60  in gap  50  as depicted by box  220 . In some examples there may not be fluid in gap  50 . Typically, signal is attenuated as it is propagated through fluid  60 . Typically the attenuation of signal  5  as it is propagated through fluid  60  is indicative of the characteristics of fluid  60  as determinably by look-up table  110 . 
     Signal  5  may be detected by detector  40  as depicted by box  230 . 
     Signal frequency may be converted into a corresponding current that is fed into an amplifying device as are known in the art with a selectable gain, as depicted by box  240 . Typically light source  10  is limited in the amount and magnitude of the signal sent to detector  40 . In some examples, the gain can be adjusted such that it amplifies the signal from light source  10  after the signal has been propagated through fluid  60 . 
     Processor  90  typically selects the gain based on information regarding pigment color and information from look-up table  110 , as depicted by box  250 . 
     The current may then be converted into a voltage, as is depicted by box  255 . 
     The signal, now converted into a voltage, e.g., a voltage signal, from attenuated signal from light source  10  is then filtered by a narrow band filter that is synchronized to the same predefined frequency as signal  5  from light source  10 , as depicted by box  260 . In some applications, densitometer  100  may be configured to seek out only the positive components of the signal, when the signal is a wave, the signal coming from light source  10  and traveling through fluid  60 ; e.g., when the signal is a wave with both positive and negative components. In some examples, densitometer  100  is configured to subtract the negative components of the signal, by calculations known in the art. 
     The received signal  7  may then be sampled by analog to digital converter  120 , by calculations as are know in the art, as depicted by box  270 , creating a digital signal. Analog to digital converter typically has a digital filter for improving the dynamic range of detector  40  or to limit noise. 
     Typically, densitometer  100  determines the % NVS of fluid  60  given signal  7 , as depicted by box  280 , by calculations known in the art. In some examples densitometer  100  determines the optical density of fluid  60  given signal  7 , as depicted by box  280 . In some examples, densitometer  100  determines other characteristics of fluid  60 , given signal  7 , as depicted by box  280 . 
     In some examples, densitometer  100  may include a non-transitory computer readable medium containing instructions to carry out one or a plurality of the aforementioned steps. 
       FIG. 3  is a flow diagram of a method to calculate a concentration of solids in a fluid according to an example. 
     Typically light source  10 , in some examples a laser generates a light signal of predefined characteristics as depicted by box  300 . The characteristics of the generated light signal, in some examples may be communicated to processor  90 . 
     In some examples, detector  40 , typically, an optical detector, which may be placed opposite light source  10  across gap  50  between at least light source  10  and detector  40  through which fluid  60  detects signal  5 , typically a light signal, as depicted by box  310 . 
     Typically, a processor identifies the light signal within a detection signal generated by detector  40  and calculates the concentration of solids, in some examples the % NVS, of fluid  60 , based on the identified light signal as it is related to the generated light signal, as depicted by box  320 . 
     Features of various examples discussed herein may be used with other embodiments discussed herein. The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be appreciated by persons skilled in the art that many modifications, variations, substitutions, changes, and equivalents are possible in light of the above teaching. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.