OPTICAL SENSOR WINDOW CLEANER

A sensor assembly includes a passageway for a process fluid, an optical window, an optical sensor, and a nozzle. The optical sensor configured to detect an optical property of the process fluid. The optical window includes an inner surface. The nozzle configured discharge an atomized fluid in a discharge direction that intersects the inner surface of the optical window. A sensor system includes a sensor assembly and conduits for supplying a gas and a liquid to a nozzle of the sensor assembly. A method of cleaning an optical window in a sensor assembly includes forming an atomized fluid and discharging the atomized fluid in a discharge direction that intersects the optical window.

TECHNICAL FIELD

This disclosure relates to sensors used to measure a property of a fluid. More specifically, this disclosure relates to optical sensors that measure an optical property of a flowing fluid.

BACKGROUND

Optical sensors can be used to determine one or more properties of a flowing fluid. Optical sensors can transmit light through a window towards the fluid. The light can be refracted at the boundary between the window and the fluid. Optical sensors can determine a refractive index of the fluid by detecting an amount, an angle, or an amount and an angle of the light refracted by the fluid. The refractive index of the fluid can be used to determine other properties of the fluid. For example, a concentration or purity of the fluid might be determined using the refractive index of the fluid. The process fluid can include liquids or a mixture including liquid(s) and solid(s).

SUMMARY

A sensor system includes a sensor assembly and a conduit that supplies a process fluid to the sensor assembly. The sensor assembly includes a passageway for the process fluid, an optical window, and an optical sensor. The optical window forms a sidewall of the passageway. The process fluid flows through the passageway and contacts the optical window. The sensor is configured to transmit light through the optical window and to detect an optical property of process fluid.

Embodiments are disclosed for a sensor system, a sensor assembly, and a method for cleaning an optical window. In an embodiment, a sensor system includes a sensor assembly. A process fluid is supplied to the sensor assembly. In some embodiments, the sensor assembly includes an optical window and an optical sensor for detecting an optical property of the process fluid.

In an embodiment, a sensor system includes a sensor assembly and a fluid circuit (e.g., conduits, piping, tubing, combinations thereof, or the like) for supplying a process fluid, a liquid, and a gas to the sensor assembly. The sensor assembly includes a passageway for the process fluid, an optical window, and a nozzle. The optical window forms a sidewall of the passageway and the process fluid contacts the optical window. The fluid circuit fluidly connects to the nozzle for supplying a liquid. The fluid circuit also fluidly connects to the nozzle for supplying a gas. The nozzle is configured to discharge an atomized fluid including the liquid and the gas in a direction that impacts the inner surface of the optical window. The atomized fluid impacts and removes material that can scatter light.

In an embodiment, a sensor assembly includes a passageway for the process fluid, an optical window, and a nozzle. The optical window forms a sidewall of the passageway and the process fluid configured to contact the optical window. The nozzle is configured to form and discharge an atomized fluid including a liquid and a gas in a direction that impacts the inner surface of the optical window.

In an embodiment, a method of cleaning an optical window in a sensor assembly includes atomizing a liquid and a gas. The sensor assembly includes a passageway for a process fluid, the optical window, and an optical sensor for the process fluid. The atomized fluid is discharged into the passageway in a direction that impacts the optical window.

DETAILED DESCRIPTION

The term “about” generally refers to a range of numbers that is considered equivalent to the recited value (e.g., having the same function or result). In many instances, the term “about” may include numbers that are rounded to the nearest significant figure.

An optical sensor can be used to detect one or more optical properties of a fluid. The fluid can be directed to flow along one side of the optical window while the optical sensor is located along another side of the window. An optical sensor can be configured to transmit light through the optical window and detect how the fluid affects the light. For example, the optical sensor may be configured to detect how the light is refracted at the transition between the optical window and the flowing fluid. For example, the optical sensor may be configured to detect the amount of light reflected by the flowing fluid. An optical property of the process fluid may be used to determine one or more other properties of the process fluid such as, for example, the concentration or purity of the process fluid.

Component(s) of the fluid can be attracted to the optical window and deposit on the optical window, forming a layer of material on the optical window. The attraction and deposition of the component(s) to the optical window can be caused by, for example, intermolecular forces between the component(s) and the material(s) of the optical window (e.g., the zeta potential of the components can drive them toward the optical window, and attraction driven by van der Waal forces once in proximity with each other). This problem may occur more significantly when the fluid includes solid particles which may adhere to the optical window more easily. Further, it has been found that the deposition becomes more difficult to remove over time. Therefore, particles deposit more strongly and become more difficult to remove the longer they remain on the optical window.

Those having ordinary skill in the art will recognize that a partial layer of material on the optical window can adversely impact the transmission of light and create erroneous measurements. In sensors that are relied upon for high accuracy measurements, such as in semiconductor manufacturing, this error can have a significant adverse impact in the semiconductor manufacturing process.

Embodiments are disclosed herein related to a sensor assembly, a sensor system, and method of cleaning an optical window in a sensor assembly. As used herein, cleaning an optical window can include, for example, removing a deposited component from the optical window to at least partially expose a surface of the optical window. A sensor system can include a sensor assembly. The embodiments described herein are capable of discharging an atomized fluid at the optical window to remove most to all of any material deposited on the optical window. Atomizing a liquid to discharge the atomized fluid can accelerate the liquid portion of the atomized fluid and lead to cavitation on the surface (e.g., implosion of a drop of the liquid portion of the atomized fluid after impacting the optical window). Without being bound by theory, it is believed that the impact of the drops of the liquid portion of the atomized fluid onto the optical window can initiate a shockwave, thereby removing deposits or material from the optical window.

FIG. 1is a schematic diagram of an embodiment of a sensor system1. The sensor system1includes a sensor assembly10configured to detect one or more optical properties of a process fluid F1. In an embodiment, the sensor assembly10detects a refractive index of the process fluid F1.

The sensor assembly10includes a passageway12, an optical window32, an optical sensor38, and a nozzle50. The passageway12includes an inlet20and an outlet22. The passageway12extends through the sensor assembly12from the inlet20to the outlet22. The process fluid F1flows through the sensor assembly10by flowing through the passageway12. The process fluid F1flows through the sensor assembly10by entering through the inlet20, flowing through the passageway12, and then exiting through the outlet22.

A first conduit60supplies the process fluid F1to the inlet20of the passageway12. The first conduit60fluidly connects a process fluid source62to the inlet20. The process fluid F1flows from the process fluid source62through the first conduit60to passageway12. In an embodiment, the process fluid source62may be a tank containing process fluid F1. In an embodiment, the process fluid source62may be a plurality of tanks containing components of the process fluid F1and the process fluid source62mixes the components to form the process fluid F1, which is then supplied by the first conduit60. The first conduit60includes a flow valve64. The flow valve64controls a flowrate f1of the process fluid F1supplied by the first conduit60to the passageway12and the sensor assembly10. In an embodiment, the flow valve64is controlled by the controller90. The controller90is configured to adjust the flow valve64to control the flowrate f1of the process fluid F1to and through the sensor assembly10.

In an embodiment, the process fluid F1is used for polishing in semiconductor wafer in semiconductor manufacturing. The process fluid F1contains liquid and abrasive particles. In an embodiment, the abrasive particles include one or more of ceria, colloidal silica, fumed silica, and lanthanum fluoride. In an embodiment, the process fluid F1contains at least 0.1 wt. % of the abrasive particles. In an embodiment, the process fluid F1contains from about 0.1 wt. % to about 30 wt. % of the abrasive particles. In an embodiment, a liquid used for the process fluid F1can include water or water-based solutions.

The process fluid F1flows along the optical window32when flowing through the passageway12from the inlet20to the outlet22. The optical sensor38is located along the optical window32. The optical sensor38transmits light through the optical window32towards the passageway12. The optical sensor38also detects the light refracted by the process fluid F1. The optical sensor38configured to detect a refractive index of the process fluid F1by detecting the light refracted by the process fluid F1.

The nozzle50can clean the optical window32. The nozzle50forms an atomized fluid52and discharges the atomized fluid52toward the optical window32. The atomized fluid52impacts the optical window32and is configured to remove material that is deposited on the optical window32. In an embodiment, the nozzle50can be referred to as an air-blast or air-assist atomizer. Operation of the nozzle50is discussed in more detail below. The atomized fluid52contains a liquid F2and a gas F3. A second conduit70supplies the liquid F2to the nozzle50and a third conduit80supplies the gas F3to the nozzle50. The nozzle50is configured to combine the liquid F2and the gas F3to form the atomized fluid52.

The second conduit70is fluidly connected to the nozzle50and supplies the liquid F2to the nozzle50. In an embodiment, the liquid F2includes one or more of water, ammonium hydroxide, and a liquid low contaminant semiconductor fabrication cleaning products (e.g., PlanarClean AG-Ce1000K, ESC 784 Cleaning Solution, or the like). In an embodiment, the water is deionized (“DI”) water. In an embodiment, the second conduit70fluidly connects a liquid source72to the nozzle50. In an embodiment, the liquid source72includes a filter and/or one or more tank(s) containing the liquid F2. In an embodiment, the liquid source72is a filter that generates DI water.

The second conduit70includes a flow valve74and a flow sensor76. The flow valve74controls the flowrate f2of the liquid F2supplied to the nozzle50. The flow sensor76detects the flowrate f2of the liquid F2through the second conduit70and supplied to the nozzle50. In an embodiment, the controller90controls the flow valve74. The controller90may control the flowrate f2of the liquid F2supplied to the nozzle50to be a particular amount or within a specific range as discussed below. The controller90may utilize the flow sensor76to detect the flowrate f2of the liquid F2being supplied to the nozzle50.

The third conduit80is fluidly connected to the nozzle50and supplies the pressurized gas F3to the nozzle50. In an embodiment, the gas F3includes one or more or an inert gas and clean dry air (CDA). In an embodiment, the gas F3is an inert gas that may include one or more of, but is not limited to, nitrogen, helium, neon, argon, krypton, xenon, and the like. In an embodiment, the gas F3is nitrogen. In an embodiment, the first conduit80fluidly connects a gas source82to the nozzle50. In an embodiment, the liquid source82includes one or both of a filter and one or more tank(s) containing the gas F3. In an embodiment, the liquid source82is a filter that produces purified nitrogen and/or argon from air.

The conduit80includes a flow valve84and a flow sensor86. The flow valve84controls the flowrate f3of the gas F3supplied to the nozzle50. The flow sensor86detects the flowrate f3of the gas F3through the conduit80and supplied to the nozzle50. In an embodiment, the controller90controls the flow valve84. The controller90may control the flowrate f3of the gas F3supplied to the nozzle50to be a particular amount or within a specific range as discussed below. The controller90may utilize the flow sensor86to detect the flowrate f3of the gas F3being supplied to the nozzle50.

FIG. 2is a cross sectional view of an embodiment of the sensor assembly10. The sensor assembly10includes the passageway12with the inlet20and the outlet22, the optical window32, the optical sensor38, the nozzle50, the second conduit70for the liquid F2, and the third conduit80for the gas F3.

The process fluid F1flows through the sensor assembly10by flowing through the passageway12. The passageway12extends from the inlet20to the outlet22. The process fluid F1is configured to enter through the inlet20and exit through the outlet22. The optical window32and the nozzle50are each positioned along the passageway12.

The optical window32forms a sidewall14of the passage12. The optical window32includes an inner surface34and an outer surface36. The outer surface36is opposite the inner surface34. In an embodiment, the inner surface34of the optical window32forms a sidewall14of the passage12. The process fluid F1contacts the inner surface34of the optical window32when flowing through the passageway12. The inner surface34of the optical window32is made of a scratch resistant material. In an embodiment, the inner surface34of the optical window32is made of diamond or sapphire. In an embodiment, the inner surface34of the optical window32is made of borosilicate glass.

The optical sensor38is attached to the optical window32. In an embodiment, the optical sensor38is attached to the outer surface36of the optical window32. The optical sensor38is configured to transmit light through the optical window32and detect light transmitted towards the optical sensor38in the optical window32. For example, the optical sensor38may transmit light in the direction D1towards the passageway32. The optical sensor38is configured to detect light refracted by the process fluid F1at the inner surface34. The detected light refraction can then be used to determine the refraction index of the process fluid F1.

The conduits70,80supply the liquid F2and the gas F3to the nozzle50. The nozzle50discharges an atomized fluid52of the liquid F2and the gas F3into the passageway12. The atomized fluid52is discharged through an opening18in the second sidewall16of the passageway12. In an embodiment, the second sidewall16is opposite to the first sidewall14. In an embodiment, the second sidewall16is formed by the nozzle50. In an embodiment, the atomized fluid52, the liquid F2, and the gas F3do not enter through the inlet20of the passageway12. The atomized fluid52is discharged at the inner surface34of the optical window32. The nozzle50discharges the atomized fluid52in a direction that impacts the inner surface34of the optical window32. In an embodiment, the direction of the atomized fluid52can be referred to as the discharge direction D2. In an embodiment, the discharge direction D2intersects the inner surface34of the optical window32. In an embodiment, the discharge direction D2is perpendicular to the inner surface34of the optical window32.

As similarly discussed above, material builds upon the inner surface34of the optical window32as the process fluid F1flows along and contracts the inner surface34of the optical window32. In an embodiment, solid abrasive particles in the process fluid F1adhere to and build up on inner surface34of the optical window32.

The nozzle50is configured to discharge the atomized fluid52at a high speed at the optical window32. The configuration and operation of the nozzle50is discussed in more detail below. Liquid F2droplets in the atomized fluid52impact the inner surface34of the optical window32at a high speed. In an embodiment, each high speed impact creates a liquid shockwave that travels outwardly along the inner surface34from the impact point. The liquid shockwave applies a shear force that removes material that has built up on the inner surface. In an embodiment, the high speed impact of a droplet on the optical window32causes cavitation at the impact point. The cavitation further acting to remove any material adhered to the inner surface34of the optical window32. In an embodiment, the atomized fluid52can remove a majority to almost all of the material adhered on the inner surface34of the optical window32. In an embodiment, a liquid selected for the liquid F2can establish a favorable zeta potential (e.g., repel vs. attract) that can, for example, prevent debris and particles from reattaching to the inner surface34of the optical window32.

In an embodiment, the discharge direction may vary from being perpendicular to the inner surface34. In an embodiment, the nozzle50may be configured to discharge the atomized fluid52in a discharge direction D4that is within 45 degrees of a direction D3that is normal to the inner surface34of the optical window32. For example, the nozzle50may be configured to discharge atomized fluid52such that an angle a between the discharge direction D4and the direction D3normal to the inner surface34is less than 45 degrees. It will be appreciated that those of ordinary skill in the art with knowledge of this disclosure will understand that the discharge direction D4can be selected to accomplish a desired cleaning effect.

InFIG. 2, the nozzle50and the passageway12are separate pieces and the nozzle50is attached with threads24. However, it should be appreciated that the nozzle50in an embodiment may be attached in a different manner such as, but not limited to, clamping, welding, machining together, suitable combinations thereof, or the like. In an embodiment, the passageway12and nozzle50may be a single continuous component.

FIG. 3is an enlarged view of the nozzle50and the conduits70,80. As described above, the conduits70,80supply the liquid F2and the gas F3to the nozzle50, respectively. In an embodiment, the nozzle50includes a chamber59that for forming the atomized fluid52from the liquid F2and the gas F3.

The nozzle50includes an inner channel54and a first inlet58A for the liquid F2. The second conduit70connects to the first inlet58A and supplies the liquid F2to the first inlet58A of the nozzle50. The first inlet58A is fluidly connected to the inner channel54. The liquid F2flows from the second conduit70to the inner channel54via the first inlet58A. The liquid F2flows through the inner channel54and into the chamber59.

The nozzle50includes an outer channel56and a second inlet58B for the gas F3. The second conduit80connects to the second inlet58B and supplies the gas F3to the second inlet58B of the nozzle50. The second inlet58B is fluidly connected to the outer channel56. The gas F3flows from the conduit80to the outer channel56via the second inlet58B. The gas F3flows through the outer channel56and into the chamber59.

The outer channel56surrounds the inner channel54. The inner channel54has an end55that is at the chamber59. The end55is opposite to the first inlet58A. In an embodiment, the outer channel56is concentric with the first channel56at the end55of the inner channel54. The liquid F2flows into the chamber59from the inner channel54while the gas F3flows into the chamber59from the outer channel54.

The gas F3exits the outer channel56and mixes into with the liquid F2in the chamber59. In mixing into the liquid F2, the gas F3disperses the liquid F2into droplets and accelerates the liquid F2droplets. In an embodiment, the gas F3exiting the outer channel56has a greater speed than the liquid F2exiting the inner channel54. The atomized fluid52is then directed from the chamber59out through the opening18of the nozzle50in the discharge direction D2. In an embodiment, the discharge direction D2is the direction of the mean velocity of the atomized fluid52at the opening18.

In an embodiment, all of the liquid F2and gas F3supplied to the nozzle50is discharged. The atomized fluid52cleans the optical window32. The nozzle50is operated by controlling the flowrates f2, f3of the liquid F2and the gas F3supplied to the nozzle50. In an embodiment, and as discussed above, the flow valves74,84(shown inFIG. 1) control the flowrates f2, f3of the liquid F2and the gas F3to the nozzle50. In an embodiment, the flow valves74,84are closed to stop the cleaning of the optical window32by the nozzle50. In an embodiment, the cleaning of the optical window32is started by opening both of the valves74,84. In an embodiment, the controller90is configured to only start the cleaning when the valve64for the process fluid F1is closed.

When cleaning of the optical window32is desired, the flow valves74,84are opened so that the liquid F2and the gas F3to the nozzle50. The nozzle50then discharges the atomized fluid52at the inner surface34of the optical window32, which cleans the inner surface34of the optical window32. In an embodiment, the atomized fluid52contains at or about 20% or less than 20% by volume of the liquid F2. In an embodiment, the atomized fluid52contains at or about 0.65% or less than 0.65% by volume of the liquid F2. In an embodiment, the atomized fluid52contains at or about 0.02% or more than 0.02% by volume of the liquid F2. In an embodiment, the atomized fluid52contains at or about 0.15% or more than 0.15% by volume of the liquid F2. In an embodiment, the atomized fluid52contains about 0.02%-20% by volume of the liquid F2.

In an embodiment, when the optical window32is being cleaned, the second conduit70supplies about 0.5-2 liters per a minute (LPM) of the liquid F2to the nozzle50. In an embodiment, when the optical window32is being cleaned, the third conduit80supplies about 10-300 standard liters per minute (SLPM) of the gas F3to the nozzle50. In an embodiment, the ratio (f2:f3) of the flowrate f2of the liquid F2to the flowrate f3of the gas F3is from about 0.05:300 to about 2:10. In an embodiment, the controller90may be configured to adjust the flow valves74,84so that the above flowrates f2, f3of liquid F2and gas F3are supplied to the nozzle50. In an embodiment, the controller90may be configured to close the flow valves74,84when the process fluid F1is flowing into through passageway12.

FIG. 4is a block diagram of an embodiment of a method100of cleaning an optical window in a sensor assembly. For example, the method100may be for cleaning the optical window32in the sensor assembly10inFIGS. 1-3. In an embodiment, the optical window32may be part of a sensor system (e.g., the sensor system1). The method starts at110.

At110, a flow of process fluid (e.g., process fluid F1) is supplied to a passageway (e.g., passageway12) of the sensor assembly (e.g., sensor assembly10). The sensor assembly includes the passageway, an optical window (e.g., optical window32), and an optical sensor (e.g., optical sensor38). The optical sensor is configured to transmit light towards the passageway through the optical window to detect an optical property of the fluid. The process fluid contacts the optical window while flowing through the passageway. The method100then proceeds to120.

At120, the flow of the process fluid to the passageway is stopped. In an embodiment, a flow valve (e.g. flow valve64) controls the flow of the process fluid. In an embodiment, stopping the flow of the process fluid120may include closing the flow valve. The method100then proceeds to130.

At130, an atomized fluid (e.g., atomized fluid52) containing a gas (e.g., gas F3) and a liquid (e.g., liquid F2) is formed. In an embodiment, forming the atomized fluid130includes supplying a flow of the liquid to a nozzle132(e.g., nozzle50). In an embodiment, the liquid is supplied to the nozzle by a conduit (e.g., conduit70). The conduit may supply the liquid to an inlet of the nozzle (e.g., first inlet58A). In an embodiment, forming the atomized fluid130includes supplying a flow of the gas to the nozzle134. In an embodiment, the gas is supplied to the nozzle by a second conduit (e.g., conduit80). The conduit may supply the gas to a second inlet (e.g., second inlet58B).

In an embodiment, forming the atomized fluid130also includes combining the flow of the liquid and the flow of the gas in the nozzle136. The flow of the liquid and the flow of the gas combine to form the atomized fluid. In an embodiment, the nozzle136includes a chamber (e.g., chamber59). The flow of liquid and the flow gas each flow into the chamber and combine in the chamber. The method100then proceeds from the130to140.

At140, the atomized fluid is discharged into the passageway by the nozzle. The atomized fluid is discharged in a discharge direction (e.g., discharge direction D2) that intersects an inner surface34of the optical window32. Liquid droplets in the atomized fluid are configured to impact the inner surface34at high speeds. Material adhered to the inner surface34of the optical window32is dislodged by the high speed impacts of the liquid droplets.

In an embodiment, the method100may be modified based on the sensor system1as shown inFIG. 1or as described above, and the sensor assembly1shown inFIGS. 1-3or as described above. For example, the method100may include stopping the supply of the liquid with a valve.

Any of aspects 1-7 can be combined with any of aspects 8-19, and any of aspects 8-15 can be combined with any of aspects 16-19.

Aspect 1. A sensor assembly, comprising: a passageway for a process fluid to flow through the sensor assembly; an optical window including an inner surface that forms a first portion of a sidewall of the passageway; an optical sensor configured to transmit light through the optical window towards the passageway to detect an optical property of the process fluid; and a nozzle for discharging a liquid and a gas in the form of an atomized fluid into the passageway in a direction that impacts the inner surface of the optical window.

Aspect 2. The sensor assembly of aspect 1, wherein the atomized fluid is discharged into the passageway through an opening in a second portion of the sidewall of the passageway.

Aspect 3. The sensor assembly of aspect 2, wherein the first portion of the sidewall and the second portion of the sidewall are arranged on opposite sides in the passageway.

Aspect 4. The sensor assembly of any one of aspects 1-3, wherein an angle between the discharge direction and a direction normal to the inner surface of the optical window is less than 45 degrees.

Aspect 5. The sensor assembly of any one of aspects 1-4, wherein the nozzle includes an outer channel for the gas and an inner channel for the liquid, the outer channel surrounding the inner channel, the nozzle forming the atomized fluid by combining the gas with the liquid.

Aspect 6. The sensor assembly of any one of aspect 1-5, wherein the atomized fluid contains about 0.05-20% by volume of the liquid.

Aspect 7. The sensor assembly of any one of aspects 1-6, wherein the liquid is deionized water and the gas is an inert gas.

Aspect 8. A sensor system, comprising: a sensor assembly for a process fluid, the sensor assembly including: a passageway for the process fluid to flow through the sensor assembly; an optical window with an inner surface that forms a sidewall of the passageway; an optical sensor configured to transmit light through the optical window towards passageway to detect an optical property of the process fluid, and a nozzle for forming an atomized fluid containing a liquid and a gas, the nozzle configured to discharge the atomized fluid into the passageway in a direction that impacts the inner surface of the optical window; a first conduit fluidly connected to the nozzle for supplying the liquid to the nozzle; and a second conduit fluidly connected to the nozzle for supplying the gas to the nozzle.

Aspect 9. The sensor system of aspect 8, wherein the process fluid contacts the inner surface of the optical window.

Aspect 10. The sensor system of one of aspects 8 or 9, wherein the atomized fluid is discharged into the passageway through an opening in the sidewall of the passageway.

Aspect 11. The sensor system of aspect 10, wherein the opening in the sidewall of the passageway and the optical window are arranged on opposite sides of the passageway.

Aspect 12. The sensor system of any one of aspects 8-11, wherein the nozzle includes an outer channel and an inner channel, the outer channel surrounding the inner channel, the first conduit supplying the liquid to the inner channel of the nozzle and second conduit supplying the gas to the outer channel of the nozzle.

Aspect 13. The sensor system of any one of aspects 8-12, wherein the first conduit supplies a flowrate of the liquid to the nozzle and the second conduit supplies a flowrate of the gas to the nozzle such that the atomized fluid contains about 0.02%-20% by volume of the liquid.

Aspect 14. The sensor system of any one of aspects 8-13, wherein the first conduit supplies a flowrate of the liquid to the nozzle and the second conduit supplies a flowrate of the gas to the nozzle, the ratio of the flowrate of the liquid to the volume of gas is from 0.05:300 to 2:10.

Aspect 15. The sensor system of any one of aspects 8-14, further comprising: a first flow valve controlling flow of the liquid through the first conduit to the nozzle; a second flow valve controlling flow of the gas through the second conduit to the nozzle; and the controller configured to close the first flow valve and the second flow valve when the process fluid is flowing into the passageway.

Aspect 16. A method of cleaning an optical window in a sensor assembly, the sensor assembly including a passageway and an optical sensor that transmits light towards a passageway via the optical window to detect an optical property of a process fluid flowing through the passageway, the method comprising: forming an atomized fluid containing a gas and a liquid; and discharging the atomized fluid into the passageway in a direction that impacts an inner surface of the optical window.

Aspect 17. The method of aspect 16, wherein forming the atomized fluid includes: supplying a flow of the liquid to a nozzle, supplying a flow of the gas to the nozzle, mixing, in the nozzle, the flow of the liquid and the flow of the gas.

Aspect 18. The method of one of aspects 16 or 17, wherein discharging the atomized fluid into the passageway in the direction that impacts the inner surface of the optical window includes directing the atomized fluid through an opening in a sidewall of the passageway in the direction.

Aspect 19. The method of any one of aspects 16-18, further comprising: supplying a flow of the process fluid to the passageway; and stopping the flow of the process fluid into the passageway before discharging the atomized fluid into the passageway.

Having thus described several illustrative embodiments of the present disclosure, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the disclosure covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respect, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the disclosure. The disclosure's scope is, of course, defined in the language in which the appended claims are expressed.