Desiccant saturation level monitoring

Methods and apparatus for a desiccant saturation monitoring system having a body with a first portion configured to hold a desiccant material and a second portion configured to position a sensor in relation to the desiccant material. A light source can irradiate the desiccant material and the sensor can detect irradiance from the desiccant material for at least one wavelength to determine saturation information for the desiccant material.

BACKGROUND

Embedded desiccant assemblies protect against moisture intrusion by adsorbing water from a partially or fully sealed enclosure. Some sensors, such as electro-optic sensors, are particularly sensitive to moisture intrusion. However, the function of the desiccant degrades as the desiccant material saturates with moisture.

Conventional techniques to detect saturation include relative humidity measurement of the desiccated volume. Other systems use desiccant that changes color to indicate when saturation occurs. The desiccant material is viewed and subjectively evaluated for saturation levels.

SUMMARY

Embodiments of the invention provide methods and apparatus for desiccant saturation level monitoring that can generate a signal that reflects a moisture saturation state of a desiccant material in a desiccated volume. In embodiments, a system includes a calibrated photonic sensor within a desiccated volume that reports spectral response changes of the desiccant material during saturation transition with high sensitivity. The signal reported by the sensor can be read in real-time to monitor the function of the desiccant. As the desiccant approaches saturation, the material can be replaced.

In one aspect, a system comprises: a sensor; a body having a first portion configured to hold a desiccant material and a second portion configured to position the sensor in relation to the desiccant material, wherein the desiccant material is configured to adsorb moisture in a desiccated volume; and a light source configured to illuminate the desiccant material, wherein the sensor is configured to detect irradiance from the desiccant material for at least one wavelength to determine saturation information for the desiccant material.

A system may further include one or more of the following features: the sensor comprises a photosensor, the sensor comprises a red, green, blue (RGB) sensor, the sensor is configured to detect irradiance from the desiccant material for red, green and blue wavelengths, the system includes memory to store wavelength information that corresponds to saturation levels of the desiccant material, the system comprises a sensor assembly containing the desiccated volume, the desiccated volume is non-hermetically sealed, the body comprises an observation chamber to position the sensor a given distance from the desiccant material, the saturation information comprises a percentage of saturation for the desiccant material, the light source is configured to emit visible light, and/or the system is secured to an aircraft.

In another aspect, a method comprises: employing a body having a first portion configured to hold a desiccant material and a second portion configured to position a sensor in relation to the desiccant material, wherein the desiccant material is configured to adsorb moisture in a desiccated volume; and illuminating the desiccant material with a light source, detecting irradiance, by the sensor, from the desiccant material for at least one wavelength to determine saturation information for the desiccant material.

A method can further include one or more of the following features: the sensor comprises a photosensor, the sensor comprises a red, green, blue (RGB) sensor, the sensor is configured to detect irradiance from the desiccant material for red, green and blue wavelengths, the desiccated volume is non-hermetically sealed, the body comprises an observation chamber to position the sensor a given distance from the desiccant material, and/or the saturation information comprises a percentage of saturation for the desiccant material.

In a further aspect, a system comprises: a means for holding a desiccant material and positioning a sensor in relation to the desiccant material, wherein the desiccant material is configured to adsorb moisture in a desiccated volume; and a light source configured to illuminate the desiccant material, wherein the sensor is configured to detect irradiance from the desiccant material for at least one wavelength to determine saturation information for the desiccant material.

DETAILED DESCRIPTION

FIG.1shows an example platform100, such as an aircraft, having a sensor assembly102that has a desiccated volume104which is partially sealed. A desiccant saturation monitoring system106monitors a saturation level of desiccant material108that adsorbs moisture from the desiccated volume104. The sensor assembly102can include a sensor110, such as an electro-optic sensor, coupled to a processing module112, which can contain circuitry and other components that are environmentally sensitive. In embodiments, the sensor assembly102can include a connection114to outside air. The connection can include a mechanism116, such as a check valve, to manage air flow in to and out of the desiccated volume104.

In the illustrated embodiment, the platform100comprises an aircraft which ascends in altitude and descends back to lower altitudes. As is well known, the air has different characteristics, e.g., temperature, humidity, pressure, etc., at different altitudes and locations. As the aircraft100descends at different locations, the amount of moisture in the partially sealed desiccated volume104may increase. If there is some level of moist air intake into the partially sealed volume104at one altitude, after a change in location and/or altitude to a cooler temperature, condensation can form on surfaces within the partially sealed volume104if the desiccant material is saturated. The undesirable effects, e.g., biological growth, rust, corrosion, optical coating damage, and circuitry degradation will occur after prolonged exposure to this condition.

As used herein, partially sealed refers to a volume that is non-hermitically sealed. The air in the desiccated volume has at least one characteristic that is different than outside air. It is understood that amount of air flow in to and out of the desiccated volume104can vary from almost complete hermetic seal to almost free flow of outside air depending upon the application. In addition, while example embodiments are shown and described in conjunction with a desiccated volume containing air, it is understood that the desiccated volume can contain any suitable fluid and desiccation material.

While example embodiments are shown and described in conjunction with an aircraft, it is understood that embodiments of the invention are applicable to systems in general in which it is desirable to determine the level of saturation of a desiccant material. For example, vehicles, fixed structures, submarines, unmanned aerial vehicles, unmanned underwater vehicles, autonomous vehicles, medical devices, medicine delivery systems, molecule filtering systems, implantable biological function sensors, and the like may have sealed or partially sealed enclosures of some kind for which desiccant monitoring is desirable. In addition, it is understood that desiccated volumes can be internal to a platform or can be removably attached to a platform.

It is understood that the same issues exist for ground vehicles as well due to exposure to weather (rain, snow, fog, etc.) but also just to diurnal cycling which causes day-to-day pressure fluctuations which may drive moisture into the volume and gas migration. This may slowly cause moisture intrusion past any non-hermitic seal.

FIG.2Ais a perspective view andFIG.2Bis a cross-sectional side view of an example desiccant saturation level monitoring system200in accordance with an example embodiment. A body includes a first portion202that defines a desiccant container204and a second portion206that includes a sensor system208to obtain moisture saturation information of a desiccant material210in the container204for adsorbing moisture in a desiccated volume, such as the desiccated volume104ofFIG.1.

In embodiments, the first portion202includes one or more apertures212to enable air flow into the container204for adsorbing moisture within the desiccated volume. In the illustrated embodiment, the aperture212is shown as an elongate slot. The apertures212can be formed in any practical number, geometry, and location to meet the needs of a particular application. For example, different systems may have different rates of air flow that require a given rate of moisture adsorption. For example, the container204can include a pressure valve (configured to open when the outside air pressure is several PSIA different than the internal pressure) through an opening which allows outside air to be directed into the cavity filled with desiccant210. Another opening similar to aperture212allows this outside air to freely flow into the product's desiccated volume104. The function of these pair of openings to ensure outside air is forced through the desiccant material at least once and is therefore mostly devoid of moisture.

At the intersection of the first and second portions202,206, the desiccant monitoring system200includes an observation chamber214that provides a standoff distance216between a sensor218and the desiccant material210. In embodiments, the sensor218and a surface of the desiccant material210should remain at a given distance to ensure accurate data. The sensor218can be coupled to a signal processing module220for processing signal information from the sensor218. The signal processing module220can be connected to remote processing modules via a suitable cable222.

In embodiments, suitable example desiccant materials include silica-gel type, 4A synthetic zeolite-type materials with heavy metal salt additives, and the like.

MIL-DTL-87934C specifies the performance and behavior of molecular sieve desiccants including those with color changing properties due to metal salt additives that are suitable for embodiments, An example desiccant material is available at https://www.sorbentsystems.com/bulksorbents.html. Suitable silica-gels include part number 640AG05. It is understood that any suitable desiccant material be used that has the property of changing color based upon a level of moisture saturation.

Irradiance refers to the radiant flux received by a surface per unit area, such as watts per square meter (W·m−2). In embodiments, irradiance refers to what is being measured by example sensors, which can also be referred to as intensity. In embodiments, each photodetector within the sensor is treated with one or more filters to block undesirable wavelengths of light. The result is that the sensor takes irradiance measurements in independent spectral bands, e.g., colors. Since the photodetectors are essentially in the same physical location and looking in the same direction, in embodiments, the relative response between the spectral band measurements provide an accurate assessment of the color of the observed object. In embodiments, a white light emitting source is the source of the light reflected off of the desiccant material.

It is understood that by convention the function of desiccant materials is defined by the amount of moisture it can adsorb as a percentage of its mass. For example, a desiccant material can be defined as having a moisture absorption capacity of twenty percent of its mass.

FIG.3shows an example photosensor assembly300for detecting irradiance characteristics of desiccant material. In the illustrated embodiments, the photosensor assembly300is located at an end of a container302(shown without desiccant material) having a series of slots to allow airflow into the container. Note that the container302is shown without the bottom. The photosensor304is configured to be a certain distance from the surface of desiccant material to provide consistent signal readings.

The photosensor assembly300senses the spectral response of the desiccant material when the integrated light source306is active. In embodiments, an infrared window can filter the energy received by the photosensor300. Infrared filtering can be performed at the standoff window or immediately in front of the photodetectors, for example.

FIG.4is a high-level block diagram of an example desiccant saturation monitoring system400including a sensor402, such as the photosensor ofFIG.3, to receive reflected light from desiccant material. A signal processing module404can receive the spectral response data from the sensor402. In embodiments, the system400can include stored spectral response and desiccant saturation level data406for comparison with present spectral response data. Based on the present spectral response data, the current desiccant saturation level can be determined and provided to a saturation level output module408which can output a desiccant saturation level signal410.

The desiccant saturation level signal410can comprise a variety of formats. In one embodiment, the desiccant saturation level signal410is active when the desiccant is above a saturation threshold. Thus, the desiccant saturation level signal410can serve as a flag that the desiccant material should be replaced. In other embodiments, the desiccant saturation level signal410comprises percent saturation information. In some embodiments, the desiccant saturation level signal410comprises saturation prediction information. For example, based on historical desiccant saturation changes on per flight basis, the desiccant saturation level signal410can predict when the saturation level will reach a given saturation threshold level.

In other embodiments, the current spectral response is processed by the signal processing module404using one or more algorithms to generate a current desiccant saturation level. For example, ratios of two or more wavelengths of the spectral response can be computed and then calibrated using laboratory reference measurements to determine an estimated desiccant saturation level.

In embodiments, the signal processing module404, spectral response data406and saturation level output module408are local to the sensor402. In other embodiments, these components are remote from the sensor402. For example, data from the sensor402can be provided to a central control or signal processing module.

In embodiments, a desiccant material saturation level monitoring system includes a photosensor that measures irradiance at one or more wavelengths. In some embodiments, the photosensor measures irradiance from the desiccant material at red (R), green (G), and blue (B) wavelengths. The photosensor can comprise an RGB sensor.

While embodiments are shown and described using red, green, and blue light measurements, it is understood that other wavelengths can be used and that any practical number of wavelengths can be measured to meet the needs of a particular application or a selected desiccant material. In some embodiments, wavelengths in the non-visible spectrum are measured and processed.

FIG.5Ais an example waveform for data collection during calibration showing the relationship between the mass500of a desiccant material and spectral response over time for a first wavelength signal502, which is red (R) in the illustrated embodiment, a second wavelength signal504, which is green (G) in the illustrated embodiment, and a third wavelength signal506, which is blue (B) in the illustrated embodiment. In embodiments, the red, green and blue signals502,504,506, can be obtained using an RGB photosensor. The red, green and blue signals502,506,506should each define a given wavelength corresponding to calibration. As is known in the art, the wavelengths for R, G, B and other wavelengths can vary from RGB sensor type, as well as from sensor to sensor. As can be seen, the mass500of the desiccant material increases and levels off as saturation is reached.

As can be seen, the red, green, and blue signals502,504,506monotonically change as the desiccant mass500increases. In the illustrated embodiment, the mass500of the desiccant material is shown changing over a period of eight days. The R, G, B signals502,504,506can be combined, such as by algorithm processing to generate the change in mass500of the desiccant.

FIG.5Bis an example waveform diagram for sensor calibration showing first, second and third wavelength signals550,552,554as the saturation level of a desiccant material increases from 0.00 percent to 25.00 percent (x-axis). In the illustrated embodiment, the first wavelength550corresponds to R, the second wavelength552corresponds to B, and the third wavelength554corresponds to G. As can be seen, any given desiccant saturation level along the x-axis corresponds to unique values for R, G, B. When the desiccant experiences color changes while becoming saturated, the photosensor can sense values for the R, G, B signals and determine the desiccant saturation level. It will be appreciated that RGB values can be stored for some set of saturation levels at a given granularity. In an alternative embodiment, the RGB values can be processed to determine a unique relative relationship to a given saturation level. For example, at least one of an R/G ratio, a B/G ratio, and/or a GB ratio can correspond to a given saturation level.

It is understood that signal wavelength data from the sensor can be processed in a variety of ways. In some embodiments, a single wavelength may be processed to determine desiccant material saturation levels. In other embodiments, relationships between R, G, B data, for example, can be used to determine saturation levels.

FIG.5Cshows an example plot of predicted desiccant material saturation level570based on a red channel response (shown as the nearby dots) normalized to the overall response. In one particular embodiment, the predicted desiccant material saturation level570is defined by an equation where x=red channel response and y=predicted desiccant saturation level. The example equation is y=(−9.38e−5)x{circumflex over ( )}2+(5.32e−3)x+0.305. In the illustrated embodiment, irradiance measurements for a single channel (red) can be converted into a predicted desiccant saturation level. The dots on the right side show the percent error of the predicted desiccant saturation level to the actual saturation level as measured by mass.

FIG.6shows notional desiccant saturation level600over time which increases in steps that may correspond to aircraft flights or missions. For example, each flight may correspond to a step602increase in desiccant saturation level600. It is understood that the size and duration of the steps can vary based upon the outside air characteristics, such as humidity and temperature, and flight parameters, such as altitude, duration, and the like.

FIG.7is a flow diagram showing an example sequence of steps for monitoring the saturation level of a desiccant material. In step700, desiccant material is illuminated by a light source, such as a white light emitting diode (LED). In step702, a photosensor measures the irradiance of the desiccant material. In embodiments, the photosensor measures energy levels, e.g., amplitude, for at least one wavelength. In some embodiments, the photosensor measures R, G, B signal levels.

In step704, the measured energy levels are processed and in step706saturation information for the desiccant material is determined. For example, one or more of R, G, B measurements can be used to compute a predicted desiccant saturation level, as described inFIG.5C. In embodiments, the saturation information includes a saturation level by percentage. In embodiments, sensor data is subject to low noise amplification in preparation for sampling by an analog-to-digital converter followed by a calibration process which normalizes the measurements for the purpose of making saturation determination. After digital sampling, the resulting measurements may be further processed such as by comparing calibrated measurements to a threshold value. An indication may be generated if saturation has occurred. Further, calibrated measurements may be processed for estimating the desiccant saturation value, as described above. In addition, calibrated measurements can be processed to estimate the remaining time until desiccant saturation will occur and report the time estimate value. In step708, the determined saturation information is output, such as being transmitted to a remote processing unit. Saturation information, can include, for example, a saturated/unsaturated determination, percent saturation, a predicted time to saturation, etc.

FIG.8shows an exemplary computer800that can perform at least part of the processing described herein, such as the processing ofFIGS.2,3,4,5A,5B,5C,6, and7. For example, the computer800can perform processing for the signal processing module404ofFIG.4and the processing steps ofFIG.7. The computer800includes a processor802, a volatile memory804, a non-volatile memory806(e.g., hard disk), an output device807and a graphical user interface (GUI) device808(e.g., a mouse, a keyboard, a display, for example). The non-volatile memory806stores computer instructions812, an operating system816and data818. In one example, the computer instructions812are executed by the processor802out of volatile memory804. In one embodiment, an article820comprises non-transitory computer-readable instructions.