Sensor system to distinguish frozen and non-frozen liquid particulates

A sensor system comprises a first sensor, a second sensor, and circuitry. The first sensor collects non-frozen liquid with a first collection efficiency, but does not collect frozen liquid. The second sensor collects non-frozen liquid with a second collection efficiency and also collects frozen liquid. The first collection efficiency and the second collection efficiency are substantially equivalent. The circuitry maintains the first sensor and the second sensor at a substantially constant temperature. The circuitry determines a measurement of the frozen liquid based on maintaining the first sensor and the second sensor at the substantially constant temperature. In some examples, multiple sensor systems can be used in combination to improve the accuracy of the measurement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related to the field of sensors, and in particular, to sensors that detect frozen and non-frozen liquid.

2. Statement of the Problem

Sensors that measure water and ice are well known. Special versions of these sensors have been developed for external airplane mounting. These special sensors collect data on ice and water concentrations in the atmosphere while the airplane is in flight.

Water Sensor

FIG. 1illustrates water sensor100in an example of the prior art. Water sensor100is attached to an airplane, and as the airplane flies, sensor100detects non-frozen water in the atmosphere. Water sensor100includes a cylinder that has a temperature sensor and that is connected to two supports. The two supports are attached to the airplane. Water sensor100also includes circuitry and associated power and temperature wiring.

The temperature wiring runs from the temperature sensor to the circuitry. The power wiring runs from the circuitry through one support and the cylinder, and then back down the other support to a ground. Although not shown for clarity, the power wiring is typically wound around a core within the cylinder, and a thermal-conducting material surrounds the power wiring to form the exterior of the cylinder. Thus, the power wiring is able to heat the cylinder based on the power supplied by the circuitry.

The circuitry controls the power transferred over the power wiring to maintain the cylinder at a constant temperature. To perform this task, the circuitry receives a signal indicating the temperature of the cylinder from the temperature sensor over the temperature wiring. In response to the cylinder temperature, the circuitry adjusts the power transferred over the power wiring to maintain the constant temperature. Thus, if the cylinder temperature drops below the constant temperature, then the power is increased, but if the cylinder temperature rises above the constant temperature, then the power is decreased.

When water strikes the surface of the cylinder, the water spreads over the cylinder surface to provide a cooling effect. To maintain the constant temperature, more power is required to evaporate the water. Ice tends to bounce off of the cylinder, so the ice does not cause a similar increase in power. Thus, the amount of power consumed by the cylinder correlates to the concentration of water in the atmosphere through which the airplane flies.

In addition to water, wind also affects the power consumed by the cylinder. Wind that strikes the cylinder also provides a cooling effect, so as the wind increases, the power required to maintain the constant temperature also rises. As the wind striking the cylinder decreases, then the power required to maintain the constant temperature also decreases. The airspeed of the airplane is the dominant factor in generating the wind that strikes the cylinder.

The circuitry receives an indication of the air speed of the airplane, so the circuitry can allocate the appropriate amount of power consumption to wind, and thus, allocate the appropriate amount of power consumption to the water that strikes the cylinder. Once the power consumption due to the water is determined, the circuitry can determine the concentration of water in the atmosphere.

Although ice tends to bounce off of the cylinder, some ice may collect on the cylinder during flight. In an ice-only precipitation event, sensor100can detect this ice due to the power increase required to melt and evaporate the collected ice. The power increase would not correlate well to the concentration of water in the atmosphere because the cylinder's collection efficiency for ice is so poor. In a mixed ice-water precipitation event, the collected ice only serves to generate error in the water precipitation rate calculation.

Water sensor100has exhibited problems in practice. Water sensor100cannot provide any accurate data regarding ice. This problem is especially acute with respect to clouds, since small ice particles are prevalent in clouds and are of interest to pilots and scientists alike. Water sensor100has also proven to be fragile when mounted on an airplane. In addition, water sensor100has two supports that require separate attachments to the airplane. Although some attachment to the airplane is required, multiple attachments are not desirable when considering the structural integrity of the airplane.

Total Ice and Water Sensor

FIG. 2illustrates ice/water sensor200in another example of the prior art. Ice/water sensor200is also attached to an airplane, and as the airplane flies, ice/water sensor200detects the combined ice and water in the atmosphere. Ice/water sensor200includes a cylinder that has a temperature sensor and that is connected to a support. The support is attached to the airplane and allows the cylinder to rotate. A vane on the cylinder, along with the pivoting support, causes one end of the cylinder to point into the wind. The cylinder has a reentrant shape at the end that points into the wind. The reentrant shape forms an inverted cone that extends into the end of the cylinder that points into the wind. As the airplane flies, ice and water that enter the cone are trapped within the cone.

Ice/water sensor200also includes circuitry and associated power and temperature wiring. The temperature wiring runs from the temperature sensor to the circuitry. The power wiring runs from the circuitry through the support and the cylinder, and then back down the support to a ground. Thus, the power wire is able to heat the cylinder based on the power supplied by the circuitry.

The circuitry and power wiring maintain the cylinder at a constant temperature. To perform this task, the circuitry receives a signal indicating the temperature of the cylinder from the temperature sensor over the temperature wiring. In response to the cylinder temperature, the circuitry adjusts the power transferred over the power wiring to maintain the constant temperature. Thus, if the cylinder temperature drops below the constant temperature, then the power is increased, but if the cylinder temperature rises above the constant temperature, then the power is decreased.

Ice and water that are trapped in the cone provide a cooling effect, so more power is required to melt the ice and evaporate the melted ice and water to maintain the constant temperature. Thus, the amount of power consumed by the cylinder correlates to the concentration of both ice and water in the atmosphere through which the airplane flies.

In addition to water, wind also affects the power consumed by the cylinder. As the wind striking the cylinder increases, then the power required to maintain the constant temperature also rises. As the wind striking the cylinder decreases, then the power required to maintain the constant temperature also decreases. The airspeed of the airplane is the dominant factor in generating the wind that strikes the cylinder.

The circuitry receives an indication of the air speed of the airplane, so the control circuitry can allocate the appropriate amount of power consumption to wind, and thus, allocate the appropriate amount of power consumption to the ice and water that strike the cylinder. Once the power-consumption due to ice and water is determined, the circuitry can determine the combined concentration of ice and water in the atmosphere.

Ice/water sensor200has exhibited problems in practice. Ice/water sensor200cannot provide any accurate data regarding only ice, or regarding only wafer. This problem is especially acute in clouds where small particles of ice are prevalent, and are of interest to pilots and scientists alike. Ice/water sensor200has also proven to be fragile when mounted on an airplane. In addition, the aerodynamics caused by pointing the cylinder into the wind causes very small particles of ice and water that should fly into the cone to fly around the cone instead. This loss of small particles adds inaccuracy to the results, especially when a cloud is encountered that contains a large concentration of these smaller ice particles.

Ice/Water Sensor System

Sensors100and200can be used together to obtain data specific to the ice concentrations in the atmosphere. Ice/water sensor200is used to get the combined ice/water concentration, and water sensor100is used to get the water-only concentration. The water-only concentration is subtracted from the combined ice/water concentration to obtain the ice-only concentration.

Unfortunately, the combined use of sensors100and200to determine the ice-only concentration is prone to error, because sensors100and200have different collection efficiencies due to their different shape and size. The collection efficiency is a ratio of the total amount of water in a given volume versus the actual amount of water that is collected and evaporated by the sensor traveling through the volume. For example, water sensor100may collect and evaporate 95% of the water in a given volume, but ice water sensor200may only collect and evaporate only 80% of the water in the same volume. When the water concentration is subtracted from the ice/water concentration, the two water concentrations are not equivalent due to the different collection efficiencies of sensors100and200. The resulting ice concentration is inaccurate because the two water concentrations were not equivalent.

In addition, ice/water sensor200does not collect some smaller ice particles, which further skews the result. The combined use of sensors100and200also leads to an undesirable number of attachments to the airplane. The combined use of sensors100and200does not provide a robust system that can stand up to the rigors of external airplane mounting.

SUMMARY OF THE INVENTION

Examples of the invention include a sensor system and its method of operation. The sensor system comprises a first sensor, a second sensor, and circuitry. The first sensor is configured to collect non-frozen liquid with a first collection efficiency, but not to collect frozen liquid. The second sensor is configured to collect non-frozen liquid with a second collection efficiency and to collect frozen liquid. The first collection efficiency and the second collection efficiency are substantially equivalent. The circuitry is configured to maintain the first sensor and the second sensor at a substantially constant temperature and to determine a measurement of the frozen liquid based on maintaining the first sensor and the second sensor at the substantially constant temperature.

Examples of the invention include a system of sensors comprising a first sensor system, a second sensor system, and circuitry. The first sensor system comprises a first sensor configured to collect non-frozen liquid with a first collection efficiency, but not to collect frozen liquid, and a second sensor configured to collect the non-frozen liquid with a second collection efficiency and to collect the frozen liquid. The first collection efficiency and the second collection efficiency are substantially equivalent. The second sensor system comprises a third sensor configured to collect the non-frozen liquid with a third collection efficiency, but not to collect the frozen liquid, and a fourth sensor configured to collect the non-frozen liquid with a fourth collection efficiency and to collect the frozen liquid. The third collection efficiency and the fourth collection efficiency are substantially equivalent. The circuitry is configured to maintain the first sensor and the second sensor at a first substantially constant temperature, and determine a first measurement of the frozen liquid based on maintaining the first sensor and the second sensor at the first substantially constant temperature. The circuitry is configured to maintain the third sensor and the fourth sensor at a second substantially constant temperature, and determine a second measurement of the frozen liquid based on maintaining the third sensor and the fourth sensor at the second substantially constant temperature. The circuitry is configured to process the first measurement and the second measurement together to produce a result. The first sensor and the second sensor have a first size, and the third sensor and the fourth sensor have a second size wherein the first size is larger than the second size. In some examples, the first sensor, the second sensor, the third sensor, and the fourth sensor comprises cylinders, where the first size comprises a first cylindrical diameter and the second size comprises a second cylindrical diameter. The first cylindrical diameter is larger than the second cylindrical diameter. Advantageously in some examples, multiple sensor systems can be used in combination to improve the accuracy of the measurements.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, the term “water” refers to liquid water, and the term “ice” refers to frozen water. Note that the accompanying figures are illustrative and are not drawn to scale.

Sensor System

FIG. 3illustrates a top view of sensor system300in an example of the invention. Sensor system300includes sensors301–303that are each coupled to interface304. Interface304can be coupled to an airplane (not shown).

FIG. 4illustrates a front view of sensor system300in an example of the invention. The airplane onFIGS. 4–6is not drawn to scale and is typically much larger than system300. Note that the direction of airplane flight is out of the page, so the direction of airflow is into the page. Note that sensors301and302are exposed to airflow that is typically generated by the movement of the airplane, but that sensor303(not shown) is shielded from the airflow by interface304and sensors301–302. Also note that sensors301and302present the same cross-sectional area to this airflow.

FIG. 5illustrates a side view of sensor system300in an example of the invention. Note the reentrant shape of the cylinder that comprises sensor302. The reentrant shape forms a triangular indentation into the side of the cylinder. The indentation runs along the length of the cylinder that faces the airflow. Advantageously, the reentrant shape of sensor302traps both ice and water. In addition, the reentrant shape along the length of the cylinder tends to trap ice better than the reentrant cone shown in prior artFIG. 2.

FIG. 6illustrates the other side view of sensor system300in an example of the invention. Note that sensor301is also cylinder, but sensor301does not have the reentrant shape. Thus, ice particles tend to bounce off of sensor301while water spreads over the surface of sensor301.

Interface304could be made of metal or some other suitable material. Interface304should be configured for attachment to the airplane with a single attachment. A single attachment only requires a single penetration of the airplane skin for attachment to the airplane. Interface304should be configured to hold sensors301–303firmly in place during flight, and also provide access to sensors301–303for the temperature and power wiring. Interface304may also house circuitry that controls system operation.

If desired, interface304could be configured to allow ground personnel to adjust the orientation of sensors301–303before a flight to optimize sensor performance based on the aerodynamic characteristics of the airplane. For example, interface304could allow sensors301–303to rotate to a new position around the axis of interface304. Interface304could allow sensors301–303to modify their angle to interface304. Interface304could allow sensor302to rotate about its own axis to modify the angle of the reentrant shape relative to the direction of flight.

Sensors

FIG. 7illustrates a cut-away view looking into the side of sensor301in an example of the invention. Sensor301has a central core that extends from one end of the cylinder to the other. The core could be air within a metal tube or-some other suitable material. Sensor301has power wiring that is wound around the core from one end of the cylinder to the other. The power wiring could be copper, nickel, or some other suitable material. Sensor301has a thermal conductor surrounding the power wiring from one end of the cylinder to the other. The thermal conductor could be brass, steel, silver solder or some other suitable material. Sensor301has a sheath around the thermal conductor. The sheath could be metal oxide or some other suitable material. A temperature sensor is also placed within or on the surface of the sheath with temperature wiring extending to the end of the cylinder at interface104. Sensor301could have a 3 mm diameter, a 10 mm diameter, or some other suitable diameter. Sensor301could be 50 mm long, 100 mm long, or some other length.

In some examples, sensor301could be manufactured as follows, although other techniques and materials could be used in other examples. A length of wire that will form the power wiring is doubled up twice to form a four-wire length with the hot and cold leads at the same end. The four-wire length is wound around the core from one end to the other so the hot and cold leads reach interface104. Thus, the power wiring enters and exits sensor301at the same end near interface104, so only one support (interface104) is required to ingress/egress the wiring. The wiring is braised to the core. The wiring, core, and a temperature sensor are placed within a sheath, and the sheath is filled with silver solder. The filled sheath is shaken and packed to remove air in the silver solder, and the sheath is sealed.

Other than its shielded orientation behind interface304, sensor303could be the same as sensor301. The difference in power consumption between sensor301and sensor303indicates the amount of water in the atmosphere. The difference in power consumption between sensor302and sensor303indicates the amount of ice and water in the atmosphere.

FIG. 8illustrates a cut-away-view looking into the side of sensor302in an example of the invention. Sensor302has a central core, winding, thermal conductor, temperature sensor, and sheath that extends from one end of the cylinder to the other in a similar fashion to sensor301. Note the reentrant shape of sensor302that forms a triangular indent in the cylinder from one end of the cylinder to the other. The triangular indent faces into the airflow to trap ice and water within the indent. In some examples, the angle of the indent is between 90 and 110 degrees.

Referring to bothFIGS. 7 and 8, note that sensors301and302have the same cross-section relative to the airflow. Since sensors301–302are typically the same length, sensors301–302present the same cross-sectional area to the air flow. Advantageously, the same cross-sectional area presented to the airflow gives sensors301and302substantially the same collection efficiency. As described above, the collection efficiency is the ratio of the total amount water in a given volume versus the actual amount of water that is collected and evaporated by a sensor traveling through the volume. Thus, sensors301–302will each collect and evaporate substantially the same amount of water in a given volume. In the context of the invention, collection efficiencies are substantially the same when they are within 5% of one another.

Sensor System Circuitry

FIG. 9illustrates a schematic view of sensor system300in an example of the invention. Sensors301–303are shown along with circuitry900. Circuitry900could be housed in interface104, within the airplane, or be located on the ground. Circuitry900could be distributed between these locations. Circuitry900receives a power feed (or uses a battery) and also receives individual temperature feeds from sensors301–303. Circuitry900individually controls the power transferred to sensors301–303to maintain the sensors at a substantially constant temperature.

The substantially constant temperature may be allowed to drift downward after a period of heating based on the desired duty cycle for the heating components. In addition, circuitry900may change the substantially constant temperature based on the measured concentrations of ice and water. For example, if the measured concentrations of ice or water is so high that the sensors may become saturated and unable to evaporate all of the water, then circuitry900could increase the substantially constant temperature, so the sensors can evaporate water faster and avoid saturation.

Circuitry900processes the individual power consumption of sensors301–303to provide the concentration of ice, the concentration of water, the concentration of combined ice and water, and the ratio of ice to water. The concentrations are typically provided in grams per cubic meter. Circuitry900determines the water concentration using the difference in power consumption between sensors301and303. Circuitry900determines the ice and water concentration using the difference in power consumption between sensors302and303. Circuitry900determines the ice concentration by subtracting the water concentration from the ice and water concentration. The ratio is determined by dividing one of the ice concentration or the water concentration by the other. Circuitry900may also process the power consumption of sensor303as compared to sensors301–302to determine the wind speed, ambient temperature, and pressure. Alternatively, circuitry900may receive a data feed from the airplane that indicates ambient temperature, pressure, and air speed, and in this alternative, sensor303may be omitted from sensor system300.

Circuitry900includes components for processing, communication, and storage. Circuitry could include software and/or firmware or some other form of machine-readable processing instructions to direct system operations. Circuitry900could use general-purpose integrated circuitry and/or special purpose circuitry. Circuitry900could provide a minimum response time of time 0.1 second (for cloud data), a minimum response time of time 1 second (for general precipitation data), or use some other response time.

To perform the calculation, circuitry900should account for the latent heat of melting ice and the latent heat of evaporating water. Since the two latent heats are different, a ratio of ice to water is estimated to handle the different latent heats for melting and evaporation in the initial ice and water concentration calculation. The estimated ratio may be generated based on some metric, such as temperature, or may be set by the operator. Once, the concentration are actually determined, the actual ratio of ice to water may be used in a second order calculation to improve the accuracy of the ice and water concentration outputs.

Combination of Sensor Systems

FIG. 10illustrates a combination1000of sensor systems in an example of the invention. Combination1000includes smaller sensor system1001, larger sensor system1002, and circuitry1003. Sensor systems1001–1002could be similar to sensor system300. Sensor system1001is referred to as smaller, and sensor system1002is referred to as larger, because the sensor diameter of smaller system2001is smaller than the sensor diameter of larger system1002. For example, the sensor diameter for system1001could be 3 millimeters, and the sensor diameter for system1002could be 10 millimeters.

Sensors systems1001–1002transfer data to circuitry1003. Circuitry1003processes the data from the multiple sensors to improve the accuracy of the measurements. Circuitry1003could be similar to circuitry900. Circuitry1003is shown as separate from systems1001–1002, but circuitry1003could be integrated within one or both of sensor systems1001–1002.

Within the same sensor system, the sensors (i.e. water-only sensor301and ice/water sensor302) have similar sizes, so the collection efficiencies of the sensors is comparable for particles of equal size and density. This collection efficiency also depends on sensor diameter, so that employment of sensor systems1001–1002having different sensor diameters enables small particles to be collected by smaller sensor system1001and the much rarer large particles to be collected by larger sensor system1002in numbers sufficient for a useful measurement. For example, small cloud particles would be collected by smaller sensor system1001, but not by larger sensor system1002. Larger precipitation particles would be collected by larger sensor system1002, but not collected sufficiently frequently by smaller sensor system1001for a useful measurement.

The collection of water drops depends on their size, and the collection of ice particles depends on their size, density, and shape. In a mixed cloud of both ice and water particles, both ice and water particles are collected together by the ice/water sensor (i.e. sensor302). Most ice particles bounce off of the water-only sensor (i.e. sensor301) which then measures water content. Thus, ice and water content may be measured independently. A correction may be desired for the water-only sensor (i.e. sensor301) because a small amount of ice may occasionally collect at the stagnation line along the cylinder, and the ice could be mistakenly interpreted as water. This situation could occur in a completely ice cloud as well as a mixed ice/water cloud. Combining data-from both sensor systems1001–1002and information on ambient temperature and particle size, shape, and density from other measurement systems (such as a video cloud microscope system) enables circuitry1003to mitigate the effect of unwanted ice on the water-only sensor from the water concentration measurement. Additional sensor systems having other sensor diameters could be used to further hone this measurement.

Variations

Those skilled in the art will appreciate numerous variations of sensor system300that fall within the scope of the invention. For example, sensor system300could be implemented on a vehicle other than an airplane, or may be mounted in a stationary position. Such alternative vehicles include cars, trucks, unmanned aerial vehicles, rockets, balloons, helicopters, and the like.

Sensor system300may not have reference sensor303. Empirical testing could be used to correlate airspeed, ambient temperature, and ambient pressure to the amount of power required to maintain the reference sensor at the target temperature. Once the correlations are determined, system300circuitry could receive and process data that indicates actual airspeed, ambient temperature, and ambient pressure based on the correlations to estimate the power that would have be required to maintain a reference sensor at the target temperature. This estimate could be used in place of actual reference sensor power data, and thus, reference sensor303could be omitted from the system.

Sensor system may use shapes other than a cylinder, such as a polygon.

Sensor system300may detect and distinguish concentrations of non-frozen and frozen liquids other than ice and water.

Sensor system300may use a gyroscope, motor, or some other mechanism to properly orient itself into the wind.

Sensor system300may be used with a camera and computer where the camera and computer characterize ice and water particles by phase, shape, and density. This data can be used to validate the outputs of circuitry900.

Advantages

Sensor system300provides ice concentrations and water concentrations for the atmosphere. The use of different sensors where one collects ice and one does not collect ice, but where both sensors have similar collection efficiencies for water improves the accuracy of the ice-only concentration over prior sensor systems. In addition, sensor system300is robust and requires minimal attachment to the airplane.