Precise Wine Distribution System Using Thermopile Liquid Flow Sensor

Xiang Zheng Tu

 

Repeatable precision distributing of small volume liquid is critical for maintaining the accuracy of ingredient concentration, product efficacy, and batch-to-batch consistency for clinical diagnostics, pharmaceutical, food and beverage, and countless other controlled precision distribution applications. While a full-bodied, pressurized system with valve assembly undoubtedly offers the greatest distributing accuracy, the cost of capital equipment often requires researchers, product developers, and manufacturers to adopt a more economical alternative to handle their precision distribution needs.

In this paper we provide a precise wine distribution system using thermopile liquid flow sensors provided by POSIFA Microsystems. As shown in the above figure, the system comprises of a pressured gas source, a wine barrel, a manifold, n solenoid valves, n thermopile liquid flow sensors, n wine butters and an electronic controller. The electronic controller is used to manage the valves open time in each distributing cycle. With feedback information from the sensors, the distribution system could self adjust the open time of the valves automatically so as to distribute the desired volumes of wine over a large range of viscosities, as well as detect air bubbles or nozzle clogs in real time.   

As well known, several different types of liquid flow sensors have been developed based on different physical principles. A best one could be thermopile liquid flow sensors. A thermopile liquid flow sensor includes a silicon substrate, a thermal insulting base recessed into the substrate, a resistive heater positioned on the center of the base surface, two thermopiles displayed on the two opposite sides of the heater and with the hot junctions and cold junctions of the thermopiles positioned on the base surface and the outside region of the base surface respectively. The thermopiles are used as the temperature difference sensing element and operated in conjunction with the heater element for thermoelectric operation.

The thermal thermopile flow sensors operate by heat transfer from a heated element to a surrounding liquid flow. As liquid flow past the heater element increases, convective heat loss increases from the heater element and the temperature difference between the base surface and the outside region of the base surface decreases witch is measured by the thermopiles. The relationship between increasing fluid flow and forced convective cooling of the heater element can be determined and used as a baseline calibration for liquid flow measurement. The fabrication of such sensors is more complicated since less conventional materials are utilized for fabrication of thermopiles but CMOS (complementary metal oxide semiconductor) compatible processing is realistic and achievable.

The thermopile liquid flow sensors are chosen to use based on the following reasons:

First, the thermopile sensing is preferable for diagnosing large mass fluid flows such as liquid. Second, the Seebeck effect of thermopiles enables higher sensitivity and unbiased output voltages with no offset or drift. Third, the thermopiles are simple enough for practical realization. Last but not least, practical realization of the thermopiles meets the sensor durability requirements.

Thermopile liquid flow sensors can be operated in three modes: constant power, constant temperature, and temperature balance. The first mode involves heating up a temperature-sensitive resistor with constant electric power and measuring its temperature. The characteristic time of the measuring process in this mode (the response time) is determined by heat capacity of the resistor's material and the intensity of exchanging heat with the environment. Due to easy realization and rapid response, the constant temperature mode is more preferable.

It is should be understood that the thermopile liquid flow sensor is better than a diaphragm-pump type liquid flow meter for such applications. Because the diaphragm-pump type liquid flow meter is not good fit for higher-pressure applications. When placed in a pressurized system or when working against high resistance, it quickly loses accuracy. 

Five-Hole Thermal Velocity Probes Used for Attitude Control of Aircrafts

Tu Xiang Zheng

The ability to measure, stabilize, and control attitude is critical for any aircraft that is required to fly autonomously. Traditionally, attitude stabilization is achieved using rate gyros to sense and correct unwanted rotations in yaw, pitch, and roll. While this method is a standard feature of many autopilot systems, it is susceptible to drift during long duration flights. The reason is that rate gyros only sense angular velocities and not angular position itself. Therefore, they do not provide an absolute orientation reference. Instead, the yaw, pitch, and roll of the aircraft must be obtained by integrating the rate signals, which can lead to substantial noise induced drift. Another approach is to use the direction of gravity, as sensed by accelerometers, to estimate and stabilize attitude. But this approach can be invalid when an aircraft makes turns, which generate centripetal forces.

The use of the multi-hole pressure probes has become common to determine total and static pressures, flow velocity, and flow directions in three-dimensional flow fields with suitable calibrations. This approach is based on Bernoulli’s equation, which states that the pressure drop across the constriction is proportional to the square of the flow rate. Using this relationship, 10 percent of full scale flow produces only 1 percent of the full scale differential pressure. At 10 percent of full scale flow, the differential pressure flow meter accuracy is dependent upon the transmitter being accurate over a 100:1 range of differential pressure. Differential pressure transmitter accuracy is typically degraded at low differential pressures in its range, so flow meter accuracy can be similarly degraded. Therefore, this non-linear relationship can have a detrimental effect on the accuracy and turndown of differential pressure flow meters.

The above shortcomings can be overcome by using five-hole thermal velocity probes that provide direct information on the air stream velocity and direction that are experienced by an aircraft. Five-hole thermal velocity probes have some advantages over other methods as their maintenance, relatively low cost, and simplicity in operation. In principle, any aerodynamic body such as cylinder, sphere, wedge, or prism, with a number of holes can be used to measure three-dimensional flows. A minimum of five holes on an aerodynamic body is required to measure the four unknowns, namely, three velocity components and two angles in mutually perpendicular planes, in three-dimensional flows. However for the sake of symmetry and extended range of measurement capability, seven-hole or more probes are preferred.

The five-hole thermal velocity probes comprise not only five air flow tubes and but also five thermal velocity sensors, each of which is installed in an air flow tube. The center tube is arranged along the longitudinal direction of an aircraft to be attached and surrounded by the other four tubes in the shape of a cross. The leading edge of the four outside tubes is cut at a 45 degree angle to the center tube. Unlike multi-hole pitot pressure probes, the front end hole is communicated with the rear end hole instead of the both end holes keeping separated by the membrane of a pressure sensor. So when a flow of air stream past the tubes the sensors installed in the tubes measure the velocity or velocity components instead of the pressure difference of the flow.

Airspeed u_air, angle-of-attack (α), and sideslip angle (β) are known as the air data quantities, which are traditionally measured using pitot pressure tubs. Now these quantities can be measured using the five-hole thermal velocity probes. Assuming: a flow of air stream blows to the flying aircraft with a velocity W_air, the individual sensors of the five-hole velocity probes will measure individual signal representing individual velocity components that can be expressed as:

V_pitch1-2 =k (2)^1/2 W_air cos (α) cos (β),                                     (1)

V_yaw1-2 = k (2)^1/2 W_air  sin (α),                                                 (2)

V_center = k  W_air  cos (α) sin (β).                                               (3)

Where V_pitch1-2 is the output of the sensor in the pitch tube 1 or 2, V_yaw1-2 is the output of the sensor in the yaw tube 1 or 2, and V_center is the output of the sensor in the center tube, and k is the sensor circuit amplification factor. The airspeed u_air, angle-of-attack (α), and sideslip angle (β) can be calculated by solving the equations (1), (2) and (3).

The thermal velocity sensors used for the five-hole velocity pitot probes are produced by POSIFA Microsystems. Unlike traditional motion sensors, these new motion sensors do not rely on optical, microwave, or acoustic sound. They only rely on heat forced convection transfer. The sensor comprises a resistive heater and two thermopiles, which are integrated in a silicon substrate and supported by a thermal insulating base recessed into the silicon substrate. Since heat forced convection transfer the air flowing past the resistor will have a cooling effect on the heated resistor. By relating the temperature difference of the thermopiles, the speed air stream can be measured. They have fast response, low power consumption and compact structure. More particularly, it is easy to figurate an electronic sensor circuit that has zero offset, free temperature drift and very low noise.

It is true that the device structure of the thermal motion sensor is similar to the thermal flow sensor that we described before. But they are different in relative motion. Relative Motion is the laws of physics which apply when air is at rest on the earth also apply when air is in any reference frame which is moving at a constant velocity with respect to the earth.

Reference frame is too important in physics. We do all calculations according to the reference frames. For instance, we are on the aircraft flying in the air, the velocity of that plane with respect to the air can be measured using the thermal motion sensor. If we are on the ground the velocity of that aircraft is the sum of the velocities of plane and the wind. The velocity of the wind can be measured using the thermal flow sensor. To sum up the velocities of the aircraft and the wind, we can determine the directions and quantities of velocity of the aircraft with respect to the ground. 

Tracking Hummingbirds Using Thermal Moving Velocity Sensor

Tu Xiang Zheng

 

For many years the only way to track wildlife was to simply follow and observe the movement and habits of an animal or to capture an animal and put a tag on it and hope that at sometime in the future that same animal would be recaptured. Today, scientists have new tools to help them to track a wide variety of animals, from butterflies to great white sharks, in order to study how they use their environment, which foods are important and to gain insights into behavior and condition of the creatures as well as to identify key breeding areas that may need protection. 

There are three types of radio tracking systems available today: VHF Radio Tracking, Satellite Tracking and Global Positioning System (GPS) Tracking. But for tracking small animals these technologies are helpless because the transmitters used are so large and heavy. Today, scientists are working on ways to make the tracking devices smaller. Among them are MEMS wireless sensing systems. MEMS technology is enabling the development of inexpensive, autonomous wireless sensors with volumes ranging down to cubic mm.  Combination with miniaturized battery technology is making it possible to check even the smallest birds and insects.

In this paper we describe tracking hummingbird using a thermal moving velocity sensor and a thermal wind sensor. As shown in Fig.1, a Bluetooth thermal moving velocity sensor tag is attached to a hummingbird and a smart phone with a thermal wind sensor is hold by an observer. When the hummingbird is flying in the space the plane projection of the hummingbird flying path will display on the screen of the smart phone. The tracking range can reach 100 meters using class 1 smart phone. Technically it's possible to boost the Bluetooth range over 1000 meters, as some vendors suggest.

A thermal moving velocity sensor includes 12 sensing units each consisting of a heater and a thermopile, which are centro-symmetrically arranged on a silicon substrate. Two opposite units are configured as a pair for measuring a moving velocity component in this direction. So the whole sensor can measure 6 different directional velocity components and each two measured adjacent velocity components are 45 degree in angel. The structure of the thermal wind sensor is similar to the thermal moving velocity sensor. An only difference is that the sensing unit number of the thermal wind sensor is 4 instead of 6. The thermal wind sensor can measure 4 different wind components respectively in x and y directions. The measured data by the thermal moving velocity sensor and thermal wind sensor are collected and processed by the smart phone.

 

Reference to Fig. 2, it is more detail to explain the working principle of tracking hummingbird using the thermal moving velocity sensor and thermal wind sensor. As can be seen, a moving plane coordinate system is set on the hummingbird with a thermal moving velocity sensor and a reference plane coordinate system is set on the ground with a thermal wind sensor and a smart phone.

For the thermal moving velocity sensor the following equations can be formed according to basic trigonometric formulas:

V_yh = u + ν cos α,                                            (1)

V_45degree = u cos 45⁰ + (v cos α) cos 45⁰,         (2)

V _xh  = ν sin α                                                  (3)

 α = arcsin (V_xh /υ)                                           (4)

where u is the velocity of the hummingbird, v is the velocity of the natural wind and α is the incident wind angle, which are relative to the moving plane coordinate system. This is a system of ternary linear equations. The values of the three variables u, v and α can be obtained by substituting the measured values of V_yh, V_45degree  and V_xh and cos 45⁰ = 0.525 into the system, and solving the system.

For the thermal wind sensor, the following equations can be formed according to basic trigonometric formulas:

V_yw = ν cos θ                                                   (5)

V_xw  = ν sin θ                                                  (6)

θ = arctan (V_yw/V_xw)                                       (7)

where v is the velocity of the natural wind and θ is the incident wind angle, which are relative to the ground plane coordinate system.

It should be understood that the measured value of the natural wind velocity in the ground plane coordinate system is the same as the measured value in the moving plane coordinate system. But the wind incident angle is different in the two plane coordinates. This means that the incident angle α in the moving plane coordinate system is replaced by the incident angle θ in the ground plane coordinate system.

According to Cartesian coordinate system conversion, the following equations are available.

y_g = x_h  sin (θ - α) + y_h  cos (θ - α)                  (8)

x_g = x_h  cos (θ - α) + y_h  sin (θ - α)                  (9)

Actually, the moving plane coordinate system can be translated to the ground coordinate system by clockwise rotation of (θ - α) degrees. After translation the data collected by the thermal moving velocity sensor can be used to calculate the velocity, flying path and moving range of the hummingbird, which are relative to the ground plane coordinate system.

This tracking technology can help determine exactly where a hummingbird is at any moment in time and often what that animal is doing. Using the data collected from a thermal moving velocity sensor, scientists can determine the day-to-day movements of a hummingbird, the size of a hummingbird's home range, what other animals share an animal's range and the types of habitats a hummingbird uses. By analyzing all this data, scientists can learn new ways to help control hummingbird populations, determine what impact development might have on a hummingbird population, and determine if there are enough individuals of a particular species in an area to allow for reproduction.