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.
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