Note: Descriptions are shown in the official language in which they were submitted.
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Background o~ the Invention
The present invention relates -to pressure and
temperature sensors and, more particularly, to a novel
hybrid pressure and temperature sensor for simultaneously
sensing pressure and temperature at a single location and
in non-interacting manner~
In many forms of apparatus, such as in heat
pumps and the like appliances, it is necessary to
simultaneously sense pressure and temperature at a parti-
cular location. Previously, such parameter sensing hasbeen carried out by the use o~ a pair of sensors at each
sensed location. This arrangement is not only relatively
costly, but, as the two transducers are not located at
exactly the same physical location within the apparatus,
also does not provide simultaneous indication of pressure
and temperature at exactly the same sensed location. It
is desirable to not only sense both pressure and tempera-
ture at the same location, in essentially non-interacting
manner, but to also sense both parameters with a sinyle
sensor having relatively low cost and a minimum parts
count.
Brief Summary of the Invention
In accordance with the invention, a sensor for
simultaneously sensing pressure and temperature at a
singl~ location in substantially non-interacting
manner, includes an insulative substrate having a patterned
thick film resistance element fabricated thereon between
first and second terminals, and a conductive plate
insulativel~ spaced from the xesistive thick film pattern
and connected to a third terminal. A pressure-tight
, support of insulative material is fabricated between the
periphery of the conductive plate surface closest to the
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substrate and the substrate surface, to provide an
interior compartment, in which the thick film resistor
is enclosed~ at a reference pressure, which may be
substantially a vacuum. The sensor is positioned at the
location at which pressure and temperature are ta be
sensed and pressure thereat exerts a force upon the
exterior surface of the conductive plate, varying the
spacing between the plate and the resistive thick film
to vary the distrihuted capacitance there between as a
function of ambient external pressure, substantially
independent of ambient temperature. The ambient
temperature changes the amount of heat energ~ to vary
the resistivity of the thick film resistor with temperature,
substantially independent of ambient pressure.
In a preferred embodiment, the substrate is
formed of alumina while the printed thick film resistor
is formed in a meander or spiral pattern.
Accordingly, it is an object of the present
invention to provide a novel sensor for simultaneously
sensing pressure and temperature at a single location in
substantially non-interacting manner.
This and other objects of the present invention
will become apparent upon consideration of the following
detailed description, when taken in conjunction with the
drawings.
srief Description of the Drawings
_
Figure 1 is a prospective view of a first
preferred embodiment of the novel pressure and temperature
sensor of the present invention;
Figure 2 is a sectional view of the sensor of
Figure 1, taken along line 2-2;
Figure 3 is a schematic diagram of equivalent
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circuit of the novel pressurance temperature sensor, and
useful in understanding theprinciples of opera-tion thereof;
and
Figure 4 is a plan view of another preferred
embodiment of the novel pressure and temperature sensor,
and of circuitry with which the sensor may be utilized.
Detailed Description of the Invention
Referring initially to Figures 1, 2 and 3, in
one preferred embodiment of our novel pressure and tempera-
ture sensor 10, an insulative substrate 11, of aluminaand the like insulative materials, has a resistance
member 12 fabricated upon one surface lla thereof.
Resistor 12 is ad~antageously a pattern of thick-film
resistance material placed upon surface lla by printing
and the like processes. As best seen in Figure 1 r one
presently preferred embodiment of resistance member 12
is a meander-line pattern covering a desired area of
length L and width W. The total length and line width,
as well as the line thickness, of the resistance film
of member 12 is predeterminately selected, along with
the resistivity of the resistance material, to provide
a desired resistance between the opposed ends 12a and
12b of the resistance element. Ends 12a and 12b are
each respectively connected to one of a pair of electrical
contacts A and B formed upon substrate surface lla. A
distributed resistance RD is thus formed between contact
terminals A and B and the resistance thereof is a function
of the temperature at which the resistance material of
resistor element 12 i5 maintained; the chan~e o~
resistance, between terminals A and B, with temperature
is predeterminately chosen by selection of the resistance
material.
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~ thin conductive electrode plate 14, which may
be of planar configuration, is insulatively supported
abo~e subs-trate surface lla to provide a distributed
capacitance CD between electrode 14 and resistance
element 12 (and each of the contact terminals A and s
associated therewith). Electrode 14 is connected by a
lead 15 to an associated contact terminal C (also
. positioned upon substrate surface lla). Electrode 14
has a length L', greater than the Iength ~ of the
~ 10 resistance pattern, and a width W', greater than the
width W of the resistance pattern, to facilitate
positioning of a support member 16 between the periphery
of the electrode surface 14a, closest to the substrate,
and the substrate surface lla. Support 16 is formed of
an insulative material and is fabricated in such manner
as to form a pressure-tight seal, along line 18, with
`. substrate surface lla. The material of support 16 also
`~ butts with, and forms a pressure-tight seal over, the
. ends 12a and 12b of the resistance member pattern. .-.
After fabrication of supporting rim 16, conductive
electrode 14 is positioned upon the rim surface 16a from
the substrate and the periphery of electrode surface
. .
14b is joined thereto in pressure-tight manner. The
volume defined by substrate surface lla, the interior
walls of support rim 16 and electrode surface 14a,
contains a quality of a dielectric material, which may
be vacuum, air and the like dielectri.c materials, introduced
during fabrication and serving as the capacitor dielectric.
Electrode 14 acts as a diaphragm deforming responsive
to ambient pressure P, at electrode surface 14b, urginy
the electrode toward, and away from, resistance member
12 with greater, or lesser, pressure and increasing,
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or decreasing, the capacitance bet~een terminal C and
each of resistance element terminals A and B. The
distance D between the interior electrode surface 14a
and substrate surface lla is predeterminately established,
by selecting the height of rim portion 16, to provide a
preselected capacitance value at a reference pressure.
Thus, ambien~ pressure external to the sensor is sensed
by variation of distributed capacitance CD, while ~mbient
temperature affects the amount of thermal energy received
by resistance member 12 within the pressure-tight compart-
ment. Deformation of electrode 14, by proper choice of the
conductive material and dimensions and shape thereof, is
essentially unaffected by the temperature external to
sensor 10.
Referring now to Figure 4, another preferred
embodiment 10' of our novel pressure and temperature
sensor also includes an insulative substrate 11 upon
a sur~ace lla of which a resistor member 12' is farbicated.
In this embodiment, resistor member 12' is fabricated as
a dual spiral of resistance material with the opposite
ends 12a' and 12b' of the resistance element connected
to contact terminals A' and B', which may be advantageously
positioned adjacent one edge of the substrate. An
annular support member 16' is fabricated upon substrate
surface lla, with an interior radius R greater than the
maximum radius R of the resistant element spiral. Annular
support rim 16' is joined to substrate top surface lla
to form a pressure tight seal therebetween. A pressure
tight seal is also formed where rim 16' passes over
end portions of resistance member 12'. A circular
conductive electrode member 14' is placed on top of
annular support rim 16' and has a maximum radius R",
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greater than the inner radius R' of support rim lG'. The
periphery of the underside of the electrode is sealed
to the top of the support rim in pressure-tight manner,
whereby a somewhat cylindrical chamber, bounded by substrate
surface of electrode 14' closest to the substrate, encloses
the spiraled resistance member 12" and a dielectric medium
at some reference pressure. Substantially circular
electrode 14' is connected to a -third contact terminal
Cl by lead 15', which may be fabricated as a conductive
film upon the ex-terior surface of support rim 16' and
substrate top surface lla.
In operation, a source 30 of D.C. potential of
magnitude Vl is coupled in series with a resistor Rt
between temperature~sensing terminals A' and B'. The
distributed resistance RD, between terminals A' and B',
forms a voltage divider with resistance Rt. A voltage
Vt appearing between contact terminals A' and B' is a
function of the magnitude of D.C. voltage Vl, the
resistance of resistor Rt and the temperature-sensitive
distributed resistance RD f the sensor. The increase of
distributed resistance RD with temperature will cause
an increase in the temperature-sensing output voltage Vt.
A source 32 of A.C. voltage of maynitude V2 is connected
in series with a fixed resistance Rp between the capacitive
electrode contact terminal C' and one of the distributed
resistance contact terminals A' and s'. Illustratively~
contact terminal B' acts as the common terminal between
the temperature sensing circuitry of source 30 and resis-
tance Rt, and the pressure-sensing circuitry of source
32 and resistance R . A voltage V appears betweeen
common terminal B' and capacitive electrode contact
terminal C' with the same frequency as that of source 32,
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and with an amplitude established by the source magnitude
V2, the resistance of resistor Rp and the pressure-sensitive
magnitude of distributed capacitance CD. An increase in
ambient pressure will move eletrode 14' closer to the
resistance element, whereby ~he capacitance between
terminals C' and B' will increase, thereby decreasing
the magnitude of the pressure-sensing voltage Vp.
Advantageously, the potential sources 30 and 32 and the
series resistors Rt and Rp are located in a temperature-
stable and pressure-stable environment, whereby the
changing magnitude of the pressure and temperature, to
be simulatan~ously measured at the location of sensor 10',
is not present at the location of the sources and series
resistors and does not a~fect the magnitudes thereof.
The magnitudes of output voltages Vt and V are then
affected only by the respective temperature and pressure
to be simultaneously measured. The output voltages Vt
and Vp are analog voltages, which may, in manner known
to the art, be converted to digital singals, using analog-
to-digital converters, voltage-to-frequency converters
and the like~ The digital signals may be processed by
microcomputers and the like, or the analog signals them-
selves may be processed by suitable analog processing
circuitry (not shown) for ad~usting the apparatus, in which
the pressure and temperature sensor is located, in accordance
with the simultaneous pressure and temperature readings
achieved by the sensor in substantially non-interacting
manner.
While the present invention has been described
with respect to several presently preferred embodiments
thereof, many modifications and variations will occur to
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those skilled in the art. It is our intent, therefore,
to be limited only by the scope of the appending claims
and no~ by the specific details recited herein.
