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BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates to ultrasonic devices. More specifically, the
present invention is directed to an ultrasonic distance measuring
apparatus.
2. Description Of The Prior Art
Ultrasonic sensor devices have been developed for measuring the movement of
a reflector element as is shown in U.S. Pat. No. 3,140,612. This type of
prior art sensor while providing a means for measuring the relative
displacement of a movable reflector element fails to provide a mwethod for
obtaining the relative separation of the reflector element from the
ultrasonic transducer elements whereby a direct measurement of the
distance may be obtained. Accordingly, it is desirable to provide an
ultrasonic distance measuring sensor for effecting a measurement of the
relative separation of a movable reflector element in a direct manner
while eliminating the effect of spurious ultrasonic reflections.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved ultrasonic
distance measuring sensor.
In accomplishing this and other objects, there has been provided, in
accordance with the present invention, distance measuring apparatus having
a movable reflector, a first and a second acoustical transducer located on
respective sides of the reflector element, energizing means for
alternately energizing the acoustical transducers and signal analyzing
means for measuring the relative separation of the reflector element from
the transducers by analyzing the frequency of operation of each transducer
.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the present invention may be had when the
following detailed description is read in connection with the accompanying
drawings in which:
FIG. 1 is a cross-sectional illustration of a differential pressure sensor
embodying an example of the present invention,
FIG. 2 is a cross-sectional illustration of a differential pressure
transmitter body for use with an external sensor,
FIG. 3 is a cross-sectional view of an external sensor for use with the
body shown in FIG. 2 and also embodying an example of the present
invention,
FIG. 4 is a cross-sectional illustration of another differential pressure
sensor structure, also embodying an example of the present invention and
FIG. 5 is a schematic illustration of a block diagram of a signal analysis
circuit suitable for use with the pressure transmitter shown in FIGS. 1 to
4.
FIG. 6 is a schematic illustration of detector circuit 126 shown in FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Detailed Description
Referring to FIG. 1 in more detail, there is shown a cross-sectional
illustration of a differential pressure transmitter embodying an example
of the present invention. For purposes of simplifying the illustration in
FIG. 1, the pressure transmitter structure is only partially shown with
the input, or barrier, diaphragm cover and the connections to input fluid
pressures being omitted since these are conventional. A first plate 2 has
a barrier diaphragm 4 attached at its peripheral edge thereto with a space
6 formed by a concave face of the plate 2 beneath the diaphragm 4
therebetween filled with a substantially incompressible fill fluid (not
shown). A fluid passage 8 through the plate 2 connects the space 6 between
the barrier diaphragm 4 and the plate 2 and an interface spacer 10 located
on the other side of the plate 2 from the barrier diaphragm 4. The
interface spacer 10 may be any suitable material for transmitting an
acoustical signal while providing an acoustical impedance match between an
acoustical transducer and an attaching wall, e.g. glass. A hole 12 through
the interface spacer 10 continues the fluid passage 8 to a second fluid
passage 14 in a first support block 16 of a dimensionally stable material
having a minimum coefficient of temperature expansion, such materials
being well-known in the art. A first acoustical, or ultrasonic, transducer
18 is located within a recess 20 in the plate 2 and is attached to the
interface spacer 10 on the other side thereof from the first support block
16. A connecting wire 22 is arranged to supply electrical power to
energize the ultrasonic transducer 18. The electrical wire connection 22
is arranged to leave the plate 2 via the recess 20 and to be connected to
suitable associated electrical signal supply means (not shown).
A sensor diaphragm 24 is arranged across the opposite face of the support
block 16 from that in contact with the interface spacer 10 which face is
provided with a concave shape to enable the fill fluid to be located
therein between the concave face and the sensor diaphragm 24. The fluid
conduit 14 through the support block 16 conducts the fill fluid from the
space 6 beneath the barrier diaphragm 4 to the space between the sensor
diaphragm 24 and the support block 16. Another fill fluid conduit 26 is
provided through the support block 16 between the first plate 10 at a
location aligned with the first transducer 18 and the concave face of the
support block 16.
The other side of the pressure transmitter is a substantial duplicate of
the structure described above using a second ultrasonic, or acoustical,
transducer element 30, a second barrier diaphragm 32, a second plate 34, a
second interface spacer 36 and a second support block 38. Thus, the second
barrier diaphragm 32 is attached at its peripheral edge to the second
plate 34 to form an internal volume 39 between a concave face of the plate
34 and the barrier diaphragm 32. A fluid passage 40 is arranged to connect
the space 39 to the other side of the plate 34. A hole 42 in the interface
spacer 36 is arranged to form a continuation of the fluid passage 40 while
a fluid passage 44 in the second support body 38 forms a further
continuation of the fluid passage between the hole 42 and the other side
of the second support body 38.
The second ultrasonic transducer is located within a recess 46 in the
second plate 34 and is connected by a connecting wire 48 to a source of an
energizing electrical signal (not shown). The second transducer element 30
is aligned with a fluid conduit 50 passing through the second support
block 38 and is attached to the interface spacer 36 on the other side of
the spacer 36 from the support block 38. The sensor diaphragm 24
concurrently covers a concave face on the support block 38 on the other
side of the support block 38 from the interface spacer 36. A pair of
convential fluid fill ports 52 and 54 are arranged to provide a means for
supplying a first and a second fill fluid to the respective fluid channels
in the pressure transmitter. The first and second support blocks 16, 38
are attached to the sensor diaphragm 24 at the outer peripheral edge of
the diaphragm 24 by any suitable means to produce a fluid tight composite
structure, e.g., a continuous weld bead. The other elements of the
pressure transmitter structure illustrated in FIG. 1 are held together
along with the elements not illustrated in FIG. 1 by conventional means,
such means being well-known in the art.
In FIG. 2, there is shown a cross-sectional illustration of a modification
of the differential pressure transmitter structure shown in FIG. 1 and
also embodying an example of the present invention. Similar reference
numbers have been used to indicate elements of this structure common to
the pressure transmitter shown in FIG. 1. Thus, the first and second
transducers 18, 30 are located in recesses 20, 46 and are connected by
respective wires 22, 48 to associated energizing signal apparatus (not
shown). The recess 20 is located in a first plate 60 which is combined
with an annularly convoluted barrier diaphragm 62 spaced from a matching
convoluted face 64 of the plate 60 to provide an internal volume for a
first fill fluid. A first acoustic interface impedance matching spacer 66
is located within a recess provided in a face of a first support body 68
adjacent to the first acoustic transducer 18. A second acoustic interface
spacer 70 is located in a recess provided in a face of a second support
body 72 adjacent to the second transducer element 30. A fluid conduit 74
is located between the interface spacer 66 and an opposite concave face of
the first support block 68 while being aligned with the transducer 18.
Similarly, a fluid conduit 76 is located in the second support block 72
between the transition spacer 70 and an opposite concave face of the
second support block 72 while being aligned with the second transducer 30.
Additionally, a second convoluted barrier diaphragm 80 is spaced from a
mating convoluted surface 82 of the second plate to provide an internal
volume for a second fill fluid therebetween.
In FIG. 3, there is shown a cross-sectional illustration of an external
differential pressure sensor for use with a pressure transmitter body as
shown in FIG. 4. Similar reference numbers have been used in FIGS. 3 and 4
to denote elements common to the structures shown in FIGS. 1 and 2. Thus,
the first acoustic transducer element 18 is mounted on a first interface
spacer 66 which, in turn, is located in a recess in a face of a first
support body 86. The second transducer 30 is mounted on a second interface
spacer 70 which, in turn, is located in a recess in a second support body
88. A first plate 90 is positioned on top of the first support body 86 and
has a hole 92 extending therethrough to allow the connecting wire 22 to be
attached between the first transducer 18 and a source of transducer
energizing signals (not shown). Similarly, a second plate 94 has a hole 96
therethrough to allow a connecting wire 48 to be attached between the
second transducer 30 and a source of transducer energizing signals (not
shown). A first fluid conduit 98 is provided in the first support block 86
to connect the concave face of the block 86 adjacent to the diaphragm 24
to one end of an externally projecting fluid pipe 100. The fluid pipe 100
is fastened with a fluid tight seal to the block 86 and projects therefrom
to provide a means for effecting a fluid connection to the fluid pipe 100.
Similarly, a second fluid conduit 102 is provided in the second support
block 88 to connect the concave face of the second block 88 adjacent to
the diaphragm 24 to one end of a second fluid pipe 104. The second fluid
pipe 104 is provided with a fluid tight seal to the block 88 and projects
therefrom to provide a connection for a fluid connector thereto.
In FIG. 4 there is shown a fluid transmitter body for use with the sensor
assembly shown in FIG. 3. The fluid transmitter body includes a body block
106 which has the convoluted barrier diaphragm 62 and 80 located adjacent
to mating convoluted surfaces 64 and 82 on opposite faces thereof. A first
fluid conduit 106 is provided within the body block 108 to connect the
space between the first barrier diaphragm 62 and the mating back-up
surface 64 with one end of a fluid pipe 110 which is sealed to the body
block 106 and projects therefrom. A second fluid conduit 112 is provided
within the body block 106 to connect the space between the second
diaphragm 80 and the back-up surface 82 to one end of a second fluid pipe
114 which is also sealed to the body block 106 and projects therefrom. The
fluid pipes 110 and 114 of the body block 106 are arranged to be connected
by any suitable means (not shown) to the projecting pipes 100 and 104
shown in the sensor assembly of FIG. 3.
In FIG. 5 there is shown a simplified block diagram of a circuit for
energizing the acoustic transducers used in the pressure transmitter shown
in FIGS. 1 through 4 for detecting the signals received from the
transducers. An exemplary pressure transmitter using a remote sensor
arrangement with input pressures P.sub.1 and P.sub.2 is shown in a
simplified representation in FIG. 5 of the remote sensor structure
previously described in respect to FIGS. 3 and 4. Similar reference
numbers have been used in FIG. 5 to indicate the elements previously
described with reference to FIGS. 3 and 4. Additionally, the remote sensor
assembly is connected to the transmitter block by fluid conduits 120 and
122 which connect the respective projecting fluid pipes previously
described with reference to FIGS. 3 and 4. A first transducer driver 124
is connected to the first transducer 18 to provide an energizing signal
therefor. A first detector circuit 126 is also connected to the first
transducer 18 to receive an output signal therefrom. The output of the
detector circuit is applied to a first voltage controlled oscillator 130
to adjust its frequency output signal. The output of the voltage
controlled oscillator 130 is applied to the detector circuit and to the
driver circuit. Additionally, the output of the voltage controlled
oscillator 130 is applied to a computing or signal analyzing circuit 132
as an indication of the signal derived from the reception of an acoustic
signal by the first transducer 18. The signal analyzing circuit 132 has an
output 133 on which is ultimately provided an output representative of the
differential pressure between input pressures P.sub.1 and P.sub.2.
Similarly, a second driver circuit 134 is connected to the second
transducer 30 to provide an energizing signal thereto. A second detector
circuit 136 is connected to the second transducer 30 to receive an output
signal therefrom. The output signal from the detector 136 is applied to a
second voltage controlled oscillator 138 to adjust its frequency. The
output signal from the voltage controlled oscillator 138 is applied to the
second driver circuit 134 and to the second detector circuit 136 and to
the analyzing circuit 132 to provide an input signal thereto indicative of
the output signal from the second transducer 30. A timing control circuit
139 is used to supply timing signals to control the sequence of operation
of the detectors 126, 136, the drivers 124, 134 and the computation
circuit 132. While two pairs of driver and detector circuits are shown in
FIG. 5, it is obvious that a single pair of driver and detector circuits
could be used with suitable switching circuits controlled by the timing
control 139 for multiplexing the single pair of circuits between the
respective transducers and voltage controlled oscillators.
A schematic illustration of a circuit suitable for use as a detector
circuit, i.e., detector 126, is shown in FIG. 6. An output signal from the
respective transducer, i.e., transducer 18, is applied through a first
timing signal controlled signal gate 140 to the input of a signal
amplifier 142. An output from the amplifier 142 is applied to the input of
a zero crossing detector 144 and an amplitude detector 146, such devices
being well-known in the art. The outputs from the zero crossing detector
144 and the amplitude detector 146 are applied to the corresponding inputs
of a two-input AND gate 148. The output of the AND gate 148 is applied to
the input of a single-shot astable multivibrator 150 to produce an output
pulse therefrom which is applied to the input of a phase comparator 152.
The phase comparator 152 is used to compare the phase of the pulse signal
from the single-shot 150 with the output of a corresponding voltage
controlled oscillator, i.e., V.C.O. 130, applied to the phase comparator
152 through a second timimg signal controlled signal switch 156. An output
from the phase comparator 152 is applied to a sample-and-hold circuit 154
having an output applied to control the frequency of the V.C.O. 130. The
output of the V.C.O. 130 is also applied to the input of the driver 124 as
previously described with respect to FIG. 5.
The operation of the present invention to detect the distance of the
reflector diaphragm within the pressure transmitter from an acoustic
transducer may be simplified in the general case of a distance measuring
apparatus. At the start of operation, i.e., time equals zero, the first
transducer would emit an acoustic pulse, e.g., 100 KH, aimed at the
reflector which is assumed to be at a distance X from that transducer. At
a time
##EQU1##
where C the speed of sound in the medium separating the transducer from
the reflector, the reflected signal would arrive back at the first
transducer. Immediately thereafter, a second acoustic pulse is sent from
the second transducer to the reflector. The second pulse is reflected off
the other side of the reflector and arrives back at the second transducer
at a time
##EQU2##
where X.sub.O is the distance between the two transducers. If the two time
periods are designated T1 and T2 then
##EQU3##
If during time T1, an RC filter is switched by a control means responding
to the times T.sub.1 and T.sub.2 to a reference voltage and during T2 is
grounded, the filter output will be
##EQU4##
which provides the position determining function. While this operation
would provide a non-interfering alternate mode of operation to avoid
interference between signals transmitted through the reflector diaphragm,
it is not directly applicable to the determination of a diaphragm position
in a relatively small pressure transmitter wherein the diaphragm position
would require the measurement of micro-inches over a total diaphragm
movement of thousandths of an inch, e.g., 0.005 inches, as represented by
differences in arrival times of picoseconds, i.e., 10.sup.-12.
In order to provide this capability, the circuit shown in FIG. 6 is used to
detect phase differences in the reflected signals on each side of the
reflector when compared with a corresponding output of a voltage
controlled oscillator driving the transducer on the same side of the
reflector element, e.g., 6 KH difference in a 100 KH signal. Thus, the
detector circuit on each side of the reflector element functions in the
manner of a phase-lock-loop type of circuit to maintain the frequency of a
corresponding voltage controlled oscillator at a frequency having a zero
phase relationship with the reflected signal from the same side of the
reflector element. This frequency is determined by the position of the
reflector element and is, accordingly, representative of the applied input
pressure, i.e., pressure P.sub.1 in the aforesaid example. Similarly, the
frequency output of the second voltage controlled oscillator 138 is
representative of the second input pressure P.sub.2. A sample-and-hold
circuit may be used in each detector circuit, i.e., sample-and-hold
circuit 154, to maintain the frequency of the corresponding voltage
controlled oscillator, i.e., oscillator 130, during the alternate
operation of the circuit illustrated in FIG. 5.
The two frequency outputs F.sub.1 and F.sub.2 from the voltage controlled
oscillators 124, 134, respectively, are applied to the computation circuit
132 for analysis to produce an output signal representative of
differential pressure. The computation circuit 132 may be either analog in
nature in which case it could directly with the frequency signals from the
voltage controlled oscillators or digital in operation in which case it
would use analog-to-digital converters, digital processor circuits, i.e.,
a digital computer, and, if necessary for a suitable output on line 133, a
digital to analog converter, such devices being well-known in the art. In
either case, the computation is performed on either a solution of
##EQU5##
with the former being preferred since it affords less sensitivity to
temperature effects and is linear with respect to the diaphragm distance
transmitter structure. The latter computation however yields a
compensation for the inherent non-linearity for the diaphragm deflection
equation. Both of these techniques are preferable over a simple
relationship between a difference in the frequencies, i.e., .DELTA.f, and
the differential pressure which is also inherently non-linear. Of course,
other linearizing techniques, such as using a stored table of linearized
values in a digital memory, may also be employed. The resulting output
from the computing circuit 132 is the relative distance of the reflector
from the transducers which is representative of the difference in the
input pressure P.sub.1 and P.sub.2, i.e., differential pressure.
Accordingly, it may be seen that there has been provided, in accordance
with the present invention, an improved distance measuring apparatus and a
differential pressure transmitter utilizing the same.
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