Note: Descriptions are shown in the official language in which they were submitted.
1 Background of the Invention
Digital gauges have been used in the prior art, for
example, a weighing scale with a digital readout and also fluid
pressure measurement devices with a digital readout. Several
systems have used a load cell to develop a voltage proportional
to the weigh~ of an object but many of these devices have been
large and cumbersome and quite expensive. Other systems have
used pressure transducers or a variable electrode capacitor but
all have been relatively large and cumbersome and require
excessive electrical energy.
Accordingly the problem to be solved is how to achieve
a small compact portable digital readout force gauge which is
accurate and yet requires a minimum of electrical energy lnput.
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Summary of the Invention
This problem may be solved by a digital readout gauge,
comprising, in combination, a housing, a chamber in said housing,
wall means in said chamber movable with changes of force on said
wall means, means to apply a changeable force on said wall means,
an electrical circuit in said housing, a battery in said housing
and connected to supply power to said electrical circuit, said
electrical circuit including a piezoelectric crystal mounted to
be stressed in accordance with movement of said movable wall means,
output conductors connected to said crystal to generate an analog
voltage thereacross upon stressing of said crystal, an analog to
digital converter connected to receive a voltage in accordance
with the voltage on said output conductors to convert the analog
signal of said crystal voltage output into a digital signal, and
a digital readout gauge display connected to the output of said
converter to display a digital value in accordance with the
crystal voltage output.
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1 An object o~ the invention is to provide a digital
readout gauge which may be hand held and a portable self-
contained unit.
Another object of the invention is to provide a
digital readout tire pressure gauge.
Another object of the invention is to provide a
digital readout force gauge utilizing a piezoelectric crystal~
Other objects and a ~uller understanding of the
invention may be had by referring to the following description
and claims, taken in conjunction with the accompanying drawing.
':
Brief Description of the Drawing
FIG. 1 is a longitudinal sectional view of the digital
readout gauge embodying the invention;
FIG. 2 is a partial top view partly in sectio~ of the
gauge of FIG. l;
FIG. 3 is a schematic diagram of the electrical
circuit used in the digital gauge; and
FIG. 4 is a longitudinal sectional partial view of
20 a modification. - ;
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Description of the Pre~erred Embodiments
FIGS~ 1 and 2 show the mechanical construction o~ a
digital readout gauge 11, which, in this embodiment is a portable
self-contained unit. The gauge 11 includes a housing 12 and this
housing includes a sleeve-like handle 14 telescoped over part o~
the housing. The housing also includes a nosepiece 13 secured
to the housing in any suitable manner such as the threads 15.
The nosepiece 13 has a valve mouth 16 leading to a pressure
chamber 17. The valve mouth 16 is adapted to be slidably
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847
1 applied to and over an ordinary tire valve 18 having the
usual depressable valve core 21 to open the valve mechanism
itself.
A valve deflator 24 has a central axial projection 25
to engage and depress the end of the valve core 21. The valve
deflator 24 carries a seal washer 29 which slidably seals against
the internal bore of the valve mouth 16 and also resiliently
seals against the end of the tire valve 18 to seal the air
pressure from the tire within the pressure chamber 17. This air
under pressure is admitted to the chamber 17 through apertures
30 in the valve deflator 24 and through a filter 31.
A conduit 33 leads from the valve deflator 24 to the
chamber 17.
A movable wall 35 is provided in the pressure chamber
17 and in this embodiment this movable wall is a metal diaphragm
36 clamped between an annular ring 37 on the nosepiece 13 and
a shoulder 38 on the housing 12.
An electrical circuit 43 is provided within the housing
12 and this electrical circuit may include integrated circuits
and other miniature components mounted on a printed circuit board
44 slidably received in slots in the housing 12. One or more
batteries 45 may be provided within the housing 12 with access to
the batteries through a removable plug 46 in the handle 14. The
batteries provide the electrical power to operate the electrical
circuit 44.
The housing 12 includes an inner sleeve 47 within the
telescoping tubular handle 14. A flanged bushing 48 is p.rovided
in the end of the inner sleeve 47, and a spring 49 ac~s between
the bushing 48 and the pluy 46, urging the handle 14 to the rear.
This is resisted by an inwardly turned shoulder 50 on handle 14
enyageable with an abutment 51 on the housing 12. A switch
extension 52 is provided on the plug 46 to engage the battery 50
upon the yauge being pressed against the valve 18.
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~,
1 A piezoelectric crystal 53 is mounted to ~e stressed
in accordance with movement of the movable wall or diaphragm 36.
In this embodiment the crystal 53 is mounted in a suitable manner
to the diaphragm, as by soft solder. Conductors are mounted to
receive voltage from the crystal and this may be one conductor 54
connected to one face and another conductor connected to the
opposite face, which conveniently may be a connection to the
metal diaphragm 36 through the metal housing 12. A digital
readout display 55 is provided in the housing 12, as better
shown in FIG. 2. A reset switch 56 is provided in the housing 12
to reset the digital display to zero with the switch button 57
accessible from the exterior o~ the housing 12.
The closing of the extension 52 onto the rear-most
battery 45 is a power switch which enables the readout display
55. In the preferred embodiment, the closing o~ this switch 52
energizes the entire electrical circuit 43.
FIG. 3 illustrates a preferred embodiment of the
electrical circuit 43. This electrical circuit includes generally
~ the crystal 53 supplying a peak detec~or 60 in turn supplying an
output to an analog to digital converter 61 and this supplies a
digital signal to a segment decoder 62 which supplies the
segment driving signals to the digital~readout display 55.
; The battery 45 supplies electrical energy to power the
; electrical circuit 43 through the power switch 52 to a voltage
terminal 63. This is a positive voltage terminal supplying the
peak aetector 60, digital display 55 and segment decoder 62.
This positive voltage terminal 63 also supplies a DC to DC
converter 64 which has a negative output voltage terminal 65
supplying negative operating voltages to the peak detector 60 and
primarily to the analog to digital converter 61.
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1 The peak detector 60 includes an operational amplifier
68 having positive and negative power supply terminals connected
to the positive and negative voltage terminals 63 and 65,
respectively. The non-inverting input terminal 69 is connected
through a resistor 70 to the output o~ the crystal 53. The
output terminal 71 o~the operational amplifier 68 is connected
through a forward conducting diode 72 and resistor 73 to a
capacitor 74 to ground. Due to the diode 72 only positive outputs
are supplied to the capacitor 74 which charges to the peak value
of theoutput of the crystal 53, as multiplied by the gain of
the operational amplifier 68. The output after the diode 72 is
returned as a feedback connection to the inverting terminal 75
to establish the action of the operational amplifier 68 as a
detector. The reset switch 56 is connected across the capacitor
74 to discharge this capacitor and reset the digital display 55
to zero.
The DC to DC converter 64 is utilized to provide a
negative operating voltage at the terminal 65 and thus avoid the
requirement for an additional batter~ to supply a negative
operating voltage to the analog to digital converter 61~ This DC
to DC converter 64 is supplied with positive operating voltage
from the terminal 63 and includes a transistor 7~, a field effect
transistor 80, Zener diode 81, transformer 82, capacitor 83 and
diode 84. The circuit acts as a high efficiency blocking
oscillator-type converter. The self-oscillation charges the
capacitor 83 and when the voltage across this capacitor reaches
a value equal to the sum of the Zener voltage plus the pinch-off
voltage of the FET transis~or 80, then the oscillations cease.
The circuit resumes oscillation when the output voltage falls
below this value and it will be noted that the voltage across the
capacitor 83 is the voltage at the negative output terminal 65.
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1 The positive voltage supply terminal 63 supplies
operating voltage to a current regulator 88 with the output
connected through a potentiometer 89 and a resistor 90 to
ground. The tap 91 of the potentiometer 89 is connected to
supply current regulated power to the analog to digital
converter 61 at a terminal 92. Terminal 93 o~ this converter
61 is connected to the negative supply terminal 65 for operating
voltages. This converter 61 has an input at terminal 94 from
the peak detector 60. It has a digital output on the lines 95
to the segment decoder 62. The output on these lines 95 is a
digital output in a binary code of first, second and third bits
relative to a common logic zero conductor. This binary code
digital information is supplied to the segment decoder 62 which
supplies the necessary signals through seven coupling resistors
96 to the seven-segment display numerals 97-99 of the digital
readout display 55. The segment decoder 62 is a binary to
decimal decoder changing the binary digital information into
decimal type information for easy reading on the digital display
55. This also provides a floating decimal point indication with
a reading of 0.10 to 99.9.
The display numerals 97-99 are each mounted through a
driver transistor 101-103, respectively, to ~round. The bases of
these transistors 101-103 axe connec~ed to the A/D converter 61
to turn on these transis~ors at the appropriate time to drive
these numerals 97-99.
In one practical circuit constructed in accordance with
the teachings of the invention, the peak detector 60 utilized an
RCA CA3130 model operational amplifier, the current regulator 88
was a Siliconix, Inc. C~033 regulator, and the A/D converter 61
was a Siliconix, Inc. LD130 and the segment decoder 62 was a
Texas Instruments, Inc. 74C48.
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1 Operation
The digital readout gauge 11 is usable as an extremely
portable self-contained force gauge. Force applied to the
movable wall 35 results in stressing the piezoelectric crystal
53 to develop a voltage on the output conductors 54. In the
embodiment shown the gauge 11 is a pressure gauge and utilizes
the pressure chamber 17. This chamber normally has only
atmospheric pressure therein which is taken as the zero condition.
When the gauge 11 is applied to a tire type valve 18, for
example, then the air pressure within the structure, such as a
tire, is applied to the pressure chamber 17. This occurs
because the valve mouth 16 is slid over the valve 18, the
deflator projection 25 engages and depresses the valve core 21.
At the same time the seal washer 29 engages the end of the valve
stem to seal the combined valve and pressure chamber 17 against
external leakage. The resilience of the seal washer 29 accepts -~
slight differences in geometry of various valves 18. The
telescoping of the housing 12 inside the handle 14 ac~uates
the power switch 52. The closing of this switch permits
illumination of the display 55, and in the preferred embodiment
energizes the electrical circuit 43 contained with in the handle
14 and shown schematically in FIG. 3.
Let is be assumed thatthe pressure within the vessel
- to whi~h the valve 18 i5 connected is 28.2 psi. This fluid
pressure is passed through the aperture 30 into the pressure
chamber 17 to move the diaphragm 36. This stresses the
piezoelectric crystal 53 and develops an analog vol~age thereon
- proportional to this pressure. The closing of the power switch
52 by application of the gauge to the valve has energized the
electrical circuit 43 shown in FI~. 3. Accordingly, the analog
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1 voltage developed by the crystal 53 will be passed to and
amplified by the operational amplifier 68 connected as a peak
detector 60. In one circuit constructed with the invention,
the output of the crystal 53 was one millivolt per pound per
square inch and accordingly, in the example above, the output
of the crystal would be 28.2 millivolts. This voltage is
amplified by the amplifier 6~ and passed to charge the capacitor
74. Even if the peak value of the pressure within the pressure
chamber 17 decreases, the peak reading remains for a long period
of time. This might be as much as ten minuies if desired. The
reading may be sto,red as a charge on the capacitor 7~ and the
impedance value of this capacitor is decreased to shorten the
time of holding this peak value. If another force or pressure
is to be measured shortly after the first such measurement, then
the reset switch 56 should be closed momentarily to discharge
the capacitor 74. Otherwise, the charge on this capacitor would
only slowly decay and a false reading could be given if the
second force or pressure is less than the first. This is true
even though the power switch 52 is deactivated and again reacti-
vated for the second measurement. This deactivation of the power
switch 52 will deenergize the entire circuit 43 but does not
discharge the capacitor 74.
The peak reading, iIl the above example 28.2 psi, is
passed to the A/D converter 61. This is an analog voltage which
is converted into a digital voltage in the form of binary bits
on the conductors or lines 95. The segment decoder 62 is a
binary to decimal converter which converts this binary coded
information into a decimal information to drive the display
numerals 97-99 of the digital readout display 55. In the ahove
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1 example the numerals 28.2 will be displayed on the readout
display 55 during energization of this circuit 43. If the
gauge 11 is continuously applied to valve 18 and the reset
switch 56 closed, then this will short and discharge the
capacitor 74 so that the display 55 reads 00Ø
FIG. 4 illustrates a modified form of digital readout
gauge 111 contained in the portable housing 112 having a nose
piece 113. Many parts may be the same as in the embodiment of
FIGS. 1 and 2 such as the valve mouth 16, the valve deflator 24,
seal washer 29 and filter 31. The conduit 33 leads to a pressure
chamber 117 which has a movable wall 135 and in this particular
embodiment the movable wall 135 is the piezoelectric crystal 53
itself. This crystal is secured between a shoulder 137 on the
nosepiece 113 and a resilient washer 138 in the housing 12. The
orce within this pressure chamber 117 acts directly on the
crystal 53 to move and stress this crystal so as to develop an
output voltage on the output conductors 54 thereof. The
remainder of the components may be the same as in the gauge 11 of
F~GS. 1 and 2.
The gauges 11 and 111 illustrate a digital readout
forc~ gauge which displays a d1gital signal on the display 55
which is proportional to an applied force, with the force being
applied to stress the piezoelectric crystal 53. In each of these
gauges the crystal is mounted to be stressed in accordance with
the movement of a movable wall and this wall is in a pressure
chamber which can at least momentarily contain the fluid pressure.
This contained fluid pressure stresses the movable wall and
stresses the crystal. The entire gauge may be mounted in a very
small and extremely portable housing 12 or 112 to easily be
applied to a tire valve 18 for example, to determine the amount
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L8~7
1 of fluid pressure within this container to which th~ valve is
at~ached. The sleeve 47 telescopes inside the tubular handle
14, as resisted by the spring 49. The power switch 52 is
actuated by a change from the first position to a second
pOSitiOIl of these two sleeves to energize the entire electrical
circuit 43. This enables the digital readout display 55. The
peak detector 60 maintains the peak reading observed within the
pressure chamber 17, regardless of whether this pressure might
decrease after its initial maximum value. The reset switch 56
is connected to discharge th~ capacitor 7~ so that the gauge
- 11 or 111 is xeady for measurement of another and smaller value
of force.
While we have illustra~ed and described a preferred
embodiment of our invention, it will be understood that this
is by way of example only and not to be construed as limiting.
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N~MBER S~EET
11 digital readout gauge 68 op. amp.
12 housing 69 non-inverting input
13 nosepiece 70 resistor
14 handle portion 71 output of 68
15 threads . 72 diode
16 valve mouth 73 resistor
17 pressure chamber 74 capacitor
18 tire valve 75 inverting terminal
21 valve core
79 transistor
24 valve deflator 80 FET transis-tor
25 central projection ~1 Zener diode
26 82 transformer
27 ~3 capacitor
28 84 diode
29 seal washer
30 apertures
31 filter
88 current regulator
33 conduit 89 Pot
34 90 resistor
35 movable wall 91 blade of 89
36 diaphragm 92 terminal
37 annular ring 93 terminal
38 shoulder 94 terminal
95 lines
96 coupling resistors
97-99 numerals
101-103 driver transistor
43 electrical circuit
44 printed circuit board
45 batteries
46 removable plug
47 inner sleeve
48 ~langed b~ushing
49 spring
50 shoulder in 14 111 digital readout gauge
51 abutment in 12 112 housing
52 switch extension 113 nosepiece
53 piezoelectric crystal
54 conductors to 53
digital readout display
56 reset switch 117 pressure chamber
57 switch button 135 movable wall
137 shoulder
.138 resilient washer
60 peak detector
61 A/D converter
62 segment decoder
63 ~voltage terminal
64 DC to DC converter
65 -voltage terminal
12
