Note: Descriptions are shown in the official language in which they were submitted.
S~
VIB!~ATING BE,l\M PRESSllRE Sl N~SOR
A(.i~GROUND Ol: '1`11~ INVEN'I'ION
1. Field of the In~ention
The present invention relates to digital output pressure
sensors using a vibrating ~eam as a sensing elcment.
2. I'r;or Art
In the prior art, various sensors whictl use vibrating
beams have becn advanced. Usually some type of dig;tal pulse is
provided to indicate the force or pressure derived force on the
In beam. Some of the sensors utilize piezoelectric sensing, such ias
United States Patent No 's 3,470,~nO and 3,479,536. ~ type of
pivoting beam that is constrained in its path of movement is also
shown in United States Patent No. 3,649,857.
An additional patent relating to vibrating beams is
Patent No. 3,664,237 which is of general interest. Capacitance
sensing of vibrating beams is illustrated ;n lJ.S. Patent No.'s
3,187,579 and 3,762,223. In both of these patents the sensing capaci-
tor plate is on the opposite side of a member from the drive coil.
A piezoelectric beam which flexes transversely becausc
2() of accelerations in the mass at the end oF the heam, or bccausc of
impact of micro meteroids is shown in Unite~ States Patcnt No.
3,304,773. ~n acceleromcter using a vihrilting i)e~m witll ca;),lcit.lllcc
sensing is sJlown ;n ll.S, I'atcllt No. 3,505,8~.fi.
lJnitcd States l'atcnt No. 4,149,~22 issuc(l Al)ril 17, 1'.)7'9
shows a vibratory wire pressure sensor which discloses a thin wire
th~t is held undcr a spring load to create a ~retens iOII, and is lo-~clcd
by ~ressurc so that the natural frcqucncy of the wirc ci~anges. Ii~c
lever which is utilized to load the vibrating wire is mountcd with a
cross flexure connection that pcrmits -rclativcly Frce l);votal movc-
ment. For sensing, a current from an oscillator is ~)in~ tllrougil tl-le
wire and thi s current reacts with a magnctic fickl From .l ~)crTnarlcllt
magnct therc1)y callsirlg thc wire to movc. Iilis prodllccs a b.lck lMI:
and positive Fccdi)ack at the currcnt generating oscillat(>r cir(lJit
sustains the vibration of the wirc. Ihus tllc s(llliOr (liicloscd in
35 I'atcllt No. ~,l49,~22 docs not utilizc call:lcitivc~ tyl~c iull~
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SUMMARY OF THE INVENTION
The present invention relates to a pressure sensor and more
particularly to a pressure sensor which loads and affects the natural
frequency of a vibrating beam. rhe frequency is sensed and provided
to the output in the form of digital pulses that can provide a direct
digital measurement or readout of the pressure being measured.
The beam is loaded through a pivotally mounted lever, as
shown, which aids in isolating unwanted stresses during loading of
the beam.
The excitation for the beam is from a coil driven by an
oscillator, and the sensing is capacitance. Tnere is, thus little
interaction between the excitation and the sensing signals, which
enhances accuracy.
In the particular embodiment shown, the excitation coil and
the pick-off capacitor plate are mounted on the same side of the
vibrating beam, to simplify mounting, and also to simplify
adjustments as to the spacing between the drive coil, the sensing
capacitor, and the vibrating beam. Other advantages include fewer
parts, better control on parasitic resonances, and components of
sensing circuit may be mounted on the pick-off assembly.
With the vibrating beam mounted as disclosed there is
substantially no current in the beam, so that the beam has little
undesirable effect on the drive coil or the pick-off capacitor
perforrnance.
BRIEF ~ESCRIPTION OF THE ~RAWINGS
Figure l is a top plan view of the pressure sensor
including sensing means made according to the present invention;
Figure 2 is an elevational view taken as on line 2--2 in
Figure l with parts broken away;
Figure 3, which is on the same sheet as Figure 2, is a
fragmentary sectional view taken as along line 3--3 in Figure 2;
Figure 4, which is on the same sheet as Figure l, is a view
taken on line 4- 4 in Figure 3;
Figure 5 is a sectional view taken as on line 5--5 in
3~ Figure l;
FIgure 6 is a fragrnentary top plan view of a rnodified form
of the invention;
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Figure 7, which is on the same sheet as Figure 2, is a side
view of the coil and pick-up assembly used with the device of Figure
6 taken as on line 7--7 in Figure 6;
FIgure 8 is a view taken as on line 8--8 in Figure 7; and
Figure 9 is a schematic representation of a simplified
drive and sensing circuitry used with the sensor of the present
invention.
D~SCRIP~ION OF THE PREFERRED EMBODIMENT
- In Figures 1 and 2, a general layout of a sensor made
according to the present invention is shown. Such a sensor assembly
is indicated generally at 10, and includes an outer housing 11 that
provides a base for mounting the various components. The housing
base indicat~d at 12 is a flat plate, and the housing includes
upright walls 13 and 14. The exterior surface of housing 11
preferably has a silicone rubber coating approximately .062 inches in
thickness deposited thereon to dampen exterior vibrations. Walls 13
are provided with apertures and mounting means for mounting a pair of
bellows indicated at 15 and 16, respectively.
This bellows 16 has an end collar 17 that forms a small
ring which fits partially within and is retained in a recess in a
clamp 23A. The clamp 23A slidably fits over and may be slid along a
tang 23 which forms a portion of a pivoting, loading lever assembly
indicated generally at 24. The tang 23 extends between the bellows
15 and 16. The bellows 15 has an end ring 17A which partially fits
with a recess in tang 23 and is thus connected to the tang 23. The
bellows 15 and 16 transfer to the tang 23 loads from pressure which
expand the bellows in an axial direction. The tang 23 has dove tail
edge portions over which the clamp 23A mates and slides. The bellows
are of ordinary design used with sensors and normally are at a rest
or balanced position as shown. A first pressure inlet 20 is
connected to the bellows 15, and a second pressure inlet 21 is open
to the bellows 16. The bellows, of course, when subjected to
pressure will tend to expand axially and extend their inner ends
adjacent the tang 23 and clamp 23A. Thus, as shown, differentials in
pressure will cause a shift in the position of the tang 23.
The clamp 23A can be slid and adjusted transversely to the
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direction of movement of the bellows along tang 23 so that the moment
of bellows 16 about the hinge like pivot shown at 27 can be shifted with
respect to the moment of the bellows 15 about hinge 27. This
movement of the clamp 23A along the tang 23 permits adjustment of the
force from one bellows or the other so that whcn equal pressurc is
applied to bellows 15 and 16, the resultant force (moments) is zero.
The lever assembly 24, as shown in plan vicw, includes
a mounting block 25 that in turn is attached to the base wall 12
of the housing 11. ~he lever assembly 24 is made from a unitary
piece of material. ~ moving lever portion 30 is joined to block 25
through a hinge-like pivot shown at 27. The pivot is formed as a
substantially reduced cross section thickness joining the block 25
and portion 30 along the axis of pivot. Thus the lever assembly
has a mounting portion 25 and a pivoting lever portion 30. The
pivoting lever portion 30 clears the base 12 of the housing so that
it may pivot under pressure differentials. Suitable spacers may be
placed under block 25 to raise the lever portion 30 away from base
12.
'rhe lever portion 30 pivots about the hinge or pivot por-
tion 27, which has little stiffness to pivoting, but has great
stiffness resisting twisting of the lever portion 30 about an axis
parallel to the plane of pivotal movemellt. 'I'his stiffness i~ ul-io
effective against acceleration in a directioll along tlle l)ivotal axis.
'I'he lover portion is connected to tang 23 by a connector section 31.
A loading beam indicated generally at 35 is made of a
single block of magnetic material, preferably Ni-Span C, alloy ~n2,
~h. Cl, t~ C/G ~r~ C7 ~ V 7Q
~*~e-by the International ~ickel Company. I,oading beam 35 inclucles
a center vibrating beam section 42 that is positioned between and
integral with first and second isolator sections 43 ancl ~4 which
support the vibrating beam section 42. Isolator section 43 is
mounted at its outer encl opposite its junction to the vibrating beam
section as at 36 to a support lug 37 which can be part o~ the hlock 25.
l'he outer end of isolator section 43 may also be separately mountecl
to the base 12 of the housing. The connection to support 37 is a
fixecl connection, such as so~dering or brazing. 'I'he outer encl of thc
isolator section 43 can also be pinned or fastenecl with su-itable cap
screws.
~4~s~n
l`he outer end of the isolator section 44, which is the
opposite encl of the loading beam 35, is mountcd as at 40 to a support
41 protruding from the pivoting lever portion 30. The mounting can
be made in any desired manner.
The sensor assembly is acceleration balanced on at least
two axis, that is, an acceleration in the "Y" axis or the "X" axis
shown in Figure l will have little or no effect as the sum of the
torque moments on the sensor side of the pivot axis is the same as
the sum of the torque moments on the bellows side. The sensor is not
so balanced in the "Z" axis (shown in Figure 7) as the stiffness of
the pivot is effective in substantially reducing acceleration effects
from a force applied along this axis. It is also possible to
balance the torque moments about this axis if desired. Due to
tolerances, every sensor assembly has a somewhat different torque
moment. The effect of these tolerances with respect to acceleration
preferably is minim~ed by depositing small amounts of a material,
preferably solder in the areas near pivot 27 to equalize the torgue
moments about that axis as shown at 27A in Figure l.
l'he vibrating beam section 42 is thus supported by isolator
sections ~3 and 44 between supports 37 and 41. 7'he beam section 42
is thus subjected to forces that are exerted by movement of the
pivoting lever portion 30. The isolator sections 43 and 44 are each
rclieved in its center ~ortion to form a pair of thin strll~s.
It can be seen therefore that .my movcment of the tang 2-,
between the bellows 15 and 16 because of deflections or movements of
the bellows will cause thc tang 23 to pivot the pivoting lcver
portion 30 ahout pivot 27. l`he movement causes a change in thc
tension or compression stress or loading of the vibrating beam
section 42. The change in loading of the vibrating beam section 42
will change its resonant frequency of vibration The change ;n
resonant frequency will be proportional to the pressurc differential
present in pressure inlets 20 and 21, and thus the bellows 15 and lG.
One pressure inlet can be open to atmosphere or be evacuated, so thc
value of an individual pressure can be meiasured as well. I'urtllcr,
one bellows may be removed.
l'hc beam is driven or excited into resonance through thc
use of a coil which in turn is excited by an AC signal controllcd at
~4~5~C)
resonant frequency. ~urther, at rest the beam is nominally balanced,
not in compression nor tension; thus is not subject to creep and relax-
ation of the supporting structure or the beam which,contribute to sta-
bility problems. Preferably, the beam is operated at lower stresses
within the elastic limits of the beam material.
The isolators 43 and 44 each include a mass 43A and 44A
extending perpendicular to the beam section 42 and each has spaced
isolation springs 43B and 43C and 44B and 44C, respectively. These
isolators decouple the vibrating beam section 42 from the en~ mountings
to reduce energy losses which lower the beam "Q". It should be
noted that small stress reducing radii are used at the junction between
vibrating beam section 42 and the masses 43A and 44A.
In the design of the beam section 42 and isolators 43 and
44 it is important that no single element has a natural frequency that
can be easily driven by the beam section 42 itself which must sweep
a wide frequency range to be useful. If the other elements have a
natural frequency which can be driven by the beam section 42, the
beam section 42 will tend to excite such element in the system,
particularly if its natural frequency is equal to or in some multiple
of (i.e. 1, 2, 3, and 4 times) beam freq-lency. When this happens the
offectiveness of the isolators is reduced thus reducing the beams "Q"
and changing its frequency. The result of this is a sharp ~is-
continuity in the beam's linearity or smoothness with applied stress.
In addition, it can be seen that the center beam can he easily clriven
at its resonant frequency and two times its resonant frequeTlcy, since
with each half cycle of the beam there is one pull on the ends of
the vibrating beam section 42. The beam deflects to opposite sides
of its at rest plane during operation.
In practice, it is not possible to make the isolators so
low in frequency t1lat they cannot be driven by the vibrating bearn since
they would have to be very long and th-in. 'Ihu.s the ovcr.lll scnsor
size would be large and the system would be clifficult to manufactllre.
lt is possible as discussed above, for the vibratiTlg beanl-;ection to
drive the isolator springs at tlleir seconcl, or -third or higher o~der
harmonics.
Also, in practice it is not possible to makc tllese isolator
springs so high in frequency that they cannot he drivcn and still providc
1~4~5~à0
the necessary low frequency isolation. Thus it can be seen that the
isolator spring frequency must be chosen to provide a "window" so as
not to interfere with the vibrating beam section 42 through its
stressed frequency range. That is, when stress is appliecl to the
vibrating beam section 42 its natural frequency and twice this fre-
quency should not coincide with prominent resonant frequencies of the
isolator springs 43B and 43C and 44B and 44C. The widest "window"
is provided when the fundamental isolator spring frequency for each
of these four springs is greater than the highest vibrating beam
10 section frequency, which occurs at full scale stress, but lower
than twice the rest frequency of the vibrating beam section 42.
A specific example of the beam section 42 includes a beam
section .0047 inches thick, with approximate limits of not less than
.001 inches and not greater than .010 inches. The beam section is
c .250 inches long, with approximate limits of not less than .10
inches and not greater than .50 inches and it is .042 inches wide, with
approximate limits of not less than .020 and not greater than
.100.
The unstressed natural frequency is directly proportional
to the beam thickness and inversely proportional to the square of
the beam length and is about 14.5 Kl-lz using a suitable material
such as Ni-Span C. Ni-Span C is used for its uniquo com~ination
of excellent spring properties and substantially zcro temperature
coefficient over a wide range of temperatures. Other natural
froquencies could have been chosen.
I`lle change in frequency is determiTIecl by the stress in
the beam which is generated by the force provided by the lever
assembly 24. In one example, this is about 2.5 pouncls provided
by one-half inch diameter bellows at one atmosphcre. The stress in
the vibrating beam section 42 can be adjusted without changing the heam
section's unstressed frequency by changing the width. In thc cxample,
the stress was acljusted to about lO,OOO psi using Ni-Span C. 'I'his stress
is ideal since it is very low compared to the yielcl strength of Ni-S~all C
and thus an extremely low system hysteresis errors res~llt. In adclition,
long term changes in frequency arc not cncountcrecl. Thc rcs-llting changc
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in frequency of vibrating beam section 42 is about 2300 llz or about
16% of full scale frequency which can be provided either by putting
the beam in compression or in tension. Thus, for this example, a
zero to onc atmosphere pressure change yields a resonant frequency
change from 14.5 ~Iz up to 16.8 Kllz.
For the isolator springs, as discussed above, the
frequencies are adjusted in the same manner as for the vibrating beam
section 42, to be greater than 16.8 ~z but less than two times 14.5
KHz or 29 KHz. In practice it has been found that an isolator spring
frequency of between 22 ~llz to 24 ~Iz works well. The springs 43B
and 43C and 44B and 44C are made .012 inches thick by .315 inches
long for simpler construction. The isolation mass (43A and 44A)
is thus adjusted to yield an isolator system frequency of 2600 Hz,
which provides an excellent isolator to vibrating beam section
frequency ratio and thus a very low transmissibility.
The mechanical construction of the coil and pick-off is
shown in Figures 1 through 4, in particular. As shown, a ceramic
mounting block 50 is mounted onto a disc member 51. The disc member
is metal and can be bra~ed to the block S0 in a usual manner. If
desirecl, the block may be pinned to the disc. The disc member 51
fits within a recess 52 in the base 12 (see Pigure 2) of the housing,
so that the block 50 protrudes into the housing. The disc can be
rotated in the recess 52 to a desired position. Thc disc is then
soldere~ into place to hold it securely in rotational position during
use. 'I'he block 50 is madc of a nonmagnetic, nonelectrical conclucting
solid matcrial such as machinable sintered alumina or a similar ccrlmic
material. As shown, the block 50 inclucles a raised portion 53 that
has a surface 53A which is closely adjacent and parallcl to the plane
of the vibrating beam section 42. The block 53 fits between the
ends of isolator sections 43 and 44. Block 53 has a cylinclrical
recess 54 defined therein extending inwardly from 1 surface 57
opposite from the surface 53A (see ~igurc 3). A manclrcl mcmber 55 is
mounted in this recess, and can be boncled to the hlock 53 by elcctrically
conductive epoxy or solder. The mandrel 55 is preferahly made from mag-
netic stainless steel, and preferably a high "mu" or high magnetic pcr-
s~n
- meability material.
The mandrel has a disc end 56 and between the surface
57 of the bloek 53 and the dise 56 there is a eoil indicated at
58 that is wound in plaee. Thisis generally a single wound coil
having a suitable number of turns to generate the neeessary n~agnetic
foree for driving the heam as will be explained.
On faee 53A of the bloek 53 that is adjaeent and facing
the vibrating beam section 42 an eleetrieally conductive strip 61
forming a eapaeitor plate is sereened onto the eeramic material
and then fired in plaee. The eiapaeitor plate 61 is shown in ~igure 1.
Additional e]eetrieal eomponents ean be mounted direetly to the surflee
of the ceramic bloek 50, and the various components eonnected to the
eapaeitor plate by sereened on strips of con~uetive materia]. Sueh
eomponents are identified subsequently in this speeifieat:ion.
The surfaee 57 of the bloek 53 whieh is adjacent to the
eoil 58, and on an opposite side of the bloek 53 from the capaeitor
plate 51 may be metalized to provide for a shield to prevent inter-
ferenee from the eurrent in the eoil 58 from aEfeeting the eapaeitance
sensed between the v;brating heam seetion 42 and the eap.lcitor
plate 61.
it can be seen th~t by rotating the dise 51 the spacing
hetween the ear)aeitor pIate .ancI the vibratillg l-enm sectioIl 42 c~n be
ndjusted at tlle time of assembly. 'I'he l)lock 50 r~ .lte or dis~
51 are instnlled after the heaIn 35 is in pl;Ice~ 'I'lle s~.acillg betwee
plate 61 nnd the vihrating be~Im seetion 42 is about .0()5 inches.
The v-ibrating beam section 42 o-f tlIe be.Im forms the otller
plate of a variable eapaeitor in conj~mction with pl~te Gl. 'I'he
vibrating beatn section 42 is grounded. Note tha-t hlock 50 may be
supplied with circuit feed through pin 50A and connector openiIlgs 5()I3
if desired.
In Figures 6 and 7 a modif;ed form oi' the corIstructiorl is
shown. 'I'he beatn 35 iarld the lever assembIy 24 (in particlIlar thc pivot-
ing portion 30) and the bellows mounting are substantirIlly tlle simIe.
The mounting bloek 25 is modified for mountiIlg a modified drive .alld
~ick-o~f sensor assembly 7~. A sllart 75 is molJnted in a provide(I
operIing in the block 25 as can be .secn in l:igure G and suitable set
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S~C~
-10-
screws 76 permit the longitudinal adjustment of thc shaft 75 rclative
to the vibrating beam section 42. The shaft 75 in turn is attached
to a disc 79 wh:ich has a rod 78 extending coil support rnandrcl
outwardly therefrom. The disc 79 can be bonded to the end of the shaft
75 in the usual manner with epoxy or other bonding material. A coil
82 is l~ound onto the mandrel 78 between the inner surfacc of the disc
79 and a surface 83 of a cerarnic disc pick-up member 84. It should
be noted that the coil mandrel 78 extends into a reccss in thc
ceramic disc 84, a desired distance, and this mandrel 78 is suitably
fastened to the ceramic pick-up to hold the two parts together and
in place after the coil has been wound into place on the coil mandrcl.
The ceramic disc 84 as shown also has electrically
conductive surfaces shown by shading in ligure 8 thereon thereby
permitting the circuitry or portions thereof to be mounted proximatc
to the beam. The components mounted on the disc 84 prefcrably include
a capacitor plate 85 which corresponds to the plate 61, with sui.table
connecting strips 86 which lead to a thick film hybrid resistor
87, and thick film capacitor 88 which can be cemented to and
clcctrically connected to the str:ips 86. Suitable contact poi.nts
ZO 87~ and 88~ cnn bc p:rovided for connecti.ng to thc othcr cnds o-f the
capacitor 88 and resistor 87. As can be scen, the hyb-r;d capacitor
88 and thc roxistor 87 are mounted closc:ly adj.lcent to tllc cal)a(:itor
platc 85, and protrude fron) tl-e ccramic disc mcmbcr so that tlle
vibriating beam section 42 fits between these two components. The
vibrating beam section 42 .is spaced closely :froTn, and generally
parlllcl to thc capac:itor plate 85.
In operation, the beam in c:ithcr Form of the invcntion
is vibrated hy energi~ing the associated coi]. ~ milgnetic flux
is generated and causcs the vibrat:illg bcam sect iOIl 42 to deflcct in
oppositc d:irections gcncrally porpcndicul.:lr to :its iongitudirlal
plane. 'l'hc mandrc:l 55 or 78 extends through tho ccraMic hlock 53
or 84 a substanti.al distancc so that tho magnetic ficld is couplcd
to the beam section 42. T}le changes in cap.lcit~lncc oi~ thc capacitor
arc scnscd and in effcct control thc dr;vc circuit to rcs()llate thc
bc.lrn scction .Is well as providc a frc~ucncy outl~ut. ~ny charlgc in
diFferential pressure causcs a shift of the tang which results :in
S~
pivoting lever portion 3n about the pivot axis 27 to change the
compression or tension load on vi~rating beam section ~2, causing
a change in the resonant frequency of the be~n. The change will be
sensed by the changing of the frequency of the signal from the
capacitor formed between vibrating beam section 42 and either plate
61 or plate 85, depending on the sensor that is positioned a~jaccnt
the beam. This change in signal is representative of the clifferential
in pressure in relation to the reference pressure frequency. Preferably
the beam is driven at its fundamental frequency, however, the capacitor
pick-off permits relocation of the pick-off capacitor as to be sensitive
to any desired harmonic of the fundamental frequency or other desired
frequcncy .
Figure 9 shows a simplified electrical schematic diagram
of a circuit for deriving a frequency output signal from the vibrating
beam of the present invention. The circuit can be in several different
embodiments. In Figure 9~ vibrating beam section 42 is shown supported
between isolators 43 and 44 as described previously. A capacitive pick-
up electrode shown at 61 (it coul,~ also be electrode 85) is spaced
from vibrating bearn section 42 to form a variable capacitor.
The circuit shown in Figure 9 includes a supply voltage
terlninal 9(), a ground terminal 91, and an output terminal 92. A
source (not shown) of a supply voltage V+ is connected to supply
voltage terminal 90. Connected betweon terrninal 90 and ground term,inal
9l are a resistor 93 ancl coil 58 (or 82). A l)C current f'lows thlougl
resistor 93 and coil 58 to produce a steady magnetic field out of
mandrel or core 54 (or 75). 'I'he steady magnetic field produced by the
DC current through coil 58 could be replaced by a permaneTIt magnet,
if desired.
Also connected-~between terminal 90 and pick-off electrode
61 is a bias resistor 88 (shown mounted on the ceramic disc iTI Figure 7).
Bias resistor 88 provides a nc bias current at junction 9$ whele resistor
88 ancl electrode 61 are connected. ~s a result, the volt.Lge across
the variable capacitor Eorrned by vibrating beam sectioll ~2 and pick-off'
electrode 61 is a funct-ion of -the I~C current allCI thc fre(luerlcy of
vibr.ltiorl of vibr.lting bearn section 42.
The signal derived ~rom junction 95 is provided tllro~lgh
.4~S~
-l2-
a filter capacitor S7 (shown mounted in Figure 7) to an amplifier 97.
The amplifier output of amplifier 97 is supplied to output terminal
92 as the output signal of the circuit. The output of amplifier 97
is .llso connected through feedback ca~acitor 98 to junction ~9 which
is the junction of resistor 93 and drive coil 58.
When the circuit is turned on the magnetic field from coil
58 will shiFt the beam section 42. ~he capacitance between the beam
section 42 and plate 61 affects the i.nput to amplifier 97 through bias
resistor 88 and capacitor 87. The output of amplifier 97 changes the
feedback signal on capacitor 98 which in turn affects the current through
coil 5~. Any change in current through coil 58 changes the magnetic
field through vibrating beam section 42 and the vi.brating beam section
42 will again shift. The vibrating ~eam section 42 thus is excited
to its natural -frcqucncy and the out~ut of amplifier 97 wi.ll vary at
lS this frequency. The components are selected to provide appropriate
phasing to provide the oscillations at the desired frequency range.
The circuit shown in Figure 9 therefore derives a time
varying output signal whose fre4uency is a function of the frequency
of bcam section 42. This output signal can then be converted to a
digital or an analog signal and provides an indication of tlc tension
or compression in beam section 42 which cllanges the frccluency and wllich
.is a function of the prcssure to be scnsod.
Tlle actual circuit components for thc ampl:if:ier 97
alld othcr componellts for convcrting thc signal at output tcrmin.l]
92 to a digital OI' analog signal csln be mounted as shown schcmatically
in ligure 1 OT if dcsired all of the components may le mounte~ on
block 50 as shown in Figurc 4.
If low frequency vibrations from external sources ~such
as aircraft vibrations if the sensor is used in an aircraft) causc
low frequcncy osc-illation in thc OUtpllt signal an(l xuitablc filtcrs
can bc used to cl:iminate any SIIC}l unwanted oscil.l.ltions.
