CA1168887A - Pressure transducer - Google Patents
Pressure transducerInfo
- Publication number
- CA1168887A CA1168887A CA000392054A CA392054A CA1168887A CA 1168887 A CA1168887 A CA 1168887A CA 000392054 A CA000392054 A CA 000392054A CA 392054 A CA392054 A CA 392054A CA 1168887 A CA1168887 A CA 1168887A
- Authority
- CA
- Canada
- Prior art keywords
- pressure
- transducer
- plates
- signal
- substrate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/12—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means by making use of variations in capacitance, i.e. electric circuits therefor
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
- G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
- G01L9/0075—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance using a ceramic diaphragm, e.g. alumina, fused quartz, glass
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0082—Transmitting or indicating the displacement of capsules by electric, electromechanical, magnetic, or electromechanical means
- G01L9/0086—Transmitting or indicating the displacement of capsules by electric, electromechanical, magnetic, or electromechanical means using variations in capacitance
Abstract
ABSTRACT
A pressure transducer (26) is disclosed. A multiplicity of signal plates (Cs, Cr, Csf, Crf) are disposed on a first quartz disc (88). Opposing the signal plates (Cs, Cr, Csf, Crf) across a gap formed by an annular frit 92 is a common plate 94 disposed on a second quartz disc (86). The signal plates (Cs, Cr, CsF, Crf) and common plate (94) Form capacitors which are operable to modulate alter nating excitation signals applied to the signal plates. The capa-citances vary the modulation during deflections of the discs (86, 88) as a result of pressure changes and the common plate 94 algebraically sums the modulated excitation signals into a single output from the transducer (26).
A pressure transducer (26) is disclosed. A multiplicity of signal plates (Cs, Cr, Csf, Crf) are disposed on a first quartz disc (88). Opposing the signal plates (Cs, Cr, Csf, Crf) across a gap formed by an annular frit 92 is a common plate 94 disposed on a second quartz disc (86). The signal plates (Cs, Cr, CsF, Crf) and common plate (94) Form capacitors which are operable to modulate alter nating excitation signals applied to the signal plates. The capa-citances vary the modulation during deflections of the discs (86, 88) as a result of pressure changes and the common plate 94 algebraically sums the modulated excitation signals into a single output from the transducer (26).
Description
The invention pertains generally to a pressure transducer and in more particular1y directed to a pressure transducer of the quartz capacitive type.
Quartz capacitive pressure transducers are conventionally known in the art for the advantageous measuring of an unknown pressure. The general form for these transducers includes at least one flexible diaphragm formed of a vi~reous materlal such as quartz wlth a capacitor plate dls-posed thereon. Opposing the first capacitor plate and separated by a gap therebetween is a second capacitor plate that is disposed on either a stationary quartz base or another quartz diaphragm member. Usually, the opposing members are separated by an annular frit and the resulting cham-ber evacuated. The flexible diaphragm is exposed to a difference in pres-sures which cause a mechanical deflection proportional to the difference.
When the diaphragm deflects9 the gap distance will vary accordingly and thus chan~c ~he capaci~ance value be~ween the two plates. Therefore, t~e capacitance value of the transducer changes proportionally to the variances in pressure and is a measure thereof.
When the capacitance is excited with a carrier frequency, a modulation is induced ~Ihen the capacitance varies to change some elec-trical characteristic uf the excitation. The induced changes on the e~citation can thereafter be processed by electrical circuitry to yield an electrical signal representative of the pressure measured. The com-bination of the capacitive transducer and an electrical processing pro-vides a facile ~echnique for generating pressure measurements.
The inherent sensitivity of these transducers is related to the magnitude of capac;tance variation with respect to variation in pressure. Quartz is preferred for the diaphragm material because ~f its mechanical hysteresis in flexure is extremely low. The hysteresis exhibited by quartz is at least two orders of magnitude smaller than th3t available from the best steel. This deflec~ion repeatability permits the pressure measurements of the transducer to be accurate without drift and creep. Combined with its deflection characteristic, a quartz diaphragm has a substantial temperature insensitivity that im~roves reliability of the measurement. In addition to sensitivity 1 ~ 7 and temperature stabil.i-ty, the quartz diaphragm also lends mechanical rugyedness and con-tamination resistance -to these transducers.
One particularly advantayeous absolute pressure measur-ing system which uses a dual eonfigurat.ion of quartz capacitive pressure transducers is described in ~.S. Patent No. 4,322,977 entitled: "Pressure Measuring System" in the name of Robert C. Sell, John R~ ',heler, and John M. Juhasz.
The referenced patent diseloses a highly accurate pres-sure measuring system which ineorporates a elosed loop system and yields a digital outpu-t. The previously developed system comprises a pressure sensitive capaeitor and a stable reference capacitor contained within a first quartz capacitive sensing transducer. The pressure sensitive capacitor and reference eapacitor are excited by sinusoidal signals 180 out of phase with each other. The outputs of the eapsule are conneeted to a summing junction thereby producing a sensing signal which is proportiona]. to ehanges in the measured pressure. The summing junction output is used to exeite a seeond quartz capacitive feedbaek transdueer com~ected in a negative feedback loop to another input of the summing junetion7 The feedback transducer also eontains a pressure sensitive capaeitor and a reference capaeitor exeited 180 out of phase with eaeh other by a feedbaek signal. The output eurrent from the feedback transdueer is utilized to null or balanee the sensing signal and is -thus a measure of the pressure sensed when the summing junetion ou-tput is zero.
.
~ ' sd/(`J~ -2-I
~ J ~ 7 Addi-ti.onally, the system loop includes a digital - inte~rator means or counter Eor the direct measurement of the number of the discrete incremen-ts of feedback signal necessary to nu].l the output of the summing junc-tion. The digital readout of the counter is thereby directly related to the desired pressure measurement.
Since in the steady state condition, the system loop can be considered as having an infinite gain, the transfer function of the system is substantially e~uivalent to the ratio of the difference of the capacitances of the sensing trans-ducer to the difference of the capacitances sd/(~,i~ -2A~
.
- 3 ~
of the feedback ~ransducer multiplied by the maximum digital count. This ratio varies when pressure variances change the pressure sensittve capa~
citances in both the sensing transducer and the feedback transducer. The manner in which these values vary Tn both the numerator and denominator determines the pressure (P) versus digital numb~r (N) characteristic of the measuring system.
It wa~ taugh~ in Sell et al. that an advantageous output function for the system could be implemented by compressing more of the digital count at the lower pressure values than at h1gher values.
Advantageously, this meant that a digital word with fewer bits could be used for the same accuracy over the entire pressure range. This was accomplished in one particular embodiment of Sell et al. by utilizing t~ie feedback transducer to provide variable increments of feedback current with respect to pressure. Smaller increments were used at lower pres-sures and larger increments at higher pressures thereby adding to the resolution at the low end of the scale.
Ilowevcr, to obtain the correct pressure versus digital number output characteristic for this system, the two separate quart~ trans-ducers must be chosen so that each pressure sensitive capacitor and reference capacitor varies in a correct relationship to each other.
Ideally, thc slopes of the transducers should be identical. It was fcund thaL ~o produce accuracies of 1% of point over a 100-to-1 pressure range the plate separation differences between the two transducers have to be matched extremely closely. ~urther, the diaphragm or plate thick-ness and frit placemenlA as measured from the diaphragm center had to vary in the correct marner. This is because all of these variables change the slope of the pressure VerSlJS capacitance curves for the transducers. Since all of ~he variables are production variables which can change from transducer to transducer during manufacture, it is extremely difficult to maintain these variables within the necessary range of tolerances for the desired accuracies.
Therefore, until the present invention, the method used to provide the necessary accuracies for the system was to manufacture transducers to reasonable production standards and thereafter sort the transducers by their actual pressure vs. capacitance characterist;cs.
~ .
I ;1 6~38 - 4 .
Once the individual ~ransducer characteristics were recorded, a matching process was initiated to pairlthose transducers which were close enough in charactcristics te~e~h~r.
Tllis method is more time consuming than necessary and rela-tively expensive. Moreover, a substantial number of the transducers are wasted frorn any production run s;nce statistically It can be shown that while all of the transducers may be within production tolerances, there will be a certain number which are sti'll unable to be matched to a corresponding transduc~r.
Moreover, in the referenced prior art measurTny system the summation of alternating output signals of four capacitors was required.
ThTs was accomplished by soldering the wire leads from the individual capacitors together at an electrical node. This combinatlon of si~nals, external to the transducer, is more noise and Interference susceptible than necessary. Therefore, it would be highly desirable to combine the alternating signals of the system internal to ~he transducer so as to alleviate the problem.
SUM'~ARY OF THE INVENTION
_ .
The invention provides a quartz capacitive transducer charac-terized by at least one common p'late disposed on one of the quartz sub-strates for forming capacitors with a multiplicity of signal plates dis-posed on tll~ other quartz substrate~
The transduc~r thus includes a multiplicity of capacitors formed between tl-e ~uartz substrates which have a common plate. The common plate provides a means for algebraically summing all of the'signals inpu~ to the opposing signal plates together. The summation process is internal to the transducer and much less susceptible to noise.
In a preferred embodiment, the number of capacitors formed on the transducer is four~ Two pressure sensitive capacitors and two rela-tively pressure insensitive reference capacitors are provided to allowthe direct substitution of a single transducer for the two transducers used i n the raferenced measuri ng system.
The production of a quartz capacitive transducer in this manner reduces the number of quartz diaphragms and deposition processes neces-sary to provide the foùr capacitors necessary for the high resolution 8~87 pressure measuring system of Sell et al. Since only one transducer must be manufactured instead of two, production and material costs are reduced. Size and weight of the fTnal measuring system is also reduced.
More importantly, the produc:tion variables that change the slope of the pressure versus capacitance curves for this ~pe of transducer are perfectly matched. No longer does the plate separation, frit radius, and diaphragm thickness need to be matched between two transducers. Now all ;four signal plal:es are dTsposed on the same quartz disc facing a common plate on the opposing quartz dlsc and these vart~
ables are pcrfectly matched, i.e., they are identical. This elimina-tion of production variables from the pressure versus capacitance curves of the transducer obviates the need for the expensive matching technique used previously for the dual transducer configuration.
Still further, because the common plate combines all of the signals internally to the transducer into one output or error signal, there is less likelihood of interference or noise producing distortion in the pressure measur~ng system. Moreover, in the single transducer ; configuration, the transducer lends itself ~ore readily to internal and external shielding. An external ground shield is provided around tllc trans~ucer ~o produce the external shielding while internally a common conductive separator shields the signal capacitor plates.
Additionallyj by providing the capacitor plates on one surface the trimming of not only each capacitor to the correct value, but also that of the ratio necessitated for the Sell et al. a can be accornplished tn a more facile manner. In a calibration step a laser can be used after the transducer is assembled to produce the desired characteristic. This eliminates the tedious zero and span adjustments that must be made for other transducers.
3o These and other objects, features, and aspects of the inventTon will be more clearly understood and better described if a reading of the detailed description is undertaken in conjunction with the appended drawings wherein:
Figure 1 is a system block diagram view of a prior art pres-sure measuring system utilizing a dual quart~ capacitive transducer configuration;
,:
. .
~ ~ 6~
Figure 2 is a yraphical represen-tation of the digital ou-tput number N as a ~unction of pressure P for the pressure measuring system illustra-ted in Figure l;
Figure 3 is a sectional side view of a mounting structure for a quartz capacitive transducer constructed in accordance with the invention;
Figure 4 is a top view, with a casing member removed, of the mounting structure for the quartz capacitive transducer illustrated in Figure 3;
Figure 5 is a bottom view, with a casing member removedr of a mounting structure for the quartz capacitive transducer illustrated i.n Figures 3 and 4;
Fi.gure 6 is a detailed electrical schematic view of the quartz capacitive transducer illustrated in Figures 3, 4 and 5;
Figure 7 is a cross-sectional side view of the quartz capacitive transducer illustrated in Figures 3, 4 and 5;
Figure 8 is a top view of the quartz capacitive trans-ducer illustrated in Figure 7, with the top quartz disc removed;
Figure 9 is a bottom view of the quartz capacitive transducer illustrated in Figures 7 and 8, with the bottom quartz ; disc removed;
Figure 10, appearing on the same sheet as Figure 6, is a graphical representation of the change in capacltance as a function of pressure for the capacitances Cs and Cr of the trans-ducer illustra-ted in Figures 7, 8, and 9; and Figure 11, appearing on the same sheet as Figure 6, is a graphical representation of the change in capacitance as a function of pressure for the capacitances Cs-f and Csr of the .~ .
sd/~ 6-.
pressure transducer illustrated in Figures 7, 8~ and 9.
DETAILED DESCRIPTION
Illustrated in Figure 1 is the prior art pressure measuring system of Sell et alO which includes a quartz capacitive sensing transducer 10 and a quartz capacitive :Eeed-back transducer 12. The dual transducer configuration is more fully described in the Sell et al. application. Each of the transducers 10, 12 contain a pressure sensitive capacitor Cs, Csf and a relatively pressure insensitive capacitor Cr, Crf respectively. The sensing transducer 12 is fed by an alternating signal generator 24 in phase and out of phase sd/~r~ -6A-,.,",~
: ~ ' 1 3 ~
by signals Vr, -Vr to produce a current Is whtch is proportional to the pressure Pa in chamber 13. The current Is is d;~r- ~ with a feedback current If to produce an error current le in a summing junc-tion 14. This error current is operated on by a system loop 16 which produces a digital number N. The digital number N which is an integra-tion of thc error current le is fed back to a register 18. The regis-t~r 1~ transmits the digital number N to a multiplying digital to analog converter (MDAC) 20. The MDAC further receives the inverted excitation signal -Vr and generates the signal -Vr f(N). The output of the MDAC
is an alternating signal of phase -Vr whose amplitude is a function of' the digital number N. The ouput of the ~1DAC is subsequently fed in phase to Csf and out of phase to Crf via an inverting amplifier 22.
The outputs of the feed~ack capacitors are summed to output a differ-ential current which is the feedback current If.
In the referenced Sell et al. ~ ~ n it is taught that the error curren~ le is used to incrementally change the N number to cause the balancing of the feedback current If and pressure sensitive current Is. This nulling of the error current le will then produce a digital number N which is a measure of the pressure in the chamber 13.
Moreover, making the feedback current If a function of the pressure by using the quartz capacitive transducer 10, it is known that a compres-sion of thc diyital numbers N will occur at lower pressures. This allows a more advantageous system whereby fewer bits need to be used for the same accuracy of the pressure measurements and whereby the slew rates of the system are better controlled.
The desired characteristic response of the system illustrated in Figure 1, is graphically represented in Figure 2 where the digital number N is shown as a function of pressure P. From inspection it can be seen that there is a greater change in digi~al number N for incre-mertal changes in pressure at lower pressure values than at higher pres-sure values. The slope dN/dP is initially large and thereafter gradually decreases as the pressure approaches the maximum measured pressure, P2.
This provides the increased resolution at lower pressure values because o-F the compression of tIIe digital numbers at the low end of the pressure SC2 le.
The invention performs the function of the transducer 10 and transducer 12 by providing a single quartz capacitive transducer con-taining four capacitors similar to Cs Cr Csf and Crf. The four capacitors are formed such that if connected identically to those shown in Figure 1 ~hen the N versus P characteristic of the system will be substantially commensurate to that illustrated in Figure 2.
This transducer is shown as element 26 in Figures 3 4 and 5 where a technique for mounting the capsule-shaped transducer in a pressurized environment is illustrated. In these Figures a common prin~ed circuit board 28 is shown which has a ~enerally c7rcu-lar aperture cut out t~ provide a moun~ing space for the transducer 26.
FcrmTng a sealed pressure chamber around the transducer and aperture are two opposing cup-shaped cas7ng members 32 and 34O The upper casing member 32 has a port 30 for connection to the source of pressure that is to be measured. The port 30 can communicate with the pressure source by any suitable conduit means.
The transducer 26 is mounted within the enclosed chamber by three generally C-shaped retainer clamps 40 42 and ~4. The retainer clamps which are equal angularly spaced on the transducer 26 are prefer-ably formed of an elas.omeric material~ Clamps 40 42 44 hold the capsule 26 under slight compression in their central mounting channels when casing mcmbers 32 36 are assembled. The transducer floats in these retainer clamps and is exposed to the pressure within the enclosed chamber. A fluidic seal for the pressure chamber is maintained around the periphery of the casing members 32 34 by 0-rings 36 38 fitted into annular slots cut in the casing members.
Connecting a processing circuit (not shown) of the circuit board 28 to the transducer 26 are transducer terminals 46 48 50 52 54 56 and 72. These transducer terminals are connected to terminal strips 5~ 60 64 68 62 and 70 respectively by soldering .jumper wires between the two. Cutouts 93 95 and 97 are provided on the quartz discs to permit connection to the terminals. The processing circuit is prefer-ably the pressure measuring system as shown in Figure l. A detailed elec-trical schemat k of th~ transducer 26 shown in Figure 6 illustrates it co~tains a pressure sensitive sensing capacitor Cs a relatively pres-sure insensitive reference capacitor Cr a pressure sensitive g feedback capacitor Csf, and a relatively pressure insensitive Feed-back reference capacitor Crf.
The schematic illustrates that the terminals l~6, 50, 52, and 54 are electrically connected to separate or signal capacitor pla~es while terminal 72 is electrically connected to one common capacitor plate. Input signals to the terminals 46~ 50, 52, and 54 will be modulated by the change in capacitances between the signal plates and the common plate. An algebraic summation in the common pla~es will combine the modulated input slgnals to generate one output signal vTa terminal 72.
It is readily seen that the transducer 26 may be ~sed to take the place of the pressure transducer 10, pressure transducer 12, and the summing junction 14 in the system of the first figure. Thus, the input terminals 52 and 54 would be fed by the alternating genera-tor 24 wi~h excitation signals Vr and -Vr, respectively. Similarly, transducer input terminals 50 and 46 would be fed by the output of the MDAC 20 and its inversion via inverting 22. Output termTnal 72 which is connected to the common plate for all four capacitors receives the sum of the four oscillating currents and will output the error current le.
The sin91e transducer ;16 is thus electrically equivalent to the two transducers illustrated in the first Figure.
Additionally, the transducer 26 is provided with an external ground shield 55 (shown schematically in Figure 6) which connects to ; the transducer terminal 56. The external ground shield 55 is for thepurpose of shunting to ground s~ray electromagnetic radiation and inter-ference from outside the transducer. Likewise, an internal ground shield 57 (shown schematically in Figure 6) is provided between the capacitor plates and connects to the transducer lead 48. Since all four capacitors are coIltained within the transducer and excited by oscillatin~ voltages some intercapacitance interference is bound to take place. The internal ground shield 57 intercepts this urwanted self-inter-ference and shunts it to ground. Terminals 48 and 56 are therefore connected in the pressure measuring circuit to either signal ground or chassis ground.
., Returning for a moment to Figures 4 and 5, the external ground shield 55 comprises a conduc-tive pattern vapor deposited or screened on the top and bottom of the transducer 260 The pattern for the conductor that is placed on the top of the trans-ducer is shown as 7~ in Figure 4 and the pattern placed on the bottom of the transducer is shown as 78 in Figure 5. Pattern 76 essentially covers the top of the transducer 26 and is elec-trically connected to the terminal 56 by a solder joint.
Basically, the same shape of pattern 78 is screened or vapor deposited on the reverse side of the transducer except for a pair of arcuate windows 80 and 82.~ The arcuate windows are to allow optically transparent openings through the quartz disc to permit laser trimming of the signal plates within the transducer.
The windows 80 and 82 may be of any shape desired, but that illustrated is preferred for the particular embodiment shown in the drawings. The conductive pattern 76 and pattern 78 are electrically connected together by a wire jumper 75 connecting solder point 74 to solder point 84. The external ground shield substantially surrounds the outside of the transducer in a conductive pattern to shield it from interference and noiseO
Figure 7 illustrates a cross section of the transducer 26 wherein the layering of the device is clearly shown. The first layer comprises the conductive pattern 76 for the external shield which is supported by an insulative quartz substrate 86 in the shape oE a disc~ A common electrode 94 has been plated on the inner surface of the disc 86. Cutouts 93 and 95 are provided for easy access to the transducer terminals~ Similarly, a quartz disc 88 has an electrode 90 segmented into four ~, .
sd ~1~ -10-;
.
capacitor siynal plates disposed on its inner surface and the conductive pattern 78 plated on its outer surface. The two electrodes 90 and 94 oppose each other across a separation to form the Eour capacitors of the device. An annular frit 92 provides a separation or gap and a means for sealing the transducer 26 to a reference pressure. Generally, for accuracy it is desirable for -the chamber formed by the frit to ~e evacuated to a substantial vacuum~ Preferably, the frit is a vitreous material which has temperature expansion properties similar to the quartz disc~so In Figure 8 the elec-trode 90 is shown segmented into four separate signal plates for capacitors, Cs, Cr, Csf, Crf.
The segmentation of the electrode is provided by initiall~
screening or depositing a layer of conductive material on the quartz disc in a basic circular pattern with the associate terminals. A laser is then used to burn through the conductive pattern and separate the electrode into electricall~ continuous areas to form the plates in the shapes illustratedO These capacitor plates, when they oppose the common pla-te formed by the electrode 94r make wp the four capacitors of the transducer.
Each of the four are connected to their respective transducer terminals 46, 50~ 52, 54 by conductive paths. For example, the conductive paths 96~ 98~-100 and 102 connect terminals 46~ 50 52, and 54 to the segments labelled Crf, Csf, Cs~ and Cr, respectivelyO The terminal lead 4~ is elec-trically continuous with a conductive path 104 which surrounds each segment and separates each plate from the others. The conductive path 104 which is insulated from the capacitor plates comprises the internal ground shield and prevents self-interference between ~r sd~r., f~ -11-the segments by intercepting radiations from the adjacent plates and shunting them to ground.
The cutout 97 ls clearly shown in Figure 8 and provides for a facile connector to the common plate 94 and terminal 72 illustrated in Figure 9 With the configurations shown, each signal plate is separated from the common plate by a gap and forms a capacitor -therewith. The pressure versus capacitance characteristic for each signal capacitance is determined by the area of the signal plate, its shape, and its positioning with respect to the center of the quartz disc. The area of a signal plate determines the initial capaci-tance at a reference pressure and its shape and positioning determine the dynamic characteristic of the capacitor~
Since the quartz disc deflects a maximum distance at the center and proportionally less farther away from the center, a greater change in capacitance will be generated from those conductive areas which are most centrally located.
Generally, the segmeIlted signal plates of electrode 90 are formed by two regions. The first is a central inner region which is generally circular in shape and the second is an outer region which is generally ring shapedO The two pressure sensitive capacitors Csf and Cs~ because of the greater deflection of the quartz diaphragms toward the center, occupy the central region. Each of the pressure sensitive capacitors comprise relatively half of the central region except for the exact center where the pressure sensitive capacitor Cs includes a semicircular portion 106.
The ring of the outer region is generally divided into sd/`_i -12-' .
' .
two substantially equal area crescent-shaped portions which are the signal plates for reference capacitors Crf and Cr. Since ~he outer area is less deformable with pressure than the central region, the reference capacitors are relatively insensitive to pressure as compared to the pressure sensitive capacitors Csf and Cs.
How the actual capacitance of each of the capacitors Cs, Csf, Cr, and Cfr varies as a function oE pressure is illustrated in Figures 10 and 11.
It is seen that the pressure sensitive capacitors Cs, Csf have capacitance characteristic curves 100, 106 which increase as a function of pressure while the reference capacitors Cr, Csf have relatively insensitive pressure char-acteristic curves 102, 10~. The reference capacitor curves when subtracted from the pressure sensitive capacitor curves generate curves lO~, 110. The two curves 10~, 110 form the numerator and denominator, respectively, of the desired transfer function when the transducer 26 is connected in the measuring system shown in Figure l.
As was previously noted in Sell et al. the transfer function of the pressure measuring system in a steady state condition is equivalent to:
N Cs - Cr Nmax Csf - Crf For the desired compression of digital numbers at the lower pressure values of the system, N as a function of pressure should vary as the curve 21 shown in Figure 2. From inspection dN/dP is larger at the low end of the scale and becomes smaller with increasing pressure~ Therefore, proportionally more of the digital numbers are available for pressure resolution at -the low end of the scale. The initial difference ~point 112 of Figure ll) between the feedback capacitors Csf, Crf sets the maximum resolution of the system as it represents the smallest increment in feed-back current. The feedback increments thereafter become larger with increasing pressure according to the curve llO.
;~
sd~ -12A-1 7 6 ~ 7 llowever, to obta;n/increasing curve 21 ~ ~he transfer function, it is n~cessary to have the numerator Cs - Cr increase Faster for increasing pressures than the denominator CsF - Crf. This is accomplished by the ;urve 100 represelltative of Cs increasing faster for increasing pressures than curve 106 representative oP Csf. Return-ing to Figure 8 for a momsnt, it is the semicircular portion 106 of Cs that causes this action becaus~ of its extra area locat~d exactly at the center oF maximum deflection for the quartz dTsc. This e~fect is enhanced because of the cutout portion of Csf into which portion 106 lo protrudes. The radius oF the central portion 106 can be varied ~o con-trol this change.
Additionally, at manufacture, Cs and Csf should be substan-tially equivalent and Cr slTghtly larger than Crf. These values can bo produced by changing the radius of the cut s~parating the individual pl~tes on ~luar~ ~isc 88 and the arcuate extent of each.
After assembly, the reFerence capacitor Cr and Crf can be tlin~led by laser through the ground shield windows 80, 82 to provide the ~/~s~ ~c/
e*a~ curve 21 in Figure 2. At Pl, Cr will be trimmed such that Cs ~ Cr thereby giving the zero point For the system. At P2, Crf is trimmed such that Cs - Cr ~ Csf - Cr~F thereby providing ~he transFer function wi~h the valu~ o~ I at Cl so ~hat a ~ull scale pressure o~ P2 is repre-sented by ~he maxilllum di~ al number, Nmax.
Wllile Lhe pret~rred embodiment of the inventlon has been shown and described, it will be obvious co those skilled in the art that various modiFications and variations may be made thereto without departing From the spirit and scope o-F the inven~ion as hereinafter defined in the appended claims.
~ I
Quartz capacitive pressure transducers are conventionally known in the art for the advantageous measuring of an unknown pressure. The general form for these transducers includes at least one flexible diaphragm formed of a vi~reous materlal such as quartz wlth a capacitor plate dls-posed thereon. Opposing the first capacitor plate and separated by a gap therebetween is a second capacitor plate that is disposed on either a stationary quartz base or another quartz diaphragm member. Usually, the opposing members are separated by an annular frit and the resulting cham-ber evacuated. The flexible diaphragm is exposed to a difference in pres-sures which cause a mechanical deflection proportional to the difference.
When the diaphragm deflects9 the gap distance will vary accordingly and thus chan~c ~he capaci~ance value be~ween the two plates. Therefore, t~e capacitance value of the transducer changes proportionally to the variances in pressure and is a measure thereof.
When the capacitance is excited with a carrier frequency, a modulation is induced ~Ihen the capacitance varies to change some elec-trical characteristic uf the excitation. The induced changes on the e~citation can thereafter be processed by electrical circuitry to yield an electrical signal representative of the pressure measured. The com-bination of the capacitive transducer and an electrical processing pro-vides a facile ~echnique for generating pressure measurements.
The inherent sensitivity of these transducers is related to the magnitude of capac;tance variation with respect to variation in pressure. Quartz is preferred for the diaphragm material because ~f its mechanical hysteresis in flexure is extremely low. The hysteresis exhibited by quartz is at least two orders of magnitude smaller than th3t available from the best steel. This deflec~ion repeatability permits the pressure measurements of the transducer to be accurate without drift and creep. Combined with its deflection characteristic, a quartz diaphragm has a substantial temperature insensitivity that im~roves reliability of the measurement. In addition to sensitivity 1 ~ 7 and temperature stabil.i-ty, the quartz diaphragm also lends mechanical rugyedness and con-tamination resistance -to these transducers.
One particularly advantayeous absolute pressure measur-ing system which uses a dual eonfigurat.ion of quartz capacitive pressure transducers is described in ~.S. Patent No. 4,322,977 entitled: "Pressure Measuring System" in the name of Robert C. Sell, John R~ ',heler, and John M. Juhasz.
The referenced patent diseloses a highly accurate pres-sure measuring system which ineorporates a elosed loop system and yields a digital outpu-t. The previously developed system comprises a pressure sensitive capaeitor and a stable reference capacitor contained within a first quartz capacitive sensing transducer. The pressure sensitive capacitor and reference eapacitor are excited by sinusoidal signals 180 out of phase with each other. The outputs of the eapsule are conneeted to a summing junction thereby producing a sensing signal which is proportiona]. to ehanges in the measured pressure. The summing junction output is used to exeite a seeond quartz capacitive feedbaek transdueer com~ected in a negative feedback loop to another input of the summing junetion7 The feedback transducer also eontains a pressure sensitive capaeitor and a reference capaeitor exeited 180 out of phase with eaeh other by a feedbaek signal. The output eurrent from the feedback transdueer is utilized to null or balanee the sensing signal and is -thus a measure of the pressure sensed when the summing junetion ou-tput is zero.
.
~ ' sd/(`J~ -2-I
~ J ~ 7 Addi-ti.onally, the system loop includes a digital - inte~rator means or counter Eor the direct measurement of the number of the discrete incremen-ts of feedback signal necessary to nu].l the output of the summing junc-tion. The digital readout of the counter is thereby directly related to the desired pressure measurement.
Since in the steady state condition, the system loop can be considered as having an infinite gain, the transfer function of the system is substantially e~uivalent to the ratio of the difference of the capacitances of the sensing trans-ducer to the difference of the capacitances sd/(~,i~ -2A~
.
- 3 ~
of the feedback ~ransducer multiplied by the maximum digital count. This ratio varies when pressure variances change the pressure sensittve capa~
citances in both the sensing transducer and the feedback transducer. The manner in which these values vary Tn both the numerator and denominator determines the pressure (P) versus digital numb~r (N) characteristic of the measuring system.
It wa~ taugh~ in Sell et al. that an advantageous output function for the system could be implemented by compressing more of the digital count at the lower pressure values than at h1gher values.
Advantageously, this meant that a digital word with fewer bits could be used for the same accuracy over the entire pressure range. This was accomplished in one particular embodiment of Sell et al. by utilizing t~ie feedback transducer to provide variable increments of feedback current with respect to pressure. Smaller increments were used at lower pres-sures and larger increments at higher pressures thereby adding to the resolution at the low end of the scale.
Ilowevcr, to obtain the correct pressure versus digital number output characteristic for this system, the two separate quart~ trans-ducers must be chosen so that each pressure sensitive capacitor and reference capacitor varies in a correct relationship to each other.
Ideally, thc slopes of the transducers should be identical. It was fcund thaL ~o produce accuracies of 1% of point over a 100-to-1 pressure range the plate separation differences between the two transducers have to be matched extremely closely. ~urther, the diaphragm or plate thick-ness and frit placemenlA as measured from the diaphragm center had to vary in the correct marner. This is because all of these variables change the slope of the pressure VerSlJS capacitance curves for the transducers. Since all of ~he variables are production variables which can change from transducer to transducer during manufacture, it is extremely difficult to maintain these variables within the necessary range of tolerances for the desired accuracies.
Therefore, until the present invention, the method used to provide the necessary accuracies for the system was to manufacture transducers to reasonable production standards and thereafter sort the transducers by their actual pressure vs. capacitance characterist;cs.
~ .
I ;1 6~38 - 4 .
Once the individual ~ransducer characteristics were recorded, a matching process was initiated to pairlthose transducers which were close enough in charactcristics te~e~h~r.
Tllis method is more time consuming than necessary and rela-tively expensive. Moreover, a substantial number of the transducers are wasted frorn any production run s;nce statistically It can be shown that while all of the transducers may be within production tolerances, there will be a certain number which are sti'll unable to be matched to a corresponding transduc~r.
Moreover, in the referenced prior art measurTny system the summation of alternating output signals of four capacitors was required.
ThTs was accomplished by soldering the wire leads from the individual capacitors together at an electrical node. This combinatlon of si~nals, external to the transducer, is more noise and Interference susceptible than necessary. Therefore, it would be highly desirable to combine the alternating signals of the system internal to ~he transducer so as to alleviate the problem.
SUM'~ARY OF THE INVENTION
_ .
The invention provides a quartz capacitive transducer charac-terized by at least one common p'late disposed on one of the quartz sub-strates for forming capacitors with a multiplicity of signal plates dis-posed on tll~ other quartz substrate~
The transduc~r thus includes a multiplicity of capacitors formed between tl-e ~uartz substrates which have a common plate. The common plate provides a means for algebraically summing all of the'signals inpu~ to the opposing signal plates together. The summation process is internal to the transducer and much less susceptible to noise.
In a preferred embodiment, the number of capacitors formed on the transducer is four~ Two pressure sensitive capacitors and two rela-tively pressure insensitive reference capacitors are provided to allowthe direct substitution of a single transducer for the two transducers used i n the raferenced measuri ng system.
The production of a quartz capacitive transducer in this manner reduces the number of quartz diaphragms and deposition processes neces-sary to provide the foùr capacitors necessary for the high resolution 8~87 pressure measuring system of Sell et al. Since only one transducer must be manufactured instead of two, production and material costs are reduced. Size and weight of the fTnal measuring system is also reduced.
More importantly, the produc:tion variables that change the slope of the pressure versus capacitance curves for this ~pe of transducer are perfectly matched. No longer does the plate separation, frit radius, and diaphragm thickness need to be matched between two transducers. Now all ;four signal plal:es are dTsposed on the same quartz disc facing a common plate on the opposing quartz dlsc and these vart~
ables are pcrfectly matched, i.e., they are identical. This elimina-tion of production variables from the pressure versus capacitance curves of the transducer obviates the need for the expensive matching technique used previously for the dual transducer configuration.
Still further, because the common plate combines all of the signals internally to the transducer into one output or error signal, there is less likelihood of interference or noise producing distortion in the pressure measur~ng system. Moreover, in the single transducer ; configuration, the transducer lends itself ~ore readily to internal and external shielding. An external ground shield is provided around tllc trans~ucer ~o produce the external shielding while internally a common conductive separator shields the signal capacitor plates.
Additionallyj by providing the capacitor plates on one surface the trimming of not only each capacitor to the correct value, but also that of the ratio necessitated for the Sell et al. a can be accornplished tn a more facile manner. In a calibration step a laser can be used after the transducer is assembled to produce the desired characteristic. This eliminates the tedious zero and span adjustments that must be made for other transducers.
3o These and other objects, features, and aspects of the inventTon will be more clearly understood and better described if a reading of the detailed description is undertaken in conjunction with the appended drawings wherein:
Figure 1 is a system block diagram view of a prior art pres-sure measuring system utilizing a dual quart~ capacitive transducer configuration;
,:
. .
~ ~ 6~
Figure 2 is a yraphical represen-tation of the digital ou-tput number N as a ~unction of pressure P for the pressure measuring system illustra-ted in Figure l;
Figure 3 is a sectional side view of a mounting structure for a quartz capacitive transducer constructed in accordance with the invention;
Figure 4 is a top view, with a casing member removed, of the mounting structure for the quartz capacitive transducer illustrated in Figure 3;
Figure 5 is a bottom view, with a casing member removedr of a mounting structure for the quartz capacitive transducer illustrated i.n Figures 3 and 4;
Fi.gure 6 is a detailed electrical schematic view of the quartz capacitive transducer illustrated in Figures 3, 4 and 5;
Figure 7 is a cross-sectional side view of the quartz capacitive transducer illustrated in Figures 3, 4 and 5;
Figure 8 is a top view of the quartz capacitive trans-ducer illustrated in Figure 7, with the top quartz disc removed;
Figure 9 is a bottom view of the quartz capacitive transducer illustrated in Figures 7 and 8, with the bottom quartz ; disc removed;
Figure 10, appearing on the same sheet as Figure 6, is a graphical representation of the change in capacltance as a function of pressure for the capacitances Cs and Cr of the trans-ducer illustra-ted in Figures 7, 8, and 9; and Figure 11, appearing on the same sheet as Figure 6, is a graphical representation of the change in capacitance as a function of pressure for the capacitances Cs-f and Csr of the .~ .
sd/~ 6-.
pressure transducer illustrated in Figures 7, 8~ and 9.
DETAILED DESCRIPTION
Illustrated in Figure 1 is the prior art pressure measuring system of Sell et alO which includes a quartz capacitive sensing transducer 10 and a quartz capacitive :Eeed-back transducer 12. The dual transducer configuration is more fully described in the Sell et al. application. Each of the transducers 10, 12 contain a pressure sensitive capacitor Cs, Csf and a relatively pressure insensitive capacitor Cr, Crf respectively. The sensing transducer 12 is fed by an alternating signal generator 24 in phase and out of phase sd/~r~ -6A-,.,",~
: ~ ' 1 3 ~
by signals Vr, -Vr to produce a current Is whtch is proportional to the pressure Pa in chamber 13. The current Is is d;~r- ~ with a feedback current If to produce an error current le in a summing junc-tion 14. This error current is operated on by a system loop 16 which produces a digital number N. The digital number N which is an integra-tion of thc error current le is fed back to a register 18. The regis-t~r 1~ transmits the digital number N to a multiplying digital to analog converter (MDAC) 20. The MDAC further receives the inverted excitation signal -Vr and generates the signal -Vr f(N). The output of the MDAC
is an alternating signal of phase -Vr whose amplitude is a function of' the digital number N. The ouput of the ~1DAC is subsequently fed in phase to Csf and out of phase to Crf via an inverting amplifier 22.
The outputs of the feed~ack capacitors are summed to output a differ-ential current which is the feedback current If.
In the referenced Sell et al. ~ ~ n it is taught that the error curren~ le is used to incrementally change the N number to cause the balancing of the feedback current If and pressure sensitive current Is. This nulling of the error current le will then produce a digital number N which is a measure of the pressure in the chamber 13.
Moreover, making the feedback current If a function of the pressure by using the quartz capacitive transducer 10, it is known that a compres-sion of thc diyital numbers N will occur at lower pressures. This allows a more advantageous system whereby fewer bits need to be used for the same accuracy of the pressure measurements and whereby the slew rates of the system are better controlled.
The desired characteristic response of the system illustrated in Figure 1, is graphically represented in Figure 2 where the digital number N is shown as a function of pressure P. From inspection it can be seen that there is a greater change in digi~al number N for incre-mertal changes in pressure at lower pressure values than at higher pres-sure values. The slope dN/dP is initially large and thereafter gradually decreases as the pressure approaches the maximum measured pressure, P2.
This provides the increased resolution at lower pressure values because o-F the compression of tIIe digital numbers at the low end of the pressure SC2 le.
The invention performs the function of the transducer 10 and transducer 12 by providing a single quartz capacitive transducer con-taining four capacitors similar to Cs Cr Csf and Crf. The four capacitors are formed such that if connected identically to those shown in Figure 1 ~hen the N versus P characteristic of the system will be substantially commensurate to that illustrated in Figure 2.
This transducer is shown as element 26 in Figures 3 4 and 5 where a technique for mounting the capsule-shaped transducer in a pressurized environment is illustrated. In these Figures a common prin~ed circuit board 28 is shown which has a ~enerally c7rcu-lar aperture cut out t~ provide a moun~ing space for the transducer 26.
FcrmTng a sealed pressure chamber around the transducer and aperture are two opposing cup-shaped cas7ng members 32 and 34O The upper casing member 32 has a port 30 for connection to the source of pressure that is to be measured. The port 30 can communicate with the pressure source by any suitable conduit means.
The transducer 26 is mounted within the enclosed chamber by three generally C-shaped retainer clamps 40 42 and ~4. The retainer clamps which are equal angularly spaced on the transducer 26 are prefer-ably formed of an elas.omeric material~ Clamps 40 42 44 hold the capsule 26 under slight compression in their central mounting channels when casing mcmbers 32 36 are assembled. The transducer floats in these retainer clamps and is exposed to the pressure within the enclosed chamber. A fluidic seal for the pressure chamber is maintained around the periphery of the casing members 32 34 by 0-rings 36 38 fitted into annular slots cut in the casing members.
Connecting a processing circuit (not shown) of the circuit board 28 to the transducer 26 are transducer terminals 46 48 50 52 54 56 and 72. These transducer terminals are connected to terminal strips 5~ 60 64 68 62 and 70 respectively by soldering .jumper wires between the two. Cutouts 93 95 and 97 are provided on the quartz discs to permit connection to the terminals. The processing circuit is prefer-ably the pressure measuring system as shown in Figure l. A detailed elec-trical schemat k of th~ transducer 26 shown in Figure 6 illustrates it co~tains a pressure sensitive sensing capacitor Cs a relatively pres-sure insensitive reference capacitor Cr a pressure sensitive g feedback capacitor Csf, and a relatively pressure insensitive Feed-back reference capacitor Crf.
The schematic illustrates that the terminals l~6, 50, 52, and 54 are electrically connected to separate or signal capacitor pla~es while terminal 72 is electrically connected to one common capacitor plate. Input signals to the terminals 46~ 50, 52, and 54 will be modulated by the change in capacitances between the signal plates and the common plate. An algebraic summation in the common pla~es will combine the modulated input slgnals to generate one output signal vTa terminal 72.
It is readily seen that the transducer 26 may be ~sed to take the place of the pressure transducer 10, pressure transducer 12, and the summing junction 14 in the system of the first figure. Thus, the input terminals 52 and 54 would be fed by the alternating genera-tor 24 wi~h excitation signals Vr and -Vr, respectively. Similarly, transducer input terminals 50 and 46 would be fed by the output of the MDAC 20 and its inversion via inverting 22. Output termTnal 72 which is connected to the common plate for all four capacitors receives the sum of the four oscillating currents and will output the error current le.
The sin91e transducer ;16 is thus electrically equivalent to the two transducers illustrated in the first Figure.
Additionally, the transducer 26 is provided with an external ground shield 55 (shown schematically in Figure 6) which connects to ; the transducer terminal 56. The external ground shield 55 is for thepurpose of shunting to ground s~ray electromagnetic radiation and inter-ference from outside the transducer. Likewise, an internal ground shield 57 (shown schematically in Figure 6) is provided between the capacitor plates and connects to the transducer lead 48. Since all four capacitors are coIltained within the transducer and excited by oscillatin~ voltages some intercapacitance interference is bound to take place. The internal ground shield 57 intercepts this urwanted self-inter-ference and shunts it to ground. Terminals 48 and 56 are therefore connected in the pressure measuring circuit to either signal ground or chassis ground.
., Returning for a moment to Figures 4 and 5, the external ground shield 55 comprises a conduc-tive pattern vapor deposited or screened on the top and bottom of the transducer 260 The pattern for the conductor that is placed on the top of the trans-ducer is shown as 7~ in Figure 4 and the pattern placed on the bottom of the transducer is shown as 78 in Figure 5. Pattern 76 essentially covers the top of the transducer 26 and is elec-trically connected to the terminal 56 by a solder joint.
Basically, the same shape of pattern 78 is screened or vapor deposited on the reverse side of the transducer except for a pair of arcuate windows 80 and 82.~ The arcuate windows are to allow optically transparent openings through the quartz disc to permit laser trimming of the signal plates within the transducer.
The windows 80 and 82 may be of any shape desired, but that illustrated is preferred for the particular embodiment shown in the drawings. The conductive pattern 76 and pattern 78 are electrically connected together by a wire jumper 75 connecting solder point 74 to solder point 84. The external ground shield substantially surrounds the outside of the transducer in a conductive pattern to shield it from interference and noiseO
Figure 7 illustrates a cross section of the transducer 26 wherein the layering of the device is clearly shown. The first layer comprises the conductive pattern 76 for the external shield which is supported by an insulative quartz substrate 86 in the shape oE a disc~ A common electrode 94 has been plated on the inner surface of the disc 86. Cutouts 93 and 95 are provided for easy access to the transducer terminals~ Similarly, a quartz disc 88 has an electrode 90 segmented into four ~, .
sd ~1~ -10-;
.
capacitor siynal plates disposed on its inner surface and the conductive pattern 78 plated on its outer surface. The two electrodes 90 and 94 oppose each other across a separation to form the Eour capacitors of the device. An annular frit 92 provides a separation or gap and a means for sealing the transducer 26 to a reference pressure. Generally, for accuracy it is desirable for -the chamber formed by the frit to ~e evacuated to a substantial vacuum~ Preferably, the frit is a vitreous material which has temperature expansion properties similar to the quartz disc~so In Figure 8 the elec-trode 90 is shown segmented into four separate signal plates for capacitors, Cs, Cr, Csf, Crf.
The segmentation of the electrode is provided by initiall~
screening or depositing a layer of conductive material on the quartz disc in a basic circular pattern with the associate terminals. A laser is then used to burn through the conductive pattern and separate the electrode into electricall~ continuous areas to form the plates in the shapes illustratedO These capacitor plates, when they oppose the common pla-te formed by the electrode 94r make wp the four capacitors of the transducer.
Each of the four are connected to their respective transducer terminals 46, 50~ 52, 54 by conductive paths. For example, the conductive paths 96~ 98~-100 and 102 connect terminals 46~ 50 52, and 54 to the segments labelled Crf, Csf, Cs~ and Cr, respectivelyO The terminal lead 4~ is elec-trically continuous with a conductive path 104 which surrounds each segment and separates each plate from the others. The conductive path 104 which is insulated from the capacitor plates comprises the internal ground shield and prevents self-interference between ~r sd~r., f~ -11-the segments by intercepting radiations from the adjacent plates and shunting them to ground.
The cutout 97 ls clearly shown in Figure 8 and provides for a facile connector to the common plate 94 and terminal 72 illustrated in Figure 9 With the configurations shown, each signal plate is separated from the common plate by a gap and forms a capacitor -therewith. The pressure versus capacitance characteristic for each signal capacitance is determined by the area of the signal plate, its shape, and its positioning with respect to the center of the quartz disc. The area of a signal plate determines the initial capaci-tance at a reference pressure and its shape and positioning determine the dynamic characteristic of the capacitor~
Since the quartz disc deflects a maximum distance at the center and proportionally less farther away from the center, a greater change in capacitance will be generated from those conductive areas which are most centrally located.
Generally, the segmeIlted signal plates of electrode 90 are formed by two regions. The first is a central inner region which is generally circular in shape and the second is an outer region which is generally ring shapedO The two pressure sensitive capacitors Csf and Cs~ because of the greater deflection of the quartz diaphragms toward the center, occupy the central region. Each of the pressure sensitive capacitors comprise relatively half of the central region except for the exact center where the pressure sensitive capacitor Cs includes a semicircular portion 106.
The ring of the outer region is generally divided into sd/`_i -12-' .
' .
two substantially equal area crescent-shaped portions which are the signal plates for reference capacitors Crf and Cr. Since ~he outer area is less deformable with pressure than the central region, the reference capacitors are relatively insensitive to pressure as compared to the pressure sensitive capacitors Csf and Cs.
How the actual capacitance of each of the capacitors Cs, Csf, Cr, and Cfr varies as a function oE pressure is illustrated in Figures 10 and 11.
It is seen that the pressure sensitive capacitors Cs, Csf have capacitance characteristic curves 100, 106 which increase as a function of pressure while the reference capacitors Cr, Csf have relatively insensitive pressure char-acteristic curves 102, 10~. The reference capacitor curves when subtracted from the pressure sensitive capacitor curves generate curves lO~, 110. The two curves 10~, 110 form the numerator and denominator, respectively, of the desired transfer function when the transducer 26 is connected in the measuring system shown in Figure l.
As was previously noted in Sell et al. the transfer function of the pressure measuring system in a steady state condition is equivalent to:
N Cs - Cr Nmax Csf - Crf For the desired compression of digital numbers at the lower pressure values of the system, N as a function of pressure should vary as the curve 21 shown in Figure 2. From inspection dN/dP is larger at the low end of the scale and becomes smaller with increasing pressure~ Therefore, proportionally more of the digital numbers are available for pressure resolution at -the low end of the scale. The initial difference ~point 112 of Figure ll) between the feedback capacitors Csf, Crf sets the maximum resolution of the system as it represents the smallest increment in feed-back current. The feedback increments thereafter become larger with increasing pressure according to the curve llO.
;~
sd~ -12A-1 7 6 ~ 7 llowever, to obta;n/increasing curve 21 ~ ~he transfer function, it is n~cessary to have the numerator Cs - Cr increase Faster for increasing pressures than the denominator CsF - Crf. This is accomplished by the ;urve 100 represelltative of Cs increasing faster for increasing pressures than curve 106 representative oP Csf. Return-ing to Figure 8 for a momsnt, it is the semicircular portion 106 of Cs that causes this action becaus~ of its extra area locat~d exactly at the center oF maximum deflection for the quartz dTsc. This e~fect is enhanced because of the cutout portion of Csf into which portion 106 lo protrudes. The radius oF the central portion 106 can be varied ~o con-trol this change.
Additionally, at manufacture, Cs and Csf should be substan-tially equivalent and Cr slTghtly larger than Crf. These values can bo produced by changing the radius of the cut s~parating the individual pl~tes on ~luar~ ~isc 88 and the arcuate extent of each.
After assembly, the reFerence capacitor Cr and Crf can be tlin~led by laser through the ground shield windows 80, 82 to provide the ~/~s~ ~c/
e*a~ curve 21 in Figure 2. At Pl, Cr will be trimmed such that Cs ~ Cr thereby giving the zero point For the system. At P2, Crf is trimmed such that Cs - Cr ~ Csf - Cr~F thereby providing ~he transFer function wi~h the valu~ o~ I at Cl so ~hat a ~ull scale pressure o~ P2 is repre-sented by ~he maxilllum di~ al number, Nmax.
Wllile Lhe pret~rred embodiment of the inventlon has been shown and described, it will be obvious co those skilled in the art that various modiFications and variations may be made thereto without departing From the spirit and scope o-F the inven~ion as hereinafter defined in the appended claims.
~ I
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A capacitive pressure transducer comprising:
a first substrate of insulative material;
a second substrate of insulative material;
at least one of said substates being flexible and deforming in response to a pressure change;
a first signal plate of electrically conductive material formed on a surface of said first substrate;
a second signal plate of electrically conductive material formed on said first substrate surface;
a third signal plate of electrically conductive material formed on said first substrate surface;
a fourth signal plate of electrically conductive material formed on said first substrate surface; and a fifth common plate of electrically conductive material formed on a surface of said second substrate;
said first and second substrates positioned from each other such that a gap exists between said plates on said first and second surfaces wherein first, second, third and fourth capacitors are formed between said first, second, third, and fourth plates and said fifth plate respectively, said fifth plate serving as a common plate for combining alternating excitation signals input to said signal plate into a single signal.
a first substrate of insulative material;
a second substrate of insulative material;
at least one of said substates being flexible and deforming in response to a pressure change;
a first signal plate of electrically conductive material formed on a surface of said first substrate;
a second signal plate of electrically conductive material formed on said first substrate surface;
a third signal plate of electrically conductive material formed on said first substrate surface;
a fourth signal plate of electrically conductive material formed on said first substrate surface; and a fifth common plate of electrically conductive material formed on a surface of said second substrate;
said first and second substrates positioned from each other such that a gap exists between said plates on said first and second surfaces wherein first, second, third and fourth capacitors are formed between said first, second, third, and fourth plates and said fifth plate respectively, said fifth plate serving as a common plate for combining alternating excitation signals input to said signal plate into a single signal.
2. A capacitive pressure transducer as described in claim 1, wherein:
at least one of said first and second substrates is composed of quartz.
at least one of said first and second substrates is composed of quartz.
3. A capacitive pressure transducer as described in claim 2, wherein:
said gap between the first and second substrates is sealed and referenced to a predetermined pressure.
said gap between the first and second substrates is sealed and referenced to a predetermined pressure.
4. A capacitive transducer as described in claim 1, wherein:
said first capacitor is pressure sensitive and varies as a function of movements of said one flexible substrate.
said first capacitor is pressure sensitive and varies as a function of movements of said one flexible substrate.
5. A capacitive transducer as described in claim 4, wherein.
said second capacitor is pressure sensitive and varies as a function of movements of said flexible substrate.
said second capacitor is pressure sensitive and varies as a function of movements of said flexible substrate.
6. A capacitive transducer as described in claim 5, wherein:
said third capacitor is relatively pressure insensitive.
said third capacitor is relatively pressure insensitive.
7. A capacitive transducer as described in claim 6, wherein:
said fourth capacitor is relatively pressure insensitive.
said fourth capacitor is relatively pressure insensitive.
8. A capacitive transducer as described in claim 7, wherein:
said first and second plates are disposed in a relatively flexible area of said flexible substrate.
said first and second plates are disposed in a relatively flexible area of said flexible substrate.
9. A capacitive transducer as described in claim 8, wherein.
said third and fourth plates are disposed in a relatively inflexible area of said flexible substrate.
said third and fourth plates are disposed in a relatively inflexible area of said flexible substrate.
10. A capacitive transducer as described in claim 7 wherein:
said first and second substrates are disc shaped and have circular faces opposing each other; and said first and second plates are disposed in a circular central region of the first substrate disc.
said first and second substrates are disc shaped and have circular faces opposing each other; and said first and second plates are disposed in a circular central region of the first substrate disc.
11. A capacitive transducer as described in claim 10, wherein:
said third and fourth plates are disposed around said central region in a ring-shaped peripheral region of the first substrate disc.
said third and fourth plates are disposed around said central region in a ring-shaped peripheral region of the first substrate disc.
12. A quartz capacitive transducer for the measurement of pressure having a first substrate of quartz and a second substrate of quartz separated by a gap wherein at least one of said substrates is flexible with respect to pressure and having conductive areas forming capacitor plates disposed on each of the substrates, said transducer characterized by:
at least one common plate disposed on one of the sub-strates for forming capacitors with four signal plates disposed on the other substrate, wherein said common plate combines the variations in capacitance of said signal plates.
at least one common plate disposed on one of the sub-strates for forming capacitors with four signal plates disposed on the other substrate, wherein said common plate combines the variations in capacitance of said signal plates.
13. A quartz capacitive transducer as defined in claim 12 which further includes:
a conductive ground shield, electrically connected to ground, disposed on said other substrate and insulatively separating said signal plates.
a conductive ground shield, electrically connected to ground, disposed on said other substrate and insulatively separating said signal plates.
14. A pressure transducer comprising:
a first quartz disc having a deformation characteristic substantially invariable with temperature;
a circular common plate disposed in the center of said first disc and formed of a conductive material;
means for electrically connecting said common plate to an output terminal;
a second quartz disc having a deformation characteristic substantially invariable with temperature;
four signal plates disposed on said second disc and formed of conductive material;
means for electrically connecting said signal plates to a plurality of input signal terminals, and an annular frit separating said first and second quartz discs and providing a chamber for a reference pressure;
said first and second discs deflecting with respect to changes in pressure such that the capacitances between at least one of the signal plates and said common plate vary;
means for inputting alternating excitation signals to said integral inputs whereby the output signals from said output terminal is the algebraic sum of the excitation signals modulated by the change in capacitance of the plurality of capacitors formed between said signal plates and said common plate.
a first quartz disc having a deformation characteristic substantially invariable with temperature;
a circular common plate disposed in the center of said first disc and formed of a conductive material;
means for electrically connecting said common plate to an output terminal;
a second quartz disc having a deformation characteristic substantially invariable with temperature;
four signal plates disposed on said second disc and formed of conductive material;
means for electrically connecting said signal plates to a plurality of input signal terminals, and an annular frit separating said first and second quartz discs and providing a chamber for a reference pressure;
said first and second discs deflecting with respect to changes in pressure such that the capacitances between at least one of the signal plates and said common plate vary;
means for inputting alternating excitation signals to said integral inputs whereby the output signals from said output terminal is the algebraic sum of the excitation signals modulated by the change in capacitance of the plurality of capacitors formed between said signal plates and said common plate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/247,482 US4422335A (en) | 1981-03-25 | 1981-03-25 | Pressure transducer |
| US247,482 | 1981-03-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1168887A true CA1168887A (en) | 1984-06-12 |
Family
ID=22935103
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000392054A Expired CA1168887A (en) | 1981-03-25 | 1981-12-11 | Pressure transducer |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4422335A (en) |
| EP (1) | EP0061359B1 (en) |
| JP (1) | JPS57169645A (en) |
| CA (1) | CA1168887A (en) |
| DE (1) | DE3263468D1 (en) |
Families Citing this family (88)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4532809A (en) * | 1981-10-05 | 1985-08-06 | Allied Corporation | Pressure measuring systems with increased accuracy for a constant resolution |
| US4422125A (en) * | 1982-05-21 | 1983-12-20 | The Bendix Corporation | Pressure transducer with an invariable reference capacitor |
| US4459856A (en) * | 1982-11-10 | 1984-07-17 | Case Western Reserve University | CMOS Bridge for capacitive pressure transducers |
| US4563906A (en) * | 1983-11-23 | 1986-01-14 | Camtech, Inc. | Load measurement apparatus including miniature instrumented hydrostatic cell |
| US4600836A (en) * | 1984-04-03 | 1986-07-15 | The Babcock & Wilcox Company | Diaphragm deflection sensor for fused silica diaphragm module |
| US4542436A (en) * | 1984-04-10 | 1985-09-17 | Johnson Service Company | Linearized capacitive pressure transducer |
| US4618856A (en) * | 1985-05-03 | 1986-10-21 | Allied Corporation | Stall surge detector |
| US4689999A (en) * | 1985-07-26 | 1987-09-01 | The Garrett Corporation | Temperature compensated pressure transducer |
| JPS62211533A (en) * | 1986-03-13 | 1987-09-17 | Yokogawa Electric Corp | Capacity type converting device |
| US4730496A (en) * | 1986-06-23 | 1988-03-15 | Rosemount Inc. | Capacitance pressure sensor |
| FI84401C (en) * | 1987-05-08 | 1991-11-25 | Vaisala Oy | CAPACITIVE TRYCKGIVARKONSTRUKTION. |
| US4864463A (en) * | 1988-04-19 | 1989-09-05 | Allied-Signal Inc. | Capacitive pressure sensor |
| US4971517A (en) * | 1988-12-27 | 1990-11-20 | Allied-Signal Inc. | Turbine blade clearance controller |
| DE9013959U1 (en) * | 1990-10-08 | 1990-12-13 | Leybold Ag, 6450 Hanau, De | |
| DE4031791A1 (en) * | 1990-10-08 | 1992-04-09 | Leybold Ag | CAPACITY GAUGE SENSOR |
| US5142921A (en) * | 1990-10-29 | 1992-09-01 | Litton Systems, Inc. | Force balance instrument with electrostatic charge control |
| DE4107345C2 (en) * | 1991-03-07 | 1995-12-07 | Fraunhofer Ges Forschung | Pressure measuring arrangement |
| US5224383A (en) * | 1991-06-14 | 1993-07-06 | Industrial Sensors, Inc. | Melt pressure measurement and the like |
| DE4142101A1 (en) * | 1991-11-28 | 1993-06-03 | Lueder Ernst Prof Dr Ing | PRESSURE MEASUREMENT ARRAY WITH HIGH LINEARITY |
| US5445031A (en) * | 1991-11-28 | 1995-08-29 | Endress+Hauser Gmbh+Co. | Pressure-measuring arrangement with high linearity |
| CH689131A5 (en) * | 1992-03-12 | 1998-10-15 | Verres Ind Sa | Warning device for monitoring a space defined at least partially by a surface barrier. |
| AU4637493A (en) * | 1992-08-10 | 1994-03-03 | Dow Deutschland Inc. | Process and device for monitoring vibrational excitation of an axial compressor |
| CA2142189A1 (en) * | 1992-08-10 | 1994-02-17 | Hilger A. Walter | Adaptor for mounting a pressure sensor to a gas turbine housing |
| WO1994003863A1 (en) * | 1992-08-10 | 1994-02-17 | Dow Deutschland Inc. | Process for detecting fouling of an axial compressor |
| EP0654161B1 (en) * | 1992-08-10 | 1999-06-16 | Dow Deutschland Inc. | Process and device for monitoring and for controlling of a compressor |
| JP2569293B2 (en) * | 1993-07-24 | 1997-01-08 | エンドレス ウント ハウザー ゲゼルシャフト ミット ベシュレンクテル ハフツング ウント コンパニー | Capacitive pressure sensor with high linearity |
| US5431065A (en) * | 1994-03-31 | 1995-07-11 | Panex Corporation | Multiple capacitor transducer |
| US5637802A (en) * | 1995-02-28 | 1997-06-10 | Rosemount Inc. | Capacitive pressure sensor for a pressure transmitted where electric field emanates substantially from back sides of plates |
| US6484585B1 (en) | 1995-02-28 | 2002-11-26 | Rosemount Inc. | Pressure sensor for a pressure transmitter |
| US5672808A (en) * | 1996-06-11 | 1997-09-30 | Moore Products Co. | Transducer having redundant pressure sensors |
| US5753820A (en) * | 1996-10-25 | 1998-05-19 | Arthur D. Little, Inc. | Fluid pressure sensing unit incorporating diaphragm deflection sensing array |
| US5954850A (en) * | 1996-11-22 | 1999-09-21 | Bernot; Anthony J. | Method for making glass pressure capacitance transducers in batch |
| SE9700613D0 (en) * | 1997-02-20 | 1997-02-20 | Cecap Ab | Sensor element with temperature measurement |
| US6324914B1 (en) | 1997-03-20 | 2001-12-04 | Alliedsignal, Inc. | Pressure sensor support base with cavity |
| US6058780A (en) * | 1997-03-20 | 2000-05-09 | Alliedsignal Inc. | Capacitive pressure sensor housing having a ceramic base |
| US6387318B1 (en) | 1997-12-05 | 2002-05-14 | Alliedsignal, Inc. | Glass-ceramic pressure sensor support base and its fabrication |
| US20040099061A1 (en) | 1997-12-22 | 2004-05-27 | Mks Instruments | Pressure sensor for detecting small pressure differences and low pressures |
| DE19847563A1 (en) * | 1998-04-17 | 1999-10-28 | Micronas Intermetall Gmbh | Capacitative sensor for pressure determination by deformation of a membrane causing a change in capacitance |
| US6508131B2 (en) | 1999-05-14 | 2003-01-21 | Rosemount Inc. | Process sensor module having a single ungrounded input/output conductor |
| US6295875B1 (en) | 1999-05-14 | 2001-10-02 | Rosemount Inc. | Process pressure measurement devices with improved error compensation |
| DE19946315C2 (en) * | 1999-09-28 | 2001-11-15 | Pharmaserv Marburg Gmbh & Co K | Conductivity sensor |
| US6508129B1 (en) | 2000-01-06 | 2003-01-21 | Rosemount Inc. | Pressure sensor capsule with improved isolation |
| US6561038B2 (en) | 2000-01-06 | 2003-05-13 | Rosemount Inc. | Sensor with fluid isolation barrier |
| US6505516B1 (en) | 2000-01-06 | 2003-01-14 | Rosemount Inc. | Capacitive pressure sensing with moving dielectric |
| US6520020B1 (en) | 2000-01-06 | 2003-02-18 | Rosemount Inc. | Method and apparatus for a direct bonded isolated pressure sensor |
| JP3620795B2 (en) | 2000-01-06 | 2005-02-16 | ローズマウント インコーポレイテッド | Grain growth in electrical interconnects for microelectromechanical systems. |
| US6698294B2 (en) * | 2000-09-07 | 2004-03-02 | Vega Grieshaber Kg | Pressure cell with temperature sensors and pressure measuring method |
| JP3346379B2 (en) * | 2000-09-21 | 2002-11-18 | 三菱電機株式会社 | Angular velocity sensor and manufacturing method thereof |
| US6516672B2 (en) | 2001-05-21 | 2003-02-11 | Rosemount Inc. | Sigma-delta analog to digital converter for capacitive pressure sensor and process transmitter |
| US6839546B2 (en) | 2002-04-22 | 2005-01-04 | Rosemount Inc. | Process transmitter with wireless communication link |
| US6848316B2 (en) | 2002-05-08 | 2005-02-01 | Rosemount Inc. | Pressure sensor assembly |
| US20060162435A1 (en) * | 2003-07-03 | 2006-07-27 | Jun Watanabe | Quartz type pressure sensor, and production method therefor |
| US8145180B2 (en) | 2004-05-21 | 2012-03-27 | Rosemount Inc. | Power generation for process devices |
| US8160535B2 (en) | 2004-06-28 | 2012-04-17 | Rosemount Inc. | RF adapter for field device |
| US7262693B2 (en) * | 2004-06-28 | 2007-08-28 | Rosemount Inc. | Process field device with radio frequency communication |
| US7560788B2 (en) * | 2004-09-20 | 2009-07-14 | General Electric Company | Microelectromechanical system pressure sensor and method for making and using |
| US7201057B2 (en) | 2004-09-30 | 2007-04-10 | Mks Instruments, Inc. | High-temperature reduced size manometer |
| US7141447B2 (en) | 2004-10-07 | 2006-11-28 | Mks Instruments, Inc. | Method of forming a seal between a housing and a diaphragm of a capacitance sensor |
| US7137301B2 (en) | 2004-10-07 | 2006-11-21 | Mks Instruments, Inc. | Method and apparatus for forming a reference pressure within a chamber of a capacitance sensor |
| US7680460B2 (en) | 2005-01-03 | 2010-03-16 | Rosemount Inc. | Wireless process field device diagnostics |
| US7204150B2 (en) | 2005-01-14 | 2007-04-17 | Mks Instruments, Inc. | Turbo sump for use with capacitive pressure sensor |
| US7334484B2 (en) * | 2005-05-27 | 2008-02-26 | Rosemount Inc. | Line pressure measurement using differential pressure sensor |
| US8452255B2 (en) | 2005-06-27 | 2013-05-28 | Rosemount Inc. | Field device with dynamically adjustable power consumption radio frequency communication |
| JP4752417B2 (en) * | 2005-09-16 | 2011-08-17 | パナソニック電工株式会社 | Sensor device |
| US7379792B2 (en) * | 2005-09-29 | 2008-05-27 | Rosemount Inc. | Pressure transmitter with acoustic pressure sensor |
| US7415886B2 (en) * | 2005-12-20 | 2008-08-26 | Rosemount Inc. | Pressure sensor with deflectable diaphragm |
| US7308830B2 (en) * | 2006-01-26 | 2007-12-18 | Rosemount Inc. | Pressure sensor fault detection |
| US8898036B2 (en) | 2007-08-06 | 2014-11-25 | Rosemount Inc. | Process variable transmitter with acceleration sensor |
| US7484416B1 (en) | 2007-10-15 | 2009-02-03 | Rosemount Inc. | Process control transmitter with vibration sensor |
| WO2009154748A2 (en) | 2008-06-17 | 2009-12-23 | Rosemount Inc. | Rf adapter for field device with low voltage intrinsic safety clamping |
| US8694060B2 (en) | 2008-06-17 | 2014-04-08 | Rosemount Inc. | Form factor and electromagnetic interference protection for process device wireless adapters |
| US8929948B2 (en) | 2008-06-17 | 2015-01-06 | Rosemount Inc. | Wireless communication adapter for field devices |
| US8847571B2 (en) | 2008-06-17 | 2014-09-30 | Rosemount Inc. | RF adapter for field device with variable voltage drop |
| US8049361B2 (en) | 2008-06-17 | 2011-11-01 | Rosemount Inc. | RF adapter for field device with loop current bypass |
| US7870791B2 (en) * | 2008-12-03 | 2011-01-18 | Rosemount Inc. | Method and apparatus for pressure measurement using quartz crystal |
| US8327713B2 (en) | 2008-12-03 | 2012-12-11 | Rosemount Inc. | Method and apparatus for pressure measurement using magnetic property |
| US7954383B2 (en) | 2008-12-03 | 2011-06-07 | Rosemount Inc. | Method and apparatus for pressure measurement using fill tube |
| US8626087B2 (en) | 2009-06-16 | 2014-01-07 | Rosemount Inc. | Wire harness for field devices used in a hazardous locations |
| US9674976B2 (en) | 2009-06-16 | 2017-06-06 | Rosemount Inc. | Wireless process communication adapter with improved encapsulation |
| US8429978B2 (en) | 2010-03-30 | 2013-04-30 | Rosemount Inc. | Resonant frequency based pressure sensor |
| JP5527015B2 (en) * | 2010-05-26 | 2014-06-18 | セイコーエプソン株式会社 | Element structure, inertial sensor, electronic equipment |
| US8234927B2 (en) | 2010-06-08 | 2012-08-07 | Rosemount Inc. | Differential pressure sensor with line pressure measurement |
| US8132464B2 (en) | 2010-07-12 | 2012-03-13 | Rosemount Inc. | Differential pressure transmitter with complimentary dual absolute pressure sensors |
| US10761524B2 (en) | 2010-08-12 | 2020-09-01 | Rosemount Inc. | Wireless adapter with process diagnostics |
| US9016133B2 (en) * | 2011-01-05 | 2015-04-28 | Nxp, B.V. | Pressure sensor with pressure-actuated switch |
| US9310794B2 (en) | 2011-10-27 | 2016-04-12 | Rosemount Inc. | Power supply for industrial process field device |
| US8752433B2 (en) | 2012-06-19 | 2014-06-17 | Rosemount Inc. | Differential pressure transmitter with pressure sensor |
| US9048901B2 (en) | 2013-03-15 | 2015-06-02 | Rosemount Inc. | Wireless interface within transmitter |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2172802A1 (en) * | 1972-02-22 | 1973-10-05 | Herve Marcel | |
| US3858097A (en) * | 1973-12-26 | 1974-12-31 | Bendix Corp | Pressure-sensing capacitor |
| US4064550A (en) * | 1976-03-22 | 1977-12-20 | Hewlett-Packard Company | High fidelity pressure transducer |
| JPS5329174A (en) * | 1976-08-30 | 1978-03-18 | Hewlett Packard Yokogawa | Device for detecting variation of capacitance |
| DK139644B (en) * | 1976-12-30 | 1979-03-19 | Nils Aage Juul Eilersen | Capacitive power meter. |
| US4152748A (en) * | 1977-05-05 | 1979-05-01 | Arkans Edward J | Multiple transducer |
| US4288835A (en) * | 1979-04-16 | 1981-09-08 | The Bendix Corporation | Pressure sensor |
| US4227419A (en) * | 1979-09-04 | 1980-10-14 | Kavlico Corporation | Capacitive pressure transducer |
| US4322977A (en) * | 1980-05-27 | 1982-04-06 | The Bendix Corporation | Pressure measuring system |
-
1981
- 1981-03-25 US US06/247,482 patent/US4422335A/en not_active Expired - Lifetime
- 1981-12-11 CA CA000392054A patent/CA1168887A/en not_active Expired
-
1982
- 1982-02-04 EP EP82400191A patent/EP0061359B1/en not_active Expired
- 1982-02-04 DE DE8282400191T patent/DE3263468D1/en not_active Expired
- 1982-03-23 JP JP57046158A patent/JPS57169645A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0526132B2 (en) | 1993-04-15 |
| US4422335A (en) | 1983-12-27 |
| JPS57169645A (en) | 1982-10-19 |
| EP0061359B1 (en) | 1985-05-15 |
| EP0061359A1 (en) | 1982-09-29 |
| DE3263468D1 (en) | 1985-06-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1168887A (en) | Pressure transducer | |
| US3952234A (en) | Pressure transducers | |
| CA1264419A (en) | Temperature compensated pressure transducer | |
| US4207604A (en) | Capacitive pressure transducer with cut out conductive plate | |
| US4562742A (en) | Capacitive pressure transducer | |
| US4295376A (en) | Force responsive transducer | |
| US4388668A (en) | Capacitive pressure transducer | |
| US4151578A (en) | Capacitive pressure transducer | |
| US4196632A (en) | Dual capacitance type bonded pressure transducer | |
| US4735098A (en) | Dual diaphragm differential pressure transducer | |
| US4336567A (en) | Differential pressure transducer | |
| CA1300925C (en) | Media isolated differential pressure sensors | |
| US4064550A (en) | High fidelity pressure transducer | |
| US4422125A (en) | Pressure transducer with an invariable reference capacitor | |
| US4358814A (en) | Capacitive pressure sensor | |
| US4542436A (en) | Linearized capacitive pressure transducer | |
| US4829826A (en) | Differential-pressure transducer | |
| US4864463A (en) | Capacitive pressure sensor | |
| US5396803A (en) | Dual balanced capacitance manometers for suppressing vibration effects | |
| US4628403A (en) | Capacitive detector for absolute pressure | |
| US5233875A (en) | Stable capacitive pressure transducer system | |
| US3965746A (en) | Pressure transducer | |
| US3479879A (en) | Manometer | |
| CA1239806A (en) | Capacitive sensing cell made of brittle material | |
| US4357834A (en) | Displacement converter |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |