CA2035909A1 - Measurement coupling for low capacitances - Google Patents
Measurement coupling for low capacitancesInfo
- Publication number
- CA2035909A1 CA2035909A1 CA002035909A CA2035909A CA2035909A1 CA 2035909 A1 CA2035909 A1 CA 2035909A1 CA 002035909 A CA002035909 A CA 002035909A CA 2035909 A CA2035909 A CA 2035909A CA 2035909 A1 CA2035909 A1 CA 2035909A1
- Authority
- CA
- Canada
- Prior art keywords
- measurement
- capacitances
- oscillator
- measured
- coupling
- 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.)
- Abandoned
Links
- 230000008878 coupling Effects 0.000 title claims abstract description 38
- 238000010168 coupling process Methods 0.000 title claims abstract description 38
- 238000005859 coupling reaction Methods 0.000 title claims abstract description 38
- 238000005259 measurement Methods 0.000 title claims abstract description 37
- 238000007600 charging Methods 0.000 claims abstract description 6
- 230000001681 protective effect Effects 0.000 claims 1
- 230000000694 effects Effects 0.000 description 3
- 239000003990 capacitor Substances 0.000 description 2
- 101150038444 Ment gene Proteins 0.000 description 1
- 210000004899 c-terminal region Anatomy 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 235000019988 mead Nutrition 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2605—Measuring capacitance
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Resistance Or Impedance (AREA)
Abstract
(57) Abstract Coupling for measurement of low capacitances (C1,C2,C3). The coupling comprises an oscil-lator, such as an LC or RC oscilllator, whose output frequency (fo) is a function of the capaci-tance to be measured and connected between the input terminal (16) of the oscillator and the ground. The capacitances (C1,C2,C3) to be meas-ured are connected alternatingly to the input terminal (16) of the oscillator. With the excep tion of the capacitance to be connected between the input terminal (16) of the oscillator and the ground for measurement, the other capacitances to be measured are connected, by one of their terminals, to a wire (19) common of the capaci-tances (C1,C2,C3) to be measured and, by the other one of their terminals, to the output of the voltage follower. The input of the voltage fol-lower is connected to the input terminal (16) of the oscillator coupling. The voltage follower consists of an operation amplifier (20), whose output is connected to its inverting input, to which the capacitances (C2,C3) that are not be-ing measured are connected so that there are no voltage differences and, consequently, no charg-ing currents in their terminals.
Description
;~ ~ 3 .~
Measurernent coupling for low capacitances 5 The invention concerns a coupling~for measurement of low capacitances, said coupling comprising an oscillator, such as an LC or RC oscillator, whose outpu~ frequency is a function of the capacitance to be measured and con-nected between the input terminal of the oscillator and the ground, the capaci-tances to be measured being connected alternatingly to the input terminal of 10 said oscillator.
In prior art, a number of dlfferent oscillator couplings are known which includea LC or RC circuit as a component affecting the frequency. In a way known in prior art, these oscillator couplings are used for measurement of capaci-15 tance, because7 by using the calculation formulas of each oscillator coupling,from the oscillator frequency it is possible to determine the capacitance when the values of the other components in the coupling are known.
In prior art, va~ious LC and RC oscillators are also known in which one 20 terminal of their capacitance C is connected to the ground. In the case of measurement of low capacitances, the latter couplings, however, involve the drawback and problem that various uncontrolled stray capacitances are con-nected in parallel with said capacitance C of the measurement oscillator, whereby the accuracy of measurement is impaired. ~hese problems are the 25 more extensive, the lower the capacitances that are measured.
The measurement of low capacitances is quite common in various detector techniques and in telemetry, e.g. in radiosondes, in which, for measurement of meteorological quantities, different capacitive detectors are used whose - 30 capacitance is relatively low, typically within the range of 1...100 pF. In~u~r~ respect with theseiprior-art measurement methods and couplings, reference is made to the following patents of the applicant: US 4,295,090, U~ 4,295,091, FI 54664, FI 57319.
3 ~
The object of the present invention is to avoid the drawbacks tbat have come 5 -out -above and to provide a measureme:nt oscillator- coupling that is well suitable for rneasurement of low capacitances and also for measurement arrangements in which a change-over switch is employed by whose means different detector capacitances and reference capacitances are connected to the input of the measurement oscillator alternatingly in a suitable measure-10 ment sequence.
An object of the present invention is to provide a measuremen~ oscillatorcoupling by whose means low capacitances, typically of an order of 0...100 pF, can be measured more accurately than in prior art, without disturbing effects 15 from stray capacitances and equivalent.
It is a particular object of the present invention to provide a measurement coupiing which is suitable for use in radiosondes in connection with capacitive detectors that measure meteorological quantities.
In view of achieving the objectives stated aboYe and those that will come out later, the invention is mainly characteri~ed in that, with the exception of the capacitance to be connected between the input 25 terminal of the oscillator and the ground for measurement, the other capaci-tances to be measured are connected, by one of their terminals, to a wire common of the capacitances to be measured and, by the other one of their terminals, to the output of the voltage follower, 30 that the input of said voltage follower~is connected to the input terminal of^- the oscillator coupling, and `:
.~ , ~ ' .
~i ~1~33~0~
that said voltage follower consists of an operation amplifier, whose output is connected to its inverting input, to which the capacitances that are not being measured are connected so that there are no voltage differences and, conse-quently, no charging currents in their terrninals.
According to the invention, when the input of the voltage follower, preferably the input of the operation amplifier, is connected to the terminals of the capacitances that are not being measured, the opposite terminals of these capacitances will be at the same potential, so that, in the coupling, no such 10 charging currents of said capacitances occur as could affect the output frequency of the measurement oscillator. In the coupling, various stray capacitances and DC leakage currents may occur within the scope of the properties of the operation amplifier or equi~alent acting as the voltage follower.
When the invention is applied, stray capacitances may also occur at the side of the common wire between the capacitances to be measured and the input of the measuremen~ oscillator. The effect of these stray capaçitances can be eliminated by on this wire employing a shield, which is connected to the output 20 of the voltage follower. In said shielding, it is in the other respects possible to apply the principles that are stated in the applicant's Fl Patent No. 57319.
As a rule, a coupling in accordance with the invention is optimal when the measurement oscillator is a sine-wave oscillator, because in such a case the ?5 requirement of speed of the voltage follower is lowest. The amplifier of the voltage follower must amplify sufficiently, because in the contrary case the amplitude remains lower at the output than it is at the input, and in such a case stray capacitances begin to have a detrimental effect on the accuracy of measurement.
-`
- ~ In the following, the invention will be described in~-dètail~ith reference to some exemplifying embo~iments of the invention illustrated in the figures in ~,03'~9~39 the drawing, the invention being by no means strictly confined ta the details of said embodiments.
Figure 1 shows a prior-art oscillator wiring which constitutes a starting point 5 of the present invention.
F`igure 2 shows a measurement oscillator wiring in accordance with the inven~
tionj by whose means three low capacitan,ces are measured, said capacitances being alternatingly connected to the input of the measurement oscillator.
In Fig. 1 a RC oscillator in itself known is shown, in which an inverter 10 thathas hysteresis is used. In respect of this coupling and of its application to the measurement of low capacitances and to sonde telemetry, reference is made to the applicant's Fl Patents Nos. 54,664 and 57,319 and to US Patents Nos.
15 4,295,090 and 4,295,091. At the input terminal 16 of the oscillator shown in Fig. 1 and, thus, at the C-terminals of the capacitor, in relation to the ground, a voltage Uo(t) 3s effective, whose wave forrn is drawn at Fig. 1.
The curve of the voltage Uo(t) is composed of the parts of the discharge and 20 charging curves of the capacitor C and of the stray capacitance CH connected in parallel with it, the time constant of said curve parts being to = l/R (C~CH)-From the output terminals 18 of the oscillator wiring shown in Fig. 1, a rectangular wave Ul(t) is obtained, whose frequency fO = I/T is a function of the capacitance C+CH connected between the input terminal 16 of the oscil-25 lator coupling and the ground.
As comes out from the above~ the stray capacitances CH have a direct effecton the output frequency fO of the oscillator coupling, which spoils the accuracy of measurement of low capacitances. These problems are accentuated further 30 if a prior-art change-over switch is placed at the input side of a coupling in accordance with Fig. ~1r ~by meaDs of which~ change-over switch the various capacitive detectors and reference capacitances are alternatingly connected to `
~e: 3.~09 the measurement oscillator, whose output frequency is a function fO = F(CM) of the capacitance CM to be measured.
Fig. 2 shows an example of a measurement coupling in accordance with the 5 invention, by whose means the problems described above are solved.
The coupling shown in Fig. 2 comprises the capacitances Cl ,Cz and C3, of which, for example; C1 is a precisely known reference capacitance and Cz and C3 are capacitances to be measured, being, for example, detectors that 10 measure the pressure (P), the temperature (T), and/or the relative humidity (U) in a radiosonde. One of the terminals of the capacitances Cl,C2 and C3 are connected together and, jointly by means of the wire 19, further to the input terminal 16 of the inverter 10. The opposite terminals of the capacitances Cl,C2 and C3 are connected to the switches 11,12 and 13. Said switches 11,12 15 and 13 have two positions, and in one of their positions tbe capacitances Cl,C2 and C3 are connected, by the intermediate of the contact 15, to the ground, and in the other one of the positions of the switches 11,12 and 13, the capaci-tances Cl,C2 and C3 are connected to the wire 21 or con~act, which is con-n~cted to the output terTninal of the operation amplifier 20, which acts as a 20 voltage follower. The * terrninal of the input of the voltage follower 20 is connected to the input terininal 16 of the inverter 10.
In accordance with the, in itself known, mode of coupling of the voltage follower, the output of the operation amplifier 20 is connected to the -25 terrninal of its input, which is illustrated by the wire 22. It is a part of theproperties of the voltage follower and of its operation amplifier 20 or an equivalent component that the input resistance of the voltage follower R~n ~
oo and the output resistance Rout ~ O in an ideal case. In such a case~ the output voltage of the voltage follower is U2 = UO.
According to ~ig.-;2,:-thetcapacitance Cj~ is-connected between the ground and the input terminal 16 of the inverter 10, in which case the output frequency of the measurement oscillator is Fo = F(C1). The capacitances C2 and C3 are connected, by the intermediate of the wires 14 and 21, to the output of the voltage follower 20, where the voltage U2 = UO prevails. Thus, at the terminals of the capacitances C2 and C3 there is no difference in voltage at all, so that 5 there are no charging currents at same.
The switches 11,1~ and 13 are controlled by a control unit 1~ so that one terminal of each capacitance Cl,C2 and ~C3 is, in its turn, connec~ed to the ground and, thus, to act upon the input of the measurement oscillator, at which 10 stage the other capacitances are connected between the + terminal of the input and the output of the voltage follower 20.
A stray capacitance may also occur at the side of the common wire 19 of the capacitances C1,C2,C3 to be measured. The effects of these stray capacitances 15 can be prevented by providing the wire 19 with a shield 19a, which is con-nected to the output of the voltage follower by means of a wire 23.
, Above, the invention has been described in relation to such an application only wherein a RC oscillator is used. Within the scope of the invention, it is, 20 however, possible to use any other suitable oscillator coupling in itself known, for example a LC oscillator, which is advantageous because of the good sine wave provided by it.
In the following, the patent claims will be given, and the various details of the ~5 invention rnay show variation within the scope of the inventive idea defined in said claims and differ from the details stated above for the sake of example only.
Measurernent coupling for low capacitances 5 The invention concerns a coupling~for measurement of low capacitances, said coupling comprising an oscillator, such as an LC or RC oscillator, whose outpu~ frequency is a function of the capacitance to be measured and con-nected between the input terminal of the oscillator and the ground, the capaci-tances to be measured being connected alternatingly to the input terminal of 10 said oscillator.
In prior art, a number of dlfferent oscillator couplings are known which includea LC or RC circuit as a component affecting the frequency. In a way known in prior art, these oscillator couplings are used for measurement of capaci-15 tance, because7 by using the calculation formulas of each oscillator coupling,from the oscillator frequency it is possible to determine the capacitance when the values of the other components in the coupling are known.
In prior art, va~ious LC and RC oscillators are also known in which one 20 terminal of their capacitance C is connected to the ground. In the case of measurement of low capacitances, the latter couplings, however, involve the drawback and problem that various uncontrolled stray capacitances are con-nected in parallel with said capacitance C of the measurement oscillator, whereby the accuracy of measurement is impaired. ~hese problems are the 25 more extensive, the lower the capacitances that are measured.
The measurement of low capacitances is quite common in various detector techniques and in telemetry, e.g. in radiosondes, in which, for measurement of meteorological quantities, different capacitive detectors are used whose - 30 capacitance is relatively low, typically within the range of 1...100 pF. In~u~r~ respect with theseiprior-art measurement methods and couplings, reference is made to the following patents of the applicant: US 4,295,090, U~ 4,295,091, FI 54664, FI 57319.
3 ~
The object of the present invention is to avoid the drawbacks tbat have come 5 -out -above and to provide a measureme:nt oscillator- coupling that is well suitable for rneasurement of low capacitances and also for measurement arrangements in which a change-over switch is employed by whose means different detector capacitances and reference capacitances are connected to the input of the measurement oscillator alternatingly in a suitable measure-10 ment sequence.
An object of the present invention is to provide a measuremen~ oscillatorcoupling by whose means low capacitances, typically of an order of 0...100 pF, can be measured more accurately than in prior art, without disturbing effects 15 from stray capacitances and equivalent.
It is a particular object of the present invention to provide a measurement coupiing which is suitable for use in radiosondes in connection with capacitive detectors that measure meteorological quantities.
In view of achieving the objectives stated aboYe and those that will come out later, the invention is mainly characteri~ed in that, with the exception of the capacitance to be connected between the input 25 terminal of the oscillator and the ground for measurement, the other capaci-tances to be measured are connected, by one of their terminals, to a wire common of the capacitances to be measured and, by the other one of their terminals, to the output of the voltage follower, 30 that the input of said voltage follower~is connected to the input terminal of^- the oscillator coupling, and `:
.~ , ~ ' .
~i ~1~33~0~
that said voltage follower consists of an operation amplifier, whose output is connected to its inverting input, to which the capacitances that are not being measured are connected so that there are no voltage differences and, conse-quently, no charging currents in their terrninals.
According to the invention, when the input of the voltage follower, preferably the input of the operation amplifier, is connected to the terminals of the capacitances that are not being measured, the opposite terminals of these capacitances will be at the same potential, so that, in the coupling, no such 10 charging currents of said capacitances occur as could affect the output frequency of the measurement oscillator. In the coupling, various stray capacitances and DC leakage currents may occur within the scope of the properties of the operation amplifier or equi~alent acting as the voltage follower.
When the invention is applied, stray capacitances may also occur at the side of the common wire between the capacitances to be measured and the input of the measuremen~ oscillator. The effect of these stray capaçitances can be eliminated by on this wire employing a shield, which is connected to the output 20 of the voltage follower. In said shielding, it is in the other respects possible to apply the principles that are stated in the applicant's Fl Patent No. 57319.
As a rule, a coupling in accordance with the invention is optimal when the measurement oscillator is a sine-wave oscillator, because in such a case the ?5 requirement of speed of the voltage follower is lowest. The amplifier of the voltage follower must amplify sufficiently, because in the contrary case the amplitude remains lower at the output than it is at the input, and in such a case stray capacitances begin to have a detrimental effect on the accuracy of measurement.
-`
- ~ In the following, the invention will be described in~-dètail~ith reference to some exemplifying embo~iments of the invention illustrated in the figures in ~,03'~9~39 the drawing, the invention being by no means strictly confined ta the details of said embodiments.
Figure 1 shows a prior-art oscillator wiring which constitutes a starting point 5 of the present invention.
F`igure 2 shows a measurement oscillator wiring in accordance with the inven~
tionj by whose means three low capacitan,ces are measured, said capacitances being alternatingly connected to the input of the measurement oscillator.
In Fig. 1 a RC oscillator in itself known is shown, in which an inverter 10 thathas hysteresis is used. In respect of this coupling and of its application to the measurement of low capacitances and to sonde telemetry, reference is made to the applicant's Fl Patents Nos. 54,664 and 57,319 and to US Patents Nos.
15 4,295,090 and 4,295,091. At the input terminal 16 of the oscillator shown in Fig. 1 and, thus, at the C-terminals of the capacitor, in relation to the ground, a voltage Uo(t) 3s effective, whose wave forrn is drawn at Fig. 1.
The curve of the voltage Uo(t) is composed of the parts of the discharge and 20 charging curves of the capacitor C and of the stray capacitance CH connected in parallel with it, the time constant of said curve parts being to = l/R (C~CH)-From the output terminals 18 of the oscillator wiring shown in Fig. 1, a rectangular wave Ul(t) is obtained, whose frequency fO = I/T is a function of the capacitance C+CH connected between the input terminal 16 of the oscil-25 lator coupling and the ground.
As comes out from the above~ the stray capacitances CH have a direct effecton the output frequency fO of the oscillator coupling, which spoils the accuracy of measurement of low capacitances. These problems are accentuated further 30 if a prior-art change-over switch is placed at the input side of a coupling in accordance with Fig. ~1r ~by meaDs of which~ change-over switch the various capacitive detectors and reference capacitances are alternatingly connected to `
~e: 3.~09 the measurement oscillator, whose output frequency is a function fO = F(CM) of the capacitance CM to be measured.
Fig. 2 shows an example of a measurement coupling in accordance with the 5 invention, by whose means the problems described above are solved.
The coupling shown in Fig. 2 comprises the capacitances Cl ,Cz and C3, of which, for example; C1 is a precisely known reference capacitance and Cz and C3 are capacitances to be measured, being, for example, detectors that 10 measure the pressure (P), the temperature (T), and/or the relative humidity (U) in a radiosonde. One of the terminals of the capacitances Cl,C2 and C3 are connected together and, jointly by means of the wire 19, further to the input terminal 16 of the inverter 10. The opposite terminals of the capacitances Cl,C2 and C3 are connected to the switches 11,12 and 13. Said switches 11,12 15 and 13 have two positions, and in one of their positions tbe capacitances Cl,C2 and C3 are connected, by the intermediate of the contact 15, to the ground, and in the other one of the positions of the switches 11,12 and 13, the capaci-tances Cl,C2 and C3 are connected to the wire 21 or con~act, which is con-n~cted to the output terTninal of the operation amplifier 20, which acts as a 20 voltage follower. The * terrninal of the input of the voltage follower 20 is connected to the input terininal 16 of the inverter 10.
In accordance with the, in itself known, mode of coupling of the voltage follower, the output of the operation amplifier 20 is connected to the -25 terrninal of its input, which is illustrated by the wire 22. It is a part of theproperties of the voltage follower and of its operation amplifier 20 or an equivalent component that the input resistance of the voltage follower R~n ~
oo and the output resistance Rout ~ O in an ideal case. In such a case~ the output voltage of the voltage follower is U2 = UO.
According to ~ig.-;2,:-thetcapacitance Cj~ is-connected between the ground and the input terminal 16 of the inverter 10, in which case the output frequency of the measurement oscillator is Fo = F(C1). The capacitances C2 and C3 are connected, by the intermediate of the wires 14 and 21, to the output of the voltage follower 20, where the voltage U2 = UO prevails. Thus, at the terminals of the capacitances C2 and C3 there is no difference in voltage at all, so that 5 there are no charging currents at same.
The switches 11,1~ and 13 are controlled by a control unit 1~ so that one terminal of each capacitance Cl,C2 and ~C3 is, in its turn, connec~ed to the ground and, thus, to act upon the input of the measurement oscillator, at which 10 stage the other capacitances are connected between the + terminal of the input and the output of the voltage follower 20.
A stray capacitance may also occur at the side of the common wire 19 of the capacitances C1,C2,C3 to be measured. The effects of these stray capacitances 15 can be prevented by providing the wire 19 with a shield 19a, which is con-nected to the output of the voltage follower by means of a wire 23.
, Above, the invention has been described in relation to such an application only wherein a RC oscillator is used. Within the scope of the invention, it is, 20 however, possible to use any other suitable oscillator coupling in itself known, for example a LC oscillator, which is advantageous because of the good sine wave provided by it.
In the following, the patent claims will be given, and the various details of the ~5 invention rnay show variation within the scope of the inventive idea defined in said claims and differ from the details stated above for the sake of example only.
Claims (8)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Coupling for measurement of low capacitances (C1,C2,C3), said coupling comprising an oscillator, such as an LC or RC oscillator, whose output frequency (f0) is a function of the capacitance to be measured and connected between the input terminal (16) of the oscillator and the ground, the capaci-tances (C1,C2,C3) to be measured being connected alternatingly to the input terminal (16) of said oscillator, c h a r a c t e r i z e d in that, with the exception of the capacitance to be connected between the input terminal (16) of the oscillator and the ground for measurement, the other capacitances to be measured are connected, by one of their terminals, to a wire (19) common of the capacitances (C1,C2,C3) to be measured and, by the other one of their terminals, to the output of the voltage follower, that the input of said voltage follower is connected to the input terminals (16)of the oscillator coupling, and that said voltage follower consists of an operation amplifier (20), whose outputis connected to its inverting input, to which the capacitances (C2,C3) that are not being measured are connected so that there are no voltage differences and, consequently, no charging currents in their terminals.
2. Measurement coupling as claimed in claim 1, c h a r a c t e r i z e d in that, for the time of the measurement, one electrode of the capacitance (C1) that is being measured is connected to the ground (15) by the intermediate of a connector switch (11).
3. Measurement coupling as claimed in claim 1 or 2, c h a r a c t e r i z e d in that, in the measurement-oscillator coupling, an inverting amplifier (10) that has hysteresis is employed, which is feed-back connected by a resistor (R).
. Measurement coupling as claimed in claim 1 or 2, c h a r a c t e r i z e d in that the measurement oscillator is a sine-wave oscillator.
5. Measurement coupling as claimed in claim 1 , c h a r a c -t e r i z e d in that the common wire (19) of the capacitances (C1,C2,C3) to be measured is provided with a shield (19a), for example with a protective sheath, which is connected to the output of the voltage follower (20).
6. Measurement coupling as claimed in claim 1 , c h a r a c -t e r i z e d in that the measurement coupling comprises two or more capaci-tances (C1,C2,C3) to be measured, at least one of which is a reference capaci-tance, whereas the others are detector capacitances to be measured.
7. Measurement coupling as claimed in claim 6, c h a r a c t e r i z e d in that the capacitances to be measured are capacitive detectors of a radiosonde which measure meteorological quantities, such as pressure (P), temperature (T), and/or relative humidity (U).
8. Measurement coupling as claimed the claim 1 , c h a r -a c t e r i z e d in that the capacitances to be measured are of an order of 0...100 pF.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI900592 | 1990-02-07 | ||
| FI900592A FI84666C (en) | 1990-02-07 | 1990-02-07 | MAETKOPPLING FOER SMAO KAPASITANSER. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2035909A1 true CA2035909A1 (en) | 1991-08-08 |
Family
ID=8529843
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002035909A Abandoned CA2035909A1 (en) | 1990-02-07 | 1991-02-07 | Measurement coupling for low capacitances |
Country Status (9)
| Country | Link |
|---|---|
| AU (1) | AU6949191A (en) |
| BR (1) | BR9100486A (en) |
| CA (1) | CA2035909A1 (en) |
| DE (1) | DE4103433A1 (en) |
| FI (1) | FI84666C (en) |
| FR (1) | FR2657963A1 (en) |
| GB (1) | GB2242279A (en) |
| IT (1) | IT1245137B (en) |
| ZA (1) | ZA91506B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19513022C1 (en) * | 1995-04-06 | 1996-08-14 | Siemens Ag | Differential capacitance measuring circuit for pressure sensor |
| DE19625666C1 (en) * | 1996-06-26 | 1998-01-15 | Siemens Ag | Readout shaft and capacitive measuring sensor |
| DE102004006020A1 (en) | 2004-02-06 | 2005-08-25 | E + E Elektronik Ges.M.B.H. | Circuit arrangement for capacitive humidity measurement and method for operating the same |
| US8030949B2 (en) * | 2008-10-31 | 2011-10-04 | Testo Ag | Measurement method for determining moisture content |
| CN101738422B (en) * | 2009-12-23 | 2012-09-05 | 北京宝力马传感技术有限公司 | Humidity measuring device and method |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3886447A (en) * | 1972-05-17 | 1975-05-27 | Iwatsu Electric Co Ltd | Capacitance-voltage converter |
| GB2058364B (en) * | 1979-09-01 | 1983-03-23 | Ferranti Ltd | Capacitance measuring apparatus |
| US4794320A (en) * | 1987-08-10 | 1988-12-27 | Moore Products Co. | Multi-frequency capacitance sensor |
-
1990
- 1990-02-07 FI FI900592A patent/FI84666C/en not_active IP Right Cessation
-
1991
- 1991-01-21 AU AU69491/91A patent/AU6949191A/en not_active Abandoned
- 1991-01-23 ZA ZA91506A patent/ZA91506B/en unknown
- 1991-01-29 GB GB9101869A patent/GB2242279A/en not_active Withdrawn
- 1991-02-05 DE DE4103433A patent/DE4103433A1/en not_active Ceased
- 1991-02-06 IT ITMI910300A patent/IT1245137B/en active IP Right Grant
- 1991-02-06 BR BR919100486A patent/BR9100486A/en not_active Application Discontinuation
- 1991-02-07 CA CA002035909A patent/CA2035909A1/en not_active Abandoned
- 1991-02-07 FR FR9101380A patent/FR2657963A1/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FI900592A (en) | 1991-08-08 |
| GB2242279A (en) | 1991-09-25 |
| FR2657963A1 (en) | 1991-08-09 |
| GB9101869D0 (en) | 1991-03-13 |
| FI900592A0 (en) | 1990-02-07 |
| DE4103433A1 (en) | 1991-08-08 |
| FI84666B (en) | 1991-09-13 |
| FI84666C (en) | 1991-12-27 |
| IT1245137B (en) | 1994-09-13 |
| AU6949191A (en) | 1991-08-08 |
| ITMI910300A0 (en) | 1991-02-06 |
| ITMI910300A1 (en) | 1992-08-06 |
| ZA91506B (en) | 1991-10-30 |
| BR9100486A (en) | 1991-10-29 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Toth et al. | A low-cost, smart capacitive position sensor | |
| US6992492B2 (en) | Capacitive sensor | |
| US4924172A (en) | Capacitive sensor and electronic circuit for non-contact distance measurement | |
| KR100379622B1 (en) | Static capacitance-to-voltage converter and converting method | |
| US4206401A (en) | Length measuring system | |
| US4918376A (en) | A.C. capacitive gauging system | |
| US3753373A (en) | Transducer system | |
| Kuenen et al. | Measurement of dielectric absorption of capacitors and analysis of its effects on VCOs | |
| EP0166706B1 (en) | Method for the measurement of capacitances, in particular of low capacitances | |
| CA2035909A1 (en) | Measurement coupling for low capacitances | |
| KR100341966B1 (en) | Impedance-to-voltage converter and converting method | |
| Bertone et al. | Investigation of a capacitance-based displacement transducer | |
| US5156045A (en) | Method related to impedance detectors in radiosondes | |
| US4167697A (en) | Capacitive pick-off circuit | |
| JPH02156103A (en) | Inspection machine for wall thickness of glass vessel | |
| JPH02156102A (en) | Inspection machine for wall thickness of glass vessel | |
| Barrie | Measurement of very low dielectric losses at radio frequencies | |
| SU1767451A1 (en) | Metering transducer with capacity sensor | |
| EP1077367A4 (en) | Capacitive force gauge | |
| GB1569977A (en) | Level sensing | |
| Ansari et al. | A novel direct reading active-RC system for measurements of in-circuit, discrete, and incremental capacitances | |
| Ghidini et al. | A 15 ppm resolution measurement system for capacitance transducers | |
| SU938118A1 (en) | Device for measuring conductive material dielectric permeability | |
| Toth et al. | A low-cost, accurate and fast capacitive displacement sensor with microcontroller interfacing | |
| RU2034288C1 (en) | Meter of grain moisture |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |