CA1262372A - Method for the measurement of capacitances, in particular of low capacitances, wherein two references are used - Google Patents
Method for the measurement of capacitances, in particular of low capacitances, wherein two references are usedInfo
- Publication number
- CA1262372A CA1262372A CA000482808A CA482808A CA1262372A CA 1262372 A CA1262372 A CA 1262372A CA 000482808 A CA000482808 A CA 000482808A CA 482808 A CA482808 A CA 482808A CA 1262372 A CA1262372 A CA 1262372A
- Authority
- CA
- Canada
- Prior art keywords
- measurement
- signals
- capacitances
- circuit
- capacitance
- 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
- 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)
- Transmission And Conversion Of Sensor Element Output (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method for the measurement of capacitances, in par-ticular of low capacitances, utilizes measurement electronics which includes a measurement oscillator whose output frequency is a function of the capacitance to be connected to the input termi-nals of a circuit determining the frequency of such oscillator.
In the method, two reference capacitances are used, whose elec-trical values are placed within the range of measurement and which are connected, being alternately exchanged with the capaci-tance or capacitances to be measured, to the measurement oscilla-tor while making use of a switching arrangement. Two external auxiliary references are used in the method. The auxiliary ref-erence signals obtained from the auxiliary references are com-pared with the corresponding output signals of the measurement electronics, derived from the reference capacitances. Signals representing the differences between the output signals and the signals coming from the external auxiliary references are formed.
Feedback signals controlling the measurement electronics circuit are formed from the signals. The measurement electronics is con-trolled by the feedback signals in such a direction that the dif-ferential signals approach zero or a preset corresponding value.
The output signal corresponding to the capacitance to be measured is determined by the measurement electronics adjusted correctly.
The object is to provide a more precise method as well as such a two-reference measurement method and measurement circuit in which complicated computation operations are avoided. The output vari-ables corresponding to the reference detectors remain unchanged, even if the measurement electronics should creep. Such a circuit may be used in the telemetry of radiosondes in the measurement of atmospheric pressure, temperature and/or humidity.
A method for the measurement of capacitances, in par-ticular of low capacitances, utilizes measurement electronics which includes a measurement oscillator whose output frequency is a function of the capacitance to be connected to the input termi-nals of a circuit determining the frequency of such oscillator.
In the method, two reference capacitances are used, whose elec-trical values are placed within the range of measurement and which are connected, being alternately exchanged with the capaci-tance or capacitances to be measured, to the measurement oscilla-tor while making use of a switching arrangement. Two external auxiliary references are used in the method. The auxiliary ref-erence signals obtained from the auxiliary references are com-pared with the corresponding output signals of the measurement electronics, derived from the reference capacitances. Signals representing the differences between the output signals and the signals coming from the external auxiliary references are formed.
Feedback signals controlling the measurement electronics circuit are formed from the signals. The measurement electronics is con-trolled by the feedback signals in such a direction that the dif-ferential signals approach zero or a preset corresponding value.
The output signal corresponding to the capacitance to be measured is determined by the measurement electronics adjusted correctly.
The object is to provide a more precise method as well as such a two-reference measurement method and measurement circuit in which complicated computation operations are avoided. The output vari-ables corresponding to the reference detectors remain unchanged, even if the measurement electronics should creep. Such a circuit may be used in the telemetry of radiosondes in the measurement of atmospheric pressure, temperature and/or humidity.
Description
~6Z3 ~
The present invention relates to a method for the mea-surement of capacitances. More particularly, the invention relates to a me-thod for the measurement of low capacitances, in which method measurement electronics is used. The measurement electronics includes a measurement oscillator, whose output fre-quency is a func-tion of the capacitance to be connec-ted to the input terminals of the circui.t determining the frequency of said oscillator. The method utilizes two reference capacitances whose electrical values are placed within the range of measurement and which are connected, being alternatingly exchanged with the capacitance or capacitances to be measured, to the measurement oscillator via a switching arrangement.
One starting point of the present invention is the prior art technology, for example, from applicant's Finnish Patents Nos . 54, 664 and 57, 319, corresponding to United States Patents Nos . 4, 295, 090 and 4, 295,091, respec-tively. These patents disclose a method for the measurement of low capaci-tances, as well as an electronic changeover switch to be used in this connec-tion, in particular for telemeter use in sondes.
Capacitive detectors are used in radiosondes, for the measurement of various parameters, in particular of atmospheric pressure, temperature and/or humidity. The magnitude of the capacitances of the detectors depends on the parameter being mea-sured. The capacitance of these detectors are often relatively low, from a few pF to some dozens or, at the maximum, about 100 pF. The measurement of low capacitance is problematic, for example, due to stray capacitance, variations in supply voltage, and other disturbances. Furthermore, the detectors have to some extent varying properties, so that they have, for example, indi-vidual non-linearity and dependence on temperature.
i In telemeter applications, in particular, when, for example, temperature, humidity or pressure or other, correspond-ing parameters are measured by electric or electromechanical v 3~7~
detectors, i-t is known in the prior art, in connection with the measurement electronics, to provide one or several references which are stable and precisely known and by means of which it is possible to compensate for individual properties of -the measure-ment circuit and/or of -the detector, as well as their variations in time.
In connec-tion with capacitive de-tectors, it is known in prior art to use a reference capacitance, which is, alternatingly with the measuring capaci-tance, connected to the measurement cir-cuit, usually the input circuit determining -the frequency of -the RC-oscilla-tor. By appropriately adjus-ting the measurement cir-cuit or in some other way, the outpu~ variable of the measurement circuit, derived from -the reference capacitance, can be brought to the correct level at each particular time.
It is known in the prior art to use measurement cir-cuits o~
i one reference, in par-ticular bridge connections, in which the measurement is, however, precise only when the electrical value of the reference is close to the value of the detector, e.g., when the bridge is in equilibrium. The more distant the value of the detector is from the reference, the greater will be the various errors, for example, errors caused by changes in the dynamics of the electronic measurement circuit. An advantage of connections with one reference is, however, the simplicity of the measurement circuit. This prior art method is described hereinafter in greater detail with reference to Fig. 1.
As advantage in measurement arrangements with two or more references is accuracy of the measurement, even within wide ranges of measurement. A drawback, however, is the com-plexity of the measurement method and the related computation.
The method of measurement with two references is described hereinafter in greater detail with reference to Fig. 2.
The invention further develops the measurement meth-ods and circuits for low capacitances, for example, about 0 to20 100 pF, applied by the inventor and known in the prior art, so that said methods and circuits become more precise.
The present invention also provides a measurement method and measurement circuit with two references in which complicated computation operations, necessary in determining the results of capacitance measurements in the prior art, are avoided.
The invention again provides a measurement method and "self-adjusting~ measurement electronics in which the out-put variables corresponding to the reference detectors remain30 invariable even if the ~measurement electronics should creep, for example, due to variations in temperature or other circum-stances.
~Z~37~
According to one aspect of the present invention -there is provided a method for the measurement of capaci-tances, particularly low capacitances, said method utilizing measurement electronics including switching means and a mea-surement oscillator having an output frequency which is a function of the capacitance to be connected to the input ter-minals of a measuring circuit determining the frequency of said oscillator, said method further utilizing two external auxiliary references providing auxiliary reference signals, and two reference capacitances having electrical values placed within the range of measurement, said reference capacitances and a capacitance to be measured being alternately connected to said oscillator via said switching means, said method com-prising the steps of comparing the auxiliary reference signals from said two external auxiliary references with the corre-sponding output signals of said measurement electronics, derived from said reference capacitances; forming differential signals representing the differences between said output sig-nals and said auxiliary reference signals from said external auxiliary references; forming feedback signals from said dif-ferential signals; controlling said measurement electronics circuit by said feedback signals in such a direction that said differential signals approach zero or a preset corresponding value; and deter~ining the output signals corresponding to the capacitance to be measured via said measurement electronics, when said measurement electronics is so adjusted.
Thus according to the method of the present inven-tion two external auxiliary references are used. The auxil-iary reference signals obtained from the external auxiliary references are compared with the corresponding output signals of the measurement elect~onics, derived from the reference capacitances. Differential signals representing the differ-~ 23~'~
ences between the output signals and the signals from theexternal auxiliary references are formed. The differential signals form feed'oack signals for controlling the circuit.
The measurement electronics is controlled by the feedback sig-nals in such a direction that the differential signals, or equivalent, approach zero or a preset corresponding value.
The measurement electronics determines the output signal cor-responding to the capacitance to be measured when said mea-surement elec-tronics is adjusted correctly by means of the foregoing method steps.
In accordance with the invention there is fitted in the measurement circuit external auxiliary references corre-sponding to the output variables obtained in response to the capacitance references proper. The auxiliary references are stable and independent from the measurement electronics and from its creep, as well as from various interference sources.
The variables obtained from the auxiliary references are com-pared with the output variables derived from the capacitance references proper, and differential signals are formed on the basis of said references. The differential signals are per-mitted, on one hand, to act in the manner of a constant term upon the measurement electronics and, on the other hand, to act upon the steepness of the measurement electronics summ-ingly during so many measurement cycles as a sort or iteration process, so that the difference between the capacitance refer-ence and the external reference becomes zero or sufficiently close to zero.
The comparison preferably occurs so that the differ-ential signal derived from the first external auxiliary refer-ence and from the first capacitance reference is made to actupon the measurement ele~tronics in the manner of a constant term. In other words, the differential signal is made to act ' ?~
~, i?
upon the offset of the measurement electronics. The differen-tial signal derived from the second external auxiliary refer-ence and from the second capacitance reference is, in the aforedescribed manner, made to act upon the steepness, for example, the amplification of the measurement electronics. If the measurement circuit or measurement method has an output variable which is a variable frequency, one of the differen-tial signals is made to act upon the basic frequency of the measurement electronics and the other differential signal is made to act upon its dynamics, that is, upon the change in frequency per a certain unit of change in capacitance.
In one embodiment of the method of the present invention said differential signals are formed during a plu-rality of so many measurement cycles that said differential signals can be made stepwise to approach zero or to become close enough to zero, whereupon the corresponding output vari-able of said capacitance to be measured is determined. Suit-ably the method further utilizes a first comparator and a sec-ond comparator, said method further comprising the steps of controlling a constant term or o*fset of said measurement electronics via a control signal formed in said first compara-tor on the basis of one differential signal, controlling the steepness or amplification of said measurement electronics via a control signal obtained from said second comparator on the basis of the other said differential signal, and summingly adjusting during so many measurement cycles as an iteration process that the variables indicating the difference between said reference capacitances and said external auxiliary re*er-ences are made equal to zero or to a preset constant. Desir-ably said switching means includes an electronic changeoverswitch, a control circui~ controlling said changeover switch and a clock controlling said control circui-t, said method fur-- 5a -ther comprising alternately connecting said capacitance to be measured and both said reference capacitances to said oscilla-tor via said changeover switch and deriving first and second control signals from said control circuit for controlling said first comparator via said first control signal and controlling said second comparator via said second control signal.
Preferably the method further utilizes a pair of frequency dividers and a plurality of gates, said method further com-prising providing a basic measurement frequency of about 100 kHz and lowering said basic measurement frequency via saidfrequency dividers to such a low level that delays and changes in said gates do not interfere with the measurement result.
More desirably the method further comprises providing a DC
voltage output signal. Suitably the method further comprises providing an output signal which is a frequency burst having a frequency containing information of the magnitude of said capacitance to be measured. Preferably the method further comprises determining the number of pulses in said frequency burst and utilizing the result of said determination as a mea-sure of said capacitance to be measured. Suitably the methodfurther comprises deducting the number of pulses corresponding to the value of one of the references from the number of pulses in said frequency burst, and utilizing the result of said deduction to determine said capacitance to be measured.
In a further aspect thereof the present invention provides a method for the measurement of capacitances, parti-cularly low capacitances, in telemetry of radiosondes for the measurement of atmospheric pressure, temperature and~or humid-ity, said method utilizing measurement electronics including switching means and a measurement oscillator having an outputfrequency which is a function of the capacitance to be con-nected to the input terminals of a measuring circuit determin-- 5b -ing the frequency of said oscillator, said method further uti-lizing two external auxiliary references providing auxiliary reference signals and two reference capacitances, having elec-trical values placed within the range of measurement, said reference capacitances and a capacitance to be measured being alternately connected to said oscillator via said switching means, said method comprising the steps of comparing the aux-iliary reference signals from said two external auxiliary ref-erences with the corresponding output signals of said measure-ment electronics, derived from said reference capacitances;forming differential signals representing the differences between said output signals and said auxiliary reference sig-nals from said external auxiliary references; forming feedback signals from said differential signals; controlling said mea-surement electronics circuit by said feedback signals in such a direction that said differential signals or equivalent approach zero or a preset corresponding value; and determining the output signals corresponding to the capacitance to be mea-sured via said measurement electronlcs, when said measurement electronic is adjusted correctly via the foregoing method steps.
The present invention also provides a circuit for the measurement of capacitances, particularly low capaci-tances, said circuit comprising measurement electronics including switching means and a measurement oscillator having an oukput frequency which is a function of the capacitance to be connected to the input terminals of a measuring circuit determining the frequency of said oscillator; two external auxiliary references providing auxiliary reference signals;
two reference capacitances having electrical values placed within the range of meas~rement, said reference capacitances and a capacitance to be measured being alternately connected -- ~;c --3 ~'~
to said oscillator via said switching means, said auxiliary reference signals from said two external auxiliary references being compared with the correspondi.ng output signals of said measurement electronics, derived from said reference capaci-tances, differential signals representing the differences between said output signals and said auxiliary reference sig-nals from said external auxiliary references being formed, feedback signals being formed from said differential signals and controlling said measurement electronics circuit in such a direction that said differential signals approach zero or pre-set corresponding value, said measurement electronics deter-mining the output signals corresponding to the capacitance to be measured when said measurement electronics is so adjusted.
- 5d -~2~
The present invention will be further illus-trated by way of the accompanying drawings, in which:-Fig. 1 is a graphical presentation of the characteris-tic curves (straigh-t lines) of a single-reference measurement method in a system of xy-coordinates;
Fig. 2 is a graphical presentation of the characteris-tic curves of a two-reference measurement system, in a manner corresponding to Fig. l;
Fig. 3 is a block diagram of an embodiment of the cir-cuit of the invention for undertaking the measurement method of the invention; and Fig. 4 is a circuit diagram of an embodiment of the measurement eiec-tronics circuit of the clrcuit of Fig. 3.
Fig. 1 illustrates a single-reference measurement method in a system of xy-coordinates. By means of a reference, which is, for example, a capacitance whose electrical value is at the middle of the range Xl of measurement, a point xOyO is fixed, through which the straight line ko illustrating the measurement electronics runs. The coordinate x stands for -the input vari-able, that is, in the present case, the magnitude of the capaci-tance to be measured, and y stands for the outpu-t variable, that is, in the presen-t case, for example, a DC voltage or a variable frequency. However, due to the creeping of the measurement elec-tronics and to other circumstances, the straight line illustrat-ing the properties of the system diverges from the basic straightline ko between the example lines kl and k2 shown by dashed lines and dot-dashed lines, respectively. Thereby, within the permit-ted margins of error, the measurement range Xl around xO becomes relatively narrow.
In a corresponding manner, FigO 2 illustrates a two-~2~37%
reference measurement method, which is the starting point of thepresent inven-tion, in a manner corresponding to Fig. 1. In the method of Fig. 2, two references 1 and 2 are applied. These ref-erences fix two points in the system of xy-coordinates. These are the points xlyl and x2,y2. The straigh-t line ko placed through these points is the linear basic opera-tion ine of the system. In practice, due to changes in temperature or to other circumstances, the characteristic curves of the system vary on both sides of the straight line ko between the curves ~1 and f2.
Thereby, within the margins of error, it is possible to accom-plish a range of measurement X2, which is greater than x2-xl.
Thus, as compared with the single-reference measurement method, a range of measurement X2 can be accomplished which is greater by at least one order.
It is possible, by the method of the invention here-inafter described in greater detail, to eliminate the complicated computation operations required in the prior art in connection with a measurement circuit of two references. Thus, the present invention provides an advantageous measurement method and mea-surement circuit which may be carried into effect or practiced quite simply readily. An exemplifying embodiment of the circuit of the invention is described with reference to Fig.s 3 and 4.
The system of Fig. 3 comprises a capacitance (CM) 12 to be measured and two reference capacitances 10 and 11 (CRl and CR2). The values between the reference capacitances 10 and 11 correspond to the points xl and x2 shown in Fig. 2, between which said points, and even outside them, the measurement range X2 extends. The measurement circuit includes an electronic changeover switch 13 having a control circuit 15, which, in turn, is controlled by a clock 14. Under the control of the control signals a,rl,r2 fro,m the control circuit 15, the changeoYer switch 13 connects the capacitance CM to ~e measured and the ref-erence capacitances CRl and CR2 alternatingly to the measurementelectronics 16.
.~ :
3 ~'~
In a known manner, the measurement electronics 16 includes, for example, an RC oscillator, the capacitance to be measured, which is as a rule within the range of 0 to 100 pF, and the reference capacitances, alternatingly connected to the input circuit which determines the frequency of said oscillator. The measurement electronics 16 also includes frequency dividers and other known switchin~ arrangements, so that the measurement elec-tronics produces an output variable such as, Eor example, a DC
voltage or a frequency which varies substantially linearly on the basis of the electrical value of the capaci-tance CM.
It is assumed that the output variable of the measure-ment electronics 16 is a voltage Ul The voltage Ul is passed to the first comparison circuit 19 and to the second comparison cir-cuit 20. In accordance with the invention, two external auxil-iary reference circuits 17 and 18 are used in the measurement circuit and method. The reference circuits 17 and 1~ provide, for example, DC voltages URl and UR2, each of which is passed to a corresponding one of the comparlson circuits 19 and 20. The differential voltages Ul and U2 of the external auxiliary refer-ence voltages URl and UR2 and of the output voltage Ul of the measurement electronics are input voltages of th0 comparison cir-cuits 19 and 20. The comparison circuits 19 and 20 are con-trolled by the control pulse sequences rl and r2 from the control circuit 15 of the changeover switch 13. Thus, output voltages Ucl and Uc2 are obtained from the comparison circults 19 and 20.
The measurement electronics 16 is controlled by the output volt-ages Ucl and Uc2 via the RC circuits 21 and 22 (low pass fil-ters).
The inventlon is preferably accomplished so that the first control signal Ucl acts, in the manner of a constant term, upon the measurement electronics 16, that is, on the so-called offset of said measurement electronics. The second control sig-nals Uc2 again acts upon the steepness, for example, the ampli-tude o~ the measurement electronics.
37~
The control signals ~cl and Uc2 affect the measurement electronics in such a direction that the differential voltages U
and U2 are reduced stepwise, and the feedback effect is repeated, for example, as controlled by the control circuit 15 of the Ghangeover switch, for the duration of so many measurement cycles that said differential voltages can be made to approach zero stepwise. ~fter the differential voltages Ul and U2 have been brought sufficiently close to the zero point, the measurement electronics 16 has been adjusted "correctly". The changeover switch 13 is then controlled by the control circuit 15 to connect the capacitance 1~ to be measured to the measurement electronics.
At the same time, the control circuit 15 controls a holding element 23, or another, corresponding component, so that the output signal U1 of the measurement electronics 16 is con-nected, as such, or as appropriately scaled, so as to provide the outlet sig~al Uout ~ig. 4 shows a circuit diagram of an embodiment of the measurement electrdnics for low capacitance detectors (o to 100 pF). The measurement frequency is about 100 k~z, which frequency is not processed as such, but is divided by frequency dividers 25 and 26 to a sufficient extent to a lower frequency in order to prevent delays in gates and other components and the changes therein from affecting thé measurement result. A multicap cir-cuit 27, which is an essential part in the circuit and is a patented special circuit expressly for measurement by capacitive detectors, is described in the aforementioned Finnish Patents Nos. 57,664 and 57,319, corresponding to United 5tates Patents Nos. 4,295,090 and 4,295,091, respectively. The variable being examined is time. The auxiliary reference is a time obtained from the crystal oscillator 24 and further from the pin 3 of the frequency divider microcircuit 25 (4024). The zeroing occurs a little later (pins 3 and 6 are ones~. A second auxiliary refer-ence is not needed, because a different division number has been taken from the other frequency divider microcircuit 26 (4040) via ..~..
the references CRl and CR2.
The comparison of the time differences is carried out by gates 31 and 32. Gates 33 and 34 assure that the correction currents may ac-t upon the voltages of the capacitors Cl of 47 nF
only when the references CR1 and CR2 are being measured. The output signal UOUt is, in the circuit of Fig. 4, a frequency burst, whose frequency contains the information on the electrical magnitude of the detector capacitance CM to be measured. The output may also be connected in the same manner as with the ref-erences CRl and CR2, whereby a pulse is obtained whose width (duration of half cycle) contains information of the electrical value of the detector capacitance.
The circui-t o-f Fig. 4 permits the calculation of the number of pulses in the frequency burst or, with minor modifica--tions, a burst is obtained from which the number of pulses cor-responding to the value of one of the references CRl and CR2 is derived. The latter alternative embodimen-ts do not require a crystal oscillator, because the pulse numbers are abstract num-bers.
... _
The present invention relates to a method for the mea-surement of capacitances. More particularly, the invention relates to a me-thod for the measurement of low capacitances, in which method measurement electronics is used. The measurement electronics includes a measurement oscillator, whose output fre-quency is a func-tion of the capacitance to be connec-ted to the input terminals of the circui.t determining the frequency of said oscillator. The method utilizes two reference capacitances whose electrical values are placed within the range of measurement and which are connected, being alternatingly exchanged with the capacitance or capacitances to be measured, to the measurement oscillator via a switching arrangement.
One starting point of the present invention is the prior art technology, for example, from applicant's Finnish Patents Nos . 54, 664 and 57, 319, corresponding to United States Patents Nos . 4, 295, 090 and 4, 295,091, respec-tively. These patents disclose a method for the measurement of low capaci-tances, as well as an electronic changeover switch to be used in this connec-tion, in particular for telemeter use in sondes.
Capacitive detectors are used in radiosondes, for the measurement of various parameters, in particular of atmospheric pressure, temperature and/or humidity. The magnitude of the capacitances of the detectors depends on the parameter being mea-sured. The capacitance of these detectors are often relatively low, from a few pF to some dozens or, at the maximum, about 100 pF. The measurement of low capacitance is problematic, for example, due to stray capacitance, variations in supply voltage, and other disturbances. Furthermore, the detectors have to some extent varying properties, so that they have, for example, indi-vidual non-linearity and dependence on temperature.
i In telemeter applications, in particular, when, for example, temperature, humidity or pressure or other, correspond-ing parameters are measured by electric or electromechanical v 3~7~
detectors, i-t is known in the prior art, in connection with the measurement electronics, to provide one or several references which are stable and precisely known and by means of which it is possible to compensate for individual properties of -the measure-ment circuit and/or of -the detector, as well as their variations in time.
In connec-tion with capacitive de-tectors, it is known in prior art to use a reference capacitance, which is, alternatingly with the measuring capaci-tance, connected to the measurement cir-cuit, usually the input circuit determining -the frequency of -the RC-oscilla-tor. By appropriately adjus-ting the measurement cir-cuit or in some other way, the outpu~ variable of the measurement circuit, derived from -the reference capacitance, can be brought to the correct level at each particular time.
It is known in the prior art to use measurement cir-cuits o~
i one reference, in par-ticular bridge connections, in which the measurement is, however, precise only when the electrical value of the reference is close to the value of the detector, e.g., when the bridge is in equilibrium. The more distant the value of the detector is from the reference, the greater will be the various errors, for example, errors caused by changes in the dynamics of the electronic measurement circuit. An advantage of connections with one reference is, however, the simplicity of the measurement circuit. This prior art method is described hereinafter in greater detail with reference to Fig. 1.
As advantage in measurement arrangements with two or more references is accuracy of the measurement, even within wide ranges of measurement. A drawback, however, is the com-plexity of the measurement method and the related computation.
The method of measurement with two references is described hereinafter in greater detail with reference to Fig. 2.
The invention further develops the measurement meth-ods and circuits for low capacitances, for example, about 0 to20 100 pF, applied by the inventor and known in the prior art, so that said methods and circuits become more precise.
The present invention also provides a measurement method and measurement circuit with two references in which complicated computation operations, necessary in determining the results of capacitance measurements in the prior art, are avoided.
The invention again provides a measurement method and "self-adjusting~ measurement electronics in which the out-put variables corresponding to the reference detectors remain30 invariable even if the ~measurement electronics should creep, for example, due to variations in temperature or other circum-stances.
~Z~37~
According to one aspect of the present invention -there is provided a method for the measurement of capaci-tances, particularly low capacitances, said method utilizing measurement electronics including switching means and a mea-surement oscillator having an output frequency which is a function of the capacitance to be connected to the input ter-minals of a measuring circuit determining the frequency of said oscillator, said method further utilizing two external auxiliary references providing auxiliary reference signals, and two reference capacitances having electrical values placed within the range of measurement, said reference capacitances and a capacitance to be measured being alternately connected to said oscillator via said switching means, said method com-prising the steps of comparing the auxiliary reference signals from said two external auxiliary references with the corre-sponding output signals of said measurement electronics, derived from said reference capacitances; forming differential signals representing the differences between said output sig-nals and said auxiliary reference signals from said external auxiliary references; forming feedback signals from said dif-ferential signals; controlling said measurement electronics circuit by said feedback signals in such a direction that said differential signals approach zero or a preset corresponding value; and deter~ining the output signals corresponding to the capacitance to be measured via said measurement electronics, when said measurement electronics is so adjusted.
Thus according to the method of the present inven-tion two external auxiliary references are used. The auxil-iary reference signals obtained from the external auxiliary references are compared with the corresponding output signals of the measurement elect~onics, derived from the reference capacitances. Differential signals representing the differ-~ 23~'~
ences between the output signals and the signals from theexternal auxiliary references are formed. The differential signals form feed'oack signals for controlling the circuit.
The measurement electronics is controlled by the feedback sig-nals in such a direction that the differential signals, or equivalent, approach zero or a preset corresponding value.
The measurement electronics determines the output signal cor-responding to the capacitance to be measured when said mea-surement elec-tronics is adjusted correctly by means of the foregoing method steps.
In accordance with the invention there is fitted in the measurement circuit external auxiliary references corre-sponding to the output variables obtained in response to the capacitance references proper. The auxiliary references are stable and independent from the measurement electronics and from its creep, as well as from various interference sources.
The variables obtained from the auxiliary references are com-pared with the output variables derived from the capacitance references proper, and differential signals are formed on the basis of said references. The differential signals are per-mitted, on one hand, to act in the manner of a constant term upon the measurement electronics and, on the other hand, to act upon the steepness of the measurement electronics summ-ingly during so many measurement cycles as a sort or iteration process, so that the difference between the capacitance refer-ence and the external reference becomes zero or sufficiently close to zero.
The comparison preferably occurs so that the differ-ential signal derived from the first external auxiliary refer-ence and from the first capacitance reference is made to actupon the measurement ele~tronics in the manner of a constant term. In other words, the differential signal is made to act ' ?~
~, i?
upon the offset of the measurement electronics. The differen-tial signal derived from the second external auxiliary refer-ence and from the second capacitance reference is, in the aforedescribed manner, made to act upon the steepness, for example, the amplification of the measurement electronics. If the measurement circuit or measurement method has an output variable which is a variable frequency, one of the differen-tial signals is made to act upon the basic frequency of the measurement electronics and the other differential signal is made to act upon its dynamics, that is, upon the change in frequency per a certain unit of change in capacitance.
In one embodiment of the method of the present invention said differential signals are formed during a plu-rality of so many measurement cycles that said differential signals can be made stepwise to approach zero or to become close enough to zero, whereupon the corresponding output vari-able of said capacitance to be measured is determined. Suit-ably the method further utilizes a first comparator and a sec-ond comparator, said method further comprising the steps of controlling a constant term or o*fset of said measurement electronics via a control signal formed in said first compara-tor on the basis of one differential signal, controlling the steepness or amplification of said measurement electronics via a control signal obtained from said second comparator on the basis of the other said differential signal, and summingly adjusting during so many measurement cycles as an iteration process that the variables indicating the difference between said reference capacitances and said external auxiliary re*er-ences are made equal to zero or to a preset constant. Desir-ably said switching means includes an electronic changeoverswitch, a control circui~ controlling said changeover switch and a clock controlling said control circui-t, said method fur-- 5a -ther comprising alternately connecting said capacitance to be measured and both said reference capacitances to said oscilla-tor via said changeover switch and deriving first and second control signals from said control circuit for controlling said first comparator via said first control signal and controlling said second comparator via said second control signal.
Preferably the method further utilizes a pair of frequency dividers and a plurality of gates, said method further com-prising providing a basic measurement frequency of about 100 kHz and lowering said basic measurement frequency via saidfrequency dividers to such a low level that delays and changes in said gates do not interfere with the measurement result.
More desirably the method further comprises providing a DC
voltage output signal. Suitably the method further comprises providing an output signal which is a frequency burst having a frequency containing information of the magnitude of said capacitance to be measured. Preferably the method further comprises determining the number of pulses in said frequency burst and utilizing the result of said determination as a mea-sure of said capacitance to be measured. Suitably the methodfurther comprises deducting the number of pulses corresponding to the value of one of the references from the number of pulses in said frequency burst, and utilizing the result of said deduction to determine said capacitance to be measured.
In a further aspect thereof the present invention provides a method for the measurement of capacitances, parti-cularly low capacitances, in telemetry of radiosondes for the measurement of atmospheric pressure, temperature and~or humid-ity, said method utilizing measurement electronics including switching means and a measurement oscillator having an outputfrequency which is a function of the capacitance to be con-nected to the input terminals of a measuring circuit determin-- 5b -ing the frequency of said oscillator, said method further uti-lizing two external auxiliary references providing auxiliary reference signals and two reference capacitances, having elec-trical values placed within the range of measurement, said reference capacitances and a capacitance to be measured being alternately connected to said oscillator via said switching means, said method comprising the steps of comparing the aux-iliary reference signals from said two external auxiliary ref-erences with the corresponding output signals of said measure-ment electronics, derived from said reference capacitances;forming differential signals representing the differences between said output signals and said auxiliary reference sig-nals from said external auxiliary references; forming feedback signals from said differential signals; controlling said mea-surement electronics circuit by said feedback signals in such a direction that said differential signals or equivalent approach zero or a preset corresponding value; and determining the output signals corresponding to the capacitance to be mea-sured via said measurement electronlcs, when said measurement electronic is adjusted correctly via the foregoing method steps.
The present invention also provides a circuit for the measurement of capacitances, particularly low capaci-tances, said circuit comprising measurement electronics including switching means and a measurement oscillator having an oukput frequency which is a function of the capacitance to be connected to the input terminals of a measuring circuit determining the frequency of said oscillator; two external auxiliary references providing auxiliary reference signals;
two reference capacitances having electrical values placed within the range of meas~rement, said reference capacitances and a capacitance to be measured being alternately connected -- ~;c --3 ~'~
to said oscillator via said switching means, said auxiliary reference signals from said two external auxiliary references being compared with the correspondi.ng output signals of said measurement electronics, derived from said reference capaci-tances, differential signals representing the differences between said output signals and said auxiliary reference sig-nals from said external auxiliary references being formed, feedback signals being formed from said differential signals and controlling said measurement electronics circuit in such a direction that said differential signals approach zero or pre-set corresponding value, said measurement electronics deter-mining the output signals corresponding to the capacitance to be measured when said measurement electronics is so adjusted.
- 5d -~2~
The present invention will be further illus-trated by way of the accompanying drawings, in which:-Fig. 1 is a graphical presentation of the characteris-tic curves (straigh-t lines) of a single-reference measurement method in a system of xy-coordinates;
Fig. 2 is a graphical presentation of the characteris-tic curves of a two-reference measurement system, in a manner corresponding to Fig. l;
Fig. 3 is a block diagram of an embodiment of the cir-cuit of the invention for undertaking the measurement method of the invention; and Fig. 4 is a circuit diagram of an embodiment of the measurement eiec-tronics circuit of the clrcuit of Fig. 3.
Fig. 1 illustrates a single-reference measurement method in a system of xy-coordinates. By means of a reference, which is, for example, a capacitance whose electrical value is at the middle of the range Xl of measurement, a point xOyO is fixed, through which the straight line ko illustrating the measurement electronics runs. The coordinate x stands for -the input vari-able, that is, in the present case, the magnitude of the capaci-tance to be measured, and y stands for the outpu-t variable, that is, in the presen-t case, for example, a DC voltage or a variable frequency. However, due to the creeping of the measurement elec-tronics and to other circumstances, the straight line illustrat-ing the properties of the system diverges from the basic straightline ko between the example lines kl and k2 shown by dashed lines and dot-dashed lines, respectively. Thereby, within the permit-ted margins of error, the measurement range Xl around xO becomes relatively narrow.
In a corresponding manner, FigO 2 illustrates a two-~2~37%
reference measurement method, which is the starting point of thepresent inven-tion, in a manner corresponding to Fig. 1. In the method of Fig. 2, two references 1 and 2 are applied. These ref-erences fix two points in the system of xy-coordinates. These are the points xlyl and x2,y2. The straigh-t line ko placed through these points is the linear basic opera-tion ine of the system. In practice, due to changes in temperature or to other circumstances, the characteristic curves of the system vary on both sides of the straight line ko between the curves ~1 and f2.
Thereby, within the margins of error, it is possible to accom-plish a range of measurement X2, which is greater than x2-xl.
Thus, as compared with the single-reference measurement method, a range of measurement X2 can be accomplished which is greater by at least one order.
It is possible, by the method of the invention here-inafter described in greater detail, to eliminate the complicated computation operations required in the prior art in connection with a measurement circuit of two references. Thus, the present invention provides an advantageous measurement method and mea-surement circuit which may be carried into effect or practiced quite simply readily. An exemplifying embodiment of the circuit of the invention is described with reference to Fig.s 3 and 4.
The system of Fig. 3 comprises a capacitance (CM) 12 to be measured and two reference capacitances 10 and 11 (CRl and CR2). The values between the reference capacitances 10 and 11 correspond to the points xl and x2 shown in Fig. 2, between which said points, and even outside them, the measurement range X2 extends. The measurement circuit includes an electronic changeover switch 13 having a control circuit 15, which, in turn, is controlled by a clock 14. Under the control of the control signals a,rl,r2 fro,m the control circuit 15, the changeoYer switch 13 connects the capacitance CM to ~e measured and the ref-erence capacitances CRl and CR2 alternatingly to the measurementelectronics 16.
.~ :
3 ~'~
In a known manner, the measurement electronics 16 includes, for example, an RC oscillator, the capacitance to be measured, which is as a rule within the range of 0 to 100 pF, and the reference capacitances, alternatingly connected to the input circuit which determines the frequency of said oscillator. The measurement electronics 16 also includes frequency dividers and other known switchin~ arrangements, so that the measurement elec-tronics produces an output variable such as, Eor example, a DC
voltage or a frequency which varies substantially linearly on the basis of the electrical value of the capaci-tance CM.
It is assumed that the output variable of the measure-ment electronics 16 is a voltage Ul The voltage Ul is passed to the first comparison circuit 19 and to the second comparison cir-cuit 20. In accordance with the invention, two external auxil-iary reference circuits 17 and 18 are used in the measurement circuit and method. The reference circuits 17 and 1~ provide, for example, DC voltages URl and UR2, each of which is passed to a corresponding one of the comparlson circuits 19 and 20. The differential voltages Ul and U2 of the external auxiliary refer-ence voltages URl and UR2 and of the output voltage Ul of the measurement electronics are input voltages of th0 comparison cir-cuits 19 and 20. The comparison circuits 19 and 20 are con-trolled by the control pulse sequences rl and r2 from the control circuit 15 of the changeover switch 13. Thus, output voltages Ucl and Uc2 are obtained from the comparison circults 19 and 20.
The measurement electronics 16 is controlled by the output volt-ages Ucl and Uc2 via the RC circuits 21 and 22 (low pass fil-ters).
The inventlon is preferably accomplished so that the first control signal Ucl acts, in the manner of a constant term, upon the measurement electronics 16, that is, on the so-called offset of said measurement electronics. The second control sig-nals Uc2 again acts upon the steepness, for example, the ampli-tude o~ the measurement electronics.
37~
The control signals ~cl and Uc2 affect the measurement electronics in such a direction that the differential voltages U
and U2 are reduced stepwise, and the feedback effect is repeated, for example, as controlled by the control circuit 15 of the Ghangeover switch, for the duration of so many measurement cycles that said differential voltages can be made to approach zero stepwise. ~fter the differential voltages Ul and U2 have been brought sufficiently close to the zero point, the measurement electronics 16 has been adjusted "correctly". The changeover switch 13 is then controlled by the control circuit 15 to connect the capacitance 1~ to be measured to the measurement electronics.
At the same time, the control circuit 15 controls a holding element 23, or another, corresponding component, so that the output signal U1 of the measurement electronics 16 is con-nected, as such, or as appropriately scaled, so as to provide the outlet sig~al Uout ~ig. 4 shows a circuit diagram of an embodiment of the measurement electrdnics for low capacitance detectors (o to 100 pF). The measurement frequency is about 100 k~z, which frequency is not processed as such, but is divided by frequency dividers 25 and 26 to a sufficient extent to a lower frequency in order to prevent delays in gates and other components and the changes therein from affecting thé measurement result. A multicap cir-cuit 27, which is an essential part in the circuit and is a patented special circuit expressly for measurement by capacitive detectors, is described in the aforementioned Finnish Patents Nos. 57,664 and 57,319, corresponding to United 5tates Patents Nos. 4,295,090 and 4,295,091, respectively. The variable being examined is time. The auxiliary reference is a time obtained from the crystal oscillator 24 and further from the pin 3 of the frequency divider microcircuit 25 (4024). The zeroing occurs a little later (pins 3 and 6 are ones~. A second auxiliary refer-ence is not needed, because a different division number has been taken from the other frequency divider microcircuit 26 (4040) via ..~..
the references CRl and CR2.
The comparison of the time differences is carried out by gates 31 and 32. Gates 33 and 34 assure that the correction currents may ac-t upon the voltages of the capacitors Cl of 47 nF
only when the references CR1 and CR2 are being measured. The output signal UOUt is, in the circuit of Fig. 4, a frequency burst, whose frequency contains the information on the electrical magnitude of the detector capacitance CM to be measured. The output may also be connected in the same manner as with the ref-erences CRl and CR2, whereby a pulse is obtained whose width (duration of half cycle) contains information of the electrical value of the detector capacitance.
The circui-t o-f Fig. 4 permits the calculation of the number of pulses in the frequency burst or, with minor modifica--tions, a burst is obtained from which the number of pulses cor-responding to the value of one of the references CRl and CR2 is derived. The latter alternative embodimen-ts do not require a crystal oscillator, because the pulse numbers are abstract num-bers.
... _
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for the measurement of capacitances, par-ticularly low capacitances, said method utilizing measurement electronics including switching means and a measurement oscilla-tor having an output frequency which is a function of the capaci-tance to be connected to the input terminals of a measuring cir-cuit determining the frequency of said oscillator, said method further utilizing two external auxiliary references providing auxiliary reference signals and two reference capacitances having electrical values placed within the range of measurement, said reference capacitances and a capacitance to be measured being alternately connected to said oscillator via said switching means, said method comprising the steps of comparing the auxil-iary reference signals from said two external auxiliary refer-ences with the corresponding output signals of said measurement electronics, derived from said reference capacitances; forming differential signals representing the differences between said output signals and said auxiliary references signals from said external auxiliary references; forming feedback signals from said differential signals; controlling said measurement electronics circuit by said feedback signals in such a direction that said differential signals approach zero or a preset corresponding value; and determining the output signals corresponding to the capacitance to be measured via said measurement electronics, when said measurement electronics is so adjusted.
2. A method as claimed in claim 1, wherein said dif-ferential signals are formed during a plurality of so many mea-surement cycles that said differential signals can be made step-wise to approach zero or to become close enough to zero, where-upon the corresponding output variables of said capacitance to be measured is determined.
3. A method as claimed in claim 2, which further uti-lizes a first comparator and a second comparator, said method further comprising the steps of controlling a constant term or offset of said measurement electronics via a control signal formed in said first comparator on the basis of one differential signal, controlling the steepness or amplification of said mea-surement electronics via a control signal obtained from said sec-ond comparator on the basis of the other said differential signal and summingly adjusting during so many measurement cycles as an iteration process that the variables indicating the difference between said reference capacitance and said external auxiliary references are made equal to zero or to a preset constant.
4. A method as claimed in claim 3, wherein said switching means includes an electronic changeover switch, a con-trol circuit controlling said changeover switch and a clock con-trolling said control circuit, said method further comprising alternately connecting said capacitance to be measured and both said reference capacitances to said oscillator via said changeover switch and deriving first and second control signals from said control circuit for controlling said first comparator via said first control signal and controlling said second com-parator via said second control signal.
5. A method as claimed in claim 4, which further uti-lizes a pair of frequency dividers and a plurality of gates, said method further comprising providing a basic measurement frequency of about 100 kHz and lowering said basic measurement frequency via said frequency dividers to such a low level that delays and changes in said gates do not interfere with the measurement result.
6. A method as claimed in claim 5, further comprising providing a DC voltage output signal.
7. A method as claimed in claim 5, further comprising providing an output signal which is a frequency burst having a frequency containing information of the magnitude of said capaci-tance to be measured.
8. A method as claimed in claim 7, further comprising determining the number of pulses in said frequency burst and uti-lizing the result of said determination as a measure of said capacitance to be measured.
9. A method as claimed in claim 8, further comprising deducting the number of pulses corresponding to the value of one of the references from the number of pulses in said frequency burst, and utilizing the result of said deduction to determine said capacitance to be measured.
10. A method for the measurement of capacitances, par-ticularly low capacitances, in telemetry of radiosondes for the measurement of atmospheric pressure, temperature and/or humidity, said method utilizing measurement electronics including switching means and a measurement oscillator to be connected to the input terminals of a measuring circuit determining the frequency of said oscillator, said method further utilizing two external aux-iliary references providing auxiliary reference signals and two reference capacitances having electrical values placed within the range of measurement, said reference capacitances and a capaci-tance to be measured being alternately connected to said oscilla-tor via said switching means, said method comprising the steps of comparing the auxiliary reference signals from said two external auxiliary references with the corresponding output signals of said measurement electronics, derived from said reference capaci-tances; forming differential signals representing the differences between said output signals and said auxiliary reference signals from said external auxiliary references; forming feedback signals from said differential signals; controlling said measurement electronics circuit by said feedback signals in such a direction that said differential signals or equivalent approach zero or a preset corresponding value; and determining the output signals corresponding to the capacitance to be measured via said measure-ment electronics, when said measurement electronics is adjusted correctly via the foregoing method steps.
11. A circuit for the measurement of capacitances, particularly low capacitances, said circuit comprising measure-ment electronics including switching means and a measurement oscillator having an output frequency which is a function of the capacitance to be connected to the input terminals of a measuring circuit determining the frequency of said oscillator; two exter-nal auxiliary references providing auxiliary reference signals;
two reference capacitances having electrical values placed within the range of measurement, said reference capacitances and a capacitance to be measured being alternately connected to said oscillator via said switching means, said auxiliary reference signals from said two external auxiliary references being com-pared with the corresponding output signals of said measurement electronics, derived from said reference capacitances, differen-tial signals representing the differences between said output signals and said auxiliary reference signals from said external auxiliary references being formed, feedback signals being formed from said differential signals and controlling said measurement electronics circuit in such a direction that said differential signals approach zero or a preset corresponding value, said mea-surement electronics determining the output signals corresponding to the capacitance to be measured when said measurement electron-ics is so adjusted.
two reference capacitances having electrical values placed within the range of measurement, said reference capacitances and a capacitance to be measured being alternately connected to said oscillator via said switching means, said auxiliary reference signals from said two external auxiliary references being com-pared with the corresponding output signals of said measurement electronics, derived from said reference capacitances, differen-tial signals representing the differences between said output signals and said auxiliary reference signals from said external auxiliary references being formed, feedback signals being formed from said differential signals and controlling said measurement electronics circuit in such a direction that said differential signals approach zero or a preset corresponding value, said mea-surement electronics determining the output signals corresponding to the capacitance to be measured when said measurement electron-ics is so adjusted.
12. A circuit as claimed in claim 11, wherein said dif-ferential signals are formed during a plurality of so many mea-surement cycles that said differential signals can be made step-wise to approach zero or to become close enough to zero, where-upon the corresponding output variable of said capacitance to be measured is determined.
13. A circuit as claimed in claim 12, further compris-ing a first comparator providing a first control signal control-ling a constant term or offset of said measurement electronics on the basis of one differential signal and a second comparator pro-viding a second control signal controlling the steepness or amplification of said measurement electronics on the basis of the other said differential signal, whereby summing adjustment is during so many measurement cycles as an iteration process that the variables indicating the difference between said reference capacitances and said external auxiliary references are made equal to zero or to a preset constant.
14. A circuit as claimed in claim 13, wherein said switching means includes an electronic changeover switch, a con-trol circuit controlling said changeover switch and a clock con-trolling said control circuit, said changeover switch alternately connecting said capacitance to be measured and both said refer-ence capacitances to said oscillator via said changeover switch, said control circuit providing first and second control signals for controlling said first comparator via said first control sig-nal and controlling said second comparator via said second con-trol signal.
15. A circuit as claimed in claim 14, further compris-ing a plurality of gates and a pair of frequency dividers for lowering a basic measurement frequency of about 100 kHz to such a low level that delays and changes in said gates do not interfere with the measurement result.
16. A circuit as claimed in claim 15, further compris-ing a DC voltage output signal.
17. A circuit as claimed in claim 16, further compris-ing an output signal which is a frequency burst having a fre-quency containing information of the magnitude of said capaci-tance to be measured.
18. A circuit as claimed in claim 17, further compris-ing means for determining the number of pulses in said frequency burst, the result of said determination being a measure of said capacitance to be measured.
19. A circuit as claimed in claim 18, further compris-ing means for deducting the number of pulses corresponding to the value of one of the references from the number of pulses in said frequency burst, the result of said deduction determining said capacitance to be measured.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI842193 | 1984-05-31 | ||
| FI842193A FI69932C (en) | 1984-05-31 | 1984-05-31 | MAINTENANCE FOUNDATION CAPACITORS SPECIFIC FOR SMAR CAPACITORS VID VILKER MAN ANVAENDER TVAO REFERENSER |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1262372A true CA1262372A (en) | 1989-10-17 |
Family
ID=8519172
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000482808A Expired CA1262372A (en) | 1984-05-31 | 1985-05-30 | Method for the measurement of capacitances, in particular of low capacitances, wherein two references are used |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS60262067A (en) |
| AU (1) | AU587578B2 (en) |
| BR (1) | BR8502572A (en) |
| CA (1) | CA1262372A (en) |
| DE (1) | DE3519390A1 (en) |
| FI (1) | FI69932C (en) |
| FR (1) | FR2565353B1 (en) |
| GB (1) | GB2159965B (en) |
| IT (1) | IT1200492B (en) |
| ZA (1) | ZA853855B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI74549C (en) * | 1986-02-13 | 1988-02-08 | Vaisala Oy | MAETNINGSFOERFARANDE FOER IMPEDANSER, SAERSKILT SMAO KAPACITANSER. |
| DE19524387C1 (en) * | 1995-07-04 | 1996-11-07 | Siemens Ag | Capacitance difference measuring circuit for capacitive sensor |
| CN102096057B (en) * | 2010-11-16 | 2013-10-02 | 北京航天测控技术有限公司 | Calibration method and device of capacitance measurement circuit |
Family Cites Families (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE970798C (en) * | 1953-05-16 | 1958-10-30 | Rolf Scheunert Dr Ing | Arrangement for measuring preferably very small capacities or changes in capacitance |
| DE1026860B (en) * | 1956-05-24 | 1958-03-27 | Die Bundesrepublik Deutschland | Beat compensator |
| US3480857A (en) * | 1967-12-27 | 1969-11-25 | Ibm | Digital method and apparatus for measuring small inductances and capacitances |
| DE2508033A1 (en) * | 1975-02-25 | 1976-09-02 | Zinn Erich | Measurement of capacitance and loss factor - using automatic range finding network involving relays and comparators |
| US4041382A (en) * | 1976-08-16 | 1977-08-09 | The Sippican Corporation | Calibrating a measurement system including bridge circuit |
| GB2006970B (en) * | 1977-09-23 | 1982-03-31 | Testut Aequitas | Capacitance measuring device |
| FI57319C (en) * | 1977-10-14 | 1980-07-10 | Vaisala Oy | ADJUSTMENT OF CAPACITY IN CAPACITY |
| FI54664C (en) * | 1977-10-14 | 1979-01-10 | Vaisala Oy | ELECTRONIC EQUIPMENT IN THE SYNERNIZATION FOR TELEMETER MANAGEMENT IN THE SONDER |
| US4130796A (en) * | 1977-12-07 | 1978-12-19 | Westinghouse Electric Corp. | Calibrating and measuring circuit for a capacitive probe-type instrument |
| AU530552B2 (en) * | 1978-04-07 | 1983-07-21 | Minister of Public Works of Nsw | Wave level measuring apparatus |
| JPS5528157A (en) * | 1978-08-19 | 1980-02-28 | Fuji Electric Co Ltd | Displacement converter |
| US4295091B1 (en) * | 1978-10-12 | 1995-08-15 | Vaisala Oy | Circuit for measuring low capacitances |
| FR2446037A1 (en) * | 1979-01-03 | 1980-08-01 | Vaisala Oy | Procedure in radio sonde - used when transferring signals measured with capacitive sensors, to surface station by radio transmitter (sf 28.2.79) |
| DE2901516C2 (en) * | 1979-01-16 | 1985-01-24 | VEGA Grieshaber GmbH & Co, 7620 Wolfach | Arrangement for generating a signal proportional to a capacitance |
| US4322977A (en) * | 1980-05-27 | 1982-04-06 | The Bendix Corporation | Pressure measuring system |
| SE436936B (en) * | 1981-01-29 | 1985-01-28 | Asea Ab | INTEGRATED CAPACITY SENSOR |
| US4398426A (en) * | 1981-07-02 | 1983-08-16 | Kavlico Corporation | Linear capacitive pressure transducer system |
| DE3321580A1 (en) * | 1983-06-15 | 1984-12-20 | Philips Patentverwaltung Gmbh, 2000 Hamburg | Device for measuring temperature in order to compensate temperature-dependent errors in a capacitive differential-pressure sensor |
-
1984
- 1984-05-31 FI FI842193A patent/FI69932C/en not_active IP Right Cessation
-
1985
- 1985-05-21 ZA ZA853855A patent/ZA853855B/en unknown
- 1985-05-22 AU AU42749/85A patent/AU587578B2/en not_active Ceased
- 1985-05-30 IT IT20967/85A patent/IT1200492B/en active
- 1985-05-30 CA CA000482808A patent/CA1262372A/en not_active Expired
- 1985-05-30 BR BR8502572A patent/BR8502572A/en not_active IP Right Cessation
- 1985-05-30 DE DE19853519390 patent/DE3519390A1/en active Granted
- 1985-05-31 FR FR8508231A patent/FR2565353B1/en not_active Expired
- 1985-05-31 JP JP60118680A patent/JPS60262067A/en active Pending
- 1985-05-31 GB GB08513830A patent/GB2159965B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FI69932B (en) | 1985-12-31 |
| GB2159965A (en) | 1985-12-11 |
| BR8502572A (en) | 1986-02-04 |
| JPS60262067A (en) | 1985-12-25 |
| FR2565353A1 (en) | 1985-12-06 |
| GB8513830D0 (en) | 1985-07-03 |
| ZA853855B (en) | 1986-03-26 |
| FI69932C (en) | 1986-05-26 |
| IT1200492B (en) | 1989-01-18 |
| DE3519390C2 (en) | 1990-10-25 |
| AU4274985A (en) | 1985-12-05 |
| FI842193A0 (en) | 1984-05-31 |
| DE3519390A1 (en) | 1985-12-12 |
| GB2159965B (en) | 1988-06-29 |
| IT8520967A0 (en) | 1985-05-30 |
| AU587578B2 (en) | 1989-08-24 |
| FR2565353B1 (en) | 1986-12-26 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4437164A (en) | Ridge circuit compensation for environmental effects | |
| CA1052886A (en) | Capacitive thickness gauging | |
| US6828779B2 (en) | Circuit for compensating for time variation of temperature in an inductive sensor | |
| US5455513A (en) | System for measuring properties of materials | |
| US3970925A (en) | Direct reading reactance meter | |
| JPH0260986B2 (en) | ||
| CA1268210A (en) | Method for the measurement of capacitances, in particular of low capacitances | |
| CN1849517B (en) | Method and apparatus for measuring active, reactive power of system and module, impedance of electrical component | |
| CA1262372A (en) | Method for the measurement of capacitances, in particular of low capacitances, wherein two references are used | |
| Muciek | Digital impedance bridge based on a two-phase generator | |
| Atmanand et al. | A microcontroller-based quasi-balanced bridge for the measurement of L, C and R | |
| US7084622B2 (en) | Methods for eliminating magnetic field and temperature related errors in magnetic sensors used for the measurement of coating thickness | |
| US5412998A (en) | Torque measuring system | |
| WO2000070368A1 (en) | Proximity sensor method and apparatus that is insensitive to temperature, noise and length of wire | |
| Atmanand et al. | A novel method of measurement of L and C | |
| US4795969A (en) | Load loss standard for testing and calibrating high voltage power measuring systems | |
| EP0166705A2 (en) | A method for measuring of capacities, particular low ones | |
| JP2954449B2 (en) | Capacitance measuring circuit and LCR meter having the same | |
| Crovini et al. | Resistance comparisons at nanovolt levels using an isolating current ratio generator | |
| SU1441175A1 (en) | Displacement transducer | |
| RU2121155C1 (en) | Method and device for calibrating electromagnetic ohmmeters | |
| SU1446548A1 (en) | Method of eddy-current inspection of non-ferromagnetic articles | |
| SU1218334A1 (en) | Method of heavy direct currents | |
| SU1201743A1 (en) | Electromagnetic coating thickness gauge | |
| RU2085962C1 (en) | Magnetic-field metering device |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |