RU1795550C - Displacement-to-code converter - Google Patents

Abstract

The invention relates to a measurement technique and is intended to automate the measurement and control of various non-electric quantities that can be converted to moving a plate of a differential capacitive sensor. The aim of the invention is to improve the accuracy of the translate to code converter. To this end, a displacement transducer in code containing a differential capacitive sensor 1 with two fixed and one movable 2 plates, two amplifiers 15, 16, a subtraction unit, the first current-limiting element made in the form of a resistor 9, introduced a frequency divider 19, digital a frequency meter 20 and five current-limiting elements made in the form of resistors 10-14, the subtraction unit is made in the form of a frequency subtraction unit, each of the fixed plates of the differential capacitive sensor is made in the form of three identical isol sections 9-11 and 12-14, which together with the movable plate 2 and the corresponding amplifiers 15.16 form two RC generators 21, 22. This eliminates the influence of the supply voltage, changes in temperature and humidity on the environment measurement accuracy. 1 ill. f. ate with

Description

The invention relates to a measurement technique and is intended to automate the measurement and control of various non-electric quantities that can be converted to moving a plate of a differential capacitive sensor.

A device for measuring displacement is known, comprising a differential capacitive sensor, first and second amplifiers, the outputs of which are connected to a voltage difference generator, a reference generator, and a voltage source, the outputs of the reference generator being connected to the inputs of the amplifiers and to the extreme plates of the differential capacitive sensor, middle the plate of which is connected to a voltage source.

A disadvantage of the known device is the low accuracy and stability of measurements.

Closest to the claimed are a displacement converter into a code containing a differential capacitive sensor, first and second amplifiers, the outputs of which are connected to the extreme plates of the differential capacitive sensor and to the inputs of the voltage difference, the output of which is connected to the information input of the analog-digital the inverter, a clock connected to the triggering input of the time slot driver and a voltage source connected; from the inputs of the amplifiers v. to the middle plate of the differential capacitive sensor through a key, the control input of which is connected to the first output of the time slot driver, the second output of which is connected to the control input of the analog-to-digital converter.

A disadvantage of the known transducer is also the low accuracy and stability of measurements, due to the low accuracy of analog measuring circuits and the dependence of the parameters of the shaper of time intervals and integrators on the supply voltage and threshold voltage of operation, temperature and humidity. In addition, the use of an analog-to-digital converter at the output of the comparison unit (voltage difference generator) introduces an additional error.

The purpose of the invention is to improve the accuracy of the translate to code converter.

. This goal is achieved by the fact that the first and second amplifiers, the outputs of which are connected to the first and second inputs of the subtraction unit, the first, current-limiting, to the displacement transducer in the code containing the differential capacitive sensor with two fixed and one movable plates

element, a frequency divider, a digital frequency meter and five current-limiting elements are introduced, the subtraction unit is made in the form of a frequency subtraction unit, each of the fixed plates of the differential capacitive sensor is made in the form of three identical isolated sections, the first extreme sections of the first and second fixed plates of the differential capacitive sensor connected to the first inputs

5, respectively, of the first and second amplifiers and with the first terminals of the first and second current-limiting elements, respectively, the second terminals of which are connected to the middle sections of the first and second fixed plates of the differential capacitive sensor k, respectively, with the first terminals of the third and fourth current-limiting elements, respectively, whose second terminals are connected

5 with the second extreme sections of the first and second fixed plates of the differential capacitive sensor, respectively, and with the first terminals of the fifth and sixth, respectively, current-limiting elements, the second terminals of which are connected to the outputs of the first and second amplifiers respectively, the output of the frequency subtraction unit through the frequency divider is connected to the input of the digital frequency meter, the output of which is the output of the converter, the movable plate of the differential capacitive sensor and the second inputs of the first and second amplifiers lei connected to a common bus.

0 The drawing shows a functional diagram of the transducer to move the code, the Converter contains a differential capacitive sensor 1, formed by a movable plate 2 and sections 3-8

5 fixed plates, current-limiting elements made in the form of resistors 9-14, amplifiers 15, 16, common bus 17, frequency subtraction unit 18, frequency divider 19 and digital frequency meter 20.

0 Movable plate 2 together with sec. cm 3-5, resistors 9-11 and amplifier 15 forms an RC generator 21, the same movable plate 2 together with sections 6-8, resistors 12-414 and amplifier 16

5 form an RC oscillator 22.

The converter operates as follows.

In each measurement cycle, the frequency difference of the RC generators 21, 22, the positive feedback circuit, is measured

the connections of which are formed by the capacitances of the differential capacitive sensor 1 and the resistors 9-14, whereby the measured value of the frequency difference of the output voltages of the RC generators 21-22 becomes proportional to the measured displacement.

The frequencies fi and faRC-generators 21 and 22, in which the shoulder capacitances Ci and C2 of the differential capacitive sensor 1 are used as the chart capacitance, will be equal to:

t 1 d0 + Ad.

f2

2 R Ci 2nR m 1 do-Ad 2 L: R C2 2 JT R m

where dp is the distance between the stationary 9-11 and 12-14 sections and the movable 2 plates in the middle position of the latter:

Ad- measured displacement

m is a design parameter depending on the design of the capacitive sensor 1 and the area of sections 3-9;

R is the resistance of the resistors 9-14.

It follows from (1) that the difference frequency f at the output of the frequency subtraction unit 18 will be proportional to the measured displacement.

fi-fi- M; (2)

f

l: Km

from where the measured displacement will be equal.

Л d K0f, (3) where Ko. JiRm is the coefficient of proportionality.

Thus, using the shoulders of the differential capacitive sensor 1 as the frequency-setting capacitance of the RC generators 21, 22 and measuring the frequency difference of the RC generators 21, 22, we obtain a linear relationship between the measured difference frequency and the measured displacement.

The initial frequency of the foRC generators 21.22, corresponding to the initial average position of the middle plate 2 of the sensor 1, is selected so as to provide the necessary accuracy and resolution of the measurements. The quantity fo according to (1) is equal to

dc

10 2JTRm whence for Ko follows the expression

Co flcRm

do 2T0

According to (3), the error d d of the measurement of the displacement is determined by the error d f of the measurement of the difference frequency f at the selected coefficient Ko,

5- k0 (a f

Ј. Then

(5)

thirty

5 For a resolution A d of measurement equal to such a change in the amount of movement at which the readings of the digital frequency counter 20 are changed by one, in accordance with (3) and (4) we obtain

10 Ad. (6)

 °

From (5) and (6) it follows that the accuracy and resolution of measurements at a selected initial gap value do

5 are determined by the initial frequency of the fo RC generators 21.22, the higher they are, the higher; higher frequency fo.

When the device is turned on, the RC generators 21 and 22 operate in a continuous mode, generating sinusoidal voltages, the frequency of which is determined by the position of the moving middle plate 2 of the differential capacitive sensor 1. moreover, when the plate 2 moves through 25, the frequencies of the RC generators 21, 22 change are in opposite directions, for example, RC oscillators 21. 22 are fed to the inputs of the frequency subtraction unit 18, at the output; which the voltage of the difference frequency is generated, which is proportional to the displacement of the middle plate 2 of the sensor, 1 from the initial equilibrium position.

The differential frequency of the output voltage of the block 18 using the scale

35, the frequency divider 19 decreases by a predetermined number of times and is transmitted to a digital frequency meter 2Q where it is measured and displayed on a digital indicator. Moreover, as follows from expression (3), the coefficient of deletion40 or of the scaler frequency divider 19 should be equal to K0.

A scaled frequency divider 19 is used to match the maximum frequency of the signal at the output of block 18, which corresponds to the maximum measurable displacement, with the minimum counter capacity of the digital frequency counter 20, the value of which is equal to the maximum displacement of the plate 2, measured in some units, for example microns. In other words, a large-scale frequency divider 19 is needed so that regardless of the choice of frequency of the RC oscillators 21, 22

55, the frequency of the signal supplied to the input of the digital frequency counter 20, and hence the readings of the frequency counter 20 were equal to the measured displacement in microns. Block 19 is implemented as a cascade connection.

the required number of triggers with a counting input. .

The digital frequency counter 20 operates cyclically, periodically measuring the frequency of the pulse voltage of the difference frequency f continuously supplied to its input, and is intended for measuring and digitally displaying the frequency of the pulse signals arriving at its input from the output of the scale frequency divider 19. A typical structure of the digital frequency meter includes a pulse counter, a time slot generating unit (timer), and an indicator. In principle, by adjusting the time interval determined by the timer for counting the number of pulses arriving at the counter, it is possible to achieve the equality of the number of pulses arriving at the counter with the displacement in microns. This eliminates the need for a large-scale frequency divider 19, however, the resolution of the measurement may not be ensured.

The frequency of the pulse signal at the output of the frequency subtraction unit 18 is equal to the frequency difference modulus of the RC generators 21 and 22, which corresponds to using the movable plate 2 as the working displacement to the other side from the initial equilibrium position. In this case, the maximum measured displacement is approximately d0. There are two possibilities for expanding twice the linear operating range of the measured displacements.

Firstly, it is possible to determine the algebraic frequency difference of the RC generators 21 and 22. In this case, a unit must be entered in block 1.8 to record the change in the z phase of the difference frequency signal when the movable plate 2 passes through the middle position and take this change into account by changing the sign of the digital readings frequency counter 20. In this case, it is also necessary to introduce a digital computing unit providing zero reading of the digital displacement indicator when the plate 2 is in one of the extreme positions despite to zero

frequency counter reading 20.

Secondly, by changing the R value of the resistors 9-11 or 12-14 of one of the RC generators 21, 22, it is possible to ensure that the frequencies of the RC generators 21, 22 are equal

one of the extreme positions of the movable middle plate 2 of the differential capacitive sensor 1. In this case, the readings of the digital frequency meter 20 will be 0. This way of expanding the measuring range of movement twice as simple is the most simple and practically the most acceptable ..

..AND

Used in the measurement

The real signal is the frequency of the RC oscillators. 21.22 depends only on the parameters of the sensor 1 and resistors 9-14; it can be selected accurately and stabilized by using high-precision and highly stable resistors 9-14. Changes in ambient temperature and humidity cause identical changes in the frequency of both RC generators 21,22 and these changes in frequency will be mutually compensated in block 18

subtracting frequencies. In this case, the frequency of the RC oscillators 21, 22 is set by resistors 9-14, based on a given measurement resolution. As a result, the accuracy and stability of the converter are improved.

. Formulas of the invention

A displacement to code converter comprising a differential capacitive sensor with two fixed and one movable plate, first and second amplifiers, the outputs of which are connected respectively to the first and second inputs of the subtraction unit, the first current-limiting element, characterized in that, in order to increase the accuracy of the converter, into it a frequency divider, a digital frequency meter and five current-limiting elements are introduced, the subtraction unit is made in the form of a frequency subtraction unit, each of the fixed plates of the differential the capacitive sensor is made in the form of three identical isolated sections, the first

the extreme sections of the first and second fixed plates of the differential capacitive sensor are connected to the first inputs of the first and second amplifiers, respectively, and to the first terminals of the first and second current-limiting elements, respectively, the second terminals of which are connected to the middle sections of the first and second fixed plates of the differential capacitive sensor and the first the conclusions of the third and fourth current-limiting elements, respectively, the second conclusions of which are connected to the second extreme sections E, respectively, the first and second fixed plates of the differential capacitive sensor and to first terminals of said fifth and, respectively,

of the sixth current-limiting elements is the output of the converter, the movable second terminals of which are connected to the output of the plate by differential capacitances of the first and second amplified sensors, respectively, and the second inputs of the first and litters, the output of the subtraction unit. The frequencies of the second amplifiers are connected to a common bus - through a frequency divider is connected to the input n. digital frequency meter, the output of which