SU1552124A2 - Capacity meter for force-balance transducers of mechanical quantities - Google Patents

Abstract

The invention relates to a measuring technique and can be used in measuring small deviations of a capacitance from a nominal value and capacitive indicators of the mismatch of compensation sensors of mechanical quantities. The aim of the invention is to increase the accuracy and increase the sensitivity of the conversion, which is achieved by eliminating the DC amplifier voltage voltages close to the amplitude of the rectangular voltage generator at equal values of the measured capacitances. The capacitance meter contains two stationary electrodes 1 and 2, movable electrode 3, square voltage generator 4, resistors 5 and 6, diodes 7-10, capacitors 11-14, summing resistors 15-18, DC differential amplifier 19, common bus 20. 2 Il.

Description

The invention relates to the measurement technique, is an improvement of the invention according to the author. St. No. 1196779 and can be used when measuring small deviations of the capacitance from the nominal value in capacitive indicators of the mismatch of compensation sensors of mechanical quantities ..

The purpose of the invention is to improve the accuracy and increase the sensitivity of the conversion.

The invention solves the problem of converting small capacitance deviations from nominal values to voltage, | Figure 1 shows a circuit diagram of a capacitance meter for compensation sensors of mechanical quantities; figure 2 -

Graphic dependence of the nonlinearity of the meter characteristics on the ratio of the time constant (or pulse duration) of the generator and the time constant formed

capacitors and resistors of a double T1-shaped non-linear quadrupole for a capacitance range of 0.1 (10%) of the original value when the area of the capacitor plates overlaps.

The device contains two stationary electrodes 1 and 2, a movable electrode 3, a generator 4 of double-pole pr - angular voltage (HPL), the first and second resistors 5 and 6, the first, second, third and fourth diodes 7-10, the first, the second, third, and fourth capacitors 11–14, the first, second, third, and fourth summing resistors 15–18, DC differential amplifier 19, common bus 20, with the output of a two-pole rectangular generator 4 connected to the first pins of the first and second resistors 5 and 6, the second pin of the first the resistor 5 is connected to the anode of the first, the cathode of the third diode 7 and 9 and the first fixed electrode 1, the second terminal of the second resistor 6 is connected to the anode of the second cathode of the fourth diode 8 and 10 and the second fixed electrode 2, while the movable electrode 3 is connected to the common bus 20, the cathode of the first diode 7 is connected to the first I of the first summing resistor 15, and the first capacitor

11, the cathode of the second diode 8 is connected to the first terminals of the second summing resistor 16 and the second capacitor 12, the anode of the third diode is connected to the first terminals of the third summing resistor 17 and the third capacitor 13, and the anode of the fourth diode is connected to the first terminals of the fourth summing resistor 18 and the fourth capacitor 14, the second terminals of the first and second summing resistors 15 and 16 are combined and connected to the first input of a differential dc amplifier, the second input of which is connected to the combined second and second and third terminals of summing resistors 16 and 17. In the device fixed electrodes

II and 2 and the movable electrode 3 form the compared capacitors of the differential capacitive mismatch indicator, constituting a double T-shaped non-linear quadripole

The first diode 7 and the first capacitor

IIform the first peak detector and, accordingly, the second elements 8 and 12 - the second, the third elements 9 and 13 - the third, and the fourth elements 10 and 14 - the fourth peak detectors, the first and fourth summing resistors 15 and 18 form one adder,

and the second and third summing resistors 16 and 17 are another adder.

Capacity meter works as follows.

Upon receipt of a two-pole rectangular voltage from generator 4 to circuits formed by resistors 5 and 6 and capacitors with electrodes 1-3, an alternating voltage occurs on stationary electrodes 1 and 2, the form of which is formed by segments of exponentials. At point 21, the voltage equal to the sum of the voltages on the capacitors 11 and 14. Since the diodes 7 and 10, connected respectively to the resistors 5 and 6, pass the voltage of different polarity, the voltage on the adder formed by the resistors 15 and 18, at point 21 is equal to

U E, + E iS-TSer + f)

(ABOUT

The voltage on the adder formed by resistors 16 and 17 at point 22 is equal to

LV - (E; tu-Rc, - + T) + (E - | xg t) j

(.)

where is e

R

the amplitude of the output voltage of the rectangular voltage generator 4 is the resistance of resistors 5 and 6; / С ,, С2- measurable capacities -}

tu is the pulse duration of the generator 4.

Since the period of the rectangular voltage generator at the operational amplifier is T 2.2 (RC) f, where (RC) r is the constant time of the GUI master circuit, the pulse duration tu T l, l (RC) r . Thus, when С С Ј and U, U2 0, the inputs of the differential amplifier 19 of the direct current voltage will be equal to zero and the output of the differential amplifier 1 of the direct current voltage will be zero.

Since when moving the moving electrode 3, the capacitances change in different directions, the voltage at the inputs of the differential amplifier 19 of the direct current undergoes corresponding changes and a difference signal appears at the output

U - Uo 2 (-

(1Т4 j.UHOr

e t "c.i4 +1

l -

 HH "c) g 3

e iRCiH +

(3)

where (rc,) 4 and (rc2) 4. - time constants formed by capacitors and resistors of a double T-shaped non-linear quadrupole 0

Experimental and theoretical study of the described circuit of the circuit allows one to reveal the possibility of linearizing the static characteristic of the circuit.

To obtain a linear dependence of the output signal on capacitance change, it is necessary to choose certain ratios between the Rectangular voltage generator time constant and the time constant formed by capacitors and resistors of a double T-shaped non-linear quadrupole (RC) r / (Re). These relationships depend on

6

(

c from the method of changing the capacitance: either by changing the gaps between the plates of double T-shaped nonlinear quadrupole capacitors, or by changing the overlap areas of the plates of these capacitors

For the case of changing the gaps between, the capacitor plates of the time constant, the time of the driving circuit of the rectangular voltage generator depends on the time constant of the double T-shaped non-linear four-pole device as follows

BUT

(RC) r y-y (RC) 4,

0

five

0

five

0

five

0

five

where, 32 for range

capacity equal to 0.2 of the original value; , 35 for a range of 0.5 from the original value; , 45 for a range equal to the initial capacity value.

When the area of the capacitor plates overlaps, the parameter A takes the following values:

, 60 for a capacitance range of 0.1 of the original value; , 58 for a range of 0.2 from

initial value; 55 dl range 0.33 from

initial value; , 50 for a range of 0.4 of the original value; , 44 for a range of 0.5 from the original value. With a deviation from the accepted optimal ratio for these capacitance ranges, the characteristic becomes nonlinear.

The dependence of nonlinearity for the range of capacitance change equal to 0.1 of the initial value when changing the area of overlap of the capacitor plates is shown in Fig.2.

2, the nonlinearity curve is monotonous, has one extremum, and at the optimum point the nonlinearity of the characteristic is practically zero.

The characteristics for other ranges of capacitance changes with changes in area and with changes in gaps between the plates of capacitors have a similar appearance.

 /to

FIG g

Claims (1)

Formula of the invention Capacitance meter for compensation sensors of mechanical quantities according to auth. No. 1196779, which involves the fact that, in order to increase accuracy and increase sensitivity, third and fourth diodes, third and fourth capacitors, first, second, third and fourth summing resistors are introduced, while the cathodes of the third and fourth diodes, respectively connected to the anodes of the first and second diodes, the cathodes of which are connected respectively to the first terminals of the first and second summing resistors, the anode of the third diode is connected to the first terminals of the third summing resistor and the third capacitor, the second terminal which is connected to the common bus, and the anode of the fourth diode is connected to the first terminals of the fourth summing resistor and fourth capacitor, the second terminal of which is connected to the common bus, the second conclusions of the first and fourth summing resistors are combined and connected to the first input of the differential DC amplifier, the second input of which connected to the combined second terminals of the second and third summing resistors.