SU1677667A1 - Capacitive pickup transducer - Google Patents

Abstract

The invention relates to a measurement technique, in particular to devices for monitoring and measuring electrical circuit parameters. The aim of the invention is to improve the measurement accuracy. The converter contains a source of 1 reference voltage, three switches 2,3 and 4, a measured capacitive sensor 6, represented by a two-element replacement circuit containing an informative capacitive element 7 and a resistive element 8, exemplary elements - a capacitor 5 and a resistor 10, a coupling capacitor 9, the imbalance signal amplifier 11 of the measuring circuit, the output of which is connected to the information inputs of the synchronous detectors 15 and 21. The synchronous detector 15 performs the function

Description

The invention relates to a measurement technique, in particular, to devices for measuring electrical circuit parameters.

The purpose of the invention is to increase the measurement accuracy.

Fig. 1 shows the functional electrical circuit of the measuring transducer of a capacitive sensor; 2 of FIG. 3, a diagram of voltage at various points of a measuring transducer of a capacitive sensor.

The capacitive transducer measuring transducer contains a source of voltage reference 1, the first 2, second 3, third 4 switches, exemplary capacitor 5, capacitive sensor 6 including capacitive 7, resistive 8 elements, first coupling capacitor 9, exemplary resistor 10, imbalance amplifier 11 the measuring circuit, which includes an operational amplifier 11, a first capacitor 12, a feedback resistor 13, an operational amplifier 14, a first synchronous detector 15, which includes a second coupling capacitor 16, a fourth 17 and fifth switches 18, the second capacitor 19, the second operational amplifier 20, the second synchronous detector 21, which includes the third coupling capacitor 22, the sixth switch 23, the third capacitor 24, the third operational amplifier 25, the control unit 26, which includes the time setting capacitor 27 , the resistor 28, the first 29, the second 30 elements 2I - NOT, the first trigger 31, the third element 2I 32, the second trigger 33, the first 34 and the second 35 elements 2I.

The outputs of the positive and negative voltages of source 1 are connected respectively to the first and second information inputs of switch 3. The first information inputs of switches 2 and 4 are connected to the common bus of the device, and the outputs of switches 2 and 3 are connected respectively to potential terminals of an exemplary capacitor 5 and capacitive sensor 6. The output of the switch 4 through the separation

the capacitor 9 is connected to the potential output of the reference resistor 10. The current outputs of the reference capacitor 5, the capacitive sensor 6 and the reference resistor 10 are connected to the input of the imbalance signal amplifier of the measuring circuit (USN) 11, the output of which is connected to the information inputs of synchronous detectors (SD) 15 and 21. The output of the synchronous detector 15 is connected to the second information input of the switch 2 and is the first output of the converter, and the output of the LED 21 is connected to the second information input of the switch 4 and is the second in output transducer. The control outputs of the switches 2,3 and 4 are connected to the first output of the control unit (CU) 26, the control input of the CAB21 is connected to the second output of the CU 26. The first and second control inputs of the CID 15 are connected respectively to the network and the fourth outputs of the CU 26,

The elements 7 and 8 are connected in parallel and simulate the measured capacitance and active conductivity of the capacitive sensor 6, the input of which is connected to the output of the switch 3, and the output to the input of the amplifier 14.

The first terminals of the capacitor 12 and the resistor 13 are connected to the inverting input of the operational amplifier (OU) 14 and are the input of the simplified system of common law 11, the second terminals of the capacitor 12 and the resistor 13 are connected to the output of the opamp 14 and the non-inverting input of the OU 14 is connected to common bus device.

The input of the coupling capacitor 16 is the information input of the LED 15, the inputs of the switches (keys) 17 and 18 are respectively the first and second inputs of the control of the LED 15. The movable contacts of the keys 17 and 18 are connected to the second output of the coupling capacitor 16, the fixed contact of the key 18 is connected to non-inverting input of the OA 20 and is connected to the common bus device. The fixed contact key 17 is connected to the first output of the storage capacitor 19 and the inverting input of the op-amp 20.

the output of which is connected to the second terminal of the capacitor 19 and is the output of the LED 15.

The input of the coupling capacitor 22 is the information input of the LED 21, the second output of the coupling capacitor 22 is connected to the movable contact of the switch 23, the first fixed contact of which is connected to the inverting input of the op-amp 25, and the first output of the capacitor 24, the second fixed contact of the switch 23 is connected to the non-inverter OU 25 and connected to the common bus of the device, OU output connected to the second, the output of the capacitor 24 and is the output of the LED 21.

The first pins are the time of the setting capacitor 27 and the resistor 28 are interconnected and connected to the inputs of the element 2I — NOT 29. The second terminal of the resistor 28 is connected to the inputs of the element 2I — NOT

30 and connected to the second input of the element 2I 32. The output of the element 2I- NOT 30 is connected to the second output of the capacitor 27 and T is connected to the input of the trigger 31. The non-inverting output of the trigger 31 is connected to the first input of the element 2I 32 and T is the input of the trigger 33, and also the first output of the control unit 26. The output of element 2I 32 is connected to the first input of element 2I 34 and the second input of element 2I 35, the second input of element 2I 34 and the first input of element 2I 35 are connected respectively to the non-inverting and inverting outputs T - trigger 33, and the outputs of elements 34 and 35 are respectively in orym and third outputs BU 26. The inverting output T - Trigger

31 is the fourth output of the CU 26.

Measuring transducer capacitive sensor operates as follows.

Elements 29, 30, 27, and 28 implement a rectangular voltage generator, the shape of the output voltage taken from the output of element 2I — NOT 30, is shown in Fig. 2.1. This voltage is applied to the input of the T-flip-flop 31. The output voltage taken from the non-inverting output of the flip-flop 31 (Fig.2.2) controls the operation of the switches 2,3 and 4 and determines the operation cycle of the converter

The output voltage of the element 2I 32 (Fig. 2.4) sets the equilibration time intervals that are formed after the end of the transient process in the measuring circuit of the converter. The output voltage taken from the outputs of the T-flip-flop 33 (the output voltage taken from the non-inverting output of the T-flip-flop 33 is shown in FIG. 2.3) sets the operation cycle

the converter, ensuring the independence of the balancing processes both in the active and in the reactive component of the capacitance sensor. The shape of the output voltages generated at the outputs of elements 2I 34 and 35 is shown in Figures 2.5 and 2.6, respectively. These voltages alternately control the operation of the LEDs 15 and the LEDs 21. When the active component of the capacitance of the capacitance sensor is under-compensated, due to the presence of a parasitic resistive element 8 (resistor), a signal is generated at the output of the simplified-state system 11, in which there is a linearly varying component . The shape of the output voltage of the STS at the time of the transition process in the device, due to the balancing of both components of the impedance of the capacitive sensor 6, is shown in Fig. 2.7. This linearly varying component of the output voltage of the STC 11, through the capacitor 22 (at the time the switch 23 of the signal-controlled logical unit from the output of element 2I 34) is triggered, is input to the op-amp 25, changes its output voltage and balances the current, flowing through the parasitic resistor 8. The exemplary resistor 10 was used as an exemplary active resistance measure. The purpose of the coupling capacitor 9 (Ce) - the formation of a two-pole current flowing through the exemplary resistor 8 n be the requirement: T «RoCg, where T - half period of the output voltage taken from the output T - flop 31. The equilibration reactive component 6 comprises a capacitive sensor in the actuation of the variable component of the output voltage of the STS 11 to zero. This is achieved by transferring the charge of the coupling capacitor 16 to the inverting input of the op-amp 20, which is part of the DM 15. Achieving a state of equilibrium in the device consists in balancing the charges on the measured 7 and sample 5 capacitors, as well as balancing the currents flowing through the resistor 8 and an exemplary resistor 10. In this case, the conversion functions of this device are the expression:

Uebix.1 uon

Re

ivykh.2 --i0p, (1)

Cx

Co Rx, where ivykh.1 is the output voltage of the converter, taken from the output of the SD 15;

and output 2 — the output voltage of the converter taken from the output of LED 21;

Don the voltage taken from the outputs of ION 1, taking into account the fact that the magnitude of the voltages at the outputs of ION 1 relative to the common bus of the converter is equal to Uon / 2;

Cx is the capacitance of the element 7 of the capacitive sensor b;

C0 is the resistance value of the element 8. shunting the capacitive sensor 6;

Ro is the resistance value of the reference resistor 10.

Alternately, the balancing of each of the components of the complex resistance of the measured capacitive sensor (which is given by the control unit operation algorithm) is described by linear equations:

 . O (1 - Co) P1 +

 + (

1-cc

Cl6 nl -I C12C19 / J

(2)

C22tT n2,

()

t C22 n2 I

+ 1 + (i -tNgt-P

Rx C12 C24 Cl2 C24 / J

where m is the number of balances of equilibration of the measured capacitance of the element 7;

nz is the number of steps for balancing the resistive element 8;

and output1 0, arbitrary values of output voltages of DM 15 and DM 21 before the start of measurement (initial conditions);

Ci2, Ci6, Cig, C22 - capacitance value of capacitors 12,16,19,22;

g - the duration of the time interval (removed from the output of the logical element 2 and 34) of the control signal for the operation of the LED 21.

The shape of the output voltages at the time of the transient process caused by balancing the device UBuxi ni - carrying information about the measured capacitance of the sensor 7 and 0V2 P2 - carrying information about the resistance value of the element 8 shunting the sensor, with a value of a 1 and ai 1, is shown in FIG. 2.8 and 2.9, where: "1 CoCi6 / Ci2Cig is the transmission coefficient of the negative feedback loop and the balance circuit of the measured capacitance 7; 02 C22 t / RoCi2C2 is the transmission coefficient of the negative feedback loop of the balance circuit of the current flowing through the element 8.

Analyzing expression (2), we can conclude that: a) with ui, ai 1, the operation of the transducers is approximated by a first-order inertial link (Fig. 2.8 and

2.9); b) with ui-az 1, the converter is balanced in three periods, with one cycle being required to balance the active component of the capacitive sensor and two cycles for

balancing the reactive component of the capacitance impedance of the capacitive sensor (in this case, the transient is called critical); c) at 2 "1-transition

the process is damped oscillatory in nature; d) at a, ai 2, the converter is self-excited and goes into self-oscillatory mode.

As a result of using this

the technical solution is the possibility of creating simple impedance measuring transducers represented by a two-element replacement circuit with high metrological characteristics.

Claims (4)

Claims 1. Capacitive transducer measuring transducer comprising a first operational amplifier that has a circuit feedback between the first input and the output and the second input of which is connected to the common bus of the converter and the first synchronous detector connected in series, the second synchronous detector, the first and second terminals for connecting a capacitive sensor, the first terminal being connected to the input of the first operational amplifier, and the outputs of the first and second synchronous detectors are respectively first and second outputs capacitive transducer transducer, characterized in that, in order to improve accuracy, the reference voltage source is introduced, first, second and the third switch, the first capacitor, the reference capacitor, the reference resistor, the first coupling capacitor, and the block, the first input of the control unit connected to the control inputs of the first, second and third switches, the second output of the control unit connected to the control input of the second synchronous detector, third and fourth the outputs of the control unit are connected respectively to the first and second control inputs of the first synchronous detector, the first information inputs of the first and third switches with unified with the common bus of the measuring transducer capacitive sensor, the second information inputs are connected respectively to the output of the first and second synchronous detectors, the first and second outputs of the voltage source are connected respectively to the first and second information inputs of the second switch, the output of which is connected to the second terminal for connecting a capacitive sensor, the output of the first switch through an exemplary capacitor, and the output of the third switch through a series-connected isolating capacitor and an exemplary resistor, are connected to the input th first operational amplifier, the input of the second synchronous detector is connected to the input of the first synchronous detector, and a first capacitor connected in parallel with the feedback circuit of the operational amplifier of the first communication. 2, the converter according to claim 1, of l and h and y and the fact that the first synchronous detector contains the fourth and fifth switches, the second operational amplifier, the second capacitor, the second separation capacitor, and the input of the second separation capacitor connected to the input of the first synchronous detector, its output connected to the information input of the fourth and fifth switches, the outputs of which are respectively connected to the first and second inputs of the second operational amplifier, the first input of the second operational amplifier through The second capacitor is connected to its output, and its second input is connected to the common bus of the converter, the output of the second operational amplifier is connected to the output of the first synchronous detector, the control inputs of the fourth and fifth switches are respectively connected to the first and second inputs of the first synchronous detector. the detector. 3. The converter according to claim 1, wherein the second synchronous detector contains a third operational amplifier, a third capacitor, a third discharge capacitor, a sixth switch, and the input of the third coupling capacitor is connected to the input the second synchronous detector, its output is connected to the information input of the sixth key, the first and second outputs of which are connected respectively to the first and second inputs of the third operational amplifier, the first input of which is connected via a third capacitor to its output, and its second input is with a common converter bus, the output of the third operational amplifier is connected to the output of the second synchronous detector, the control input of the sixth switch is connected to the control input of the second synchronous detector. 4. The converter according to claim 1, that is to say that the control unit contains the time specifying the capacitor, the resistor, the first and second elements 21/1 - NOT, the first and second triggers, the first, the second and the third element 2I, with the output of the first element 2I - NOT connected in series with the second element 2I - NOT, the first trigger, the second trigger, the second input of the first element 2I, the output of which is connected to the second output of the control unit, the first terminals of the master capacitor and the resistor connected with the input of the first element 2I - NOT, the second terminals to respectively, are connected to the output and input of the second element 2I —NE; the output of the first trigger is connected to the first output of the control unit; the second output of the second trigger is connected to the first input of the second element 2I, the output of which is connected to the third output of the control unit; the second output of the first trigger is connected to the fourth output of the control unit, the first trigger output through the first input of the third element 2I is connected to the first input of the first element 2I and the second input of the second element 2I, the second output of the second trigger is connected to p th output control unit.