SU1746330A1 - Device for measuring capacitance of sensor - Google Patents

Abstract

The invention relates to a measurement technique and is intended to measure an information parameter of a capacitive sensor. The purpose of the invention is to reduce the measurement error by switching two channels. The voltage source 1 is connected to the contact of the key 2. The second and third contacts of the key are connected to terminals 3 and 4, to which the terminals of the measured and reference capacitances are connected, respectively. The second terminals of the capacitors are connected by a third terminal 5 with the output of an exemplary capacity bis input to the amplifier 7. Its output is connected to the second output of the exemplary capacity and to the input of the rectifier 8. Its output is connected to the contact of the second key 9, the second and third contacts of which are connected respectively to the inputs of the logometer 10. Moreover, the controlled inputs of the keys are connected to the output of the multivibrator 11, the second input of the amplifier and the second output of the voltage source are connected to the common bus, and the voltage source is a sinusoidal generator April voltage. 1 il. yy

Description

The invention relates to electrical engineering and can be used to measure the informative parameter of capacitive sensors.

The purpose of the invention is to reduce errors due to the influence of cable capacity and input resistance due to the fact that the first and second keys, a rectifier, a logometer and a multivibrator are inserted into the device, while the switching contact of the first key is connected to the output of the voltage source, and the opening and closing contacts to the second and the third terminals, respectively, with the input of the rectifier connected to the output of the amplifier, and the output to the switching contact of the second key, which commutes the input voltage to the two inputs of the logometer, while key operates multivibrator.

The drawing shows a functional diagram of the device.

The device consists of a voltage source 1, first 2 and second 9 keys, a multivibrator 11, the output of which is connected to the controlled inputs of the first and second keys, measured by Cx and the reference capacitance of the sensor, the first conclusions of which are combined together and connected through the first terminal 5 to the amplifier input 7, and the output of the voltage source is connected to the switching contact of the first key, the opening contact of the key is connected to the second terminal 3, and the closing to the third terminal 4, an exemplary capacitance 6 is connected between the output and input of the amplifier, whose output through the rectifier 8 is connected to the switching contact of the second key, the outputs of which are connected to the input of the logometer 10.

The device operates as follows.

The voltage from the output of the voltage source is supplied to the switching contact of the first switch 2. The switch 2 connects in the first cycle between the output of the voltage source 1 and the input of the amplifier 7 the reference capacitance Sop. The voltage output from the amplifier 7, equal

U1 Con = Uo ~ x

B

through the rectifier 8 and the second switch 9, which works synchronously with the first, it is supplied to the logometer 10. In the second cycle, the switch 2 connects the measured capacitance Cx between the output of the voltage source 1 and the input of the amplifier 7. The voltage output from the amplifier 7. equal

Uic _x = U ₀ ^ x

Lo _χ __________________________1________________.

4- 1 / ΐ J- Cx j__1 \

Ku V Co JwCoRbxJ also through the rectifier 8 and the second switch 9 is supplied to the logometer 10, which divides the two voltages Uicx / Uicon

Ui Cx ₌ C _{x χ}

Ul Sop Sop ₊ 1 A ₊ £ gn + V \ _χ Ku \ _____ Ср J ft) Ср R _BX 1 ¹⁺ 1 / ^{1+ + +} ) is / .x)

The error of such a conversion will be equal to _._______ Sop - C _x __________ ___ ^G Co (1 + K _y ) + Ck + 1 / Jft) R _B x

Sop ~ Cx Co (1 + Ku) + Cx

Claims (1)

Claim A device for measuring the capacitance of the sensor, containing a voltage source, first and second keys, a multivibrator, the output of which is connected to the controlled inputs of the first and second keys, a measured and reference capacitance of the sensor, the first conclusions of which are connected to the terminal and input of the amplifier, characterized in that, with In order to reduce the error from the influence of the cable capacitance and input resistance, an exemplary capacitance, a rectifier, a logometer, a second and third terminal are additionally introduced into it, and the output of the voltage source is connected to a switch contact terminal of the first key, while the opening contact of the key is connected to the second terminal, and the closing to the third terminal, the second terminal is connected to the second output of the measured capacitance of the sensor, the third terminal is connected to the second output of the reference capacitance of the sensor, the first output of the reference capacitance is connected to the input of the amplifier, and the second output is with the output of the amplifier and the input of the rectifier, the output of the rectifier is connected to the switching contact of the second key, the outputs of which are connected to the input of the logometer, and the voltage source is a generator with inusoidal voltage.