SU1629877A1 - Capacitance meter - Google Patents

Abstract

The invention relates to a measuring technique and is intended for use in measuring devices on CNC machines as an embedded contactless capacitive measuring sensor with autonomous power supply. The purpose of the invention is to improve the accuracy and stability of measurements. The clock generates square wave signals with a clock frequency. On the leading edge of each of these signals, the waiting multivibrators 2 and 3 are executed simultaneously on one chip. The durations of the output pulse signals of the waiting multivibrators 2 and 3 are proportional to the values of the measured 4 and compensating 5 capacitances, respectively. Determination of the sign of the difference in capacitance values is carried out by two logical elements AND 7 and 8 and / 5-trigger 9. The capacitance meter also contains the logical element EXCLUSIVE OR 6 and the display unit 10 of 3 Il and (L

Description

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The invention relates to a measuring technique and is intended for use in measuring devices on CNC machines as an embedded contactless capacitive measuring sensor with autonomous power supply.

The aim of the invention is to improve the accuracy and stability of measurements.

FIG. 1 shows a diagram of a capacitance meter; in fig. 2 shows an example of its use in a measuring head; in fig. 3 - time diagrams. ,

The capacitance meter contains (Fig. 1) serially connected clock pulse generator and standby multivibrator 2, standby multivibrator 3, measurable capacitance 4 (Cx) and compensating capacitance 5 (Cof,}, logic element EXCLUSIVE OR 6, logic elements AND 7 and 8, / 5-flip-flop 9, display unit 10. The output of the generator 1 clock pulses is connected to the first input of the waiting multivibrator 3, to the second input of which a compensating capacitor 5 is connected. The measured capacitance 4 is connected to the second input of the waiting multivibrator 2, out which is connected to the first inputs of an EXCLUSIVE OR 6 logic element and AND 8 logic element, the output of a standby multivibrator 3 is connected to the second input of an EXCLUSIVE OR 6 logic element and the first input of a logical element AND 7, the output of the EXCLUSIVE OR 6 logic element is connected to the second inputs of logical elements And 7 and 8, the output of the logic element And 7 is connected to the S-input / 5-flip-flop 9, the output of the logical element And 8 - to the L-input / 5-flip-flop 9 and the first input of the display unit 10, the second and third inputs of which connected to the pr m th and inverse outputs / 5-flip-flop 9, respectively. Both waiting multivibrator 2 and 3 are made on a single chip integrated circuit.

One use case for an electrical capacitance meter is (Fig. 2) a measuring head for CNC machines, comprising a body 11, an external measuring probe in the form of a tubular grounded screen 12 with a tip 13, a support flange 14 bonded to the probe, a group of contact elements 15 and 16, placed respectively on the flange and the housing 11. The screen 12 is separated from the tip 13 by a dielectric strip 17. The screen 12 and the tip 13 are made of electrically conductive material. Inside the tubular screen 12 is placed insulated wire 18, electrically connected to the tip 13, the latter may have a different shape, including the shape of a ball. The head also contains an internal probe in the form of a tubular grounded screen 19 with a tip 20. Screen 19 is separated from n0

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the end cap 20 with a dielectric strip 21. The screen 19 and the tip 20 are made of an electrically conductive material. Inside the tubular screen 19 is placed insulated wire 22, electrically connected to the tip 20. The latter may have a different shape, including the shape of a ball. The internal probe is located in a special compartment 23 located inside the measuring head and communicating through openings (not shown) with the external environment. Compartment 23 is provided with a micrometer screw 24 electrically connected to the body 11 of the measuring head and passing through it to the outside. The outer end of the micrometer screw 24 has a slit 25 for adjustment, the inner - electrically conductive pad 26 is circular in shape, located relative to the center of the tip 20.

The electric part of the measuring head is made according to the scheme described by the capacitance meter shown in FIG. 1. The measurable capacitance Cx is formed between the tip 13 and the test surface 27, the compensating capacitance Con is formed by the tip 20 and the electrically conductive pad 26.

The meter capacitance works as follows.

The clock pulse generator 1 generates square-wave signals with a clock frequency fr. On the leading edge of each of these signals, stand-by multivibrators 2 and 3 are simultaneously launched, made with the same electrical circuits on the same chip (one body of the integrated circuit), the duration of the output pulse signal The standby multivibrator 2 is proportional to the value of the measured capacitance 4, which is switched on in time to the specified circuit of the indicated multivibrator 2. The duration of the output the pulse signal of the standby multivibrator 3 is proportional to the magnitude of the compensating capacitance 5 (Sop), which in its magnitude and other technical parameters (for example, no TKE) is close to the measured capacitance 4 (Cx). A change in the measured capacitance 4 (Cx) by ± DS corresponds to a proportional change in the duration of the pulse signal of the waiting multivibrator 2 by a value of ± D7 (Fig. 3), obtained by extracting the difference in duration signal between the pulse signals of the waiting multivibrators 2 and 3 by the logical element EXCLUSIVE OR 6. The determination of the sign ("+ corresponds to an increase in the value of the measured capacitance 4, and" to its decrease) is carried out by two logical elements AND 7 and 8 and Y with a 5-trigger 9 (Fig. 3), the signals of which are received to respective inputs of unit 10 display.

The determination of the capacitance Cx is carried out as follows.

Assume that the standby multivibrator 2 has the capacity of the standby multivibrator 3. In this case, the equality C-Cp is established initially when the device is adjusted by adjusting the variable capacitance Sop until the moment of equality of the output signals of both multivibrators, i.e. or Top-Ta a.0, where Top is the duration of the output signal of the waiting multivibrator 3; Tilm.- duration of the output signal of the waiting multivibrator 2. Then the capacitance Cx can be determined from the ratio

T M-T0n KR (C + Cx) -KRC0,:, but since, then

Tv-M.- Ton KRCoa + KRCJl-KRCon KRClc or

.

When choosing a resistor R, the same for both pending multivibrators 2 and 3 and equal to such a value that its product by a constant coefficient K is equal to 1, we get

,

i.e., the duration of the differential signal D7 is equal to the value of the measured capacitance Cx and is determined by measuring the duration of this interval.

The value of the capacitance Cx can also be determined as follows. Let us measure the duration of the differential signal D7 and add or subtract this value from T0 ", i.e., for the duration of the signal we get

/ o / 1- A A Sol - OR

(SOYA-C) / (, from here

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c l / gp subject to K., we get

A A T

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/ on 1ilm. &, silt, m 1 n A /. At T “Am.Top we will receive

IvbtvbL. op A A A Sop

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DG + / SchS, -Sol) / (,

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ON CONDITION / (/, GET

. Then

Ty $ m - OR . Top + DT,

but since it is 7 on const, the operation of determining the value of the measured capacitance is reduced to the simple addition of the measured value D7 with a constant value of Top, which can be done both in manual, on and in automatic mode in display unit 10.

The coefficient K is determined experimentally for each specific series of integrated circuits and depends on the threshold values of the specific series, for example, for the K561 / series (0.69.

The work of the electric circuit of the measuring head is carried out similarly to the work of the capacitance meter, while the magnitude of the measurement result

proportional to the size of the gap between the tip 13 and the controlled surface 27.

Improving the accuracy and stability of measurements occurs due to the same

effects of factors such as, for example, changes in the magnitude of the supply voltage, changes in temperature, humidity, atmospheric pressure, and aging of the elements of the electric circuit, etc., on

Both Qs are waiting for a multivibrator, made on the same chip of an integrated circuit using the same electrical circuit diagrams, which causes the same increase or decrease in the duration of their output pulse signals, but practically does not affect the change in the magnitude of the difference signal between them.

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Claims (1)

Invention Formula The capacitance meter, containing a series-connected clock generator and the first standby multivibrator, as well as a display unit, the measurement object is connected to the second input of the first standby multivibrator, and a compensating capacitance differing in t & l to increase accuracy and stability. measurements, the second pending multivibrator, the logical element EXCLUSIVE OR, two logical elements AND and / 5-trigger, output 0 clock pulse generator connected to the first input of the second monostable multivibrator, a first monostable multivibrator output connected to a first input of the exclusive OR gate and the first input of the first logic ele5 ment And output of the second monostable multivibrator is connected to a second input of the exclusive OR gate and the first input of the second logic element AND, the output of the logical element EXCLUSIVE OR is connected to the second inputs of the first and second logical elements AND, the output of the first logical element and OR is connected to the S-input / -triggera, the output of the second AND gate is connected to / -Log / 5 flip-flop, the output 5 of the first logic element I is connected to the first input of the display unit, the second and third inputs of which are connected respectively to the direct and inverse outputs of the A S-flip-flop, waiting for the second input of the second The brush of the multivibrator is connected to a compensated multivibrator made on the same crisp capacitance, both of which are waiting for a tall integrated circuit.  27 at 3 FIG. 2 Fig.Z