SU1666972A2 - Device for measuring specific conductance of current-conducting specimens - Google Patents

Abstract

The invention relates to instrumentation engineering and can be used to measure the value of specific electrical conductivity in electrically conductive products. The aim of the invention is to expand the functionality by providing a measurement of the size of the gap between the eddy current transducer and the electrically conductive product and providing an indication of the permissible value of the electrical conductivity of the electrically conductive product. The device contains 1 - 3 alternating current generators, switches 4, 5, eddy current transducer 6, exciting coil 7, measuring coil 8, amplifier 9, amplitude detector 10, clock generator 11, blocks 12 - 14 of memory, subtraction blocks 15 - 18 , scale converter 19, division unit 20, exponential functional converter 22, indicators 23, 26, 33, control block 24, comparator 25, voltage sources 27, 28, adjustable scale converter 29, switch 30, block 31 of addition, approximator 32 source 34 reference voltage, comparator 35, relay 36. A feature of the invention is the introduction of an approximator 32 and an indicator connected in series, as well as a source 34, a reference voltage connected in series with a comparator 35 and relay 36, and the input of the approximator 32 is connected to the output of subtracter 15 and the second input of the comparator 35 is connected to the output of the approximator 32. 1 c.p. f-ly, 4 ill.

Description

The invention relates to a measuring and control technique, can be used to measure the value of the specific electrical conductivity of electrically conductive products, and is in addition to the author. No. 1583828.

The aim of the invention is to expand the functionality by providing measurements of the size of the gap between the eddy current transducer and the electrically conductive product and providing an indication of the permissible value of the electrical conductivity of the electrically conductive product.

FIG. Figure 1 shows the structural electrical circuit of a device for measuring the value of the specific electrical conductivity of electrically conductive products; in fig. 2-4 are graphs illustrating the operation of the invention.

A device for measuring the value of the specific electrical conductivity of electrically conductive products contains the first 1, second 2 and third 3 alternators, the outputs of which are independently, separately connected to the three inputs of the first switch 4, the second switch 5 connected in series by a eddy current transducer (EPR) 6 with the excitation coil 7 and the measuring coil 8. amplifier 9 and amplitude detector 10, the output of which is connected to the switch 5, the generator 11 clock pulses, the output of which is connected to the control One of the switches 4 and 5, the first 12, the second 13, the third 14 memory blocks, the inputs of which are independently connected to the three outputs of the switch 5, the first 15, the second 16, the third 17, the fourth 18 subtraction blocks, the first large-scale converter 19, the block 20 divisions, the first input of which is connected to the output of the first subtraction unit 16, the output of which is serially connected to the second large-scale converter 21, the exponential functional converter 22 and the first indicator 23, the output of the third subtracting unit 18 is connected to the input of the control unit 24 nor with the input of the first comparator 25, to the output of which the second indicator 26 is connected, which is a light indicator, such as a green LED, as well as a first adjustable reference voltage source 27, connected in series to a second adjustable reference voltage source 28, first unit 15 subtracting, adjustable scale converter 29, third switch

30 (key) and an addition unit 31, the output of which is connected to the second input of the second subtraction unit 16, the output of the third subtraction unit 17 is connected to the second input of the unit

20 divisions and to the second input of the subtracting unit 15, and the output of the source 27 of the reference voltage is connected to the second input of the unit

31 additions, as well as series-connected approximator 32, the input of which

0 is connected to the output of the first subtraction unit 15, and the third indicator 33, the third source 34 of the reference voltage, the second comparator 35 and the relay 36, and the second input of the second

5 of the comparator 35 is connected to the output of the approximeter 32.

The output of control unit 24 is connected to the control inputs of generators 1-3, the output of the first memory block 12 is connected to

0 with the first input of the subtracting unit 16 and through the large-scale converter 19 with the first input of the subtracting unit 18, the output of the second storage unit 13 is connected to the second input of the subtracting unit 18 and to the first input

5 of the third subtracting unit 17, the output of the third memory unit 14 is connected to the second input of the subtracting unit 17 and to the third input of the subtracting unit 18, the output of the switch 4 is connected to the exciting coil 7, and

0 measuring coil 8 is connected to the input of amplifier 9.

A device for measuring the magnitude of the specific electrical conductivity of electrically conductive products operates as follows.

The generator 11 clock pulses produces sawtooth pulses. Each of the switches 4 and 5 contains an analog-to-digital converter (ADC), to the input

0 which receives the sawtooth signals from the generator 11, the decoder, the inputs of which are connected to the output of the ADC. and three switches (field effect transistors). In switch 4, six outputs of the decoder are connected in pairs

5 and are connected independently to the control inputs of the three keys, and in the switch 5, independently even outputs (2.4 and 6 outputs) of the decoder are connected to the control inputs of the three keys. Thanks to this in

0 during one period of the signal from the generator output 11 in switches 4 and 5, the first, second and third keys will be closed in series, with the opening of the corresponding keys in switches 4 and 5

5 will occur simultaneously, and the closure of the keys in the switch 5 will occur with a time delay relative to the closure of the keys of the switch 4, which eliminates the influence of transients. Using the first, second and

The third switch 4 keys connect generators 1 3 to coil 7, respectively, and using the first, second and third switches 5 keys, the output of detector 10 is connected to memory blocks 12-14, respectively.

The sinusoidal current generators 1–3 operate at a frequency (frp and od (respectively, where n1. The output voltage U of the measuring coil 8 is amplified by the amplifier 9 and rectified by the amplitude detector 10. Thus, in the first cycle (the first keys) in the memory unit 12, the magnitude of the amplified voltage of the coil 8 U1 obtained at the frequency of the exciting current (O in the second cycle (the second keys are closed) in the block 13 of the memory is remembered U2, obtained at the frequency of the exciting current (ify and in the third tact (closed third key i) in memory block 14, the value 11z obtained at the frequency of the exciting current a% is stored. During one period of the signal from the generator 11, three measurement cycles U are carried out. According to the theory of eddy current transducers (EPR), the relative amplitude of the EPR UU / Uo, where Do is the amplitude of the VTP in the air (ft O), when installing the VTP over a conducting half-space, will depend on the absolute value of two generalized parameters ft and a, where ft Va // 0 о a - 2H / R; R is the radius of the greater VTP coil, m; o - specific electrical conductivity, cm / m; at - circular frequency of the excitation current, Hz; fi0 - magnetic constant

(“About 4l 10 gn / m); H is the gap between the ECP and the conductive product, m.

To approximate the real dependence U f (/ T), an expression of the form

U a0 + ai In ft (1)

where a0, ai are coefficients, the validity of which is confirmed by the dependences U f (ln ft) shown in FIG. 2 (they are based on known dependencies for ECP with a value of r / R of 0.75, where r is the radius of the smaller coil).

For operation in the linear region, the U f (In / 3) dependencies are changed by ohm (and respectively 0) 2, and the magnitude /) is changed until the equality 2Ui U2-U3 0 is fulfilled, and the U f (ln / J) relation is described expression (1), since the value 2Ui-U2 U3 is proportional to the value #U

not

E (VD:

, 2

So that the expressions valid for the value of U are also true for the values of Ui, U2 and Uz. the amplitudes of the currents of the generators 1-3 are chosen so that the value of 5 U0 is the same when the ECP is excited by 6 currents with frequencies a), (l, and.

The measurement process consists of two stages: calibration and own measurement.

10 The control unit 24 in one of the variants consists of a series-connected button (the input of the control unit 24), an amplifier and a micromotor, which rotates the frequency-generating resistors of the generators 1-3.

5In the calibration process, the operator installs without a gap () VTP b on the reference product with a known value of a - sgat and closes the button of the control unit 24. Control block 24 will be simultaneously

0 change the frequencies of the generators 1-3 until the output voltage of the subtraction unit 18 is set to zero. The scale converter factor 19 is chosen to be two,

5 therefore in the established mode the equality 2Ui-U2-U3 0 will be observed. This means the validity of the expression f1).

At the moment of zero voltage at output 0 of subtraction unit 18 (2Ui-U2 U3 0), the comparator 25 will operate and the indicator 26 will turn on (the green LED will be lit). This will mean that the device operates in the steady state and further frequencies w. (1%, and OJ3. Will not change, while in blocks 12-14 of memory, the values Ui, U2 and Cs will be stored respectively. Ui a0 + ailn / 3T. -) 0 and 2 ao-f-ailnf / Vn). one

Uz a0 -f ailn (/ Zag / Vn). where Dn R Vr / 7i // о Ът, J and from the output of the subtracting unit 17 to the second input of the division unit 20 will receive the value U2 - Uz ailrj n. After the indicator 26 lights up, the operator opens the button of the control unit 24, opens the switch 30, if it was closed, calibrates the device, changing the voltage value of the adjustable source 27 of the reference voltage Ucn 1 until the indicator 23 shows a value equal to In this case, the first input of dividing unit 20 will receive a signal Ui - Uon.i, and from the output of scale converter 21. The conversion factor of which is equal to 2ln p. To the input of exponential functional converter 22 will receive a signal

five

0

five

(2)

Ui -Uon.l

 2ln p. Since the indicator 23 according to U2 - shows the value of aet, then we have

t.1 ..- 1 n nj

 U2-U3 (3)

Solving the system of equations (2), we get

. "

With this in mind and the expression for d / 3, it creates a gap D Hi in the range of its possible change in the control process.

After changing the value of the interfering parameter, the operator changes the transmission coefficient S of the adjustable scale converter 29 until the indicator 23 shows a value equal to the value of Oet. In this case, the L) 4, Us and Ue values will be stored in memory blocks 12-14 respectively. equal

eat

(four)

where M is ln (R // ouJi).

Analysis of expressions (4) and (3) shows that

Uon.i-ao-M (5)

After such operations, the operator closes the switch (key) 30 and changes the value of the output voltage of the second regulated source 28 of the reference voltage -Uon 2 until the indicator 23 shows the value of at.

Since the values of Ui, 1) 2 and Uz have not changed, the indication of the indicator 23 sr aet will be if, from the output of the addition unit 31, the signal equal to Uon.1 is still fed to the input of the subtraction unit 16 (see Expression (3)). For this, the output of the switch 30 must be fed to the input of the addition unit 31, a signal equal to zero, i.e. Both inputs of subtraction unit 15 should receive the same signals, therefore Uon.2 ailn n. Subsequently, the values of Uon.2 and Uon 1 do not change, and blocks 27 and 28 serve as, as it were, memory blocks of values of reference voltages.

The value of the coefficient ai, determined with the aid of the value U2-U3, is further used to measure the relative value of the specific electrical conductivity of the material under test. However, under the influence of the interfering parameters of the monitored product - the gap H, the values of the coefficients ai and a0 can change significantly. In the device and in the prototype, the values of the coefficients ai and BQ found during the calibration process are adjusted depending on the magnitude of the change in the interfering parameter of the tested product. For this operator, do not remove the eddy current transducer 6 from the reference sample,

-

  a0 + ai.

Us Eo 4-31 In (floor VfT).

Ue a0 + ai In (/ Sn / Vn),

(6)

where a0, ai - the values of the coefficients a0 and ai when N D Hi.

Since the value arrives at the second input of dividing unit 20, taking into account (3) it has:

 o U5

2 nnl

and

(hi e and (7)

where U is the voltage at the output of the add 31 block.

Taking into account the expression (4), we get

With „-e

and, h

(8) From the analysis of expressions (7) and (8) it can be seen.

what

.m

If we assume that the transmission coefficient of the individual blocks included in the device does not change during the control, then when the interfering parameter is changed by the value of A Hi. the coefficients a0 and ai change by the values of Yes0 CoDH1I 40 D 3i Ci D Hi and therefore we can write a0 a0 + Yes0 a0 4 Co A Hi, (10) ai ai 4 Aai ai 4 Ci AHi, (11)

Yes0 Aai Aai K, (12)

45 where Co, Ci, k C0 / Ci - coefficients of proportionality.

Since the first and second inputs of the subtraction unit 15 receive the values and and 5, respectively, and the second input of the adding unit 31 receives the value Uon 1, we have

(U5-U6HU2-U3) S + Uoni U where S is the set value of the transmission coefficient of the adjustable large-scale 55 converter 29.

In view of (5) and (9), we have

.o1.-about.

s tu, -u, Hu, -u, r (Ut-u «) - (4i Ull

The resulting expression with (12) can be written in wil

. -Yohm I / i J o L

a, inn 2t rm

u En tt

Ln and 1 la

Thus, the transmission coefficient S of the scale converter 29 depends on the value of the coefficient k. Further, the value of S is not changed.

During the measurement step, the eddy converter 6 is mounted on the product under test. In general, the value of the interfering parameter H will change to the value L Hz A Hi, and the values ai and ao, respectively, on La-i and Lao0 will be in blocks 12–14 respectively, the values U, Ua and

U а0 + ai In Л Ue ao + a In (flu Vn) + a1 In () j

where ai, ао values of the coefficients ai and ao at Н Д hb,

  ai + aai a i-fCiAH2. (14)

a o e0 + Aa0 a 0 + Aai -K. (15)

  R tft (i) (/ and.

where Ots is the specific electrical conductivity of the material of the monitored product. In the process of measurement, the signal enters the first input of the subtraction unit 15, and the signal Ue-Ug arrives at its second input. From the output of block 15, the signal L (UrU)) (Lt24J3) -ai nn-ailnn- Aa i In n (16) is fed to the input of a scale converter 29 with a conversion factor S. From the scale output

the converter 29, the signal Aai (K) is fed through the switch 30 to the first input of the addition unit 31, to the second input of which a signal arrives

.. (U2 - U3)

Don i ao - M 2TgGp

In this case, the output of the addition unit 31 will generate a signal equal to

U Aa (Kt) +, gS).

Taking into account (14), (15) and equality 1) 2 n, we have

1 30-y (Aai + ai) ao - a (17)

The signal is fed to the first input of the dividing unit 20, the second input of which receives the signal Us In n. The output signal bypass 20 division through the second large-scale Converter 21 is supplied

to the input of the exponential functional converter 22, from the output of which a signal is sent to the indicator 23

.2lnn

2 (Y7 - U)

3 1

Taking into account the first equation of system (13) and expression (17), the Wind signal will be equal. h,

ten

thirty

35

40

45

15

Thus, the indicator 23 will show the desired value of the specific electrical conductivity of the material of the controlled product.

To determine the size of the gap H, the signal L is used from the output of subtraction unit 15, which is proportional to the change in the value of the coefficient 20 ai-Aai (see Expression (16)). The possibility of determining the value of H (yy) from the change in the value of at (ai is the slope of the rectilinear sections of the dependence of Fig. 2- U - f (In /)) illustrates the graph in Fig. 3, constructed from the same data as the graph on fmg. 2

The signal L is fed to the input of the approximator 32, which takes into account the slight non-linearity of the dependence Aet p (a) (see Fig. 3). The third indicator 33, at the start of which the signal from the output of the approximator 32 arrives, will show the value N.

The approximator 32 can be adjusted using known dependencies for ECP or by practical calibration, for which, after setting the values of U0n i, Don 2 and S between GTP 6 and the product, gaps of various sizes are created (for example, laying 6 ETP 6 dielectric plates under ETP) at the same time, the approximator 32 is adjusted so that the indicator 33 indicates the desired value of the gap N.

0

five

Linear approximation of the real relationship between changes in the values of ao and ai when H is changed (see expression (12) is true for small changes in H. With the help of dependencies (2) and Fig. 3, the dependence ao - p ( ai) of the kotor shows the change in the value of ao with a change in H, expressed through a change in the value of ai. Because of the non-linearity of the real relationship Yes0 (Aai), expression (12) will be valid in a small range of change in H, therefore in this device with increasing H (a 1 0) Vits is significant

the measurement error au despite the correction of the measurement result that is available.

In order to exclude the measurement of magnitude 7 and at large gaps that do not provide the required measurement accuracy, the device is equipped with a source 34 of the reference voltage, a comparator 35 and a relay 36, the contacts of which are used to supply the supply voltage to the exponential functional converter 22. With increasing H will increase the signal from the output of approximation 32 and, if the magnitude of this signal exceeds the magnitude of the signal of the source 34 of the reference voltage - iop.z, then the comparator 35 will work, which will power the relay winding 36 t com, the transducer 22 is de-energized and the LED 23 will show O.

The desired value of Uon.3 can be obtained as follows. thus .. After setting the values of Uon.1, Uon.2, S and the settings of the approximator 32 between the VTP 6 and the reference product, the gap increases, while the measurement error a appears (the indicator 23 will change). The gap is increased until the maximum permissible measurement error is obtained. The value of Uon.3 is set so that when the gap obtained (permissible measurement error o) triggers comparator 35, the value of n is recommended to be chosen equal to n 1.3-1.5. As an approximator 32, blocks that implement piecewise linear approximation can be used.

As indicators 23 and 33, you can use either dial gauges (galvanometers) or digital voltmeters.

If an electronic digital voltmeter is used as the indicator 23, then the contacts of the relay 36 can be used

and

0.8 0.5

M

0.5 1.0 1.5 2.0 2.5 1dR FIG. 2

to supply the supply voltage not to the converter 22, but to the indicator 23, while the indicator screen (numbers) with large gaps simply will not light up. Besides

Correction of Oi measurement results when H is changed in the device provides for the measurement of an additional parameter —G gap size. control zone between the VTP 6 and the product of mechanical particles - dust,

chips, etc.) incorrect readings of the value and not displayed on indicator 23.

Claims (2)

1. Device for measuring the value of specific electrical conductivity electrically conductive products according to auth. No. 1583628, characterized in that, in order to extend the functionality by providing measurements the size of the gap between the eddy current transducer and the electrically conductive product, a serializer and a third indicator are connected in series into it; moreover, the input of the approximator is connected to the output of the fourth subtraction unit. 2. Pop-1 device, characterized in that in order to provide an indication of the permissible value of electrical conductivity of an electrically conductive product, the third reference voltage source, the output of which is connected in series with the first input of the comparator and the relay, is an exponential functional converter that is controlled; the second input of the comparator is connected to the output of the approximator. and the relay output is connected to a controllable input of an exponential function converter. &Yu Oi -0.2 -q 0.1 Q4 0.6 fig.z do 1,2 1.1 -0.5 about d-0,5 , 0 -0.25 FIG. four