RU50043U1 - Inductive voltage divider - Google Patents

Abstract

The utility model relates to electrical engineering and is intended for dividing AC voltage. The objective of the utility model is to increase the accuracy of division in a wide range of frequencies. The problem is achieved in that in an inductive voltage divider containing the previous and subsequent decades on ferromagnetic cores, on each of which are placed the first and second additional windings with taps, connected according to and in series with each other, the third and fourth additional windings similar to the first and second , and the main winding, and the number of sections and the number of turns of each additional winding is two times less than the number of sections and the number of turns of the main winding, the beginning and end of which are connected to at the beginning of the first and third additional windings and the ends of the second and fourth additional windings, respectively, and the same taps of the first and third, second and fourth additional windings are interconnected. Each decade additionally contains a non-inverting voltage amplifier with a gain equal to unity, while the input of each amplifier is connected to the middle tap of its main winding of the decade, and the output of the amplifier is connected to the common connection point of the additional windings of the decade.

Description

The utility model relates to electrical engineering and can be used as an AC voltage divider with improved metrological characteristics.

Known inductive voltage divider containing cascades made in the form of two-stage transformers on two ferromagnetic cores [Patent RU No. 39001, MPK ⁷ H 01 F 21/12. Publ. 07/10/2004, Bull. No. 19 - 2 p.]. The excitation winding is wound on one of the cores, and the previous and subsequent dividing windings are wound on both of the N insulated wire bundles, equipped with reference windings made of insulated wires placed inside the harnesses and connected to detachable connectors and multi-position paired switches that are connected to the taps dividing windings and external measuring instruments during calibration. The field winding is made of two insulated wires evenly twisted into a bundle, connected in series and sequentially, and its middle branch is connected to the middle branch of the previous dividing winding made of insulated wires uniformly twisted into a bundle, the diameter of which is three times the diameter of the wires uniformly twisted harness, subsequent dividing winding.

The disadvantage of such a divider is the increase in the error of the transmission coefficient at high frequencies (over 10 kHz) due to the relatively large values of the output impedances of the dividing windings and the mutual influence (bypass) of the previous and subsequent decades.

Also known is a multi-decade inductive voltage divider [Patent RU No. 2223564 MPK ⁷ H 01 F 21/12. Publ. 02/10/2004, Bull. No. 4 - 18 pp.], Containing the previous and subsequent decades, each of which is made

from the first and second additional five-section windings with taps, connected in series and sequentially with each other, and the main ten-section winding, the beginning, end and middle tap of which are connected respectively to the beginning of the first, end of the second and common connection point of the additional five-section windings, multi-position switches. In the previous and subsequent decades, located on a common ferromagnetic core, the taps of the extreme sections of the main ten-section winding, the first and second additional five-section windings are interconnected, while in the previous decade the end of the third and the beginning of the fourth additional six-section windings are connected to the middle tap of the main ten-section winding, and the remaining taps, with the exception of the extreme taps, are connected to the corresponding taps of the first and second additional five-section windings

The disadvantage of such a divider is an increase in the error of the transmission coefficient at low frequencies due to shunting the next decade by the previous decade, and at high frequencies due to the relatively large output impedances at the taps of the previous decade and the shunting effect of the load.

Known inductive voltage divider [A.S. USSR No. 1049991, MKI ² H 01 F 21/12. Publ. 10/23/1983, Bull. Number 39. - 4c.], Selected as a prototype, containing the previous and subsequent decades on ferromagnetic cores, on each of which are placed the first and second additional windings with taps, connected in series and sequentially with each other, the third and fourth additional windings similar to the first and second, and the main winding, the middle of which is connected to the common point of the additional windings, and the number of sections and the number of turns of each additional winding is half the number of sections and the number of turns of the main winding, the beginning and which is connected to the beginnings of the first and third additional windings and the ends of the second and fourth additional windings, respectively, and the same taps of the first and

the third, second and fourth additional windings are interconnected.

The device has the following disadvantages:

1. Despite the small error of the transfer coefficient of the main winding, which is a binary divider, it is not possible to completely symmetry, i.e. ensure the independence of the upper and lower halves of the decade winding (only independent five-section sub-dividers and allow to achieve high accuracy of the decade in the entire operating frequency range). This is due to the relatively high output impedance of the main winding, consisting of resistance and leakage inductance, connected in series.

2. In the low-frequency region, due to shunting of decades of each other and the load of the output of the inductive voltage divider, the error of the divider at all output taps of the decades increases. This is due to the relatively high output active resistances of decades.

3. On the upper frequency sub-range, the output impedance is determined by the reactive component, the scattering inductance, which has a maximum value on the average fifth tap of each decade. This leads to an increase in the error of the transmission coefficient with a capacitive load connected to the output of the inductive voltage divider.

The objective of the utility model is to increase the accuracy of division in a wide range of frequencies by reducing the output impedances of decades.

The problem is achieved due to the fact that in the inductive voltage divider, as well as in the prototype, containing the previous and next decades on ferromagnetic cores, each of which contains the first and second additional windings with taps, connected according to and in series with each other, the third and fourth additional windings, similar to the first and second, and the main winding, and the number of sections and the number of turns of each additional winding is half the number of sections and the number of turns of the main winding and the end of which

connected to the beginnings of the first and third additional windings and the ends of the second and fourth additional windings, respectively, and the same taps of the first and third, second and fourth additional windings are interconnected. According to a utility model, each decade additionally contains a non-inverting voltage amplifier with a gain equal to unity, while the input of each amplifier is connected to the middle tap of its main winding of the decade, and the output of the amplifier is connected to a common point of connection of the additional windings of the decade.

The error of the output voltage of the claimed device is determined by the error of the decade windings, the error due to their mutual influence, as well as bypass output of the inductive voltage divider by the load. To a greater extent, these errors depend on the accuracy of the main winding as a binary divider and its output impedance. In the device, an increase in the accuracy of voltage division is achieved by reducing the output impedances of the main and decade windings of decades using non-inverting voltage amplifiers.

As you know, modern non-inverting voltage amplifiers with a gain of unity are accurate integrated amplifiers with high metrological characteristics [Gutnikov B.C. Integrated electronics in measuring devices. - L .: Energoatomizdat, 1988. - P.30]. In these amplifiers, due to the internal negative feedback circuits, high gain stability, a large input (more than 10 MΩ) and small output (less than 0.01 Ohm) resistance are ensured [Witson J. 500 practical circuits on IP / Per. from English under the editorship of V.A. Loginova. - M .: Mir, 1992. - P.119]. Such a low output impedance is difficult to provide in the main winding, since large diameter wires are required to increase the stiffness of the bundle.

The low output impedance of the amplifier can also reduce the output impedances at the taps of a decade-long winding. Figure 1 shows the equivalent

scheme of a decade-long winding balanced by a binary divider for the low-frequency region of 20 Hz ... 10 kHz. The output resistance of the taps n of the lower r ⁿ _o (n) and upper r ^{in the} _o (n) halves are determined as follows

where r ₀ is the output active resistance of the main winding;

r _i , r _j are the active resistances of the wire sections of the upper and lower halves of the decade winding, respectively;

i, j are the numbers of sections of the upper and lower halves, respectively (i = , j = );

n - decade tap number (n = )

In the table. 1 shows the results of calculations according to (1) and (2) of the output active resistances of a decade-long winding of the prototype and the claimed device with r _i = r _j = 0.06 Ohm.

As can be seen from the table. 1, the claimed device has 1.1 ... 11 times lower output active resistance compared to the prototype, which is confirmed by the experimental data (the difference from the calculated less than 10%). Since the circuit shown in Fig. 1 and expressions (1), (2) are also valid for calculating the reactive component of the output impedance, the output scattering inductances are reduced by the same amount. The latter to a greater extent determine the output impedances of the dividers at high frequencies.

In the inventive device, a decrease in the output impedance of the main winding leads to a decrease in the errors of the decade winding, due to the inequality of the parameters of the sections of the additional windings of the upper and lower half of the decade.

Represent the inductances of the sections of the upper and lower halves in the form

L _i = L _CPB + ΔL _i, L _j = L _NRC + ΔL _j,

where L _cpv , L _avg - the average values of the inductances of the sections of the upper and lower half of the decade;

ΔL _i , ΔL _j - deviations of the inductances of the sections from their average values.

Note that the transmission coefficient of a ten-day inductive voltage divider is determined as

where U _I - input voltage;

U _{o n} - the output voltage at the outlet n;

To _n = 0,1 n is the nominal transmission coefficient;

γK (n) is the relative error of the transmission coefficient.

Then from Fig. 1 we obtain the following expressions of the relative errors of the gear ratios for the lower γK _n (n) and upper γK _in (n) half a decade

where l _o is the output impedance of the amplifier.

In the limiting case, when l _o = 0, from (3), (4) we obtain:

From these expressions it follows that with the output impedance of the amplifier equal to zero, the errors of the gear ratios at the taps of the lower and upper halves of the decade winding are caused only by the non-identical parameters of their half and do not depend on the parameters of the other. From a physical point of view with l _o = 0 ten-day divider can be considered as two independent subdelitelya serially connected to the input of each of which is energized 0,5U _Rin and limit the accuracy is determined by the parameters of its own section. Comparing expression (5) with (3) and (6) with (4), we see that γK _n ^o (n) <γK _n (n), γK _in ^o (n) <γK _in (n), i.e. . in the inventive device reduced errors due to the inequality of the parameters of the sections of the additional windings of the upper and lower half of the decade. As a result, the accuracy of the entire decade is increased.

In the inventive device, a decrease in the output impedances of the previous decade leads to a decrease in the error component due to the mutual influence of the decades at both low and high frequencies. The voltage from the output taps of the previous decade is supplied to the input of the next one with less losses than in the prototype.

The inventive device has the best load capacity. Indeed, at a nominal transmission factor of a two-decad divider

K _{n, m} = 0.1n + 0.01m (n = and m = - the numbers of the taps of the previous and subsequent decades) the output impedance Z _{out n, m of the} two-decadic divider is determined by the formula

Z _{o n, m} = Z _{o n} + Z _{o m} ,

where Z _{out n} , Z _{out m} - output impedances of the previous and subsequent decades.

In the claimed device, the introduction of amplifiers reduces the output impedances of the previous and subsequent decades, including on average, the fifth tap of each decade. Then, due to the small value of Z _{o, n, m, the} load shunts the output of the inductive voltage divider less in the entire operating frequency range, and, therefore, its accuracy increases. These conclusions are confirmed by the experimental data given in table. 2 at an active and capacitive load of 10 kOhm, 1000 pF. As can be seen from the table. 2 the relative error of the transmission coefficient of the claimed device at a frequency of 20 Hz is 1.25 ... 3 times, and at a frequency of 100 kHz, 1.2 ... 10 times less than the errors of the prototype.

Thus, in the inventive device, the introduction into each decade of a non-inverting voltage amplifier with a gain equal to one, and the connection of the input of each amplifier with the middle tap of its main winding, and its output with a common connection point of the additional windings of a decade reduces the output impedances of decades and the entire divider as a whole, as a result of which the accuracy of voltage division in a wide frequency range increases.

Figure 1 presents the equivalent circuit of a decade winding for the low-frequency region.

Figure 2 shows a schematic diagram of an inductive voltage divider.

In the table. 1 presents the values of the output active resistances of the decades of the claimed device and prototype.

In the table. 2 shows the relative errors of the transmission coefficient of the claimed device and prototype with active and capacitive load of 10 kOhm, 1000 pF.

The inductive voltage divider (figure 2) is a two-decadic voltage divider containing the previous and subsequent decades, located on the ferromagnetic cores 11 and 12. The previous decade consists of the main winding 13, four additional windings 14-17. The main winding 13 is made of a bundle of two uniformly twisted insulated wires connected in accordance and in series. A tap was made from the connection point 18. An additional second 14 and fourth 15 five-section winding with the number of sections and the number of turns is half the number of sections and the number of turns of the main winding from the second ten-wire bundle. From the third ten-wire bundle, additional first 16 and third 17 five-section windings are made. The same taps of the windings 14 and 15, 16 and 17 are connected in pairs and are output taps 19-29 of the previous decade. The beginning of the main winding is connected to the beginnings of the windings 16, 17. The middle tap 18 of the main winding is connected to the input of a non-inverting voltage amplifier 30, the gain of which is unity. The amplifier output is connected to a common connection point of the additional windings 14-17. The end of the main winding 13 is connected to the ends of the windings 14, 15. The next decade is similar and consists of the main winding 31 and additional five-section windings 32-35 with output taps 36-46. The middle tap 47 of the winding 31 is connected to the input of a second non-inverting voltage amplifier 48, similar to the first amplifier. The output of the amplifier 48 is connected to the middle tap 41 of the ten-day winding. In contrast to the previous inputs of the next decade, they are connected not with the input voltage source, but with a multi-position paired switch 49, switching the output taps of the previous decade. The bends of the next decade are connected

with a multi-position switch 50, from which the output voltage U _o is removed.

The device operates as follows. The input voltage U _in goes simultaneously to the main winding 13 and the additional windings 14-17, since they are made on the same core 11. The winding 13 is a binary divider, so there will be a voltage of 0.5U _in at its middle tap 18. This voltage is supplied to the input of amplifier 30. Since the gain of the latter is equal to unity, then its output will also have a voltage of 0.5U _in , i.e. the amplifier 30 operates in voltage follower mode. The output resistance of the repeater in the operating frequency range of 20 Hz ... 100 kHz does not exceed 0.01 Ohm, i.e. negligible, so the repeater is an ideal voltage source of 0.5U _in . This voltage is supplied to the upper 14, 15 and lower 16, 17 windings. Since the number of sections of sub-dividers is five, the voltage of each section is 0.1U _in . Thus, on taps 19-29, the resolution of the output voltage of the first decade is 0.1U _in . This voltage is supplied by the switch 49 to the input of the next decade, i.e. on windings 31-35. The total magnetic flux in the core 12 induces in these windings an EMF proportional to the number of their turns. Voltage winding sections 32-35 are 0,01U _Rin, the voltage at terminal 47 with respect to the windings 31, 34 and 35-0,05U _Rin. Next, the voltage from the middle tap 47 of the main winding 31 is fed to the input of the second amplifier 48. From the output of the latter, voltage is supplied to the midpoint 41 of the ten-day winding. Due to the low output resistance of the amplifier, the voltage at the middle tap 41 relative to the beginnings of the windings 34, 35 and the ends of the windings 32, 33 with a high accuracy is 0.05U _in . This voltage is divided by five-section windings with a resolution of 0.01U _in . At specified positions of the switches 49, 50 at the output of the inductive divider voltage U is _O = 0,35U _Rin.

A prototype of a two-decad divider was made on ferromagnetic toroidal cores 80 × 50 × 20 mm from permalloy 79 nm

(magnetic permeability μ = 120,000, induction B = 0.4 T). Decades were made the same. The main winding 13 was made of a bundle of two PETV-2 wires with a diameter of 0.25 mm, the number of turns was 300. The first 16 and third 17 additional windings were made of ten evenly twisted into a bundle of PETV-2 wires with a diameter of 0.25 mm. The second 14 and fourth 15 additional windings are made of a similar bundle. The number of turns of the additional windings is 150. Voltage amplifiers 30 and 48 with a gain of unity were made on an integrated operational amplifier 140UD26A.

Errors were determined by the method of comparison with the measure — a standard six-decade inductive voltage divider, which is part of the measuring device K2-41. At the inputs of the dividers, a voltage of 5 V of the amplitude value was supplied from the generator of sinusoidal signals GZ-109. A differential indicator DU-16 with a sensitivity of 10 nV was used as a null indicator.

Claims (1)

An inductive voltage divider containing the previous and subsequent decades on ferromagnetic cores, on each of which are placed the first and second additional windings with taps, connected in series and sequentially with each other, the third and fourth additional windings similar to the first and second, and the main winding, and the number sections and the number of turns of each additional winding is half the number of sections and the number of turns of the main winding, the beginning and end of which are connected to the beginnings of the first and third additional windings the coil and the ends of the second and fourth additional windings, respectively, and the same taps of the first and third, second and fourth additional windings are interconnected, characterized in that each decade further comprises a non-inverting voltage amplifier with a gain equal to unity, while the input of each amplifier is connected with the middle tap of its main winding of the decade, and the output of the amplifier is connected to the common point of connection of the additional windings of the decade.