SU1656471A1 - Measuring shunt - Google Patents

Abstract

The invention relates to electrical measuring technology and can be used to measure pulsed and alternating currents in various coaxial structures, such as coaxial transmission lines, accelerators, and charged particles. The purpose of the invention — improving measurement accuracy — is achieved by increasing noise immunity and expanding the frequency band of a reproducible measuring shunt. The conductive casing 4 protects the resistive element 2 from the interfering currents flowing through the outer conductor of the coaxial cable. Ferromagnetic material 5 prevents the flow of measured currents through the casing, the resistive element. 1 il.

Description

The invention relates to electrical measuring technology and can be used to measure pulsed or variable currents in coaxial structures (for example, in coaxial transmission lines, accelerators of charged particles).

The purpose of the invention is to improve the measurement accuracy by increasing noise immunity and expanding the frequency band of recorded frequencies.

The drawing shows the design of the measuring shunt.

The shunt contains a hollow conductor 1. resistive element 2, coaxial cable 3 connection with the measuring and recording equipment, hollow conductive casing 4, ferromagnetic material 5, 6 and 7 - conclusions of the resistive element 2, measuring and recording equipment 8 cable 3, a dielectric strip 9 The resistive element 2 is included in the gap of the hollow conductor 1. The hollow casing 4 covers the outside of the resistive element 2 and is connected mechanically and electrically with

a hollow conductor 1 on both sides of the resistive element 2. Between the inner surface of the casing 4 and the outer surface of the hollow conductor 1 is placed ferromagnetic material 5. The first pin 6 of the resistive element is connected to the inner conductor, and the second pin 7 is connected to the screen of the coaxial cable, and A 6 resistive element connected to the inner conductor of the communication cable is placed between the resistive element 2 and the ferromagnetic material 5. A dielectric strip 9 is placed between the resistive element 2 and its About conclusion 6.

As a resistive element, discrete resistors (for example, C2-10, TVO), uniformly distributed around the discontinuity circle, or a thin-walled thin-alloy pipe section (for example, nichrome) can be used. The pipe wall thickness is chosen so that it is at least 4 times less than the depth

Sh

O (L

a VI

skin layer at all frequencies of the measured current.

As a ferromagnetic material that fills the internal volume of the casing, it is advisable to use ring ferrite cores (for example, from ferrites of marks 1000НН, 1000НМ, 2000НН, 2000НМ) placed concentrically to the hollow conductor. The sizes and number of cores are chosen based on the following conditions.

The fall of the flat part of the transient response on the duration of the measured pulse is not more than the specified one, ie:

R- K

where // o - 4 L-10 is a magnetic constant;

// - magnetic permeability of the core material;

h is the width of the core;

D, d - outer and inner diameter of the cores, respectively;

N is the number of cores;

so the pulse duration of the measured current;

K is the allowable decay of the flat part of the transient response (usually K 5%);

R is the resistance of the resistive element.

No saturation of the core material should occur, i.e.

 Vn n

j I (t) dt

to

R

where l (t) is the measured current;

to the time of the beginning of the measured pulse;

1 and the duration of the measured pulse;

S is the cross-sectional area of the core;

Int induction saturation of the core material.

The output of the resistive element connected to the inner conductor of the coaxial communication cable can be made in various ways. If there are no special requirements for shunt speed, then any wire can be used as such. If, however, it is necessary to achieve maximum speed, it is necessary to perform it in the form of a cylindrical tubular electrode concentric to the resistive element. In this case, it is advisable to transmit a signal taken from a resistive element using several identical cables connected to a resistive

0

five

U

five

0

five

0

5 0 5

element uniformly around the circumference of the shunt.

A hollow conductor is usually a piece of a cylindrical pipe made of an alloy with a high conductivity (copper and its alloys, steel, aluminum and its alloys) with flanges for insertion into a dissecting coaxial structure. As a hollow conductor, the outer conductor of the coaxial structure can also be used directly.

The casing may be of arbitrary shape, but it must ensure that the ferromagnetic material is placed inside the required amount. The thickness of the casing wall is chosen from the condition that it is at least 5-10 times greater than the depth of the skin layer.

As a unit of measurement and recording, you can use any electron oscilloscope that has the appropriate bandwidth and sensitivity, for example C8-13. C8-12. С9-4А, С7-10Б, СРГ5.

Works shunt as follows.

Due to the skin effect, the measured current will flow along the inner surface of the hollow conductor 1. Due to the presence of a discontinuity, all this current must flow through the resistive element 2, creating a voltage drop U on it,

U Psh-1,

where Rm is the resistance of the resistive element;

I is the measured current

which, using a coaxial cable 3, is fed to the recording apparatus 8. The electrically conductive casing 4 protects the resistive element 2 from disturbing currents flowing through the outer conductor of the coaxial structure and prevents the emission of parasitic electromagnetic fields into the outer space by a break in the hollow conductor. Ferromagnetic material 5 prevents the flow of measured currents through the casing, the resistive element mines. The dielectric strip 9 isolates the resistive element 2 from its pin 6 connected to the inner conductor of the coaxial cable 3.

When the device is operating under the conditions of strong electromagnetic interference in the outer conductor of the coaxial, an interfering current is induced in the p. In the prototype, this current causes the appearance of an interference signal

Un In Pi,

where gsh is the resistance of the resistive element,

superimposed on the main signal. In the proposed device because of the screen

the casing effect, the interference signal is less K times:

To

Z12

where Zi2, - L 2 va e

resistance

casing connections;

d is the thickness of the skin layer;

-7 g

// about 4-l-10 magnetic constant nm

on ;

/ l- relative magnetic permeability of the housing material;

e is the radius of the casing;

OS specific conductivity of the material of the casing,

A- top shchi and a wall of the casing;

f is the frequency of the disturbing current;

I - the length of the casing.

Calculations using this formula show that a casing made of well-conducting material (copper, aluminum or their alloys, steel) provides almost complete interference suppression (K 1010-1011).

The same degree of improvement in shielding, as follows from the principle of reciprocity, should be provided by the casing and for parasitic electromagnetic fields radiated by a break into outer space,

In this construction, parallel to the resistive element, the circuit includes the outer surface of the hollow conductor - the inner surface of the housing - the outer surface of the hollow conductor. Input

resistance to this ZPx circuit. firstly, it is entirely regulated by the design of the shunt, and secondly, due to the fact that the internal cavity of the casing is filled with ferromagnetic material, wears

mainly inductively active, with ZBX RIU up to the upper limiting frequency of the resistive element. As in practice, the upper limiting frequency of the resistive element is many times higher than the first resonant frequency of the parasitic circuit, the proposed solution allows the frequency range of the reproducible frequencies to be repeatedly extended to the upper ICTOT.

Claims (1)

Invention Formula A measuring shunt containing a resistive element, built-in is a gap of a hollow conductor, and one outlet of the resistive element is connected to the internal conductor of the coaxial communication cable with the measuring and recording unit, in order to improve the measurement accuracy by improving the noise immunity and expansion of the recorded frequency band, an additional hollow electrically conductive casing filled with ferromagnetic material is introduced into it, a gap in the hollow conductor and a resistive element are placed in the casing, with Unification with the outer surface of the hollow conductor, wherein the output of the resistive element connected to the inner conductor of the cable connection is disposed between the ferromagnetic material and resistive element.