SU1594438A1 - Apparatus for measuring derivative of current - Google Patents

Abstract

The invention relates to a measurement technique and can be used for non-contact remote measurement of a first or second derivative of a current in a conductor. In order to improve measurement accuracy by reducing the dynamic accuracy in remote measurements, both terminals of the outer conductor of the coaxial cable of the winding 3 are interconnected, and one of the terminals of the central conductor of the winding 3 is connected to the electrometric converter 7 through the action of current in the conductor 2, a magnetic flux is generated in the ferromagnetic core 1, which is converted into an electrical signal in the winding 3, via conductors 5 and 6 of line 4 to the input of the transducer 7. On the sub-bus 18 command to set the measurement mode of the first or second derivative, the measurement result is fed to the clamp 9. In the first case, the capacitor 10 through the switch 14 converts the amplifier 8 into an integrator, in the second case the measuring resistor 11 is turned on through the switch 13. Resistors 15 and 16 provide the operating mode amplifier 8. Bus 17 encodes the reset signal and switch 12 closes, discharging capacitor 10. 3 sludge.

Description

The invention relates to a measuring technique and can be used for non-contact remote measurement of the first or second production of 1} current in a conductor.

The aim of the invention is to improve the measurement accuracy by reducing the dynamic error during remote measurements.

FIG. 1 shows a functional diagram of the device; in fig. 2 and 3-time diagrams of the input and output voltages of the units of the device and the measurement modes of the first and second current derivatives, respectively. ; The device for measuring the derivative of current contains a ferromagnetic ferdecnik 1, primary winding 2, you are conductive, a passage along the axial line of core 1, a recurrent winding 3 covering 1 |) uniformly distributed turns of a ferromagnetic core 1 and made with a coaxial cable, line 4 connections, including conductors 5 and 6

The electrometric current converter 7 contains an electrometric amplifier 8, its output is connected to the output terminal 9, integrating 1 | 1 capacitor 10, measuring {resistor 11, bit 12, ana-Negative switches 13 and 14, resis 15 and 1b "External terminals The wires of the coaxial cable ends of the winding 3 are connected via conductor 3 of the communication line 4 to the common bus of the electrometric converter 7, and the output of the inner conductor of one of the ends of the coaxial winding 3 is connected to the input of the electrometer 4 of the communication line 4 Cesky current converter 7. The input of the electrometric converter 7 is connected to a single terminal of the bit switch 12 and the terminals of the normally open contact of the analog switch 13 and the normally closed contact of the analog switch 14. The normally closed contact of the analog switch 13 and the normally open contact of the analog switch 14 are respectively connected through resistors 15 and 16 with a common bus device. I switch - the contacts of the analog switches 13 and 14 are connected through the measuring resistor 11 and the integrating capacitor 10, respectively, with you

five

0

five

0

the course of the electrometric amplifier 8. Input control of the bit key

12 is connected to the bus 17 Reset. Control inputs for analog switches

13 and 14 are connected to the bus 18 Mode of operation.

The device works in the following way.

Before starting the measurement, after supplying the supply voltage, the output voltage of the electrometric current transducer in the measurement mode of the first derivative of the current is different from zero (Fig. 2 g). At time t, a command is received for the initial installation of the electrometric converter 7 (Fig. 2e) and its output voltage is set close to zero (Fig. 2g). When a controlled current pulse appears in the primary winding 2 (FIG. 2 a), a magnetic flux создает is generated in the ferromagnetic core 1 1 and penetrates the turns W of the secondary winding 3. The electromotive force and J at the ends of the inner conductor of the secondary winding cable 3 penetrate the coupling speed (Fig.26) g.

dV, dt

dt

(one)

Between the inner conductor of the secondary winding 3 and the outer conductor (shield) of the coaxial cable, from which the secondary winding 3 is made, there is a distributed capacitance CQ. Thus, when EMF appears and between the short-circuited outer sheath of the cable and the inner conductor of the cable, which is connected via line 4 to the input of the electrometric converter 7, a current flows If, the level of which is proportional to the second time derivative of the controlled current 1 (Fig. 2) ):

50

t s --- (s) - 5 dt dt

-CoWH.hln - .- (2)

De mo h

magnetic permeability of core 1; winding size 3 along the axis

er;

g and g

515

- respectively, the outer and inner radii of the ferromagnetic core 1. Since the integrating capacitor 10 is included in the negative feedback circuit of the electrometric amplifier 8, the output signal Uj of the electrometric current converter 7 is proportional to the first derivative

current Ifl (Fig. 2 g):

 (3)

-iwp ..- (1.-i)

. dt

TO

where C ,, is the capacity of the integrating capacitor 10; capacity of communication line 4; amplification gain of an electrometric amplifier 8 with open-loop feedback, K 1.

 Due to the fact that the electrometric amplifier 8 is covered by a deep negative feedback and its non-inverting input is connected to the common bus of the device, its input voltage is close to zero (the fraction of millivolt) and recharging of the capacity of the link 4 does not occur. Due to this, the dynamic measurement error of the derivative of the monitored current caused by the capacitance C is reduced, and the higher the gain K of the electrometric amplifier 8, the less effect the capacitance Cd has on the measurement result.

In the control of the second derivative of current 1, the electrometric converter 7 operates in the mode of a resistive converter of small currents and its output voltage U. is proportional to the input current If (Fig. 2

X ,, g):

and, R ,, or subject to (2):

With t-1

-)

V-l

(3)

(four)

 RriC, W / y hln4-

dt

(five)

Diagrams th1 fig. 3 a, b correspond to the diagrams of FIG. 2 a, b, v. This

ten

20

In the case, as in the current integrator mode, due to deep negative feedback, the input voltage of the electrometric amplifier 8 is close to zero and recharging of the capacitance of link 4 almost does not occur. This results in Y. a decrease in the dynamic error of measurement of the second derivative of the monitored current.

Claims (1)

Invention Formula A device for measuring the derivative of a current containing a ferromagnetic 25 a core with a primary winding made in the form of a conductor passing along the center line of a ferromagnetic core; a secondary winding that covers evenly distributed 30 turns in a ferromagnetic core to a coaxial cable, which is different in order to increase accuracy measurement due to the reduction of the dynamic error during remote measurements, an electrometric current transducer is additionally introduced into it, with a common bus through which the first conductor of the communication line The external conductors of the coaxial cable are connected to the external conductors, and the internal conductor of one of the ends of the coaxial cable is connected through the second conductor of the communication line to the input of an electrometric current converter, the output of which is the output of the device, and the inputs for controlling the mode of operation and initial installation of an electrometric converter The current is connected respectively to the tires. Mode of operation and Reset. 35 40 45