SU970247A1 - Direct current measuring device - Google Patents

Description

The device relates to electrical measuring equipment and can be used for contactless measurement of direct current and verification of various current meters. A device for measuring direct current, containing a magnetic modulator, whose indicator winding through a passive filter, an AC amplifier and a phase detector is connected to a feedback unit and a reading unit, is known, and the exciter winding and frequency divider are connected to a master oscillator, which connected to the control input of the phase detector. A constant current is passed through the measuring winding. A disadvantage of this device is the dependence of the signal to be converted on the transmission coefficients of the magnetic modulator, the passive filter, the AC amplifier of the phase detector, the feedback unit and the reading unit, and the intensity of the external magnetic fields. The closest to the technical essence of the invention is a device for measuring direct current, comprising a magnetic modulator consisting of two magnetic cores, on which are wound excitation windings, a feedback winding, a measuring winding and an indicator winding. The winding is connected to a pulse generator. The indicator winding is connected to a selective amplifier, the output of which is connected to the feedback winding through an analog-digital converter and a feedback circuit. The output of the analog-digital converter is connected to the digital reading unit, and the control unit controls the operation of the analog-digital converter and the digital reading unit. A disadvantage of this device is the low measurement accuracy due to the fact that the measurement error of the current depends on the change in the transmission coefficient of the feedback circuit, the error from the change in the conversion ratio of the direct circuit, the error from the change in the resistance of the input shunt and the error due to the influence of external magnetic fields. fields. The main way to reduce the error of instability in the conversion ratio of the direct circuit is to apply deep negative feedback. However, increasing the depth of the negative feedback reduces the conversion rate of the current meter and leads to a deterioration of the dynamic characteristics of the circuit right up to stability disturbance, i.e. loss of performance. The error of the change in the transmission coefficient along the feedback circuit depends on the time and temperature unstable; resistance in the feedback circuit and its reduction is associated with technological difficulties. SECONDARY MAGNETIC FIELDS Additively affect the measurement of the current converted by a magnetic modulator into a constant magnetic field. Dp reduction of their effect requires careful magnetic shielding, in particular, the magnetic modulator of this device is enclosed in a triple permalloy shield. Magnetic screens are mainly made of permalloys, the processing of which is complex. The error associated with the change in the resistance of the input shun is determined by its temperature and time instability. V The purpose of the invention is to improve the accuracy of DC measurement. The goal is achieved by the fact that a device for measuring direct current, containing a magnetic modulator, consisting of two magnetic cores, on which are wound excitation windings connected to the Yervoy output of the pulse generator, measuring winding, feedback winding, indicator winding, connected to the main input of the selective amplifier, the output of which is connected to the input of the analog-digital converter and through the feedback circuit to the feedback winding, control unit, the first and second you ode which are connected to the control inputs of the analog-digital converter and a measuring indicator unit, the second pulse generator output is connected to a second selective amplifier rhodom further three key introduced Obrazcova and the additional winding bias / generatrr winding. a current I bias, a variable resistor, a digital dividing unit and a key management unit, the exemplary winding being connected via the first switch to the source of the reference current, the secondary winding, the variable resistor and the second switch connected in series and connected in parallel to the measuring winding, the offset winding with the bias current generator, the input of the digital dividing unit is connected to the output of the analog-digital converter, and the output is connected to the input of the digital reading unit, the third key is connected in series with the measuring winding, the input of the key management unit is connected to the third output of the control unit, and the output is the Q control inputs of the three keys, while the fourth output of the control unit is connected to the control input of the digital dividing unit. The drawing shows a block diagram of the proposed device. The device contains a magnetic modulator 1 consisting of two magnetic cores 2 and 3 on which windings 4 and 5 are wound, measuring 6, additional 7, sample 8 and indicator 9 windings, feedback winding 10 and bias 11 The windings 4 and 5 of the excitation-J are connected to the pulse generator 12, which is connected to the selective amplifier 13. The exemplary winding 8 via the first switch 14 is connected to the source 15 of the reference current. Parallel to the measuring winding 6, an additional circuit is connected, which consists of the additional winding 7 connected in series, the variable resistor 16 and the second switch 17. The bias winding 11 is connected to the bias current generator 18. The indicator winding 9 is connected to a selective amplifier 13, the output of which is connected to the feedback winding 10 via an analog-to-digital converter 19 and a feedback circuit 20. The output of the analog-digital converter 19 is connected via a digital dividing unit 21 to a digital reading unit 22. A third switch 23 is connected in series with the measuring winding 6. The control unit is connected to the analog-to-digital converter 19, the digital dividing unit 21, the digital reading unit 22 and the unit 25 key management, which is connected to the keys 14,17 and 23 and controls their operation. The device has two modes of operation; Measure and Set Zero. In the Measurement mode, the key 23 is closed and the current is measured periodically in four cycles. The measured current Tu flows through the measuring winding 6. From the bias current generator 18, through the bias winding 11, a bias current ICM flows through all clock cycles. The generator 12 pulses in all clock cycles feeds the excitation pulses to windings 4 and 5 and sync pulses to the selective amplifier 13. Pulses excitation causes magnetic cores 2 and 3 to saturate twice during the period, and opposite magnetic fluxes are created in these cores. In the first measurement cycle, the signal from the control unit 24, using the key control unit 25, opens the keys 14 and 17. The magnetic modulator converts the external and internal voltages (created by the measured current and the bias current) of the constant magnetic fields to the emf of even frequency harmonics. excitations recorded in the indicator winding 9. And using the electoral amplifier 13, the entire frequency spectrum is filtered, amplified and transformed into a constant, current only the second harmonica. The resulting constant TQK ,. served on the feedback circuit 20, which converts its feedback current flowing through the negative feedback winding 10. At the same time, this direct current is converted into a number of pulses by means of an analog-digital preformer 19, which I record in a digital dividing unit 11. After the second measurement cycle, the keys 14 and 17 are passed through the reference winding 8. . An additional circuit is connected in parallel with the measuring winding with the help of switch 17; For this purpose, the number of turns of the additional winding 7 is chosen and the resistance value of the variable resistor 16 is such that the measuring twist 6 and the additional 7 windings are equal. In addition, additional winding 7 include meetings. but in relation to the measuring winding 6, thus the windings 6 and 7 create in the cores 2 and 3 equal magnitudes, but opposite in direction, magnetic fluxes and, consequently, the resulting magnetic flux they create in cores 2 and 3 is zero . As in the first cycle, in the second measurement cycle, the external and internal (created by the sample current and the bias current) permanent magnetic fields are measured using the above block I and converted into a number of pulses and recorded into a digital dividing unit 21. In the third cycle Pa3Nbi measurements key 14 and convert the external field strengths and the magnetic field generated by the bias current into the number of pulses, which, as before, are recorded in the digital dividing block 21 e, measuring the measurement results The first two measurements are taken, the time step, and the difference is divided by the second. flash on block 22 as a resistive current. and the input of the analogue 19 serves b K ,, - (. l2. the strength of a constant magnetic field created by the measured current 1 flowing through the measuring winding 6 with the number of turns 7,; length of the core magnetic core line; current flowing through the winding 10 feedbacks with the number of turns of the bias current generator flowing through the bias winding 11 with the number of turns of the magnetic field in the cores, created by the external magnetic fields; the conversion efficiency of the selective amplifier 13; the intensity of the constant m agility field, the current generated by the field displacement of the field; the transmission coefficient of the magnetic modulator 1. and is determined by the frequency of the feedback. By substituting the value of the current t, into equation (1), we determine the current Ii Г V / (c At the output of the analog-digital converter 19, the current I / t is converted into the number of pulses Ny L1 - AALL KIU AUn f 1 v, l, 1 w, j..uo e- mln. ,, ± ± d), K ,,., .. is the conversion factor of the analog-digital converter. In the second cycle, the IZ winding 8 with the number of turns Wj is passed through the current IQ from the source 15 of the reference current. Ampervits WJ are compensated with the help of ampere turns I J J WJ, since parallel to the measuring winding b an additional circuit is connected from the series-connected auxiliary winding 7 and the variable resistor 16 (this avoids switching the measured current circuit Ij) condition X, -1; "; i, (| 5"; - 5 H) 0.

where R, R, R are respectively the active resistances of the windings b and 7 and the variable resistor 16.

As a result, the intensity of a constant magnetic field in the cores, converted into a number of NO pulses, is

 ., Kdip (,). E l vvNvKHvP-oc oc (5)

I-.

This number is recorded in the digital display unit 21.

In the third cycle, the sample current TO is disconnected. In this case, cores 2 and 3 are affected by a bias magnetic field and an external magnetic field of + LF intensity. In order not to analyze the sign of the intensity of the external field in the digital division unit, the magnitude of the magnetic field bias voltage H is chosen greater than the maximum possible value of the external magnetic field strength.

As a result, after conversion in a digital dividing unit

In the second cycle, open the key 23, 5 convert the intensity to the number of pulses subtract it from the number N, recorded in the digital dividing unit in the previous cycle. Considering that in the second cycle, the value of N is determined by ...

Km.ll to IU to DTS.P g

 K IU K ATS.P f .. y .. (9)

 e-K KHvfoc, get the difference N, -Nn, equal to

l

N -N. Kn-jKAun I. J „,. (ten)

 ..llL „.x /„ - - x

,

and indicate it on the digital reading unit. By varying the resistance of the variable resistor 16, the zero reading of the digital reading unit is set.

The zero setting of the device can be carried out either before the measurement, or periodically after some time during which the device operated in the Measurement mode.

The advantage of the proposed device is that the circuit of the measured current does not commute, which, in turn, is important when measuring

current in continuous technological will be recorded the number of pulses equal to. (b) V K + Gd. - KichRlg OS in the fourth cycle from the measurement results of the first NX and the second NQ cycles subtract the measurement result of the third cycle c. and the first difference is divided by the second - e5 -: - g -1 - .. C) The resulting number, proportional to the measured current I, is indicated by the digital reading unit 22. After that, the next conversion cycle begins. In the Setup Zero mode, the device operates as follows. Cycle conversion consists of two cycles, with the key 14 in this mode is open, and the key 17 is closed, In the first cycle the key 23 is closed. As before, the magnetic field strength of the cores 2 and 3 is converted into the number of pulses MI and recorded in the digital dividing unit 21, the value of N / | is defined by the expression -l-kY; 7.s,; -, X W слsln - n),

processes, in scientific research and in the measurement of large currents.

The current measurement error of the proposed device is of the order of +7. The device eliminates the additive error of the current measurement due to the influence of external magnetic fields, which are unchanged during the measurement, and substantially weakens the effect of slowly varying external magnetic fields.

Claims (2)

1. Berkman R.Ya., Bondaruk V.L., Q Rokhlin L.I. DC magnetotransistor amplifiers. Measuring equipment, 1972, p.56. 2. Vishenchuk I.M., Kurdydyk R.V., Rylik M.G. et al. Digital integrating volt-ammeter. -In book: Testing and measuring equipment, Lviv, 1975, p.77. (Prototype). V, A .L. S v vvorw VX / f6