CN205826736U - A kind of high accuracy single-turn cored structure formula electric current Online Transaction Processing - Google Patents

Abstract

The utility model provides a high-precision single-turn through-core current on-line testing system, which includes an active zero-flux current transformer, a signal processing circuit, an analog-to-digital conversion and a single-chip microcomputer control circuit; the active zero-flux current transformer includes Primary coil, secondary coil, detection coil, main magnetic ring, auxiliary magnetic ring, compensation coil and error compensation circuit; signal processing circuit includes preamplifier circuit, active band-pass filter, true effective value conversion circuit and the second Amplifying circuit; analog-to-digital conversion and single-chip microcomputer control circuit including double-integral A/D conversion circuit, single-chip minimum control system and LCD display module. The utility model has the advantages of accurate current detection and high precision, and adopts a single-turn through-the-heart connection mode. When measuring, the zero-flux current sensor can be directly set on the cable to be tested, which is convenient for measurement and high in safety performance, and is suitable for various household appliances. , Power supply, cables, terminal blocks, medical equipment and safety leakage current test of strong current system.

Description

A high-precision single-turn through-core current online testing system

technical field

The utility model relates to a current measurement system, in particular to a high-precision single-turn through-core current measurement system.

Background technique

In engineering practice and scientific experiments, it is often necessary to measure the leakage current online. For example, in a substation, the insulation status of high-voltage equipment is analyzed by measuring the leakage current of the grounding wire of high-voltage equipment. These leakage currents are very small, generally between a few μA and hundreds of mA, and it is difficult for ordinary current measuring instruments to measure them. Therefore, it is of great practical significance to study small current on-line measuring instruments.

At present, there are two common measurement methods for tiny DC currents. One is direct amplification, that is, direct current-voltage conversion and then voltage amplification. Since it is DC amplification, this method is easily affected by the imbalance and drift of electronic device characteristics and affects the stability and accuracy of the work. The other is chopping modulation, which converts the DC signal into an AC voltage first, then amplifies the AC voltage, and finally converts it into a DC voltage. This method overcomes the shortcomings of the direct amplification method but the circuit is complex.

Contents of the invention

In order to solve the above-mentioned problems, the utility model provides a high-precision single-turn core-through current online testing system, including an active zero-flux current transformer, a signal processing circuit, an analog-to-digital conversion and a single-chip microcomputer control circuit; , the active zero-flux current transformer includes a primary coil, a secondary coil, a detection coil, a main magnetic ring, an auxiliary magnetic ring, a compensation coil and an error compensation circuit; the signal processing circuit includes a preamplifier circuit, an active Source band-pass filter, true RMS conversion circuit and the second amplifying circuit; the analog-to-digital conversion and single-chip microcomputer control circuit include double-integral A/D conversion circuit, single-chip minimum control system and LCD display module; when the primary line When the snare is on the cable of the measured current, a changed magnetic flux will be generated on the main magnetic ring and the auxiliary magnetic ring; the detection coil is used to induce the induced current generated by the changed magnetic flux; the error compensation circuit is used to Phase-shifting the induced current, the compensation coil is used to receive the phase-shifted induced current; the secondary coil is used to induce voltage, and the preamplifier circuit and active band-pass wavelet are used to The induced voltage is amplified and filtered, and the effective value calculation circuit is used to convert and calculate the processed voltage to calculate the effective value of the induced voltage; the second amplifying circuit is used to calculate the effective value of the voltage Amplification, the analog-to-digital conversion and the single-chip microcomputer control circuit are used to perform analog-to-digital conversion on the amplified effective value of the voltage, and display the measurement results through the LCD display module.

Further, the primary coil is a single turn.

Further, the error compensation circuit includes a preamplifier, a phase shift circuit, a bandpass filter and a V/I conversion circuit.

The beneficial effects of the utility model are: in order to accurately measure the size of the tiny current on-line, the utility model utilizes the zero-flux current sensor technology to design a high-precision current on-line measuring instrument, and adopts a single-turn through-the-heart connection mode, which can be used during measurement. The zero-flux current sensor is directly placed on the cable under test, which has the advantages of convenient measurement and high safety performance, and is suitable for testing the safety leakage current of various household appliances, power supplies, cables, terminals, medical instruments and high-voltage systems .

Description of drawings

Fig. 1 is a design block diagram of the current measuring instrument system of the present utility model;

Fig. 2 is the zero flux error compensation circuit diagram of the current measuring instrument system of the present invention;

Fig. 3 is the signal processing circuit diagram of the current online measuring instrument of the present utility model;

Fig. 4 is the analog-to-digital conversion circuit and its control circuit diagram of the current measuring instrument system of the present utility model;

Fig. 5 is a flow chart of the single-chip microcomputer software control algorithm of the current measuring instrument system of the present invention.

detailed description

The utility model will be further described below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, the high-precision single-turn core-through current online testing system of the present invention includes three major parts: an active zero-flux current transformer, a signal processing circuit, an analog-to-digital conversion and a single-chip microcomputer control circuit.

Among them, the active zero-flux current transformer includes a primary coil (single turn), a secondary coil, a detection coil, a main magnetic ring, an auxiliary magnetic ring, a compensation coil and an error compensation circuit.

The signal processing circuit is composed of a preamplifier circuit, an active bandpass filter, a true effective value conversion circuit and a second amplifying circuit.

The analog-to-digital conversion and single-chip microcomputer control circuit includes a double-integral A/D conversion circuit, a single-chip microcomputer minimum control system and an LCD display module.

When the primary coil of the single-turn core-through zero-flux circuit transformer is set on the cable of the measured current, a changing magnetic flux will be generated on the main and auxiliary magnetic rings, and the current induced by the detection coil will be shifted by the error compensation circuit. After phase processing, it is added to the compensation coil of the transformer to make the current I ₃ induced by the secondary coil of the current transformer more accurate.

The voltage induced by the secondary coil is processed by the pre-amplifier circuit and the active band-pass wavelet, and then sent to the effective value calculation circuit to calculate the effective value of the induced voltage signal, and now the voltage amplitude is amplified by the second amplifier circuit , the analog-to-digital conversion is carried out, and finally the measurement results are displayed with the LCD display module.

According to the working principle of the AC transformer, when the current transformer is working, it satisfies the following magneto-electromotive force balance equation:

N ₁ I ₁ +N ₁ I ₀ =N ₂ I ₂ (1)

Among them, N ₁ and I ₁ are the coil turns and current of the primary winding, N ₂ and I ₂ are the coil turns and current of the secondary winding, and I ₀ is the excitation current of the primary winding coil. It can be seen from formula (1) that due to the existence of N ₁ I ₀ , N ₁ I ₀ is not equal to N ₂ I ₂ , therefore, reducing the size of N ₁ I ₀ can improve the measurement accuracy of the transformer. The zero-flux current transformer is made according to this principle, as shown in Figure 1, the magnetic induction current is generated through the detection coil on the main magnetic ring, and after being processed by the error compensation circuit, it is added to the compensation coil of the transformer to increase The excitation current forces the excitation current I ₀ of the primary winding coil to decrease, improving the measurement accuracy of the current transformer.

Fig. 2 is a circuit diagram of zero-flux error compensation, which is mainly composed of a preamplifier U ₁ , a phase shift circuit U ₂ , a band-pass filter U ₃ and a V/I conversion circuit U ₄ . The preamplifier is designed with a chopper-stabilized high-precision operational amplifier ICL7650, which has the characteristics of high gain, high common-mode rejection ratio, small offset and low drift. R ₅ , R ₄ , C ₆ , R ₆ and TL1001 are equal-amplitude phase-shifting circuits. When the values of R ₄ and C ₆ are changed, the signal phase will change. R ₇ , C ₉ , C ₁₉ , R ₈ , R ₉ , R ₁₀ and TL1001 form a band-pass filter. The center frequency of the filter is set to 50HZ, which can effectively filter out interference signals. CA3080 is a transconductance operational amplifier with superior performance, which can realize V/I conversion, adjust the value of R ₁₃ , and change the bias current of the transconductance operational amplifier.

As shown in Figure 1, the amplitude of the voltage signal induced by the secondary winding coil is very small and mixed with interference signals. Before the A/D conversion, the tiny signal should be amplified, filtered and processed.

Figure 3 is the signal processing circuit diagram of the measuring instrument, which is mainly composed of a preamplifier circuit, an active band-pass filter, a true effective value conversion circuit and a second amplifying circuit. The ICL7650 chip is a high-performance chopper-stabilized zero-stabilized high-precision operational amplifier, and its magnification is determined by resistors R ₂ and R ₃ . The signal amplified by the pre-amplification circuit is mixed with other interference signals, which must be filtered out by a band-pass filter circuit, and the center frequency of the filter is set to 50HZ. In order to improve the current measurement accuracy, this tester uses AD637 to design a high-precision true RMS conversion circuit, as shown in Figure 3. The amplitude of the converted voltage signal is still relatively small, and further amplification is required for A/D conversion. U ₄ , R ₉ , and R ₁₀ are proportional amplifier circuits, and their amplification factor is determined by the ratio of R ₁₀ and R ₉ .

In order to improve the accuracy of A/D conversion, this measurement adopts a double-integral A/D conversion circuit with anti-interference ability. Figure 4 shows the A/D conversion circuit and single-chip control circuit diagram, which mainly includes double-integral A/D conversion circuit, single-chip minimum Control system and LCD display module. R ₃ and C ₆ are the anti-mixing low-pass filter of the A/D converter, and the analog signal enters the 35th pin of the ICL7109 converter through this filter. The single-chip computer reads the converted digital signal through the P1 port, and after processing, the LCD display module displays the current value of the conductor under test.

Figure 5 is the flowchart of the single-chip microcomputer software control algorithm of this measuring instrument. It can be seen from the figure that when the program is running, the single-chip microcomputer first performs the initialization operation, and then reads the voltage of the STATUS pin of the ICL7109 through the P0.0 port to understand the A/D converter. If the voltage read is high, it means that the ICL7109 is in the process of A/D conversion, and the MCU waits for a while before reading the voltage of the STATUS pin. If the read voltage is low voltage, it indicates that the ICL7109A/D conversion is over, and at this time, the MCU can read the converted data. When reading data, the single-chip microcomputer sets the P0.4 port to low voltage, first reads the lower 8-bit data, and then reads the upper 8-bit data. After the single-chip microcomputer reads the data, it calculates the current value of the conductor under test and displays it through the LCD module.

The above descriptions are only preferred embodiments of the present utility model, and are not intended to limit the present utility model. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present utility model shall be included in this utility model. within the scope of protection of utility models.

Claims (3)

1. a high accuracy single-turn cored structure formula electric current Online Transaction Processing, it is characterised in that:

Including, active zero-flux current transformer, signal processing circuit and analog digital conversion and single chip machine controlling circuit；

Described active zero-flux current transformer includes primary coil, secondary coil, detection coil, main magnet ring, auxiliary magnet ring, benefit Taste coil and error compensation circuit；

Described signal processing circuit includes that pre-amplification circuit, active band-pass filter, true effective value converting circuit and the 2nd are amplified Circuit；

Described analog digital conversion and single chip machine controlling circuit include biproduct typing A/D change-over circuit, single-chip microcomputer minimum control system and LCD display module；

When on the cable that described primary coil is enclosed within tested electric current, the magnetic flux of change will be produced on main magnet ring, auxiliary magnet ring； The faradic current that described detection coil is produced by the magnetic flux changed for sensing；Described error compensation circuit is for described sensing Electric current carries out phase shift process, and described bucking coil is for receiving the faradic current after phase shift processes；

Described secondary coil is used for induced voltage, and described pre-amplification circuit and active band lead to small echo device for described faradism Pressure is amplified and Filtering Processing, and described virtual value counting circuit voltage after processing carries out conversion Calculation, calculates The virtual value of induced voltage；

Described 2nd amplifying circuit is used for being amplified described voltage effective value, described analog digital conversion and single chip machine controlling circuit Voltage effective value after amplifying carries out analog digital conversion, and by described LCD display module, measurement result is shown.

A kind of high accuracy single-turn cored structure formula electric current Online Transaction Processing the most according to claim 1, it is characterised in that: described Primary coil is single turn.

A kind of high accuracy single-turn cored structure formula electric current Online Transaction Processing the most according to claim 2, it is characterised in that: described Error compensation circuit includes preamplifier, phase-shifting circuit, band filter and V/I change-over circuit.