CN104868749A

CN104868749A - Current transmitter

Info

Publication number: CN104868749A
Application number: CN201510048831.0A
Authority: CN
Inventors: 米哲涛; 朱文琴; 朱胜平; 周俊; 关克; 胡冬青; 曲品
Original assignee: Ningbo CSR Times Transducer Technology Co Ltd
Current assignee: Ningbo CRRC Times Transducer Technology Co Ltd
Priority date: 2015-01-30
Filing date: 2015-01-30
Publication date: 2015-08-26

Abstract

The invention relates to a current transmitter. The current transmitter includes a power source circuit, an I/V conversion circuit, a rectifying and filtering circuit and a V/I conversion circuit; the rectifying and filtering circuit includes a four-channel operational amplifier and a filtering circuit; an A channel and a B channel in the four-channel operational amplifier are adopted as a rectifying circuit; a C channel in the four-channel operational amplifier is adopted as an amplifying circuit; after being connected with a resistor D, the same-direction input end of the A channel is connected with the ground; after being connected with a resistor B, the output end of the I/V conversion circuit is connected with the reverse-direction input end of the channel B; after being connected with a resistor A, the output end of the I/V conversion circuit is connected with the reverse-direction input end of the channel A; a resistor D is connected between the reverse-direction input end of the channel A and the negative pole of a diode A; a resistor G is connected between the reverse-direction input end of the channel B and the negative pole of a diode B; the output end of the channel A is connected with the positive pole of the diode A; the output end of the channel B is connected with the positive pole of the diode B; the negative pole of the diode A and the negative pole of the diode B are connected together, and then are connected with resistors, capacitors and the filtering circuit, and thereafter are connected into the same-direction input end of the channel C of the four-channel operational amplifier; and the channel A, channel B and channel C are powered by the same power source circuit.

Description

A kind of current transducer

Technical field

The present invention relates to a kind of current transducer.

Background technology

Existing current transducer circuit, as shown in Figure 1, it comprises power circuit, I/V(current/voltage) change-over circuit, rectification and filter circuit, V/I(voltage/current) change-over circuit, the electric current that current transducer is measured is converted to voltage signal by I/V change-over circuit, then exports through rectification and filter circuit, V/I change-over circuit.Its rectification and filtering part are often converted to desirable d. c. voltage signal the alternating voltage that I/V conversion comes, and process with RMS conversion chip, its cost is higher.

Summary of the invention

Technical problem to be solved by this invention be overcome prior art above-mentioned deficiency and a kind of current transducer is provided, make that its structure is simple, cost is low.

The present invention solves the problems of the technologies described above adopted technical scheme:

A kind of current transducer, comprise power circuit, I/V change-over circuit, rectification and filter circuit, V/I change-over circuit, it is characterized in that: described rectification and filter circuit comprise four-way transport and placing device and resistance capacitance filter circuit, first in four-way transport and placing device, second two passages are as rectification circuit, third passage is as amplifying circuit, first passage is connected to the ground after input contact resistance fourth in the same way, be connected with second passage reverse input end after I/V change-over circuit output is connected with resistance second, be connected with first passage reverse input end after I/V change-over circuit output is connected with resistance first, contact resistance fourth between the negative pole of first passage reverse input end and diode first, contact resistance heptan between the negative pole of second passage reverse input end and diode second, first channel output end connects the positive pole of diode first, second channel output end connects the positive pole of diode second, the negative pole of diode first and the negative pole of diode second link together, access the input in the same way of four-way transport and placing device third passage again after contact resistance capacitor filter, first, second, the third three passages are powered by same power circuit.

Output and the reverse input end of above-mentioned third passage increase voltage gain circuit.

Compared with prior art, the invention has the advantages that: by rationally arranging rectification and filter circuit, utilizing 4 passages to amplify transport and placing device, and choose reasonable amplifier passage wherein carrys out simplified structure, reduce device number, thus it is miniaturized to be convenient to circuit design printed board, reduces costs.

Accompanying drawing explanation

Fig. 1 is the circuit block diagram of existing current transducer.

Fig. 2 is the circuit diagram of the rectification of embodiment of the present invention current transducer and filter circuit.

Fig. 3 is the voltage oscillogram before embodiment of the present invention rectification and filter circuit.

Fig. 4 is the voltage oscillogram after embodiment of the present invention rectification and filter circuit.

Embodiment

Below in conjunction with accompanying drawing embodiment, the invention will be further described.

As shown in Figure 2, rectification and filter circuit adopt four-way transport and placing device N1, N1A, N1B in four-way transport and placing device N1 bis-passages as rectification circuit, N1C passage as amplifying circuit, N1A passage is connected to the ground after input 3 pin contact resistance R3 in the same way, input signal is connected with N1B passage reverse input end 5 pin after resistance R5, be connected with N1A passage reverse input end 2 pin after being connected with resistance R4, contact resistance R7 between contact resistance R6, N1B passage reverse input end 6 and the negative pole of diode VD2 between the negative pole of N1A passage reverse input end and diode VD1; N1A channel output end 1 pin connects the positive pole of diode VD1, N1B channel output end 7 pin connects the positive pole of diode VD2, the negative pole of diode VD1 and the negative pole of diode VD2 link together, access input in the same way 10 pin of the N1C passage in four-way transport and placing device again after contact resistance capacitance resistance R8, electric capacity C4, resistance R9, electric capacity C5 filter circuit, three passages are powered by same power circuit 15V.

The electric current that current transducer is measured is by instrument transformer isolation sampling, the ac current signal Iin of 0 to a few A is converted to the small area analysis signal of mA rank, then be converted to voltage signal V, the I/V conversion links namely in Fig. 1 by resistance R1+R2 sampling, wherein V meets formula below:

V=Iin/N*(R1+R2) …………………………………………（1）

In formula, V, Iin are root-mean-square value, and N is the current mutual inductor coil number of turn.

Because its load capacity of current transformer (i.e. load circuit Rload) is very little, be generally hundreds of ohm, therefore the voltage V after corresponding I/V conversion is generally at hundreds of mV, and be AC signal, we not only will realize the output of voltage signal ideal signal in rectification & filtering link for this reason, also to carry out the amplification of voltage simultaneously, be convenient to the process of subsequent conditioning circuit.

Voltage signal is converted to the direct current signal of standard, realize effective value and export, in the present embodiment, circuit uses single power supply, requires lower, and can reduce power unit cost to the power supply processing section in Fig. 1.

Rectification and filter circuit carry out rectification AC signal, and the signal being less than 0V in alternating voltage is converted to direct current signal, see Fig. 3,4 respectively before and after rectification and filtering, from figure, contrast visible rectification and filter effect fine.

Specific works mechanism is as follows: when R1+R2 sampling voltage is less than 0V, in four-way amplifier N1 LM2902DR, passage N1A works, 3 pin current potentials (reference voltage is 0V) are greater than 2 pin current potentials, it is just that N1A exports, VD1 conducting, R5=R4 when its output voltage gain is-R5/R4(circuit design, can carry out 1:1 negative voltage like this and be converted to direct current signal); When sampling is greater than 0, N1B works, and 5 pin potential voltages are followed by 1:1, VD2 conducting, and after rectification, waveform is exactly that " under the axle " in sinusoidal AC wave form figure partly " is moved to " on axle as seen from Figure 3, forms pulsating direct current signal.

Filtering part adopts resistance, the second-order filter circuit of electric capacity realizes (R8, C4, R9, C5 and N1C forms second-order low-pass filter, use second-order low-pass filter circuit, the ripple voltage of output voltage can be reduced), after filtering, its output voltage is only about 0.9 of root-mean-square value before rectification, consider that sampled voltage only has hundreds of mV simultaneously, voltage gain circuit is added between N1C 9 pin and 8 pin, improve voltage swing, be convenient to subsequent conditioning circuit and carry out 4 ~ 20mA signal transacting, its voltage gain is: H=(R11+RP1)/R10+1 ... (2).

Voltage gain circuit is: reverse input end 9 pin and output 8 pin that are connected in parallel on N1C passage after contact resistance R10 between the reverse input end of N1C passage and ground, resistance R11 and adjustable resistance RP1 series connection.

Go back shunt capacitance C7 between reverse input end 9 pin of N1C passage and output 8 pin, electric capacity C7 plays the effect of elimination amplifier high-frequency self-excitation.

Claims

1. a current transducer, comprise power circuit, I/V change-over circuit, rectification and filter circuit, V/I change-over circuit, it is characterized in that: described rectification and filter circuit comprise four-way transport and placing device and resistance capacitance filter circuit, first in four-way transport and placing device, second two passages are as rectification circuit, third passage is as amplifying circuit, first passage is connected to the ground after input contact resistance fourth in the same way, be connected with second passage reverse input end after I/V change-over circuit output is connected with resistance second, be connected with first passage reverse input end after I/V change-over circuit output is connected with resistance first, contact resistance fourth between the negative pole of first passage reverse input end and diode first, contact resistance heptan between the negative pole of second passage reverse input end and diode second, first channel output end connects the positive pole of diode first, second channel output end connects the positive pole of diode second, the negative pole of diode first and the negative pole of diode second link together, access the input in the same way of four-way transport and placing device third passage again after contact resistance capacitor filter, first, second, the third three passages are powered by same power circuit.

2. current transducer as claimed in claim 1, is characterized in that: output and the reverse input end of described third passage increase voltage gain circuit.

3. current transducer as claimed in claim 2, is characterized in that: described voltage gain circuit is: contact resistance between the reverse input end of the third passage and ground, and resistance and adjustable resistance are connected in parallel on reverse input end pin and the output of the third passage after connecting.