CN1029873C - Method and apparatus for measuring high dc current - Google Patents

Abstract

The present invention discloses a measuring method for big direct current and a measuring instrument specially designed for implementing the method. The measuring method has the main technical scheme that voltage signals of selected A and B points which are spaced for certain length on a conductive busbar L1 are extracted; arbitrary point on the conductive busbar L1 is then selected, and a temperature signal is extracted by a temperature sensor; the voltage signals and the temperature signal are then input to the measuring instrument; the voltage signals and the temperature signal are processed by the measuring instrument; a current indication value is calculated by an input formula R=L/S. rho and an Ohm law formula I=V/R, and the measured current indication value is displayed.

Description

Method and apparatus for measuring high dc current

The invention belongs to the method for automatic measurement and the equipment of D.C. high-current, be specially adapted to industry such as metallurgy, chemical industry, charcoal element on-the-spot D.C. high-current is measured and controlled.

Hall zero magnetic-flux measurement instrument is all adopted in the measurement of generally adopting in metallurgy, chemical industry, charcoal element, mechanical industry to on-the-spot D.C. high-current at present, and its principle of work as shown in Figure 1.Fig. 1 is the principle of work synoptic diagram of Hall zero magnetic-flux measurement instrument.With reference to Fig. 1.On measuring head rectangle iron core T, be wound with feedback line chart L ₂Hall element H is housed in the iron core air gap.Tested busbar L ₁Pass measuring head, work as L ₁In DC current I is arranged ₁By the time, in iron core T, produce magnetic flux φ ₁, at φ ₁Effect under also will produce a Hall voltage on the Hall element.This electromotive force is output one feedback current I after high-gain amplifier K amplifies and handles ₂, I ₂By tickler L ₂In iron core, produce magnetic flux φ ₂, φ ₂With φ ₁Direction power is anti-.So just, constitute the negative feedback varitrol of a closed loop.When Amplifier Gain K is enough big, φ ₂Will with φ ₁Equate that positive and negative two magnetic fluxs are cancelled out each other, the magnetic flux in the iron core approaches zero.

Measuring head adopts a plurality of passages, and the magnetic flux in each passage of measuring instrument reaches flat permanent and when approaching zero, uses magnetic circuit and closes current law and can get:

$I_1=\sqrt{2}\underset{\mathrm{I\; =\; 1}}{\overset{h}{\mathrm{\Σ}}}{I}_{2}i$

I in the formula ₁One tested electric current

I ₂One feedback current

$\sqrt{2}$ One feedback umber of turn

H one tickler number

By following formula as seen: after port number h and the tickler number of turn are determined, feedback current I ₂With measured current I ₁Be directly proportional.Use I ₂Can represent I ₁The size of quantity, I ₂Can record by the voltage drop on the measuring resistance R.

There are following shortcoming in above-mentioned measuring method and equipment: it is big and the occasion of impact arranged not fit into mechanical vibration; The primary instrument technological requirement is high and can not long-distance transmissions; Can not on-the-spot effect current measurement precision.

Task of the present invention is to provide a kind of new measuring method and measuring equipment for the problems referred to above that overcome the prior art existence.

Task of the present invention realizes with following technical scheme:

Principle: the conductive bus bar of present industrial use is essentially copper bar or aluminium row, and these two kinds of conductors all have certain resistance, and its resistance is made linear change with gradient of temperature within the specific limits, and formula is:

R＝L/S，ρ

In the formula: R resistance

The L conductor length

The S conductor cross-sectional area

The ρ temperature-coefficient of electrical resistance

From following formula as can be known, for the conductor of certain-length,, just can calculate resistance value as long as know temperature; As long as collect voltage change and temperature change value on the certain-length conductor according to Ohm law l=V/R.The temperature-coefficient of electrical resistance of conductor and computing formula input computing machine, computing machine will calculate current value according to the voltage that collects, temperature signal and computing formula.

Concrete technology: the present invention includes method and measuring equipment that signal is taken out from conductive bus bar for implementing the signal that this method is taken out is handled and shown.

Fig. 2 is a principle of work synoptic diagram of the present invention.

With reference to Fig. 2, the method that its signal takes out is: at conductive bus bar L ₁Go up at a distance of 2 of A, the B of certain-length and draw a lead extraction voltage signal respectively, at conductive bus bar L ₁A, B point-to-point transmission on optionally a bit extract temperature signal with temperature sensor F, the voltage signal input end C, the D that then voltage signal are input to measuring instrument are input to temperature signal input end g, h, i with temperature signal by three leads.The distance of A, B point-to-point transmission is according to voltage isolation amplifier (1) input value decision in the measuring equipment.

Measuring equipment comprises by resistance R ₁, R ₂, capacitor C ₁, C ₂The voltage signal processing section that secondary capacitance-resistance filter of forming and voltage isolation amplifier (1) constitute, processes temperature signal part (2), the converter (3) that the temperature isolation amplifier constitutes, the calculating section (4) of connection converter (3) and display part (5) composition that result of calculation is shown, the input end J of the output termination voltage isolation amplifier (1) of capacitance-resistance filter ₁, J ₂, voltage isolation amplifier (1) and temperature every.

The input end K that connects converter (8) from the output terminal of amplifier (2) respectively ₁, K ₂Secondary capacitance-resistance filter part mainly is power frequency interference and the rectified wave interference that is used for removing long-distance transmissions; Voltage isolation amplifier (1), voltage signal and temperature signal that temperature isolation amplifier (2) is used for taking out amplify, converter (3) is used for converting voltage signal and temperature signal from voltage isolation amplifier and temperature isolation amplifier to digital signal or frequency signal, send into computing machine part (4) then, computing machine calculates resistance according to gathering the temperature of coming by the formula R=L/S ρ that imports, Ohm law formula I=V/R computing machine by input goes out tested electric current again, sends into display and shows.In force, converter part (3) can adopt the A/D analog to digital converter that analog signal conversion is become digital signal, also can adopt the A/F frequency converter that analog signal conversion is become frequency signal.Calculating section can be with computing machine or single-chip microcomputer, and display is any.

Above-mentioned measuring method and have primary instrument by the measuring instrument of technique scheme manufacturing and transfer distance, against violent vibration is moving and impact, measuring accuracy height, advantage such as power consumption is little.

Embodiment:

Resistance R ₁, R ₂: 47 ohm

Capacitor C ₁, C ₂: 470 microfarads

Voltage isolation amplifier (1): the GBS-13 of silver swallow-aeroplane computer company temperature isolation amplifier (2): the GBS-29 of silver swallow-aeroplane computer company

Converter: A/D analog to digital converter

Computing machine: IBM-PC computing machine

A point on conductive bus bar and B point respectively bore a hole and tapping with boring, and with bolt two leads are separately fixed at A point, B point.

Reach performance index:

Precision 0.1%

The primary instrument signal transfers distance greater than 200 meters

Power consumption is less than 200 watts

Claims (4)

1, a kind of large direct current measuring method comprises signal from conductive bus bar L ₁The method of last taking-up, its signal removing method is at conductive bus bar L ₁Upward respectively drawing a lead extraction voltage signal at a distance of A, the B of certain-length at 2 is transported on voltage signal input end C, the D of measuring equipment, at conductive bus bar L ₁Arbitrarily a bit the extracting temperature signal with temperature sensor and be transported on the temperature signal input end ghi of measuring equipment of last A, B point-to-point transmission by R=L/S ρ formula and the Europe female law formula I=V/R of measuring equipment according to input, calculated and shown the current indication that records,

In the formula: R resistance

LA, B point-to-point transmission conductor length

The S conductor is the conductive bus bar cross-sectional area

ρ conductor resistance temperature coefficient.

2, a kind of is to implement in the described method of claim 1 signal that takes out to be handled, the measuring equipment of collection and demonstration, and this measuring equipment comprises by resistance R ₁, R ₂, capacitor C ₁, C ₂Processes temperature signal part (2), the converter (3) that the voltage signal processing section that secondary capacitance-resistance filter of forming and voltage isolation amplifier (1) constitute, temperature isolation amplifier (2) constitute, is connected the calculating section (4) of converter (3) and the display part (5) that result of calculation is shown, capacitance-resistance filter output terminal partly is connected to the input end J of voltage isolation amplifier (1) ₁, J ₂On, the output terminal of voltage isolation amplifier (1) connects the input end K of converter (3) ₁, the output terminal of temperature isolation amplifier (2) connects the input end K of converter (3) ₂

3, measuring equipment according to claim 2 is characterized in that converter (3) is A/D analog to digital converter or A/F voltage to frequency converter.

4, measuring equipment according to claim 2 is characterized in that display part (5) is any display.