CN202141757U - Intelligent measuring instrument of periodical heavy current - Google Patents

Abstract

The utility model provides an intelligent measuring instrument of periodical heavy current. Hardware of the instrument includes a data collection part, a measuring range automatically-converting circuit, an amplifying circuit part and an A/D converting part. A small system of single-chip microcomputer having a keyboard and a display part is used for control. After the data collection part samples, a wave-pattern search is conducted through a sampling value to obtain a sampling point of a period. A subprogram controls the amplifying circuit and the A/D converting part to respond to button pushing interruption and A/D converting interruption. A calculation result is converted to a BCD code and output through the display part. The AC measuring instrument designed according to the scheme in the utility model can be used to measure heavy currents of hundreds or thousands of amperes and the measuring range of the measuring instrument can be regulated automatically. The intelligent measuring instrument of the periodical heavy current can be adaptive for measuring both sinusoidal current and non-sinusoidal current. By using the intelligent measuring instrument of the periodical heavy current, an effective value, an average value, a peak value and the like of the to-be-measured current can be measured separately. The intelligent measuring instrument of the periodical heavy current has a low cost and a wide application prospect.

Description

The intelligent measurement instrument of the big electric current of a kind of periodicity

Technical field

The utility model belongs to current instruments technical field

Background technology

Periodically big electric current can't use conventional reometer to measure because of its numerical value is huge; The present invention proposes with magnetic potentiometer as sensor, be equipped with the scheme that intelligentized circuit is accomplished measuring task; The electromagnetic principle of this scheme has been described; Designed the intelligent measuring circuit, also analyzed simultaneously and produced a variety of causes of measuring error, and provided relative counter measures.

Summary of the invention

The utility model technical matters to be solved provides the intelligent measurement instrument of simple in structure, the easy to operate big electric current of property measuring period.

The technical scheme that the utility model adopted is; The intelligent measurement instrument of the big electric current of a kind of periodicity, hardware mainly comprise part of data acquisition, range automatic switching circuit, amplification circuits and A/D conversion portion, are controlled by the single-chip microcomputer mini system that has keyboard and display part; After part of data acquisition is sampled; Carry out the waveform search through sampled value, obtain the sampled point of one-period, subroutine control amplifying circuit and A/D conversion portion; Response button is interrupted and AD interrupts, and result of calculation converts binary-coded decimal to and exports through the display part.

Said amplification circuits adopts the accurate amplifier that amplifies of one-level.

Said automatic range translation circuit, the CD4052 of employing selects a multi-way switch for two four, is used for the selection of range selector.

Described A/D change-over circuit adopts middling speed, high-precision 12 A/D converter ADC1210, and inside has sample/hold circuit, and its voltage request is 5 volts.

Described A/D change-over circuit adopts ADC0809, and slewing rate is 100 μ s.

The alternating current ammeter that adopts this conceptual design to form can measure hundreds of extremely big electric currents of thousands of amperes, and range is adjusted automatically; Sine or non-sinusoidal current all adapt to; Can measure effective value, mean value and the peak value etc. of tested electric current respectively; With low cost.If the change sensor, and do corresponding software adjustment, then can carry out the measurement of other physical quantity, therefore be with a wide range of applications.

Description of drawings

The structured flowchart of Fig. 1 intelligent measure circuit instrument;

Fig. 2 automatic range translation circuit;

Fig. 3 A/D change-over circuit figure;

Fig. 4 measurement instrument work main program flow block diagram.

Embodiment

If the magnetic potentiometer total length is L; Establish big current i in intercepting differential section on the L

and locate to have produced average magnetic induction density and

and

in differential section and have angle β between the two, then:

①

In the formula, φ is the magnetic flux that passes magnetic potentiometer xsect A that big current i is set up.If be full of enameled wire ω circle on the magnetic potentiometer unit length, the magnetic linkage on differential section dL then

dΨ＝ωdL·φ＝ωBAcosβdL ②

So be that magnetic linkage on the magnetic potentiometer of L does at total length

③

3. 2. substitution formula of formula is had:

④

According to Amp; The line integral

that can know the last B of L along the closed-loop path equals to pass the electric current algebraic sum of annular space that magnetic potentiometer surrounds and the product of air relative permeability μ, that is:

⑤

By formula 4., 5. obtain:

Ψ＝ω ²AμLi ⑥

I is tested AC great current in the formula.6. can calculate the induced potential at the enameled wire two ends that are around on the magnetic potentiometer by formula

$e=\frac{\mathrm{d\&Psi;}}{\mathrm{dt}}={\mathrm{\&omega;}}^2\mathrm{LA\&mu;}\frac{\mathrm{di}}{\mathrm{<figure-callout\; id="7"\; label="dt"\; filenames="HSA00000483956500021.png"\; state="\{\{state\}\}">dt</figure-callout>}}$ ⑦

7. formula explains that the induced potential e that is set up by magnetic linkage Ψ is directly proportional with the rate of change of tested current i, so this method only is applicable to the measurement of exchange current.And there be

, then to obtain with this formula discretize

$i_n=\frac{1}{{\mathrm{\&omega;}}^2\mathrm{LA\&mu;}}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{e}_{\mathrm{<figure-callout\; id="8"\; label="m"\; filenames="HSA00000483956500021.png"\; state="\{\{state\}\}">m</figure-callout>}}$ ⑧

M is the interior in short-term sampling number of τ in the formula, e _mBe sampled value, i _nBe the mean value of τ in the time.8. formula is the formula that calculates big current peak and mean value, wherein compares with periodic quantity when very little as τ, and formula calculated value 8. can be considered instantaneous value, in a series of instantaneous values, comprises peak value; When τ was taken as one-period, formula calculated value 8. was mean value.

Because current effective value

With this formula discretize, substitute continually varying function of voltage in the one-period with limited sampled voltage digital quantity in the one-period, then

Δ T in the formula _nBe the time interval of adjacent double sampling; N is the sampling number of one-period.

If the time interval of every adjacent double sampling all equates, i.e. Δ T _nBe constant Δ T, then

So have

With 8. substitution of formula, obtain This formula is the calculating formula of the current effective value of discretize.If only take a sample once in the time at τ, then

$I=\sqrt{\frac{1}{N-1}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}{\left(\frac{1}{{\mathrm{\&omega;}}^2\mathrm{LA\&mu;}}\right)}^2}=\sqrt{\frac{1}{(N-1){\left({\mathrm{\&omega;}}^2\mathrm{LA\&mu;}\right)}^2}\underset{n=1}{\overset{\mathrm{<figure-callout\; id="2"\; label="N\; e\; n"\; filenames="HSA00000483956500021.png"\; state="\{\{state\}\}">N</figure-callout>}}{\mathrm{\&Sigma;}}}{e}_n^{}{}_2^{}}$ ⑨

The intelligence system of the utility model design is exactly 9. to calculate the effective value of AC great current according to formula.

(1) native system is made up of hardware and software two parts, and hardware mainly comprises four major parts, that is: range automatic switching circuit, amplification circuits, A/D conversion portion, single-chip microcomputer mini system (containing keyboard and display part).Amplification circuits must be carried out linear amplification to it because the induced potential that magnetic potentiometer produces is very little.Amplifier adopts integrated transporting discharging, in native system, should make amplifying element keep favorable linearity.This is the accurate amplification of one-level, and the amplifier that is therefore adopted should have the characteristics that volume is little, low in energy consumption, precision is high, noise is low and input bias current is low.

(2) therefore the automatic range translation circuit if adopt fixing range, for little electric current, then can cause measuring error excessive because tested big change in current scope maybe be very big; And for too big electric current, again can outrange.So the present invention adopts Automatic Range-changing Circuit, to improve measuring accuracy and scope.Physical circuit is seen Fig. 2.CD4052 selects a multi-way switch for two four among the figure, is used for the selection of range selector.The range conversion range of this circuit is 1～64.The path of P1.0 and P1.1 determine switch.

(3) A/D change-over circuit sample circuit adopts middling speed, high-precision 12 A/D converter ADC1210, and inside has sample/hold circuit, therefore need not to add in addition; Its voltage request is 5 volts.Realize that 12 A/D conversion needs 100 μ s, and 10 A/D conversion needs 30 μ s, can be as required by software setting.Because ADC1210 output does not have the ternary latch of buffering, need to increase latching logic.Under the not too strict situation of accuracy requirement, can adopt cheap ADC0809 (8).Slewing rate is 100 μ s.Physical circuit is seen Fig. 3.

(4) single-chip microcomputer mini system native system comprises single-chip minimum system part and keyboard display part.This mini system is the core of intelligent measure circuit, is calculated, shown that the judgement of output and keyboard commands input is carried out by it.Single-chip microcomputer adopts 8031, do not lose when cutting off the power supply for data among the maintenance RAM, and can be separately the supplemental powered battery of RAM.Show and adopt static the demonstration and decoded mode, show and form by 6 LED.Keyboard adopt to interrupt input mode, takies 8031 INT1 mouth, and keyboard commands comprise and begin to measure, stop to measure etc.Single-chip microcomputer at first calculates judgement to the AD data, to confirm suitable range, then data is calculated, and is shown output with charactron.

The maximum characteristics of native system adopt software replace hardware to realize intelligent measuring exactly, and error is corrected compensation.Software is made up of master routine and a few sub program, is controlling total system and is working in an orderly manner.Main program flow is seen Fig. 4.

After the start, system at first carries out initialization, gets into the monitor state of master routine, shows friendly interface " HELLO "; System wait button then, and key commands judged, to carry out corresponding action.System carries out the waveform search according to sampled value, writes down first zero crossing; Acquisition waveforms with this as the starting point again obtains the sampled point of one-period.After the waveform search is accomplished, get into corresponding current peak, mean value, effective value counting subroutine, and convert result of calculation to binary-coded decimal so that carry out the numeral demonstration according to keyboard instruction.The subroutine response button is interrupted and AD interrupts.The generation reasons of error is a lot, mainly contains the sampling error of non-linear and A/D converter spare of mapping fault, the amplifying circuit of magnetic potentiometer.To the reason that error produces, can on software, give correction-compensation.In addition, single-chip microcomputer also has the error of calculation, therefore when design software, should take all factors into consideration from computing velocity and precision.

Claims (3)

1. the intelligent measurement instrument of the big electric current of periodicity; It is characterized in that hardware comprises part of data acquisition, range automatic switching circuit, amplification circuits and A/D conversion portion; Amplifying circuit connects the range automatic switching circuit; The range automatic switching circuit connects the A/D conversion portion, single-chip microcomputer mini system control A/D conversion portion and range automatic switching circuit.

2. the intelligent measurement instrument of the big electric current of a kind of periodicity as claimed in claim 1 is characterized in that, amplification circuits adopts the accurate amplifier that amplifies of one-level.

3. the intelligent measurement instrument of the big electric current of a kind of periodicity as claimed in claim 1 is characterized in that, the automatic range translation circuit, and the CD4052 of employing selects a multi-way switch for two four, is used for the selection of range selector.

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