CN102466751A - Current measuring apparatus - Google Patents
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- CN102466751A CN102466751A CN2010105344515A CN201010534451A CN102466751A CN 102466751 A CN102466751 A CN 102466751A CN 2010105344515 A CN2010105344515 A CN 2010105344515A CN 201010534451 A CN201010534451 A CN 201010534451A CN 102466751 A CN102466751 A CN 102466751A
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Abstract
The invention provides a current measuring apparatus which comprises a first introduction terminal, a second introduction terminal, a current sampling unit which comprises a heavy current sampling resistor and a first resistor, a measuring unit and a control unit. The current sampling unit comprises a first current measuring terminal and a second current measuring terminal. The heavy current sampling resistor employs a four-wire resistor connection method. One group of terminals at two ends of the resistor is measuring terminals, and one of the measuring terminals is taken as the first current measuring terminal and is coupled with the first introduction terminal. Another group at the two ends of the resistor is sampling terminals, and one of the sampling terminals is coupled with one end of the first resistor through crosstalk isolation. The current measuring apparatus can accurately measure low current, reduce influence of temperature fluctuation introduced by element heating in heavy current measurement on measurement of moderate current and the low current, and raise precision of the measurement of the moderate current and the low current.
Description
Technical field
A kind of current measuring device of the present invention relates to the electric variable measurement field, particularly relates to the current measurement field.
Background technology
In the prior art, a lot of measuring equipments has the current measurement ability, and such as reometer, multimeter, also increasing in some oscillograph and the test macro has the current measurement ability.Current measurement circuit commonly used at present has two current measurement terminals 1,2, sample circuit 3, metering circuit 4, control circuit 5, and wherein current measurement terminal 1,2 is respectively applied for Super-Current Measurement and small current measurement, and is as shown in Figure 1.With the dc current measurement is example, and the measurement range of big electric current typically refers to the scope of 200mA-10A, and the measurement range of little electric current is often referred to the scope that is less than or equal to 200mA.When measuring big electric current, such as, when electric current was 200mA-10A, the electric current Super-Current Measurement terminal 1 of will flowing through, converted the input end that voltage signal outputs to metering circuit 4 into via the sample circuit shown in the frame of broken lines 3 then at Super-Current Measurement end 6.During measured current, such as, when electric current was 2mA-200mA, electric current flow through small current measurement terminal 2, and either-or switch 7, converts the input end that voltage signal outputs to metering circuit 4 into via sample circuit 3 then at small current measurement end 8.When measuring weak current, such as, when electric current for being less than or equal to 2 MAHs, electric current flows through small current measurement terminal 2, either-or switch 7, converts another input end that voltage signal outputs to metering circuit 4 into via sample circuit 3 then at micro current end 9.Metering circuit 4 is multifunctional circuits, and inside comprises the multi-way switch change-over circuit of that road signal being measured in order to select, and in order to measuring the programmable amplifying circuit that range segments, also comprises A/D change-over circuit etc.When carrying out AC measurment, also can comprise the treatment circuit that is used to carry out the AC/DC conversion of signals in the circuit.Under the control of control circuit 5, metering circuit 4 can be measured a current signal of input, and measurement result is outputed to control circuit 5, is used for calculating, data processing, control or demonstration.
Be used for the sample circuit 3 that the current signal with input converts voltage signal into multiple different circuits structure is arranged; The simplest sample circuit 3 is passive current-to-voltage converting circuits; As, the passive current-to-voltage converting circuit that is made up of the resistance 11 that is connected between Super-Current Measurement end 6 and the common port 10 is when input current is flowed through resistance 11; Current signal promptly is converted into voltage signal; Voltage on this resistance 11 is the voltage signal after the conversion, outputs to an input end of metering circuit 4, is used for measuring.
A plurality of measuring junctions also can a shared passive sample circuit; Such as small current measurement end 8 and Super-Current Measurement end 6; A shared sample circuit 14 that is connected in series and forms by resistance 12,13; With reference to figure 2, wherein end points 15 has formed the output terminal of sample circuit 14, and this end points 15 is used to connect metering circuit 4.The accuracy of measuring for the weak current that improves direct current, again with reference to figure 1, when being less than or equal to the DC current of 2mA, in sample circuit 3, micro current end 9 can connect an active electric current voltage conversion circuit 16, and is as shown in Figure 4.
Active electric current voltage conversion circuit 16 has multiple circuit structure; Its most typical circuit is to be made up of an input end 17 that is connected on active electric current voltage conversion circuit 16 and the resistance 19 between the output terminal 18 and an operational amplifier 20; With reference to figure 3; The negative polarity input end of this amplifier 20 input end 17 that is connected in series, the output terminal 21 of this amplifier 20 connects the output terminal 18 of active current-to-voltage converting circuit 16, and the positive polarity input end of amplifier 20 connects common port 10.This circuit can convert the weak current from input end 17 into voltage signal, and through output terminal 18 this magnitude of voltage is outputed to metering circuit 4.
Above-mentioned current measurement circuit is a circuit structure the most common in the prior art, in a lot of products, has all obtained application, just adopts this circuit structure such as Fluke8808A.
The problem that current measurement circuit of the prior art exists is:
1. for measuring when being less than or equal to the little electric current of 2mA, use active electric current voltage conversion circuit 16 to be connected with micro current end 9.Because the signal Processing limited bandwidth of active electric current voltage conversion circuit, generally in 1kHz, it is not suitable for generally reaching the little electric current ac current measurement of 10kHz; Because the AC characteristic of active electric current voltage conversion circuit is poor, for example input impedance is complicated in addition, and its frequency response is uneven.Therefore, the high frequency characteristics of the interchange small current measurement of prior art can not satisfy accurate Testing requirement.
2. medium current is measured in loop and the Super-Current Measurement loop; Shared measuring junction and common port are formed sampling circuit; Resistance 13 heatings cause sampling loop internal heat imbalance to introduce the thermoelectrical potential error thus when measuring big electric current; See that Fig. 2 can not recover normally in the temperature of resistance 13 at once, so thermoelectrical potential can influence medium current and measure, cause the measuring error of medium current.Even medium current is measured loop and the not shared same measuring junction in Super-Current Measurement loop; Owing to use same common port, resistance 11 heatings cause measuring the measuring error that thermal unbalance in the loop still can be introduced thermoelectric potential difference and cause medium current when measuring big electric current.
Therefore, need a kind of can solve exist in the prior art in current measurement circuit because the problem that the heat that Super-Current Measurement produces exerts an influence to the measurement of little electric current, the current measurement circuit that can accurately measure at medium and small range.
Summary of the invention
The objective of the invention is to realize a kind of current measurement circuit; This circuit can be measured accurate measured current; And the temperature fluctuation that element heating is introduced when reducing Super-Current Measurement is to the influence of medium current and small current measurement, the precision of raising medium current and small current measurement.
The present invention provides a kind of current measuring device; Comprise first and second and import current sample parts, measurement component and the control assembly of holding, comprising the big current sampling resistor device and first resistor; Described current sample parts have the first current measurement end and the second current measurement end
Wherein said big current sampling resistor device uses the four-wire ohm connection; One group of terminal at these resistor two ends is a measurement terminal; One in the measurement terminal imports end as the first current measurement end and first and is coupled; Another of these resistor two ends organized and is the sampling terminal, an end coupling through the crosstalk isolation and first resistor in the sampling terminal.
Preferably, another the common end grounding in the big current sampling resistor device measurement terminal as current measuring device, in the said big current sampling resistor device sampling terminal one with said measurement terminal ground connection dividually.
Preferably, the end with first resistor after a terminal in the said big current sampling resistor device sampling terminal is isolated through crosstalking is coupled and ground connection, another terminal and metering circuit coupling in the said big current sampling resistor device sampling terminal.
Preferably, after isolating through crosstalking, a terminal in the said big current sampling resistor device sampling terminal is coupled another terminal ground connection in the said big current sampling resistor device sampling terminal with the end coupling of first resistor and with metering circuit.
Preferably, in said another group terminal is to realize through these two terminal spaces are connected at a distance of a segment distance and with the lead that prolongs through the isolation of crosstalking with the end coupling of first resistor.
Preferably; This current measuring device further comprises second resistor; With with second import the end coupling controlled first switch; Second resistor in series is connected between the second current measurement end and first resistor and the 3rd current measurement end is provided, and controlled first switch is an either-or switch, is used to make second to import end and the conducting of one of said second current measurement end and said the 3rd current measurement end.
Preferably, crosstalking between the end of in the sampling terminal of said big current sampling resistor device and first resistor isolated through the lead realization of prolongation is set between the big current sampling resistor device and first resistor.
Preferably, crosstalking between the end of in the sampling terminal of said big current sampling resistor device and first resistor isolated through the isolation channel realization is being set between the big current sampling resistor device and first resistor on the PCB.
The present invention provides a kind of current measuring device; Comprise printed-wiring board (PWB), be used for the big current sampling resistor of Super-Current Measurement and be used for the little current sampling resistor of small current measurement; Said big current sampling resistor is welded on respectively on the different welding positions of said printed-wiring board (PWB) with said little current sampling resistor; Have a fluting on the wherein said printed-wiring board (PWB), said fluting is arranged between the welding position of welding position and said little current sampling resistor of said big current sampling resistor.
Preferably, the distance that a bit arrives said fluting on the said big current sampling resistor arbitrarily is less than the distance that a bit arrives said fluting on the said little current sampling resistor arbitrarily.
Preferably, described fluting has enough length, and the direct line that makes any position on the said big current sampling resistor arrive any position on the said little current sampling resistor all passes through described fluting.
Preferably, said big current sampling resistor independently is used for Super-Current Measurement, described little current sampling resistor independently is used for small current measurement.
Preferably; Said little current sampling resistor is connected in series and constitutes by being welded on a plurality of sampling resistors on the said printed-wiring board (PWB); Described fluting has enough length, and the direct line that makes any position on the said big current sampling resistor arrive any position on any sampling resistor in said a plurality of sampling resistor that is connected in series all passes through described fluting.
Current measuring device of the present invention can be reometer, also can be other instrument with current measurement ability, comprise multimeter, oscillograph, testing synthesis parameter measuring equipment.
The beneficial effect of technical scheme of the present invention is; Through the big current sampling loop of dc current measurement and medium current and little current sampling loop are separated; Eliminated thermoelectrical potential that the heating of big current sampling resistor device causes and temperature drift influence to medium current measurement and small current measurement; Thereby reduced the source of error of medium current and small current measurement, and then improved measuring accuracy.
Further, the present invention uses two resistors that are connected in series to detect little electric current, and the signal Processing bandwidth of the sample circuit that constitutes thus is very big, can be adapted to little electric current ac current measurement.For example when test-3dB signal, bandwidth surpasses 300kHz.
Description of drawings
Fig. 1 illustrates prior art and has the synoptic diagram that two electric currents import the current measuring device of end.
Fig. 2 illustrates the synoptic diagram of the sample circuit in the prior art current measuring device.
Fig. 3 illustrates the schematic diagram of active electric current voltage conversion circuit in the prior art current measuring device.
Fig. 4 illustrates the synoptic diagram that prior art has the current-to-voltage converting circuit current measuring device.
Fig. 5 illustrates the circuit diagram according to the multimeter of the embodiment of the invention 1.
Fig. 6 illustrates a kind of circuit diagram of active clamp circuit.
Fig. 7 illustrates the circuit diagram according to the digital multimeter of the embodiment of the invention 2.
Fig. 8 illustrates the circuit diagram according to the digital multimeter of the embodiment of the invention 3.
Fig. 9 illustrates the circuit diagram according to the digital multimeter of the embodiment of the invention 4.
Figure 10 illustrates the PCB layout according to the sample circuit of the embodiment of the invention 1.
Embodiment
With reference to the accompanying drawings and combine embodiment, specify according to current measuring device of the present invention.
Fig. 5 illustrates the circuit diagram according to for example a kind of digital multimeter 500 of a kind of current measuring device of the embodiment of the invention 1.Digital multimeter 500 has first electric current and imports end 501, the second electric currents importing end 502, the first switch S 540, sample circuit 550, metering circuit 570 and processor system 580.
Another terminals 534 of a said end of resistor R 530 are connected with the other end 521 of resistor R 520; Terminals 531 of the other end of resistor R 530 are connected with the common port 503 of sample circuit 550 and are connected with the earth terminal COM that measures the loop, and its another terminals 533 are connected with AC measurment circuit 572 and are connected one of input as this switch with the first input end 561 of second switch S560.
Second switch S560 is the either-or switch that receives processor system 580 controls; Its first input end 561 is connected with the terminal 533 of resistor R 530; Its second input end 563 is connected with terminal 521, AC measurment circuit 572 and the sampling loop common port AGND of resistor R 520; Its output terminal 562 is connected with direct current measurement loop 571, is used for control survey circuit 570 and with which sampling loop is communicated with.
Measure big electric current, for example during 200mA～10A, foreign current is input to current measurement circuit from big current input terminal 501.Big electric current flows through big current input terminal 501, current foldback circuit 504, big current sampling resistor R530 and public terminal 503 and has been composed in series the Super-Current Measurement loop successively.Big current sampling resistor device R530 uses four-wire ohm to connect method, between its sampling end 534 and 533, produces current sampling voltage behind the current flows through resistor R530.Switch S 560 switches to terminal 561 1 ends, connects sampling loop common port AGND and direct current measurement circuit 571.Resistor R 510, resistor R 520, direct current measurement circuit 571; The terminal 534 of switch S 560 and resistor R 530 and 533 is formed big current sampling loop; Be used for current sampling voltage on the measurement resistor R530, current sampling voltage outputs to A/D convertor circuit 573 after amplifying through the direct current measurement circuit.A/D convertor circuit 573 becomes numerical coding to deliver to processor system 580 voltage transitions.Processor system 580 calculates the size of tested electric current according to the resistance of sampling voltage and resistor R 530 and indicates through output unit 581.
Measure medium current, for example during 2mA～200mA, foreign current is input to current measurement circuit from current input terminal 502.First switch S 540 switches to terminal 541 1 ends, and medium current flows through current input terminal 502, current foldback circuit 505, switch S 540, medium current sample resistance device R520, big current sampling resistor R530 and measures the medium current measurement loop that loop public terminal 503 is composed in series successively.Electric current produces current sampling voltage at resistor R 520 two ends.Second switch S560 switches to terminal 563 1 ends.Resistor R 510, resistor R 520, direct current measurement circuit 571; Second switch S560 forms the medium current sampling loop; Be used for current sampling voltage on the measurement resistor R520, current sampling voltage outputs to A/D convertor circuit 573 after amplifying through the direct current measurement circuit.A/D convertor circuit 573 becomes numerical coding to deliver to processor system 580 voltage transitions.Processor system 580 calculates the size of tested electric current according to the resistance of sampling voltage and resistor R 520 and indicates through output unit 581.
Measured current, for example during 0.2mA～2mA, foreign current is input to current measurement circuit from current input terminal 502.First switch S 540 switches to terminal 543 1 ends, and little electric current flows through the small current measurement loop that current input terminal 502, current foldback circuit 505, switch S 540, little current sampling resistor device R510, medium current sample resistance device R520, big current sampling resistor device R530 and metering circuit public terminal 503 are composed in series successively.Electric current produces current sampling voltage on resistor R 510 and resistor R 520.Second switch S560 switches to terminal 563 1 ends.Resistor R 510, resistor R 520, direct current measurement circuit 571, second switch S560 are formed little current sampling loop, are used for detecting the current sampling voltage on resistor R 510 and the resistor R 520.Current sampling voltage outputs to A/D convertor circuit 573 after amplifying through direct current measurement circuit 571.A/D convertor circuit 573 becomes numerical coding to deliver to processor system 580 voltage transitions.Processor system 580 calculates the size of tested electric current according to the resistance sum of sampling voltage and resistor 510 and resistor 520 and indicates through output unit 581.
Existing current measurement circuit often adopts the active electric current voltage conversion circuit to be used to measure Weak current.Because the AC characteristic of active electric current voltage conversion circuit is not so good, is not suitable for alternating current and converts voltage signal to.In the digital multimeter according to the embodiment of the invention 2, current sampling circuit 550 uses little current sampling resistor device R510 to replace the active electric current voltage conversion circuit.This current sampling circuit 550 can be used for the sampling of alternating current sample circuit DC current, reaches good ac current measurement effect.
In the present embodiment, medium current and little current sampling loop are all without the sampling terminal of resistor R 530.Metering circuit directly is connected with the terminal 521 of resistor R 520; And for big current sampling loop, metering circuit is connected to the terminal 521 of resistor R 520 earlier, connects the sampling end 534 that lead is coupled to resistor R 530 through one section then.By big current sampling loop is separated with medium and small current sampling loop, the sum of errors that can avoid big current sampling resistor device R530 heating to introduce disturbs.Be to realize this purpose, in the present embodiment, directly do not connect between the terminal 534 of resistor R 530 and the terminal 521 of resistor R 520, be coupled with therebetween have certain-length lead to realize crosstalking isolation.This lead of isolating of being used to crosstalk is separated from the locus with resistor R 510 and R520 with Super-Current Measurement resistor R 530 on the one hand; With avoid resistor R 530 to flow through big electric current time heating interference, to avoid the interference of this isolations simultaneously with the thermoelectrical potential of lead introducing to resistor R 510 and R520.
AC great current, measure the measurement loop correspondence of loop when exchanging medium current and exchanging small current measurement with big electric current, medium current and the little electric current of measuring DC current.In the sampling loop, the output terminal 562 of second switch S560 is switched to input terminal 561, and sampling loop is the loop for being made up of sampling end 534 and 533, capacitor C1 and the AC measurment circuit 572 of resistor R 510, resistor R 520, resistor R 530 all.Deliver to the AC measurment circuit behind the current sampling voltage process C1 isolated DC component on the resistor; Output to A/D convertor circuit after the AC compounent of AC measurment circuit amplified current sampling voltage, A/D convertor circuit becomes numerical coding to deliver to processor system voltage transitions.Processor system calculates the effective value of AC signal and calculates the effective value of tested electric current AC compounent according to the resistance of currently used sample resistance device, indicates through output unit at last.
According to those skilled in the art's technique known; Also can comprise the effective value counting circuit in the AC measurment circuit; The DC voltage with AC compounent voltage effective value equivalence of effective value counting circuit output converts numerical coding to through A/D convertor circuit and delivers to processor system, and processor system can not done effective value calculating just can obtain the effective value of sampling voltage AC compounent comparatively accurately.
The change-over switch S540 that is used for medium current and little electric current current measurement circuit, the change-over switch S560 in big electric current and medium current and little current sampling loop is through processor system 580 controls.The user can select measurement range in advance through input media 582.The measurement range that processor system 580 is selected according to the user is controlled the switching of first switch S 540 and second switch S560.Microprocessor system also can be selected best measurement range automatically according to the result of current measurement.
Second switch S560 for example is an electronic switch in the present embodiment, also can be relay, solid-state relay, isolated gate FET etc.
Fig. 7 illustrates the circuit diagram according to for example a kind of multimeter 700 of a kind of current measuring device of the embodiment of the invention 2.Digital multimeter 700 has first electric current and imports end 701, the second electric currents importing end 702, the first switch S 740, sample circuit 750, metering circuit 770 and processor system 780.
Compare with the multimeter 500 of the embodiment of the invention 1, in the multimeter 700 of embodiment 2, sample circuit 750 is different from embodiment 1 with the connected mode of second switch S760.Second switch S760 is the either-or switch that receives processor system 780 controls; Its first input end 761 is connected with the terminal 734 of resistor R 730; Its second input end 763 is connected with the output terminal 751 of sample circuit 750; Its output terminal 762 and direct current measurement loop 771 and 772 couplings of AC measurment loop are used for control survey circuit 770 and with which sampling loop are communicated with.
Big current sampling resistor device R730 uses the four-wire ohm connection, and its terminal 731 and 732 is for measuring the measurement terminal in the loop, and its terminal 733 and 734 is the sampling terminal in the sampling loop.Terminals 732 of one end of resistor R 730 are connected as first measuring junction and the first importing end 701 of sample circuit 750; Another terminals 734 of a said end of resistor R 730 are connected with the first input end 761 of second switch S760; Terminals 731 of the other end of resistor R 730 are connected with the common port 703 of sample circuit 750 and are connected with terminal COM; Its another terminals 733 are connected with 772 with metering circuit 771 and are connected with the earth terminal AGND of sampling loop.
Measure big electric current for example during 200mA～10A, foreign current is input to current measurement circuit from big current input terminal 701.Big electric current flows through big current input terminal 701, current foldback circuit 704, big current sampling resistor device R730 and public terminal 703 and has been composed in series the Super-Current Measurement loop successively.Big current sampling resistor device R730 uses four-wire ohm to connect method, between its sampling end 734 and 733, produces current sampling voltage behind the current flows through resistor R730.Second switch S760 switches to terminal 761 1 ends.Direct current measurement circuit 771, the terminal 734 and 733 of second switch S760 and resistor R 730 is composed in series big current sampling loop successively, is used for current sampling voltage on the measurement resistor R730.Current sampling voltage outputs to A/D convertor circuit 773 after amplifying through direct current measurement circuit 771, and A/D convertor circuit becomes numerical coding to deliver to processor system 780 voltage transitions.Processor system 780 calculates the size of tested electric current according to the resistance of sampling voltage and resistor R 730 and indicates through output unit 782.
Measure medium current, for example during 2mA～200mA, foreign current is input to current measurement circuit from current input terminal 702.First switch S 740 switches to terminal 741 1 ends, and medium current flows through the medium current that current input terminal 702, current foldback circuit 705, first switch S 740, medium current sample resistance device R720, big current sampling resistor device R730 sampling end 733 and public terminal 703 be composed in series successively measures the loop.Electric current produces current sampling voltage at resistor R 720 two ends.Second switch S760 switches to terminal 763 1 ends.Resistor R 710, resistor R 720, direct current measurement circuit 771, second switch S760 is composed in series the medium current sampling loop successively, is used for current sampling voltage on the measurement resistor R720.Current sampling voltage outputs to A/D convertor circuit 773 after amplifying through direct current measurement circuit 771.A/D convertor circuit 773 becomes numerical coding to deliver to processor system 780 voltage transitions.Processor system 780 calculates the size of tested electric current according to the resistance of sampling voltage and resistance 720 and indicates through output unit 782.
Measured current, for example during 0.2mA～2mA, foreign current is input to current measurement circuit from current input terminal 702.First switch S 740 switches to terminal 743 1 ends, and little electric current flows through the small current measurement loop that current input terminal 702, current foldback circuit 705, first switch S 740, little current sampling resistor device R710, medium current sample resistance device R720, big current sampling resistor device R730 sampling end 733 and public terminal 703 are composed in series successively.Electric current produces current sampling voltage on resistor R 710 and resistor R 720.Second switch S760 switches to terminal 763 1 ends.Resistor 710, resistor 720, direct current measurement circuit 771; Second switch 760 is formed little current sampling loop; Be used for detecting the current sampling voltage on resistor R 710 and the resistor R 720, current sampling voltage outputs to A/D convertor circuit 773 after amplifying through direct current measurement circuit 771.A/D convertor circuit 773 becomes numerical coding to deliver to processor system 780 voltage transitions.Processor system 780 calculates the size of tested electric current according to the resistance sum of sampling voltage and resistor R 710, resistor R 720 and indicates through output unit 782.
In the present embodiment, medium current and little current sampling loop are all without the sampling terminal of resistor R 730.Metering circuit directly is connected with the terminal 721 of resistor R 720 and is connected with the earth terminal AGND of sampling loop; And for big current sampling loop, metering circuit is connected to the terminal 721 of resistor R 720 earlier, connects the sampling end 733 that lead is coupled to resistor R 730 through one section then.By big current sampling loop is separated with medium and small current sampling loop, the sum of errors that can avoid big current sampling resistor device R730 heating to introduce disturbs.Be to realize this purpose, in the present embodiment, directly do not connect between the terminal 733 of resistor R 730 and the terminal 721 of resistor R 720 and the sampling loop earth terminal AGND, be coupled with therebetween have certain-length lead to realize crosstalking isolation.This lead of isolating of being used to crosstalk is separated from the locus with resistor R 710 and R720 with Super-Current Measurement resistor R 730 on the one hand; With avoid resistor R 730 to flow through big electric current time heating interference, to avoid the interference of this isolations simultaneously with the thermoelectrical potential of lead introducing to resistor R 710 and R720.
AC great current, the measurement loop when exchanging medium current and exchanging small current measurement follow the measurement loop of big electric current, medium current and the little electric current of measuring DC current corresponding.Big current sampling refluxes by resistor R 730 sampling ends 733 and 734, second switch S760 terminal 761 and 762, and capacitor C1 and AC measurment circuit are composed in series successively; Medium current and little current sampling reflux by resistor R 710, resistor R 720, second switch R760 terminal 763 and 762, and capacitor C 1 is composed in series with AC measurment circuit 722 successively.Deliver to AC measurment circuit 722 behind the current sampling voltage process C1 isolated DC component on the resistor.Output to A/D convertor circuit 773 after the AC compounent of AC measurment circuit amplified current sampling voltage.A/D convertor circuit 773 becomes numerical coding to deliver to processor system 780 voltage transitions.Processor system 780 calculates the effective value of AC signal and calculates the effective value of tested electric current AC compounent according to the size of currently used sample resistance, indicates through output unit at last.
According to those skilled in the art's technique known; Also can comprise the effective value counting circuit in the AC measurment circuit, the DC voltage with AC compounent voltage effective value equivalence of effective value counting circuit output converts numerical coding to through A/D convertor circuit and delivers to processor system.Processor system can not done effective value calculating just can obtain the effective value of sampling voltage AC compounent comparatively accurately.
First switch S 740 of medium current and little electric current current measurement circuit, big electric current is controlled through microprocessor system with the second switch S760 in medium current and little current sampling loop.The user can select measurement range in advance through input media, and the measurement range that microprocessor system is selected according to the user is controlled the switching of first switch S 740 and second switch S760.Microprocessor system 780 also can be selected best measurement range automatically according to the result of current measurement.
Fig. 8 illustrates the circuit diagram according to for example a kind of multimeter 800 of a kind of current measuring device of the embodiment of the invention 3.Digital multimeter 800 has first electric current and imports end 801, the first switch block S840, sample circuit 850, second switch parts S860, metering circuit 870 and control processing circuit 880.
Compare with the multimeter 700 of the embodiment of the invention 2; In the multimeter 800 of embodiment 3; Adopt two electric currents that import in end 801 alternate embodiments 2 to import end, adopt first switch S 740 in the first switch block alternate embodiment 2 that comprises the first switch S 840A and second switch S840B.In the present embodiment; The first switch S 840A is the single-pole switch of controlled treatment circuit 880 control foldings; The first switch S 840A is connected between the first current measurement end 832 that imports end 801 and sample circuit 850, is used to control line conduction or the open circuit between the described importing end 801 and the first current measurement end 832.Second switch S840B is the single-pole triple-throw (SPTT) switch of controlled treatment circuit 880 controls.Second switch S840B is connected between current foldback circuit 804 and resistor R 810 and the resistor R 820, is used for the conducting or the disconnection of circuit between Control current and said importing end 801 and resistor R 810, the resistor R 820.
Measure big electric current, for example during 200mA～10A.It is closed that control processing circuit is controlled the first switch S 840A, and control second switch 840B switches to its terminal 844 places.Import end 801, current foldback circuit 804, the first switch S 840A, the terminal 832 of resistor R 830 is formed current measurement circuit with terminal 831.Control processing circuit CS S860 connects its terminal 861 and terminal 862, metering circuit 870, and switch S 860, the terminal 834 of resistor R 830 is formed big current sampling loop with terminal 833.Electric current flows through that to measure behind the loop at the sampling loop two ends of resistor R 830 be that the terminal 834 of resistor R 830 produces sampling voltage with terminal 833 two ends, and metering circuit converts sampling voltage to digital quantity and is coupled to processor system 880.Control processing circuit calculates the size of tested electric current according to the size of sampling voltage and resistor R 830.
Measure medium current, for example during 2mA～200mA.Control processing circuit is controlled the first switch S 840A and is broken off, and control second switch S840B switches to its terminal 841 places.Import end 801, current foldback circuit 804, second switch S840B, resistor R 820 is formed current measurement circuit.Control processing circuit CS S860 connects its terminal 863 and terminal 862, metering circuit 870, and switch S 860, resistor R 810 is formed the medium current sampling loop with resistor R 820.Electric current produces sampling voltage at the two ends of resistor R 820 after flowing through and measuring the loop, and metering circuit converts sampling voltage to digital quantity and is coupled to control processing circuit.Control processing circuit calculates the size of tested electric current according to the size of sampling voltage and resistor R 820.
Measure the little electric current of Denging, for example during 0.2mA～2mA.Control processing circuit is controlled the first switch S 840A and is broken off, and control second switch S840B switches to its terminal 843 places.Import end 801, current foldback circuit 804, second switch S840B, resistor R 820, resistor R 810 is formed current measurement circuit.Control processing circuit CS S860 connects its terminal 863 and terminal 862, metering circuit 870, and switch S 860, resistor R 810 is formed the little current sampling loop of waiting with resistor R 820.Electric current produces sampling voltage at the two ends of resistor R 810 and R820 after flowing through and measuring the loop, and metering circuit converts sampling voltage to digital quantity and is coupled to control processing circuit.Control processing circuit calculates the size of tested electric current according to the size of sampling voltage, resistor R 810 and resistor R 820.
In the present embodiment, medium current and little current sampling loop are all without the sampling terminal of resistor R 830.Metering circuit directly is connected with the terminal 821 of resistor R 820 and is connected with the earth terminal AGND of sampling loop; And for big current sampling loop, metering circuit is connected to the terminal 821 of resistor R 820 earlier, connects the sampling end 833 that lead is coupled to resistor R 830 through one section then.By big current sampling loop is separated with medium and small current sampling loop, the sum of errors that can avoid big current sampling resistor device R830 heating to introduce disturbs.Be to realize this purpose, in the present embodiment, directly do not connect between the terminal 833 of resistor R 830 and the terminal 821 of resistor R 820 and the sampling loop earth terminal AGND, be coupled with therebetween have certain-length lead to realize crosstalking isolation.This lead of isolating of being used to crosstalk is separated from the locus with resistor R 810 and R820 with Super-Current Measurement resistor R 830 on the one hand; With avoid resistor R 830 to flow through big electric current time heating interference, to avoid the interference of this isolations simultaneously with the thermoelectrical potential of lead introducing to resistor R 810 and R820.
The first switch S 840A, second switch S840B, big electric current is controlled through control processing circuit with the switch block S860 in medium current and little current sampling loop.The user can select measurement range in advance through input media, and the measurement range that control processing circuit is selected according to the user is controlled the switching of the first switch S 840A and second switch S840B and switch block S860.Control processing circuit also can be selected best measurement range automatically according to the result of current measurement.
According to the current measurement circuit of the embodiment of the invention 3,, easy to use and be difficult for makeing mistakes because have only an input end.
Fig. 9 illustrates the circuit diagram according to for example a kind of multimeter 900 of a kind of current measuring device of the embodiment of the invention 4.Digital multimeter 900 has first electric current and imports end 901, the second electric currents importing end 902, sample circuit 950, second switch S960, metering circuit 970 and control processing circuit 980.
Measure big electric current, for example during 200mA～10A.Import end 901, current foldback circuit 904, the terminal 931 of big current sampling resistor device S930 is formed current measurement circuit with terminal 932.Processor system CS S960 connects its terminal 961 and terminal 962.Metering circuit 970, switch S 960, the terminal 934 of big current sampling resistor device R930 is formed big current sampling loop with terminal 933.Electric current produces sampling voltage at sampling loop 934 and 933 two ends of sampling resistor R930 after flowing through and measuring the loop, and metering circuit converts sampling voltage to digital quantity and is coupled to processor system.Processor system calculates the size of tested electric current according to the size of sampling voltage and sampling resistor R930.
Measured current is for example during 0.2mA～200mA.Import end 902, current foldback circuit 905, medium and small current sampling resistor device R920 forms current measurement circuit.Processor system CS S960 connects its terminal 963 and terminal 962.Metering circuit 970, switch 907, sampling resistor R920 are formed little current sampling loop.Electric current produces sampling voltage at sampling resistor R920 two ends after flowing through and measuring the loop, and metering circuit converts sampling voltage to digital quantity and is coupled to control processing circuit.Control processing circuit calculates the size of tested electric current according to the size of sampling voltage and sampling resistor R920.
In the present embodiment, little current sampling loop is without the sampling terminal of resistor R 930.Metering circuit directly is connected with the terminal 921 of resistor R 920 and is connected with the earth terminal AGND of sampling loop; And for big current sampling loop, metering circuit is connected to the terminal 921 of resistor R 920 earlier, connects the sampling end 933 that lead is coupled to resistor R 930 through one section then.By big current sampling loop is separated with medium and small current sampling loop, the sum of errors that can avoid big current sampling resistor device R930 heating to introduce disturbs.Be to realize this purpose, in the present embodiment, directly do not connect between the terminal 933 of resistor R 930 and the terminal 921 of resistor R 920 and the sampling loop earth terminal AGND, be coupled with therebetween have certain-length lead to realize crosstalking isolation.This lead of isolating of being used to crosstalk is separated from the locus with resistor R 920 with Super-Current Measurement resistor R 930 on the one hand; With avoid resistor R 930 to flow through big electric current time heating interference, to avoid the interference of this isolations simultaneously with the thermoelectrical potential of lead introducing to resistor R 920.
Big electric current is controlled through control processing circuit with the second switch S960 in little current sampling loop.The user can select measurement range in advance through input media, and the measurement range that control processing circuit is selected according to the user is controlled the switching of second switch S960.Control processing circuit also can be selected best measurement range automatically according to the result of current measurement.
Figure 10 illustrates the PCB layout according to the sample circuit of the embodiment of the invention 1.Below with reference to Figure 10 and Fig. 1 and combine embodiments of the invention 1 to specify the locus PCB implementation arranged apart of Super-Current Measurement resistor of the present invention and medium and small current measurement resistance device.
The present invention provides a kind of current measuring device; Comprise printed-wiring board (PWB) with line pattern shown in figure 10; Be useful on the big current sampling resistor device and the little current sampling resistor device that is used for small current measurement of Super-Current Measurement on it; Said big current sampling resistor is welded on respectively on the different welding positions of said printed-wiring board (PWB) with said little current sampling resistor; Have a fluting on the wherein said printed-wiring board (PWB), said fluting is arranged between the welding position of welding position and said little current sampling resistor device of said big current sampling resistor device.
Resistor R 530 is with isolating through lead 113 between resistance R 510 and the R520, and resistor R 510 for example can be 2.7 centimetres with the distance of R520 and resistor R 530.Isolation channel 111 length between resistance R 530 and resistor R 510, R520 for example can be 1.6 centimetres.
Because resistor R 530 is bigger with the distance between resistor R 510 and the R520; And there is isolation channel 111 in the centre; Can reduce the temperature rise at resistance R 510 and R520 place greatly through PCB and isolation channel when resistance R 530 adstante febres; For example can generate heat to the influence of resistor R 510 and R520 thereby reduce resistor R 530 than low 10 degrees centigrade of resistor R 530 place's temperature.
Among Figure 10, the distance that a bit arrives said fluting 111 on the said big current sampling resistor device 100 arbitrarily is less than the distance that a bit arrives said fluting on the said medium and small current sampling resistor device arbitrarily.Described fluting 111 has enough length, and the direct line that makes any position on the said big current sampling resistor device 100 arrive any position on the said medium and small current sampling resistor device all passes through described fluting.Further, said big current sampling resistor device can independently be used for Super-Current Measurement and described medium and small current sampling resistor device can independently be used for small current measurement.
Said medium and small current sampling resistor device is by a plurality of sampling resistors that are welded on the said printed-wiring board (PWB); Resistor 101 and 102 for example; Formation is connected in series; Described fluting 111 has enough length, and the direct line that makes any position on the said big current sampling resistor device 100 arrive any position on any sampling resistor in said a plurality of sampling resistor that is connected in series all passes through described fluting 111.
Should be appreciated that the embodiments described herein is schematic and nonrestrictive.Those skilled in the art can have a better understanding to technical scheme of the present invention, and can under spirit of the present invention and aim, carry out various modifications and modification to embodiments of the invention through reading instructions.Protection scope of the present invention is only limited the claims of enclosing.
Claims (13)
1. current measuring device; Comprise and first and second import end, comprise the big current sampling resistor that is connected in series and current sample parts, measurement component and the control assembly of first resistor; Described current sample parts have the first current measurement end and the second current measurement end
It is characterized in that:
Said big current sampling resistor device uses the four-wire ohm connection; One group of terminal at these resistor two ends is a measurement terminal; One in the measurement terminal imports end as the first current measurement end and first and is coupled; Another of these resistor two ends organized and is the sampling terminal, an end coupling through the crosstalk isolation and first resistor in the sampling terminal.
2. current measuring device according to claim 1 is characterized in that,
Another common end grounding in the big current sampling resistor device measurement terminal as current measuring device, in the said big current sampling resistor device sampling terminal one with said measurement terminal ground connection dividually.
3. current measuring device according to claim 2 is characterized in that,
End with first resistor after a terminal in the said big current sampling resistor device sampling terminal is isolated through crosstalking is coupled and ground connection, another terminal and metering circuit coupling in the said big current sampling resistor device sampling terminal.
4. current measuring device according to claim 2 is characterized in that,
After isolating through crosstalking, a terminal in the said big current sampling resistor device sampling terminal is coupled another terminal ground connection in the said big current sampling resistor device sampling terminal with the end coupling of first resistor and with metering circuit.
5. current measuring device according to claim 1 is characterized in that,
One in the said sampling terminal is to realize through these two terminal spaces are connected at a distance of a segment distance and with the lead that prolongs through the isolation of crosstalking with the end coupling of first resistor.
6. current measuring device according to claim 1 is characterized in that, this current measuring device further comprises second resistor and controlled first switch that is coupled with the second importing end,
Second resistor in series is connected between the second current measurement end and first resistor and the 3rd current measurement end is provided,
Controlled first switch is an either-or switch, is used to make second to import end and the conducting of one of said second current measurement end and said the 3rd current measurement end.
7. current measuring device according to claim 1; It is characterized in that the lead of isolating through prolongation is set of crosstalking between the end of in the sampling terminal of said big current sampling resistor device and first resistor is realized between the big current sampling resistor device and first resistor.
8. current measuring device according to claim 1; It is characterized in that crosstalking between the end of in the sampling terminal of said big current sampling resistor device and first resistor isolated through realizing between the big current sampling resistor device and first resistor, isolation channel being set on the PCB.
9. current measuring device; Comprise printed-wiring board (PWB), be used for the big current sampling resistor device of Super-Current Measurement and be used for the little current sampling resistor device of small current measurement; Said big current sampling resistor device is welded on respectively on the different welding positions of said printed-wiring board (PWB) with said little current sampling resistor device, it is characterized in that:
Have fluting on the said printed-wiring board (PWB), said fluting is arranged between the welding position of welding position and said little current sampling resistor device of said big current sampling resistor device.
10. current measuring device according to claim 9 is characterized in that: the distance that a bit arrives said fluting on the said big current sampling resistor device arbitrarily is less than the distance that a bit arrives said fluting on the said little current sampling resistor device arbitrarily.
11. current measuring device according to claim 10 is characterized in that:
Described fluting has enough length, and the direct line that makes any position on the said big current sampling resistor device arrive any position on the said little current sampling resistor device all passes through described fluting.
12. current measuring device according to claim 11 is characterized in that: said big current sampling resistor device independently is used for Super-Current Measurement, and described little current sampling resistor device independently is used for small current measurement.
13. according to claim 11 or 12 described current measuring devices; It is characterized in that: said little current sampling resistor device is connected in series and constitutes by being welded on a plurality of sampling resistors on the said printed-wiring board (PWB); Described fluting has enough length, and the direct line that makes any position on the said big current sampling resistor device arrive any position on any sampling resistor in said a plurality of sampling resistor that is connected in series all passes through described fluting.
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| CN107167649A (en) * | 2017-05-23 | 2017-09-15 | 杭州兆华电子有限公司 | A kind of electret microphone current testing circuit and its method of testing |
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