CN2819229Y - Digital low ohmmeter - Google Patents
Digital low ohmmeter Download PDFInfo
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- CN2819229Y CN2819229Y CN 200520042981 CN200520042981U CN2819229Y CN 2819229 Y CN2819229 Y CN 2819229Y CN 200520042981 CN200520042981 CN 200520042981 CN 200520042981 U CN200520042981 U CN 200520042981U CN 2819229 Y CN2819229 Y CN 2819229Y
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- resistance
- digital low
- voltage
- diode
- current
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Abstract
The utility model relates to a digital low ohmmeter, which is composed of a constant current source, a current commutator, a bidirectional-clamp input protection circuit, a low noise and high sensitivity amplifier, an A/ D converter, a displayer, etc. The digital low ohmmeter can select forward current measurement or backward current measurement, eliminates the influence of the thermal electric potential in a measuring loop and the measuring result is exact and reliable. The low noise and high sensitivity amplifier of the digital low ohmmeter is composed of multiple operational amplifiers which are operated in parallel, and the highest resolution power of the digital low ohmmeter achieves 0.01 mu omega.
Description
Affiliated technical field
The utility model relates to a kind of digital low resistance measurement instrument, refers in particular to be applicable to the test of electric wire and cable conductor direct current resistance, has the digital low-resistance table of bidirectional current measurement function, high sensitivity, high resolution.
Background technology
In standard GB/T3048.2 " electric wire electrical performance test method part 2: metal material resistivity test " and GB/T3048.4 " electric wire electrical performance test method the 4th part: conductor DC resistance test ", all stipulated in the test of electric wire direct current resistance must to carry out the bidirectional current measurement during less than 0.1 Ω when measured resistance, promptly read one under the forward current reading and the reading under inverse current, then two readings are got arithmetic mean as The ultimate results, this is because thermoelectrical potential and the contact electricity that unavoidably exists owing to the temperature imbalance in measuring the loop, equal on potential end, to be connected in series an offset voltage, can cause the very big error of low-resistance measurement result.Because this offset voltage is opposite to the influence of measurement result forward or backwards, this influence has been disappeared by low in the process that bidirectional measurement is averaged, thereby has improved the accuracy and the reliability of measurement result.
In the prior art, adopt double bridge and digital low-resistance table to measure low-resistance value usually.Double bridge can realize that the bidirectional current of electric wire and cable conductor resistance is measured by insert the commutation plug-in strip between current terminal C1, C2 and tested lead.Digital low-resistance table is not owing to need to carry out the numerous and diverse time-consuming balancing run of electric bridge, the numeral direct-reading is quick and convenient, obtained application more and more widely in the electric wire fields of measurement, but existing digital low-resistance table has a shortcoming, promptly can not carry out reverse-current metering, this is because in existing digital low-resistance table, for the back-emf that prevents inductive load to measuring the harm in loop, on the current potential input end, inserted the reverse protection diode, when forward current is measured, this diode is in reverse blocking state, does not have influence to measuring; And when reverse-current metering, this diode will be in the forward conduction state, causes the change of input voltage, causes measuring error.The best result of existing in addition digital low-resistance table distinguishes that power is 0.1 μ Ω, when the cross section of the long copper conductor of 1m greater than 173mm
2The time, its resistance value is less than 100 μ Ω, and meter reading has only 3 position effective digitals, and the accuracy of measurement result and resolving power all can not satisfy in the national standard performance requirement to electric wire and cable conductor direct current resistance testing equipment.
Summary of the invention
Can not carry out the lower defective of bidirectional current measurement, sensitivity and resolving power in order to overcome existing digital low-resistance table, the utility model provides a kind of digital low-resistance table, the technical feature of this low-resistance table satisfies the equipment performance requirement of electric wire direct current resistance test in the national standard fully, instrument can implementation criteria the bidirectional current measuring operation of regulation, its sensitivity has also improved ten times than existing digital low-resistance table, best result distinguishes that power has reached 0.01 μ Ω, can satisfy the measurement requirement of complete series electric wire direct current resistance.
The technical scheme of the utility model technical solution problem is: the measurement electric current of constant current source output is connected C1, C2 current terminal by inverter, inverter can be made of mechanical switch, relay or electronic switch, its effect be can select to measure electric current forward (C1 for just, C2 is for negative) or oppositely (C1 for negative, C2 for just) by measured resistance, implement the bidirectional current measurement.In order to prevent the harm of induced potential that the inductive type load produces to input amplifier, must insert excess voltage protection on the current potential input end of instrument, in the utility model, adopted two-way clamper protection circuit against input over-voltage, specific practice is: the voltage source of E+ and two low internal resistances of E-is set in instrument, and the negative pole of positive clamping diode D1 is connected with forward voltage E+, positive pole is connected with potential end P1; The positive pole of back clamping diode D2 is connected with reverse voltage E-, negative pole is connected with potential end P1.When forward current was measured, the voltage of establishing E+ was V
E+Definitely planting of E-voltage is V
E-The forward voltage drop of D1 is V
D1The forward voltage drop of D2 is V
D2Measure state at forward current, as input voltage V
X＞V
E++ V
D1The time, the D1 conducting, the forward input voltage is clamped at V
E++ V
D1On, in like manner, at the reverse-current metering state, as input voltage V
X＜-(V
E-+ V
D2) time, the D2 conducting, oppositely input voltage is clamped at-(V
E-+ V
D2) on, no matter it is positive and negative therefore to measure electric current, input voltage V
XBe limited in V
E++ V
D1And-(V
E-+ V
D2) between, protected input amplifier effectively, work as V
E+＞V
X＞-V
E-The time D1 and D2 oppositely end, do not have influence to measuring.
V
E+With V
E-The selection of numerical value is with instrument input voltage V
INMaximal value relevant, select lower V
E+And V
E-Voltage helps the protection of instrument input end, but has limited V
XMaximum input voltage, vice versa.Work as V
XMaximum input voltage during less than 0.6V, E+ and E-can be made of diode and resistance, introduce the diode operation electric current from power supply V+ and V-, the magnitude of voltage of E+ and E-is the forward voltage drop of diode, reliable operation, cheap can be passed through big electric current again, works as V
XMaximum input voltage when higher, E+ and E-can be made of several diode in series and resistance, also can be made of stabilivolt and resistance.
When oppositely ending, above-mentioned D1 and D2 be meant D1 to measuring the argumentation of not having influence, the reverse cut-off current of D2 is zero ideal state, actual device is really not so, survey factually, the forward conduction electric current is several amperes an ordinary silicon commutation diode, its reverse cut-off current is at the microampere order of magnitude, measuring its influence for the low-resistance of pin-point accuracy can not ignore, clamp diode D1 in the utility model, D2 is by the base stage and the collector of triode, PN junction between the emitter constitutes, with the NPN triode is example, concrete connection is: base stage is for anodal, and collector and emitter are connected together as negative pole.Survey factually, the reverse cut-off current of PN junction between the base stage of triode and collector, the emitter than little three orders of magnitude of reverse cut-off current of the commutation diode of same current grade, can be ignored fully to the influence of low-resistance measurement.In addition, D1, D2 also can be made of the PN junction between the grid of technotron and drain electrode, the source electrode, and practical effect is also fine.
In order to realize the technical indicator of high sensitivity high resolution, input amplifier must adopt high precision, low noise, from steady zero operational amplifier, but adopt its technical feature of single operational amplifier of prior art always limited, still can not satisfy the component that the utility model proposes is the technical indicator of 0.01 μ Ω, this is because according to Ohm law: R=U/I, work as I=10A, R=0.01 μ Ω, can be in the hope of U=0.1 μ V, the sensitivity and the noise voltage level that is to say amplifier must be better than 0.1 μ V, the technical merit that this combinational circuit that is present digital voltmeter more than 61/2 by complexity just can reach is difficult to realize with existing single operational amplifier.The low noise high-sensitivity amplifier is made of parallel a plurality of operational amplifiers in the utility model, and the output terminal of operational amplifier is connected in parallel by resistance, receives the last output voltage as amplifier of capacitor filtering C then.The principle that this circuit reduces noise is as follows: the DC voltage of each operational amplifier output is a linear superposition on capacitor filtering C, the straight voltage of the output of amplifier is the arithmetic mean of each output dc voltage, and the noise signal of each operational amplifier output takes place at random, the noise voltage of amplifier output is the root-mean-square value of each operational amplifier output noise voltage, and for instance: the VD of certain amplifier is V
O, the output noise magnitude of voltage is V
N, signal to noise ratio (S/N ratio) is V
O/ V
N, now form amplifier with 4 these identical amplifiers of performance, output dc voltage is (V
O+ V
O+ V
O+ V
O)/4=V
O, output noise voltage is (V
N 2+ V
N 2+ V
N 2+ V
N 2)
1/2/ 4=V
N/ 2, this shows, after adopting the output in parallel of 4 amplifiers, the DC voltage of amplifier output is constant, and output noise voltage only is 1/2 of single amplifier, and signal to noise ratio (S/N ratio) also rises to 2 times of single amplifier, can prove by mathematical operation: compare with single amplifier, this amplifier reduces noise, improves the multiple of signal to noise ratio (S/N ratio), equals the square root of amplifier number in the amplifier.For the components and parts cost consideration, and the amplifier number of through transport is between 2-16, though the multiple that performance improves is limited, for the amplifier that operates in the device performance ultimate limit state, it also is extremely valuable that technical feature is improved several times.
The beneficial effects of the utility model are, can implement the bidirectional current measuring operation of national Specification in digital low-resistance table, compare with traditional double bridge, the utlity model has digital direct-reading, measure advantages such as quick, simple to operation; With existing digital low-resistance epiphase ratio; the utility model can be measured the influence of thermoelectrical potential in the offset measurement loop by bidirectional current; accuracy of measurement and stability are improved; input protection is perfect, higher reliability is arranged; parallel running by a plurality of amplifiers; reduce circuit noise, improved measurement sensitivity and resolving power.
Description of drawings
Below in conjunction with drawings and Examples the utility model is further specified.
Fig. 1 is a theory diagram of the present utility model.
Fig. 2 is an embodiment of the utility model low noise high-sensitivity amplifier.
Embodiment
Electric current I is measured in the output of the I+ of constant current source and I-end in Fig. 1, and this electric current can select forward current to measure or reverse-current metering by inverter, and measured resistance is connected with the measuring resistance of gauge internal in the loop, measures electric current I by measured resistance R
XProduce voltage V
X=IR
X, this voltage obtains voltage V after amplifying A times by low noise high sensitivity volt amplifier
I, V
I=A*V
X=A*I*R
X, send between the signal voltage input end VIN+ and VIN-of 41/2 A/D converter V
I=A*V
X=A*I*R
XElectric current I is by measuring resistance R
SProduce voltage V
S=IR
S, this voltage amplification B obtains voltage V after doubly
R, V
R=B*V
S=B*I*R
S, send between the reference voltage input VREF+ and VREF-of A/D converter, according to the principle of work of biproduct somatotype A/D converter, following relation is arranged between its digital quantity output D and the analog quantity input:
D＝K*V
I/V
R＝R
X*K*A/(B*R
S)
K is the analog to digital conversion coefficient in the following formula, and A/D converter is as adopting ICL7135 type, K=10000; A/D converter is as adopting the ICL7129 type, and the K value has two kinds of selections, K=10000 during common sensitivity, and K=100000 during high sensitivity, both measurement sensitivity differs ten times, can switch arbitrarily on demand.
By above-mentioned computing and formula replacement, digital quantity output D and measured resistance value R have been realized
XBetween linear transformation, and cancellation the measurement electric current I, illustrate and adopt numerical scale formula metering circuit shown in Figure 1, can change the measurement electric current within the specific limits arbitrarily and not influence measurement result, greatly reduce accuracy requirement, improved the accuracy and the stability of instrument measurement simultaneously the constant current source output current value.Certainly, the utility model also can adopt " constant current source---voltage table " formula metering circuit that present digital low-resistance mark adopts usually.
The enlargement factor A of amplifier depends on and resistance R in Fig. 2
1With R
2Numerical value, A=R
2(R
1+ R
2); Operational amplifier should select that high precision, low temperature waft for use, low maladjustment voltage, low noise fine quality, as OP27, OP37, OPA227, LT1007, ICL7652 etc.
With the utility model technology is that the basic parameter of the PC36A direct current resistance measurer made of core is: measure electric current: 0.707mA-14.1A; Measurement range 0.01 μ Ω-199.99 Ω; Class of accuracy: 0.05 grade.
Claims (6)
1. a digital low-resistance table is made of constant current source, inverter, two-way clamper input protection road, low noise high-sensitivity amplifier, A/D converter, display etc., it is characterized in that: the measurement electric current of constant current source output is connected C1 and C2 current terminal by inverter, and the negative pole of positive clamping diode D1 is connected with forward voltage E+, positive pole is connected with potential end P1; The positive pole of back clamping diode D2 is connected with reverse voltage E-, negative pole is connected with potential end P1.
2. digital low-resistance table according to claim 1, it is characterized in that: E+ and E-are made of diode and resistance, and the voltage value of E+ and E-is the forward voltage drop of diode.
3. digital low-resistance table according to claim 1, it is characterized in that: E+ and E-are made of stabilivolt and resistance.
4. digital low-resistance table according to claim 1 is characterized in that: clamp diode D1, D2 are made of the PN junction between the base stage of triode and collector, the emitter.
5. digital low-resistance table according to claim 1 is characterized in that: clamp diode D1, D2 are made of the PN junction between the grid of technotron and drain electrode, the source electrode.
6. digital low-resistance table according to claim 1 is characterized in that: the low noise high-sensitivity amplifier is made of parallel a plurality of operational amplifiers, and the output terminal of operational amplifier is connected in parallel by resistance and is connected on the filter capacitor C.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 200520042981 CN2819229Y (en) | 2005-06-29 | 2005-06-29 | Digital low ohmmeter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 200520042981 CN2819229Y (en) | 2005-06-29 | 2005-06-29 | Digital low ohmmeter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN2819229Y true CN2819229Y (en) | 2006-09-20 |
Family
ID=37005289
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 200520042981 Expired - Lifetime CN2819229Y (en) | 2005-06-29 | 2005-06-29 | Digital low ohmmeter |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN2819229Y (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101498749B (en) * | 2008-02-01 | 2012-06-20 | 凯迈（洛阳）测控有限公司 | Accurate resistor measuring apparatus and method thereof |
| CN108008191A (en) * | 2017-11-06 | 2018-05-08 | 湖北三江航天万峰科技发展有限公司 | A kind of precision aid of Minitype resistance |
| CN109212318A (en) * | 2017-07-04 | 2019-01-15 | 重庆无线绿洲通信技术有限公司 | Resistance value measuring circuit and method, device for monitoring temperature, battery pack and management system |
-
2005
- 2005-06-29 CN CN 200520042981 patent/CN2819229Y/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101498749B (en) * | 2008-02-01 | 2012-06-20 | 凯迈（洛阳）测控有限公司 | Accurate resistor measuring apparatus and method thereof |
| CN109212318A (en) * | 2017-07-04 | 2019-01-15 | 重庆无线绿洲通信技术有限公司 | Resistance value measuring circuit and method, device for monitoring temperature, battery pack and management system |
| CN108008191A (en) * | 2017-11-06 | 2018-05-08 | 湖北三江航天万峰科技发展有限公司 | A kind of precision aid of Minitype resistance |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C14 | Grant of patent or utility model | ||
| GR01 | Patent grant | ||
| EE01 | Entry into force of recordation of patent licensing contract |
Assignee: Shanghai Tai Ou Electronics Co., Ltd. Assignor: Yuanzhong Electronic Equipments Factory, Shanghai Contract record no.: 2010310000070 Denomination of utility model: Digital low ohmmeter Granted publication date: 20060920 License type: Exclusive License Record date: 20100519 |
|
| ASS | Succession or assignment of patent right |
Owner name: SHANGHAI TAIOU ELECTRONICS CO., LTD. Free format text: FORMER OWNER: YUANZHONG ELECTRONIC EQUIPMENTS FACTORY, SHANGHAI Effective date: 20100613 |
|
| C41 | Transfer of patent application or patent right or utility model | ||
| COR | Change of bibliographic data |
Free format text: CORRECT: ADDRESS; FROM: 200083 NO.1, LANE 74, GUANGLING 1ST ROAD, HONGKOU DISTRICT, SHANGHAI CITY TO: 200083 NO.1, LANE 74, GUANGLING 1ST ROAD, SHANGHAI CITY |
|
| TR01 | Transfer of patent right |
Effective date of registration: 20100613 Address after: 200083 Shanghai City Guangling road 74 Lane No. 1 Patentee after: Shanghai Tai Ou Electronics Co., Ltd. Address before: 200083 Shanghai city Hongkou District Guangling road 74 Lane No. 1 Patentee before: Yuanzhong Electronic Equipments Factory, Shanghai |
|
| CX01 | Expiry of patent term |
Expiration termination date: 20150629 Granted publication date: 20060920 |
|
| EXPY | Termination of patent right or utility model |