Summary of the invention
The technical problem to be solved in the present invention is that existing two-wire system metering system error is comparatively large, poor practicability.
In order to solve the problems of the technologies described above, the invention provides a kind of portable microhmmeter, comprise microprocessor, sensor signal amplifying circuit, dual-Hall sensor, current coil, super capacitor, charging circuit, charging control switch, rechargeable battery, voltage-dividing detection circuit, voltage amplifier circuit, display, electric discharge on-off circuit, electric current obtains on-off circuit, voltage obtains on-off circuit and interface circuit;
Interface circuit is provided with 1 pin, 2 pin, 3 pin and 4 pin, four terminals; Rechargeable battery after charging control switch for charging circuit is powered; The charging output terminal of charging circuit is connected with the charging end of super capacitor; Feeder ear one tunnel of super capacitor is connected with 4 pin of interface circuit after current coil, and microprocessor is sent in another road after voltage-dividing detection circuit dividing potential drop; Two sensing heads of dual-Hall sensor carry out current signal detection to current coil, and are carried out sending into microprocessor after amplification processes to the current signal detected by sensor signal amplifying circuit; Voltage signal between 2 pin of interface circuit and 3 pin amplifies after process through voltage amplifier circuit sends into microprocessor; Be connected with sampling resistor between 2 pin of interface circuit and 3 pin, between 3 pin and 4 pin, be connected with reference resistance;
Charging control switch, electric discharge on-off circuit, electric current obtain on-off circuit and voltage acquisition on-off circuit is formed by electronic switch, a side terminal ground connection of the electronic switch of electric discharge circuit, and opposite side terminals are connected to 4 pin of interface circuit; One side terminal ground connection of the electronic switch of current parameters acquisition cuicuit, opposite side terminals are connected to 2 pin of interface circuit; One side terminal ground connection of the electronic switch of voltage parameter acquisition cuicuit, opposite side terminals are connected to 1 pin of interface circuit;
Microprocessor obtains the electronic switch controling end that on-off circuit and voltage obtains on-off circuit respectively and is connected with charging control switch, electric discharge on-off circuit, electric current.
Adopt charging circuit to be super capacitor charging, thus provide electric energy for microhmmeter, avoid the electric power management circuit using volume larger, effectively reduce the volume of microhmmeter, be convenient to detection and carry; Adopt the voltage of voltage-dividing detection circuit Real-time Collection super capacitor, thus start discharge examination in time after charging complete, improve detection efficiency; Adopt four-wire system detection method, effectively can reduce the error of detection, and can realize the demarcation of voltage and current, practicality is stronger; Adopt microprocessor to control the electronic switch break-make of current parameters acquisition cuicuit and voltage parameter acquisition cuicuit respectively, thus the collection realizing electric current and voltage is demarcated; Adopt current coil and dual-Hall sensor effectively can improve the accuracy of detection of electric current.
As further restriction scheme of the present invention, a sensing head of dual-Hall sensor is arranged in current coil, and another sensing head is corresponding to be arranged at outside current coil.Be arranged in current coil by dual-Hall sensor sensing head, another sensing head is corresponding to be arranged at outside current coil, can realize cancelling out each other for the disturbing effect of earth magnetism, make the measured value of dual-Hall sensor more accurate.
As further restriction scheme of the present invention, sensor signal amplifying circuit is differential amplifier circuit, carries out differential amplification respectively to the two-way current detection signal of dual-Hall sensor.Adopt differential amplifier circuit, make the size accuracy of dual-Hall sensor measurement electric current unaffected.
As further restriction scheme of the present invention, electronic switch is triode or metal-oxide-semiconductor.Adopt triode or metal-oxide-semiconductor to realize electronic switch, not only structure is simple, and cost is also lower, facilitates integrated batch production.
As further restriction scheme of the present invention, comprise a display screen be connected with microprocessor.Utilize display screen can show testing result in real time.
Beneficial effect of the present invention is: (1) adopts charging circuit to be super capacitor charging, thus provides electric energy for microhmmeter, avoids the electric power management circuit using volume larger, effectively reduces the volume of microhmmeter, be convenient to detection and carry; (2) adopt the voltage of voltage-dividing detection circuit Real-time Collection super capacitor, thus start discharge examination in time after charging complete, improve detection efficiency; (3) adopt four-wire system detection method, effectively can reduce the error of detection, and can realize the demarcation of voltage and current, practicality is stronger; (4) adopt microprocessor to control the electronic switch break-make of current parameters acquisition cuicuit and voltage parameter acquisition cuicuit respectively, thus the collection realizing electric current and voltage is demarcated; (5) current coil and dual-Hall sensor is adopted effectively can to improve the accuracy of detection of electric current.
Embodiment
As shown in Figure 1, portable microhmmeter of the present invention comprises: microprocessor, sensor signal amplifying circuit, dual-Hall sensor, current coil, super capacitor, charging circuit, charging control switch, rechargeable battery, voltage-dividing detection circuit, voltage amplifier circuit, display, electric discharge on-off circuit, electric current obtain on-off circuit, voltage obtains on-off circuit and interface circuit.
Wherein, interface circuit is provided with 1 pin, 2 pin, 3 pin and 4 pin, four terminals; Rechargeable battery after charging control switch for charging circuit is powered; The charging output terminal of charging circuit is connected with the charging end of super capacitor; Feeder ear one tunnel of super capacitor is connected with 4 pin of interface circuit after current coil, and microprocessor is sent in another road after voltage-dividing detection circuit dividing potential drop; Two sensing heads of dual-Hall sensor carry out current signal detection to current coil, and are carried out sending into microprocessor after amplification processes to the current signal detected by sensor signal amplifying circuit; Voltage signal between 2 pin of interface circuit and 3 pin amplifies after process through voltage amplifier circuit sends into microprocessor; Be connected with the sampling resistor R1 of 100 ohm between 2 pin of interface circuit and 3 pin, between 3 pin and 4 pin, be connected with the reference resistance R2 of 100 ohm;
Charging control switch, electric discharge on-off circuit, electric current obtain on-off circuit and voltage acquisition on-off circuit is formed by electronic switch, a side terminal ground connection of the electronic switch of electric discharge circuit, and opposite side terminals are connected to 4 pin of interface circuit; One side terminal ground connection of the electronic switch of current parameters acquisition cuicuit, opposite side terminals are connected to 2 pin of interface circuit; One side terminal ground connection of the electronic switch of voltage parameter acquisition cuicuit, opposite side terminals are connected to 1 pin of interface circuit;
Microprocessor obtains the electronic switch controling end that on-off circuit and voltage obtains on-off circuit respectively and is connected with charging control switch, electric discharge on-off circuit, electric current.
As shown in Figure 2, electric current of the present invention obtains on-off circuit and is made up of triode Q1, the resistance R3 of a NPN type and resistance R4, the base stage of triode Q1 is connected to microprocessor after resistance R3, the grounded emitter of triode Q1, the collector of triode Q1 is connected to 2 pin of interface circuit after resistance R4.By the break-make of Microprocessor S3C44B0X triode Q1, realize switching function.
As shown in Figure 3, voltage of the present invention obtains on-off circuit and is made up of the resistance R5 of metal-oxide-semiconductor Q2 and 51k ohm for a N raceway groove, the grid of metal-oxide-semiconductor Q2 is connected to microprocessor, and the drain electrode of metal-oxide-semiconductor Q2 is connected to 1 pin of interface circuit, the source ground of metal-oxide-semiconductor Q2 after resistance R5.By the break-make of Microprocessor S3C44B0X metal-oxide-semiconductor Q2, realize switching function.
Microhmmeter of the present invention, when detecting, needs to perform following steps:
1, super capacitor is charged
1 pin of interface circuit, 2 pin, 3 pin and four the terminals zero loads of 4 pin, charging control switch is opened by microprocessor, rechargeable battery is powered to super capacitor, voltage-dividing detection circuit carries out dividing potential drop to the voltage of super capacitor simultaneously, gather port by the A/D of microprocessor to gather the magnitude of voltage after dividing potential drop, thus obtain the real-time voltage of super capacitor, after super capacitor charging complete, broken by Microprocessor S3C44B0X charging control switch.
2, voltage is demarcated
1 pin of interface circuit, 2 pin, 3 pin and four the terminals zero loads of 4 pin, certain constant current source is exported to voltage amplifier circuit by microprocessor, voltage amplifier circuit is made to export the voltage being about 700mV when zero load, and the output voltage UU base of test record voltage amplifier circuit now; Microprocessor needs to control electric current and obtains on-off circuit disconnection, and control voltage acquisition on-off circuit closes, and forms corresponding voltage detection circuit.
The voltage of voltage amplifier circuit to sampling resistor R1 amplifies, and it is real to gather by the real-time A/D of microprocessor the output voltage Uu obtaining voltage amplifier circuit; And the value of the resistance R5 in on-off circuit is obtained according to voltage, the corresponding output voltage Uu reason of a sampling resistor R1 voltage can be obtained by reckoning in theory; These two coefficients are obtained voltage calibration coefficient KU=Uu reality/Uu as ratio manage.
3, electric current is demarcated
1 pin of interface circuit, 2 pin, 3 pin and four the terminals zero loads of 4 pin, Microprocessor S3C44B0X electric current obtains on-off circuit and disconnects, and export certain constant current to sensor signal amplifying circuit, its unloaded output is made to be about the voltage of 300mV, and the output voltage UI base of test record sensor signal amplifying circuit now; Microprocessor controls the electronic switch closes that electric current obtains on-off circuit again, control the electronic switch closes that electric current obtains on-off circuit simultaneously, electric current flows through current coil, the size of dual-Hall sensor actual induction electric current, output signal to sensor signal amplifying circuit, real by microprocessor Real-time Obtaining voltage U i now; And obtain the value of the resistance R5 in on-off circuit according to electric current, in theory by calculating that can obtain a sensor signal amplifying circuit theoretical current Ii now manages and the output voltage Ui of correspondence manages; Ii reality and Ii base can be obtained according to corresponding proportionate relationship; And the theoretical value of two current parameters and actual value are obtained current calibration coefficient KI=Ii reality/Ii as ratio manage.
4, micro-ohm device is detected
Device under test is accessed four-wire system test lead, the electronic switch that Microprocessor S3C44B0X voltage obtains on-off circuit and electric current acquisition on-off circuit disconnects, control the electronic switch closes of electric discharge on-off circuit, the output voltage Uu recording voltage amplifier circuit is in real time existing simultaneously; The voltage U i of sensor signal amplifying circuit is existing; According to microprocessor internal record data corresponding relation, Ui is now converted into current parameters Ii existing, then data measured is substituted into specific formulation:
Calculate the resistance obtaining micro-ohm device, and undertaken by Microprocessor S3C44B0X display showing the resistance obtained.
Above content is described in detail to micro-ohm level measuring method in conjunction with instantiation; can not assert that the concrete enforcement of this method is confined to these explanations; for person of an ordinary skill in the technical field; under the prerequisite not departing from this method design; some simple deduction or replace can also be made, all should be considered as belonging to the protection domain that claims that this programme submits to are determined.