CN210982577U - Universal meter - Google Patents

Abstract

The utility model provides a universal meter, which comprises a shell, wherein an integrated circuit board is arranged in the shell and mainly comprises a display circuit board, a simulation circuit board and an interface circuit board, the simulation circuit board is horizontally arranged at the bottom of the shell, the display circuit board is vertically arranged at the front end in the shell, the interface circuit board is vertically arranged at the rear end in the shell, the processing speed of the circuit board is greatly improved by taking the simulation circuit board as a core circuit board, the display circuit board takes ARM-core A7 as a processor, a singlechip with lower processing speed and an ARM-core M series processor are eliminated, the input of key signals can be rapidly received, the display circuit board is electrically connected with the simulation circuit board through a straight needle European connector, the straight needle European connector is convenient to use, the contact property is better, the mutual division of labor is clear, the working efficiency is improved.

Description

Universal meter

Technical Field

The utility model relates to a measure technical field, in particular to universal meter.

Background

The utility model discloses a 201810221870.X utility model discloses a universal meter, which is provided with a voice broadcast switch, and the voice broadcast switch is connected with a L ED lamp to realize that the voice broadcast switch reminds through an alarm flashing lamp when exceeding the range of the universal meter, thereby eliminating the potential safety hazard;

at present, the technology only reforms additional functions of a multimeter, and does not deeply reform the accuracy of multimeter measurement, and researchers find that the multimeter on the market has the following problems that firstly, when the multimeter works, the ADC sampling time is irregular, the obtained sampling result contains power frequency noise, secondly, only external signals are collected under normal conditions, for example, an external input signal is S, an ideal sampling result is R & ltS & gt, but temperature can affect a circuit, an error E is introduced, the sampling result can be added with the error and is R & ltS & gt + E, and finally, when the input of an amplifier is continuously switched, the parasitic capacitance of an amplifier circuit cannot be ignored on a high-resistance tested circuit, namely, the tested circuit needs to continuously charge and discharge the parasitic capacitance, so that the high-resistance output measurement is not accurate, based on the three problems of the multimeter, the prior art needs to be improved urgently.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide an universal meter and direct current measurement embodiment to the direct current measurement problem of effectively solving.

In a first aspect, an embodiment of the present invention provides a multimeter.

In some optional embodiments, the integrated circuit board comprises a housing, the housing is internally provided with the integrated circuit board, the integrated circuit board mainly comprises a display circuit board, a simulation circuit board and an interface circuit board, the simulation circuit board is horizontally arranged at the bottom of the housing, the display circuit board is vertically arranged at the front end of the interior of the housing, and the interface circuit board is vertically arranged at the rear end of the interior of the housing;

optionally, the display circuit board is electrically connected to the analog circuit board through the straight pin european connector, and is configured to receive a key signal input of the operation panel, and transmit a signal to the analog circuit board through the straight pin european connector, specifically, the analog circuit board is a core circuit board and selects an FPGA (field programmable gate array) with a model of XC6S L X16 as a processor, the display circuit board uses an ARM-cortixa 7 as the processor, and the display circuit board is electrically connected to the analog circuit board through the straight pin european connector with a model of Nextron 710-1100-3048-S;

optionally, the interface circuit board is integrated with a plurality of interfaces, including a GPIB (general purpose interface bus) interface, AN L AN (local area network) interface, a USB connector interface, a power interface, and the like, and the interface circuit board is electrically connected to the analog circuit board through a SATA connection line, and is configured to receive signal input of the interface panel and input the signal to the analog circuit board through the SATA connection line;

optionally, an operation panel is arranged on the outer side of the display circuit board, the operation panel is arranged at the front end of the outer side of the shell, a display screen is arranged on the operation panel, the display screen 11 is electrically connected with the display circuit board through a flat cable, the analog circuit board transmits processed signals and data through a straight needle European connector, and finally the processed signals and data are displayed through the display screen 11.

By adopting the optional embodiment, the circuit board of the whole multimeter device consists of the display circuit board, the analog circuit board and the interface circuit board, each circuit board is responsible for corresponding plate functions, the display circuit board is responsible for displaying and receiving key signals of the operation panel, the interface circuit board is responsible for transmitting the input information of the external equipment to the analog circuit board for processing, the analog circuit board is a core circuit board of the whole device and is responsible for processing the input information and data of the display circuit board and the interface circuit board, and the three circuit boards are orderly arranged and are convenient for circuit inspection and later maintenance.

In combination with the first aspect, an embodiment of the present invention further provides a first optional implementation manner of the first aspect, where the analog circuit board includes an input selection module, a function selection circuit module, a dc amplification circuit, an ac circuit, a frequency measurement circuit, a current source module, and an analog-to-digital conversion circuit;

optionally, the input selection module mainly comprises an input selection circuit, an SATA connection line, a straight pin european connector and a switch, wherein the input selection circuit is electrically connected to the switch, and selects the input of the display circuit board and the input of the interface circuit board through the switch;

optionally, the function selection module mainly includes relay, analog switch and selection circuit, analog switch includes one-level analog switch, second grade analog switch and tertiary analog switch, the high voltage divider is connected to the relay electricity, and the one-level analog switch is connected to the high voltage divider electricity, direct current amplifier circuit is connected to second grade analog switch electricity, tertiary analog switch is connected to the selection circuit electricity, and is equipped with DC amplifier on the direct current amplifier circuit, and DC amplifier electricity connection analog-to-digital conversion circuit, and FPGA is connected to analog-to-digital conversion circuit output electricity, and capacitor measurement module output electricity connection FPGA.

Optionally, the dc amplifying circuit is a single-ended to differential plus offset amplifying circuit, and amplifies a dc signal and adjusts positive and negative signals to be supplied to an ADC (analog-to-digital converter) for input;

optionally, an ac amplifier is disposed on the ac circuit and used for adjusting the magnitude of the ac signal, specifically, the adjusted ac magnitude is converted into an effective value by an effective value measuring circuit, and the ac amplifier is electrically connected to the frequency measuring circuit; the frequency measuring circuit is electrically connected to the rear side of the alternating current circuit, and the output end of the frequency measuring circuit is electrically connected with the FPGA and used for measuring the frequency;

optionally, the current source module includes a reference source, a current source, a dc amplifier, and a capacitance measurement module, the capacitance measurement module is provided with two threshold comparators, the threshold comparators are distributed at left and right ends of the capacitance to compare the voltage of the capacitance, so as to control charging and discharging of the capacitance through the current source, specifically, the threshold comparator is L M393, when the threshold comparator at the left end detects that the voltage of the capacitance is low, the current source charges the capacitance, similarly, when the threshold comparator at the right end detects that the voltage of the capacitance is high, the current source discharges the capacitance, the current source is electrically connected with the reference source and the relay, the reference source is electrically connected with an analog-to-digital conversion circuit, and the analog-to-digital conversion circuit realizes conversion from a high-precision analog signal to a digital signal.

By adopting the optional embodiment, the analog circuit board realizes the processing of each signal and data through the mutual interconnection work of the input selection module, the function selection circuit module, the direct current amplification circuit, the alternating current circuit, the frequency measurement circuit, the current source module and the analog-to-digital conversion circuit, and the processing comprises the selection of a measurement object, the direct current amplification, the analog-to-digital conversion and the like.

With reference to the first aspect or the first optional implementation manner of the first aspect, an embodiment of the present invention further provides a second optional implementation manner of the first aspect, wherein a power switch is disposed at a lower left corner of the operation panel, an L ED lamp is disposed at a lower side of the power switch, L ED under the power switch is turned off to indicate that no AC power is connected, if L ED is orange, it indicates that the instrument is connected to the AC power and in a standby state, and if green, it indicates that the instrument is powered on, a display screen 11 is disposed on the operation panel, soft keys are disposed at a lower side of the display screen 11, and include a Home key, an alert key, an Auto zero key, a Terminals key and a More key, 6 menu bars are disposed at a bottom of the display screen 11, and the 6 menu bars are controlled by the soft keys, an operation key is disposed at a right side of the display screen 11, and rear ends of the operation key and the soft keys are both directly disposed on the display circuit board.

Optionally, the operation key includes a DCV key for configuring DC (direct current) voltage measurement, the range can be adjusted to 100mV, 1V, 10V, 100V or 750V, if the Shift key is pressed first and then the DCV key is pressed, the DC current measurement is configured, and the range can be adjusted to 100 μ a, 1mA, 10mA, 100mA, 1A, 3A or 10A;

optionally, the operation key includes an ACV key for configuring an AC (alternating current) voltage range, the AC voltage range is adjustable by 100mV, 1V, 10V, 100V, or 750V, if a Shift key is pressed first and then an ACV key is pressed, an AC current measurement is configured, and the AC current range is adjustable by 100 μ a, 1mA, 10mA, 100mA, 1A, 3A, or 10A;

optionally, the operation key comprises an ohm 2w key for configuring 2-wire resistance measurement, the range of measurement ranges comprises 100 Ω, 1k Ω, 10k Ω, 100k Ω, 1M Ω, 10M Ω, 100M Ω and 1G Ω,

optionally, the operation keys include a Freq key, a Shift key is pressed first, and then the Freq key is pressed for measuring capacitance, and the range of the measurement range includes 1nF, 10nF, 100nF, 1 μ F, 10 μ F and 100 μ F; and a cursor positioning keyboard is arranged on the lower side of the operating key.

By adopting the optional embodiment, the function signals are input to the display circuit board through the operation keys on the operation panel to select and control other functions of the multimeter.

With reference to the first aspect or the first optional implementation manner of the first aspect, an embodiment of the present invention further provides a third optional implementation manner of the first aspect, wherein a HI-L O sensing terminal, a HI-L O input terminal, and an AC/DC (alternating current/direct current) current input terminal are sequentially disposed on the right side of the front end of the operation panel from top to bottom, a front-back switch is disposed under the AC/DC current input terminal, an interface panel is disposed at the rear end of the housing, a HI-L O sensing terminal and a HI-L O input terminal are sequentially disposed on the left side of the interface panel from top to bottom, and the HI-L O sensing terminal, the HI-L O input terminal, and the rear end of the AC/DC current input terminal on the operation panel are electrically connected to the analog circuit board through a banana plug when the switch is not pressed, and the HI-L O sensing terminal, the rear end of the HI-L O input terminal on the rear interface panel are electrically connected to the analog circuit board through the banana plug when.

Optionally, the AC/DC (alternating current/direct current) current input terminal includes a 3A current input terminal and a 10A current input terminal, and a 10A current input terminal is disposed on the left side of the 3A current input terminal;

optionally, a GPIB (general purpose interface bus) interface is disposed in the middle of the interface circuit board, and is used to electrically connect the GPIB interface to the PC end through a cable, and set a GPIB address of the instrument, AN L AN (local area network) interface is disposed on a lower side of the GPIB interface, and is used to connect the PC end and set a dynamic IP address protocol, and a USB connector interface is disposed on a right side of the local area network interface, and is used to connect a power interface disposed on a right upper side of the USB connector interface, and is used to connect a power source.

With this alternative embodiment, the HI-L O sense terminal and the HI-L O input terminal may be used for external stylus to measure current or voltage, resistance, etc., and the switch may select to use the terminals on the operation panel or the terminals on the interface panel as required, which is convenient to use.

With reference to the first aspect or the first optional implementation manner of the first aspect, an embodiment of the present invention further provides a fourth optional implementation manner of the first aspect, wherein the housing is shaped like a rectangular parallelepiped, a rubber shock pad is disposed outside each vertex angle of the housing, both ends of the housing and the rubber shock pad are fixedly connected to the housing through nuts, both left and right sides of the housing are provided with air vents, the air vents are circular with a diameter of 1.5 mm, both left and right sides of a front end of the housing are provided with handle stretching devices, each handle stretching device includes an external housing, a pull shaft, a handle, a fixing buckle, a circular hole, a fixing hole, a spring, and an internal housing, the circular holes are disposed on the left and right sides of the housing, and the fixing holes are disposed around the circular holes, specifically, the fixing holes are totally 6, and are uniformly distributed around the circular holes, the included angle between each two adjacent fixing holes and the circle center of the round hole is 60 degrees, an external shell sleeve is arranged on the outer side of the round hole, a handle is arranged on the outer side of the external shell sleeve, a pull shaft is arranged in the middle of the inside of the external shell sleeve, fixing buckles are arranged on the periphery of the pull shaft, specifically, the fixing buckles are totally provided with 3 fixing buckles which are uniformly distributed on the periphery of the pull shaft, the included angle between each two adjacent fixing buckles and the circle center of the pull shaft is 120 degrees, a spring is arranged at the right end of the pull shaft, and the right end of the spring is fixedly connected with the internal shell sleeve;

optionally, the external housing, the pull shaft, the circular hole, the internal housing, the left end of the spring, and the right end of the spring are all arranged on a horizontal straight line.

Optionally, the diameter of the external housing and the diameter of the internal housing are equal and 2 cm longer than the diameter of the circular hole, and the diameter of the pull shaft is 1 cm shorter than the diameter of the circular hole.

Optionally, the fixing buckle is specifically a cylindrical buckle, and the diameter of the fixing buckle is 0.5 cm shorter than that of the fixing hole.

Adopt this optional embodiment, can be convenient make whole universal meter be in comfortable use angle through adjustment handle stretching device, avoid using fatigue for a long time, perhaps can reduce the reading mistake that leads to because universal meter inclination problem to a certain extent.

In a second aspect, an embodiment of the present invention provides a direct current measurement circuit embodiment of a multimeter.

In some optional embodiments, the dc measurement circuit embodiment comprises: including analog switch, and analog switch includes one-level analog switch, second grade analog switch and tertiary analog switch, outside direct current signal (including direct current voltage, direct current etc.) is through the selection of first order analog switch function, get into the buffer and realize signal buffering, through the steady zero process amplifier of second grade analog switch chopper, third grade analog switch realizes direct current and the selection of interchange virtual value signal, through single-ended to differential circuit processing, enter into the ADC, wherein, the signal can carry out the benchmark before entering into the ADC, transmit to display screen 11 through entering into FPGA at last and showing after handling.

The present embodiment designs the dc measurement circuit in three aspects:

(1) due to the fact that sampling time of the ADC is irregular, the obtained sampling result contains power frequency noise;

in the embodiment, the sampling integral time of the ADC in the direct current measuring circuit is repeatedly adjusted to be integral multiple of the power frequency period, so that the fluctuation caused by the power frequency is eliminated in the sampling result, and the power frequency suppression effect is achieved.

(2) In order to solve the problem that an error occurs in an acquisition result caused by only acquiring an external signal, because an error is easily introduced by an external factor, the sampling result is influenced, for example, a temperature influence circuit is introduced, and an error E is introduced, the error E is added to the sampling result, and the sampling result is R ═ S + E;

in the dc measurement circuit of this embodiment, a cross-sampling method is adopted, an external signal is collected first, and then an internal reference ground is collected, a normal result is R-S-G, if the temperature affects the circuit, the error E needs to be added for both of those two measurements, an external signal collection result is S + E, an internal collection result is S-E, and then an expression of a final sampling result R is: and when the result is (S + E) - (G + E) ═ S-G, the error E does not exist, and the final sampling result is not influenced by the temperature.

(3) When the input of the amplifier is switched continuously, the parasitic capacitance of the amplifier circuit is not negligible to the high-resistance tested circuit, which is equivalent to that the tested circuit needs to charge and discharge the parasitic capacitance continuously, so that the measurement of the high-resistance output is inaccurate;

the direct current measurement circuit of this embodiment is with the help of buffer and analog switch combination design, and analog switch switches to the buffer earlier, precharges the electric capacity of amplifier earlier, charges to the level that is close external signal, switches to external signal again on, measures external signal, can reduce the ingestion to external signal current like this, eliminates parasitic capacitance influence.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the embodiments of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts. The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings. Like reference numerals refer to like parts throughout the drawings. The drawings are not intended to be drawn to scale in actual dimensions, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a block diagram illustrating an overall structure of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 2 is a block diagram of an integrated circuit board of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 3 is a schematic diagram of an operating panel of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 4 is a schematic diagram illustrating an interface panel of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 5 is a block diagram of an analog circuit board structure of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 6 is a block diagram illustrating a direct current measurement process of an embodiment of the multimeter according to the present invention;

FIG. 7 shows a graph of eliminating power frequency noise for an embodiment of a multimeter provided by the present invention;

FIG. 8 is a schematic diagram illustrating a handle stretching assembly of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 9(a) is a diagram illustrating a structure of a horizontal adjustment of a handle of an embodiment of the multimeter provided by the present invention;

FIG. 9(b) is a 60 degree adjustment structure diagram of a handle of an embodiment of the multimeter provided by the present invention;

FIG. 10 shows a DC measurement circuit diagram of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 11(a) is a schematic diagram illustrating a DC voltage measurement terminal connection of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 11(b) is a schematic diagram illustrating a 3A current terminal connection for direct current measurement of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 11(c) is a schematic diagram illustrating a DC current measurement 10A current terminal connection of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 12 is a circuit diagram illustrating an input selection circuit of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 13 is a circuit diagram illustrating function selection for an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 14 shows a frequency measurement circuit diagram of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 15 shows an analog-to-digital conversion circuit diagram of an embodiment of a multimeter provided by an embodiment of the present invention;

FIG. 16 shows a capacitance module charging and discharging circuit diagram of an embodiment of a multimeter provided by an embodiment of the present invention;

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is to be understood that the described embodiments are only some optional embodiments of the present invention, not all embodiments, and may be selectively referred to or not referred to for use, not for the purpose of limiting the scope of the present invention and its application, wherein the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.

In order to solve among the prior art at during operation ADC sampling time irregular, the sampling result who derives contains the power frequency noise, secondly, external signal is only gathered to the prevailing conditions, the error can appear in the sampling result, and at last, when constantly switching over the input of amplifier, amplifier circuit's parasitic capacitance is to high resistance measured circuit non-ignorable, is equivalent to measured circuit need constantly to parasitic capacitance charge-discharge, measures unsafe shortcoming to high resistance output like this, the embodiment of the utility model provides a universal meter.

According to a first aspect of the embodiments of the present invention, an alternative embodiment of a multimeter is provided.

Referring to fig. 1 and fig. 2, fig. 1 shows an overall structural block diagram of an embodiment of a multimeter provided by an embodiment of the present invention, and fig. 2 shows an integrated circuit board structural block diagram of an embodiment of a multimeter provided by an embodiment of the present invention;

the universal meter comprises a shell 1, wherein an integrated circuit board is arranged in the shell 1 and mainly comprises a display circuit board 2, a simulation circuit board 3 and an interface circuit board 4, the simulation circuit board 3 is horizontally arranged at the bottom of the shell 1, the display circuit board 2 is vertically arranged at the front end in the shell 1, and the interface circuit board 4 is vertically arranged at the rear end in the shell 1;

the display circuit board 2 is electrically connected with the analog circuit board 3 through the straight pin European connector 12 and is used for receiving key signal input of an operation panel arranged on the outer side of the display circuit board 2 and transmitting signals to the analog circuit board 3 through the straight pin European connector 12, specifically, the analog circuit board 3 is a core circuit board and selects an FPGA with the model of XC6S L X16 as a processor, the display circuit board 2 takes ARM-cortix A7 as the processor, and the display circuit board 2 is electrically connected with the analog circuit board 3 through the straight pin European connector 5 with the model of Nextron 710-1100-3048-S.

Optionally, fig. 4 shows AN interface panel schematic diagram of AN embodiment of the utility model, a plurality of interfaces are integrated on the interface circuit board 4, including GPIB (general purpose interface bus) interface 5, L AN (local area network) connector 6, USB connector interface 7, power source interface 8, etc., and the interface circuit board 4 is electrically connected to the analog circuit board 3 through the SATA connecting wire 9, the interface panel 21 is provided at the outer side of the interface circuit board 4, the interface extends from the interface panel 21 and is used for the external device, and the interface circuit board 4 inputs the signal input from the external device through the interface to the analog circuit board 3 through the SATA connecting wire 9;

optionally, fig. 3 shows the utility model provides a multimeter embodiment's operating panel schematic diagram, the display circuit board 2 outside is equipped with operating panel 10, and operating panel 10 sets up the outside front end at shell 1, is equipped with display screen 11 on operating panel 10, and display screen 11 passes through winding displacement electricity and connects display circuit board 2, signal and data that analog circuit board 3 will handle are transmitted to display circuit board 2 through straight needle european style connector 12, finally show through display screen 11.

By adopting the optional embodiment, the circuit board of the whole multimeter device consists of the display circuit board, the analog circuit board and the interface circuit board, each circuit board is responsible for corresponding plate functions, the display circuit board is responsible for displaying and receiving key signals of the operation panel, the interface circuit board is responsible for transmitting the input information of the external equipment to the analog circuit board for processing, the analog circuit board is a core circuit board of the whole device and is responsible for processing the input information and data of the display circuit board and the interface circuit board, and the three circuit boards are orderly arranged and are convenient for circuit inspection and later maintenance.

With reference to the first aspect, embodiments of the present invention further provide a first optional embodiment of the first aspect.

Referring to fig. 5, 12, 13, 14 and 15, fig. 5 is a block diagram of an analog circuit board structure of an embodiment of a multimeter provided by an embodiment of the present invention; FIG. 12 is a circuit diagram illustrating an input selection circuit of an embodiment of a multimeter provided by an embodiment of the present invention; FIG. 13 is a circuit diagram illustrating function selection for an embodiment of a multimeter provided by an embodiment of the present invention; FIG. 14 shows a frequency measurement circuit diagram of an embodiment of a multimeter provided by an embodiment of the present invention; FIG. 15 shows an analog-to-digital conversion circuit diagram of an embodiment of a multimeter provided by an embodiment of the present invention;

the analog circuit board 3 comprises an input selection module, a function selection circuit module, a direct current amplification circuit, an alternating current circuit, a frequency measurement circuit, a current source module and an analog-to-digital conversion circuit.

Optionally, the input selection module mainly comprises an input selection circuit, an SATA connection line, a straight pin european connector, and a switch, and is configured to select input of the display circuit board 2 and the interface circuit board 4;

optionally, the function selection module mainly comprises a relay, an analog switch and a selection circuit, the analog switch comprises a first-stage analog switch, a second-stage analog switch and a third-stage analog switch, the relay is electrically connected with the high-voltage divider, the high-voltage divider is electrically connected with the first-level analog switch, the device is used for selecting a measuring object which can be current, voltage, capacitance, resistance and the like, the secondary analog switch is electrically connected with the direct current amplifying circuit, the selecting circuit is electrically connected with the tertiary analog switch, the selection circuit is controlled to be direct current measurement or alternating current measurement through the three-level analog switch, a direct current amplifier is arranged on the direct current amplifying circuit, the direct current amplifier is electrically connected with the analog-to-digital conversion circuit, the output end of the analog-to-digital conversion circuit is electrically connected with the FPGA, and the direct current amplifying circuit is electrically connected with the capacitance measuring module, and the output end of the capacitance measuring module is electrically connected with the FPGA.

Optionally, the dc amplifying circuit is a single-ended to differential plus offset amplifying circuit, and amplifies the dc signal and adjusts the positive and negative signals to a range that meets the input of the ADC;

optionally, an ac amplifier is disposed on the ac circuit and is configured to adjust the magnitude of the ac signal, and the specifically adjusted ac magnitude is converted into an effective value by the effective value measurement circuit;

optionally, the frequency measurement circuit is electrically connected to the rear side of the ac circuit, and an output end of the frequency measurement circuit is electrically connected to the FPGA for measuring the frequency;

optionally, the current source module includes a reference source, a current source, a dc amplifier, and a capacitance measurement module, the current source is electrically connected to the reference source and the relay, the reference source is electrically connected to the analog-to-digital conversion circuit, the analog-to-digital conversion circuit realizes conversion from high-precision analog signals to digital signals,

optionally, refer to fig. 16, fig. 16 shows a capacitance module charge-discharge circuit diagram of multimeter embodiment that the embodiment of the utility model provides a, capacitance measurement module is equipped with two threshold comparators, thereby threshold comparator distributes and compares the voltage of electric capacity at the left and right sides of electric capacity and charges and discharge through current source control electric capacity, and is concrete, and the threshold comparator model is L M393, and when the threshold comparator of left end detected the voltage of electric capacity lower, then the electric capacity was charged to the current source, and is same, when the threshold comparator of right-hand member detected the voltage of electric capacity higher, then the electric capacity was discharged to the current source.

By adopting the optional embodiment, the analog circuit board realizes the processing of each signal and data through the mutual interconnection work of the input selection module, the function selection circuit module, the direct current amplification circuit, the alternating current circuit, the frequency measurement circuit, the current source module and the analog-to-digital conversion circuit, and the processing comprises the selection of a measurement object, the direct current amplification, the analog-to-digital conversion and the like.

With reference to the first aspect or the first optional embodiment of the first aspect, the present invention further provides a second optional embodiment of the first aspect.

Referring to fig. 3, fig. 3 shows a schematic view of an operation panel of an embodiment of the multimeter provided by the embodiment of the present invention, a power switch 13 is disposed at a lower left corner of the operation panel 10, the power switch 13 is electrically connected to the display circuit board 2, an L ED lamp is disposed at a lower side of the power switch 13, a L ED under the power switch 13 is extinguished, which indicates that no AC power is connected, if L ED is orange, it indicates that the instrument is connected to the AC power and in a standby state, and if it is green, it indicates that the instrument is powered on;

the operating panel 10 is provided with a display screen 11, a soft key 14 is arranged on the lower side of the display screen 11, the soft key 14 comprises a Home key, an Aperture key, an Auto key, an Autozero key, a Terminals key and a More key, 6 menu bars are arranged at the bottom of the display screen 11 and controlled by the soft key 14, an operating key 15 is arranged on the right side of the display screen 11, and the rear ends of the operating key 15 and the soft key 14 are directly arranged on the display circuit board 2.

Optionally, the operation key 15 includes a DCV key, which is used to configure DC voltage measurement, and the range can be adjusted by 100mV, 1V, 10V, 100V or 750V, if the Shift key is pressed first and then the DCV key is pressed, then DC current measurement is configured, and the range can be adjusted by 100 μ a, 1mA, 10mA, 100mA, 1A, 3A or 10A;

optionally, the operation key 15 includes an ACV key, which is used to configure an AC voltage range, where the AC voltage range can be adjusted to 100mV, 1V, 10V, 100V, or 750V, if a Shift key is pressed first and then an ACV key is pressed, an AC current measurement is configured, and the AC current range can be adjusted to 100 μ a, 1mA, 10mA, 100m A, 1A, 3A, or 10A;

optionally, the operation key 15 includes an ohm 2w key for configuring 2-wire resistance measurement, and the range of measurement ranges includes 100 Ω, 1k Ω, 10k Ω, 100k Ω, 1M Ω, 10M Ω, 100M Ω, and 1G Ω;

optionally, the operation key 15 includes a Freq key, and the Shift key is pressed first and then the Freq key is pressed for measuring capacitance, and the range of the measurement range includes 1nF, 10nF, 100nF, 1 μ F, 10 μ F, and 100 μ F; and a cursor positioning keyboard is arranged on the lower side of the operating key 15.

By adopting the optional embodiment, the function signals are input to the display circuit board through the operation keys on the operation panel to select and control other functions of the multimeter.

With reference to the first aspect or the first optional embodiment of the first aspect, the present invention provides a third optional embodiment of the first aspect.

Referring to fig. 1 and 3, fig. 1 shows an overall structure block diagram of an embodiment of the multimeter provided by the embodiment of the present invention, fig. 3 shows an operation panel schematic diagram of an embodiment of the multimeter provided by the present invention, the right side of the front end of the operation panel 10 is sequentially provided with a HI-L O sensing terminal 16, a HI-L O input terminal 17 and an AC/DC (alternating current/direct current) current input terminal, the AC/DC (alternating current/direct current) current input terminal includes a 3A current input terminal 18 and a 10A current input terminal 19, the lower side of the AC/DC (alternating current/direct current) current input terminal is provided with a front-back switch 20, the rear end of the case 1 is provided with an interface panel 21, the left side of the interface panel 21 is sequentially provided with a HI-3668O sensing terminal 16 and a banana-HI 1O current input terminal 17 from top to bottom, and when the switch 20 is not pressed, the HI-L O sensing terminal, the AC/DC input terminal 16 and the banana-3526 HI 1O current input terminal 17 are electrically connected to a HI 1O input terminal 17, and when the switch 20 is not pressed, the AC/DC input terminal is electrically connected to a distance measuring plug is measured by using an analog input terminal 15, a front-back switch 20 and a analog input terminal, a front-back switch 20 and a front-back switch 20, a analog input terminal is connected to an analog input terminal 24 and a analog input terminal connected to an analog terminal 24 and a analog terminal connected to an analog input terminal connected to an analog terminal 24 and a analog terminal connected to an analog terminal connected;

optionally, refer to fig. 4, fig. 4 shows the utility model provides AN operation panel schematic diagram of multimeter embodiment, be equipped with GPIB (general purpose interface bus) interface 5 in the middle of interface circuit board 4 for electrically connect GPIB interface 5 to the PC end through the cable for set up the GPIB address of instrument, 5 downside of GPIB (general purpose interface bus) interface is equipped with L AN (local area network) connector 6, is used for connecting the PC end and sets up dynamic IP address protocol, and L AN connector 6 right side is equipped with USB connector interface 7, is used for connecting PC end transmission and download file, USB connector interface 7 upper right side is equipped with power source 8, is used for the switch on.

With this alternative embodiment, the HI-L O sense terminal and the HI-L O input terminal may be used for external stylus to measure current or voltage, resistance, etc., and the switch may select to use the terminals on the operation panel or the terminals on the interface panel as required, which is convenient to use.

With reference to the first aspect or the first alternative embodiment of the first aspect, an embodiment of the present invention further provides a fourth alternative embodiment of the first aspect,

referring to fig. 1, fig. 1 shows an overall structure block diagram of an embodiment of the multimeter provided by the embodiment of the present invention, the case 1 is a cuboid, a rubber shock pad 22 is arranged outside each vertex angle of the case 1, both ends of the case 1 and the rubber shock pad 22 are fixedly connected with the case 1 through nuts, both left and right sides of the case 1 are provided with air holes 23, and the air holes 23 are circular with a diameter of 1.5 mm;

referring to fig. 8, 9(a) and 9(b), fig. 8 is a schematic structural view illustrating a handle stretching device of an embodiment of the multimeter provided by the embodiment of the present invention; FIG. 9(a) is a diagram illustrating a structure of a horizontal adjustment of a handle of an embodiment of the multimeter provided by the present invention; FIG. 9(b) is a 60 degree adjustment structure diagram of a handle of an embodiment of the multimeter provided by the present invention; the left side and the right side of the front end of the shell 1 are respectively provided with a handle stretching device, the handle stretching devices comprise an external shell 24, a pulling shaft 25, a handle 26, fixing buckles 27, round holes 28, fixing holes 29, a spring 30 and an internal shell 31, the round holes 28 are arranged on the left side and the right side of the shell 1, the fixing holes 29 are arranged around the round holes 28, specifically, 6 fixing holes 29 are uniformly distributed around the round holes 28, the included angle between the circle center of each two adjacent fixing holes 29 and the round holes 28 is 60 degrees, the external shell 24 is arranged outside the round holes, the handle 26 is arranged outside the external shell 24, the pulling shaft 25 is arranged in the middle inside the external shell 24, the fixing buckles 27 are arranged around the pulling shaft 25, specifically, the fixing buckles 27 are provided with 3 uniform distributed around the pulling shaft 25, the included angle between each two adjacent fixing buckles 27 and the circle center of the pulling shaft 25 is 120 degrees, the right end of the pull shaft 25 is provided with a spring 30, the right end of the spring 30 is fixedly connected with the built-in shell sleeve 31, the inclination angle of the multimeter can be adjusted through the adjusting handle stretching device, specifically, the included angle between adjacent fixing buckles 27 is 120 degrees, the included angle between adjacent fixing holes 29 is 60 degrees, the circle centers of the fixing buckles 27 and the fixing holes 29 are on a horizontal straight line, the fixing buckles 27 can extend into the fixing holes 29 so that the handle 26 is fixed and does not rotate any more, thus the adjusting handle stretching device realizes the adjustment of the inclination angle of the whole device of the multimeter, when the fixing buckles 27 extend into the fixing holes 29, the spring 30 is in a normal stretching state, when the handle stretching device is adjusted, the external shell sleeve 24 is firstly pulled outwards, the external shell sleeve 24 is fixedly connected with the pull shaft 25, and therefore the right end of the pull shaft 25 also drives the spring 30 to pull outwards, at this moment, the fixing buckle 27 is pulled out from the fixing hole 29, the spring 30 is in a stretching state, the rotating handle 26 is stretched outwards at each time, the fixing buckle 27 is aligned and fixed with the fixing hole 29, and the inclination angle of 60 degrees is changed by rotating once, so that the multimeter can be observed and used more conveniently in use.

Optionally, the external housing 24, the pull shaft 25, the circular hole 28, the internal housing 31, the left end of the spring 30 and the right end of the spring 30 are all arranged on a horizontal straight line, so that when the handle is pulled, the track of the pull shaft 25 changes the direction, the external housing 24 and the internal housing 31 have the same diameter and are 2 cm longer than the circular hole 28, the diameter of the pull shaft 25 is 1 cm shorter than the diameter of the circular hole 28, so that the pull shaft 25 can be pulled in the circular hole 28, the diameter of the internal housing 31 is 2 cm longer than the diameter of the circular hole 28, when the pull shaft 25 is pulled out to stretch the spring 30 to a certain extent, the diameter of the internal housing 31 is large to prevent the pull shaft 25 from being pulled out continuously, the fixed buckle 27 is specifically a cylindrical buckle, the diameter of the fixed buckle 27 is 0.2 cm shorter than the diameter of the fixed hole 29, and the difference of 0.2 cm can enable the fixed buckle 27 to be inserted and pulled out smoothly, and the fixing buckle 27 can be well fixed with the fixing hole 29 after being inserted into the fixing hole 29.

Adopt this optional embodiment, can be convenient make whole universal meter be in comfortable use angle through adjustment handle stretching device, avoid using fatigue for a long time, perhaps can reduce the reading mistake that leads to because universal meter inclination problem to a certain extent.

In a second aspect, an embodiment of the present invention provides a direct current measurement circuit embodiment of a multimeter.

In some alternative embodiments, referring to fig. 6 and 10, fig. 6 shows a block diagram of a direct current measurement process of an embodiment of the multimeter provided by the present invention; fig. 10 shows a direct current measurement design circuit diagram of an embodiment of the multimeter provided by an embodiment of the present invention.

The processing procedure of the direct current measurement embodiment comprises the following steps: the direct current measurement circuit, the analog switch that is equipped with in the direct current measurement circuit includes one-level analog switch, second grade analog switch and tertiary analog switch, outside direct current signal (including direct current voltage, direct current etc.) passes through the selection of first order analog switch function, get into the buffer and realize signal buffering, it is steady zero through second grade analog switch chopper, then through amplifier amplification, third level analog switch realizes direct current and alternating current effective value signal selection, pass through single-ended to differential value circuit processing again, enter into ADC (analog-to-digital converter), wherein, the signal can carry out the benchmark before entering the ADC, transmit to display screen 11 after entering FPGA handles at last and show.

In combination with the second aspect, the embodiment of the present invention further provides a first optional embodiment of the second aspect, and referring to fig. 7, fig. 7 shows a graph of eliminating power frequency noise coordinates of an embodiment of the multimeter provided by the embodiment of the present invention;

in order to solve under ordinary application, ADC sampling time is irregular, the sampling result who comes out contains the problem of power frequency noise, the utility model discloses with ADC sampling integral time process repeatedly adjust to the integer multiple of power frequency cycle, make the sampling result eliminate the fluctuation that the power frequency caused, reach the power frequency suppression effect, cross and carry out the integral to average direct current input on certain period of time, realize noise suppression, if set up integral time as the integer multiple of power supply line cycle (P L C), these errors (and harmonic thereof) will be close to zero after the process is averaged, the universal meter provides three kinds of integrals and selects (1, 10 and 100P L C), be used for realizing normal mode noise suppression, the universal meter measures power frequency (50Hz or 60Hz) earlier, then confirm corresponding integral time, horizontal axis and axis represent sampling time and phase place respectively, as long as A and B's sampling integral cycle is the integer multiple of power frequency noise cycle, no matter where phase place from then A and B begin, can calculate A and B's area equals, thereby the problem of power frequency noise has effectively been solved.

Combine the second aspect, the embodiment of the utility model provides a second optional embodiment of second aspect is still provided, in order to solve and only gather the external signal, the collection result can the error problem appear, because the error is introduced easily to the external factor and can be influenced the sampling result, for example introduce the temperature influence circuit, introduce error E, this error E can be added to the sampling result so, the sampling result is R ═ S + E, the utility model discloses a cross acquisition method gathers the external signal earlier, gathers the internal reference ground again, and normal result is R ═ S-G, if the temperature influence circuit, these twice measurement all need add this error E, and the external signal acquisition result is S + E, and the internal acquisition result is S-E, then final sampling result R expression formula is: the result shows that no error E exists, which indicates that the final sampling result is not influenced by the temperature; in addition, the thermoelectric voltage is the most common error source in the low level direct current voltage measurement, the thermoelectric voltage is generated by using heterogeneous metals for circuit connection at different temperatures, each connection between the metals forms a thermocouple, and the thermocouple generates voltage in proportion to the connection temperature, therefore, since the input terminal of the digital multimeter is made of copper alloy, the optimum connection can be formed by using a crimping connection mode between copper wires, and the thermocouple voltage and temperature variation in the low level voltage measurement can be reduced to the maximum extent.

In combination with the second aspect, the embodiment of the present invention further provides a third optional embodiment of the second aspect, when the input of the amplifier is switched continuously, the parasitic capacitance of the amplifier circuit is not negligible to the high-resistance tested circuit, which is equivalent to that the tested circuit needs to continuously charge and discharge the parasitic capacitance, so that the measurement of the high-resistance output is not accurate. In order to solve the problem, the utility model discloses when the terminal is for opening a way (if input resistance is >10G omega), ambient temperature when between 0 ℃ to 30 ℃, digital multimeter's measuring circuit has about 30 pA's input bias current, because there is input bias current, digital multimeter's input electric capacity will be "charged", with the help of buffer and analog switch integrated design, analog switch switches to the buffer earlier, the electric capacity of amplifier precharges earlier, charge to the level that is close external signal, switch to on the external signal again, measure external signal, can reduce the ingestion to external signal electric current like this, eliminate the parasitic capacitance influence.

The following measurement is performed for the embodiment with the direct current voltage and the direct current as optional embodiments, and the specific steps are as follows:

referring to fig. 11(a), for the direct voltage measurement embodiment, fig. 11(a) shows a schematic diagram of a direct voltage measurement terminal connection of an embodiment of the present invention:

firstly, configuring a test meter pen, connecting an HI-L O input terminal with the test meter pen externally, connecting the HI input terminal with a red test meter pen, connecting a L O input terminal with a black test meter pen, and respectively connecting the HI input terminal with equipment to be tested.

And secondly, measuring according to a DCV key on the operation panel 10, then according to an Aperture key included in the soft key 14 and selecting power line cycle times (P L C), wherein 1, 10 and 100P L C provide normal mode (line frequency noise) inhibition, 100P L C is selected to provide optimal noise inhibition and resolution, a Range key is used for measuring to select a Range, a [ + ] key, a [ - ] key and a Range key on the operation panel 10 can be used for selecting the Range, an Auto (automatic Range adjustment) key is used for automatically selecting the Range according to input for measuring, compared with a manual Range, the automatic Range adjustment is convenient, the automatic Range adjustment can be adjusted upwards to 120% of the current Range and downwards to below 10% of the current Range, and the Auto zero key is used for automatically returning to zero to provide the most accurate measurement value.

Step three: after the automatic zero resetting is started, the multimeter internally measures the offset after each measurement, and then subtracts the measurement value from the previous reading, so that the influence of the offset voltage on the input circuit of the multimeter on the measurement accuracy can be avoided; with auto-zero disabled, the multimeter makes one measurement of the offset and subtracts the offset value from all the later measured parameters, and each time the function, range, or integration time is changed, the multimeter makes a new offset measurement.

Step four: specifying the input impedance of the test stylus specifies the input impedance of the measurement terminals, which may be automatic or 10 Μ Ω, automatic mode selection high impedance, suitable for 100mV, 1V, and 10V ranges, while 10 Μ Ω is suitable for 100V and 1000V ranges, in most cases 10 Μ Ω is high enough to load most of the circuitry, and also low enough to stabilize the readings of the high impedance circuitry.

Referring to fig. 11(b) and 11(c), for the direct current measurement embodiment, fig. 11(b) shows a schematic diagram of a direct current measurement 3A current terminal connection of an embodiment of the multimeter provided by the present invention; FIG. 11(c) is a schematic diagram illustrating a DC current measurement 10A current terminal connection of an embodiment of a multimeter provided by an embodiment of the present invention;

the method comprises the steps that when the current smaller than 1A is measured, a 3A current input terminal is connected with a red test meter pen, an L O input terminal is connected with a black test meter pen, and when the current larger than 1A is measured, a 10A current input terminal is connected with the red test meter pen, a L O input terminal or the black test meter pen, and the red test meter pen, the L O input terminal or the black test meter pen are respectively connected with the equipment to be tested.

Pressing the Shift key on the operation panel 10 and then pressing the DCV key, i.e. equal to pressing the DCI key to measure the direct current, the default condition is the selected state in the soft key 14, using the cursor positioning keyboard to specify the integration time in the power line cycle number (P L C) for measurement, 1, 10 and 100P L C provide the line frequency noise suppression in the normal mode, wherein, selecting 100P L C can provide the best noise suppression and resolution,

step three: by default, the 3A current input terminal is selected, the Terminals key included in the soft key 14 is used to switch between the 3A current input terminal and the 10A current input terminal, and when it is changed to the 10A current input terminal, the measurement range automatically becomes 10A.

Step four: selecting a measuring Range according to a Range key for measurement, or selecting the measuring Range by using [ + ], [ - ] and [ Range ] keys on a front panel, and automatically selecting the measuring Range according to input by an Auto (automatic Range adjustment) key, compared with a manual measuring Range, the automatic Range adjustment is more convenient, and the automatic Range adjustment can be adjusted upwards to 120% of the current measuring Range and downwards to less than 10% of the current measuring Range; the More key included in the soft key 14 is pressed to switch between two page settings for auto-zero, after the auto-zero is enabled (On), the multimeter will measure the offset internally after each measurement, and then subtract the measurement value from the previous reading, thus avoiding the offset voltage On the multimeter input circuit from influencing the measurement accuracy, under the condition of disabling (Off) auto-zero, the multimeter will measure the offset once, and subtract the offset value from all the parameters measured later, and when the function, the measurement range or the integration time is changed each time, the multimeter will measure a new offset.

In addition, the flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

For those skilled in the art to which the invention pertains, a plurality of alternatives or modifications can be made to the described embodiments without departing from the concept of the invention, and these alternatives or modifications should be considered as belonging to the protection scope of the invention.

Claims (5)

1. A multimeter comprising a case, characterized in that: an integrated circuit board is arranged in the shell and mainly comprises a display circuit board, a simulation circuit board and an interface circuit board;

the analog circuit board is horizontally arranged at the bottom of the shell, the display circuit board is vertically arranged at the front end inside the shell, and the interface circuit board is vertically arranged at the rear end inside the shell;

the analog circuit board comprises an input selection module, a function selection circuit module, a direct current amplification circuit, an alternating current circuit, a frequency measurement circuit, a current source module and an analog-to-digital conversion circuit.

2. A multimeter as described in claim 1, wherein: the input selection module mainly comprises an input selection circuit, an SATA connecting wire, a straight needle European connector and a selector switch;

the input selection circuit is electrically connected with the selector switch, and the input of the display circuit board and the input of the interface circuit board are selected through the selector switch;

the interface circuit board is electrically connected with the analog circuit board through the SATA connecting wire, receives signal input of the interface panel at the front end and inputs the signal to the analog circuit board through the SATA connecting wire.

3. A multimeter as described in claim 1, wherein: the function selection module mainly comprises a relay, an analog switch and a selection circuit;

the analog switch comprises a first-stage analog switch, a second-stage analog switch and a third-stage analog switch;

the relay is electrically connected with the high-voltage divider, the high-voltage divider is electrically connected with the first-stage analog switch, the second-stage analog switch is electrically connected with the direct-current amplification circuit, and the selection circuit is electrically connected with the third-stage analog switch.

4. A multimeter as described in claim 1, wherein: the direct current amplifying circuit is a single-end-to-differential plus-bias amplifying circuit, amplifies direct current signals and adjusts positive and negative signals to be supplied to ADC input.

5. A multimeter as described in claim 1, wherein: the current source module comprises a reference source, a current source, a direct current amplifier and a capacitance measuring module;

the current source is electrically connected with the reference source and the relay, and the reference source is electrically connected with the analog-to-digital conversion circuit;

the capacitance measuring module is provided with two threshold comparators which are distributed at the left end and the right end of the capacitor to compare the voltage of the capacitor and control the charge and discharge of the capacitor through a current source.

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