CN114778918A - Current measuring device and method - Google Patents

Abstract

The present application relates to a current measuring device and method. The device comprises: the device comprises a measuring branch formed by connecting a plurality of sampling resistors in series, a plurality of switches in one-to-one correspondence with the plurality of sampling resistors, a first operational amplifier, a second operational amplifier, a first analog-to-digital converter, a second analog-to-digital converter and a processor. And selecting which sampling resistors in the measuring branch are connected into the measuring circuit through switches in one-to-one correspondence with the sampling resistors. The resistance value of the measuring branch is changed by replacing the closed switch, and the measuring range of current measurement is further switched. And when the voltage value to be measured is within the measuring range of the second analog-to-digital converter and the closed switch is not replaced, determining the current value to be measured according to the measured value of the second analog-to-digital converter. And when the second analog-to-digital converter is replacing the closed switch, determining the current value to be measured according to the measurement value of the first analog-to-digital converter. The device can keep the measurement of the current signal during the switching of the measuring range.

Description

Current measuring device and method

The present application claims priority from the chinese patent office, chinese patent application No. 202110851775X entitled "current measuring device and method", filed 27/7/27/2021, the entire contents of which are incorporated herein by reference.

The present application claims priority from the chinese patent office, chinese patent application No. 202110853081X entitled "current measuring device and method", filed 27/7/27/2021, the entire contents of which are incorporated herein by reference.

Technical Field

The present disclosure relates to circuit measurement technologies, and in particular, to a current measurement device and method.

Background

With the development of electronic circuit technology, the requirements for the continuity and accuracy of the measured current are higher and higher. For different current signals, different measuring ranges are required to be used for measurement, so that the measurement accuracy is improved.

In the conventional technology, the switching of the measuring range is realized by controlling the action of a selection switch.

However, since the selective switch needs a certain time to operate, the conventional solution may cause the current measurement channel to be disconnected during the selective switch operation, thereby causing interruption and leakage of current measurement, and causing inaccurate measurement.

Disclosure of Invention

In view of the above, it is desirable to provide a current measuring device and method that can maintain accurate current measurement during the switching of the range.

A current measurement device, the device comprising: the range switching circuit comprises a plurality of sampling resistors and a plurality of range selection switches which are in one-to-one correspondence; the sampling resistors are connected in series, the sampling resistors at two ends are respectively a first resistor and a second resistor, and one end of each sampling resistor, which is close to the first resistor or far away from the second resistor, is a first end; the first end of each range selection switch is connected with the second end of the corresponding sampling resistor, and the second ends of the plurality of range selection switches are connected together; at least one of the plurality of range selection switches is closed, and the first end of the first resistor and the second ends of the plurality of range selection switches are the input end and the output end of the current signal to be measured in the range switching circuit; the maximum measuring range measuring unit comprises a first operational amplifier and a first analog-to-digital converter which are connected; the first operational amplifier is respectively connected with the first end and the second end of the first resistor and is used for measuring the voltage formed by the current signal to be measured on the first resistor, generating a voltage measurement signal and scaling the voltage measurement signal; the first analog-to-digital converter is used for measuring the voltage measurement signal obtained by scaling the first operational amplifier to obtain a first voltage value; the adjustable measuring range measuring unit comprises a second operational amplifier and a second analog-to-digital converter which are connected; the second operational amplifier is respectively connected with the first end of the first resistor and the second end of the second resistor and is used for measuring the voltage formed by the current signal to be measured on the plurality of sampling resistors, generating a voltage measurement signal and scaling the voltage measurement signal; the second analog-to-digital converter is used for measuring the voltage measurement signal after the second operational amplifier is zoomed to obtain a second voltage value; and the processor is respectively connected with the first analog-to-digital converter, the control ends of the plurality of range selection switches and the second analog-to-digital converter, and is used for determining and outputting a current value corresponding to the current signal to be measured based on the first voltage value when the closed range selection switch is switched.

In one embodiment, the processor is configured to receive a range switching instruction including a target range, where the target range corresponds to one of the plurality of range selection switches, and a measurement range of the adjustable range measurement unit when the range selection switch corresponding to the target range is closed is a target range; within a first set time length after the range switching instruction is received, closing a range selection switch corresponding to the target range; disconnecting the range selection switch which is closed when the range switching instruction is received between a first set time length and a second set time length after the range switching instruction is received, wherein the second set time length is greater than the first set time length; within a second set time length after the measuring range switching instruction is received, determining and outputting a current value corresponding to the current signal to be measured based on the first voltage value; and determining and outputting a current value corresponding to the current signal to be measured based on the second voltage value outside a second set time length after the range switching instruction is received.

In one embodiment, the processor is configured to determine whether the scaled voltage measurement signal of the second operational amplifier is outside the measurement range of the second analog-to-digital converter beyond a second set duration after receiving the range switching command; if the voltage measurement signal obtained by scaling the second operational amplifier is determined to be out of the measurement range of the second analog-to-digital converter, determining a current value corresponding to the current signal to be measured based on the first voltage value and outputting the current value; and if the voltage measurement signal obtained by scaling the second operational amplifier is within the measurement range of the second analog-to-digital converter, determining a current value corresponding to the current signal to be measured based on the second voltage value and outputting the current value.

In one embodiment, the processor is configured to determine a proportion of the second voltage value in a measurement range of the second analog-to-digital converter; when the proportion of the second voltage value in the measuring range of the second analog-to-digital converter is between the upper proportion limit and the lower proportion limit, determining that the voltage measuring signal scaled by the second operational amplifier is in the measuring range of the second analog-to-digital converter; and when the proportion of the second voltage value in the measurement range of the second analog-to-digital converter is greater than the upper proportion limit or less than the lower proportion limit, determining that the voltage measurement signal scaled by the second operational amplifier is out of the measurement range of the second analog-to-digital converter.

In one embodiment, the processor is configured to, when the second voltage value gradually increases, take a first upper ratio limit as the upper ratio limit and a first lower ratio limit as the lower ratio limit; and when the second voltage value is gradually reduced, taking a second proportion upper limit as the proportion upper limit, taking a second proportion lower limit as the proportion lower limit, wherein the second proportion upper limit is smaller than the first proportion upper limit, and the second proportion lower limit is smaller than the first proportion lower limit.

In one embodiment, the apparatus further comprises: the intermediate range measuring unit comprises a third operational amplifier and a third analog-to-digital converter which are connected with each other; the third operational amplifier is respectively connected with the first end of the first resistor and the second end of a third resistor, and is used for measuring the voltage formed by the current signal to be measured between the first resistor and the third resistor, generating a voltage measurement signal and carrying out scaling, wherein the third resistor is one of the plurality of sampling resistors except the first resistor and the second resistor; the third analog-to-digital converter is used for measuring the voltage measurement signal obtained by scaling the third operational amplifier to obtain a third voltage value; the processor is further connected with the third analog-to-digital converter and used for determining whether sampling resistors corresponding to the closed range selection switches before and after switching are connected in series between the third resistor and the second end of the second resistor within a second set time length after the range switching instruction is received; if the sampling resistors corresponding to the closed range selection switches before and after switching are connected in series between the third resistor and the second end of the second resistor, determining a current value corresponding to the current signal to be measured based on the third voltage value; and if the closed range selection switch before switching and/or the closed range selection switch after switching are/is connected in series between the third resistor and the first end of the first resistor, determining a current value corresponding to the current signal to be measured based on the first voltage value.

In one embodiment, if it is determined that the scaled voltage measurement signal of the second operational amplifier is outside the measurement range of the second analog-to-digital converter, the processor is configured to determine whether a sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the first end of the first resistor; if the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the first end of the first resistor, determining a current value corresponding to the current signal to be measured based on the first voltage value; and if the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the second end of the second resistor, determining and outputting a current value corresponding to the current signal to be measured based on the third voltage value.

In one embodiment, the processor is configured to determine whether the scaled voltage measurement signal of the third operational amplifier is outside the measurement range of the third analog-to-digital converter if the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the second end of the second resistor; if the voltage measurement signal obtained by scaling the third operational amplifier is determined to be out of the measurement range of the third analog-to-digital converter, determining a current value corresponding to the current signal to be measured based on the first voltage value and outputting the current value; and if the voltage measurement signal obtained by scaling the third operational amplifier is determined to be within the measurement range of the third analog-to-digital converter, determining a current value corresponding to the current signal to be measured based on the third voltage value and outputting the current value.

In one embodiment, the apparatus further comprises: at least one short-circuit switch, correspond to said sampling resistance one-to-one; the first end of the sampling resistor is connected with the first end of the corresponding sampling resistor, and the second end of the sampling resistor is connected with the input end of the second operational amplifier connected with the second end of the second resistor and used for being closed when the corresponding range selection switch is closed.

In one embodiment, the processor is configured to determine, based on the first voltage value, a target range of the adjustable range measuring unit when the range selection switch corresponding to the first resistor is closed, where the target range corresponds to one of the plurality of range selection switches, and the measurement range of the adjustable range measuring unit when the range selection switch corresponding to the target range is closed is the target range; within a first set time length after the target range is determined, closing a range selection switch corresponding to the target range; disconnecting all the range selection switches except the range selection switch corresponding to the target range between the first set time length and the second set time length after the target range is determined; and determining a first current value corresponding to the current signal to be measured and outputting the first current value based on the first voltage value within a second set time length after the target measuring range is determined.

In one embodiment, the processor is configured to determine a proportion of the first current value in each measurement range of the adjustable range measurement unit; screening out the proportion smaller than the upper limit of the proportion and larger than the lower limit of the proportion; determining the measuring range corresponding to the maximum proportion in the screened proportions as the target range; the upper limit of the proportion is a judgment reference for determining whether the second current value exceeds the upper limit of the measuring range of the adjustable range measuring unit; the lower proportional limit is a judgment reference for determining whether the second current value is lower than the lower measuring range limit of the adjustable measuring range measuring unit; the second current value is a current value corresponding to the current signal to be measured and determined based on the second voltage value.

In one embodiment, the processor is configured to determine the target range of the adjustable range measurement unit based on the first current value when the first current value is within the second large measurement range of the adjustable range measurement unit.

In one embodiment, the processor is configured to output the first current value determined at the first time when the first current value determined at the first time is outside the second large measurement range of the adjustable range measurement unit; when the first current value determined at the first moment is within the second large measuring range of the adjustable range measuring unit, determining the target range of the adjustable range measuring unit based on the first current value determined at the first moment; judging whether the first current value determined at the second moment is out of the second large measuring range of the adjustable measuring range measuring unit or not; wherein the second time is after the first time.

In one embodiment, the processor is configured to determine whether the first current value is greater than an upper value of the second large measurement range of the adjustable range measurement unit or less than a lower value of the second large measurement range of the adjustable range measurement unit; if the first current value is larger than the upper limit value of the second large measuring range of the adjustable measuring range measuring unit or smaller than the lower limit value of the second large measuring range of the adjustable measuring range measuring unit, determining that the first current value is out of the second large measuring range of the adjustable measuring range measuring unit; and if the first current value is smaller than the upper limit value of the second large measuring range of the adjustable range measuring unit and larger than the lower limit value of the second large measuring range of the adjustable range measuring unit, determining that the first current value is in the second large measuring range of the adjustable range measuring unit.

In one embodiment, the processor is used for determining a second current value corresponding to the current signal to be measured based on the second voltage value outside a second set time length after the target measuring range is determined; when the second current value determined at the first moment is within the target range and the target range is the minimum measuring range of all measuring ranges of the second current value determined at the first moment, outputting the second current value determined at the first moment; when the second current value determined at the first moment is out of the target range, or the target range is not the minimum measurement range in all measurement ranges of the second current value determined at the first moment, closing a range selection switch corresponding to the first resistor; judging whether the second current value determined at the second moment is within the target range or not and whether the target range is the minimum measurement range in all measurement ranges of the second current value determined at the second moment or not; wherein the second time is after the first time.

In one embodiment, the processor is configured to close the range selection switch corresponding to the first resistor when the second current value is outside the target range, or the target range is not the minimum measurement range of all measurement ranges of the second current value.

A method of current measurement, the method comprising:

the current signal to be measured passes through the pass switching circuit; the range switching circuit comprises a plurality of sampling resistors and a plurality of range selection switches which are in one-to-one correspondence; the sampling resistors are connected in series, the sampling resistors at two ends are respectively a first resistor and a second resistor, and one end of each sampling resistor, which is close to the first resistor or far away from the second resistor, is a first end; the first end of each range selection switch is connected with the second end of the corresponding sampling resistor, and the second ends of the plurality of range selection switches are connected together; the first end of the first resistor and the second ends of the plurality of range selection switches are the input end and the output end of a current signal to be measured in the range switching circuit;

closing at least one of the plurality of span select switches;

measuring the voltage formed by the current signal to be measured on the first resistor through a first operational amplifier, generating a voltage measurement signal and scaling;

measuring the voltage measurement signal obtained by scaling the first operational amplifier through a first analog-to-digital converter to obtain a first voltage value;

measuring the voltage formed by the current signal to be measured on the plurality of sampling resistors through a second operational amplifier, generating a voltage measurement signal and scaling;

measuring the amplified voltage signal of the second operational amplifier after being zoomed through a second analog-to-digital converter to obtain a second voltage value;

and if the closed range selection switch is switched, determining a current value corresponding to the current signal to be measured based on the first voltage value and outputting the current value.

The current measuring device and the method form a range switching circuit by a plurality of sampling resistors and a plurality of range selection switches which are in one-to-one correspondence, the sampling resistors are connected in series, the sampling resistors at two ends are respectively a first resistor and a second resistor, one end of each sampling resistor, which is close to the first resistor or far away from the second resistor, is a first end, the first end of each range selection switch is connected with the second end of the corresponding sampling resistor, the second ends of the range selection switches are connected together, at least one of the range selection switches is closed, and the first end of the first resistor and the second ends of the range selection switches are input ends and output ends of current signals to be measured. So that the current signal to be measured only passes through the first resistor and the sampling resistor between the sampling resistors corresponding to the closed range selection switch; in addition, the sampling resistor between the sampling resistor corresponding to the closed range selection switch and the second resistor is short-circuited. The number of sampling resistors through which the current signal to be measured passes can be changed by selecting different range selection switches to be closed, so that the size of the resistor through which the current signal to be measured passes is changed, and the voltage formed by the current signal to be measured on the sampling resistors is controlled within the measurement range of the measurement unit under the condition that the size of the current signal to be measured is different, so that the measurement unit can perform accurate measurement.

The method comprises the steps that a first operational amplifier and a first analog-to-digital converter are connected to form a maximum measuring range measuring unit, the first operational amplifier is connected with a first end and a second end of a first resistor respectively, the voltage formed by a current signal to be measured on the first resistor is measured, a voltage measuring signal is generated and is zoomed, and the first analog-to-digital converter measures the zoomed voltage measuring signal of the first operational amplifier to obtain a first voltage value. Since the maximum range measuring unit measures only the voltage formed on one resistor of the first resistor, the maximum range measuring unit can realize measurement within the maximum range.

The second operational amplifier and the second analog-to-digital converter are connected to form an adjustable measuring range measuring unit, the second operational amplifier is respectively connected with the first end of the first resistor and the second end of the second resistor, the voltage of the current signal to be measured formed on the plurality of sampling resistors is measured, a voltage measuring signal is generated and is scaled, and the second analog-to-digital converter measures the scaled voltage measuring signal of the second operational amplifier to obtain a second voltage value. Because the voltage formed on the sampling resistors is determined by the closed range selection switch, and the closed range selection switch can be selected according to the size of the current signal to be measured so as to control the voltage formed on the sampling resistors within the measurement range of the measurement unit, the measurement range of the adjustable range measurement unit can be adjusted to be matched with the current signal to be measured, and the accurate measurement within a small range is realized.

When the closed range selection switch is switched, the second voltage value measured by the adjustable range measuring unit is inaccurate, and at the moment, the processor determines and outputs the current value corresponding to the current signal to be measured according to the first voltage value, so that the continuity and the accuracy of current measurement can be still maintained under the condition that the measurement result of the adjustable range measuring unit is inaccurate.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the descriptions of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following descriptions are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a current measuring device according to an embodiment;

FIG. 2 is a flow diagram of current output during span switching in one embodiment;

FIG. 3 is a flow diagram of current output over-range in one embodiment;

FIG. 4 is a schematic structural diagram of a current measuring device according to another embodiment;

FIG. 5 is a flow chart of current output during span switching in another embodiment;

FIG. 6 is a flow chart of current output over range in another embodiment;

FIG. 7 is a flow chart of current output over-range in yet another embodiment;

FIG. 8 is a flow chart of the manner in which a current measuring device operates in one embodiment;

FIG. 9 is a flow diagram of current output during span switching in one embodiment;

FIG. 10 is a schematic diagram of a gradual voltage change in one embodiment;

FIG. 11 is a schematic structural view of a current measuring device in yet another embodiment;

FIG. 12 is a flow chart illustrating a method of current measurement according to one embodiment.

Description of reference numerals:

10-sampling resistor, 11-first resistor, 12-second resistor, 13-third resistor, 20-switch, 21-first short-circuit switch, 30-first operational amplifier, 40-first analog-to-digital converter, 31-second operational amplifier, 41-second analog-to-digital converter, 50-processor, 32-third operational amplifier, and 42-third analog-to-digital converter.

Detailed Description

To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Embodiments of the present application are set forth in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the present application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

It will be understood that, as used herein, the terms "first," "second," and the like may be used herein to describe various elements, but these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

Spatially relative terms, such as "under," "below," "beneath," "under," "above," "over," and the like, may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements or features described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary terms "under" and "under" can encompass both an orientation of above and below. In addition, the device may comprise additional orientations (e.g., rotated 90 degrees or other orientations) and the spatial descriptors used herein interpreted accordingly.

It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or be connected to the other element through intervening elements. Further, "connection" in the following embodiments is understood to mean "electrical connection", "communication connection", or the like, if there is a transfer of electrical signals or data between the connected objects.

As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises/comprising," "includes" or "including," etc., specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. Also, as used in this specification, the term "and/or" includes any and all combinations of the associated listed items.

The current measuring method in the current measuring device usually adopts a mode of precisely detecting a resistor and an operational amplifier, the resistance value of the resistor is known, the actual current value can be measured by measuring the voltage of the current flowing through two ends of the resistor and then by ohm law I ═ U/R. The measuring method has the advantages of low cost, high precision and small volume. By adopting the method, the influence of power parameters, design cost and other factors on the detection resistor is considered, so different detection resistors need to be selected according to the magnitude of the measurement current to form different measurement channels to switch different ranges. During the process of switching the range, the situation of inaccurate measurement may occur. In view of the above, a current measuring apparatus and method capable of maintaining accurate measurement of current during switching of the range are provided.

In one embodiment, as shown in fig. 1, there is provided a current measuring device comprising: the device comprises a plurality of sampling resistors 10, a plurality of range selection switches 20, a first operational amplifier 30, a first analog-to-digital converter 40, a second operational amplifier 31, a second analog-to-digital converter 41 and a processor 50 which are in one-to-one correspondence. Wherein:

the range switching circuit comprises a plurality of sampling resistors 10 and a plurality of range selection switches 20 which correspond to one another. The sampling resistors 10 are connected in series, the sampling resistors 10 at two ends are respectively a first resistor 11 and a second resistor 12, and one end of each sampling resistor 10 close to the first resistor 11 or far away from the second resistor 12 is a first end; the first end of each range selection switch 20 is connected with the second end of the corresponding sampling resistor 10, and the second ends of the range selection switches 20 are connected together; at least one of the plurality of range selection switches 20 is closed, and the first end of the first resistor 11 and the second end of the plurality of range selection switches 20 are the input end and the output end of the current signal to be measured in the range switching circuit.

Illustratively, in the plurality of sampling resistors 10, the resistance values sequentially increase from the first resistor 11 to the second resistor 12, and the resistance value of the first resistor 11 is the smallest and the resistance value of the second resistor 12 is the largest.

Illustratively, the range selection switch 20 may be one of a switch tube, a relay switch, and a single pole switch.

A maximum range measuring unit including a first operational amplifier 30 and a first analog-to-digital converter 40 connected; the first operational amplifier 30 is respectively connected to the first end and the second end of the first resistor 11, and is configured to measure a voltage formed by the current signal to be measured on the first resistor 11, generate a voltage measurement signal, and perform scaling; the first analog-to-digital converter 40 is configured to measure the scaled voltage measurement signal of the first operational amplifier 30 to obtain a first voltage value.

Illustratively, the first operational amplifier 30 and the second operational amplifier 31 may be one of general operational amplifiers F003, F007, F030, a high speed operational amplifier F051B, a high precision operational amplifier F714, a high impedance operational amplifier CF072, and a low power operational amplifier F010.

Illustratively, the first analog-to-digital converter 40 and the second analog-to-digital converter 41 may be one of ADCs 0808, AD7678, AD9221, AD9223, and AD 9220.

The adjustable measuring range measuring unit comprises a second operational amplifier 31 and a second analog-to-digital converter 41 which are connected; the second operational amplifier 31 is respectively connected to the first end of the first resistor 11 and the second end of the second resistor 12, and is configured to measure a voltage formed by the current signal to be measured on the plurality of sampling resistors 10, generate a voltage measurement signal, and perform scaling; the second analog-to-digital converter 41 is configured to measure the voltage measurement signal scaled by the second operational amplifier 31 to obtain a second voltage value.

And the processor 50 is respectively connected with the first analog-to-digital converter 40, the control ends of the plurality of range selection switches 20 and the second analog-to-digital converter 41, and is used for determining and outputting a current value corresponding to the current signal to be measured based on the first voltage value when the closed range selection switch 20 is switched.

Illustratively, the Processor 50 may be a Central Processing Unit (CPU), and may be one of other general purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate arrays (FPGAs) or other Programmable logic devices, discrete Gate or transistor logic devices, discrete hardware components, and the like. The general purpose processor may be a microprocessor or any conventional processor.

In this embodiment, a range switching circuit is formed by a plurality of sampling resistors and a plurality of range selection switches in one-to-one correspondence, the plurality of sampling resistors are connected in series, the sampling resistors at two ends are respectively a first resistor and a second resistor, one end of each sampling resistor, which is close to the first resistor or is far away from the second resistor, is a first end, the first end of each range selection switch is connected with the second end of the corresponding sampling resistor, the second ends of the plurality of range selection switches are connected together, at least one of the plurality of range selection switches is closed, and the first end of the first resistor and the second ends of the plurality of range selection switches are input ends and output ends of current signals to be measured. So that the current signal to be measured only passes through the first resistor and the sampling resistor between the sampling resistors corresponding to the closed range selection switch; in addition, the sampling resistor between the sampling resistor corresponding to the closed range selection switch and the second resistor is short-circuited. The number of sampling resistors through which the current signal to be measured passes can be changed by selecting different range selection switches to be closed, so that the size of the resistor through which the current signal to be measured passes is changed, and the voltage formed by the current signal to be measured on the sampling resistors is controlled within the measurement range of the measurement unit under the condition that the size of the current signal to be measured is different, so that the measurement unit can perform accurate measurement.

The method comprises the steps that a first operational amplifier and a first analog-to-digital converter are connected to form a maximum measuring range measuring unit, the first operational amplifier is connected with a first end and a second end of a first resistor respectively, the voltage formed by a current signal to be measured on the first resistor is measured, a voltage measuring signal is generated and is zoomed, and the first analog-to-digital converter measures the zoomed voltage measuring signal of the first operational amplifier to obtain a first voltage value. Since the maximum range measuring unit measures only the voltage formed on one resistor of the first resistor, the maximum range measuring unit can realize measurement within the maximum range.

And the second analog-to-digital converter measures the voltage measurement signal of the second operational amplifier after being scaled to obtain a second voltage value. Because the voltage formed on the sampling resistors is determined by the closed range selection switch, and the closed range selection switch can be selected according to the size of the current signal to be measured so as to control the voltage formed on the sampling resistors within the measurement range of the measurement unit, the measurement range of the adjustable range measurement unit can be adjusted to be matched with the current signal to be measured, and the accurate measurement within a small range is realized.

When the closed range selection switch is switched, the second voltage value measured by the adjustable range measuring unit is inaccurate, and at the moment, the processor determines and outputs the current value corresponding to the current signal to be measured according to the first voltage value, so that the continuity and the accuracy of current measurement can be still maintained under the condition that the measurement result of the adjustable range measuring unit is inaccurate.

In one embodiment, as shown in FIG. 2, processor 50 is configured to perform the steps of:

s202, a range switching command containing a target range is received.

Specifically, the target range corresponds to one of the plurality of range selection switches 20, and the measurement range of the adjustable range measurement unit when the range selection switch 20 corresponding to the target range is closed is the target range.

And S204, within the first set duration after the range switching instruction is received, closing the range selection switch corresponding to the target range.

And S206, disconnecting the range selection switch which is closed when the range switching instruction is received between the first set time length and the second set time length after the range switching instruction is received.

Specifically, the second set duration is greater than the first set duration.

And S208, determining and outputting a current value corresponding to the current signal to be measured based on the first voltage value within a second set time length after the range switching instruction is received.

And S210, determining and outputting a current value corresponding to the current signal to be measured based on the second voltage value outside the second set time length after the range switching instruction is received.

In practical applications, if the range selection switch 20 corresponding to the target range is the same as the range selection switch 20 corresponding to the first resistor 11, the current value corresponding to the current signal to be measured may be determined based on the first voltage value and output, in addition to the second set time period after receiving the range switching command.

In this embodiment, when the processor receives the range switching instruction, the range selection switch corresponding to the target range is turned on first, and then the previously turned-on range selection switch is turned off, so that it can be ensured that at least one of the range selection switches is turned on in the range switching process, and the maximum range measurement unit can perform accurate measurement. In the measuring range switching process, the measuring value of the adjustable measuring range measuring unit may be inaccurate, and at the moment, the current value corresponding to the current signal to be measured is determined based on the first voltage value, so that the accuracy and the continuity of current measurement can be ensured. After the measuring range is switched, the measuring value of the adjustable measuring range measuring unit is accurate, and then the current value corresponding to the current signal to be measured is determined based on the second voltage value, so that a more accurate measuring result can be obtained.

In one embodiment, as shown in FIG. 3, processor 50 is configured to perform the following steps:

s302, determining whether the voltage measuring signal after the scaling of the second operational amplifier is out of the measuring range of the second analog-to-digital converter. If the scaled voltage measurement signal of the second operational amplifier is outside the measurement range of the second analog-to-digital converter, executing S304; if the scaled voltage measurement signal of the second operational amplifier is within the measurement range of the second analog-to-digital converter, S306 is executed.

Specifically, the processor 50 is configured to determine a ratio of the second voltage value in the measurement range of the second analog-to-digital converter 41; when the proportion of the second voltage value in the measurement range of the second analog-to-digital converter 41 is between the upper proportion limit and the lower proportion limit, determining that the voltage measurement signal scaled by the second operational amplifier 31 is in the measurement range of the second analog-to-digital converter 41; when the proportion of the second voltage value in the measurement range of the second analog-to-digital converter 41 is greater than the upper limit of the proportion or less than the lower limit of the proportion, it is determined that the voltage measurement signal scaled by the second operational amplifier 31 is outside the measurement range of the second analog-to-digital converter 41.

The ratio of the second voltage value in the measurement range of the second analog-to-digital converter 41 is exemplarily: the difference between the second voltage value and the minimum value of the measuring range of the second analog-to-digital converter 41 is divided by the difference between the maximum value and the minimum value of the measuring range of the second analog-to-digital converter 41.

Step S302 is executed after the second set time length after the range switching command is received.

In such a way, whether the signal to be measured after the second operational amplifier is scaled is out of the measurement range of the second analog-to-digital converter is judged, so that whether the second analog-to-digital converter exceeds the measurement range is determined, and whether the second voltage value output by the second analog-to-digital converter is reliable and accurate is determined.

And S304, determining a current value corresponding to the current signal to be measured based on the first voltage value and outputting the current value.

And S306, determining a current value corresponding to the current signal to be measured based on the second voltage value and outputting the current value.

For example, S302, S304 and S306 may be executed in conjunction with S208, that is, after receiving the second set duration after the range switching command, determining whether the scaled voltage measurement signal of the second operational amplifier is outside the measurement range of the second analog-to-digital converter, and outputting the second voltage value if the scaled voltage measurement signal of the second operational amplifier is within the measurement range of the second analog-to-digital converter.

In this embodiment, the processor first determines whether the current adjustable-range measuring unit exceeds the measuring range by determining whether the scaled voltage measuring signal is within the measuring range of the second analog-to-digital converter, so as to determine whether the second voltage value output by the adjustable-range measuring unit is accurate. If the scaled voltage measurement signal is outside the measurement range of the second analog-to-digital converter, it indicates that the adjustable range measurement unit has exceeded the measurement range at this time, the output second voltage value is inaccurate, and the measurement accuracy can be ensured by using the first voltage value output by the maximum range measurement unit. If the scaled voltage measurement signal is within the measurement range of the second analog-to-digital converter, it indicates that the adjustable range measurement unit does not exceed the measurement range at this time, and the output second voltage value is accurate, and the measurement precision can be improved by using the second voltage value output by the adjustable range measurement unit.

In one embodiment, as shown in fig. 4, the apparatus further comprises a third operational amplifier 32, a third analog-to-digital converter 42. Wherein:

the intermediate range measuring unit comprises a third operational amplifier 32 and a third analog-to-digital converter 42 which are connected with each other. The third operational amplifier 32 is connected to the first end of the first resistor 11 and the second end of the third resistor 13, respectively, and is configured to measure a voltage formed between the first resistor 11 and the third resistor 13 by the current signal to be measured, generate a voltage measurement signal, and perform scaling.

Specifically, the third resistor 13 is one sampling resistor 10 of the plurality of sampling resistors 10 except for the first resistor 11 and the second resistor 12.

The third analog-to-digital converter 42 is configured to measure the scaled voltage measurement signal of the third operational amplifier 32 to obtain a third voltage value.

The processor 50 is further connected to the third analog-to-digital converter 42 for performing the following steps:

in step S400, it is determined whether the sampling resistors 10 corresponding to the closed range selection switches 20 before and after switching are all connected in series between the third resistor 13 and the second end of the second resistor 12 within a second set time period after receiving the range switching instruction.

In step S402, if the sampling resistors 10 corresponding to the closed range selection switches 20 before and after switching are connected in series between the third resistor 13 and the second end of the second resistor 12, the current value corresponding to the current signal to be measured is determined based on the third voltage value.

In step S404, if the range selection switch 20 closed before switching and/or the range selection switch 20 closed after switching is connected in series between the third resistor 13 and the first end of the first resistor 11, the current value corresponding to the current signal to be measured is determined based on the first voltage value.

Specifically, if the measurement range when the range switch corresponding to the first resistor is closed is different from the measurement range when the range switch corresponding to the second resistor is closed by a large difference, such as five or six orders of magnitude, the maximum range measurement unit cannot distinguish a small current signal to be measured, and at this time, the intermediate range measurement unit is used for measurement, so that the small current signal to be measured can be distinguished, and the continuity and accuracy of current measurement can be maintained under the condition that the measurement result of the adjustable range measurement unit is inaccurate.

In this embodiment, a third operational amplifier and a third analog-to-digital converter are connected to form an intermediate range measurement unit, the third operational amplifier is connected to the first end of the first resistor and the second end of the third resistor, respectively, the voltage formed by the current signal to be measured between the first resistor and the third resistor is measured, a voltage measurement signal is generated and scaled, and the third analog-to-digital converter measures the scaled voltage measurement signal of the third operational amplifier to obtain a third voltage value. Because the voltage formed between the first resistor and the third resistor is greater than the voltage formed on the first resistor, the current signal to be measured which can be measured by the intermediate range measuring unit is less than the current signal to be measured which can be measured by the maximum range measuring unit, and the measurement with the measurement range smaller than that of the maximum range unit and the measurement accuracy larger than that of the maximum range unit can be realized.

In one embodiment, as shown in FIG. 5, processor 50 is configured to perform the steps of:

s502, a range switching command including a target range is received.

S504, whether sampling resistors corresponding to the closed range selection switches before and after switching are connected in series between the third resistor and the second end of the second resistor or not is determined. If the sampling resistors corresponding to the range selection switches closed before and after switching are connected in series between the third resistor and the second end of the second resistor, step S506 is executed, and if the range selection switch closed before switching and/or the range selection switch closed after switching are connected in series between the third resistor and the first end of the first resistor, step S508 is executed.

And S506, determining and outputting the current value of the current signal to be measured based on the third voltage value within a second set time length after the range switching instruction is received.

And S508, determining and outputting the current value of the current signal to be measured based on the first voltage value within a second set time length after the measuring range switching instruction is received.

And S510, within a first set duration after the range switching instruction is received, closing a range selection switch corresponding to the target range.

S512, the range selection switch which is closed when the range switching instruction is received is switched off between the first set time length and the second set time length after the range switching instruction is received.

And S514, after the second set time period, determining and outputting the current value of the current signal to be measured based on the second voltage value.

In this embodiment, if the sampling resistors corresponding to the closed range selection switches before and after switching are all connected in series between the third resistor and the second end of the second resistor, the measurement ranges corresponding to the closed range selection switches before and after switching are all small, and at this time, the third voltage value output by the middle measurement unit is selected to determine the current value of the current signal to be measured, so that the small current signal to be measured can be distinguished, and the continuity and accuracy of current measurement can be still maintained under the condition that the measurement result of the adjustable range measurement unit is inaccurate. If the closed range selection switch before switching and/or the closed range selection switch after switching are/is connected in series between the third resistor and the first end of the first resistor, the measurement range corresponding to the closed range selection switch before switching and/or after switching exceeds the measurement range corresponding to the middle measurement unit, at the moment, the third voltage value output by the middle measurement unit is inaccurate, the first voltage value output by the maximum range measurement unit is selected to determine the current value of the current signal to be measured, and the accuracy of current measurement can be ensured.

In one embodiment, as shown in FIG. 6, processor 50 is configured to perform the following steps:

s602, determining whether the scaled voltage measurement signal of the second operational amplifier is outside the measurement range of the second analog-to-digital converter. If it is determined that the scaled voltage measurement signal of the second operational amplifier is outside the measurement range of the second analog-to-digital converter, step S604 is performed. If it is determined that the scaled voltage measurement signal of the second operational amplifier is within the measurement range of the second analog-to-digital converter, step S606 is executed.

And S604, determining whether the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the first end of the first resistor. If the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the second end of the second resistor, step S608 is executed. If the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the first end of the first resistor, step S610 is executed.

And S606, determining a current value corresponding to the current signal to be measured based on the second voltage value and outputting the current value.

And S608, determining a current value corresponding to the current signal to be measured based on the third voltage value and outputting the current value.

And S610, determining a current value corresponding to the current signal to be measured based on the first voltage value and outputting the current value.

In the embodiment, when the voltage measurement signal scaled by the second operational amplifier is within the measurement range of the second analog-to-digital converter, the current value corresponding to the current signal to be measured is determined based on the second voltage value. And when the voltage measurement signal after the scaling of the second operational amplifier is out of the measurement range of the second analog-to-digital converter, determining whether the sampling resistor corresponding to the closed range selection switch is connected between the third resistor and the first end of the first resistor in series. And if the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the second end of the second resistor, determining a current value corresponding to the current signal to be measured based on the third voltage value. And if the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the first end of the first resistor, determining a current value corresponding to the current signal to be measured based on the first voltage value. By the measuring method, the current signal to be measured can be measured as accurately as possible on the premise of ensuring that the measuring range is not exceeded.

In one embodiment, as shown in FIG. 7, processor 50 is configured to perform the steps of:

s702, determining whether the voltage measurement signal scaled by the third operational amplifier is outside the measurement range of the third analog-to-digital converter. If it is determined that the scaled voltage measurement signal of the third operational amplifier is outside the measurement range of the third analog-to-digital converter, step S704 is executed. If it is determined that the scaled voltage measurement signal of the third operational amplifier is within the measurement range of the third analog-to-digital converter, step S706 is performed.

Specifically, if the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the second end of the second resistor, it is determined whether the voltage measurement signal scaled by the third operational amplifier is outside the measurement range of the third analog-to-digital converter.

In particular, determining whether the scaled voltage measurement signal of the third operational amplifier is outside the measurement range of the third analog-to-digital converter may be similar to determining whether the scaled voltage measurement signal of the second operational amplifier is outside the measurement range of the second analog-to-digital converter and will not be described in detail herein.

And S704, determining a current value corresponding to the current signal to be measured based on the first voltage value, and outputting the current value.

And S706, determining a current value corresponding to the current signal to be measured based on the third voltage value and outputting the current value.

In this embodiment, when the sampling resistor corresponding to the closed range selection switch is connected in series between the third resistor and the second end of the second resistor, the processor first determines whether the intermediate range measurement unit exceeds the measurement range by determining whether the scaled voltage measurement signal is within the measurement range of the third analog-to-digital converter, so as to determine whether the third voltage value output by the intermediate range measurement unit is accurate. If the scaled voltage measurement signal is outside the measurement range of the third analog-to-digital converter, it indicates that the intermediate range measurement unit has exceeded the measurement range at this time, the output third voltage value is inaccurate, and the measurement accuracy can be ensured by using the first voltage value output by the maximum range measurement unit. If the scaled voltage measurement signal is within the measurement range of the third analog-to-digital converter, it indicates that the intermediate range measurement unit does not exceed the measurement range at this time, and the output third voltage value is accurate, and the measurement precision can be improved by using the third voltage value output by the intermediate range measurement unit.

In one embodiment, as shown in FIG. 8, processor 50 is configured to perform the following steps:

and S800, when the range selection switch corresponding to the first resistor is closed, determining the target range of the adjustable range measuring unit based on the first voltage value.

Specifically, the target range corresponds to one of the range selection switches, and the measurement range of the adjustable range measurement unit when the range selection switch corresponding to the target range is closed is the target range.

And S810, closing a range selection switch corresponding to the target range within the first set time length after the target range is determined.

And S820, disconnecting all the range selection switches except the range selection switch corresponding to the target range between the first set time length and the second set time length after the target range is determined.

And S830, determining and outputting a first current value corresponding to the current signal to be measured based on the first voltage value within a second set time length after the target measuring range is determined.

In this embodiment, when the range selection switch corresponding to the first resistor is turned off, the target range of the adjustable range measurement unit is determined according to the first voltage value, the range selection switch corresponding to the target range is turned on within the first set duration after the target range is determined, and all the range selection switches except the range selection switch corresponding to the target range are turned off between the first set duration and the second set duration after the target range is determined, so that the automatic switching of the measurement range of the adjustable range measurement unit can be realized, and at least one of the range switches is turned on in the range switching process during the process of switching the measurement range, and the maximum range measurement unit can perform accurate measurement. In the process of switching the measuring range, the second voltage value measured by the adjustable measuring range measuring unit is inaccurate. And in a second set time length after the target range is determined, determining and outputting a first current value corresponding to the current signal to be measured based on the first voltage value, so that the continuity and the accuracy of the current measurement can be still maintained under the condition that the measurement result of the adjustable range measurement unit is inaccurate.

In one embodiment, as shown in FIG. 9, processor 50 is configured to perform the following steps:

and S900, closing the range selection switch corresponding to the first resistor.

Specifically, after the range selection switch corresponding to the first resistor is closed, the maximum range measurement unit can accurately measure the current signal to be measured, and determine a first current value corresponding to the current signal to be measured based on the obtained first voltage value.

S910, determining a first current value corresponding to the current signal to be measured based on the first voltage value, and determining whether the first current value is within the second large measurement range of the adjustable range measurement unit. If the first current value is within the second large measuring range of the adjustable measuring range measuring unit, executing step S930; if the first current value is outside the second large measurement range of the adjustable range measurement unit, step S920 is executed.

Specifically, the processor 50 is configured to determine whether the first current value is greater than an upper limit value of the second large measurement range of the adjustable-range measurement unit or less than a lower limit value of the second large measurement range of the adjustable-range measurement unit; if the first current value is larger than the upper limit value of the second large measuring range of the adjustable measuring range measuring unit or smaller than the lower limit value of the second large measuring range of the adjustable measuring range measuring unit, determining that the first current value is outside the second large measuring range of the adjustable measuring range measuring unit; and if the first current value is smaller than the upper limit value of the second large measuring range of the adjustable measuring range measuring unit and larger than the lower limit value of the second large measuring range of the adjustable measuring range measuring unit, determining that the first current value is in the second large measuring range of the adjustable measuring range measuring unit.

S920, a first current value is output.

Specifically, after step S920 is performed, step S910 is performed. After the first current value determined at the first moment is output, judging whether the first current value determined at the second moment is out of the second large measuring range of the adjustable measuring range measuring unit or not; wherein the second time is after the first time.

Specifically, after the first current value is output, a new signal to be measured is received, and at this time, it may be determined again whether the first current value measured by the current maximum range measuring unit is within the second large measurement range of the adjustable range measuring unit, that is, after step S920 is executed, step S910 is executed again.

Specifically, if the first current value is outside the second large measurement range of the adjustable range measurement unit, it represents that the first current value can be measured only by using the maximum measurement range measurement unit or the maximum measurement range of the adjustable range measurement unit, and the first current value at this time is the most accurate value that can be measured by the current measurement device, and the first current value at this time is output without determining the target range.

The second large measuring range of the adjustable measuring range measuring unit is the measuring range next to the maximum measuring range from the plurality of measuring ranges of the adjustable measuring range measuring unit. Taking fig. 1 as an example, the range changeover switch 20 corresponding to the measurement range of the maximum range measurement unit is the same as the range changeover switch 20 corresponding to the first resistor 11. When the range switch 20 corresponding to the first resistor 11 is closed, the adjustable range measuring unit only measures the voltage formed on the first resistor 11, and the current value corresponding to the current signal to be measured can reach the maximum value, that is, the measuring range of the adjustable range measuring unit is the maximum measuring range at this time. The range switch 20 corresponding to the second large measurement range of the adjustable range measurement unit is the same as the range switch 20 corresponding to the sampling resistor 10 connected to the first resistor 11. When the range switch 20 corresponding to the sampling resistor 10 connected to the first resistor 11 is closed, the adjustable range measuring unit measures the voltage formed on the sampling resistor 10 connected to the first resistor 11 and the first resistor 11, and the current value corresponding to the current signal to be measured can reach the second maximum value, that is, the measurement range of the adjustable range measuring unit is the second maximum measurement range. For example, if the measurement range of the maximum range measurement unit is 5A, and the measurement range of the adjustable range measurement unit includes 5A range, 3A range, 1.5A range, etc., the measurement range of the adjustable range measurement unit is 5A range, and the measurement range of the adjustable range measurement unit is the second largest measurement range, which is 3A range.

And S930, determining the target range of the adjustable range measuring unit based on the first current value.

Specifically, the processor 50 is configured to determine a proportion of the first current value in each measurement range of the adjustable range measurement unit; screening out the proportion smaller than the upper limit of the proportion and larger than the lower limit of the proportion; determining the measuring range corresponding to the maximum proportion in the screened proportions as a target range; the upper proportional limit is a criterion for determining whether the second current value exceeds the upper measuring range limit of the adjustable range measuring unit, the lower proportional limit is a criterion for determining whether the second current value is lower than the lower measuring range limit of the adjustable range measuring unit, and the second current value is a current value corresponding to the current signal to be measured and determined based on the second voltage value.

And S940, within the first set time length after the target range is determined, closing the range selection switch corresponding to the target range.

And S950, switching off all the range selection switches except the range selection switch corresponding to the target range between the first set time length and the second set time length after the target range is determined.

And S960, determining and outputting a first current value corresponding to the current signal to be measured based on the first voltage value within a second set time length after the target measuring range is determined.

Specifically, the second set duration is longer than the first set duration, so that the range selection switches before and after switching are simultaneously closed between the first set duration and the second set duration, and the continuity of current measurement is ensured. By setting the first set time length and the second set time length, at least one range selection switch is ensured to be closed at any time, so that the current measurement is not interrupted. Meanwhile, the second set duration also ensures that the switching action of the range selection switch is completely finished.

And S970, determining a second current value corresponding to the current signal to be measured based on the second voltage value outside the second set time length after the target range of the adjustable range measuring unit is determined, and judging whether the second current value is in the target range of the adjustable range measuring unit and whether the target range is the minimum measuring range of all measuring ranges of the second current value. If the second current value is outside the target range of the adjustable range measuring unit, or the target range is not the minimum measuring range of all measuring ranges of the second current value, executing step S900; if the second current value is within the target range of the adjustable-range measuring unit and the target range is the minimum measuring range of all measuring ranges of the second current value, step S980 is executed.

Specifically, the step of judging whether the second current value is out of the target range of the adjustable range measuring unit comprises the following steps: dividing the difference value between the second current value and the minimum value of the measuring range of the adjustable range measuring unit by the difference value between the maximum value and the minimum value of the measuring range of the adjustable range measuring unit to obtain the proportion of the second current value in the measuring range of the adjustable range measuring unit; when the proportion of the second current value in the measuring range of the adjustable range measuring unit is between the upper proportion limit and the lower proportion limit, determining that the second current value is in the measuring range of the adjustable range measuring unit; and when the proportion of the second current value in the measuring range of the adjustable range measuring unit is greater than the upper limit of the proportion or less than the lower limit of the proportion, determining that the second current value is outside the measuring range of the adjustable range measuring unit.

Specifically, the step of determining whether the target measurement range is the minimum measurement range of all measurement ranges of the second current value includes:

step S9700, dividing the difference between the second current value and the minimum value of the measurement range of each measurable second current value of the adjustable-range measurement unit by the difference between the corresponding maximum value and the corresponding minimum value of the measurement range, and determining the proportion of the second current value in the measurement range of each measurable second current value of the adjustable-range measurement unit.

Step S9702, if the measurement range corresponding to the maximum ratio of the second current value in the ratio occupied in the measurement ranges of each measurable second current value of the adjustable-range measurement unit is not the target range, determining that the target range is not the minimum measurement range of all the measurement ranges of the second current value.

Step S9704, if the measurement range corresponding to the maximum ratio of the second current value in the ratio occupied in the measurement ranges of each measurable second current value of the adjustable-range measurement unit is the target range, determining that the target range is the minimum measurement range of all the measurement ranges of the second current value.

Specifically, in the measurement range of the adjustable range measurement unit, in which the second current value can be measured, the measurement range with the largest proportion of the second current value is the minimum measurement range in which the second current value can be measured. The measured second current value is already the most accurate value that can be measured by the current measuring device.

And S980, outputting a second current value.

Specifically, after step S980 is performed, step S970 is performed. That is, after the second current value determined at the first time is output, whether the second current value determined at the second time is within the target range or not and whether the target range is the minimum measurement range of all measurement ranges of the second current value measured at the second time or not are judged.

In this embodiment, first, the range selection switch corresponding to the first resistor is closed, and at this time, the maximum range measurement unit is used to measure the current signal to be measured, so as to obtain the first voltage value. And then determining a first current value corresponding to the current signal to be measured based on the first voltage value, and judging whether the first current value is in the second large measuring range of the adjustable range measuring unit. If the first current value is not in the second large measuring range of the adjustable range measuring unit, the first current value represents that the first current value can be measured only by using the maximum measuring range measuring unit or the maximum measuring range of the adjustable range measuring unit, the first current value at the moment is the most accurate value which can be measured by the current measuring device, the target range does not need to be determined, and the first current value at the moment is output. And then receiving the current signal to be measured at the next moment, and judging whether the current signal to be measured at the next moment is in the second large measuring range of the adjustable range measuring unit again.

And if the first current value is within the second large measuring range of the adjustable range measuring unit, determining the target range of the adjustable range measuring unit based on the first current value. The target range is the minimum range which can measure the first current value and does not exceed the range in all the measuring ranges of the adjustable range measuring unit. Thereby achieving the most accurate measurement of the first current value.

And in a first set time length after the target range is determined, controlling a range selection switch corresponding to the target range to be closed, between the first set time length and a second set time length, disconnecting all range selection switches except the range selection switch corresponding to the target range, and in the second set time length after the target range is determined, determining and outputting a first current value corresponding to the current signal to be measured based on the first voltage value. Therefore, at any moment, at least one range selection switch is closed, so that the current measurement is not interrupted, and the continuity of the current measurement is ensured. And the second time length is set to ensure that the switching action of the range selection switch is completely finished. And in the process of switching the range selection switch, a first current value is output, so that the current measurement is ensured to be uninterrupted.

And then, determining a second current value corresponding to the current signal to be measured based on the second voltage value outside a second set time length after the target measuring range is determined. And judging whether the second current value is in the target range of the adjustable range measuring unit or not, and whether the target range is the minimum measuring range of all measuring ranges of the second current value or not. If the second current value is outside the target range of the adjustable range measuring unit, or the target range is not the minimum measuring range of all measuring ranges of the second current value, it represents that the second current value at this time is inaccurate, or the second current value can be measured by using a smaller measuring range of the adjustable range measuring unit, so as to obtain a more accurate value, so that the second current value at this time is not output, but the range selection switch corresponding to the first resistor is closed again.

If the second current value is within the target range of the adjustable range measuring unit and the target range is the minimum measuring range of all measuring ranges of the second current value, the second current value is output because the second current value measured at the moment is the most accurate value which can be measured by the current measuring device.

In summary, the above-mentioned device can automatically switch the measurement range according to the current signal to be measured, and the current signal to be measured does not exceed the minimum measurement range of the measurement range, i.e. the device can measure the most accurate measurement range of the current signal to be measured. Therefore, the measuring range can be automatically switched to the optimal measuring range according to the current signal to be measured, the measuring accuracy is guaranteed, when the plurality of range selection switches are switched to the closed range selection switches, the second voltage value measured by the adjustable range measuring unit is inaccurate, at the moment, the processor determines and outputs the current value corresponding to the current signal to be measured according to the first voltage value, and the continuity and the accuracy of the current measurement can be still maintained under the condition that the measuring result of the adjustable range measuring unit is inaccurate.

In one embodiment, the processor 50 is further configured to, when the second voltage value gradually increases, take the first upper scale limit as the upper scale limit and the first lower scale limit as the lower scale limit; when the second voltage value is gradually reduced, the second proportion upper limit is used as the proportion upper limit, the second proportion lower limit is used as the proportion lower limit, the second proportion upper limit is smaller than the first proportion upper limit, and the second proportion lower limit is smaller than the first proportion lower limit.

Taking fig. 10 as an example, Vth1+ represents a first upper ratio limit, Vth0+ represents a second upper ratio limit, Vth 0-represents a first lower ratio limit, and Vth 1-represents a second lower ratio limit. As shown in fig. 10, the first upper proportional limit Vth1+ is greater than the second upper proportional limit Vth0+, and the first lower proportional limit Vth 0-is greater than the second lower proportional limit Vth 1-.

The arrows in fig. 10 represent the trend of the voltage change, and the solid line indicates the selected upper or lower proportional limit. When the second voltage value gradually increases, the first upper scale limit Vth1+ is selected as the upper scale limit as shown in the upper left diagram in fig. 10, and the first lower scale limit Vth 0-is selected as the lower scale limit as shown in the lower right diagram in fig. 10. When the second voltage value gradually decreases, as shown in the upper right diagram in fig. 10, the second upper scale limit Vth0+ is selected as the upper scale limit, and as shown in the lower left diagram in fig. 10, the second lower scale limit Vth 1-is selected as the lower scale limit.

Specifically, the second voltage value gradually increases, that is, the second voltage value at the next time is greater than the second voltage value at the previous time within the set time period. The second voltage value gradually decreases, that is, the second voltage value at the next moment is smaller than the second voltage value at the previous moment in the set time length.

Illustratively, the processor 50 includes a hysteresis comparator for changing the upper scale limit of the processor 50 to a first upper scale limit and the lower scale limit to a first lower scale limit as the voltage value gradually increases, and changing the upper scale limit of the processor 50 to a second upper scale limit and the lower scale limit to a second lower scale limit as the voltage value gradually decreases.

Illustratively, the first upper proportion limit, the first lower proportion limit, the second upper proportion limit and the second lower proportion limit are determined according to an actual noise value of the current signal to be measured.

In this embodiment, when the voltage value gradually increases, the upper proportional limit and the lower proportional limit of the processor are changed to the first upper proportional limit and the first lower proportional limit, and when the voltage value gradually decreases, the upper proportional limit and the lower proportional limit of the processor are changed to the second upper proportional limit and the second lower proportional limit, respectively. The first upper proportion limit, the first lower proportion limit, the second upper proportion limit and the second lower proportion limit are determined according to an actual noise value. Therefore, when the voltage value acquired by the analog-to-digital converter is noisy, voltage fluctuation caused by noise is covered by the hysteresis width, so that the processor is prevented from being influenced by the noise when judging whether the second analog-to-digital converter exceeds the measuring range, the processor is prevented from frequently replacing the current value output by selection due to the influence of the noise, and the current value output by the processor is more stable.

In one embodiment, as shown in fig. 11, the device further comprises at least one short-circuit switch 21. At least one short-circuit switch 21 is in one-to-one correspondence with the sampling resistors 10, a first end of the short-circuit switch is connected with a first end of the corresponding sampling resistor 10, and a second end of the short-circuit switch is connected with an input end of a second operational amplifier 31 connected with a second end of the second resistor 12, and the short-circuit switch is closed when the corresponding range selection switch 20 is closed.

In this embodiment, by setting the short-circuit switch, when the corresponding sampling resistor is not connected to the measurement branch, the sampling resistor is short-circuited. Therefore, the phenomenon that the line parasitic capacitance of the sampling resistor reduces the line bandwidth of the measuring branch is avoided, and the measuring sensitivity is higher.

In one embodiment, as shown in fig. 12, there is provided a current measuring method including the steps of:

s1202, the current signal to be measured is passed through the routine switching circuit.

Specifically, the range switching circuit comprises a plurality of sampling resistors and a plurality of range selection switches which are in one-to-one correspondence; the sampling resistors are connected in series, the sampling resistors positioned at two ends are respectively a first resistor and a second resistor, and one end of each sampling resistor, which is close to the first resistor or far away from the second resistor, is a first end; the first end of each range selection switch is connected with the second end of the corresponding sampling resistor, and the second ends of the range selection switches are connected together; the first end of the first resistor and the second ends of the plurality of range selection switches are the input end and the output end of the current signal to be measured in the range switching circuit.

S1204, at least one of the plurality of span select switches is closed.

And S1206, measuring the voltage formed by the current signal to be measured on the first resistor through the first operational amplifier, generating a voltage measurement signal and scaling.

S1208, measuring the scaled voltage measurement signal of the first operational amplifier through the first analog-to-digital converter to obtain a first voltage value.

And S1210, measuring the voltage formed by the current signal to be measured on the plurality of sampling resistors through a second operational amplifier, generating a voltage measurement signal and scaling.

And S1212, measuring the amplified voltage signal of the second operational amplifier after being scaled by the second analog-to-digital converter to obtain a second voltage value.

S1214, when the closed range selection switch is switched, determining and outputting a current value corresponding to the current signal to be measured based on the first voltage value.

In this embodiment, a range switching circuit is composed of a plurality of sampling resistors and a plurality of range selection switches in one-to-one correspondence, the plurality of sampling resistors are connected in series, the sampling resistors at two ends are respectively a first resistor and a second resistor, one end of each sampling resistor, which is close to the first resistor or is far away from the second resistor, is a first end, the first end of each range selection switch is connected with the second end of the corresponding sampling resistor, the second ends of the plurality of range selection switches are connected together, at least one of the plurality of range selection switches is closed, and the first end of the first resistor and the second ends of the plurality of range selection switches are input ends and output ends of current signals to be measured. In this way, the current signal to be measured only passes through the sampling resistor between the first resistor and the sampling resistor corresponding to the closed range selection switch, and the sampling resistor between the sampling resistor corresponding to the closed range selection switch and the second resistor is short-circuited. The number of sampling resistors through which the current signal to be measured passes can be changed by selecting different range selection switches to be closed, so that the size of the resistor through which the current signal to be measured passes is changed, and the voltage formed by the current signal to be measured on the sampling resistors is controlled within the measurement range of the measurement unit under the condition that the size of the current signal to be measured is different, so that the measurement unit can perform accurate measurement.

The method comprises the steps that a first operational amplifier and a first analog-to-digital converter are connected to form a maximum measuring range measuring unit, the first operational amplifier is connected with a first end and a second end of a first resistor respectively, the voltage formed by a current signal to be measured on the first resistor is measured, a voltage measuring signal is generated and is zoomed, and the first analog-to-digital converter measures the zoomed voltage measuring signal of the first operational amplifier to obtain a first voltage value. Since the maximum range measuring unit measures only the voltage formed across one resistor of the first resistor, the maximum range measuring unit can realize measurement in the maximum range.

The second operational amplifier and the second analog-to-digital converter are connected to form an adjustable measuring range measuring unit, the second operational amplifier is respectively connected with the first end of the first resistor and the second end of the second resistor, the voltage of the current signal to be measured formed on the plurality of sampling resistors is measured, a voltage measuring signal is generated and is scaled, and the second analog-to-digital converter measures the scaled voltage measuring signal of the second operational amplifier to obtain a second voltage value. Because the voltage formed on the sampling resistors is determined by the closed range selection switch, and the closed range selection switch can be selected according to the size of the current signal to be measured so as to control the voltage formed on the sampling resistors within the measurement range of the measurement unit, the measurement range of the adjustable range measurement unit can be adjusted to be matched with the current signal to be measured, and the accurate measurement within a small range is realized.

When the plurality of range selection switches are switched to the closed range selection switch, the second voltage value measured by the adjustable range measurement unit is inaccurate, and at the moment, the processor determines and outputs the current value corresponding to the current signal to be measured according to the first voltage value, so that the continuity and the accuracy of current measurement can be still maintained under the condition that the measurement result of the adjustable range measurement unit is inaccurate.

It should be understood that although the various steps in the flowcharts of fig. 2, 3, 5-9, 12 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not limited to being performed in the exact order illustrated and, unless explicitly stated herein, may be performed in other orders. Moreover, at least some of the steps in fig. 2, 3, 5-9, and 12 may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of performing the steps or stages is not necessarily sequential, but may be alternated or alternated with other steps or at least some of the other steps.

It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above may be implemented by hardware instructions of a computer program, which may be stored in a non-volatile computer-readable storage medium, and when executed, may include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), for example.

In the description herein, references to the description of "some embodiments," "other embodiments," "desired embodiments," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic depictions of the above terms do not necessarily refer to the same embodiment or example.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is specific and detailed, but not to be understood as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent application shall be subject to the appended claims.

Claims (17)

1. A current measuring device, characterized in that the device comprises:

the range switching circuit comprises a plurality of sampling resistors (10) and a plurality of range selection switches (20) which correspond to one another one by one; the sampling resistors (10) are connected in series, the sampling resistors (10) at two ends are respectively a first resistor (11) and a second resistor (12), and one end, close to the first resistor (11) or far away from the second resistor (12), of each sampling resistor (10) is a first end; a first end of each range selection switch (20) is connected with a second end of the corresponding sampling resistor (10), and second ends of the plurality of range selection switches (20) are connected together; at least one of the plurality of range selection switches (20) is closed, and the first end of the first resistor (11) and the second ends of the plurality of range selection switches (20) are the input end and the output end of the current signal to be measured in the range switching circuit;

a maximum range measurement unit comprising a first operational amplifier (30) and a first analog-to-digital converter (40) connected; the first operational amplifier (30) is respectively connected with the first end and the second end of the first resistor (11) and is used for measuring the voltage formed by the current signal to be measured on the first resistor (11), generating a voltage measurement signal and scaling the voltage measurement signal; the first analog-to-digital converter (40) is used for measuring the voltage measurement signal after the scaling of the first operational amplifier (30) to obtain a first voltage value;

the adjustable measuring range measuring unit comprises a second operational amplifier (31) and a second analog-to-digital converter (41) which are connected; the second operational amplifier (31) is respectively connected with the first end of the first resistor (11) and the second end of the second resistor (12) and is used for measuring the voltage formed by the current signal to be measured on the plurality of sampling resistors (10), generating a voltage measurement signal and scaling the voltage measurement signal; the second analog-to-digital converter (41) is used for measuring the voltage measurement signal obtained by scaling the second operational amplifier (31) to obtain a second voltage value;

and the processor (50) is respectively connected with the first analog-to-digital converter (40), the control ends of the plurality of range selection switches (20) and the second analog-to-digital converter (41), and is used for determining and outputting a current value corresponding to the current signal to be measured based on the first voltage value when the closed range selection switch (20) is switched.

2. The apparatus of claim 1, wherein the processor (50) is configured to receive a range switching command including a target range, the target range corresponding to one of the plurality of range selection switches (20), and the measurement range of the adjustable range measurement unit when the range selection switch (20) corresponding to the target range is closed is the target range; within a first set duration after the range switching instruction is received, closing a range selection switch (20) corresponding to the target range; the range selection switch (20) which is closed when the range switching instruction is received is switched off between a first set time and a second set time after the range switching instruction is received, wherein the second set time is longer than the first set time; within a second set time length after the measuring range switching instruction is received, determining and outputting a current value corresponding to the current signal to be measured based on the first voltage value; and determining and outputting a current value corresponding to the current signal to be measured based on the second voltage value outside a second set time length after the range switching instruction is received.

3. The apparatus of claim 2, wherein the processor (50) is configured to determine, outside a second set time period after receiving the range switching command, whether the scaled voltage measurement signal of the second operational amplifier (31) is outside the measurement range of the second analog-to-digital converter (41); if the voltage measurement signal scaled by the second operational amplifier (31) is determined to be out of the measurement range of the second analog-to-digital converter (41), determining a current value corresponding to the current signal to be measured based on the first voltage value and outputting the current value; and if the voltage measurement signal scaled by the second operational amplifier (31) is determined to be in the measurement range of the second analog-to-digital converter (41), determining a current value corresponding to the current signal to be measured based on the second voltage value, and outputting the current value.

4. The apparatus of claim 3, wherein the processor (50) is configured to determine a proportion of the second voltage value in a measurement range of the second analog-to-digital converter (41); when the proportion of the second voltage value in the measuring range of the second analog-to-digital converter (41) is between the upper proportion limit and the lower proportion limit, determining that the voltage measuring signal scaled by the second operational amplifier (31) is in the measuring range of the second analog-to-digital converter (41); when the proportion of the second voltage value in the measuring range of the second analog-to-digital converter (41) is larger than the upper proportion limit or smaller than the lower proportion limit, determining that the voltage measuring signal scaled by the second operational amplifier (31) is out of the measuring range of the second analog-to-digital converter (41).

5. The apparatus of claim 4, wherein the processor (50) is configured to, when the second voltage value is gradually increased, take a first upper scale limit as the upper scale limit and a first lower scale limit as the lower scale limit; and when the second voltage value is gradually reduced, taking a second proportion upper limit as the proportion upper limit, taking a second proportion lower limit as the proportion lower limit, wherein the second proportion upper limit is smaller than the first proportion upper limit, and the second proportion lower limit is smaller than the first proportion lower limit.

6. The apparatus of any of claims 3-5, further comprising:

the intermediate range measuring unit comprises a third operational amplifier (32) and a third analog-to-digital converter (42) which are connected with each other; the third operational amplifier (32) is respectively connected with the first end of the first resistor (11) and the second end of the third resistor (13) and is used for measuring the voltage formed by the current signal to be measured between the first resistor (11) and the third resistor (13) and generating a voltage measurement signal and carrying out scaling, and the third resistor (13) is a sampling resistor (10) except the first resistor (11) and the second resistor (12) in the plurality of sampling resistors (10); the third analog-to-digital converter (42) is used for measuring the voltage measurement signal after the scaling of the third operational amplifier (32) to obtain a third voltage value;

the processor (50) is further connected with the third analog-to-digital converter (42) and is used for determining whether sampling resistors (10) corresponding to the closed range selection switches (20) before and after switching are connected in series between the third resistor (13) and the second end of the second resistor (12) within a second set time length after the range switching instruction is received; if the sampling resistors (10) corresponding to the closed range selection switches (20) before and after switching are connected in series between the third resistor (13) and the second end of the second resistor (12), determining a current value corresponding to the current signal to be measured based on the third voltage value; and if the closed range selection switch (20) before switching and/or the closed range selection switch (20) after switching are/is connected in series between the third resistor (13) and the first end of the first resistor (11), determining the current value corresponding to the current signal to be measured based on the first voltage value.

7. The apparatus of claim 6, wherein the processor (50) is configured to determine whether the sampling resistor (10) corresponding to the closed span selection switch (20) is connected in series between the third resistor (13) and the first end of the first resistor (11) if it is determined that the scaled voltage measurement signal of the second operational amplifier (31) is outside the measurement span of the second analog-to-digital converter (41); if the sampling resistor (10) corresponding to the closed range selection switch (20) is connected in series between the third resistor (13) and the first end of the first resistor (11), determining a current value corresponding to the current signal to be measured based on the first voltage value; and if the sampling resistor (10) corresponding to the closed range selection switch (20) is connected in series between the third resistor (13) and the second end of the second resistor (12), determining a current value corresponding to the current signal to be measured based on the third voltage value.

8. The apparatus of claim 7, wherein the processor (50) is configured to determine whether the scaled voltage measurement signal of the third operational amplifier (32) is outside the measurement range of the third analog-to-digital converter (42) if the sampling resistor (10) corresponding to the closed range selection switch (20) is connected in series between the third resistor (13) and the second end of the second resistor (12); if the voltage measurement signal scaled by the third operational amplifier (32) is determined to be out of the measurement range of the third analog-to-digital converter (42), determining a current value corresponding to the current signal to be measured based on the first voltage value and outputting the current value; and if the voltage measurement signal scaled by the third operational amplifier (32) is determined to be in the measurement range of the third analog-to-digital converter (42), determining a current value corresponding to the current signal to be measured based on the third voltage value, and outputting the current value.

9. The apparatus of any one of claims 1 to 5, further comprising:

at least one short-circuit switch (21) corresponding to the sampling resistor (10) one by one; the first end of each sampling resistor (10) is connected with the first end of the corresponding sampling resistor, and the second end of each sampling resistor is connected with the input end of the second operational amplifier (31) connected with the second end of the second resistor (12) and used for being closed when the corresponding range selection switch (20) is closed.

10. The apparatus of claim 1, wherein the processor (50) is configured to determine a target range of the adjustable range measurement unit based on the first voltage value when the range selection switch (20) corresponding to the first resistor (11) is closed, the target range corresponding to one of the plurality of range selection switches (20), the measurement range of the adjustable range measurement unit when the range selection switch (20) corresponding to the target range is closed being the target range; within a first set time length after the target range is determined, closing a range selection switch (20) corresponding to the target range; disconnecting all the range selection switches (20) except the range selection switch (20) corresponding to the target range between the first set time length and the second set time length after the target range is determined; and determining a first current value corresponding to the current signal to be measured and outputting the first current value based on the first voltage value within a second set time length after the target measuring range is determined.

11. The apparatus of claim 10 wherein the processor (50) is configured to determine a fraction of the first current value at each measurement range of the adjustable range measurement unit; screening out the proportion smaller than the upper limit of the proportion and larger than the lower limit of the proportion; determining the measuring range corresponding to the maximum proportion in the screened proportions as the target range; the upper limit of the proportion is a judgment reference for determining whether the second current value exceeds the upper limit of the measuring range of the adjustable range measuring unit; the lower proportional limit is a judgment reference for determining whether the second current value is lower than the lower measuring range limit of the adjustable measuring range measuring unit; the second current value is a current value corresponding to the current signal to be measured determined based on the second voltage value.

12. The apparatus of claim 10 wherein the processor (50) is configured to determine the target range of the adjustable range measurement unit based on the first current value when the first current value is within the second large measurement range of the adjustable range measurement unit.

13. The apparatus of claim 10 wherein the processor (50) is configured to output the first current value determined at a first time when the first current value determined at the first time is outside the second wide measurement range of the adjustable range measurement unit; when the first current value determined at the first moment is within the second large measuring range of the adjustable range measuring unit, determining the target range of the adjustable range measuring unit based on the first current value determined at the first moment; judging whether the first current value determined at the second moment is out of the second large measuring range of the adjustable measuring range measuring unit or not; wherein the second time is after the first time.

14. The apparatus of claim 12 or 13, wherein the processor (50) is configured to determine whether the first current value is greater than an upper value of the second large measurement range of the adjustable range measurement unit or less than a lower value of the second large measurement range of the adjustable range measurement unit; if the first current value is larger than the upper limit value of the second large measuring range of the adjustable measuring range measuring unit or smaller than the lower limit value of the second large measuring range of the adjustable measuring range measuring unit, determining that the first current value is out of the second large measuring range of the adjustable measuring range measuring unit; and if the first current value is smaller than the upper limit value of the second large measuring range of the adjustable measuring range measuring unit and larger than the lower limit value of the second large measuring range of the adjustable measuring range measuring unit, determining that the first current value is in the second large measuring range of the adjustable measuring range measuring unit.

15. The device according to any one of claims 10 to 13, wherein the processor (50) is configured to determine a second current value corresponding to the current signal to be measured based on the second voltage value outside a second set time period after the target measuring range is determined; when the second current value determined at the first moment is within the target range and the target range is the minimum measuring range of all measuring ranges of the second current value determined at the first moment, outputting the second current value determined at the first moment; when the second current value determined at the first moment is out of the target range or the target range is not the minimum measurement range in all measurement ranges of the second current value determined at the first moment, closing a range selection switch (20) corresponding to the first resistor (11); judging whether the second current value determined at the second moment is within the target range and whether the target range is the minimum measurement range in all measurement ranges of the second current value determined at the second moment; wherein the second time is after the first time.

16. The apparatus of claim 15 wherein the processor (50) is configured to close the range selection switch (20) associated with the first resistor (11) when the second current value is outside the target range or the target range is not the smallest of all of the target ranges of the second current value.

17. A method of measuring current, the method comprising:

the current signal to be measured passes through the pass switching circuit; the range switching circuit comprises a plurality of sampling resistors and a plurality of range selection switches which are in one-to-one correspondence; the sampling resistors are connected in series, the sampling resistors at two ends are respectively a first resistor and a second resistor, and one end of each sampling resistor, which is close to the first resistor or far away from the second resistor, is a first end; the first end of each range selection switch is connected with the second end of the corresponding sampling resistor, and the second ends of the plurality of range selection switches are connected together; the first end of the first resistor and the second ends of the plurality of range selection switches are the input end and the output end of a current signal to be measured in the range switching circuit;

closing at least one of the plurality of span select switches;

measuring the voltage formed by the current signal to be measured on the first resistor through a first operational amplifier, generating a voltage measurement signal and scaling;

measuring the voltage measurement signal after the first operational amplifier is scaled through a first analog-to-digital converter to obtain a first voltage value;

measuring the voltage formed by the current signal to be measured on the plurality of sampling resistors through a second operational amplifier, generating a voltage measurement signal and scaling;

measuring the amplified voltage signal of the second operational amplifier after being scaled through a second analog-to-digital converter to obtain a second voltage value;

and if the closed range selection switch is switched, determining a current value corresponding to the current signal to be measured based on the first voltage value and outputting the current value.

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