CN211426630U - Digital electric meter capable of reducing current measurement error - Google Patents

Abstract

The utility model relates to a digital electric meter capable of reducing current measurement errors. The utility model comprises: a sampling circuit connected to an electronic device through a current sampling terminal, current sampling is performed on the electronic device to generate a sampling signal, the sampling circuit comprises a plurality of sampling resistors with different resistance values, the sampling signal is transmitted to an amplifier circuit through a buffer circuit, the amplifier circuit amplifies the sampling signal at a selected amplification factor, an analog-to-digital conversion circuit converts the amplified sampling signal into a digital signal, a microprocessor can execute a designated automatic shift measurement mode, in which the microprocessor starts current sampling according to a preset minimum measurement gear, and the microprocessor automatically switches to select a sampling resistor to be connected to the current sampling terminal according to the size of the digital signal, the resistance value of the selected sampling resistor is not lower than the resistance value of the sampling resistor corresponding to the minimum measurement gear, the error generated when measuring current can be reduced, and the digital electric meter can be ensured to have better measurement accuracy.

Description

Digital Energy Meters That Reduce Current Measurement Errors

technical field

The utility model relates to a digital electric meter (Digital Multimeter, DMM), in particular to a digital electric meter that can reduce the current measurement error.

Background technique

Since the gap between the current consumption and standby current of electronic equipment is becoming more and more obvious, if the electronic equipment uses batteries again, the manufacturer will pay more attention to the consumption current and standby current when designing the circuit of the electronic equipment. However, the difference between the consumption current and the standby current will be very large. The minimum value of the standby current can be several microamps (μA) or less, but the maximum value of the current consumption can be several amperes (A).

If the user uses a digital power meter (DMM) to measure the consumption current and standby current of the aforementioned electronic device, the measurement range of the digital power meter can be adjusted appropriately. Because the current consumption is relatively large, at this time, in order to measure the current consumption, the user can directly select the larger current measurement gear manually. At this time, the measurement error will be relatively small and will not affect the measurement results.

However, if you want to measure the standby current and consumption current of the electronic device at the same time, you need to use an automatic shift function of the digital meter to measure the electronic device. The electronic device itself will perform the standby action for a period of time, then the digital meter will automatically Switch to a suitable gear to start measuring the standby current, and then the electronic device itself will switch to the action mode. At this time, the digital meter will automatically switch to a suitable gear to start measuring the consumption current, so that the measurement of large current and small current can be taken into account. Users do not need to manually switch frequently. Because the standby current is relatively small, the automatic shifting function of the general digital meter will start to measure from a minimum gear. The current sampling resistance of this minimum gear is relatively large (100Ω). Please refer to Figure 2. The equivalent resistance is represented by R1, and the sampling resistance inside the digital meter is represented by R2. Here, take R1=1KΩ and R2=100Ω as an example to calculate, the original standby current of the electronic device to be tested is: 1V/1KΩ=1mA (millisecond) Ampere), when the digital meter measures the electronic equipment to be tested, the measured current is: 1V/(1KΩ+100Ω)=0.909mA, therefore, the size of the measurement error is: (1mA-0.909mA) /1mA×100%=9.1%. That is to say, when using this minimum gear to measure the standby current, there will be a 9.1% error between the measured data and the actual value. For the measurement results that require high accuracy, this error value may not meet the measurement requirements. .

Utility model content

The utility model provides a digital electric meter which can reduce the current measurement error, which can be used by the user to set the minimum measurement gear position according to the requirements, so as to avoid the large measurement error caused by the excessive sampling resistance.

The utility model can reduce the current measurement error of the digital electric meter, which includes:

a sampling circuit, connected to the electronic device through a current sampling terminal, and sampling the current of the electronic device to generate a sampling signal, the sampling circuit comprising a plurality of sampling resistors with different resistance values;

a buffer circuit, the input terminal of which is connected to the current sampling terminal;

an amplifying circuit, the input end of which is connected to the output end of the buffer circuit, and is provided with a plurality of different magnification ratios to amplify the sampling signal;

an analog-to-digital conversion circuit, the input end of which is connected to the amplifying circuit, and converts the amplified sampling signal into a digital signal;

A microprocessor is connected to the sampling circuit, the amplifying circuit and the analog-to-digital conversion circuit. When the microprocessor executes a specified automatic shift measurement mode, the microprocessor starts according to a preset minimum measurement gear Carry out current sampling, and during the current sampling process, the microprocessor automatically switches and selects a sampling resistor to connect to the current sampling terminal according to the size of the digital signal, and the resistance value of the selected sampling resistor is not lower than the corresponding minimum measurement gear. The resistance value of the sampling resistor.

In one embodiment, the plurality of sampling resistors include a first sampling resistor, a second sampling resistor and a third sampling resistor;

The sampling circuit includes:

A first switch has a first input end, a first output end and a second output end, the first input end is connected to the current sampling end, the first output end is connected to the first sampling resistor, wherein the The first input terminal can be switched to be connected to the first output terminal or the second output terminal;

A second switch has a second input terminal, a third output terminal and a fourth output terminal, the second input terminal is connected to the second output terminal of the first switch; the third output terminal is connected to the second sampling terminal a resistor, the fourth output terminal is connected to the third sampling resistor; the second input terminal can be switched to be connected to the third output terminal or the fourth output terminal;

Wherein, the resistance value of the first sampling resistor is smaller than the resistance value of the second sampling resistor, and the resistance value of the second sampling resistor is smaller than the resistance value of the third sampling resistor.

In one embodiment, the resistance value of the first sampling resistor is 0.1Ω, the resistance value of the second sampling resistor R2 is 1Ω, and the resistance value of the third sampling resistor R3 is 100Ω.

In one embodiment, the buffer circuit includes an operational amplifier.

In one of the embodiments, the sampling resistance corresponding to the minimum measurement gear is the second sampling resistance.

In one of the embodiments, the amplification circuit provides 1X, 10X and 100X magnification.

In one of the embodiments, when the third sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a magnification of 100 times, the digital electric meter operates at a measurement gear of 100 microamps;

When the third sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a 10-fold magnification, the digital electric meter operates at a measurement gear of 1 mA;

When the second sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a magnification of 100 times, the digital electric meter operates at a measurement gear of 10 mA;

When the second sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a 10-fold magnification, the digital electric meter operates at a measurement gear of 100 mA;

When the first sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a 10-fold magnification, the digital electric meter operates at a measurement gear of 1 ampere;

When the first sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a magnification of 1 times, the digital electric meter operates at a measurement gear of 3 amperes.

In one embodiment, the microprocessor reads the digital signal and converts it into a current value, and compares the current value with an upper switching value and a lower switching value to automatically switch the measurement gear.

In one embodiment, the microprocessor is connected to an operation interface and a display interface.

The digital electric meter of the present invention provides a designated automatic shift measurement mode, and the user sets a minimum measurement gear by himself. The sampling resistance corresponding to the minimum measurement gear is relatively small. When the current measurement is selected, it can maintain the minimum measurement range specified by the user without switching to a larger sampling resistance, which can reduce the error generated when measuring the current and ensure that the digital meter has better measurement accuracy.

Description of drawings

Fig. 1: The circuit block diagram of the utility model digital electric meter.

Figure 2: Equivalent circuit diagram of an existing digital electric meter measuring standby current with a large sampling resistance.

reference number

100 digital meters

10 Sampling circuit

20 Snubber circuit

30 Amplifier circuit

40 analog-to-digital converters

50 Microprocessors

60 Operation interface

70 Display interface

200 Electronics

K1B first switch

K2B second switch

R1 first sampling resistor

R2 second sampling resistor

R3 third sampling resistor

A Current sampling terminal

Detailed ways

The technical means adopted by the present invention to achieve the intended purpose of the utility model are further described below in conjunction with the drawings and the preferred embodiments of the present invention.

Please refer to FIG. 1 , the present invention is a digital electric meter 100 capable of reducing current measurement error, which is connected to an electronic device 200 via a current sampling terminal A to measure relevant electrical parameters of the electronic device 200 . The digital electric meter 100 of the present invention includes a sampling circuit 10 , a buffer circuit 20 , an amplifying circuit 30 , an analog-to-digital converter (ADC) 40 , and a microprocessor 50 .

The sampling circuit 10 is used for sampling the electronic device 200 to generate a sampling signal S. The sampling circuit 10 includes a first switch K1B, a second switch K2B, a first sampling resistor R1, a second sampling resistor R2 and A third sampling resistor R3.

The first switch K1B has a first input end (Pin 4), a first output end (Pin 5), and a second output end (Pin 3), the first input end is connected to the current sampling end A, the first An output terminal is connected to the first sampling resistor R1, wherein, at the internal contact of the first switch K1B, the internal contact of the first input terminal is selectively switched and connected to the first output terminal according to the control of the microprocessor 50 or the internal contact of the second output.

The second switch K2B has a second input terminal (Pin 4), a third output terminal (Pin 5), and a fourth output terminal (Pin 3), and the second input terminal is connected to the second input terminal of the first switch K1B Output terminal; the third output terminal is connected to the second sampling resistor R2, the fourth output terminal is connected to the third sampling resistor R3, wherein, inside the second switch K2B, the internal contact of the second input terminal is based on the microprocessor Under the control of the controller 50, the internal contacts connected to the third output terminal or the fourth output terminal are selectively switched.

In this embodiment, the resistance value of the first sampling resistor R1 is 0.1Ω, providing a measurement range of 1A or 3A. The resistance value of the second sampling resistor R2 is 1Ω, providing a measurement range of 10mA or 100mA. The resistance value of the third sampling resistor R3 is 100Ω, providing a measurement range of 100μA or 1mA. How to switch and select the six measurement gears represented by the first sampling resistor R1 to the third sampling resistor R3 will be described in further detail below.

An input end of the buffer circuit 20 is connected to the current sampling end A, and an output end of the buffer circuit 20 is connected to the amplifying circuit 30 , wherein the buffer circuit 20 is mainly composed of an operational amplifier (OP), such as an IC type. It is the operational amplifier integrated circuit of OPA2188AID.

An input end of the amplifying circuit 30 is connected to the output end of the buffer circuit 20. In this embodiment, the amplifying circuit 30 provides three magnification ratios, which can be switched to provide 1 times (×1) and 10 times (×10) respectively. And the magnification of 100 times (×100), the magnification of the amplifying circuit 30 is controlled and selected by the microprocessor 50 . The sampling signal S is transmitted to the amplifying circuit 30 through the buffer circuit 20 , and the sampling signal S is amplified by the amplifying circuit 20 .

An input end of the analog-to-digital conversion circuit 40 is connected to the amplifying circuit 30 to receive the amplified sampling signal S and convert it into a digital signal.

The microprocessor 50 is connected to the analog-to-digital conversion circuit 40 to read the digital signal generated by the conversion, and according to the magnitude of the digital signal, control whether to switch the connection of the first sampling resistor R1 to the third sampling resistor R3 and The magnification of the amplifying circuit 30 is adjusted.

The microprocessor 50 can be connected to an operation interface 60 for the user to perform setting operations on the digital electric meter 100 , such as manually switching the measurement range, setting the minimum measurement range, selecting the measurement mode, and the like.

The microprocessor 50 can be further connected to a display interface 70 , and the display interface can display the measurement data, setting screen or related information of the digital electric meter 100 .

First, it is explained that the first sampling resistor R1, the second sampling resistor R2, and the third sampling resistor R3 can be combined with the magnification provided by the amplifying circuit 30 to form six different measurement gears, and each measurement gear corresponds to a The measurable current value is shown in the following table:

Measuring gear (Ampere) Sampling resistor Magnification 100μA The third sampling resistor R3 ×100 1mA The third sampling resistor R3 ×10 10mA The second sampling resistor R2 ×100 100mA The second sampling resistor R2 ×10 1A The first sampling resistor R1 ×10 3A The first sampling resistor R1 ×1

Taking the selection of the measurement gear 100 μA as an example: the microprocessor 50 controls the first input terminal (Pin4) of the first switch K1B to switch to the second output terminal (Pin 3), and the first input terminal of the second switch K2B (Pin 4) is switched and connected to the second output terminal (Pin 3), and is selected to the third sampling resistor R3 of 100Ω through the connection of the first switch K1B and the second switch K2B; the microprocessor 50 controls the amplification Circuit 30 provides a magnification of 100 times. Through the microprocessor 50 to complete the aforementioned control, the digital electric meter 100 can operate in the measurement range of 100 μA.

Taking the selection of the measurement gear 10mA as an example: the microprocessor 50 controls the first input terminal (Pin4) of the first switch K1B to switch and connect to the second output terminal (Pin 3), and the first input terminal of the second switch K2B (Pin 4) is switched and connected to the first output terminal (Pin 5), and is selected to the second sampling resistor R2 of 1Ω through the connection of the first switch K1B and the second switch K2B; the microprocessor 50 controls the amplification Circuit 30 provides a magnification of 100 times. Through the microprocessor 50 to complete the aforementioned control, the digital electric meter 100 can operate in the measurement range of 10 mA.

Taking the selection of measurement gear 1A as an example: the microprocessor 50 controls the first input terminal (Pin4) of the first switch K1B to switch to the first output terminal (Pin5), and the second switch K2B can maintain the previous state Without switching, the first sampling resistor R1 of 0.1Ω is selected through the connection of the first switch K1B; the microprocessor 50 controls the amplifying circuit 30 to provide a magnification of 10 times. Through the microprocessor 50 to complete the aforementioned control, the digital electric meter 100 can operate in the measurement gear of 1A. The other three measurement gear switching methods only change different magnifications, so they will not be described in detail.

The digital electric meter 100 of the present invention provides a “specified automatic shift measurement mode” for the user to select and operate. In the specified automatic shift measurement mode, the user specifies a minimum measurement gear through the operation interface 60 and sets the The minimum measurement gear is stored in the microprocessor 50. For example, the digital meter 100 can provide five measurement gears of 100μA, 1mA, 10mA, 100mA, and 1A for the user to choose and designate as the minimum measurement gear. The internal resistance corresponding to the 100μA measurement gear is the maximum, but if the internal resistance of the electronic device 200 is much larger than 100Ω or the measurement error can be tolerated, the user can still specify 100μA as the minimum measurement gear.

When the digital meter 100 operates in the designated automatic shift measurement mode, the microprocessor 50 automatically switches to the minimum measurement gear preset by the user. In the following embodiments, 10 mA is used as the minimum measurement gear for illustration. Even if the second sampling resistor R2=1Ω, the magnification is 100 times; at this time, the sampling current flowing through the sampling resistor R2 will be converted into a voltage, that is, the sampling signal S is a voltage signal, and the voltage signal is amplified by the The circuit 30 amplifies, and the amplified voltage signal is converted into a digital signal by the analog-to-digital circuit 40. After reading the digital signal, the microprocessor 50 converts it into a measured current value. The value TH1 is compared with the next switching value TH2 to determine whether to switch the measurement gear.

According to a preferred embodiment of the present invention, the setting standard of the upper switching value TH1 is obtained by multiplying the measurable current value of the measuring gear by a first ratio, for example, the first ratio is set to 120%. The standard for making the lower switching value TH2 is obtained by multiplying the measurable current value of the measuring gear by a second ratio, for example, the second ratio is set to 10%.

For example, if the current measurement gear is 10mA, the upper switching value TH1 and the lower switching value TH2 are:

TH1=10mA×120%=12mA

TH2=10mA×10%=1mA

If the microprocessor 50 judges that the current measurement current value is greater than 12mA, it will automatically upgrade from the current measurement gear 10mA to the previous measurement gear 100mA; The gear 10mA will automatically downshift to the next measurement gear 1mA; if the current measurement current value is determined to be between 1mA and 12mA, the current measurement gear will be maintained. Repeatedly judging the magnitude of the measured current value, and automatically upshifting or downshifting to a suitable measurement gear.

However, it should be noted that in the “specified automatic shift measurement mode” of the present invention, because the user has preset the minimum measurement gear as 10mA, even if the measurement current value is less than 1mA, the microprocessor 50 will still It will be maintained at the minimum measurement gear of 10mA, and will not be automatically downshifted; and the automatic upshift will not be limited. When the measurement current value is greater than the upper switching value TH1, the measurement gear will be automatically upshifted by one step.

When the minimum measurement gear of the digital electricity meter 100 of the present invention is set to 100 μA, the digital electricity meter 100 of the present invention is equivalent to executing the “general automatic shift measurement mode” of a general digital electricity meter, that is, gradually increasing from the minimum measurement gear files.

To sum up, the digital electric meter of the present invention provides a designated automatic shift measurement mode, which can be used by the user to specify a minimum measurement gear. Measurement gear, because the sampling resistance value corresponding to the minimum measurement gear is relatively small, so it can reduce the error generated when measuring the current and ensure that the digital meter has better measurement accuracy.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those skilled in the art, without departing from the scope of the technical solution of the present invention, can make some changes or modifications to equivalent examples of equivalent changes by using the technical content disclosed above, provided that the technical solutions of the present invention are not deviated from the technical solution of the present invention. content, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solutions of the present invention.

Claims (9)

1. A digital electric meter capable of reducing current measurement error for measuring an electronic device, wherein the digital electric meter capable of reducing current measurement error comprises: a sampling circuit, connected to the electronic device through a current sampling terminal, and sampling the current of the electronic device to generate a sampling signal, the sampling circuit comprising a plurality of sampling resistors with different resistance values; a buffer circuit, the input terminal of which is connected to the current sampling terminal; an amplifying circuit, the input end of which is connected to the output end of the buffer circuit, and is provided with a plurality of different magnification ratios to amplify the sampling signal; an analog-to-digital conversion circuit, the input end of which is connected to the amplifying circuit, and converts the amplified sampling signal into a digital signal; A microprocessor is connected to the sampling circuit, the amplifying circuit and the analog-to-digital conversion circuit. When the microprocessor executes a specified automatic shift measurement mode, the microprocessor starts according to a preset minimum measurement gear Carry out current sampling, and during the current sampling process, the microprocessor automatically switches and selects a sampling resistor to connect to the current sampling terminal according to the size of the digital signal, and the resistance value of the selected sampling resistor is not lower than the corresponding minimum measurement gear. The resistance value of the sampling resistor. 2. The digital electric meter capable of reducing current measurement error as claimed in claim 1, wherein the plurality of sampling resistors comprise a first sampling resistor, a second sampling resistor and a third sampling resistor; The sampling circuit includes: A first switch has a first input end, a first output end and a second output end, the first input end is connected to the current sampling end, the first output end is connected to the first sampling resistor, wherein the The first input terminal can be switched to be connected to the first output terminal or the second output terminal; A second switch has a second input terminal, a third output terminal and a fourth output terminal, the second input terminal is connected to the second output terminal of the first switch; the third output terminal is connected to the second sampling terminal a resistor, the fourth output terminal is connected to the third sampling resistor; the second input terminal can be switched to be connected to the third output terminal or the fourth output terminal; Wherein, the resistance value of the first sampling resistor is smaller than the resistance value of the second sampling resistor, and the resistance value of the second sampling resistor is smaller than the resistance value of the third sampling resistor. 3. The digital electric meter capable of reducing current measurement error as claimed in claim 2, wherein the resistance value of the first sampling resistor is 0.1Ω, the resistance value of the second sampling resistor R2 is 1Ω, and the third sampling resistor has a resistance value of 1Ω. The resistance value of the resistor R3 is 100Ω. 4. The digital electric meter capable of reducing current measurement error as claimed in claim 3, wherein the buffer circuit comprises an operational amplifier. 5 . The digital electric meter capable of reducing current measurement error as claimed in claim 4 , wherein the sampling resistance corresponding to the minimum measurement gear is the second sampling resistance. 6 . 6 . The digital electric meter capable of reducing current measurement errors as claimed in claim 5 , wherein the amplifying circuit provides 1 times, 10 times and 100 times of magnification. 7 . 7. The digital electric meter capable of reducing current measurement error as claimed in claim 6, wherein: When the third sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a magnification of 100 times, the digital electric meter operates at a measurement gear of 100 microamps; When the third sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a 10-fold magnification, the digital electric meter operates at a measurement gear of 1 mA; When the second sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a magnification of 100 times, the digital electric meter operates at a measurement gear of 10 mA; When the second sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a 10-fold magnification, the digital electric meter operates at a measurement gear of 100 mA; When the first sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a 10-fold magnification, the digital electric meter operates at a measurement gear of 1 ampere; When the first sampling resistor is switched and connected to the current sampling terminal, and the amplifying circuit provides a magnification of 1 times, the digital electric meter operates at a measurement gear of 3 amperes. 8. The digital electric meter capable of reducing current measurement error as claimed in claim 7, wherein the microprocessor reads the digital signal and converts it into a current value, and associates the current value with an up-switching value Compare with the following switching value to automatically switch the measurement gear. 9 . The digital electric meter capable of reducing current measurement error as claimed in claim 8 , wherein the microprocessor is connected with an operation interface and a display interface. 10 .

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