A measuring circuit and automatic measuring method

Abstract

This invention relates to vehicle-mounted weighing systems in the sanitation field, and more particularly to a measurement circuit and an automatic measurement method. The measurement circuit includes a pre-input circuit, an operational amplifier circuit, a range switching circuit, an A / D conversion circuit, and an MCU unit connected along the current direction. The pre-input circuit includes a switchable input branch for the measured object (S1), a ground input branch (S3), and a reference voltage input branch (S2). When the reference voltage input branch (S2) is connected, the circuit change coefficient λ is obtained by using the MCU unit reading Vrn before the circuit parameter change and the MCU unit reading Vrn´ after the circuit parameter change. When the measured object input branch (S1) is connected, the corrected measurement result Vn is obtained based on the MCU unit reading Vn before the circuit parameter change, using the circuit change coefficient λ.

Description

Technical Field

[0001] This invention relates to vehicle-mounted weighing systems in the field of sanitation, and more particularly to a highly stable and high-precision measurement circuit and automatic measurement method. Background Technology

[0002] In recent years, with the advancement and development of urban-rural integration, and the popularization and promotion of Internet of Things (IoT) technology, smart city construction has gradually been put on the agenda. Smart sanitation, as an important component of smart city construction, is receiving increasing attention. However, smart sanitation requires a clear smart sanitation management indicator system to guide and evaluate the construction of smart sanitation systems in various regions. This includes designing waste collection, transportation, and disposal models based on population, area, and natural conditions. Smart sanitation, relying on IoT and mobile internet technologies, enables real-time management of all personnel, vehicles, materials, and processes involved in sanitation management. It rationally designs and plans sanitation management models, improves the quality of sanitation operations, reduces sanitation operating costs, and uses digital evaluation to promote the effectiveness of waste sorting management.

[0003] Meanwhile, garbage truck collection weighing and monitoring systems are ubiquitous. However, due to objective external conditions, the existing weighing systems currently have the following defects or deficiencies.

[0004] Due to the inherent properties of semiconductor components, as temperature changes and time increases, the measurement circuit will inevitably experience operational amplifier zero-point drift and range drift, making the stability of the measurement data unreliable.

[0005] During the entire weighing system collection process, the collected material can be as light as 1-2 kg or as heavy as 300-400 kg or more. If only one range and one calibration coefficient are used, the changes in the various weighing points of the sensor will be disproportionate due to the influence of the weighing mechanism, and the accuracy of the results will inevitably be greatly reduced. Summary of the Invention

[0006] To address the aforementioned problems, the primary objective of this invention is to provide a highly stable and accurate measurement circuit that completely suppresses uncontrollable circuit parameters affected by temperature and time, namely zero-point drift and range drift, thereby ensuring the long-term stability and accuracy of the circuit's measurement parameters.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A highly stable and high-precision measurement circuit includes a preamplifier circuit, an operational amplifier circuit, a range switching circuit, an A / D conversion circuit, and an MCU unit connected along the current direction. The preamplifier circuit includes a switchable input branch for the measured object (S1), a ground input branch (S3), and a reference voltage input branch (S2). When the reference voltage input branch (S2) is connected, the circuit change coefficient λ is obtained by using the MCU unit reading Vrn before the circuit parameter change and the MCU unit reading Vrn´ after the circuit parameter change. When the measured object input branch (S1) is connected, the corrected measurement result Vn is obtained based on the MCU unit reading Vn before the circuit parameter change, using the circuit change coefficient λ.

[0009] The present invention adopts the above-mentioned technical solution, which relates to a high-stability and high-precision measurement circuit. The high-stability and high-precision measurement circuit consists of three parts: a front-end circuit, an intermediate circuit, and a rear-end circuit. The front-end circuit consists of a measurement object input branch S1, a ground input branch S3, and a reference voltage input branch S2. The intermediate circuit consists of an operational amplifier, a range switching circuit, and an A / D conversion circuit. The rear-end circuit mainly consists of a data processing MCU circuit.

[0010] In this scheme, when the ground input branch S3 is connected, Vin=Vgnd=0V, and the MCU reading can reveal the initial zero-point value Vn1=K1V01+V0, including zero-point drift and range drift. Then, by connecting the reference voltage input branch S2, the circuit change coefficient λ is obtained from the MCU unit reading Vrn before the circuit parameter change and the MCU unit reading Vrn´ after the circuit parameter change. This corrects the measurement result Vn, thus completely suppressing the uncontrollable circuit parameters affected by temperature and time, i.e., zero-point drift and range drift, ensuring the long-term stability and accuracy of the circuit's measurement parameters.

[0011] Preferably, the reference voltage input branch S2 uses two resistors in the same row to equalize the voltage, so that it will not change with time and temperature.

[0012] Preferably, the measurement object input branch S1 and the reference voltage input branch S2 are connected via a second relay (RLY2), and the ground input branch S3 is connected via a first relay (RLY1). Using a low-power relay as the selection switch, instead of a semiconductor analog switch, reduces cost and minimizes the impact of temperature and time, ensuring the stability of the hardware circuit parameters.

[0013] In a further preferred embodiment, the range switching circuit includes an amplifier, a resistor R1 connected upstream of the negative input terminal of the amplifier, and a first range branch, a second range branch, and a third range branch capable of switching between the amplifier. Each of the first, second, and third range branches includes a first resistor RX connected to the positive input terminal of the amplifier, and a second resistor Ry connected in parallel with the amplifier. One end of the second resistor Ry is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the first resistor RX is grounded, RX = R1 / / Ry, and the range coefficient of this range branch is KN = Ry / R1.

[0014] In this scheme, considering that the weight collected during the weighing system recovery process may vary greatly, multiple range branches are set up. Based on the fact that multiple range branches are adapted to different weighing ranges, a more accurate and suitable calibration coefficient is used in the range, so as to make the weighing data more accurate.

[0015] Preferably, the third range branch and the second range branch are connected by a third relay (RLY3) and a fourth relay (RLY4), and the first range branch is connected by a fourth relay (RLY4). Similarly, using a low-power relay as the selection switch instead of a semiconductor analog switch is less costly and less affected by temperature and time, ensuring the stability of the hardware circuit parameters.

[0016] Furthermore, the third relay (RLY3) and the fourth relay (RLY4) in this scheme are double-pole double-throw relays, which can simultaneously switch the connection of the first resistor RX and the second resistor Ry on the first range branch, the second range branch and the third range branch.

[0017] In the specific implementation plan, this plan adopts three ranges, specifically:

[0018] The first range branch includes a resistor R2 that can be connected to the positive input terminal of the amplifier, and a resistor R3 connected in parallel with the amplifier. One end of the resistor R3 is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the resistor R2 is grounded, R2=R1 / / R3, and the range coefficient of the first range branch is K1=R3 / R1.

[0019] Preferably, the second range branch includes a resistor R22 that can be connected to the positive input terminal of the amplifier, and a resistor R4 connected in parallel with the amplifier. One end of the resistor R4 is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the resistor R22 is grounded, R22=R1 / / R4, and the range coefficient of the second range branch is K2=R4 / R1.

[0020] Preferably, the third range branch includes a resistor R222 that can be connected to the positive input terminal of the amplifier, and a resistor R5 connected in parallel with the amplifier. One end of the resistor R5 is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the resistor R222 is grounded, R222=R1 / / R5, and the range coefficient of the third range branch is K3=R5 / R1.

[0021] The symbol " / / " above represents parallel connection.

[0022] The second objective of this invention is to provide a highly stable and accurate automatic measurement method, characterized by employing the measurement circuit described above and executing the following algorithm:

[0023] Step 1: Power on the device, connect the MCU control ground input branch S3, and disconnect the reference voltage input branch S2 and the measurement object input branch S1; assuming that the operational amplifier is selected with range K1, the operational amplifier zero drift is V01, and the high-precision A / D converter zero drift is V0, then the input signal Vin=Vgnd=0V, and the final result read by the MCU is: Vn1=K1(V01+0)+V0①;

[0024] Step 2: The MCU controls the reference voltage input branch S2 to be turned on, and the ground input branch S3 and the measurement object input branch S1 to be turned off. At this time, the input signal Vin=Vref, and the final signal result read by the MCU is: K1(V01+Vref)+V0;

[0025] Step 3: Calculate the initial value of the reference voltage Vrn = K1(V01+Vref)+V0 - Vn1 = K1Vref;

[0026] Step 4: Set the initial value λ=1.

[0027] Step 5: The MCU controls the input branch S1 of the measured object to be turned on, the ground input branch S3 to be turned on and the reference voltage input branch S2 to be turned off. The signal result read by the MCU is Vn2=K1 (V01+Vsig)+V0.

[0028] Calculate the actual sensor signal value Vn = Vn2 - Vn1 = K1Vsig;

[0029] After correction and calculation, Vn = Vn´ / λ, where in the first measurement, Vn´ = Vn and λ = 1;

[0030] Step 6: Within a certain time period, update the zero-point value and reference voltage value, and recalculate the λ value. Repeat step 5.

[0031] The technical solution involves a highly stable and accurate automatic measurement method that periodically corrects the circuit variation coefficient λ, thereby automatically measuring the result Vn.

[0032] In a further embodiment, the automatic measurement method employs multiple measurement ranges, with data calibration within each range. It collects at least five data points and uses the least squares method for linear fitting. Specifically, variable x represents the actual measured weight, and variable y represents the standard reference weight. These variables satisfy a linear relationship within a certain range, i.e., y = ax + b. By measuring N sets of values ​​(xi, yi), in this example, values ​​of 10 or higher are used. Based on the least squares method, the total sum of squared errors is...

[0033]

[0034] Different values ​​of a and b will lead to different index values. We need to find a set of values ​​of a and b that minimizes the above index. According to the knowledge of multivariable calculus, we take the partial derivatives with respect to a and b respectively, and the partial derivatives are 0.

[0035]

[0036] Simplifying the above equation, we can obtain

[0037]

[0038] final

[0039] Formula (1)

[0040] in, and Let y and x be the average values ​​of the measured values, respectively; from this, the expression for the linear function can be obtained.

[0041] Based on the above expression, calculate and save a and b according to the range. When the weighing system is actually working, measure the weight x, and calculate the actual weight y according to the formula y=ax+b. y is very close to the value of the standard object in this range, thus greatly improving the accuracy of the system. Attached Figure Description

[0042] Figure 1 This is a block diagram of a high-stability and high-precision measurement circuit.

[0043] Figure 2 This is a schematic diagram of a high-stability and high-precision measurement circuit.

[0044] Figure 3 The flowchart shows the software for suppressing circuit zero-point and range drift.

[0045] Figure 4This is a flowchart of the calculation of the least squares method for linear fitting coefficients.

[0046] Figure 5 This is a flowchart of the actual weighing calculation software. Detailed Implementation

[0047] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0048] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0049] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more, unless explicitly defined otherwise.

[0050] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0051] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature. Example

[0052] like Figure 1 and 2 As shown, this embodiment relates to a highly stable and high-precision measurement circuit, including a pre-input circuit, an operational amplifier circuit, a range switching circuit, an A / D conversion circuit, and an MCU unit connected along the current direction. The pre-input circuit includes a switchable input branch for the measured object (S1), a ground input branch (S3), and a reference voltage input branch (S2). When the reference voltage input branch (S2) is connected, the circuit change coefficient λ is obtained by using the MCU unit reading Vrn before the circuit parameter change and the MCU unit reading Vrn´ after the circuit parameter change. When the measured object input branch (S1) is connected, the corrected measurement result Vn is obtained based on the MCU unit reading Vn before the circuit parameter change, using the circuit change coefficient λ.

[0053] This technical solution relates to a high-stability and high-precision measurement circuit, which consists of three parts: a front-end circuit, an intermediate circuit, and a back-end circuit. The front-end circuit consists of a measurement object input branch S1, a ground input branch S3, and a reference voltage input branch S2. The intermediate circuit consists of an operational amplifier, a range switching circuit, and an A / D conversion circuit. The back-end circuit mainly consists of a data processing MCU circuit.

[0054] In this scheme, when the ground input branch S3 is connected, Vin=Vgnd=0V, and the MCU reading can reveal the initial zero-point value Vn1=K1V01+V0, including zero-point drift and range drift. Then, by connecting the reference voltage input branch S2, the circuit change coefficient λ is obtained from the MCU unit reading Vrn before the circuit parameter change and the MCU unit reading Vrn´ after the circuit parameter change. This corrects the measurement result Vn, thus completely suppressing the uncontrollable circuit parameters affected by temperature and time, i.e., zero-point drift and range drift, ensuring the long-term stability and accuracy of the circuit's measurement parameters.

[0055] The reference voltage input branch S2 uses two resistors in the same row to equalize the voltage, so it will not change with time and temperature.

[0056] The measurement object input branch S1 and the reference voltage input branch S2 are connected via a second relay (RLY2), and the ground input branch S3 is connected via a first relay (RLY1). Using a low-power relay as the selection switch, instead of a semiconductor analog switch, reduces cost and minimizes susceptibility to temperature and time effects, ensuring the stability of the hardware circuit parameters.

[0057] In a further preferred embodiment, the range switching circuit includes an amplifier, a resistor R1 connected upstream of the negative input terminal of the amplifier, and a first range branch, a second range branch, and a third range branch capable of switching connections to the amplifier. Each of the first, second, and third range branches includes a first resistor RX (X=2, 22, 222 in the figure) connected to the positive input terminal of the amplifier, and a second resistor Ry (X=3, 4, 5 in the figure) connected in parallel with the amplifier. One end of the second resistor Ry is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the first resistor RX is grounded, RX=R1 / / Ry, and the range factor of this range branch is KN=Ry / R1. In this scheme, considering that the weight collected during the weighing system recovery process may vary greatly, multiple range branches are set up. Based on the fact that multiple range branches are adapted to different weighing ranges, a more accurate and suitable calibration coefficient is used in the range, so as to make the weighing data more accurate.

[0058] As shown in the figure, the third and second range branches are connected via a third relay (RLY3) and a fourth relay (RLY4), while the first range branch is connected via a fourth relay (RLY4). Similarly, using a low-power relay as the selection switch instead of a semiconductor analog switch reduces cost and minimizes the impact of temperature and time, ensuring the stability of the hardware circuit parameters. Furthermore, the third relay (RLY3) and fourth relay (RLY4) in this design are double-pole double-throw relays, which can simultaneously switch the connection of the first resistor RX and the second resistor Ry on the first, second, and third range branches.

[0059] In the specific implementation plan, this plan adopts three ranges, specifically:

[0060] The first range branch includes a resistor R2 that can be connected to the positive input terminal of the amplifier, and a resistor R3 connected in parallel with the amplifier. One end of resistor R3 is connected between resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of resistor R2 is grounded, R2=R1 / / R3, and the range coefficient of this first range branch is K1=R3 / R1.

[0061] The second range branch includes a resistor R22 that can be connected to the positive input terminal of the amplifier, and a resistor R4 connected in parallel with the amplifier. One end of resistor R4 is connected between resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of resistor R22 is grounded, R22=R1 / / R4, and the range coefficient of this second range branch is K2=R4 / R1.

[0062] The third range branch includes a resistor R222 that can be connected to the positive input terminal of the amplifier, and a resistor R5 connected in parallel with the amplifier. One end of resistor R5 is connected between resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of resistor R222 is grounded, R222 = R1 / / R5, and the range factor of this third range branch is K3 = R5 / R1.

[0063] Explanation of the hardware implementation principles for the zero-point drift suppression and range drift suppression functions of the above circuit:

[0064] ●Before circuit parameter transformation

[0065] (1) First, the MCU control reference ground selection switch S3 is turned on, and switches S1 and S2 are turned off. That is, in the schematic diagram, the normally closed contact of relay RLY1 is closed. As shown in the schematic diagram, assuming that the range selected by the op-amp is K1, the zero drift of the op-amp is V01, and the zero drift of the high-precision A / D converter is V0.

[0066] At this time, the input signal Vin=Vgnd=0V, and the final result read by the MCU is: Vn1=K1V01+V0 ①.

[0067] (2) Then, the MCU controls the measurement object selection switch S1 to turn on, and switches S2 and S3 to turn off. That is, in the schematic diagram, the normally open contact of relay RLY1 is closed, and the normally closed contact of relay RLY2 is closed.

[0068] Then, the input signal Vin = Vsig, and the final signal result read by the MCU is: Vn2 = K1 (V01 + Vsig) + V0②.

[0069] (3) Finally, the difference between the two signal results read by the MCU is the actual signal value:

[0070] Vn = Vn2 - Vn1 = K1Vsig ③.

[0071] Similarly, when the op-amp is selected with ranges K2 and K3, then Vn = K2Vsig and Vn = K3Vsig.

[0072] ●After circuit parameters change

[0073] (1) Assuming that the operational amplifier zero drift is V01', the high-precision A / D converter zero drift is V0', and the amplification factor drift is K1' as time and temperature change, then the changes in ①, ②, and ③ above are as follows:

[0074] ① becomes: Vn1´=K1´V01´+V0´ ④

[0075] It becomes: Vn2´==K1´(V01´+Vsig)+V0´ ⑤

[0076] It becomes: Vn´= Vn2´ -Vn1´ =K1´Vsig ⑥

[0077] Similarly, when the op-amp is selected with ranges K2´ and K3´, then Vn = K2´Vsig and Vn = K3´Vsig.

[0078] Assuming the circuit amplification factor K1 remains constant (K1=K1´), in practice, since relays are used for range switching, K1 is also basically unchanged in a short time. Therefore, ③ and ⑥ are equal, that is, the result is only the signal amplification (or reduction) factor, which is unrelated to the change of circuit parameters, thereby suppressing the influence caused by the change of circuit zero-point parameters.

[0079] (2) When the MCU controls the reference voltage input branch S2, the switches S1 and S3 are turned off. That is, in the schematic diagram, the normally open contact of relay RLY1 is closed and the normally open contact of relay RLY2 is closed.

[0080] At this point, the input signal Vin = Vref, and Vref uses special components and circuits, such as two resistors in the same group in the schematic to equalize the voltage, so it will not change with time and temperature. The final signal read by the MCU is:

[0081] Before the circuit parameters changed: Vrn = Vrn2 - Vrn1 = K1Vref ⑦.

[0082] Similarly, when the op-amp is selected with ranges K2 and K3, then Vn = K2Vref and Vn = K3Vref.

[0083] After the circuit parameters change: Vrn´= Vrn2´ -Vrn1´=K1´Vref ⑧.

[0084] Similarly, when the op-amp is selected with ranges K2´ and K3´, then Vn = K2´Vref and Vn = K3´Vref.

[0085] Comparing ⑦ and ⑧, we can conclude that:

[0086] Vrn / Vrn´= K1 / K1´ ⑨

[0087] Similarly, comparing ③ and ⑥, we get:

[0088] Vn / Vn´= K1 / K1´ ⑩

[0089] From ⑨ and ⑩, we get:

[0090] Vrn / Vrn´= Vn / Vn´ ⑪

[0091] Let Vrn´ / Vrn=λ, then Vn= Vn´ / λ ⑫.

[0092] It can be seen that, assuming that the circuit range parameter K1 changes over a long period of time, the measurement result Vn can be corrected by measuring the value of the reference voltage Vref and calculating the change coefficient λ, thereby suppressing the influence caused by the change of the circuit range parameter. Example

[0093] like Figure 3-5 As shown, this embodiment provides a highly stable and accurate automatic measurement method, characterized by employing the measurement circuit described above and executing the following algorithm:

[0094] Step 1: Power on the device. The MCU control ground input branch S3 is connected, while the reference voltage input branch S2 and the measured object input branch S1 are disconnected. Assuming the operational amplifier's selected range is K1, the operational amplifier's zero-point drift is V01, and the high-precision A / D converter's zero-point drift is V0, then the input signal Vin = Vgnd = 0V. The final result read by the MCU is: Vn1 = K1(V01 + 0) + V0①.

[0095] Step 2: The MCU controls the reference voltage input branch S2 to turn on, and the ground input branch S3 and the measurement object input branch S1 to turn off. At this time, the input signal Vin=Vref, and the final signal result read by the MCU is: K1(V01+Vref)+V0.

[0096] Step 3: Calculate the initial value of the reference voltage Vrn = K1(V01+Vref)+V0-Vn1 = K1Vref.

[0097] Step 4: Set the initial value λ=1.

[0098] Step 5: The MCU controls the input branch S1 of the measured object to be turned on, the ground input branch S3 to be turned on, and the reference voltage input branch S2 to be turned off. The signal result read by the MCU is Vn2=K1 (V01+Vsig)+V0.

[0099] Calculate the actual sensor signal value Vn = Vn2 - Vn1 = K1Vsig.

[0100] After correction and calculation, Vn = Vn´ / λ, where Vn´ = Vn and λ = 1 during the first measurement.

[0101] Step 6: Within a certain time period, update the zero-point value and reference voltage value, and recalculate the λ value. Repeat step 5.

[0102] The technical solution involves a highly stable and accurate automatic measurement method that periodically corrects the circuit variation coefficient λ, thereby automatically measuring the result Vn.

[0103] In a further embodiment, the automatic measurement method employs multiple measurement ranges, with data calibration within each range. It collects at least five data points and uses the least squares method for linear fitting. Specifically, the variable x represents the actual measured weight, and the variable y represents the standard reference weight. These variables satisfy a linear relationship within a certain range, i.e., y = ax + b. By measuring N sets of values ​​(xi, yi), in this example, values ​​of 10 or higher, and based on the least squares method, the total sum of squared errors is...

[0104]

[0105] Different values ​​of a and b will lead to different index values. We need to find a set of values ​​of a and b that minimizes the above index. According to the knowledge of multivariable calculus, we take the partial derivatives with respect to a and b respectively, and the partial derivatives are 0.

[0106]

[0107] Simplifying the above equation, we can obtain

[0108]

[0109] final

[0110] Formula (1)

[0111] in, and Let y and x be the average values ​​of the measured values, respectively. From this, we can obtain the expression for the linear function.

[0112] Based on the above expression, calculate and save a and b according to the range. When the weighing system is actually working, measure the weight x, and calculate the actual weight y according to the formula y=ax+b. y is very close to the value of the standard object in this range, thus greatly improving the accuracy of the system.

[0113] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0114] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A measurement circuit, comprising a preamplifier circuit, an operational amplifier circuit, a range switching circuit, an A / D conversion circuit, and an MCU unit connected along the current direction; characterized in that: The pre-input circuit includes a switchable measurement object input branch S1, a ground input branch S3, and a reference voltage input branch S2. When the ground input branch S3 is connected, Vin = Vgnd = 0V, and the MCU reading can be used to obtain the initial zero value Vn1 = K1V01 + V0, which includes zero drift and range drift. When the reference voltage input branch S2 is connected, the circuit change coefficient λ is obtained by using the MCU unit reading Vrn before the circuit parameter change and the MCU unit reading Vrn´ after the circuit parameter change. When the measurement object input branch S1 is connected, the corrected measurement result Vn is obtained based on the MCU unit reading Vn´ before the circuit parameter change, using the circuit change coefficient λ. The range switching circuit includes an amplifier, a resistor R1 connected upstream of the negative input terminal of the amplifier, and a first range branch, a second range branch, and a third range branch that can switch between the amplifier. Each of the first, second, and third range branches includes a first resistor RX connected to the positive input terminal of the amplifier and a second resistor Ry connected in parallel with the amplifier. One end of the second resistor Ry is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the first resistor RX is grounded, RX = R1 / / Ry, and the range coefficient of this range branch is KN = Ry / R1. The MCU unit is configured to: use multiple ranges, collect at least five data points in each range, and obtain and store the calibration coefficients a and b of that range through a linear fitting method. In actual measurement, the actual measured value y is calculated according to the formula y = ax + b; The first range branch includes a resistor R2 that can be connected to the positive input terminal of the amplifier, and a resistor R3 connected in parallel with the amplifier. One end of the resistor R3 is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the resistor R2 is grounded, R2=R1 / / R3, and the range coefficient of the first range branch is K1=R3 / R1. The second range branch includes a resistor R22 that can be connected to the positive input terminal of the amplifier, and a resistor R4 connected in parallel with the amplifier. One end of the resistor R4 is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the resistor R22 is grounded, R22=R1 / / R4, and the range coefficient of this second range branch is K2=R4 / R1. The third range branch includes a resistor R222 that can be connected to the positive input terminal of the amplifier, and a resistor R5 connected in parallel with the amplifier. One end of the resistor R5 is connected between the resistor R1 and the negative input terminal of the amplifier, and the other end is connected to the output terminal of the amplifier. The other end of the resistor R222 is grounded, R222=R1 / / R5, and the range coefficient of the third range branch is K3=R5 / R1.

2. The measurement circuit according to claim 1, characterized in that: The reference voltage input branch S2 uses two resistors in the same row to equalize the voltage.

3. The measurement circuit according to claim 1, characterized in that: The measurement object input branch S1 and the reference voltage input branch S2 are connected by a second relay (RLY2), and the grounding input branch S3 is connected by a first relay (RLY1).

4. A measurement circuit according to claim 3, characterized in that: The third range branch and the second range branch are connected by a third relay (RLY3) and a fourth relay (RLY4), and the first range branch is connected by a fourth relay (RLY4).

5. An automatic measurement method, characterized in that: The measurement circuit as described in any one of claims 1-4 is used, and the following algorithm is executed: Step 1: Power on the device, connect the MCU control ground input branch S3, and disconnect the reference voltage input branch S2 and the measurement object input branch S1; assuming that the operational amplifier is selected with range K1, the operational amplifier zero drift is V01, and the high-precision A / D converter zero drift is V0, then the input signal Vin=Vgnd=0V, and the final result read by the MCU is: Vn1=K1(V01+0)+V0 ①; Step 2: The MCU controls the reference voltage input branch S2 to turn on, and the ground input branch S3 and the measurement object input branch S1 to turn off. At this time, the input signal Vin = Vref, and the final signal result read by the MCU is: K1(V01 + Vref) + V0; Step 3: Calculate the initial value of the reference voltage Vrn = K1(V01+Vref)+V0 - Vn1 = K1Vref; Step 4: Set the initial value λ = 1; Step 5: The MCU controls the input branch S1 of the measured object to be turned on, the ground input branch S3 to be turned on and the reference voltage input branch S2 to be turned off. The signal result read by the MCU is Vn2=K1 (V01+Vsig)+V0. Calculate the actual sensor signal value Vn = Vn2 - Vn1 = K1Vsig; After correction and calculation, Vn = Vn´ / λ, where in the first measurement, Vn´ = Vn and λ = 1; Step 6: Within a certain time period, update the zero-point value and reference voltage value, and recalculate the λ value. Repeat step 5. The automatic measurement method employs multiple measurement ranges, with data calibration within each range. It collects at least five data points and uses the least squares method for linear fitting. Specifically, variable x represents the actual measured weight, and variable y represents the standard reference weight. These variables satisfy a linear relationship within a certain range, i.e., y = ax + b. By measuring N sets of values ​​(xi, yi), in this example, values ​​of 10 or higher are used. Based on the least squares method, the total sum of squared errors is... ; Different values ​​of a and b will lead to different index values. We need to find a set of values ​​of a and b that minimizes the above index. According to the knowledge of multivariable calculus, we take the partial derivatives with respect to a and b respectively, and the partial derivatives are 0. ; Simplifying the above equation, we can obtain ; final Official (1) in, and Let y and x be the average values ​​of the measured values, respectively; from this, the expression for the linear function can be obtained. Based on the above expression, calculate and save a and b according to the range. When the weighing system is actually working, measure the weight x, and calculate the actual weight y according to the formula y=ax+b. y is very close to the value of the standard object in this range, thus greatly improving the accuracy of the system.

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