Static weighing instrument

Abstract

The utility model relates to the technical field of weighing instruments, and provides a static weighing instrument, which comprises a weight detection circuit, and the weight detection circuit comprises an operational amplifier U1, an operational amplifier U2, a triode Q2, a triode Q3 and a pressure sensor U4. The in-phase input end of the operational amplifier U1 is connected with a Vref reference voltage, the output end of the operational amplifier U1 is connected with the base electrode of the triode Q2, the collector electrode of the triode Q2 is connected with a + 12V power supply, and the emitter electrode of the triode Q2 is connected with the first power supply end of the pressure sensor U4; the inverting input end of the operational amplifier U2 is connected with the in-phase input end of the operational amplifier U1, the output end of the operational amplifier U2 is connected with the base electrode of the triode Q3, the collector electrode of the triode Q3 is connected with the second power supply end of the pressure sensor U4, the emitter electrode of the triode Q3 is connected with the-12V power supply, and the output end of the pressure sensor U4 is connected with the main control unit. According to the technical scheme, the problem that the weight information collected by a static weighing instrument in the related technology is inaccurate is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of weighing instruments, and specifically to a static weighing instrument. Background Art

[0002] Static weighing instruments are widely used in our production and life. Their main function is to collect signals from weighing sensors, display weight, and provide us with weight information. However, weighing sensors are greatly affected by ambient temperature and power supply during operation. With different working environments, the power supply of weighing sensors may fluctuate, resulting in inaccurate weight information collected by existing static weighing instruments. Utility Model Content

[0003] The utility model provides a static weighing instrument, which solves the problem of inaccurate weight information collected by the static weighing instrument in the related art.

[0004] The technical solution of the utility model is as follows:

[0005] A static weighing instrument, comprising a weight detection circuit and a main control unit, wherein the weight detection circuit is connected to the main control unit, and the weight detection circuit comprises an operational amplifier U1, an operational amplifier U2, a resistor R6, a resistor R11, a transistor Q2, a resistor R10, a resistor R12, a transistor Q3 and a pressure sensor U4;

[0006] The first power supply terminal of the operational amplifier U1 is connected to a +12V power supply, the second power supply terminal of the operational amplifier U1 is connected to a -12V power supply, the non-inverting input terminal of the operational amplifier U1 is connected to a Vref reference voltage, the inverting input terminal of the operational amplifier U1 is grounded through the resistor R6, the output terminal of the operational amplifier U1 is connected to the base of the transistor Q2, the collector of the transistor Q2 is connected to a +12V power supply, the emitter of the transistor Q2 is connected to the inverting input terminal of the operational amplifier U1 through the resistor R11, and the emitter of the transistor Q2 is connected to the first power supply terminal of the pressure sensor U4;

[0007] The first power supply end of the operational amplifier U2 is connected to a +12V power supply, the second power supply end of the operational amplifier U2 is connected to a -12V power supply, the inverting input end of the operational amplifier U2 is connected to the non-inverting input end of the operational amplifier U1, the non-inverting input end of the operational amplifier U2 is grounded through the resistor R10, the output end of the operational amplifier U2 is connected to the base of the transistor Q3, the collector of the transistor Q3 is connected to the inverting input end of the operational amplifier U2 through the resistor R12, the collector of the transistor Q3 is connected to the second power supply end of the pressure sensor U4, the emitter of the transistor Q3 is connected to the -12V power supply, and the output end of the pressure sensor U4 is connected to the main control unit.

[0008] Furthermore, the weight detection circuit in the utility model also includes a variable resistor RP2 and a resistor R13, the first end of the variable resistor RP2 is connected to the first output end of the pressure sensor U4, the second end of the variable resistor RP2 is connected to the second output end of the pressure sensor U4, and the sliding end of the variable resistor RP2 is connected to the collector of the transistor Q3 through the resistor R13.

[0009] Furthermore, the utility model also includes a voltage stabilizing circuit, which includes a variable resistor RP1, an operational amplifier U3, a resistor R4, a capacitor C2, a resistor R3, a transistor Q1 and a resistor R2. The first end of the variable resistor RP1 is connected to a 5V power supply, the second end of the variable resistor RP1 is grounded, the sliding end of the variable resistor RP1 is connected to the non-inverting input end of the operational amplifier U3, the output end of the operational amplifier U3 is connected to the inverting input end of the operational amplifier U3 through the capacitor C2, the output end of the operational amplifier U3 is connected to the base of the transistor Q1, the collector of the transistor Q1 is connected to the 5V power supply through the resistor R4, the collector of the transistor Q1 is connected to the non-inverting input end of the operational amplifier U1, the emitter of the transistor Q1 is grounded through the resistor R2, and the emitter of the transistor Q1 is connected to the inverting input end of the operational amplifier U3 through the resistor R3.

[0010] Furthermore, the weight detection circuit in the utility model also includes an operational amplifier U5, an operational amplifier U6, a resistor R16, a resistor R17, a resistor R19 and an operational amplifier U7, the non-inverting input terminal of the operational amplifier U5 is connected to the first output terminal of the pressure sensor U4, the non-inverting input terminal of the operational amplifier U6 is connected to the second output terminal of the pressure sensor U4, the output terminal of the operational amplifier U5 is connected to the inverting input terminal of the operational amplifier U5, the output terminal of the operational amplifier U5 is connected to the non-inverting input terminal of the operational amplifier U7 through the resistor R16, the output terminal of the operational amplifier U6 is connected to the inverting input terminal of the operational amplifier U6, the output terminal of the operational amplifier U6 is connected to the inverting input terminal of the operational amplifier U7 through the resistor R17, the output terminal of the operational amplifier U7 is connected to the inverting input terminal of the operational amplifier U7 through the resistor R19, and the output terminal of the operational amplifier U7 is connected to the first input terminal of the main control unit.

[0011] Furthermore, the utility model also includes a filtering circuit between the output end of the operational amplifier U7 and the first input end of the main control unit, and the filtering circuit includes a resistor R20, a resistor R21, a resistor R22, a capacitor C5, an operational amplifier U8, a resistor R23, a resistor R24 ​​and a capacitor C6. The first end of the resistor R20 is connected to the output end of the operational amplifier U7, the second end of the resistor R20 is grounded through the resistor R21, the second end of the resistor R20 is connected to the first end of the resistor R22, the second end of the resistor R22 is grounded through the capacitor C5, the second end of the resistor R22 is connected to the non-inverting input end of the operational amplifier U8, the inverting input end of the operational amplifier U8 is grounded through the resistor R23, the output end of the operational amplifier U8 is connected to the inverting input end of the operational amplifier U8 through the resistor R24, the output end of the operational amplifier U8 is connected to the second end of the resistor R20 through the capacitor C6, and the output end of the operational amplifier U8 is connected to the first input end of the main control unit.

[0012] Furthermore, the filtering circuit in the utility model also includes a capacitor C7, a capacitor C8, a resistor R28, a resistor R26, a resistor R27, an operational amplifier U9 and a resistor R25, wherein the first end of the capacitor C7 is connected to the output end of the operational amplifier U8, the second end of the capacitor C7 is connected to the first end of the capacitor C8, the second end of the capacitor C8 is grounded through the resistor R28, the second end of the capacitor C8 is connected to the in-phase input end of the operational amplifier U9, the inverting input end of the operational amplifier U9 is grounded through the resistor R26, the output end of the operational amplifier U9 is connected to the inverting input end of the operational amplifier U9 through the resistor R27, the output end of the operational amplifier U9 is connected to the second end of the capacitor C7 through the resistor R25, and the second end of the operational amplifier U9 is connected to the first input end of the main control unit.

[0013] The working principle and beneficial effects of the utility model are:

[0014] In the utility model, the weight detection circuit is used to detect the weight signal, and convert the detected weight signal into an electrical signal and send it to the main control unit. The pressure sensor U4 is greatly affected by the ambient temperature and power supply. In order to ensure that the detected weight signal is accurate, in the utility model, the operational amplifier U1, the transistor Q2, the operational amplifier U2 and the transistor Q3 constitute a complementary temperature compensation circuit. When working, the transistor Q2 and the transistor Q3 are both turned on, and the electric energy provided by the +12V power supply passes through the transistor Q2, the pressure sensor U4 and the transistor Q3 in turn to the -12V power supply to form a path. At this time, the pressure sensor U4 is in a working state. When the pressure sensor U4 senses the object to be measured, the weight signal of the object to be measured is converted into an electrical signal corresponding to the weight signal and sent to the main control unit. When the operating temperature of the pressure sensor U4 rises, the operational amplifier U1 forms a common-phase amplifier circuit, the output voltage of the operational amplifier U1 increases, the base current of the transistor Q2 increases, and the current flowing through the pressure sensor U4 increases. The operational amplifier U2 forms an inverting amplifier circuit. When the current flowing through the pressure sensor U4 increases, the voltage at the inverting input terminal of the operational amplifier U2 increases, causing the output voltage of the operational amplifier U2 to increase in the negative direction, but it is less than the emitter -12V voltage of the transistor Q3, resulting in the voltage V between the base of the transistor Q3 and the emitter of the transistor Q3. be The collector current of transistor Q3 is reduced, thereby ensuring that the voltage across the pressure sensor U4 remains unchanged. The same applies when the operating temperature of the pressure sensor U4 decreases. Therefore, the utility model utilizes the complementary characteristics of transistor Q2 and transistor Q3 to maintain the dynamic balance of the pressure sensor U4, so that the pressure sensor U4 is not affected by the ambient temperature during operation, thereby improving the accuracy of the weight information. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The utility model is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0016] Figure 1 It is a circuit diagram of the weight detection circuit in the utility model;

[0017] Figure 2 It is a circuit diagram of the voltage stabilizing circuit in the utility model;

[0018] Figure 3 It is a circuit diagram of the filter circuit in the utility model. DETAILED DESCRIPTION

[0019] In order to enable people in the technical field to better understand the present solution, the technical solution in the embodiment of the present solution will be clearly described below in conjunction with the drawings in the embodiment of the present solution. Obviously, the described embodiment is an embodiment of a part of the present solution, not all of the embodiments. Based on the embodiments in the present solution, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present solution.

[0020] The term "including" and any other variations in the specification and claims of this solution and the above drawings mean "including but not limited to", and is intended to cover non-exclusive inclusions and is not limited to the examples listed in the text. In addition, the terms "first" and "second" are used to distinguish different objects, not to describe a specific order.

[0021] Example 1

[0022] like Figure 1 As shown, this embodiment proposes a static weighing instrument, including a weight detection circuit and a main control unit, the weight detection circuit is connected to the main control unit, the weight detection circuit includes an operational amplifier U1, an operational amplifier U2, a resistor R6, a resistor R11, a transistor Q2, a resistor R10, a resistor R12, a transistor Q3 and a pressure sensor U4; the first power supply end of the operational amplifier U1 is connected to a +12V power supply, the second power supply end of the operational amplifier U1 is connected to a -12V power supply, the in-phase input end of the operational amplifier U1 is connected to a Vref reference voltage, the inverting input end of the operational amplifier U1 is grounded through a resistor R6, the output end of the operational amplifier U1 is connected to the base of the transistor Q2, the collector of the transistor Q2 is connected to the +12V power supply, and the emitter of the transistor Q2 is connected to the voltage Vref. Resistor R11 is connected to the inverting input terminal of operational amplifier U1, and the emitter of transistor Q2 is connected to the first power supply terminal of pressure sensor U4; the first power supply terminal of operational amplifier U2 is connected to +12V power supply, the second power supply terminal of operational amplifier U2 is connected to -12V power supply, the inverting input terminal of operational amplifier U2 is connected to the non-inverting input terminal of operational amplifier U1, the non-inverting input terminal of operational amplifier U2 is grounded through resistor R10, the output terminal of operational amplifier U2 is connected to the base of transistor Q3, the collector of transistor Q3 is connected to the inverting input terminal of operational amplifier U2 through resistor R12, the collector of transistor Q3 is connected to the second power supply terminal of pressure sensor U4, the emitter of transistor Q3 is connected to -12V power supply, and the output terminal of pressure sensor U4 is connected to the main control unit.

[0023] In this embodiment, the weight detection circuit is used to detect the weight signal and convert the detected weight signal into an electrical signal and send it to the main control unit. Specifically, the working principle of the weight detection circuit is:

[0024] In this embodiment, a resistance strain type pressure sensor is used as the pressure sensor U4. By utilizing the resistance strain effect of metal, when the pressure sensor U4 is mechanically deformed under the action of external force, its resistance value changes with the change of the mechanical deformation it is subjected to, and finally the applied external force is converted into an electrical signal output. The pressure sensor U4 is greatly affected by the ambient temperature and power supply. In order to ensure that the detected weight signal is accurate, in this embodiment, the operational amplifier U1, the transistor Q2, the operational amplifier U2 and the transistor Q3 constitute a complementary temperature compensation circuit. When working, the transistor Q2 and the transistor Q3 are both turned on, and the electric energy provided by the +12V power supply passes through the transistor Q2, the pressure sensor U4 and the transistor Q3 in turn to form a path to the -12V power supply. At this time, the pressure sensor U4 is in a working state. When the pressure sensor U4 senses the object to be measured, the weight signal of the object to be measured is converted into an electrical signal corresponding to the weight signal and sent to the main control unit. When the operating temperature of the pressure sensor U4 rises, the operational amplifier U1 forms a common-phase amplifier circuit, the output voltage of the operational amplifier U1 increases, the base current of the transistor Q2 increases, and the current flowing through the pressure sensor U4 increases. The operational amplifier U2 forms an inverting amplifier circuit. When the current flowing through the pressure sensor U4 increases, the voltage at the inverting input terminal of the operational amplifier U2 increases, causing the output voltage of the operational amplifier U2 to increase in the negative direction, but it is less than the emitter -12V voltage of the transistor Q3, resulting in the voltage V between the base of the transistor Q3 and the emitter of the transistor Q3. be The voltage across the pressure sensor U4 remains constant. The same applies when the operating temperature of the pressure sensor U4 decreases.

[0025] Therefore, this embodiment utilizes the complementary characteristics of the transistor Q2 and the transistor Q3 to maintain the dynamic balance of the pressure sensor U4, so that the pressure sensor U4 is not affected by the ambient temperature during operation, thereby improving the accuracy of the weight information.

[0026] like Figure 1 As shown, the weight detection circuit in this embodiment also includes a variable resistor RP2 and a resistor R13, the first end of the variable resistor RP2 is connected to the first output end of the pressure sensor U4, the second end of the variable resistor RP2 is connected to the second output end of the pressure sensor U4, and the sliding end of the variable resistor RP2 is connected to the collector of the transistor Q3 through the resistor R13.

[0027] In this embodiment, a resistance strain type pressure sensor is used as the pressure sensor U4. The pressure sensor U4 is internally composed of four pressure-sensitive elements to form an electric bridge. In the process of producing the pressure-sensitive elements, the four pressure-sensitive elements that constitute the electric bridge cannot be completely consistent due to uncontrollable factors. Therefore, the electric bridge cannot be completely symmetrical. Therefore, if the pressure sensor U4 directly weighs the weight of an object, there will be a certain error. For this reason, a zero adjustment circuit is added to this embodiment. The zero adjustment circuit is composed of a variable resistor RP2 and a resistor R13. By adjusting the resistance value of the variable resistor RP2, the output of the pressure sensor U4 can be made 0 in the absence of a measured object, thereby ensuring the accuracy of weighing the measured object.

[0028] like Figure 2 As shown, the static weighing instrument in this embodiment also includes a voltage stabilizing circuit, which includes a rheostat RP1, an operational amplifier U3, a resistor R4, a capacitor C2, a resistor R3, a transistor Q1 and a resistor R2. The first end of the rheostat RP1 is connected to a 5V power supply, the second end of the rheostat RP1 is grounded, the sliding end of the rheostat RP1 is connected to the in-phase input end of the operational amplifier U3, the output end of the operational amplifier U3 is connected to the inverting input end of the operational amplifier U3 through the capacitor C2, the output end of the operational amplifier U3 is connected to the base of the transistor Q1, the collector of the transistor Q1 is connected to the 5V power supply through the resistor R4, the collector of the transistor Q1 is connected to the in-phase input end of the operational amplifier U1, the emitter of the transistor Q1 is grounded through the resistor R2, and the emitter of the transistor Q1 is connected to the inverting input end of the operational amplifier U3 through the resistor R3.

[0029] In this embodiment, in order to improve the stability of the weight detection circuit, it is necessary to ensure that the Vref reference voltage connected to the in-phase input terminal of the operational amplifier U1 is stable and unchanged. For this reason, a voltage stabilizing circuit is added in this embodiment. After power-on, the variable resistor RP1 constitutes a voltage sampling circuit, and the voltage at the sliding end of the variable resistor RP1 is taken as the reference voltage and added to the in-phase input terminal of the operational amplifier U3. When working, the operational amplifier U3 outputs a positive voltage signal, the transistor Q1 is turned on, and then the 5V voltage is divided by the resistor R4, the switch tube Q1 and the resistor R2. The voltage on the resistor R2 is the sampling voltage and added to the inverting input terminal of the operational amplifier U3. The voltage of the collector of the transistor Q1 is used as the Vref reference voltage. When the collector voltage of the transistor Q1 increases, the divided voltage on the resistor R2 increases, thereby increasing the voltage at the inverting input terminal of the operational amplifier U3. The operational amplifier U3 constitutes a subtractor, and the voltage at the output terminal of the operational amplifier U3 decreases. Therefore, the base current of the transistor Q1 decreases, and the collector current of the transistor Q1 decreases, thereby reducing the voltage on the resistor R2. When the collector voltage of transistor Q1 decreases, the voltage division on resistor R2 decreases, thereby reducing the voltage at the inverting input terminal of op amp U3 and increasing the voltage at the output terminal of op amp U3. Therefore, the base current of transistor Q1 increases, and the collector current of transistor Q1 increases, thereby increasing the voltage at resistor R2. Therefore, when the Vref reference voltage floats, automatic adjustment can be achieved to ensure that the reference voltage at the inverting input terminal of op amp U1 remains stable.

[0030] like Figure 1 As shown, the weight detection circuit in this embodiment also includes an operational amplifier U5, an operational amplifier U6, a resistor R16, a resistor R17, a resistor R19 and an operational amplifier U7, the non-inverting input terminal of the operational amplifier U5 is connected to the first output terminal of the pressure sensor U4, the non-inverting input terminal of the operational amplifier U6 is connected to the second output terminal of the pressure sensor U4, the output terminal of the operational amplifier U5 is connected to the inverting input terminal of the operational amplifier U5, the output terminal of the operational amplifier U5 is connected to the non-inverting input terminal of the operational amplifier U7 through the resistor R16, the output terminal of the operational amplifier U6 is connected to the inverting input terminal of the operational amplifier U6, the output terminal of the operational amplifier U6 is connected to the inverting input terminal of the operational amplifier U7 through the resistor R17, the output terminal of the operational amplifier U7 is connected to the inverting input terminal of the operational amplifier U7 through the resistor R19, and the output terminal of the operational amplifier U7 is connected to the first input terminal of the main control unit.

[0031] In this embodiment, the electrical signal output by the pressure sensor U4 is relatively weak, and the main control unit cannot effectively identify the electrical signal output by the pressure sensor U4. For this reason, a signal amplification circuit is designed. The pressure sensor U4 has two output signals. The signal will cause certain losses during the transmission process, resulting in a weaker useful signal before amplification. The operational amplifier U5 and the operational amplifier U6 respectively constitute followers, and send the two output signals of the pressure sensor U4 to the in-phase input terminal and the inverting input terminal of the operational amplifier U7 respectively, reducing the loss of the signal on the line. The operational amplifier U7 constitutes a differential amplifier circuit, which is used to amplify the electrical signal output by the pressure sensor U4, and at the same time convert the two electrical signals output by the pressure sensor U4 into one electrical signal output to the first input terminal of the main control unit. The differential amplifier circuit can also suppress the common-mode interference signal to a certain extent, thereby improving the accuracy of the circuit.

[0032] like Figure 3 As shown, in this embodiment, a filtering circuit is also included between the output end of the operational amplifier U7 and the first input end of the main control unit. The filtering circuit includes a resistor R20, a resistor R21, a resistor R22, a capacitor C5, an operational amplifier U8, a resistor R23, a resistor R24 ​​and a capacitor C6. The first end of the resistor R20 is connected to the output end of the operational amplifier U7, the second end of the resistor R20 is grounded through the resistor R21, the second end of the resistor R20 is connected to the first end of the resistor R22, the second end of the resistor R22 is grounded through the capacitor C5, the second end of the resistor R22 is connected to the in-phase input end of the operational amplifier U8, the inverting input end of the operational amplifier U8 is grounded through the resistor R23, the output end of the operational amplifier U8 is connected to the inverting input end of the operational amplifier U8 through the resistor R24, the output end of the operational amplifier U8 is connected to the second end of the resistor R20 through the capacitor C6, and the output end of the operational amplifier U8 is connected to the first input end of the main control unit.

[0033] Under normal circumstances, the first input terminal of the main control unit should receive a low-frequency voltage signal. During the signal transmission process, it is easy to be injected with high-frequency noise signals, which will directly cover the useful signals, thereby affecting the accuracy of the final weight information. For this reason, in this embodiment, a filtering circuit is added between the output terminal of the operational amplifier U7 and the first input terminal of the main control unit, wherein resistor R20, resistor R21, resistor R22, capacitor C5, operational amplifier U8, resistor R23, resistor R24 ​​and capacitor C6 constitute a low-pass filter for filtering out high-frequency noise signals in the output electrical signal of the operational amplifier U7.

[0034] like Figure 3As shown, the filtering circuit in this embodiment also includes a capacitor C7, a capacitor C8, a resistor R28, a resistor R26, a resistor R27, an operational amplifier U9 and a resistor R25. The first end of the capacitor C7 is connected to the output end of the operational amplifier U8, the second end of the capacitor C7 is connected to the first end of the capacitor C8, the second end of the capacitor C8 is grounded through the resistor R28, the second end of the capacitor C8 is connected to the in-phase input end of the operational amplifier U9, the inverting input end of the operational amplifier U9 is grounded through the resistor R26, the output end of the operational amplifier U9 is connected to the inverting input end of the operational amplifier U9 through the resistor R27, the output end of the operational amplifier U9 is connected to the second end of the capacitor C7 through the resistor R25, and the second end of the operational amplifier U9 is connected to the first input end of the main control unit.

[0035] Since the electrical signal output by the pressure sensor U4 is relatively weak, it is extremely susceptible to environmental noise during signal transmission. The noise signal will also affect the accuracy of the weight information. For this reason, in this embodiment, a high-pass filter is added between the low-pass filter and the first input terminal of the main control unit. The high-pass filter is composed of capacitor C7, capacitor C8, resistor R28, resistor R26, resistor R27, operational amplifier U9 and resistor R25, and is used to filter out noise signals in the signal, and finally send the filtered electrical signal to the first input terminal of the main control unit.

[0036] The above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. Static weighing instrument, characterized in that: It includes a weight detection circuit and a main control unit, wherein the weight detection circuit is connected to the main control unit, and the weight detection circuit includes an operational amplifier U1, an operational amplifier U2, a resistor R6, a resistor R11, a transistor Q2, a resistor R10, a resistor R12, a transistor Q3 and a pressure sensor U4; The first power supply terminal of the operational amplifier U1 is connected to a +12V power supply, the second power supply terminal of the operational amplifier U1 is connected to a -12V power supply, the non-inverting input terminal of the operational amplifier U1 is connected to a Vref reference voltage, the inverting input terminal of the operational amplifier U1 is grounded through the resistor R6, the output terminal of the operational amplifier U1 is connected to the base of the transistor Q2, the collector of the transistor Q2 is connected to a +12V power supply, the emitter of the transistor Q2 is connected to the inverting input terminal of the operational amplifier U1 through the resistor R11, and the emitter of the transistor Q2 is connected to the first power supply terminal of the pressure sensor U4; The first power supply end of the operational amplifier U2 is connected to a +12V power supply, the second power supply end of the operational amplifier U2 is connected to a -12V power supply, the inverting input end of the operational amplifier U2 is connected to the non-inverting input end of the operational amplifier U1, the non-inverting input end of the operational amplifier U2 is grounded through the resistor R10, the output end of the operational amplifier U2 is connected to the base of the transistor Q3, the collector of the transistor Q3 is connected to the inverting input end of the operational amplifier U2 through the resistor R12, the collector of the transistor Q3 is connected to the second power supply end of the pressure sensor U4, the emitter of the transistor Q3 is connected to the -12V power supply, and the output end of the pressure sensor U4 is connected to the main control unit.

2. The static weighing instrument according to claim 1, characterized in that: The weight detection circuit also includes a variable resistor RP2 and a resistor R13, wherein the first end of the variable resistor RP2 is connected to the first output end of the pressure sensor U4, the second end of the variable resistor RP2 is connected to the second output end of the pressure sensor U4, and the sliding end of the variable resistor RP2 is connected to the collector of the transistor Q3 via the resistor R13.

3. The static weighing instrument according to claim 1, characterized in that: It also includes a voltage stabilizing circuit, which includes a variable resistor RP1, an operational amplifier U3, a resistor R4, a capacitor C2, a resistor R3, a transistor Q1 and a resistor R2. The first end of the variable resistor RP1 is connected to a 5V power supply, the second end of the variable resistor RP1 is grounded, the sliding end of the variable resistor RP1 is connected to the non-inverting input end of the operational amplifier U3, the output end of the operational amplifier U3 is connected to the inverting input end of the operational amplifier U3 through the capacitor C2, the output end of the operational amplifier U3 is connected to the base of the transistor Q1, the collector of the transistor Q1 is connected to the 5V power supply through the resistor R4, the collector of the transistor Q1 is connected to the non-inverting input end of the operational amplifier U1, the emitter of the transistor Q1 is grounded through the resistor R2, and the emitter of the transistor Q1 is connected to the inverting input end of the operational amplifier U3 through the resistor R3.

4. The static weighing instrument according to claim 1, characterized in that: The weight detection circuit also includes an operational amplifier U5, an operational amplifier U6, a resistor R16, a resistor R17, a resistor R19 and an operational amplifier U7, the non-inverting input terminal of the operational amplifier U5 is connected to the first output terminal of the pressure sensor U4, the non-inverting input terminal of the operational amplifier U6 is connected to the second output terminal of the pressure sensor U4, the output terminal of the operational amplifier U5 is connected to the inverting input terminal of the operational amplifier U5, the output terminal of the operational amplifier U5 is connected to the non-inverting input terminal of the operational amplifier U7 through the resistor R16, the output terminal of the operational amplifier U6 is connected to the inverting input terminal of the operational amplifier U6, the output terminal of the operational amplifier U6 is connected to the inverting input terminal of the operational amplifier U7 through the resistor R17, the output terminal of the operational amplifier U7 is connected to the inverting input terminal of the operational amplifier U7 through the resistor R19, and the output terminal of the operational amplifier U7 is connected to the first input terminal of the main control unit.

5. The static weighing meter according to claim 4, characterized in that: A filtering circuit is also included between the output end of the operational amplifier U7 and the first input end of the main control unit. The filtering circuit includes a resistor R20, a resistor R21, a resistor R22, a capacitor C5, an operational amplifier U8, a resistor R23, a resistor R24 ​​and a capacitor C6. The first end of the resistor R20 is connected to the output end of the operational amplifier U7, the second end of the resistor R20 is grounded through the resistor R21, the second end of the resistor R20 is connected to the first end of the resistor R22, the second end of the resistor R22 is grounded through the capacitor C5, the second end of the resistor R22 is connected to the in-phase input end of the operational amplifier U8, the inverting input end of the operational amplifier U8 is grounded through the resistor R23, the output end of the operational amplifier U8 is connected to the inverting input end of the operational amplifier U8 through the resistor R24, the output end of the operational amplifier U8 is connected to the second end of the resistor R20 through the capacitor C6, and the output end of the operational amplifier U8 is connected to the first input end of the main control unit.

6. The static weighing meter according to claim 5, characterized in that: The filtering circuit also includes a capacitor C7, a capacitor C8, a resistor R28, a resistor R26, a resistor R27, an operational amplifier U9 and a resistor R25. The first end of the capacitor C7 is connected to the output end of the operational amplifier U8, the second end of the capacitor C7 is connected to the first end of the capacitor C8, the second end of the capacitor C8 is grounded through the resistor R28, the second end of the capacitor C8 is connected to the in-phase input end of the operational amplifier U9, the inverting input end of the operational amplifier U9 is grounded through the resistor R26, the output end of the operational amplifier U9 is connected to the inverting input end of the operational amplifier U9 through the resistor R27, the output end of the operational amplifier U9 is connected to the second end of the capacitor C7 through the resistor R25, and the second end of the operational amplifier U9 is connected to the first input end of the main control unit.

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