Symmetrical bridge arm differential complementary circuit for methane gas detector

Abstract

The utility model discloses a symmetrical bridge arm differential complementary circuit for a methane gas detector. The symmetrical bridge arm differential complementary circuit consists of a current-limiting voltage-reducing circuit, a voltage-dividing reference circuit and an upper and lower bridge arm differential complementary circuit, the current-limiting step-down circuit forms a voltage signal VC and a first comparison signal VB, the voltage signal VC supplies power to the gas sensor, the gas sensor outputs a third comparison signal Vi, and the first comparison signal VB is used for participating in operation of the upper and lower bridge arm differential complementary circuit; the first comparison signal VB forms a second comparison signal VR through a voltage division reference circuit, the third comparison signal Vi and the second comparison signal VR are amplified and compared to output a first output signal Vo1, the first output signal Vo1 forms a signal ADCA through a low-pass filter, and the voltage value of the second comparison signal VR is slightly larger than that of the third comparison signal Vi; the first comparison signal VB and the third comparison signal Vi are amplified and compared to output a signal ADCB, the signal ADCA and the signal ADCB enter a CPU processing system at the same time to perform corresponding data processing, the low-pass filter circuit can filter power frequency interference of the mains supply, the circuit structure is simple, the function is stable, the number of related components is small, the cost of corresponding equipment is reduced, and the application range is wide. The market competitive advantage of a portable methane gas detection product using the technology is favorably improved.

Description

Technical Field

[0001] The utility model relates to the field of gas detection, in particular to a symmetric bridge arm differential complementary circuit for a methane gas detector. Background Art

[0002] At present, portable gas detector products are widely used, especially the use of coal mine methane gas detectors is more extensive. Many experts in the industry have proposed different methane gas detection circuits and processing methods, including the use of integrated processing solutions with high precision, high speed, and high integration. However, their costs are relatively high, and it is difficult to popularize them widely in mines. Especially for some small mines with relatively backward technical conditions and economic situations, it is not convenient for market promotion and application.

[0003] The patent with the patent number CN201520641620.3 and the name "Portable Methane Gas Detector" discloses a portable methane gas detector, which includes a gas sensor, a single-chip microcomputer unit, an amplification circuit, a zero-adjusting circuit, a reference voltage circuit, a constant temperature control circuit, an infrared receiving circuit, a liquid crystal display circuit, a keyboard interface circuit, and an audible and visual alarm circuit. The gas sensor is respectively connected to the zero-adjusting circuit, the constant temperature control circuit, the reference voltage circuit, and the amplification circuit. The zero-adjusting circuit is connected to the single-chip microcomputer unit, the amplification circuit is connected to the single-chip microcomputer unit, the constant temperature control circuit is connected to the single-chip microcomputer unit, and the infrared receiving circuit, the liquid crystal display circuit, the keyboard interface circuit, and the audible and visual alarm circuit are respectively connected to the single-chip microcomputer unit. The conditioning circuit in the above technical solution selects a large variety of components and has a complex circuit structure, so there is also a problem that the cost is relatively high and it is not suitable for widespread promotion in mines. Summary of the Invention

[0004] The purpose of the utility model is to provide a symmetric bridge arm differential complementary circuit for a methane gas detector. The circuit has the characteristics of using fewer components and single power supply, with low hardware cost and easy implementation, so as to reduce the equipment cost and facilitate market promotion and utilization.

[0005] The utility model adopts the following technical solutions:

[0006] A symmetric bridge arm differential complementary circuit for a methane gas detector includes a current limiting and voltage reducing circuit, a voltage dividing and reference circuit, and an upper and lower bridge arm differential complementary circuit; wherein,

[0007] The current limiting and voltage reducing circuit, on the one hand, generates a voltage signal through voltage reduction for powering the gas sensor; on the other hand, generates a first comparison signal through voltage reduction and transmits it to the voltage dividing and reference circuit and the upper and lower bridge arm differential complementary circuit respectively; the current limiting and voltage reducing circuit is respectively connected to the voltage dividing and reference circuit and the upper and lower bridge arm differential complementary circuit;

[0008] The described voltage-dividing reference circuit is used to divide the voltage of the first comparison signal to generate a second comparison signal and transmit it to the upper and lower bridge arm differential complementary circuit; the voltage-dividing reference circuit is connected to the upper and lower bridge arm differential complementary circuit;

[0009] The described upper and lower bridge arm differential complementary circuit includes a first operational amplifier and a second operational amplifier; the first operational amplifier amplifies and compares the third comparison signal output by the gas sensor and the first comparison signal output by the current-limiting and step-down circuit, and then outputs a first output signal; the second operational amplifier amplifies and compares the third comparison signal output by the gas sensor and the second comparison signal output by the voltage-dividing reference circuit, and then outputs a second output signal; the first output signal and the second output signal are respectively processed by a low-pass filter circuit to form corresponding filtered output signals, which are simultaneously input to the processor system.

[0010] The described upper and lower bridge arm differential complementary circuit includes an upper bridge arm circuit and a lower bridge arm circuit; the upper bridge arm circuit includes an upper bridge arm inverting input negative feedback amplifier circuit composed of a first operational amplifier and an upper bridge arm inverting input negative feedback circuit; the lower bridge arm circuit includes a lower bridge arm inverting input negative feedback amplifier circuit composed of a second operational amplifier and a lower bridge arm inverting input negative feedback circuit.

[0011] The described upper bridge arm circuit further includes an upper bridge arm filter circuit, and the upper bridge arm inverting input negative feedback amplifier circuit and the upper bridge arm filter circuit form an upper bridge arm inverting input negative feedback amplifier and filter circuit; the lower bridge arm circuit further includes a lower bridge arm filter circuit, and the lower bridge arm filter circuit and the lower bridge arm inverting input negative feedback amplifier circuit form a lower bridge arm inverting input negative feedback amplifier and filter circuit.

[0012] The described current-limiting and step-down circuit includes a first current-limiting and step-down sub-circuit and a second current-limiting and step-down sub-circuit; the first current-limiting and step-down sub-circuit includes a first resistor and a second resistor connected in series in sequence; the first end of the first resistor is connected to the power supply, and the second end of the second resistor is connected to the power input pin of the gas sensor; the second current-limiting and step-down sub-circuit includes a third resistor, the first end of the third resistor is connected to the power supply, and the second end of the third resistor is respectively connected to the voltage-dividing reference circuit and the upper and lower bridge arm differential complementary circuit.

[0013] The described voltage-dividing reference circuit includes a fourth resistor, a fifth resistor, and a sixth resistor; both ends of the fourth resistor are respectively connected to the current-limiting and step-down circuit and the upper and lower bridge arm differential complementary circuit; a series circuit composed of the fifth resistor and the sixth resistor, one end is connected to the second end of the fourth resistor, and the other end is grounded.

[0014] The above-mentioned upper-bridge-arm inverting input negative feedback circuit includes the seventh resistor to the tenth resistor; the third comparison signal output by the gas sensor is connected to the non-inverting input terminal of the first operational amplifier through the seventh resistor, and the second comparison signal output by the voltage division reference circuit is connected to the inverting input terminal of the first operational amplifier through the eighth resistor; one end of the ninth resistor is connected to the non-inverting input terminal of the first operational amplifier, and the other end is grounded; one end of the tenth resistor is connected to the inverting input terminal of the first operational amplifier, and the other end is connected to the output terminal of the first operational amplifier.

[0015] The above-mentioned lower-bridge-arm inverting input negative feedback circuit includes the twelfth resistor to the fifteenth resistor; the third comparison signal output by the gas sensor is connected to the inverting input terminal of the second operational amplifier through the twelfth resistor, and the first comparison signal output by the current limiting and step-down circuit is connected to the non-inverting input terminal of the second operational amplifier through the thirteenth resistor; one end of the fourteenth resistor is connected to the inverting input terminal of the second operational amplifier, and the other end is connected to the output terminal of the second operational amplifier; one end of the fifteenth resistor is connected to the non-inverting input terminal of the second operational amplifier, and the other end is grounded.

[0016] The above-mentioned upper-bridge-arm filtering circuit includes the eleventh resistor and the first capacitor; the first end of the eleventh resistor is connected to the output terminal of the first operational amplifier, and the second end is connected to the first input terminal of the CPU processor system; one end of the first capacitor is connected to the second end of the eleventh resistor, and the other end is grounded.

[0017] The above-mentioned lower-bridge-arm filtering circuit includes the sixteenth resistor and the second capacitor; the first end of the sixteenth resistor is connected to the output terminal of the second operational amplifier, and the second end is connected to the second input terminal of the CPU processor system; one end of the second capacitor is connected to the second end of the sixteenth resistor, and the other end is grounded.

[0018] The utility model improves the two-way power supply circuit into a single power supply circuit, and replaces the diode in the traditional conditioning circuit with a resistor; it reduces the hardware cost and also reduces the implementation requirements of the differential complementary circuit, making the symmetric bridge-arm differential complementary circuit more practical. Brief Description of the Drawings

[0019] Figure 1 It is a specific implementation circuit diagram of the utility model;

[0020] Figure 2 It is a circuit diagram using a dual power supply under the prior art;

[0021] Figure 3 It is a circuit diagram using a single power supply diode step-down power supply under the prior art;

[0022] Figure 4 It is a circuit diagram using a single power supply resistor step-down power supply under the prior art. Detailed Embodiment

[0023] The present utility model will be described in detail below in conjunction with the accompanying drawings and embodiments:

[0024] As shown in the attached Figure 1 figure, the symmetric bridge-arm differential complementary circuit for a methane gas detector according to the present utility model includes a current-limiting and voltage-dropping circuit, a voltage-dividing and reference circuit, and an upper and lower bridge-arm differential complementary circuit;

[0025] The current-limiting and voltage-dropping circuit, on the one hand, generates a voltage signal VC through voltage dropping for powering the gas sensor U1; on the other hand, generates a first comparison signal VB through voltage dropping and transmits it to the voltage-dividing and reference circuit and the upper and lower bridge-arm differential complementary circuit respectively; the current-limiting and voltage-dropping circuit is respectively connected to the voltage-dividing and reference circuit and the upper and lower bridge-arm differential complementary circuit;

[0026] The voltage-dividing and reference circuit is used to divide the voltage of the first comparison signal VB to generate a second comparison signal VR and transmit it to the upper and lower bridge-arm differential complementary circuit; the voltage-dividing and reference circuit is connected to the upper and lower bridge-arm differential complementary circuit;

[0027] The upper and lower bridge-arm differential complementary circuit includes a first operational amplifier U1A and a second operational amplifier U1B; the first operational amplifier U1A amplifies and compares the third comparison signal Vi output by the gas sensor U1 and the first comparison signal VB output by the current-limiting and voltage-dropping circuit and then outputs a first output signal Vo1; the second operational amplifier U1B amplifies and compares the third comparison signal Vi of the gas sensor U1 and the second comparison signal VR output by the voltage-dividing and reference circuit and then outputs a second output signal Vo2; the first output signal Vo1 and the second output signal Vo2 are respectively processed by a low-pass filter circuit to form corresponding filtered output signals ADCA and ADCB and input to the processor simultaneously.

[0028] The present utility model can still effectively guarantee the detection of methane gas while reducing the use of components, uses one-way power supply, has low required hardware cost, and thus reduces the overall equipment cost, facilitating market promotion and utilization.

[0029] In the present utility model, the current-limiting and voltage-dropping circuit includes a first current-limiting and voltage-dropping sub-circuit and a second current-limiting and voltage-dropping sub-circuit; the first current-limiting and voltage-dropping sub-circuit includes a first resistor R1 and a second resistor R2 connected in series in sequence; the first end of the first resistor R1 is connected to the power supply VA, the second end of the first resistor R1 is connected to the first end of the second resistor R2, and the second end of the second resistor R2 is connected to the power input pin P4 of the gas sensor U1; the second current-limiting and voltage-dropping sub-circuit includes a third resistor R3, the first end of the third resistor R3 is connected to the power supply VA, and the second end of the third resistor R3 is simultaneously connected to the voltage-dividing and reference circuit and the upper and lower bridge-arm differential complementary circuit.

[0030] In this embodiment, the voltage signal VC obtained by the first current-limiting and step-down sub-circuit is used to supply power to the gas sensor U1, and the second current-limiting and step-down sub-circuit is used to output the first comparison signal VB.

[0031] In the present utility model, the gas sensor U1 can adopt the existing sensor module MJC4 / 2.8J, which has a fast response speed and stable and reliable operation; the third comparison signal Vi output by the gas sensor U1 is connected to the input end of the upper and lower symmetric bridge arm differential complementary circuit. The connection method of each wiring terminal of the gas sensor U1 belongs to the conventional technology in the art and will not be elaborated here.

[0032] In the present utility model, the voltage-dividing reference circuit includes a fourth resistor R4, a fifth resistor R5, and a sixth resistor R6; the first end of the fourth resistor R4 is connected to the second end of the third resistor R3, and the second end of the fourth resistor R4 is connected to the upper and lower bridge arm differential complementary circuit; the series circuit composed of the fifth resistor R5 and the sixth resistor R6 has one end connected to the second end of the fourth resistor R4 and the other end grounded.

[0033] In this embodiment, the series circuit composed of the fifth resistor R5 and the sixth resistor R6 in the voltage-dividing reference circuit is used to suppress the voltage fluctuation caused by external factors and ensure the stable output of the second comparison signal VR.

[0034] In the present utility model, the upper and lower bridge arm differential complementary circuit includes an upper bridge arm circuit and a lower bridge arm circuit; the upper bridge arm circuit includes an upper bridge arm inverting input negative feedback circuit composed of a first operational amplifier U1A, a seventh resistor R7 to a tenth resistor R10, and an upper bridge arm filtering circuit composed of an eleventh resistor R11 and a first capacitor C1; the first operational amplifier U1A and the upper bridge arm inverting input negative feedback circuit form an upper bridge arm inverting input negative feedback amplification circuit, and the upper bridge arm inverting input negative feedback amplification circuit and the upper bridge arm filtering circuit are combined to form an upper bridge arm inverting input negative feedback amplification and filtering circuit, which is used as the upper bridge arm circuit.

[0035] Similarly, the lower bridge arm circuit includes a second operational amplifier U1B, a lower bridge arm inverting input negative feedback circuit composed of a twelfth resistor R12 to a fifteenth resistor R15, and a lower bridge arm filtering circuit composed of a sixteenth resistor R16 and a second capacitor C2; the second operational amplifier U1B and the lower bridge arm inverting input negative feedback circuit form a lower bridge arm inverting input negative feedback amplification circuit, and the lower bridge arm inverting input negative feedback amplification circuit and the lower bridge arm filtering circuit are combined to form a lower bridge arm inverting input negative feedback amplification and filtering circuit, which is used as the lower bridge arm circuit.

[0036] In the present utility model, in the upper and lower bridge arm differential complementary circuit, the second comparison signal VR output by the voltage dividing reference circuit is connected to the inverting input terminal of the first operational amplifier U1A through the eighth resistor R8; the third comparison signal Vi output by the gas sensor U1 is connected to the non-inverting input terminal of the first operational amplifier U1A through the seventh resistor R7. One end of the tenth resistor R10 is connected to the inverting input terminal of the first operational amplifier U1A, and the other end of the tenth resistor R10 is connected to the output terminal of the first operational amplifier U1A; one end of the ninth resistor R9 is connected to the non-inverting input terminal of the first operational amplifier U1A, and the other end of the ninth resistor R9 is grounded.

[0037] Meanwhile, the third comparison signal Vi output by the gas sensor U1 is connected to the inverting input terminal of the second operational amplifier U1B through the twelfth resistor R12; the first comparison signal VB output by the voltage dividing reference circuit is connected to the non-inverting input terminal of the second operational amplifier U1B through the thirteenth resistor R13; one end of the fourteenth resistor R14 is connected to the inverting input terminal of the second operational amplifier U1B, and the other end of the fourteenth resistor R14 is connected to the output terminal of the second operational amplifier U1B; one end of the fifteenth resistor R15 is connected to the non-inverting input terminal of the first operational amplifier U1A, and the other end of the fifteenth resistor R15 is grounded.

[0038] In this embodiment, the upper and lower bridge arm inverting input negative feedback amplifier circuit helps to reduce noise, improve the quality of the signal, and reduce unnecessary interference and distortion.

[0039] In the present utility model, in order to ensure that the power frequency interference of the commercial power to the first output signal Vo1 and the second output signal Vo2 can be filtered out, two groups of low-pass filter circuits are correspondingly adopted for the upper bridge arm filter circuit and the lower bridge arm filter circuit; the first group of low-pass filter circuit includes the eleventh resistor R11 and the first capacitor C1; the first end of the eleventh resistor R11 is connected to the output terminal of the first operational amplifier U1A, and the second end of the eleventh resistor R11 is connected to the first input terminal IN1 of the CPU processor system U2 for outputting the signal ADCA; one end of the first capacitor C1 is connected to the second end of the eleventh resistor R11, and the other end of the first capacitor C1 is grounded; the second group of low-pass filter circuit includes the sixteenth resistor R16 and the second capacitor C2; the first end of the sixteenth resistor R16 is connected to the output terminal of the second operational amplifier U1B, and the second end of the sixteenth resistor R16 is connected to the second input terminal IN2 of the CPU processor system U2 for outputting the signal ADCB; one end of the second capacitor C2 is connected to the second end of the sixteenth resistor R16, and the other end of the second capacitor C2 is grounded.

[0040] In the present utility model, signal ADCA and signal ADCB are respectively input to the first input terminal IN1 and the second input terminal IN2 of the CPU processor system U2. The VCC terminal of the CPU processor system U2 is powered by the power supply voltage VA, and the VSS terminal of the CPU processor system U2 is grounded.

[0041] In this embodiment, the power supply voltage VA is stepped down to obtain the first comparison signal VB. The signal VB is used for signal calculation in the subsequent upper and lower bridge arm circuits. The first comparison signal VB forms the second comparison signal VR through the voltage division reference circuit. The signal VR is the reference benchmark voltage. After introducing the full-scale methane standard gas, the gas sensor U1 outputs the third comparison signal Vi after sensing the combustible gas. The third comparison signal Vi and the second comparison signal VR are input to the first operational amplifier U1A for amplification and comparison, and then the first output signal Vo1 is output. The first output signal Vo1 passes through the low-pass filter to generate the filtered output signal ADCA. At the same time, the first comparison signal VB and the third comparison signal Vi are input to the second operational amplifier U1B for amplification and comparison, and then the second output signal Vo2 is output. The second output signal Vo2 passes through the low-pass filter to generate the filtered output signal ADCB. The signal ADCA and the signal ADCB enter the CPU processing system U2 simultaneously for corresponding data processing.

[0042] After multiple tests, the following parameters can be adopted for each electronic component in the present utility model:

[0043] Among them, R1 = 0.1R, R2 = 2R power resistors, R3 = 1R power resistor; R4 = R6 = 2K resistors, R5 = 10R resistor; R7 = R8 = 10K resistors; R9 = R10 = 150K resistors, R12 = R13 = 10K resistors, R14 = R15 = 150K resistors, R11 = R16 = 4.7K resistors, C1 = C2 = 0.1uF capacitors, and U1A and U1B are integrated chip operational amplifiers RS8522.

[0044] The following compares the symmetric bridge arm differential complementary circuit for methane gas detectors described in the present utility model with the commonly used circuits in the prior art:

[0045] As shown in the appendix Figure 2 As shown, this prior art uses two power supplies for power supply, namely 3V and 2.8V power supplies. At the same time, two power supply peripheral circuits are used, which makes the overall hardware cost price of the detector high. The hardware cost is about 5 yuan more expensive than that of the single-power-supply device. At the same time, two-point or three-point calibration is required, and the standard gas cost and labor cost are high, which is about 10 yuan more expensive than the single-point calibration cost (labor + standard gas).

[0046] As shown in the appendix Figure 3As shown, the prior art removes the 2.8V power supply and uses the voltage after diode voltage reduction to supply power to the sensor. The sensor is MCJ4 / 2.8J, a 2.8V sensor, which reduces the power supply cost and the hardware price is moderate. The single straight-line processing method requires at least two-point calibration or more than three-point calibration, wasting standard gas and manual time, and the cost is about 10 times more expensive than the single-point calibration differential algorithm in the present invention (standard gas + labor cost).

[0047] Single-point calibration requires 1 type of standard gas;

[0048] Two-point calibration requires 2 types of standard gas;

[0049] Three-point calibration requires 3 types of standard gas;

[0050] Multi-point calibration requires the number of standard gas types corresponding to the number of calibration points;

[0051] For each additional type of standard gas, it is necessary to increase the calibration and detection time of 1 person / hour of production, increase the full inspection time of 0.5 person / hour for quality inspection, and increase 1 risk point for the product; the cost increases by about 10 yuan.

[0052] As shown in the appendix Figure 4 As shown, after replacing the diode with a resistor in the prior art, the cost is reduced. However, in this method, the midpoint of the sliding rheostat and the output pins P3 and P4 of CH4 cannot form a symmetric bridge, which is prone to measurement deviation; the calibration method is the same as that of the conventional circuit shown in the appendix of the specification Figure 4 shown, increasing the standard gas or labor cost by about 10 yuan.

[0053] In summary, the present invention has the advantages of simple structure, stable operation, and few components, reducing the labor cost and component cost of the corresponding equipment, making the cost of the product using the present invention reduced, and the product also has more market competitive advantages.

Claims

1. A symmetrical bridge arm differential complementary circuit for a methane gas detector, characterized in that: It includes a current limiting and voltage reducing circuit, a voltage dividing reference circuit and an upper and lower bridge arm differential complementary circuit; wherein, The current limiting and voltage-reducing circuit, on the one hand, generates a voltage signal by voltage reduction for powering the gas sensor; on the other hand, generates a first comparison signal by voltage reduction, and transmits it to the voltage-dividing reference circuit and the upper and lower bridge arm differential complementary circuit respectively; the current limiting and voltage-reducing circuit is connected to the voltage-dividing reference circuit and the upper and lower bridge arm differential complementary circuit respectively; The voltage-dividing reference circuit is used to divide the first comparison signal to generate a second comparison signal, and transmit it to the upper and lower bridge arm differential complementary circuit; the voltage-dividing reference circuit is connected to the upper and lower bridge arm differential complementary circuit; The upper and lower bridge arm differential complementary circuit includes a first operational amplifier and a second operational amplifier; the first operational amplifier amplifies and compares a third comparison signal output by the gas sensor and a first comparison signal output by the current limiting and voltage reducing circuit, and then outputs a first output signal; the second operational amplifier amplifies and compares the third comparison signal output by the gas sensor and a second comparison signal output by the voltage dividing reference circuit, and then outputs a second output signal; the first output signal and the second output signal are respectively processed by a low-pass filtering circuit to form corresponding filtered output signals, which are simultaneously input into the processor system.

2. The symmetrical bridge arm differential complementary circuit for a methane gas detector according to claim 1, characterized in that: The upper and lower bridge arm differential complementary circuit includes an upper bridge arm circuit and a lower bridge arm circuit; the upper bridge arm circuit includes an upper bridge arm inverting input negative feedback amplifier circuit composed of a first operational amplifier and an upper bridge arm inverting input negative feedback circuit; the lower bridge arm circuit includes a lower bridge arm inverting input negative feedback amplifier circuit composed of a second operational amplifier and a lower bridge arm inverting input negative feedback circuit.

3. The symmetrical bridge arm differential complementary circuit for a methane gas detector according to claim 2, characterized in that: The upper bridge arm circuit also includes an upper bridge arm filter circuit, and the upper bridge arm inverting input negative feedback amplifier circuit and the upper bridge arm filter circuit constitute an upper bridge arm inverting input negative feedback amplifier filter circuit; the lower bridge arm circuit also includes a lower bridge arm filter circuit, and the lower bridge arm filter circuit and the lower bridge arm inverting input negative feedback amplifier circuit constitute a lower bridge arm inverting input negative feedback amplifier filter circuit.

4. The symmetrical bridge arm differential complementary circuit for a methane gas detector according to claim 1, characterized in that: The current limiting and voltage step-down circuit includes a first current limiting and voltage step-down sub-circuit and a second current limiting and voltage step-down sub-circuit; the first current limiting and voltage step-down sub-circuit includes a first resistor and a second resistor connected in series in sequence; the first end of the first resistor is connected to a power supply, and the second end of the second resistor is connected to a power input pin of a gas sensor; the second current limiting and voltage step-down sub-circuit includes a third resistor, the first end of the third resistor is connected to the power supply, and the second end of the third resistor is respectively connected to a voltage divider reference circuit and an upper and lower bridge arm differential complementary circuit.

5. The symmetrical bridge arm differential complementary circuit for a methane gas detector according to claim 1, characterized in that: The voltage-dividing reference circuit comprises a fourth resistor, a fifth resistor and a sixth resistor; the two ends of the fourth resistor are respectively connected to the current-limiting and voltage-reducing circuit and the upper and lower bridge arm differential complementary circuit; the series circuit composed of the fifth resistor and the sixth resistor has one end connected to the second end of the fourth resistor and the other end grounded.

6. The symmetrical bridge arm differential complementary circuit for a methane gas detector according to claim 2, characterized in that: The upper bridge arm inverting input negative feedback circuit includes the seventh resistor to the tenth resistor; the third comparison signal output by the gas sensor is connected to the non-inverting input terminal of the first operational amplifier through the seventh resistor, and the second comparison signal output by the voltage divider reference circuit is connected to the inverting input terminal of the first operational amplifier through the eighth resistor; one end of the ninth resistor is connected to the non-inverting input terminal of the first operational amplifier, and the other end is grounded; one end of the tenth resistor is connected to the inverting input terminal of the first operational amplifier, and the other end is connected to the output terminal of the first operational amplifier.

7. The symmetrical bridge arm differential complementary circuit for a methane gas detector according to claim 2, characterized in that: The lower bridge arm inverting input negative feedback circuit includes twelfth to fifteenth resistors; the third comparison signal output by the gas sensor is connected to the inverting input terminal of the second operational amplifier through the twelfth resistor, and the first comparison signal output by the current limiting and voltage-reducing circuit is connected to the non-inverting input terminal of the second operational amplifier through the thirteenth resistor; one end of the fourteenth resistor is connected to the inverting input terminal of the second operational amplifier, and the other end is connected to the output terminal of the second operational amplifier; one end of the fifteenth resistor is connected to the non-inverting input terminal of the second operational amplifier, and the other end is grounded.

8. The symmetrical bridge arm differential complementary circuit for a methane gas detector according to claim 3, characterized in that: The upper bridge arm filter circuit includes an eleventh resistor and a first capacitor; the first end of the eleventh resistor is connected to the output end of the first operational amplifier, and the second end is connected to the first input end of the CPU processor system; one end of the first capacitor is connected to the second end of the eleventh resistor, and the other end is grounded.

9. The symmetrical bridge arm differential complementary circuit for a methane gas detector according to claim 3, characterized in that: The lower bridge arm filter circuit includes a sixteenth resistor and a second capacitor; the first end of the sixteenth resistor is connected to the output end of the second operational amplifier, and the second end is connected to the second input end of the CPU processor system; one end of the second capacitor is connected to the second end of the sixteenth resistor, and the other end is grounded.

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