Signal conditioning circuit of catalytic combustion type gas sensor

Abstract

The utility model discloses a catalytic combustion type gas sensor signal conditioning circuit, which comprises an instrument amplifier circuit, a zero point adjusting resistor network and a passive low-pass filter circuit, and is characterized in that the zero point adjusting resistor network comprises a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4 and a fifth resistor R5; one ends of the first resistor R1, the second resistor R2 and the third resistor R3 are connected with the single chip microcomputer, the other ends of the first resistor R1, the second resistor R2 and the third resistor R3 are grounded through the fifth resistor R5, one end of the fourth resistor R4 is connected with input voltage, and the other end of the fourth resistor R4 is grounded through the fifth resistor R5.

Description

Technical Field

[0001] The utility model belongs to the field of gas valve detection, and in particular relates to a catalytic combustion type gas sensor signal conditioning circuit. Background Art

[0002] The catalytic combustion gas sensor uses the thermal effect principle of catalytic combustion. The detection element and the compensation element are paired to form a measuring bridge. Under certain temperature conditions, the combustible gas burns flamelessly on the surface of the detection element carrier and under the action of the catalyst. The carrier temperature rises, and the resistance of the platinum wire inside it also rises accordingly, causing the balanced bridge to lose balance and output an electrical signal proportional to the concentration of the combustible gas. By measuring the change in the resistance of the platinum wire, the concentration of the combustible gas can be known. This feature also makes catalytic combustion gas sensors widely used in industrial and commercial combustible gas detectors.

[0003] However, there are batch differences in the zero point of catalytic combustion gas sensors, which will cause the combustible gas detector to need to be manually adjusted during the production process in the factory. At the same time, when the combustible gas detector is installed in an industrial and commercial environment, the impurity interference gas on site will also affect the zero point parameters of the detector. When the detector has abnormal detection data, it is necessary to manually adjust it on site. The traditional adjustment solution in the industry is to use a potentiometer for adjustment. However, the manual adjustment of the potentiometer in the production process in the factory will increase production hours and labor costs. When adjusting at the installation site, the installation height and environmental factors of the detector will increase more labor costs and safety risks. Utility Model Content

[0004] In order to overcome the shortcomings of the prior art, the utility model patent provides a catalytic combustion gas sensor signal conditioning circuit. Through the sensor conditioning circuit, automatic adjustment of the sensor output zero point is achieved, providing a more intelligent and efficient solution for the mass production and subsequent maintenance of industrial and commercial combustible gas detectors.

[0005] In order to solve the above problems existing in the prior art, the technical solution adopted by the utility model is:

[0006] A catalytic combustion gas sensor signal conditioning circuit comprises an instrument amplifier circuit, a zero adjustment resistor network and a passive low-pass filter circuit.

[0007] The zero-point adjustment resistor network includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a fifth resistor R5; one end of the first resistor R1, the second resistor R2, and the third resistor R3 is connected to the single-chip microcomputer, and the other ends of the first resistor R1, the second resistor R2, and the third resistor R3 are grounded through the fifth resistor R5; one end of the fourth resistor R4 is connected to the input voltage, and the other end of the fourth resistor is grounded through the fifth resistor R5; the zero-point adjustment resistor network is used to change the output reference voltage of the instrumentation amplifier circuit.

[0008] The instrument amplifier circuit is used to amplify the difference between VINP and VINN. The instrument amplifier circuit includes a first operational amplifier U1A, a second operational amplifier U1B and a third operational amplifier U1C.

[0009] The third pin of the first operational amplifier U1A is grounded through a fifth resistor R5 , and the first pin of the first operational amplifier U1A is connected to the second pin of the first operational amplifier U1A through a sixth resistor R6 .

[0010] The fifth pin of the second operational amplifier U1B is connected to the sensor, the sixth pin of the second operational amplifier U1B is connected to the second pin of the first operational amplifier U1A through the seventh resistor R7, and the seventh pin of the second operational amplifier U1B is connected to the sixth pin of the second operational amplifier U1B through the eighth resistor R8.

[0011] The sensor is used to output VINP. The sensor includes a compensation sheet resistor RC and a detection sheet resistor RD connected in series. One end of the compensation sheet resistor RC is connected to the positive electrode of the power supply, the detection sheet resistor RD is grounded, and the fifth pin of the second operational amplifier U1B is grounded through the detection sheet resistor RD.

[0012] The compensation chip resistor RC and the detection chip resistor RD are packaged in the sensor housing. A 2.5VDC voltage is applied to one end of the compensation chip resistor RC. Current flows through the compensation chip resistor RC and the detection chip resistor RD, causing the compensation chip resistor RC and the detection chip resistor RD to heat up (RC and RD are resistors wound with platinum wire. They have the same parameters and will both heat up) to reach the operating temperature and output a detection voltage at the connection point between the two. In clean air, the ideal value of this voltage is 1.25V.

[0013] The eighth pin of the third operational amplifier U1C is connected to the passive low-pass filter circuit, the ninth pin of the third operational amplifier U1C is connected to the first pin of the first operational amplifier U1A through a ninth resistor R9, the ninth pin of the third operational amplifier U1C is connected to the eighth pin of the third operational amplifier U1C through an eleventh resistor R11, the tenth pin of the third operational amplifier U1C is connected to the seventh pin of the second operational amplifier U1B through a tenth resistor R10, and the tenth pin of the third operational amplifier U1C is grounded through a thirteenth resistor R13.

[0014] The passive low-pass filter circuit includes a twelfth resistor R12 and a first capacitor C1, one end of the twelfth resistor R12 is connected to the eighth pin of the third operational amplifier, the other end of the twelfth resistor R12 is grounded through the first capacitor C1, and the twelfth resistor R12 is electrically connected to the single-chip computer. The passive low-pass filter circuit is used to filter out high-frequency signals that enter the circuit. These signals are useless interference signals, which will cause deviations in the measurement results and affect the determination of the results. Therefore, the passive low-pass filter circuit can improve the measurement accuracy and reduce errors.

[0015] The beneficial effects of the utility model are:

[0016] The utility model is used in the production of industrial and commercial combustible gas detectors, and realizes automatic adjustment of the zero-point output parameters of sensors in different batches, which can reduce the overall production cost by 5%. At the same time, it avoids the zero-point adjustment operation in a complex on-site installation environment, further reducing the after-sales maintenance cost of the product, thereby improving the market competitiveness of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a circuit diagram of the utility model. DETAILED DESCRIPTION

[0018] The utility model will be further described below in conjunction with the accompanying drawings and the accompanying drawings.

[0019] In order to more clearly understand the above-mentioned purpose, features and advantages of the utility model, the utility model is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0020] The terms “first”, “second”, “third”, etc. are only used for distinguishing descriptions and should not be understood as indicating or implying relative importance.

[0021] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0023] Embodiment 1:

[0024] like Figure 1 As shown, a catalytic combustion gas sensor signal conditioning circuit includes an instrument amplifier circuit, a zero adjustment resistor network and a passive low-pass filter circuit;

[0025] The zero adjustment resistor network includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a fifth resistor R5; one end of the first resistor R1, the second resistor R2, and the third resistor R3 is connected to the single chip microcomputer ( Figure 1 Among them, P1, P2, and P3 are all set to OD (open drain) output, and the output state can be switched to output low level and high impedance state. P1, P2, and P3 can form eight different combinations for adjusting the reference voltage of the instrument amplifier circuit). The other ends of the first resistor R1, the second resistor R2, and the third resistor R3 are grounded through the fifth resistor R5, one end of the fourth resistor R4 is connected to the input voltage, and the other end of the fourth resistor is grounded through the fifth resistor R5; the zero point adjustment resistor network is used to change the output reference voltage of the instrument amplifier circuit.

[0026] The instrument amplifier circuit is used to amplify the difference between VINP and VINN, and the instrument amplifier circuit includes a first operational amplifier U1A, a second operational amplifier U1B and a third operational amplifier U1C;

[0027] The third pin of the first operational amplifier U1A is grounded via a fifth resistor R5, and the first pin of the first operational amplifier U1A is connected to the second pin of the first operational amplifier U1A via a sixth resistor R6;

[0028] The fifth pin of the second operational amplifier U1B is connected to the sensor, the sixth pin of the second operational amplifier U1B is connected to the second pin of the first operational amplifier U1A through the seventh resistor R7, and the seventh pin of the second operational amplifier U1B is connected to the sixth pin of the second operational amplifier U1B through the eighth resistor R8;

[0029] The sensor is used to output VINP. The sensor includes a compensation sheet resistor RC and a detection sheet resistor RD connected in series. One end of the compensation sheet resistor RC is connected to the positive electrode of the power supply, the detection sheet resistor RD is grounded, and the fifth pin of the second operational amplifier U1B is grounded through the detection sheet resistor RD.

[0030] The compensation chip resistor RC and the detection chip resistor RD are packaged in the sensor housing. A 2.5VDC voltage is applied to one end of the compensation chip resistor RC. Current flows through the compensation chip resistor RC and the detection chip resistor RD, causing the compensation chip resistor RC and the detection chip resistor RD to heat up (RC and RD are resistors wound with platinum wire. They have the same parameters and will both heat up) to reach the operating temperature and output a detection voltage at the connection point between the two. In clean air, the ideal value of this voltage is 1.25V.

[0031] The eighth pin of the third operational amplifier U1C is connected to the passive low-pass filter circuit, the ninth pin of the third operational amplifier U1C is connected to the first pin of the first operational amplifier U1A through a ninth resistor R9, the ninth pin of the third operational amplifier U1C is connected to the eighth pin of the third operational amplifier U1C through an eleventh resistor R11, the tenth pin of the third operational amplifier U1C is connected to the seventh pin of the second operational amplifier U1B through a tenth resistor R10, and the tenth pin of the third operational amplifier U1C is grounded through a thirteenth resistor R13;

[0032] The output voltage of the instrumentation amplifier circuit is:

[0033]

[0034] Note: R6=R8,R9=R10,R11=R13

[0035] The passive low-pass filter circuit includes a twelfth resistor R12 and a first capacitor C1, one end of the twelfth resistor R12 is connected to the eighth pin of the third operational amplifier, the other end of the twelfth resistor R12 is grounded through the first capacitor C1, and the twelfth resistor R12 is electrically connected to the single-chip computer. The passive low-pass filter circuit is used to filter out high-frequency signals that enter the circuit. These signals are useless interference signals, which will cause deviations in the measurement results and affect the determination of the results. Therefore, the passive low-pass filter circuit can improve the measurement accuracy and reduce errors.

[0036] The twelfth resistor R12 and the first capacitor C1 form an RC passive low-pass filter circuit to filter out the high-frequency burr signal output by the amplifier circuit. The low-pass filter cutoff frequency is:

[0037]

[0038] Specific working principle: The catalytic combustion gas sensor consists of two components: a detection plate (D) that reacts to combustible gas and a compensation plate (C) that does not react to combustible gas. Only the detection plate can burn in combustible gas, so the temperature of the detection plate rises and the resistance of the detection plate increases. On the contrary, because the compensation plate does not burn, its resistance does not change. Through an appropriate circuit, the change in resistance is converted into a change in voltage, and then the change in the concentration of the combustible gas is measured.

[0039] The present utility model is not limited to the above-mentioned optional implementation modes. Anyone can derive other various forms of products under the inspiration of the present utility model. However, no matter what changes are made in the shape or structure, all technical solutions that fall within the scope defined by the claims of the present utility model fall within the protection scope of the present utility model.

Claims

1. A catalytic combustion gas sensor signal conditioning circuit, characterized in that: Includes instrumentation amplifier circuit, zero adjustment resistor network and passive low-pass filter circuit; The zero adjustment resistor network includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a fifth resistor R5; one end of the first resistor R1, the second resistor R2, and the third resistor R3 is connected to the single chip microcomputer, and the other ends of the first resistor R1, the second resistor R2, and the third resistor R3 are grounded through the fifth resistor R5; one end of the fourth resistor R4 is connected to the input voltage, and the other end of the fourth resistor is grounded through the fifth resistor R5; The instrumentation amplifier circuit includes a first operational amplifier U1A, a second operational amplifier U1B and a third operational amplifier U1C; The third pin of the first operational amplifier U1A is grounded via a fifth resistor R5, and the first pin of the first operational amplifier U1A is connected to the second pin of the first operational amplifier U1A via a sixth resistor R6; The fifth pin of the second operational amplifier U1B is connected to the sensor, the sixth pin of the second operational amplifier U1B is connected to the second pin of the first operational amplifier U1A through the seventh resistor R7, and the seventh pin of the second operational amplifier U1B is connected to the sixth pin of the second operational amplifier U1B through the eighth resistor R8; The eighth pin of the third operational amplifier U1C is connected to the passive low-pass filter circuit, the ninth pin of the third operational amplifier U1C is connected to the first pin of the first operational amplifier U1A through a ninth resistor R9, the ninth pin of the third operational amplifier U1C is connected to the eighth pin of the third operational amplifier U1C through an eleventh resistor R11, the tenth pin of the third operational amplifier U1C is connected to the seventh pin of the second operational amplifier U1B through a tenth resistor R10, and the tenth pin of the third operational amplifier U1C is grounded through a thirteenth resistor R13; The passive low-pass filter circuit includes a twelfth resistor R12 and a first capacitor C1, one end of the twelfth resistor R12 is connected to the eighth pin of the third operational amplifier, the other end of the twelfth resistor R12 is grounded through the first capacitor C1, and the twelfth resistor R12 is electrically connected to the single-chip computer.

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