Hydrogen flame ionization detection converter

Abstract

A hydrogen flame ionization detection converter comprises a digital signal processing unit and an analog signal processing unit, and the analog signal processing unit comprises an analog signal acquisition module, an analog signal processing module and a signal conversion chip. The analog signal acquisition module is used for acquiring a signal from a hydrogen flame ion detector, the analog signal processing module comprises an analog signal amplification unit and a signal bias circuit unit, and the analog signal amplification unit is used for processing an ion current signal acquired by the analog signal acquisition module into a voltage signal with a narrowed output range; the signal bias circuit unit is used for enabling a voltage signal output by the analog signal amplification unit to fall within a common-mode signal range of the signal conversion chip, and the signal conversion chip is used for converting an analog signal into a digital signal and transmitting the digital signal to the digital signal processing unit through the magnetic isolation chip. And the digital signal processing unit is used for transmitting the processed signal to the mainboard.

Description

Technical Field

[0001] The invention relates to the field of hydrogen flame ionization detectors, and in particular to a hydrogen flame ionization detection converter. Background Art

[0002] The hydrogen flame ionization detector is a detector that uses hydrogen flame as an ionization source to ionize organic matter and generate electrical signals. The effective ion current range detected by the hydrogen flame ionization detector is 10 -14 A~10 -6 A. Existing hydrogen flame ionization converters mostly use transimpedance amplification to convert the collected ion flow into a voltage signal for display by the workstation. The design of transimpedance amplification is relatively complex, requiring precise control of the resistance of the feedback resistor, the layout and wiring of the circuit, and other factors. The required resistance is extremely high, and the transimpedance used is fixed (GΩ level). When the ion flow is too large, the transimpedance is switched to a smaller resistance to achieve the required linearity index (≥106). While amplifying the signal, the noise at the input end may also be amplified. The performance of the transimpedance amplifier may be affected by temperature. Temperature changes may cause changes in parameters such as resistance and capacitance of components in the circuit, thereby affecting the amplifier's gain, bandwidth and other performance indicators. The accuracy, temperature drift and thermal noise of the resistor will cause the detection value to shift, the baseline noise to be large, and the linearity will be affected when the relay is switched. Therefore, how to optimize the detection range of hydrogen flame ions, improve detection accuracy and reduce noise is an urgent problem to be solved. Summary of the invention

[0003] The purpose of the present invention is to provide a hydrogen flame ionization detection converter in view of the corresponding deficiencies of the prior art. The converter adopts a logarithmic amplification method to increase the detection range of hydrogen flame ions, a 32-bit ADC chip is used to identify the collected signal, a CPU performs digital processing and then transmits the processing result to a workstation for display via a 485 chip, a PCB material adopts a plate with a larger body resistivity such as a ceramic substrate to reduce the leakage current of the circuit itself, and the electromagnetic shielding of the sensitive circuit is a shielding cover with aluminum outside and steel inside.

[0004] The objective of the present invention is achieved by adopting the following scheme: a hydrogen flame ionization detection converter, comprising a digital signal processing unit and an analog signal processing unit, wherein the analog signal processing unit comprises an analog signal acquisition module, an analog signal processing module, and a signal conversion chip; the analog signal acquisition module is used to collect signals from a hydrogen flame ionization detector, the analog signal processing module comprises an analog signal amplification unit and an analog signal bias circuit unit, the analog signal amplification unit is used to process the ion flow signal collected by the analog signal acquisition module into a voltage signal with a reduced output range, the analog signal bias circuit unit is used to make the voltage signal output by the analog signal amplification unit fall within the common mode signal range of the signal conversion chip, the signal conversion chip is used to convert the analog signal into a digital signal, and transmit it to the digital signal processing unit via a magnetic isolation chip, and the digital signal processing unit is used to transmit the processed signal to a mainboard.

[0005] The analog signal amplification unit includes a bias current circuit, a bias current operational amplifier circuit, and a cross-group circuit. The voltage end of the bias current circuit is connected to a reference voltage, and the output end is connected to the bias current operational amplifier circuit. The signal end of the bias current operational amplifier circuit is connected to an analog signal acquisition module. The signal input end of the cross-group circuit is connected to the bias current operational amplifier circuit, and the output end is connected to the signal bias circuit unit.

[0006] The bias current circuit includes a first operational amplifier U16A and a first high-gain chip Q1C. The inverting input terminal of the first operational amplifier U16A is connected to a reference voltage via a resistor R60, the non-inverting input terminal is connected to an analog ground, and the reference voltage is connected via a capacitor C57. The output terminal is connected to the bias current operational amplifier circuit via a resistor R63. The collector of the first high-gain chip Q1C is connected to the output terminal of the first operational amplifier U16A via a capacitor C54, the emitter is connected to the bias current operational amplifier circuit, and the base is connected to the analog ground.

[0007] The bias current operational amplifier circuit includes a second operational amplifier U15, a second high-gain chip Q1B, and a third high-gain chip Q1A. The same-direction input terminal of the second operational amplifier U15 is connected to the bias current circuit, the reverse input terminal is connected to the analog signal acquisition module, the output terminal is connected in parallel with the emitters of the second high-gain chip Q1B and the third high-gain chip Q1A via a resistor R50, the collector of the second high-gain chip Q1B is connected to the analog signal acquisition module, the base is connected to the same-direction input terminal of the second operational amplifier U15, the emitters of the second high-gain chip Q1B and the third high-gain chip Q1A are connected to the analog ground via a capacitor C53, and the base and collector of the third high-gain chip Q1A are connected to the transimpedance circuit.

[0008] The transimpedance circuit includes a third operational amplifier U16B and a fourth high-gain chip Q1D. The non-inverting input terminal of the third operational amplifier U16B is connected to the analog ground, the reverse input terminal is connected to the collector of the fourth high-gain chip Q1D, the output terminal is connected to the signal bias circuit unit via a resistor R51, and the resistor R51 is connected to the analog ground via a capacitor C50. A parallel resistor R47 and a capacitor C46 are connected between the reverse input terminal and the output terminal of the third operational amplifier U16B. The emitter of the fourth high-gain chip Q1D is connected to the collector and base of the third high-gain chip Q1A, and the base of the fourth high-gain chip Q1D is connected to the analog ground.

[0009] The analog signal bias circuit unit comprises a voltage follower circuit and an adder circuit. The voltage ends of the voltage follower circuit and the adder circuit are connected to a reference voltage. The input end of the adder circuit is connected to a signal amplification unit, and the output end is connected to an ADC chip.

[0010] The follower circuit includes a fourth operational amplifier U24A, the same-direction input terminal of the fourth operational amplifier U24A is connected to the reference voltage via a resistor R82, and is connected to the analog ground via a resistor R86, the output terminal is respectively connected to the reference voltage and capacitor C49 via a resistor R57, the capacitor is connected to the analog ground, and the reverse input terminal is connected to the resistor R57.

[0011] The adding circuit includes a fifth operational amplifier U24B, the inverting input terminal of the fifth operational amplifier U24B is connected to the analog ground via a resistor R83, the non-inverting input terminal is connected to the signal amplification unit via a resistor R85, and is connected to the reference voltage via a resistor R87. The resistor R87 is connected in parallel with a capacitor C49. The output terminal of the fifth operational amplifier U24B is connected to the ADC chip via a resistor R84, and the resistor R84 is connected to the analog ground via a capacitor C58. A parallel resistor R67 and capacitor C68 are connected between the inverting input terminal and the output terminal of the fifth operational amplifier U24B.

[0012] The hydrogen flame ionization detection converter conversion circuit adopts a ceramic substrate.

[0013] The conversion circuit is provided with a shielding cover with aluminum outer surface and steel inner surface.

[0014] Using the above scheme, a hydrogen flame ionization detection converter includes a digital signal processing unit and an analog signal processing unit. The analog signal processing unit includes an analog signal acquisition module, an analog signal processing module, and a signal conversion chip. The analog signal acquisition module is used to collect signals from the hydrogen flame ionization detector. The analog signal processing module includes an analog signal amplification unit and an analog signal bias circuit unit. The analog signal amplification unit is used to process the ion flow signal collected by the analog signal acquisition module into a voltage signal with a smaller output range. The analog signal bias circuit unit is used to make the voltage signal output by the analog signal amplification unit fall within the common mode signal range of the signal conversion chip. The signal conversion chip is used to convert the analog signal into a digital signal and transmit it to the digital signal processing unit via a magnetic isolation chip. The digital signal processing unit is used to transmit the processed signal to the mainboard.

[0015] The analog signal amplification unit includes a bias current circuit, a bias current operational amplifier circuit, and a cross-group circuit. The voltage end of the bias current circuit is connected to a reference voltage, and the output end is connected to the bias current operational amplifier circuit. The signal end of the bias current operational amplifier circuit is connected to an analog signal acquisition module. The signal input end of the cross-group circuit is connected to the bias current operational amplifier circuit, and the output end is connected to the signal bias circuit unit.

[0016] The bias current circuit is used to increase the weak ion flow of the collector. The bias current operational amplifier circuit performs nonlinear amplification on the input signal so that the output signal and the input signal have a logarithmic function relationship. The bias current operational amplifier circuit processes the ion flow signal into a voltage signal with a smaller output range, and uses a logarithmic current amplification method to increase the effective range of 10 -14 A~10 -6 The ion flow of A is converted into a voltage signal without causing voltage over-limit, which simplifies the operation and reduces noise compared with traditional methods.

[0017] The analog signal bias circuit unit includes a follower circuit and an adder circuit, wherein the voltage end of the follower circuit is connected to a reference voltage, the voltage end of the adder circuit is connected to the reference voltage, the input end of the adder circuit is connected to a signal amplification unit, and the output end is connected to an ADC chip.

[0018] The voltage follower circuit can ensure that a high linear relationship is maintained between the output voltage and the input voltage. The adding circuit raises the collected voltage signal as the collection positive terminal of the ADC chip, and the reference voltage is the negative terminal.

[0019] The hydrogen flame ionization detection converter conversion circuit adopts a ceramic substrate, which can reduce the leakage current of the PCB board.

[0020] The conversion circuit adopts a shielding cover with aluminum outer layer and steel inner layer, and the shielding cover with aluminum outer layer and steel inner layer performs electromagnetic shielding to protect the sensitive circuit (logarithmic amplifier circuit) and reduce output noise.

[0021] The advantages of the present invention are that a logarithmic amplification method is used to replace the traditional cross-group method, the range of the detection signal is increased, the output noise is reduced, a 32-bit ADC chip is used to improve the detection accuracy, a CPU is used to digitally process the collected signal, and the signal is transmitted to the workstation via a 485 chip, thereby improving the anti-interference ability of the signal, a ceramic plate is used to reduce leakage current, and an outer aluminum and inner steel shielding cover is used to further reduce noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Design a block diagram for a hydrogen flame detector conversion circuit;

[0023] Figure 2 is a circuit diagram of an analog signal amplification unit;

[0024] Figure 3 This is a circuit diagram of an analog signal bias circuit unit. DETAILED DESCRIPTION

[0025] like Figures 1 to 3 As shown, a hydrogen flame ionization detection converter includes a digital signal processing unit and an analog signal processing unit. The analog signal processing unit includes an analog signal acquisition module, an analog signal processing module, and a signal conversion chip; the analog signal acquisition module is used to collect signals from the hydrogen flame ionization detector, the analog signal processing module includes an analog signal amplification unit and an analog signal bias circuit unit, the analog signal amplification unit is used to process the ion flow signal collected by the analog signal acquisition module into a voltage signal with a smaller output range, the analog signal bias circuit unit is used to make the voltage signal output by the analog signal amplification unit fall within the common mode signal range of the signal conversion chip, the signal conversion chip is used to convert the analog signal into a digital signal, and transmit it to the digital signal processing unit via a magnetic isolation chip, and the digital signal processing unit is used to transmit the processed signal to the mainboard.

[0026] The analog signal amplification unit includes a bias current circuit, a bias current operational amplifier circuit, and a cross-group circuit. The voltage end of the bias current circuit is connected to a reference voltage, and the output end is connected to the bias current operational amplifier circuit. The signal end of the bias current operational amplifier circuit is connected to an analog signal acquisition module. The signal input end of the cross-group circuit is connected to the bias current operational amplifier circuit, and the output end is connected to the signal bias circuit unit.

[0027] The bias current circuit includes a first operational amplifier U16A and a first high-gain chip Q1C. The second pin of the first operational amplifier U16A is connected to a reference voltage of 2.5V via a resistor R60, the third pin is connected to an analog ground, and is connected to the reference voltage of 2.5V via a capacitor C57. The first pin is connected to the bias current operational amplifier circuit via a resistor R63. The fourth pin is connected to a negative voltage of -5V and is connected to an analog ground via a capacitor C51. The eighth pin is connected to a positive voltage of +5V and is connected to an analog ground via a capacitor C60. The collector of the first high-gain chip Q1C is connected to the first pin of the first operational amplifier U16A via a capacitor C54, the emitter is connected to the bias current operational amplifier circuit, and the base is connected to the analog ground.

[0028] The bias current operational amplifier circuit includes a second operational amplifier U15, a second high-gain chip Q1B, and a third high-gain chip Q1A. The first pin of the second operational amplifier U15 is connected to the bias current circuit, the eighth pin is connected to the analog signal acquisition module, the sixth pin is connected in parallel with the emitters of the second high-gain chip Q1B and the third high-gain chip Q1A via a resistor R50, the collector of the second high-gain chip Q1B is connected to the analog signal acquisition module, the base is connected to the first pin of the second operational amplifier U15, the emitters of the second high-gain chip Q1B and the third high-gain chip Q1A are connected to the analog ground via a capacitor C53, and the base and collector of the third high-gain chip Q1A are connected to the transimpedance circuit.

[0029] The transimpedance circuit includes a third operational amplifier U16B and a fourth high-gain chip Q1D. The fifth pin of the third operational amplifier U16B is connected to the analog ground, the sixth pin is connected to the collector of the fourth high-gain chip Q1D, the seventh pin is connected to the signal bias circuit unit via a resistor R51, and the resistor R51 is connected to the analog ground via a capacitor C50. A parallel resistor R47 and a capacitor C46 are connected between the sixth pin and the seventh pin of the third operational amplifier U16B. The emitter of the fourth high-gain chip Q1D is connected to the collector and the base of the third high-gain chip Q1A, and the base of the fourth high-gain chip Q1D is connected to the analog ground.

[0030] The first operational amplifier U16A and the third operational amplifier U16B adopt the OP297GSZ-REEL7 model, the second operational amplifier U15 adopts the ADA4530-1 model, and the first high-gain chip Q1C, the second high-gain chip Q1B, the third high-gain chip Q1A, and the fourth high-gain chip Q1D all adopt the MAT14 chip.

[0031] The analog signal bias circuit unit comprises a voltage follower circuit and an adder circuit. The voltage ends of the voltage follower circuit and the adder circuit are connected to a reference voltage. The input end of the adder circuit is connected to a signal amplification unit, and the output end is connected to an ADC chip.

[0032] The follower circuit includes a fourth operational amplifier U24A, a third pin of the fourth operational amplifier U24A is connected to a reference voltage of 2.5V via a resistor R82, and is connected to an analog ground via a resistor R86, a first pin is connected to a reference voltage and a capacitor C49 via a resistor R57, and the capacitor is connected to an analog ground, and a second pin is connected to the resistor R57.

[0033] The adding circuit includes a fifth operational amplifier U24B, the sixth pin of the fifth operational amplifier U24B is connected to the analog ground via a resistor R83, the fifth pin is connected to the signal amplification unit via a resistor R85, and is connected to the reference voltage via a resistor R87, the resistor R87 is connected in parallel with a capacitor C49, the output end of the fifth operational amplifier U24B is connected to the ADC chip via a resistor R84, the resistor R84 is connected to the analog ground via a capacitor C58, and a parallel resistor R67 and capacitor C68 are connected between the sixth pin and the seventh pin of the fifth operational amplifier U24B.

[0034] The fourth operational amplifier U24A and the fifth operational amplifier U24B are of OPA2335AIDR model, the ADC chip is of ADS1283 model, and the magnetic isolation chip is of CA-IS3763LW and CA-IS3760LW model.

[0035] The hydrogen flame ionization detection converter conversion circuit uses a volume resistivity of 10 14 Ceramic substrates with a resistance of Ω·cm or more.

[0036] The hydrogen flame ionization detection converter conversion circuit is provided with a shielding cover with aluminum outer layer and steel inner layer, the relative conductivity of the aluminum layer material is 0.61, and the relative magnetic permeability of the steel is 1000.

[0037] The above technical solution is used to make the following embodiments:

[0038] A polarization high voltage of 200V or -200V is applied to the nozzle of the hydrogen flame ion detector to form an ion flow collection electric field. The collecting electrode at a distance of 5 to 9 mm from the nozzle is connected to the input port of the amplifier circuit through a platinum wire.

[0039] The ion flow obtained by the collector enters the analog signal processing module for signal processing. First, the bias current circuit is composed of the U16A precision operational amplifier and its peripheral components to increase the weak ion flow of the collector. Its output voltage value is The output current is Among them U Tis the temperature voltage equivalent of the PN junction, I s is the reverse saturation current, U 16Aout Connected to the base of Q1B, the effect of increasing the weak ion current is achieved. Secondly, U15 and its surrounding components form a logarithmic amplifier circuit The reverse saturation current I of transistor 1 is offset by Q1A. s , Among them I c is the collector current of Q1A. Finally, U16B and its peripheral devices form a cross-group circuit, and U16B and Q1D reversely solve I 1c Collector current When the input signal is below 10pA, the PN junction characteristic equation of the logarithmic circuit composed of Q1B needs to be modified to Then bring it into the calculation. From the final output transfer function, we can get that if the input ion current range is 10 6 , then the output voltage range is 10 3 .

[0040] The common-mode signal range of the 32-bit ADC chip is (AVSS+0.7, ADD-1.25)V, so the amplified voltage signal needs to fall within the recognition range. The voltage divider follower circuit composed of U24A provides a voltage reference. Then U24B forms the adding circuit

[0041] U 24Bout =U 24Aout +U 16Bout Among them, R 67 =R 83 =R 85 =R 87 , the collected voltage signal is raised as the positive terminal of the ADC chip, and the reference voltage is the negative terminal.

[0042] Finally, the digital signal after analog-to-digital conversion by the ADC chip is handed over to the CPU for processing through the magnetic isolation chip. Magnetic isolation can prevent the digital signal from affecting the analog signal, and then the CPU processes it according to the transfer function. Back-calculation is performed to linearize the voltage value into the original ion current value, which is then transmitted to the workstation via the 485 chip.

[0043] Device Description:

[0044] U16A and its peripheral circuits form a voltage bias circuit:

[0045] U15 is a fA class bias current operational amplifier circuit:

[0046] The collector voltage of Q1A is:

[0047] U16B and its peripheral devices form a transimpedance circuit:

[0048] U24A and its peripheral devices form a voltage follower circuit:

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A hydrogen flame ionization detection converter, comprising a digital signal processing unit and an analog signal processing unit, It is characterized in that The analog signal processing unit includes an analog signal acquisition module, an analog signal processing module, and a signal conversion chip; the analog signal acquisition module is used to collect signals from a hydrogen flame ion detector, the analog signal processing module includes an analog signal amplification unit and an analog signal bias circuit unit, the analog signal amplification unit is used to process the ion flow signal collected by the analog signal acquisition module into a voltage signal with a smaller output range, the analog signal bias circuit unit is used to make the voltage signal output by the analog signal amplification unit fall within the common mode signal range of the signal conversion chip, the signal conversion chip is used to convert the analog signal into a digital signal, and transmit it to the digital signal processing unit via a magnetic isolation chip, and the digital signal processing unit is used to transmit the processed signal to the mainboard.

2. The hydrogen flame ionization detection converter according to claim 1, It is characterized in that The analog signal amplification unit includes a bias current circuit, a bias current operational amplifier circuit, and a cross-group circuit. The voltage end of the bias current circuit is connected to a reference voltage, and the output end is connected to the bias current operational amplifier circuit. The signal end of the bias current operational amplifier circuit is connected to an analog signal acquisition module. The signal input end of the cross-group circuit is connected to the bias current operational amplifier circuit, and the output end is connected to the signal bias circuit unit.

3. The hydrogen flame ionization detection converter according to claim 2, It is characterized in that The bias current circuit includes a first operational amplifier U16A and a first high-gain chip Q1C. The inverting input terminal of the first operational amplifier U16A is connected to a reference voltage via a resistor R60, the non-inverting input terminal is connected to an analog ground, and the reference voltage is connected via a capacitor C57. The output terminal is connected to the bias current operational amplifier circuit via a resistor R63. The collector of the first high-gain chip Q1C is connected to the output terminal of the first operational amplifier U16A via a capacitor C54, the emitter is connected to the bias current operational amplifier circuit, and the base is connected to the analog ground.

4. The hydrogen flame ionization detection converter according to claim 2, It is characterized in that The bias current operational amplifier circuit includes a second operational amplifier U15, a second high-gain chip Q1B, and a third high-gain chip Q1A. The same-direction input terminal of the second operational amplifier U15 is connected to the bias current circuit, the reverse input terminal is connected to the analog signal acquisition module, the output terminal is connected in parallel with the emitters of the second high-gain chip Q1B and the third high-gain chip Q1A via a resistor R50, the collector of the second high-gain chip Q1B is connected to the analog signal acquisition module, the base is connected to the same-direction input terminal of the second operational amplifier U15, the emitters of the second high-gain chip Q1B and the third high-gain chip Q1A are connected to the analog ground via a capacitor C53, and the base and collector of the third high-gain chip Q1A are connected to the transimpedance circuit.

5. The hydrogen flame ionization detection converter according to claim 2, It is characterized in that The transimpedance circuit includes a third operational amplifier U16B and a fourth high-gain chip Q1D. The non-inverting input terminal of the third operational amplifier U16B is connected to the analog ground, the reverse input terminal is connected to the collector of the fourth high-gain chip Q1D, the output terminal is connected to the signal bias circuit unit via a resistor R51, and the resistor R51 is connected to the analog ground via a capacitor C50. A parallel resistor R47 and a capacitor C46 are connected between the reverse input terminal and the output terminal of the third operational amplifier U16B. The emitter of the fourth high-gain chip Q1D is connected to the collector and base of the third high-gain chip Q1A, and the base of the fourth high-gain chip Q1D is connected to the analog ground.

6. The hydrogen flame ionization detection converter according to claim 1, It is characterized in that The analog signal bias circuit unit comprises a voltage follower circuit and an adder circuit. The voltage ends of the voltage follower circuit and the adder circuit are connected to a reference voltage. The input end of the adder circuit is connected to a signal amplification unit, and the output end is connected to an ADC chip.

7. The hydrogen flame ionization detection converter according to claim 6, It is characterized in that The follower circuit includes a fourth operational amplifier U24A, the same-direction input terminal of the fourth operational amplifier U24A is connected to the reference voltage via a resistor R82, and is connected to the analog ground via a resistor R86, the output terminal is respectively connected to the reference voltage and capacitor C49 via a resistor R57, the capacitor is connected to the analog ground, and the reverse input terminal is connected to the resistor R57.

8. The hydrogen flame ionization detection converter according to claim 6, It is characterized in that The adding circuit includes a fifth operational amplifier U24B, the inverting input terminal of the fifth operational amplifier U24B is connected to the analog ground via a resistor R83, the non-inverting input terminal is connected to the signal amplification unit via a resistor R85, and is connected to the reference voltage via a resistor R87. The resistor R87 is connected in parallel with a capacitor C49. The output terminal of the fifth operational amplifier U24B is connected to the ADC chip via a resistor R84, and the resistor R84 is connected to the analog ground via a capacitor C58. A parallel resistor R67 and capacitor C68 are connected between the inverting input terminal and the output terminal of the fifth operational amplifier U24B.

9. The hydrogen flame ionization detection converter according to claim 1, It is characterized in that The hydrogen flame ionization detection converter conversion circuit adopts a ceramic substrate.

10. The hydrogen flame ionization detection converter according to claim 1, It is characterized in that The conversion circuit is provided with a shielding cover with aluminum outer surface and steel inner surface.

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