Current measurement circuit and apparatus for a quadrupole mass spectrometer

Abstract

The application discloses a current measurement circuit and device for a quadrupole mass spectrometer, and relates to the technical field of current measurement.The circuit comprises a current input end, an operational amplifier integral output module, a first negative feedback module and a second negative feedback module, the current input end is connected with the operational amplifier integral output module, the first negative feedback module and the second negative feedback module respectively, the operational amplifier integral output module is connected with the first negative feedback module and the second negative feedback module respectively, the first negative feedback module is provided with a first analog switch, the second negative feedback module is provided with a second analog switch, when the first analog switch is turned off, the first negative feedback module forms a first negative feedback loop, when the second analog switch is turned off, the second negative feedback module forms a second negative feedback loop, the operational amplifier integral output module uses positive current and negative current to offset the current to be detected to reach a balanced state, and the output voltage of the operational amplifier integral output module has a linear relationship with the input current.The circuit has the advantages of low cost and high measurement precision.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of current measurement, in particular to a current measurement circuit and device for a quadrupole mass spectrometer. BACKGROUND

[0002] A quadrupole mass spectrometer is an analytical instrument widely used in biological, medical, environmental science and other fields. Its core function is to analyze gas composition by measuring the size of ion current. The measurement principle of the mass spectrometer is based on the motion characteristics of ions in the quadrupole electric field. By applying a specific direct current and alternating current field, ions of different mass-to-charge ratios are stably passed in the electric field, thereby realizing separation and detection.

[0003] Currently, there are two types of measurement circuits for quadrupole mass spectrometers. One is to measure current by switching different sizes of feedback resistors (such as 500G, 15G, 470M, 13, etc.) through reed switches. This circuit uses Ohm's law (I=U / R) to calculate the current size, has high linearity, and can accurately measure the current. However, this circuit is prone to noise interference during gear switching, and the use of multiple high-precision resistors and reed switches increases the cost.

[0004] The other measurement circuit is to measure multiple orders of magnitude through a transistor logarithmic amplifier. This scheme uses the logarithmic amplification characteristics of the transistor to measure a wide range of currents. However, this circuit is susceptible to temperature drift, which reduces measurement accuracy. In particular, when measuring small currents (pA and below), the accuracy cannot meet the needs of high-precision analysis. In summary, the existing quadrupole mass spectrometer measurement circuits have the following technical problems: the reed switch resistor circuit has high linearity, but it is prone to noise interference during gear switching, affecting the measurement accuracy, and the cost is high; the transistor logarithmic amplifier circuit is susceptible to temperature drift, resulting in unstable measurement accuracy, especially when measuring small currents, it cannot achieve ideal accuracy. SUMMARY

[0005] The present application provides a current measurement circuit and device for a quadrupole mass spectrometer, which solves the problem of unstable measurement accuracy and high cost in the prior art.

[0006] The present application is achieved by the following technical solutions:

[0007] In a first aspect, the first embodiment of the present application provides a current measurement circuit for a quadrupole mass spectrometer, comprising: a current input end, an operational amplifier integral output module, a first negative feedback module and a second negative feedback module, wherein the current input end is connected with the operational amplifier integral output module, the first negative feedback module and the second negative feedback module respectively, the output end of the operational amplifier integral output module is connected with the first negative feedback module and the second negative feedback module respectively, the first negative feedback module is provided with a first analog switch, and the second negative feedback module is provided with a second analog switch,

[0008] The current input end is used for inputting a to-be-detected current into the operational amplifier integral output module.

[0009] The operational amplifier integral output module performs current integration on the to-be-detected current by using an integral capacitor of an operational amplifier, outputs a voltage signal, and inputs the voltage signal into the first negative feedback module and the second negative feedback module respectively.

[0010] When the first analog switch is turned off, the first negative feedback module is used for converting light energy into electric energy through a photovoltaic effect, generating a positive current compensation input into a negative phase input end of the operational amplifier integral output module, and forming a first negative feedback loop.

[0011] When the second analog switch is turned off, the second negative feedback module is used for converting light energy into electric energy through a photovoltaic effect, generating a negative current compensation input into the negative phase input end of the operational amplifier integral output module, making the negative phase input end of the operational amplifier integral output module current draw, and forming a second negative feedback loop.

[0012] The operational amplifier integral output module offsets the to-be-detected current by using the positive current and the negative current to achieve a balanced state, and the output voltage of the operational amplifier integral output module has a linear relationship with the input current.

[0013] Further, the first negative feedback module comprises a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a double NPN transistor, a first LED and a third LED, the negative electrode of the first LED is grounded, the positive electrode of the first LED is connected with the negative phase input end of the operational amplifier integral output module, one end of the second resistor, the first analog switch, the fourth resistor and the sixth resistor is connected with a power supply, the other end of the second resistor is connected with the positive electrode of the third LED, the negative electrode of the third LED is connected with the other end of the first analog switch and one collector of the double NPN transistor respectively, the other collector of the double NPN transistor is connected with the other end of the fourth resistor, one emitter of the double NPN transistor is connected with one end of the fifth resistor and the other end of the sixth resistor, the other end of the fifth resistor is grounded, the other emitter of the double NPN transistor is connected with one end of the third resistor, and the other end of the third resistor is connected with the output end of the operational amplifier integral output module.

[0014] Further, the second negative feedback module comprises a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a double PNP transistor, a second LED and a fourth LED, the positive pole of the second LED is connected with the ground, the negative pole of the second LED is connected with the negative phase input end of the operational amplifier integral output module, one end of the tenth resistor, the second analog switch, the twelfth resistor and the fourteenth resistor is connected with the ground, the other end of the tenth resistor is connected with the negative pole of the fourth LED, the positive pole of the fourth LED is connected with the other end of the second analog switch and one of the collector of the double PNP transistor, the other collector of the double PNP transistor is connected with the other end of the twelfth resistor, one of the emitter of the double PNP transistor is connected with one end of the thirteenth resistor and the other end of the fourteenth resistor, the other end of the thirteenth resistor is connected with the power supply, one of the emitter of the double NPN transistor is connected with one end of the eleventh resistor, the other end of the eleventh resistor is connected with the output end of the operational amplifier integral output module.

[0015] Further, the comparator circuit comprises a first comparator module and a second comparator module, the positive phase input end of the first comparator module is connected with the output end of the operational amplifier integral output module, the negative phase input end of the second comparator module is connected with the output end of the operational amplifier integral output module.

[0016] Further, the first LED, the second LED, the third LED and the fourth LED are selected from the same kind of infrared light emitting diode.

[0017] Further, the first LED and the third LED are located in a completely closed space isolated from external light sources, and the second LED and the fourth LED are located in a completely closed space isolated from external light sources.

[0018] Further, the integral capacitor adopts a polypropylene film capacitor.

[0019] Further, the integral capacitor adopts a C0G ceramic capacitor.

[0020] Further, the operational amplifier adopts AD4530 or LMP7721.

[0021] In the second aspect, another embodiment of the application provides a current measurement device for a quadrupole mass spectrometer, comprising the current measurement circuit for a quadrupole mass spectrometer described in the first embodiment.

[0022] Compared with the prior art, the application has the following advantages and beneficial effects:

[0023] The current measurement circuit and device for the quadrupole mass spectrometer provided by the embodiment of the application have the advantages of low cost and high measurement precision. The photovoltaic effect of the negative feedback module resets the integration capacitor, greatly reduces the leakage current while improving the reset speed, and improves the measurement accuracy. When the temperature changes, the dark current and light emitting efficiency drift of the two pairs of optocouplers are synchronized and automatically offset in the differential structure, realizing 0.2fA-level current measurement, and being suitable for superconducting device detection, ion beam analysis and other advanced scenes. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0025] Figure 1 The circuit diagram of the current measurement circuit for the quadrupole mass spectrometer provided by the first embodiment of the application is shown in FIG. 1.

[0026] Figure 2 The structure of the closed space is shown in FIG. 2.

[0027] Figure 3 The relationship curve between the voltage signal at the output end of the operational amplifier and the excitation current of LED3 and LED4 is shown in FIG. 3.

[0028] Figure 4 The circuit diagram of the first comparator module and the second comparator module in the current measurement circuit for the quadrupole mass spectrometer provided by another embodiment of the application is shown in FIG. 4. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the application more clear and obvious, the application will be further described in detail below with reference to the embodiments and drawings. The exemplary embodiments of the application and the description thereof are only used to explain the application, and should not be regarded as a limitation on the application.

[0030] Embodiment 1

[0031] As Figure 1As shown, the current measurement circuit for the quadrupole mass spectrometer provided by the first embodiment of the present application comprises a current input end, an operational amplifier integral output module, a first negative feedback module and a second negative feedback module, the current input end is connected with the operational amplifier integral output module, the first negative feedback module and the second negative feedback module respectively, the output end of the operational amplifier integral output module is connected with the first negative feedback module and the second negative feedback module respectively, the first negative feedback module is provided with a first analog switch, and the second negative feedback module is provided with a second analog switch,

[0032] The current input end is used for inputting the current to be detected into the operational amplifier integral output module.

[0033] The operational amplifier integral output module uses the integral capacitor of the operational amplifier to perform current integration on the current to be detected, outputs a voltage signal, and inputs the voltage signal into the first negative feedback module and the second negative feedback module respectively.

[0034] When the first analog switch is turned off, the first negative feedback module is used for converting light energy into electric energy through the photovoltaic effect, generating positive current compensation input into the negative phase input end of the operational amplifier integral output module, and forming a first negative feedback loop.

[0035] When the second analog switch is turned off, the second negative feedback module is used for converting light energy into electric energy through the photovoltaic effect, generating negative current compensation input into the negative phase input end of the operational amplifier integral output module, making the current of the negative phase input end of the operational amplifier integral output module draw out, and forming a second negative feedback loop.

[0036] The operational amplifier integral output module uses the positive current and the negative current to offset the current to be detected to achieve a balanced state, and the output voltage of the operational amplifier integral output module has a linear relationship with the input current.

[0037] The first negative feedback module comprises resistors R2, R3, R4, R5, R6, a double NPN transistor Q2, LED1 and LED3. The negative electrode of LED1 is connected to the ground. The positive electrode of LED1 is connected to the negative phase input end of the operational amplifier integral output module. One end of resistor R2, analog switch SW1, resistor R4 and resistor R6 is connected to the power supply. The other end of resistor R2 is connected to the positive electrode of LED3. The negative electrode of LED3 is connected to the other end of analog switch SW1 and one of the collector electrodes of double NPN transistor Q2. The other collector electrode of double NPN transistor Q2 is connected to the other end of resistor R4. One of the emitter electrodes of double NPN transistor Q2 is connected to one end of resistor R5 and the other end of resistor R6. The other end of resistor R5 is connected to the ground. The other emitter electrode of double NPN transistor Q2 is connected to one end of resistor R3. The other end of resistor R3 is connected to the output end of the operational amplifier integral output module. Double NPN transistor Q2 adopts MMDT3904. MMDT3904 is a double NPN transistor in a super small surface mount package. Two transistors are integrated in one package, mainly to meet the higher requirements of performance, space and efficiency in modern electronic circuit design.

[0038] The second negative feedback module comprises resistors R10, R11, R12, R13, R14, a double PNP transistor Q1, LED2 and LED4. The positive electrode of LED2 is connected to the ground. The negative electrode of LED2 is connected to the negative phase input end of the operational amplifier integral output module. One end of resistor R10, analog switch SW2, resistor R12 and resistor R14 is connected to the ground. The other end of resistor R10 is connected to the negative electrode of LED4. The positive electrode of LED4 is connected to the other end of analog switch SW2 and one of the collector electrodes of double PNP transistor Q1. The other collector electrode of double PNP transistor Q1 is connected to the other end of resistor R12. One of the emitter electrodes of double PNP transistor Q1 is connected to one end of resistor R13 and the other end of resistor R14. The other end of resistor R13 is connected to the power supply. The other emitter electrode of double PNP transistor Q1 is connected to one end of resistor R11. The other end of resistor R11 is connected to the output end of the operational amplifier integral output module.

[0039] LED1, LED2, LED3 and LED4 select the same kind of infrared light emitting diode. LED1 and LED3 are in a completely closed space isolated from external light sources. LED2 and LED4 are in a completely closed space isolated from external light sources. The space is formed by a copper shell and fluorine rubber. Two circuit boards are arranged on the upper and lower copper shells to form two closed light path channels. One of the two circuit boards is a current input measurement circuit (the current input end and the operational amplifier integral output module constitute), and the other is a current compensation circuit (the first negative feedback module and the second negative feedback module constitute). Such a structure can shield external light sources and improve the signal-to-noise ratio. Figure 2LED1 (sensitive) is only sensitive to the wavelength of LED3 (emitting), and vice versa, to ensure the highest photoelectric current conversion efficiency. When the temperature changes, the dark current and light emitting efficiency of the two pairs of optocouplers (LED1 / LED3 and LED2 / LED4) drift synchronously, which is automatically offset in the differential structure. The forward light intensity of the LED and the reverse photosensitive current have a symmetrical nonlinearity, and the linearity is improved after complementation.

[0040] The integral capacitor C1 is a polypropylene film capacitor or a C0G ceramic capacitor with a capacitance of 1-10 pF. The operational amplifier U1 uses a bias current of the order of fA, using an operational amplifier such as AD4530 or LMP7721.

[0041] The first negative feedback module generates a compensation input current, and the second negative feedback module generates a compensation output current. The operational amplifier U1 balances the compensation input current and the compensation output current with the current input from the input end. The node current of the negative phase input end of the operational amplifier is 0 in the balanced state. The current is injected or extracted to offset the current at the input end. At this time, the output voltage of the operational amplifier is linearly related to the input current.

[0042] Specifically, the circuit uses the integral capacitor C1 of the operational amplifier U1 to integrate the current and output a voltage signal. When the analog switches SW1 and SW2 are open, the operational amplifier U1 forms a negative feedback regulation. The output of the operational amplifier U1 adjusts the current flowing through LED3 and LED4 through the double NPN transistor Q2 and the double PNP transistor Q1. LED3 and LED4 convert photons (light waves) into electrons through the photovoltaic effect, and convert light energy into electrical energy, so that LED1 and LED2 generate current. Since the directions of LED1 and LED2 are different, LED1 generates a positive current through the photovoltaic effect, forms a compensation current i1 to the negative phase input end of the operational amplifier U1, flows into the integral capacitor C1, and forms a negative feedback. LED2 generates a negative current through the photovoltaic effect, forms a compensation current i2 to make the current of the negative phase input end of the operational amplifier U1 extracted, and forms a negative feedback. When the operational amplifier U1 reaches a stable state, the relationship between the compensation current i1, the compensation current i2, and the detected current i3 satisfies the following formula, with the input current direction being positive:

[0043] .

[0044] According to the actual point, the relationship curve between the output voltage signal of the operational amplifier Signal and the excitation current of LED3 (AM1 in the figure) and the excitation current of LED4 (AM2 in the figure) is as shown in Figure 3 The values of the compensation currents i1 and i2 can be obtained by the following formula:

[0045] ;

[0046] ;

[0047] wherein, is the excitation current flowing through the LED 3, is the reduction factor of the photovoltaic effect of the LED 3, is the excitation current flowing through the LED 4, is the reduction factor of the photovoltaic effect of the LED 4.

[0048] The reduction factor of the photovoltaic effect of the LED of different wavelengths is different due to different materials are not consistent, the same model are basically consistent, if there is an error, it can also be corrected to be consistent by calibration, and the required LED is selected according to the range to be measured, the GaAs infrared LED is selected, and the actual test finds that the LED, is about 1 / 1000, and the can be tested by a given current source.

[0049] When the analog switches SW1 and SW2 are closed, the feedback is only the integral capacitor C1, and the input current to be detected directly passes through the integral capacitor C1 for current integration, and the change slope is proportional to the current.

[0050] When the absolute value of the input current to be detected is greater than 1uA, the output of the operational amplifier U1 is between 0-2V and 3-5V, and the circuit can directly measure the current size, and the size and direction of the input current to be measured can be calculated according to the data table formed by the dot and the reduction factor of the photovoltaic effect of the corresponding LED.

[0051] When the absolute value of the input current to be detected is less than 1uA, the output of the operational amplifier U1 is between 2V-3V, and the current size can also be calculated according to the formula, but the measurement accuracy is affected by the resolution. On the basis of the circuit, a comparator circuit is added for current integration. When the operational amplifier U1 reaches balance, the analog switch SW1 and the analog switch SW2 are turned on, and the operational amplifier U1 no longer performs feedback adjustment. The input current directly passes through the integral capacitor C1 for current integration, and the integral value is output through the signal of the operational amplifier U1. The comparator circuit is shown in Figure 4 , and current integration calculation is performed. The comparator circuit includes a first comparator module and a second comparator module. The positive input end of the first comparator module is connected with the output end of the operational amplifier integration output module, and the negative input end of the second comparator module is connected with the output end of the operational amplifier integration output module.

[0052] When the residual gas analyzer selects the Faraday cup as the collector, the input is ion current, the current is positive, the input current directly passes through the integration capacitor C1 for current integration, the output voltage of the operational amplifier U1 will decrease, and the decrease slope is directly proportional to the current. The output of the operational amplifier U1 passes through the comparator U2, and the comparison value is set to 1V and 2V through the digital-to-analog converter DAC. When the output voltage of the operational amplifier U1 is less than 2V, the comparator U2 outputs a high level. When the output voltage of the operational amplifier U1 is greater than 2V, the comparator U2 outputs a low level. In addition, another comparator U3 outputs a high level when the output voltage of the operational amplifier U1 is greater than 1V, and outputs a low level when the output voltage of the operational amplifier U1 is less than 1V.

[0053] When the residual gas analyzer selects the electron multiplier as the collector, the input is electron current, the current is negative, the input current directly passes through C1 for current integration, and the output voltage of the operational amplifier U1 rises. When the voltage of the operational amplifier U1 is compared through the comparator U2, the comparison value is set to 3V and 4V through the digital-to-analog converter DAC. When the output voltage of the operational amplifier is less than 4V, the comparator U2 outputs a high level. When the output voltage of the operational amplifier is greater than 4V, the comparator U2 outputs a low level. In addition, another comparator U3 outputs a high level when the output voltage of the operational amplifier U1 is greater than 3V, and outputs a low level when the output voltage of the operational amplifier U1 is less than 3V.

[0054] When the output voltage of the operational amplifier U1 exceeds 4V or is less than 1V, the comparator U2 or the comparator U3 outputs a low level, and at the same time, the analog switch SW1 and the analog switch SW2 are turned off for a period of time for current compensation and reset. When the voltage of the operational amplifier U1 reaches equilibrium, the analog switch SW1 and the analog switch SW2 are turned on again to perform the next capacitor integration. The reset of the circuit uses photon reset, and the reset current is greatly reduced, which is almost non-existent.

[0055] When the outputs of the comparator U2 and the comparator U3 are both high levels, the integration capacitor C1 is in an integration state, and the current calculation formula is:

[0056] ;

[0057] Wherein, Q is the charge quantity of the capacitor, t is the time when both comparators are high, c is the capacitance value of the capacitor, is the changing voltage.

[0058] Since , Only the pulse timing of the single-chip microcomputer is needed to calculate the time t when both comparators are high, and the size of the current to be detected can be calculated.

[0059] The current measurement circuit for the quadrupole mass spectrometer provided by the embodiment has the advantages of low cost and high measurement accuracy. When measuring a large current of uA or more, the photoelectric current is used to offset the external input current, and high-precision balance measurement is achieved through light intensity closed-loop control. When measuring a small current of uA or less, the photoelectric current is used for reset, and the input current is integrated by a capacitor. The principle of the measurement method is that a stable integration capacitor is connected in the operational amplifier feedback loop, the weak current signal to be measured charges the capacitor, and the current signal is converted into a sawtooth voltage signal. The voltage signal is converted into a pulse output through a comparator circuit, and a single pulse represents a fixed charge amount. The total charge amount is proportional to the number of pulses, and the value of the weak current signal to be measured is obtained. However, the circuit of this method needs a reset circuit to charge or discharge the capacitor. The reset circuit is generally formed by connecting a diode in series with a resistor. This circuit has an unavoidable leakage current, which affects the accuracy of the circuit. The embodiment of the application uses the photovoltaic effect of an infrared diode to reset the integration capacitor, which improves the reset speed and greatly reduces the leakage current, improves the measurement accuracy, and can measure currents of two polarities. When the temperature changes, the dark current and light emitting efficiency drift of the two pairs of optocouplers are synchronized, and are automatically offset in the differential structure. Even the performance of the professional photodiode can be surpassed, 0.2fA-level current measurement is achieved, and the application is suitable for superconducting device detection, ion beam analysis and other advanced scenarios.

[0060] Another embodiment of the application provides a current measurement device for a quadrupole mass spectrometer, which includes the current measurement circuit for the quadrupole mass spectrometer described in the first embodiment.

[0061] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the application. It should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. A current measurement circuit for a quadrupole mass spectrometer, characterized in that, include: The system includes a current input terminal, an operational amplifier integration output module, a first negative feedback module, and a second negative feedback module. The current input terminal is connected to the operational amplifier integration output module, the first negative feedback module, and the second negative feedback module. The output terminal of the operational amplifier integration output module is connected to the first negative feedback module and the second negative feedback module. The first negative feedback module is equipped with a first analog switch, and the second negative feedback module is equipped with a second analog switch. The current input terminal is used to input the current to be detected into the operational amplifier integration output module; The operational amplifier integration output module uses the integration capacitor of the operational amplifier to integrate the current to be detected, outputs a voltage signal, and inputs the voltage signal into the first negative feedback module and the second negative feedback module respectively. When the first analog switch is turned off, the first negative feedback module is used to convert the voltage signal into electrical energy through the photovoltaic effect, and generate a positive current compensation input to the negative phase input terminal of the operational amplifier integration output module to form the first negative feedback loop. When the second analog switch is open, the second negative feedback module is used to convert the voltage signal into electrical energy through the photovoltaic effect, and generate a negative current compensation input to the negative phase input terminal of the operational amplifier integration output module, so that the current at the negative phase input terminal of the operational amplifier integration output module is extracted, forming a second negative feedback loop. The operational amplifier integration output module uses positive and negative currents to cancel out the current to be detected to achieve a balanced state, and the output voltage of the operational amplifier integration output module has a linear relationship with the input current. The first negative feedback module includes a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a dual NPN transistor, a first LED, and a third LED. The negative terminal of the first LED is grounded, and the positive terminal of the first LED is connected to the negative input terminal of the operational amplifier integration output module. One end of the second resistor, the first analog switch, the fourth resistor, and the sixth resistor is connected to the power supply. The other end of the second resistor is connected to the positive terminal of the third LED. The negative terminal of the third LED is connected to the other end of the first analog switch and one collector of the dual NPN transistor. The other collector of the dual NPN transistor is connected to the other end of the fourth resistor. One emitter of the dual NPN transistor is connected to one end of the fifth resistor and the other end of the sixth resistor. The other end of the fifth resistor is grounded. The other emitter of the dual NPN transistor is connected to one end of the third resistor. The other end of the third resistor is connected to the output terminal of the operational amplifier integration output module. The second negative feedback module includes a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a dual PNP transistor, a second LED, and a fourth LED. The positive terminal of the second LED is grounded, and the negative terminal of the second LED is connected to the negative input terminal of the operational amplifier integration output module. One end of the tenth resistor, the second analog switch, the twelfth resistor, and the fourteenth resistor is grounded, and the other end of the tenth resistor is connected to the negative terminal of the fourth LED. The positive terminal of the fourth LED is connected to the other end of the second analog switch and one collector of the dual PNP transistor. The other collector of the dual PNP transistor is connected to the other end of the twelfth resistor. One emitter of the dual PNP transistor is connected to one end of the thirteenth resistor and the other end of the fourteenth resistor. The other end of the thirteenth resistor is connected to a power supply. The other emitter of the dual PNP transistor is connected to one end of the eleventh resistor, and the other end of the eleventh resistor is connected to the output terminal of the operational amplifier integration output module. The first LED, the second LED, the third LED, and the fourth LED are all made of the same type of infrared light-emitting diode.

2. The current measurement circuit for a quadrupole mass spectrometer according to claim 1, characterized in that, It also includes a comparator circuit, which includes a first comparator module and a second comparator module. The non-inverting input terminal of the first comparator module is connected to the output terminal of the operational amplifier integrator output module, and the negative-inverting input terminal of the second comparator module is connected to the output terminal of the operational amplifier integrator output module.

3. The current measurement circuit for a quadrupole mass spectrometer according to claim 1, characterized in that, The first LED and the third LED are in a completely sealed space that isolates them from external light sources, and the second LED and the fourth LED are in a completely sealed space that isolates them from external light sources.

4. The current measurement circuit for a quadrupole mass spectrometer according to claim 1, characterized in that, The integrating capacitor is a polypropylene film capacitor.

5. The current measurement circuit for a quadrupole mass spectrometer according to claim 1, characterized in that, The integrating capacitor is a C0G ceramic capacitor.

6. The current measurement circuit for a quadrupole mass spectrometer according to claim 1, characterized in that, The operational amplifier used is either AD4530 or LMP7721.

7. A current measuring device for a quadrupole mass spectrometer, characterized in that, Includes the current measurement circuit for a quadrupole mass spectrometer as described in any one of claims 1-6.

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