A self-adjusting circuit and method for electron multiplier gain

Abstract

The invention discloses an electron multiplier gain self-adjusting circuit, which comprises: an amplifying unit for converting and amplifying an output current signal of the electron multiplier into a voltage signal; a comparing unit comprising a first comparator provided with a first threshold voltage and a second comparator provided with a second threshold voltage; the amplified voltage signal is subjected to threshold voltage comparison by the first comparator and the second comparator respectively; a counting unit comprising a first counter for counting the output of the first comparator and a second counter for counting the output of the second comparator; a control unit for calculating the ratio between the output of the first counter and the output of the second counter; when the ratio is less than the ratio threshold, the control unit adjusts the DC voltage at both ends of the electron multiplier so that the electron multiplier gain increases and enters a self-adjusting state, until the ratio is equal to 1 and enters a stable state. The invention realizes online and real-time automatic adjustment of the electron multiplier gain through a method of comparing double threshold voltages, dividing after counting and then comparing, and is simple to operate.

Description

Technical Field

[0001] The present invention relates to the technical field of triple quadrupole mass spectrometers, and more specifically, to a self-adjusting circuit and method for electron multiplier gain. Background Art

[0002] A mass spectrometer is generally composed of several main parts, such as an ion source system, an ion optical system, a radio frequency power supply system, and a signal detection system. The mass spectrometer signal detection system generally uses an electron multiplier as a detector. When it is working, a DC voltage V is applied to both ends of the electron multiplier. CEM , a uniform axial electric field is established. After the charged particles such as ions enter the electron multiplier, they collide with the inner surface of the tube and stimulate secondary electrons. CEM The generated axial electric field accelerates the generation of enough secondary electrons, which, after repeated collisions, produce a gain of 10 at the high potential end of the electron multiplier. 8 The electron beam is output by the signal processing circuit to detect the intensity of the mass spectrometer signal. The materials commonly used to make electron multipliers are mainly high-lead glass and ceramic semiconductors. However, the life of these two materials will decrease during long-term operation, causing the electron multiplier gain to decrease. According to the decrease in gain, the DC voltage V at both ends of the electron multiplier is adjusted CEM , so that the electron multiplier gain remains in a stable state, thereby keeping the mass spectrometer signal intensity in a stable state.

[0003] At present, for a mass spectrometer in normal use, there is no effective automatic detection method for the decrease of the electron multiplier gain. It requires very experienced engineers to detect the decrease of the gain according to the changes in the spectrum. The gain adjustment also requires engineers to adjust according to their experience and the changes in the spectrum, which means that the user of the mass spectrometer needs to have a lot of experience, which brings great inconvenience to the mass spectrometer users during use. The current online detection methods of the electron multiplier gain can be mainly divided into the standard gas method and the electron flow injection method. The standard gas method will cause the mass spectrometer to wait for a period of time after the gain adjustment is completed before it can be used. The electron flow injection method requires a more complex electron flow generation device and destroys the vacuum, which is more expensive and less efficient. Summary of the invention

[0004] In view of the deficiencies in the above-mentioned technologies, the present invention provides an electron multiplier gain self-adjusting circuit and method, which realizes online and real-time automatic adjustment of the electron multiplier gain by setting a dual threshold voltage comparison and a method of dividing after counting and then comparing, and is simple to operate.

[0005] In order to achieve these purposes and other advantages according to the present invention, the present invention is implemented by the following technical solutions:

[0006] An embodiment of the present invention provides an electron multiplier gain self-adjusting circuit, which includes:

[0007] An amplifying unit, which is used to convert and amplify the output current signal of the electron multiplier into a voltage signal;

[0008] A comparison unit, comprising a first comparator with a first threshold voltage and a second comparator with a second threshold voltage; the amplified voltage signal is respectively compared with the threshold voltage by the first comparator and the second comparator;

[0009] a counting unit, comprising a first counter and a second counter, wherein the first counter counts the output of the first comparator, and the second counter counts the output of the second comparator;

[0010] a control unit, configured to calculate a ratio between the first counter output and the second counter output;

[0011] When the ratio is less than a ratio threshold, the control unit adjusts the DC voltage across the electron multiplier so that the electron multiplier gain increases and enters a self-regulating state, until the ratio is equal to 1 and enters a stable state.

[0012] Preferably, it also includes:

[0013] A DA conversion unit is communicatively connected to the control unit and the electron multiplier respectively; the control unit adjusts the DC voltage across the electron multiplier through the DA conversion unit so that the electron multiplier gain is increased.

[0014] Preferably, the amplification unit includes a signal amplifier, a second resistor and a fourth resistor; the comparison unit also includes a first resistor, a third resistor, a fifth resistor and a sixth resistor;

[0015] The output current signal of the electron multiplier enters the signal amplifier through the in-phase input terminal of the signal amplifier, is converted into a voltage signal and amplified, and the amplified voltage signal enters the first comparator through the in-phase input terminal of the first comparator for threshold voltage comparison and enters the second comparator through the in-phase input terminal of the second comparator for threshold voltage comparison through the output terminal of the signal amplifier; the inverting input terminal of the signal amplifier is connected to the ground through the fourth resistor and to the output terminal of the signal amplifier through the second resistor;

[0016] The inverting input terminal of the first comparator is grounded via the first resistor and connected to a negative power supply via the third resistor; the inverting input terminal of the second comparator is grounded via the fifth resistor and connected to a negative power supply via the sixth resistor;

[0017] The first resistor and the fifth resistor are adjustable resistors. The first threshold voltage is adjusted by adjusting the first resistor; the second threshold voltage is adjusted by adjusting the fifth resistor.

[0018] Preferably, the ratio threshold is 3dB.

[0019] A method for self-adjusting the gain of an electron multiplier comprises the following steps:

[0020] Convert and amplify the current signal output by the electron multiplier into a voltage signal;

[0021] Comparing the threshold voltages of the first threshold voltage and the second threshold voltage respectively on the amplified voltage signal and counting them to obtain a first count value and a second count value;

[0022] calculating a ratio of the first count value to the second count value;

[0023] According to the result of comparing the ratio with the ratio threshold, controlling the electron multiplier to enter a self-regulating state or a stable state;

[0024] When the ratio is less than the ratio threshold, the DC voltage across the electron multiplier is adjusted so that the electron multiplier gain increases and enters a self-adjusting state, until the ratio is equal to 1 and enters a stable state.

[0025] Preferably, adjusting the DC voltage across the electron multiplier comprises the steps of:

[0026] The control unit adjusts the DC voltage across the electron multiplier through the DA conversion unit.

[0027] Preferably, the ratio threshold is 3dB.

[0028] The present invention has at least the following beneficial effects:

[0029] 1. The present invention forms a dual-threshold voltage comparison link by setting a first comparator and a second comparator, and the first threshold voltage is not equal to the second threshold voltage. By comparing the dual threshold voltages, dividing after counting and then comparing, and adjusting the DC voltages at both ends of the electron multiplier online and in real time according to the size of the comparison ratio, the electron multiplier gain is increased, and the online and real-time automatic adjustment of the electron multiplier gain is realized. The operation is simple, no standard gas is required, no complex electron flow generating device is required, and no experienced engineer is required to judge. The mass spectrometer user can quickly judge whether the gain needs to be adjusted, and the data abnormality can be corrected in time;

[0030] 2. The control unit adjusts the DC voltage across the electron multiplier through the DA conversion unit so that the electron multiplier gain increases, thereby achieving online adjustment of the electron multiplier gain.

[0031] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 It is a schematic diagram of the composition of the electron multiplier gain self-adjusting circuit of the present invention;

[0034] Figure 2 It is a schematic diagram of the circuit composition of the amplification unit and the comparison unit;

[0035] Figure 3 The figure is a schematic flow chart of the electron multiplier gain self-adjustment method according to the present invention. DETAILED DESCRIPTION

[0036] The technical solutions of the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The terms such as “having”, “including” and “comprising” used in the different embodiments of the present invention described below do not exclude the existence or addition of one or more other elements or a combination thereof; the technical features involved can be combined with each other as long as there is no conflict between them.

[0038] <Implementation Method 1>

[0039] The embodiment of the present invention provides an electron multiplier gain self-adjusting circuit, such as Figure 1As shown, it includes an amplifying unit, a comparing unit, a counting unit and a control unit. The amplifying unit is used to convert and amplify the current signal output by the electron multiplier into a voltage signal. The comparing unit includes a first comparator provided with a first threshold voltage and a second comparator provided with a second threshold voltage; the amplified voltage signal is subjected to threshold voltage comparison by the first comparator and the second comparator respectively. The counting unit includes a first counter and a second counter, the first counter counts the output of the first comparator, and the second counter counts the output of the second comparator. The control unit is used to calculate the ratio of the output of the first counter and the output of the second counter. When the gain of the electron multiplier does not change, the ratio is 1, and it enters a stable state; when the ratio is less than the ratio threshold, the control unit adjusts the DC voltage across the electron multiplier so that the gain of the electron multiplier increases and enters a self-adjusting state until the ratio is equal to 1 and enters a stable state again, at which time the gain reaches the state required by the mass spectrometer, and the signal intensity of the mass spectrometer returns to normal.

[0040] In this embodiment, a dual-threshold voltage comparison link is formed by setting a first comparator and a second comparator, and the first threshold voltage is not equal to the second threshold voltage. By comparing the dual threshold voltages, dividing after counting and then comparing, and adjusting the DC voltage across the electron multiplier online and in real time according to the comparison ratio, the electron multiplier gain is increased, thereby realizing online and real-time automatic adjustment of the electron multiplier gain. The operation is simple, and no calibration gas or complex electron flow generating device is required. There is no need for judgment by experienced engineers. The mass spectrometer user can quickly determine whether the gain needs to be adjusted, and data anomalies can be corrected in time.

[0041] Considering the fast calculation and control performance of the control unit, the preferred control unit of the present invention is a control module with FPGA. Considering that the amplification unit has the function of converting the current signal output by the electron multiplier into a voltage signal and amplifying it, the preferred amplification unit of the present invention adopts AD8001. In view of the maximum frequency of the mass spectrometer ion pulse signal is about 8MHz, in order to meet the speed requirement, the present invention preferably uses two AD8561 as the first comparator and the second comparator respectively.

[0042] As a preferred embodiment of the above embodiment, the electron multiplier gain self-adjusting circuit also includes a DA conversion unit respectively connected to the control unit and the electron multiplier. Specifically, the control unit adjusts the DC voltage across the electron multiplier through the DA conversion unit so that the electron multiplier gain increases, thereby realizing online adjustment of the electron multiplier gain. Considering the function of online adjustment of the DC voltage across the electron multiplier, the preferred DA conversion unit of the present invention adopts DAC7718.

[0043] In order to ensure the current-voltage conversion and amplification functions of the signal amplifier, and the processing speed requirements of the first comparator and the second comparator for the ion pulse signal of the mass spectrometer with the highest frequency of about 8MHz, the present invention further provides a preferred implementation of the amplification unit and the comparison unit. Figure 2 As shown, the amplification unit includes a signal amplifier, a second resistor and a fourth resistor; the comparison unit also includes a first resistor, a third resistor, a fifth resistor and a sixth resistor. The output current signal of the electron multiplier enters the signal amplifier through the signal amplifier in-phase input terminal, is converted into a voltage signal and amplified, and the amplified voltage signal enters the first comparator through the first comparator in-phase input terminal through the signal amplifier output terminal for threshold voltage comparison, and enters the second comparator through the second comparator in-phase input terminal for threshold voltage comparison; the inverting input terminal of the signal amplifier is grounded through the fourth resistor and connected to the output terminal of the signal amplifier through the second resistor; the inverting input terminal of the first comparator is grounded through the first resistor and connected to the negative power supply through the third resistor. The inverting input terminal of the second comparator is grounded through the fifth resistor and connected to the negative power supply through the sixth resistor. The first resistor and the fifth resistor are adjustable resistors, and the first threshold voltage is adjusted by adjusting the size of the first resistor; the second threshold voltage is adjusted by adjusting the size of the fifth resistor. More specifically, the first resistor is set to 100Ω, the second resistor is set to 1kΩ, the third resistor is set to 2.37kΩ, the fourth resistor is set to 49.9kΩ, the fifth resistor is set to 100Ω, the sixth resistor is set to 2.37kΩ, and the negative power supply is -5V, ensuring that the current-voltage conversion and amplification of the signal amplifier, and the threshold voltage comparison of the first comparator and the second comparator are all stable and high-performance. Based on the circuit parameters, as a further optimization, the first threshold voltage is set to be less than the second threshold voltage, and the ratio threshold is set to 3dB, which can achieve better online gain adjustment.

[0044] The following is an explanation of the process of self-adjusting the electron multiplier gain by the self-adjusting circuit provided by the present invention.

[0045] The electron multiplier generates a current signal, which is converted into a voltage signal by the AD8001 signal amplifier and amplified, and then sent to the first comparator and the second comparator for threshold voltage comparison. The first threshold voltage of the first comparator is set to V th1 , the second threshold voltage of the second comparator is set to V th2 , and V th1 <V th2The first counter counts the threshold voltage comparison output of the first comparator, which is counted as cps1, and the second counter counts the threshold voltage comparison output of the second comparator, which is counted as cps2. The FPGA chip divides cps1 and cps2 to obtain a ratio. When the ratio cps1 / cps2=1, the electron multiplier gain does not change and enters a stable state; when the ratio cps1 / cps2 is less than the ratio threshold, that is, the ratio cps1 / cps2<3dB, the FPGA chip can be used to control the DA chip online in real time to adjust the voltage V across the electron multiplier. CEM , so that the electron multiplier gain increases and enters the online real-time self-adjustment state until the ratio cps1 / cps2=1 and enters the stable state again. At this time, the gain reaches the state required by the mass spectrometer, and the mass spectrometer signal intensity returns to normal. The entire electron multiplier gain adjustment process is online, real-time, self-adjusting, and easy to operate.

[0046] <Implementation Method 2>

[0047] Based on the electron multiplier gain self-adjusting circuit provided in Embodiment 1, as Figure 3 As shown, an embodiment of the present invention provides a method for self-adjusting the gain of an electron multiplier, comprising the following steps:

[0048] S10. Amplify the electron multiplier output signal;

[0049] S20. Compare the threshold voltages of the first threshold voltage and the second threshold voltage of the amplified electron multiplier output signal and count them to obtain a first count value and a second count value;

[0050] S30. Calculate the ratio of the first count value to the second count value;

[0051] S40. Based on the result of comparing the ratio with the ratio threshold, control the electron multiplier to enter a self-regulating state or a stable state: when the ratio is less than the ratio threshold, adjust the DC voltage across the electron multiplier to enter a self-regulating state until the ratio is equal to 1 to enter a stable state.

[0052] In this embodiment, a dual threshold voltage comparison link including a first threshold voltage and a second threshold voltage is provided, and a link is performed for counting and dividing the dual threshold voltage comparison outputs and then comparing them. A real-time self-adjustment link is performed for online adjusting the DC voltage at both ends of the electron multiplier according to the counting ratio result, so that the ratio is finally adjusted to a stable state of 1. At this time, the gain reaches the state required by the mass spectrometer, and the mass spectrometer signal intensity returns to normal. The entire electron multiplier gain adjustment process is online, real-time, and self-adjusting, and is simple to operate. It does not require standard gas, nor does it require a complex electron flow generating device. It does not require judgment by experienced engineers. The mass spectrometer user can quickly determine whether the gain needs to be adjusted, and can correct data abnormalities in a timely manner.

[0053] As a further preferred embodiment of the above embodiment, adjusting the DC voltage across the electron multiplier comprises the steps of: the control unit adjusting the DC voltage across the electron multiplier through the DA conversion unit so that the electron multiplier gain increases, thereby achieving online adjustment of the electron multiplier gain. Considering the function of online adjustment of the DC voltage across the electron multiplier, the DA conversion unit of the present invention preferably adopts DAC7718.

[0054] As a further preference of the above embodiment, the ratio threshold is set to 3 dB, and when the ratio is lower than 3 dB, the electron multiplier gain can be adjusted accordingly, thereby achieving the purpose of online and real-time gain adjustment.

[0055] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. An electron multiplier gain self-adjusting circuit, characterized in that: It includes: An amplifying unit, which is used to convert and amplify the output current signal of the electron multiplier into a voltage signal; A comparison unit, comprising a first comparator with a first threshold voltage and a second comparator with a second threshold voltage; the amplified voltage signal is respectively compared with the threshold voltage by the first comparator and the second comparator; a counting unit, comprising a first counter and a second counter, wherein the first counter counts the output of the first comparator, and the second counter counts the output of the second comparator; a control unit, configured to calculate a ratio between the first counter output and the second counter output; Wherein, when the ratio is less than the ratio threshold, the control unit adjusts the DC voltage across the electron multiplier so that the electron multiplier gain increases and enters a self-regulating state, until the ratio is equal to 1 and enters a stable state; The amplification unit includes a signal amplifier, a second resistor and a fourth resistor; the comparison unit also includes a first resistor, a third resistor, a fifth resistor and a sixth resistor; The output current signal of the electron multiplier enters the signal amplifier through the in-phase input terminal of the signal amplifier, is converted into a voltage signal and amplified, and the amplified voltage signal enters the first comparator through the in-phase input terminal of the first comparator for threshold voltage comparison and enters the second comparator through the in-phase input terminal of the second comparator for threshold voltage comparison through the output terminal of the signal amplifier; the inverting input terminal of the signal amplifier is grounded through the fourth resistor and connected to the output terminal of the signal amplifier through the second resistor; The inverting input terminal of the first comparator is grounded via the first resistor and connected to a negative power supply via the third resistor; the inverting input terminal of the second comparator is grounded via the fifth resistor and connected to a negative power supply via the sixth resistor; The first resistor and the fifth resistor are adjustable resistors. The first threshold voltage is adjusted by adjusting the first resistor; the second threshold voltage is adjusted by adjusting the fifth resistor.

2. The electron multiplier gain self-adjusting circuit according to claim 1, characterized in that: Also includes: A DA conversion unit is communicatively connected to the control unit and the electron multiplier respectively; the control unit adjusts the DC voltage across the electron multiplier through the DA conversion unit so that the electron multiplier gain is increased.

3. The electron multiplier gain self-adjusting circuit according to claim 1, characterized in that: The ratio threshold is 3dB.

4. A method for self-adjusting the electron multiplier gain self-adjusting circuit as claimed in claim 1, characterized in that: It includes the steps of: Convert and amplify the current signal output by the electron multiplier into a voltage signal; Comparing the threshold voltages of the first threshold voltage and the second threshold voltage respectively on the amplified voltage signal and counting them to obtain a first count value and a second count value; calculating a ratio of the first count value to the second count value; According to the result of comparing the ratio with the ratio threshold, controlling the electron multiplier to enter a self-regulating state or a stable state; When the ratio is less than the ratio threshold, the DC voltage across the electron multiplier is adjusted so that the electron multiplier gain increases and enters a self-adjusting state, until the ratio is equal to 1 and enters a stable state.

5. The electron multiplier gain self-adjustment method according to claim 4, characterized in that: Regulating the DC voltage across the electron multiplier comprises the steps of: The control unit adjusts the DC voltage across the electron multiplier through the DA conversion unit.

6. The electron multiplier gain self-adjustment method according to claim 4, characterized in that: The ratio threshold is 3dB.

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