Flow calibration method for EPC module in gas chromatograph

Abstract

The invention discloses a flow calibration method for an EPC module in a gas chromatograph, and belongs to the technical field of flow equipment calibration, and the method comprises the following steps: S1, PID self-tuning; s2, flow calibration; and S3, flow verification. According to the method, the flow calibration work of each channel in the EPC module can be accurately and efficiently completed through the steps of PID self-tuning, flow calibration, flow verification and the like, the problem that the stability degree needs to be judged by human subjective factors in the existing calibration process is solved, and the calibration process and the calibration result can be digitized, automated and intelligent.

Description

Technical Field

[0001] The invention relates to the technical field of flow equipment calibration, and in particular to an automatic flow calibration method of an EPC module (electronic pressure control module) in a gas chromatograph (GC). Background Art

[0002] EPC is the most important component for controlling gas flow in gas chromatographs. It can accurately control the flow and pressure of gas chromatographs, improve separation efficiency and repeatability, and optimize chromatographic analysis results.

[0003] The existing calibration method for gas chromatographs is to use manual calibration and PID control. On the one hand, it relies heavily on manual judgment, and the judgment criteria are left to subjective judgment, which affects the consistency of the calibration results. On the other hand, manual calibration is time-consuming and costly, and the calibration process requires repeated verification and repeated measurement, which results in poor calibration efficiency and consistency of calibration results.

[0004] The above problems need to be solved urgently. Therefore, a flow calibration method for an EPC module in a gas chromatograph is proposed. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to solve the problems of poor calibration efficiency and poor consistency of calibration results in the existing calibration method, and provides a flow calibration method for an EPC module in a gas chromatograph.

[0006] The present invention solves the above technical problems through the following technical solutions, and the present invention comprises the following steps:

[0007] S1: PID self-tuning

[0008] Through PID self-tuning, the proportional, integral and differential parameters of the PID control algorithm of each channel in the EPC module are obtained;

[0009] S2: Flow calibration

[0010] Connect a single channel in the EPC module to a standard flow meter and perform flow calibration on the single channel in the EPC module in conjunction with the flow calibration table;

[0011] S3: Traffic Verification

[0012] Verify whether the linear coefficients of each adjacent calibration point in the flow calibration table are positive, and verify the flow accuracy of the set calibration point of the flow range of a single channel in the EPC module. When both verifications are passed, it means that the flow calibration work of the corresponding channel in the EPC module is completed.

[0013] Furthermore, in step S1, the specific processing process is as follows:

[0014] S11: For a single channel of the EPC module, set the target value F and the maximum PWM duty cycle d + 、PWM duty cycle minimum value d - , Stability judgment value σ H , judgment number N, flow calibration range, flow stability judgment conditions, flow accuracy verification conditions;

[0015] S12: When the flow rate of a single channel in the EPC module exceeds the target value F from low to high, the PWM duty cycle is set to 0, and the maximum value A0 of the flow rate displayed on the single channel on the EPC module is recorded, and the corresponding time is recorded as T0. When the flow rate of a single channel of the EPC module is lower than the target value F from high to low, the PWM duty cycle is set to 100%, and the minimum value A1 of the flow rate displayed on the EPC module is recorded, and the corresponding time is recorded as T1.

[0016] S13: Calculate the amplitude a of the current segment according to the maximum value A0 and the minimum value A1 of the flow of a single channel of the EPC module j , calculate the time interval T of the current segment based on time T0 and time T1 uj , where j represents the jth segment;

[0017] S14: Repeat steps S12-S13 multiple times to obtain multiple continuous amplitudes, calculate the variance σ of the amplitudes of 10 consecutive segments, and when the variance σ of the amplitudes of 10 consecutive segments is less than the stability judgment value σ H , then it is determined to be stable. If σ is greater than or equal to the stable judgment value σ H , then continue to calculate the variance of the amplitude from the 2nd to the 11th segment until the variance σ of the amplitude of 10 consecutive segments is qualified; when the tuning process exceeds 10 minutes, it is judged that the self-tuning has failed and the self-tuning is stopped;

[0018] S15: Calculate the proportional, integral and differential parameters of the PID control algorithm of a single channel of the EPC module using a calculation formula.

[0019] Furthermore, in step S11, the target value F is the range value of a single channel in the EPC module, the flow calibration range is the range of the standard flow meter, and the PWM duty cycle refers to the PWM duty cycle of the control end proportional valve of a single channel in the EPC module.

[0020] Furthermore, in step S15, the calculation formulas are as follows:

[0021] K p =0.6*4a / ΠT v

[0022] T i =T V / 2

[0023] T d =T V / 8

[0024] Among them, K p is the P value in the PID control algorithm, i.e. the proportional parameter, T i is the I value in the PID control algorithm, i.e. the integral parameter, T d is the D value in the PID control algorithm, i.e. the differential parameter, Π is 3.14, a is the average value of the amplitude of 10 segments when the self-tuning is successful, T v It is the average value of the 10-segment time interval when the auto-tuning is successful.

[0025] Furthermore, in step S2, the specific processing process is as follows:

[0026] S21: Initialize the flow calibration table, set all values ​​of the flow calibration table to initial default values, and obtain an initial flow calibration table;

[0027] S22: Input the flow range of a single channel in the EPC module one by one starting from the 0 point, and read the current flow measurement value from the standard flow meter, overwriting the initial default value of the original calibration point in the initial flow calibration table;

[0028] S23: When the flow measurement values ​​of all calibration points are obtained or the flow measurement values ​​exceed the range of the standard flow meter, the flow calibration steps are completed and the data points exceeding the range of the standard flow meter are deleted.

[0029] Furthermore, in step S3, the specific process of verifying whether the linear coefficients of adjacent calibration points in the flow calibration table are positive is as follows:

[0030] S301: Use a multi-point linear fitting method to fit the flow measurement values ​​of all calibration points in the flow calibration table to obtain a corresponding fitting curve;

[0031] S302: using the least square method to obtain the slope between each adjacent calibration point in the flow calibration table, that is, to obtain the linear coefficient;

[0032] S303: When the linear coefficient between any two calibration points is not a positive value, the calibration is output as failed, and the process returns to step S2.

[0033] Furthermore, in step S3, the specific process of verifying the flow accuracy of the set calibration point of the flow range of a single channel in the EPC module is as follows: input the flow rate of the set calibration point as Q0, obtain the flow measurement value of the standard flow meter as Q1, calculate the difference between Q1 and Q0 as Q c , Q cWhen compared with the flow accuracy verification conditions, if it is less than the flow accuracy verification conditions, it is considered that the flow accuracy of the set calibration point is qualified, otherwise it is unqualified. When the flow accuracy of each set calibration point is qualified, it means that the flow calibration work is completed. When the flow accuracy of any calibration point is unqualified, return to step S2.

[0034] Furthermore, in step S3, the calibration points are set as calibration points of 20%, 40%, 60%, and 80% of the flow range of a single channel in the EPC module.

[0035] Compared with the prior art, the present invention has the following advantages: the flow calibration method of the EPC module in the gas chromatograph can accurately and efficiently complete the flow calibration of each channel in the EPC module through the steps of PID self-tuning, flow calibration and flow verification, overcomes the problem that the existing calibration process requires human subjective factors to judge the degree of stability, and can digitize, automate and intelligentize the calibration process and calibration results. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the flow calibration method of the EPC module in the gas chromatograph in an embodiment of the present invention;

[0037] Figure 2 1 is a flow chart of a method for calibrating the flow rate of an EPC module in a gas chromatograph according to an embodiment of the present invention;

[0038] Figure 3 1 is a flow chart of PID self-tuning (step 1 to step 4) in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0040] like Figure 1 , 2 As shown, this embodiment provides a technical solution: a flow calibration method for an EPC module in a gas chromatograph, which performs flow calibration on a single channel in the EPC module, comprising the following steps:

[0041] Step 1: Set the target value F to 50% of the range and the maximum PWM duty cycle d + is 100%, the minimum PWM duty cycle d - is 0%, and the stability judgment value is σ H, the judgment number N is 10, the flow calibration range is 100ml / min, the flow stability judgment condition is 0.05ml / min, and the flow accuracy verification condition is 0.1ml / min.

[0042] In this step, the target value F is the range value of a single channel in the EPC module, and the flow calibration range is the range of the standard flow meter.

[0043] In this step, the PWM duty cycle refers to the PWM duty cycle of the control-end proportional valve of a single channel in the EPC module.

[0044] Step 2: When the flow of a single channel in the EPC module exceeds the target value F from low to high, the PWM duty cycle is set to 0, and the maximum value A0 of the flow displayed on the single channel on the EPC module is recorded at this time, and the corresponding time is recorded as T0. When the flow of a single channel of the EPC module decreases from high to low and is lower than the target value F, the PWM duty cycle is set to 100%, and the minimum value A1 of the flow displayed on the EPC module is recorded at this time, and the corresponding time is recorded as T1.

[0045] Step 3: Calculate the amplitude a of the current segment based on the maximum value A0 and minimum value A1 of the flow of a single channel of the EPC module j , calculate the time interval (period) T of the current segment based on time T0 and time T1 uj , where j represents the jth segment.

[0046] Step 4: Repeat steps 2-3 multiple times to calculate the variance σ of the amplitude of 10 consecutive segments. When the variance σ of the amplitude of 10 consecutive segments is less than the stability judgment value σ H , then it is determined to be stable. If σ is greater than or equal to the stable judgment value σ H Then continue to calculate the variance of the 2nd to 11th amplitude until the variance σ of the amplitude of 10 consecutive segments is qualified; when the tuning process exceeds 10 minutes, it is judged that the self-tuning has failed and the self-tuning is stopped.

[0047] Step 5: Exploitation The algorithm's empirical formula calculates the parameters of the single-channel PID control algorithm in the EPC module.

[0048] In this step, The empirical formula of the algorithm is as follows:

[0049] K p =0.6*4a / ΠT v

[0050] T i =T V / 2

[0051] T d =T V / 8

[0052] Among them, K p is the P value in the PID control algorithm, i.e. the proportional parameter, T i is the I value in the PID control algorithm, i.e. the integral parameter, T d is the D value in the PID control algorithm, i.e. the differential parameter, Π is 3.14, a is the average value of the amplitude of 10 segments when the self-tuning is successful, T v It is the average value of the 10-segment time interval when the auto-tuning is successful.

[0053] Step 6: Initialize the standard table (flow calibration table) used to calibrate the flow meter, set all values ​​in the flow calibration table to the initial default values, and then obtain the initial flow calibration table. Input the results of the initial flow calibration table one by one starting from the flow range 0 point of a single channel in the EPC module, and read the current flow measurement value from the standard flow meter to overwrite the initial default values ​​of the original calibration points in the initial flow calibration table. When the flow value measurement of all calibration points is completed or the flow measurement value exceeds the range of the standard flow meter, the automatic calibration step is completed, and the data points exceeding the range of the standard flow meter are deleted.

[0054] Step 7: The linear coefficients between adjacent calibration points need to be all positive values. Use the multi-point linear fitting method to fit the flow measurement values ​​of all calibration points, and use the least squares method to obtain the slope between each adjacent calibration point in the flow calibration table, that is, the linear coefficient. When the linear coefficient between any two calibration points is not a positive value, the output calibration fails and return to step 6.

[0055] Step 8: Verify the accuracy of the calibration points of 20%, 40%, 60%, and 80% of the flow range of a single channel in the EPC module, input the flow rate of the calibration point as 20ml / min, obtain the value of the standard flow meter flow rate as 20.05ml / min, and calculate the difference between the standard flow meter and the set flow rate (0.05ml / min). If it is less than the deviation set value (flow accuracy verification condition) of 0.1ml / min, the flow accuracy of the calibration point is considered qualified. When the flow accuracy of the four calibration points meets the accuracy requirements, the automatic calibration is considered completed.

[0056] Step 9: If the flow accuracy verification of any calibration point fails, jump back to the automatic calibration step and return to step 6.

[0057] It should be noted that this embodiment only shows the flow calibration method of a single channel in the EPC module, and the flow calibration method of the remaining channels can be performed with reference to the above method.

[0058] In summary, the flow calibration method of the EPC module in the gas chromatograph in the above embodiment can accurately and efficiently complete the flow calibration of each channel in the EPC module through steps such as PID self-tuning, flow calibration and flow verification, overcomes the problem of requiring human subjective factors to judge the degree of stability in the existing calibration process, and can digitize, automate and intelligentize the calibration process and calibration results.

[0059] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A flow calibration method for an EPC module in a gas chromatograph, characterized in that: The following steps are involved: S1: PID self-tuning Through PID self-tuning, the proportional, integral and differential parameters of the PID control algorithm of each channel in the EPC module are obtained; S2: Flow calibration Connect a single channel in the EPC module to a standard flow meter and perform flow calibration on the single channel in the EPC module in conjunction with the flow calibration table; S3: Traffic Verification Verify whether the linear coefficients of each adjacent calibration point in the flow calibration table are positive, and verify the flow accuracy of the set calibration point of the flow range of a single channel in the EPC module. When both verifications are passed, it means that the flow calibration work of the corresponding channel in the EPC module is completed.

2. The flow calibration method of an EPC module in a gas chromatograph according to claim 1, characterized in that: In step S1, the specific processing process is as follows: S11: For a single channel of the EPC module, set the target value F and the maximum PWM duty cycle d + 、PWM duty cycle minimum value d - , Stability judgment value σ H , judgment number N, flow calibration range, flow stability judgment conditions, flow accuracy verification conditions; S12: When the flow rate of a single channel in the EPC module exceeds the target value F from low to high, the PWM duty cycle is set to 0, and the maximum value A0 of the flow rate displayed on the single channel on the EPC module is recorded, and the corresponding time is recorded as T0. When the flow rate of a single channel of the EPC module is lower than the target value F from high to low, the PWM duty cycle is set to 100%, and the minimum value A1 of the flow rate displayed on the EPC module is recorded, and the corresponding time is recorded as T1. S13: Calculate the amplitude a of the current segment according to the maximum value A0 and the minimum value A1 of the flow of a single channel of the EPC module j , calculate the time interval T of the current segment based on time T0 and time T1 uj , where j represents the jth segment; S14: Repeat steps S12-S13 multiple times to obtain multiple continuous amplitudes, calculate the variance σ of the amplitudes of 10 consecutive segments, and when the variance σ of the amplitudes of 10 consecutive segments is less than the stability judgment value σ H , then it is determined to be stable. If σ is greater than or equal to the stable judgment value σ H , then continue to calculate the variance of the amplitude from the 2nd to the 11th segment until the variance σ of the amplitude of 10 consecutive segments is qualified; when the tuning process exceeds 10 minutes, it is judged that the self-tuning has failed and the self-tuning is stopped; S15: Calculate the proportional, integral and differential parameters of the PID control algorithm of a single channel of the EPC module using a calculation formula.

3. The flow calibration method of an EPC module in a gas chromatograph according to claim 2, characterized in that: In step S11, the target value F is the range value of a single channel in the EPC module, the flow calibration range is the range of the standard flow meter, and the PWM duty cycle refers to the PWM duty cycle of the control end proportional valve of a single channel in the EPC module.

4. The flow calibration method of an EPC module in a gas chromatograph according to claim 2, characterized in that: In step S15, the calculation formulas are as follows: K p =0.6*4a / ΠT v T i =T V / 2 T d =T V / 8 Among them, K p is the P value in the PID control algorithm, i.e. the proportional parameter, T i is the I value in the PID control algorithm, i.e. the integral parameter, T d is the D value in the PID control algorithm, i.e. the differential parameter, Π is 3.14, a is the average value of the amplitude of 10 segments when the self-tuning is successful, T v It is the average value of the 10-segment time interval when the auto-tuning is successful.

5. The flow calibration method of an EPC module in a gas chromatograph according to claim 2, characterized in that: In step S2, the specific processing process is as follows: S21: Initialize the flow calibration table, set all values ​​of the flow calibration table to initial default values, and obtain an initial flow calibration table; S22: Input the flow range of a single channel in the EPC module one by one starting from the 0 point, and read the current flow measurement value from the standard flow meter, overwriting the initial default value of the original calibration point in the initial flow calibration table; S23: When the flow measurement values ​​of all calibration points are obtained or the flow measurement values ​​exceed the range of the standard flow meter, the flow calibration steps are completed and the data points exceeding the range of the standard flow meter are deleted.

6. The flow calibration method of an EPC module in a gas chromatograph according to claim 3, characterized in that: In step S3, the specific process of verifying whether the linear coefficients of adjacent calibration points in the flow calibration table are positive is as follows: S301: Use a multi-point linear fitting method to fit the flow measurement values ​​of all calibration points in the flow calibration table to obtain a corresponding fitting curve; S302: using the least square method to obtain the slope between each adjacent calibration point in the flow calibration table, that is, to obtain the linear coefficient; S303: When the linear coefficient between any two calibration points is not a positive value, the calibration is output as failed, and the process returns to step S2.

7. The flow calibration method of an EPC module in a gas chromatograph according to claim 6, characterized in that: In step S3, the specific process of verifying the flow accuracy of the set calibration point of the flow range of a single channel in the EPC module is as follows: input the flow rate of the set calibration point as Q0, obtain the flow measurement value of the standard flow meter as Q1, calculate the difference between Q1 and Q0 as Q c , Q c When compared with the flow accuracy verification conditions, if it is less than the flow accuracy verification conditions, it is considered that the flow accuracy of the set calibration point is qualified, otherwise it is unqualified. When the flow accuracy of each set calibration point is qualified, it means that the flow calibration work is completed. When the flow accuracy of any calibration point is unqualified, return to step S2.

8. The flow calibration method of an EPC module in a gas chromatograph according to claim 7, characterized in that: In step S3, the calibration points are set as calibration points of 20%, 40%, 60%, and 80% of the flow range of a single channel in the EPC module.

Images