CN108803308A - The mostly logical pond temperature control system of gas based on adaptive section PID control and method - Google Patents

Abstract

The temperature control system and method of the gas multi-pass cell based on the adaptive interval PID control of the present invention belong to the field of temperature control of the gas multi-pass cell. The outer wall of the gas sample cell is wrapped with a heating film to realize the heating of the gas multi-pass cell. The PT1000 platinum resistance temperature sensor It is placed between the outer wall of the gas sample cell and the heating film to detect the working temperature of the gas multi-pass cell in real time. The gas multi-pass cell uses thermal insulation cotton as a whole to form a thermal insulation effect. Aiming at the problem of large overshoot caused by the complex structure of the controlled object and the slow response, it is improved on the basis of the traditional PID control algorithm, and the control process is subdivided into multiple intervals according to the temperature deviation value, and in each interval according to the interval value and temperature The rate of change of the deviation value is set for the proportional amplification coefficient, integral coefficient, and differential coefficient, and the adaptive interval PID control algorithm is realized to make the temperature control fast and without overshoot. It provides a reliable guarantee for the improvement of the performance of the carbon dioxide isotope detection system.

Description

Temperature control system and method for gas multi-pass pool based on adaptive interval PID control

technical field

The invention belongs to the field of temperature control of a gas multi-pass cell, and in particular relates to a temperature control system and a control method for high-precision control of a gas multi-pass cell for infrared gas isotope detection.

Background technique

The precise measurement of gas isotopes has important applications in the fields of biomedicine, hydrology, paleontology, geochemistry, and atmospheric physical chemistry. The use of laser absorption spectroscopy for gas isotope detection is very conducive to the development of a real-time online measurement system. Since the absorption coefficient of the absorption line of the gas to be measured will be affected by the temperature of the gas to be measured, the amplitude of the generated voltage signal will change with the change of the gas temperature, which will directly affect the stability and accuracy of the detection system. Therefore, in practical applications, it is necessary to adopt constant temperature measures for the gas multi-pass cell to reduce the fluctuation of gas temperature and control the absorption coefficient to be stable, so as to improve the sensitivity and response speed of the detection system and reduce the lower limit of detection.

The gas multi-pass cell is mainly composed of a quartz gas sample cell, reflecting mirrors on both sides and a complex aluminum alloy support structure. The complex structure of the gas multi-pass cell leads to a large thermal response time constant, uneven internal heat distribution, and There is an indeterminate heat exchange taking place outside. In addition, in order to maximize the response time of the gas isotope detection system, the temperature of the gas inside the gas multi-pass cell needs to converge at the fastest speed. These factors and requirements put a lot of pressure on the high-precision temperature control of the gas multi-pass cell. challenge.

PID controllers are widely used in temperature control systems. PID controllers are divided into analog PID controllers and digital PID controllers. The response speed of analog PID controllers is fast, but the parameters of analog PID controllers will be fixed as the circuit is determined. , it is difficult to make changes. The digital PID controller is a kind of linear regulator. According to the deviation between the set value and the actual value, the proportional link (P), the integral link (I) and the differential link (D) of the deviation are linearly combined to form the control quantity. Control the amount of control. The function of the integral link is to eliminate the static error, but when the system is started or the set value is changed, due to the existence of the integral link, a large deviation will be generated, resulting in the accumulation of the integral calculated by the PID, leading to integral saturation, and finally causing the system overshoot Large and stable for a long time.

At present, the basic idea of the integral separation PID control algorithm is that when the system starts, there is a large deviation between the set value and the actual value, and the integral link is removed, so as to avoid the increase of the system overshoot and the decrease of system stability due to the action of the integral link; When the actual value is close to the set value, the integral control is introduced to eliminate the static error and improve the control accuracy. However, in the actual application process, due to the complex structure of the controlled object, the response of the system is slow, the deviation in the early stage of heating is large, and the system still overshoots, and there are problems such as long stabilization time and low adjustment accuracy.

Contents of the invention

The object of the present invention is to provide a gas multi-pass cell temperature control system and method based on adaptive interval PID control for the above difficulties and the problems of complex structure and large thermal response time constant of the gas multi-pass cell in the prior art.

The present invention adopts following technical scheme:

The invention proposes a gas multi-pass cell temperature control system based on adaptive interval PID control, which is characterized in that it includes: a gas multi-pass cell and a control unit, and the gas multi-pass cell is composed of an aluminum alloy support structure and a gas sample cell The gas sample cell is set on an aluminum alloy support structure, the outer wall of the gas sample cell is covered with a heating film, the heating film completely wraps the entire outer wall of the gas sample cell, the heating film is connected to the heating film drive module, and the heating film is A polyimide heating film, a temperature sensor is set between the heating film and the outer wall of the gas sample cell, and the temperature sensor is connected to the temperature acquisition module; the outside of the gas sample cell is also covered with an insulating layer; the insulating layer is placed in a heating The outside of the film; the control unit includes a temperature acquisition module, a heating film drive module and an adaptive interval PID controller, and the temperature acquisition module and the heating film drive module are respectively connected with the adaptive interval PID controller, and the adaptive interval PID control The device includes a single-chip microcomputer, an interval control module and a parameter control module, and the interval control module, the parameter control module and the single-chip microcomputer are connected by communication.

The gas sample cell adopts a quartz gas sample cell.

The single-chip microcomputer adopts the single-chip microcomputer STM32.

The thermal insulation layer adopts thermal insulation cotton.

The temperature acquisition module includes a Huygens bridge, an instrumentation amplifier and an analog-to-digital converter chip, wherein the Huygens bridge is made up of a platinum resistor PT1000 and three resistors, and the three resistors in the Huygens bridge are respectively R1, R2, R3, the input end of the instrumentation amplifier is connected to the Huygens bridge, and the output end of the instrumentation amplifier is connected to the analog-to-digital converter chip.

R1, R2 and R3 in the Huygens bridge adopt resistors with the same temperature drift coefficient.

The instrumentation amplifier adopts instrumentation amplifier AD620.

The analog-to-digital converter chip adopts an analog-to-digital converter chip AD7705.

The heating film driving module includes a photocoupler TLP521, a MOS transistor driving chip IR2117 and a MOS transistor IRF2807, and the photoelectric coupler TLP521, the MOS transistor driving chip IR2117 and the MOS transistor IRF2807 are connected in sequence.

The present invention also proposes a temperature control method for gas multi-pass pools based on adaptive interval PID control, characterized in that the method adopts the gas multi-pass pool temperature control system based on adaptive interval PID control, which specifically includes the following step:

Step 1. Pass the gas to be measured into the gas multi-pass cell, and the temperature acquisition module performs temperature sampling, and inputs the collected current actual temperature value into the self-adaptive interval PID controller, and the kth sampling temperature actual value is youk( k), the microcontroller receives the temperature sampling data and processes it to obtain the temperature deviation value e(k), where e(k)=rin(k)-youk(k), rin(k) represents the temperature setting value, and the temperature deviation The value e(k) is input to the interval control module as an input parameter;

Step 2. The range of the current temperature value is obtained through the interval calculation function ε _k , that is, the difference between the end value and the initial value of the current temperature, 1≤k≤n, n≥5, and the change rate of the current temperature deviation value is changed by the deviation The rate calculation function gets e _c , that is, the absolute value of the difference between the current temperature actual value and the initial temperature value divided by the current temperature sampling time, and the obtained previous temperature value range ε _k and the current temperature deviation value change rate e _c As an input parameter, it is input into the parameter control module, and the adjustment coefficient is calculated is the relationship coefficient between the proportional amplification factor K _P , the integral coefficient K _I , the differential coefficient K _D and the range ε _k of the current temperature value, Among them, rin(0) is the temperature setting value in the initial state, and the actual value of the k-th sampling temperature is youk(k), is the relationship coefficient between the proportional item K _P , the differential item K _I , the integral item K _D and the rate of change e _c of the current temperature deviation value, Get the proportional amplification coefficient K _P , integral coefficient K _I , and differential coefficient K _D within the interval range ε _k where the current temperature value is located. By subdividing the temperature control process into n intervals, compare the proportional amplification coefficient K _P for each interval , integral coefficient K _I , differential coefficient K _D to calculate, get

Among them, ε ₁ , ε ₂ , ε ₃ ... ε _n are interval range values obtained by using the interval calculation function;

Step 3: Input the temperature deviation value e(k) of the kth sampling, the proportional amplification factor K _P , the integral coefficient K _I , and the differential coefficient K _D as control parameters into the adaptive interval PID controller for proportional, integral, and differential calculations to obtain The temperature output u(k) of the kth sampling, where:

In the positional digital PID control algorithm, e(k-1) represents the k-1th sampling temperature deviation value, and e(j) represents the intermediate quantity generated during the integral calculation process replaced by the rectangular numerical method after discretization;

Preset the temperature output limit value, compare u(k) with the preset temperature output limit value, and judge whether the temperature output u(k) exceeds the preset temperature output limit value, if it exceeds the preset temperature output limit value Set the temperature output limit value, then the temperature output u(k) is the preset temperature output limit value, output the preset temperature output limit value, if it does not exceed the preset temperature output limit value value, the output temperature output u(k) remains unchanged.

Through the above design scheme, compared with the prior art, the present invention can bring the following beneficial effects: the present invention heats the gas inside the gas sample cell by wrapping a heating film on the outer wall of the gas sample cell, so that the temperature of the gas inside the gas sample cell reaches a preset value At the same time, an insulation layer is set to reduce the heat exchange between the internal gas and the external environment, reduce the impact of external environmental temperature changes on the temperature control effect, and provide a constant temperature actual detection environment for the gas to be measured. The temperature control algorithm of the present invention is different from the existing traditional PID control algorithm. An adaptive interval PID control algorithm is proposed. When the system is started, the temperature deviation value e(k) is the largest, and the temperature value is calculated by the interval calculation function. At the same time, the proportional amplification factor K _P , integral coefficient K _I , and differential coefficient K _D of the adaptive interval PID controller in the initial state are calculated from the range of the temperature value and the rate of change of the temperature deviation value. Through calculation, each The optimal parameters of each process interval make the system take less time to reach the set threshold from the initial temperature and reduce the system stabilization time. When the actual temperature value is close to the set value, because the control process is subdivided according to the temperature deviation value e(k), the parameters of each interval correspond to different deviation ranges, and the control is more precise. For the controlled object with complex structure and large thermal response time constant, by subdividing the control process and optimizing the parameters of each process, more precise control is achieved, and the system achieves no overshoot and short stabilization time.

Description of drawings

The accompanying drawings described here are used to provide a further understanding of the present invention and constitute a part of the application. The schematic embodiments of the present invention and their descriptions are used to understand the present invention and do not constitute improper limitations of the present invention. In the accompanying drawings:

Fig. 1 is the structural representation of the temperature control system of the gas multi-pass pool based on the self-adaptive interval PID control of the present invention;

Fig. 2 is a schematic diagram of the adaptive interval PID control principle of the present invention;

3 is a schematic diagram of the circuit principle of the temperature acquisition module of the present invention;

Fig. 4 is a partial circuit diagram of the present invention.

The marks in the figure are as follows: 1-aluminum alloy support structure, 2-gas sample cell, 3-temperature sensor, 4-heating film, 5-insulation layer, 6-control unit.

Detailed ways

In order to avoid obscuring the essence of the present invention, well-known methods, procedures, procedures, components and circuits have not been described in detail.

In view of the complex structure of the gas multi-pass pool and the problem of large thermal response time constants, as shown in Figure 1, Figure 2, Figure 3 and Figure 4, the gas multi-pass pool temperature control system based on adaptive interval PID control proposed by the present invention includes Gas multi-pass cell and control unit 6, the gas multi-pass cell is composed of an aluminum alloy support structure 1 and a gas sample cell 2, the gas sample cell 2 is arranged on the aluminum alloy support structure 1, and the outer wall of the gas sample cell 2 Covered with a heating film 4, the heating film 4 completely wraps the outer wall of the gas sample cell 2, the heating film 4 is connected to the heating film drive module, the heating film 4 is a polyimide heating film, and the heating film 4 and the gas sample cell 2 A temperature sensor 3 is arranged between the outer walls, and the temperature sensor 3 is connected to the temperature acquisition module; the outside of the gas sample pool 2 is also provided with an insulation layer 5; the insulation layer 5 is placed outside the heating film 4; the control unit 6 includes a temperature acquisition module, a heating film drive module and an adaptive interval PID controller, the temperature acquisition module and the heating film drive module are respectively connected with the adaptive interval PID controller, and the adaptive interval PID controller includes a single-chip microcomputer, an interval control module and the parameter control module, the interval control module, the parameter control module and the single-chip microcomputer are connected by communication.

Wherein, the temperature acquisition module includes a Huygens bridge, an instrumentation amplifier and an analog-to-digital converter chip, a platinum resistor PT1000 and three resistors form a Huygens bridge, and the input of the instrumentation amplifier is connected to the Connection, the output of the instrumentation amplifier is connected to the analog-to-digital converter chip. The three resistors in the Huygens bridge are R1, R2, and R3. The resistance of the platinum resistor PT1000 changes with temperature, which causes the differential signal output of the bridge circuit to change. , the differential signal is amplified by the instrumentation amplifier and then sampled by the analog-to-digital converter. Reducing the influence of lead resistance is the key point of high-precision measurement. The temperature sensor 3 of the present invention adopts the three-wire connection method, which can effectively eliminate the influence of lead resistance and self-heating effect. In order to overcome the impact of ambient temperature changes on the accuracy of analog circuits, R1, R2 and R3 in the Huygens bridge select precision resistors with the same temperature drift coefficient. In order to suppress the impact of the noise introduced by the instrumentation amplifier itself on the detection electrical signal, the instrumentation amplifier AD620 with low temperature drift coefficient and low input noise is selected. In order to improve the accuracy of the detection circuit, a 16-bit programmable gain low-power analog-to-digital converter chip AD7705 is selected to convert the collected analog signals into digital signals.

Among them, the adaptive interval PID controller includes a single-chip microcomputer, an interval control module and a parameter control module. The interval control module, the parameter control module and the single-chip computer are connected to each other by communication. The single-chip microcomputer adopts a single-chip microcomputer STM32. The actual value of the kth sampling temperature is youk(k), and the temperature deviation value e(k) is calculated, where e(k)=rin(k)-youk(k), and rin(k) represents the temperature setting value , the PWM square wave with a specific duty cycle is output by the adaptive interval PID controller. During the temperature adjustment process, the temperature deviation value e(k) is input to the interval control module as an input parameter;

The interval range of the current temperature value is obtained through the interval calculation function, that is, the difference between the end value and the initial value of the current temperature, 1≤k≤n _{, n≥5} , and the current temperature deviation value change rate is calculated through the deviation change rate calculation function Obtain e _c , that is, divide the absolute value of the difference between the current actual temperature value and the initial temperature value by the time used for sampling the current temperature, and take the range ε _k of the obtained previous temperature value and the rate of change of the current temperature deviation value e _c as input parameters Input to the parameter control module to calculate the adjustment coefficient is the relationship coefficient between the proportional amplification factor K _P , the integral coefficient K _I , the differential coefficient K _D and the range ε _k of the current temperature value, Among them, rin(0) is the temperature setting value in the initial state, and the actual value of the k-th sampling temperature is youk(k), is the relationship coefficient between the proportional item K _P , the differential item K _I , the integral item K _D and the rate of change e _c of the current temperature deviation value, Get the proportional amplification coefficient K _P , integral coefficient K _I , and differential coefficient K _D within the interval range ε _k where the current temperature value is located. By subdividing the temperature control process into n intervals, compare the proportional amplification coefficient K _P for each interval , integral coefficient K _I , differential coefficient K _D to calculate, get

Among them, ε ₁ , ε ₂ , ε ₃ ... ε _n are interval range values obtained by using the interval calculation function;

Step 3: Input the temperature deviation value e(k) of the kth sampling, the proportional amplification factor K _P , the integral coefficient K _I , and the differential coefficient K _D as control parameters into the adaptive interval PID controller for proportional, integral, and differential calculations to obtain The temperature output u(k) of the kth sampling, where:

In the positional digital PID control algorithm, e(k-1) represents the k-1th sampling temperature deviation value, and e(j) represents the intermediate quantity generated during the integral calculation process replaced by the rectangular numerical method after discretization;

Preset the temperature output limit value, compare u(k) with the preset temperature output limit value, and judge whether the temperature output u(k) exceeds the preset temperature output limit value, if it exceeds the preset temperature output limit value Set the temperature output limit value, then the temperature output u(k) is the preset temperature output limit value, output the preset temperature output limit value, if it does not exceed the preset temperature output limit value value, the output temperature output u(k) remains unchanged.

Polyimide heating film, also known as high-temperature electric heating film, is extremely thin, very soft, and extremely flexible in shape and size, especially suitable for controlled objects with irregular shapes. A polyimide heating film is wrapped on the surface of the gas sample cell 2 of the gas multipass cell to control the internal gas temperature. When the STM32 output of the single chip microcomputer is at a high level, it is isolated by the photocoupler TLP521, and the MOS tube driver chip IR2117 is controlled to drive the MOS tube IRF2807, and the polyimide heating film is controlled to start heating.

Example 1

When the gas to be measured enters the gas multi-pass cell, the temperature of the gas multi-pass cell will change, and the resistance value of the platinum resistance PT1000 on the outer wall of the gas sample cell 2 will change, and the resistance value of the platinum resistance PT1000 will cause the Huygens bridge circuit to The output differential voltage signal changes, and the differential voltage signal is amplified by the instrument amplifier AD620, then sampled by the analog-to-digital converter AD7705, and the analog voltage signal is converted into a digital signal and input to the input terminal of the single-chip microcomputer STM32 for data processing.

The control part uses an adaptive interval PID controller to collect the kth actual temperature value youk(k), and calculate the kth temperature deviation value e(k)=rin(k)-youk(k), where rin( k) represents the temperature set point. Input the obtained temperature deviation value e(k) as an input parameter to the interval control module of the adaptive interval PID controller, perform proportional, integral and differential operations on the temperature deviation value e(k), and obtain the temperature output of the kth sampling Quantity u(k).

In order to avoid the output control quantity being too large under special circumstances, it is necessary to limit the output temperature output u(k), pre-set the temperature output limit value, and set u(k) and the preset temperature output limit Value comparison, judging whether the temperature output u(k) exceeds the preset temperature output limit value, if it exceeds the preset temperature output limit value, then the temperature output u(k) is the preset temperature output Limit value, output the preset temperature output limit value, if it does not exceed the preset temperature output limit value, the output temperature output u(k) will not change.

Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail, those skilled in the art should understand that various changes can be made to it in terms of form and details. Various changes may be made without departing from the invention as defined in the appended claims.

Claims (10)

1. The gas multi-pass pool temperature control system based on self-adaptive interval PID control, is characterized in that, comprises: gas multi-pass pool and control unit (6), and described gas multi-pass pool is made of aluminum alloy support structure (1) and gas A sample cell (2) is formed, the gas sample cell (2) is arranged on an aluminum alloy support structure (1), the outer wall of the gas sample cell (2) is covered with a heating film (4), and the heating film (4) Completely wrap the outer wall of the gas sample cell (2), the heating film (4) is connected to the heating film drive module, the heating film (4) is a polyimide heating film, and the heating film (4) and the outer wall of the gas sample cell (2) A temperature sensor (3) is set between them, and the temperature sensor (3) is connected with the temperature acquisition module; the outside of the gas sample pool (2) is also covered with an insulation layer (5); the insulation layer (5) is placed in a heating The outside of the film (4); the control unit (6) includes a temperature acquisition module, a heating film drive module and an adaptive interval PID controller, and the temperature acquisition module and the heating film drive module are respectively connected with the adaptive interval PID controller The self-adaptive interval PID controller includes a single-chip microcomputer, an interval control module and a parameter control module, and the interval control module, the parameter control module and the single-chip computer are connected to each other by communication. 2. The gas multi-pass cell temperature control system based on adaptive interval PID control according to claim 1, characterized in that: the gas sample cell (2) is a quartz gas sample cell. 3. The gas multi-pass tank temperature control system based on adaptive interval PID control according to claim 1, characterized in that: said single-chip microcomputer adopts single-chip microcomputer STM32. 4. The gas multi-pass tank temperature control system based on adaptive interval PID control according to claim 1, characterized in that: the thermal insulation layer (5) adopts thermal insulation cotton. 5. The gas multi-pass pool temperature control system based on adaptive interval PID control according to claim 1, wherein the temperature acquisition module includes a Huygens bridge, an instrument amplifier and an analog-to-digital converter chip, wherein The Huygens bridge is composed of platinum resistance PT1000 and three resistors. The three resistors in the Huygens bridge are R1, R2, and R3 respectively. The input terminal of the instrumentation amplifier is connected to the Huygens bridge. The instrumentation amplifier’s The output terminal is connected with the analog-to-digital converter chip. 6. The gas multi-pass cell temperature control system based on adaptive interval PID control according to claim 5, characterized in that: R1, R2 and R3 in the Huygens bridge adopt resistors with the same temperature drift coefficient. 7. The temperature control system of gas multi-pass pool based on adaptive interval PID control according to claim 5, characterized in that: the instrumentation amplifier adopts instrumentation amplifier AD620. 8. The gas multi-pass pool temperature control system based on adaptive interval PID control according to claim 5, characterized in that: the analog-to-digital converter chip adopts an analog-to-digital converter chip AD7705. 9. The gas multi-pass cell temperature control system based on adaptive interval PID control according to claim 1, characterized in that: the heating film drive module includes a photocoupler TLP521, a MOS tube drive chip IR2117 and a MOS tube IRF2807, The photocoupler TLP521, MOS tube driver chip IR2117 and MOS tube IRF2807 are connected in sequence. 10. A gas multi-pass pool temperature control method based on adaptive interval PID control, characterized in that the method adopts the gas multi-pass pool temperature control system based on adaptive interval PID control described in any one of claims 1-9 , including the following steps: Step 1. Pass the gas to be measured into the gas multi-pass cell, and the temperature acquisition module performs temperature sampling, and inputs the collected current actual temperature value into the self-adaptive interval PID controller, and the kth sampling temperature actual value is youk( k), the microcontroller receives the temperature sampling data and processes it to obtain the temperature deviation value e(k), where e(k)=rin(k)-youk(k), rin(k) represents the temperature setting value, and the temperature deviation The value e(k) is input to the interval control module as an input parameter; Step 2. The range of the current temperature value is obtained through the interval calculation function ε _k , that is, the difference between the end value and the initial value of the current temperature, 1≤k≤n, n≥5, and the change rate of the current temperature deviation value is changed by the deviation The rate calculation function gets e _c , that is, the absolute value of the difference between the current temperature actual value and the initial temperature value divided by the current temperature sampling time, and the obtained previous temperature value range ε _k and the current temperature deviation value change rate e _c As an input parameter, it is input into the parameter control module, and the adjustment coefficient is calculated is the relationship coefficient between the proportional amplification factor K _P , the integral coefficient K _{I , the} differential coefficient K _D and the range ε _k of the current temperature value, Among them, rin(0) is the temperature setting value in the initial state, and the actual value of the kth sampling temperature is youk(k), is the relationship coefficient between the proportional item K _P , the differential item K _I , the integral item K _D and the rate of change e _c of the current temperature deviation value, Get the proportional amplification coefficient K _P , integral coefficient K _I , and differential coefficient K _D within the interval range ε _k where the current temperature value is located. By subdividing the temperature control process into n intervals, compare the proportional amplification coefficient K _P for each interval , integral coefficient K _I , differential coefficient K _D to calculate, get Among them, ε ₁ , ε ₂ , ε ₃ ... ε _n are interval range values obtained by using the interval calculation function; Step 3: Input the temperature deviation value e(k) of the kth sampling, the proportional amplification factor K _P , the integral coefficient K _I , and the differential coefficient K _D as control parameters into the adaptive interval PID controller for proportional, integral, and differential calculations to obtain The temperature output u(k) of the kth sampling, where: In the positional digital PID control algorithm, e(k-1) represents the k-1th sampling temperature deviation value, and e(j) represents the intermediate quantity generated during the integral calculation process replaced by the rectangular numerical method after discretization; Preset the temperature output limit value, compare u(k) with the preset temperature output limit value, and judge whether the temperature output u(k) exceeds the preset temperature output limit value, if it exceeds the preset temperature output limit value Set the temperature output limit value, then the temperature output u(k) is the preset temperature output limit value, output the preset temperature output limit value, if it does not exceed the preset temperature output limit value value, the output temperature output u(k) remains unchanged.