A Temperature Control Method for Magnetic Stirrers Based on Expert Systems

Abstract

This invention discloses a magnetic stirrer temperature control method based on an expert system. First, the actual temperature of the controlled object is acquired by a temperature sensor, and the temperature deviation, heating amount, and temperature change rate of the controlled object are calculated based on the actual temperature setpoint. Then, these three values ​​are used as inputs to the expert system control module. Finally, the expert system control module outputs a corresponding pulse width control signal to control the thyristor based on the input heating amount, deviation, and temperature change rate of the controlled object, according to its rule base, ultimately achieving precise temperature control of the heating pan. This invention's magnetic stirrer temperature control method based on an expert system effectively suppresses overshoot and oscillation that occur in traditional PID control algorithms during actual temperature control, improving the accuracy of the temperature control system.

Description

Technical Field

[0001] This invention relates to the field of temperature control, specifically a method for temperature control of a magnetic stirrer based on an expert system. Background Technology

[0002] With the continuous development of society and the economy, temperature control systems based on temperature parameters are widely developed and used in daily life, industrial manufacturing, refrigeration, and other fields as important environmental factors to ensure the normal operation of various tasks, such as real-time monitoring of greenhouses and cold storage regulation. Temperature, as a physical quantity characterizing the hotness or coldness of an object, plays a crucial role in production activities and scientific experiments. Effective temperature control is essential for obtaining ideal scientific experimental data or achieving efficient production. Especially in biochemical analysis experiments, temperature errors often affect experimental samples. Therefore, high-precision, low-cost, and real-time temperature control systems urgently need to be developed by researchers.

[0003] Currently, most temperature controllers on the market employ the PID control algorithm, which boasts advantages such as simple structure, high reliability, and ease of adjustment. However, traditional PID control only effectively leverages these advantages when the mathematical model of the controlled object is known. This limits its effectiveness when dealing with complex controlled objects. Furthermore, traditional PID control algorithms often fail to achieve satisfactory control results in temperature control due to the nonlinearity and hysteresis inherent in the system, exhibiting significant limitations. However, with the development of microelectronics technology, there are increasingly higher requirements for the precision of temperature control. Reducing oscillations during temperature control, minimizing overshoot, and improving system stability have become urgent needs. Summary of the Invention

[0004] Purpose of the invention: This invention proposes a magnetic stirrer temperature control method based on an expert system, which can accurately control the temperature of the heating plate or the heated solution of a general temperature controller for biochemical experiments, thereby reducing oscillations and overshoots during temperature regulation and improving control accuracy.

[0005] Technical solution: A temperature control method for a magnetic stirrer based on an expert system, the control method comprising the following steps:

[0006] Step 1: Sample the actual temperature of the controlled object using a temperature sensor; the controlled object includes the heating plate of the magnetic stirrer and the object being heated.

[0007] Step 2: Based on the actual temperature obtained in Step 1, calculate the temperature deviation value, temperature heating amount, and temperature change rate of the controlled object.

[0008] Step 3: Use the temperature deviation value, temperature heating amount, and temperature change rate of the controlled object as inputs to the expert system control module;

[0009] Step 4: Based on the temperature information including the input temperature deviation value, temperature heating amount, and temperature change rate of the controlled object, the expert system control module selects a rule base and outputs the corresponding pulse width control signal of the control thyristor through the rule base to achieve precise control of the heating furnace plate temperature.

[0010] Furthermore, in step one, the temperature sensor includes a resistance temperature detector (RTD) and a thermocouple; the thermocouple is installed at the bottom of the heating plate of the magnetic stirrer, and the collected temperature data is recorded as the plate temperature data; the RTD is placed inside the heated container of the magnetic stirrer, and the collected temperature data is the temperature data of the heated object.

[0011] Furthermore, in step two:

[0012] 1) The formula for calculating the temperature deviation is as follows:

[0013]

[0014] In the formula, set TC The set temperature for the thermocouple, set PT TC is the set temperature of the resistance temperature detector (RTD); PT is the current temperature of the thermocouple; E is the current temperature of the RTD. TC E represents the temperature deviation between the thermocouple's set temperature and its current temperature. PT This is the temperature deviation between the set temperature of the resistance temperature detector (RTD) and its current temperature.

[0015] 2) The formula for calculating the heating amount at temperature is as follows:

[0016]

[0017] In the formula, T env For ambient temperature; ΔV TC The temperature difference between the current temperature of the thermocouple and the ambient temperature is the amount of heat generated; ΔV PT The amount of heat generated is the temperature difference between the current temperature of the resistance temperature detector and the ambient temperature.

[0018] 3) The formula for calculating the rate of temperature change of the controlled object is as follows:

[0019]

[0020] In the formula, TC n-1 PT represents the actual temperature of the object sampled by the thermocouple at time n-1. n-1 The actual temperature of the object sampled by the thermal resistor at time n-1; T is the sampling period; TCn PT represents the actual temperature of the object sampled by the thermocouple at time n. n Let n be the actual temperature of the object sampled by the thermal resistor at time n.

[0021] Furthermore, in step two, the current temperatures of the resistance temperature detector (RTD) and the thermocouple are calculated as follows:

[0022] After sorting a set of temperature data sampled by RTDs and thermocouples according to their magnitude, the average value is obtained by filtering using the following formula and then used as the current temperature of the controlled object:

[0023]

[0024] In the formula, tc n This represents the temperature data of the thermocouple located at position n after being arranged in ascending order; tc i This represents the temperature data of the thermocouple located at position i, arranged in ascending order; tc j This represents the thermocouple temperature data with the largest value after sorting; pt n This represents the resistance temperature data located at the nth position after being arranged in ascending order; pt i This represents the temperature data of the resistance temperature at position i, arranged in ascending order; pt j This represents the temperature data with the largest resistance temperature after the data is arranged; the values ​​less than tc in this set of temperature data are then considered. i And greater than tc i-j After removing the temperature data, the remaining data is averaged to obtain a temperature data that can represent the current temperature. TC is the current temperature of the thermocouple; PT is the current temperature of the resistance temperature detector.

[0025] Furthermore, step four includes the following steps:

[0026] 1) Configure the rule base within the expert system control module:

[0027] In thermocouple single feedback control, the thermocouple temperature deviation value is divided into multiple primary levels. Under each primary level, there are multiple secondary levels based on the temperature change rate of the thermocouple controlled object. Under each secondary level, there are multiple tertiary levels based on the temperature heating amount. The primary, secondary, and tertiary levels are regularized and written into the rule base of the expert system control module.

[0028] In single feedback control of RTD, the RTD temperature deviation value is divided into multiple first-level gears. Each first-level gear is further divided into multiple second-level gears based on the temperature change rate of the thermocouple controlled object. Each second-level gear is further divided into multiple third-level gears based on the temperature heating amount. The first-level, second-level, and third-level gears are regularized and written into the rule base of the expert system control module.

[0029] 2) Based on the temperature information, including the input temperature deviation value, temperature heating amount, and temperature change rate of the controlled object, the expert system control module selects the rule base;

[0030] 3) The expert system control module outputs the pulse width control signal of the corresponding control thyristor according to the rule base to control the temperature of the heating plate precisely.

[0031] Furthermore, in step four, the PWM duty cycle U output in the thermocouple single feedback control mode TC The calculation method is as follows:

[0032]

[0033] In the formula, ΔV TC P1, P2, and P3 are fixed values ​​derived from experiments. Depending on the temperature deviation, the amount of heating, and the rate of temperature change of the controlled object, different fixed values ​​will be selected for P1, P2, and P3.

[0034] The PWM duty cycle U output by the expert system control module in the single feedback control mode of the thermal resistor PT The calculation method is as follows:

[0035]

[0036] In the formula, P PT P is a fixed value derived from experiments. PT Different fixed values ​​are selected based on different combinations of temperature deviation, temperature heating amount, and temperature change rate of the controlled object.

[0037] Beneficial effects: The magnetic stirrer temperature control method based on expert system proposed in this invention achieves high-precision PWM modulation by collecting temperature information with high precision, inputting temperature deviation value, temperature heating amount and temperature change rate of the controlled object into the expert system control module, thereby effectively suppressing overshoot and oscillation that occur in the traditional PID control algorithm in actual temperature control and improving the accuracy of the temperature control system. Attached Figure Description

[0038] Figure 1 This is a control block diagram of the control method of the present invention;

[0039] Figure 2This is a schematic diagram of the thermocouple single feedback expert system control in the control method of the present invention;

[0040] Figure 3 This is a schematic diagram of the single feedback expert system control of the thermal resistor in the control method of the present invention;

[0041] Figure 4 This is a temperature change curve of the control method of the present invention during actual heating. Detailed Implementation

[0042] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the embodiments.

[0043] A method for temperature control of a magnetic stirrer based on an expert system, such as Figure 1 As shown, it includes the following steps:

[0044] Step 1: Sample the actual temperature of the controlled object using a temperature sensor;

[0045] A magnetic stirrer temperature control system based on an expert system includes a temperature controller, which comprises a thermocouple, a resistance temperature detector (RTD), a temperature sensor 1, an expert system control module 5, a first subtractor 2, a second subtractor 4, and a differentiator 3. The temperature sensor 1 includes an RTD and a thermocouple. The thermocouple is installed at the bottom of the stirring pan of the magnetic stirrer, and the temperature data it collects is recorded as the stirring pan temperature data. The RTD is placed inside the heated container of the magnetic stirrer, and the temperature data it collects is the temperature data of the heated object. The temperature sensor is electrically connected to the first subtractor 2, the second subtractor 4, and the differentiator 3, and the first subtractor 2, the second subtractor 4, and the differentiator 3 are all electrically connected to the expert system control module 5.

[0046] 1) The formula for how the resistance of a resistance temperature detector (RTD) changes with temperature is:

[0047]

[0048] In the formula, t is the temperature; R t The resistance values ​​are given at different temperatures; A = 3.90802 × 10⁻⁶. -3 B = -5.8 × 10 -7 C = 4.2735 × 10 -12 R0 is the resistance of the thermal resistor at 0℃, R0=100Ω.

[0049] As the resistance of the thermal resistor changes with temperature, the voltage across the thermal resistor in the voltage divider circuit changes and is converted into a voltage signal. This voltage signal enters the controller's AD (Analog-to-Digital) channel and is ultimately converted into a digital signal.

[0050] 2) The total circuit potential of the thermocouple is expressed as:

[0051] E AB (T,T0)=E AB (T)-E AB (T0)=E AB (T)+E BA (T0) (2)

[0052] In the formula, E AB (T) is the thermoelectric potential of the thermocouple hot junction, E AB (T0) is the thermoelectric potential of the cold junction of the thermocouple.

[0053] The total electromotive force in the thermocouple circuit is amplified by the operational amplifier circuit and then enters the AD channel of the controller to be finally converted into a digital signal.

[0054] Step 2: Based on the actual temperature obtained in Step 1, calculate the temperature deviation value, temperature heating amount, and temperature change rate of the controlled object;

[0055] The current temperature of thermocouples and RTDs is calculated as follows: After sorting a set of actual temperature data sampled from the RTDs and thermocouples according to their magnitude, the average is calculated using equation (3):

[0056]

[0057] In the formula, the controller collects a set of temperature data at the thermocouple and the resistance temperature detector (RTD); then, these temperature data are arranged in ascending order, tc n This represents the temperature data of the thermocouple located at position n after being arranged in ascending order, tc i tc represents the temperature data of the thermocouple located at position i after being arranged in ascending order. j This represents the thermocouple temperature data with the largest value after sorting; pt n This represents the temperature data of the resistance temperature at position n after being arranged in ascending order, pt i This represents the temperature data of the resistance temperature at position i, arranged in ascending order. j This represents the temperature data with the largest resistance temperature after the data is arranged; the values ​​less than tc in this set of temperature data are then considered. i And greater than tc i-j After removing the temperature data, the remaining data is averaged to obtain a temperature data that can represent the current temperature. TC is the current temperature of the thermocouple; PT is the current temperature of the resistance temperature detector.

[0058] 1) The set temperature is obtained by the first subtractor 2 as shown in formula (4). TC , set PTTemperature deviation E from the current temperatures TC and PT TC E PT ;

[0059]

[0060] In the formula, set TC The set temperature for the thermocouple, set PT TC is the set temperature of the resistance temperature detector (RTD); PT is the current temperature of the thermocouple; E is the current temperature of the RTD. TC E represents the temperature deviation between the thermocouple's set temperature and its current temperature. PT This is the temperature deviation between the set temperature of the resistance temperature detector (RTD) and its current temperature.

[0061] 2) According to the second subtractor 4 shown in formula (5), the temperature heating amount is obtained, and the current temperature TC, PT and ambient temperature T are obtained. env The temperature between the heating amount ΔV TC ΔV PT ;

[0062]

[0063] In the formula, T env For ambient temperature; ΔV TC The temperature difference between the current temperature of the thermocouple and the ambient temperature is the amount of heat generated; ΔV PT The amount of heat generated is the temperature difference between the current temperature of the resistance temperature detector and the ambient temperature.

[0064] 3) The temperature change rate Δ of the controlled object is obtained by differentiating the differentiator (3) according to formula (6). TC Δ PT ;

[0065]

[0066] In the formula, TC n-1 PT represents the actual temperature of the object sampled by the thermocouple at time n-1. n-1 The actual temperature of the object sampled by the thermal resistor at time n-1; T is the sampling period; TC n PT represents the actual temperature of the object sampled by the thermocouple at time n. n Let n be the actual temperature of the object sampled by the thermal resistor at time n.

[0067] Step 3: Use the temperature deviation value, temperature heating amount, and temperature change rate of the controlled object as inputs to the expert system control module;

[0068] Step 4: Based on the temperature information including the input temperature deviation value, temperature heating amount, and temperature change rate of the controlled object, the expert system control module selects a rule base and outputs the corresponding pulse width control signal of the control thyristor through the rule base in the expert system control module to achieve precise control of the heating furnace plate temperature.

[0069] Step four specifically includes the following steps:

[0070] 1) Configure the rule base within the expert system control module:

[0071] In thermocouple single feedback control, the thermocouple temperature deviation value is divided into multiple primary levels. Under each primary level, there are multiple secondary levels based on the temperature change rate of the thermocouple controlled object. Under each secondary level, there are multiple tertiary levels based on the temperature heating amount. The primary, secondary, and tertiary levels are regularized and written into the rule base of the expert system control module.

[0072] In single feedback control of RTD, the RTD temperature deviation value is divided into multiple first-level gears. Each first-level gear is further divided into multiple second-level gears based on the temperature change rate of the thermocouple controlled object. Each second-level gear is further divided into multiple third-level gears based on the temperature heating amount. The first-level, second-level, and third-level gears are regularized and written into the rule base of the expert system control module.

[0073] 2) Based on the temperature information, including the input temperature deviation value, temperature heating amount, and temperature change rate of the controlled object, the expert system control module selects the corresponding rule base;

[0074] 3) The expert system control module outputs the pulse width control signal of the corresponding control thyristor according to the rule base to control the temperature of the heating plate precisely.

[0075] like Figure 2 As shown, in a magnetic stirrer temperature control method based on an expert system, the expert system control module adopts a thermocouple single feedback control mode. Its inputs are the thermocouple temperature deviation, the thermocouple heating amount, and the rate of change of the controlled thermocouple temperature. A large amount of experimental data is summarized into control rules for the furnace plate. In the thermocouple single feedback control, the temperature deviation is divided into multiple levels, and each level is further divided into multiple levels based on the rate of change of the controlled thermocouple temperature and the magnitude of the thermocouple heating amount. These levels are regularized and written into the rule base of the expert system control module. The expert system control module searches for rules in the rule base according to the relevant input temperature information. The duty cycle U of the pulse width modulation signal can be changed according to the changes in the input. TC Its reasoning logic can be expressed as "if E TC andΔV TC andΔTC then U TC ".

[0076] like Figure 3 As shown, in a magnetic stirrer temperature control method based on an expert system, the expert system control module adopts a single feedback control mode for resistance temperature detectors (RTDs). Its inputs are the RTD temperature deviation, the RTD heating amount, and the rate of change of the controlled object's temperature. Extensive experimental data is summarized into control rules for the heating plate. In the single feedback control, the RTD temperature deviation is divided into multiple levels, and each level is further divided into multiple levels based on the rate of change of the controlled object's temperature and the magnitude of the RTD heating amount. These levels are regularized and written into the rule base of the expert system control module. The expert system control module searches for rules in the rule base based on the input temperature information. The duty cycle U of the pulse width modulation signal can be changed according to the changes in the input. PT Its reasoning logic can be expressed as "if E PT andΔV PT andΔ PT then U PT ".

[0077] The expert system control module includes the following rules:

[0078] Table 1 Rule Base for Thermocouple Single Feedback Control Mode

[0079]

[0080]

[0081]

[0082] Table 2 Rule Base for Single Feedback Control Mode of Resistance Temperature Detectors

[0083]

[0084]

[0085] The PWM duty cycle U output by the expert system control module in thermocouple single feedback control mode TC The calculation method is as follows:

[0086]

[0087] In the formula, ΔV TC P1, P2, and P3 are fixed values ​​derived from extensive experiments. Depending on the temperature deviation, the amount of heating, and the rate of temperature change of the controlled object, different fixed values ​​will be selected for P1, P2, and P3.

[0088] The PWM duty cycle U output by the expert system control module in the single feedback control mode of the thermal resistor PT The calculation method is as follows:

[0089]

[0090] In the formula, P PT P is a fixed value derived from extensive experiments. PT Different fixed values ​​are selected based on different combinations of temperature deviation, temperature heating amount, and temperature change rate of the controlled object;

[0091] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for temperature control of a magnetic stirrer based on an expert system, characterized in that, The control method includes the following steps: Step 1: Sample the actual temperature of the controlled object using a temperature sensor; the controlled object includes the heating plate of the magnetic stirrer and the object being heated. Step 2: Based on the actual temperature obtained in Step 1, calculate the temperature deviation value, temperature heating amount, and temperature change rate of the controlled object. Step 3: Use the temperature deviation value, temperature heating amount, and temperature change rate of the controlled object as inputs to the expert system control module; Step 4: Based on the temperature information of the input temperature deviation value, temperature heating amount, and temperature change rate of the controlled object, the expert system control module selects the rule base and outputs the corresponding pulse width control signal of the control thyristor through the rule base of the expert system control module to achieve precise control of the temperature of the heating furnace plate. Step four includes the following steps: 1) Configure the rule base within the expert system control module: In thermocouple single feedback control, the thermocouple temperature deviation value is divided into multiple primary levels. Each primary level is further divided into multiple secondary levels based on the temperature change rate of the thermocouple controlled object. Each secondary level is further divided into multiple tertiary levels based on the temperature heating amount. The primary, secondary, and tertiary levels are then regularized and written into the rule base of the expert system control module. In single feedback control of RTD, the RTD temperature deviation value is divided into multiple first-level gears. Each first-level gear is further divided into multiple second-level gears based on the temperature change rate of the thermocouple controlled object. Each second-level gear is further divided into multiple third-level gears based on the temperature heating amount. The first-level, second-level, and third-level gears are regularized and written into the rule base of the expert system control module. 2) Based on the temperature information, including the input temperature deviation value, temperature heating amount, and temperature change rate of the controlled object, the expert system control module selects the rule base; 3) The expert system control module outputs the corresponding pulse width control signal of the control thyristor based on the rule base to control the temperature of the heating furnace plate precisely; In step four, the PWM duty cycle U output under the thermocouple single feedback control mode TC The calculation method is as follows: ； In the formula, ∆V TC P1, P2, and P3 are fixed values ​​derived from experiments. Depending on the temperature deviation, the amount of heating, and the rate of temperature change of the controlled object, different fixed values ​​will be selected for P1, P2, and P3. The PWM duty cycle U output by the expert system control module in the single feedback control mode of the thermal resistor PT The calculation method is as follows: ； In the formula, P PT P is a fixed value derived from experiments. PT Different fixed values ​​are selected based on different combinations of temperature deviation, temperature heating amount, and temperature change rate of the controlled object.

2. The method for temperature control of a magnetic stirrer based on an expert system according to claim 1, characterized in that, In step one, the temperature sensor includes a resistance temperature detector (RTD) and a thermocouple. The thermocouple is installed at the bottom of the heating plate of the magnetic stirrer, and the temperature data collected is recorded as the plate temperature data; the resistance temperature detector (RTD) is placed inside the heated container of the magnetic stirrer, and the temperature data collected by it is the temperature data of the heated object.

3. The method for temperature control of a magnetic stirrer based on an expert system according to claim 2, characterized in that, In step two: 1) The formula for calculating the temperature deviation value is as follows: ； In the formula, set TC The set temperature for the thermocouple, set PT TC is the set temperature of the resistance temperature detector (RTD); PT is the current temperature of the thermocouple; E is the current temperature of the RTD. TC E represents the temperature deviation between the thermocouple's set temperature and its current temperature. PT This is the temperature deviation between the set temperature of the resistance temperature detector (RTD) and its current temperature. 2) The formula for calculating the heating amount at temperature is as follows: ； Where, T env For ambient temperature; ΔV TC The temperature difference between the current temperature of the thermocouple and the ambient temperature is the amount of heat generated; ΔV PT The amount of heat generated is the temperature difference between the current temperature of the resistance temperature detector and the ambient temperature. 3) The formula for calculating the rate of temperature change of the controlled object is as follows: ； In the formula, TC n-1 Let PT be the actual temperature of the object sampled by the thermocouple at time n-1. n-1 The actual temperature of the object sampled by the thermal resistor at time n-1; T is the sampling period; TC n PT represents the actual temperature of the object sampled by the thermocouple at time n. n Let n be the actual temperature of the object sampled by the thermal resistor at time n.

4. The method for temperature control of a magnetic stirrer based on an expert system according to claim 3, characterized in that, In step two, the current temperatures of the resistance temperature detector (RTD) and the thermocouple are calculated as follows: After sorting a set of temperature data sampled by RTDs and thermocouples according to their magnitude, the average value is obtained by filtering using the following formula and then used as the current temperature of the controlled object: ； In the formula, tc n This represents the temperature data of the thermocouple located at position n after being arranged in ascending order; tc i This represents the temperature data of the thermocouple located at position i, arranged in ascending order; tc j This represents the thermocouple temperature data with the largest value after sorting; pt n This represents the resistance temperature data located at the nth position after being arranged in ascending order; pt i This represents the temperature data of the resistance temperature at position i, arranged in ascending order; pt j The temperature data representing the highest value of the resistance temperature after the arrangement is completed; Take the temperature data that is less than tc from this set of temperature data. i And greater than tc j-i After removing the temperature data, the remaining data is averaged to obtain a temperature data that can represent the current temperature. TC is the current temperature of the thermocouple; PT is the current temperature of the resistance temperature detector.

Images