Intrinsically safe temperature control method

Abstract

The application belongs to the field of explosion prevention, and particularly relates to an intrinsic safety explosion-proof temperature control method, which comprises the following steps: A1. A sensor obtains a plurality of parameters, the parameters comprising a current temperature T n , a target temperature T d , a current intrinsic safety voltage V o and a current intrinsic safety current I o ; A2. A controller obtains a temperature difference value ΔT = |T n -T d |, and compares ΔT, T1 and T2; T1 and T2 are preset threshold values, and T1>T2; if ΔT>T1, a maximum voltage V i,max is output; if T2≤ΔT≤T1, a step voltage V i,step is output by using a step prediction model established based on a temperature control device; if ΔT<T2, a time when ΔT<T2 and a preset T adj,max time are compared, and a step prediction model or a continuous prediction model is selected according to a comparison result, the continuous prediction model outputs a voltage V i,opt ; A3. A final voltage V i,max is obtained according to the voltage V i,step , V i,opt or V i . The application has the advantages of high working efficiency and the like.

Description

Technical Field

[0001] This invention relates to the field of explosion protection, and particularly to an intrinsically safe explosion-proof temperature control method. Background Technology

[0002] In intrinsically safe temperature control designs, such as Figure 1 As shown, the safety zone power module generates a constant power supply V. i V is generated after passing through a safety barrier (Zener barrier or isolation barrier). o There exists a certain pressure drop ΔV=V o -V i Because the temperature control device requires different currents I under different ambient temperatures and target temperatures. o However, due to the design requirements of the safety barrier (current limiting and voltage limiting), it has a certain impedance, causing ΔV to change with the current I. o It changes with the changes, and V o Dynamic changes can bring about the following technical problems.

[0003] 1. This will result in low circuit efficiency and high noise in the hazardous area.

[0004] 2. The temperature control loop design becomes more complex and prone to oscillation.

[0005] 3. In severe cases, even due to V o Low voltage affects the normal operation of intrinsically safe circuits and temperature control devices.

[0006] To solve the above-mentioned technical problems, the existing technical solutions are as follows:

[0007] To ensure the minimum V o The design requirements must be met, while also satisfying I o To meet the maximum dynamic range requirement, a relatively high constant V will be selected. i The voltage causes the power consumption of the safety barrier to be P = (V) i -V o )·I o Higher temperatures result in greater temperature rise, affecting circuit drift and device lifespan. Summary of the Invention

[0008] To address the shortcomings of the existing technical solutions, this invention provides an intrinsically safe and explosion-proof temperature control method.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] An intrinsically safe explosion-proof temperature control method includes setting up a first power supply and a first safety barrier in the safe zone, and sequentially setting up a second power supply, an intrinsically safe circuit, and a temperature control device in the hazardous zone, with the first safety barrier connected to the second power supply; the temperature control method includes the following steps:

[0011] A1. The sensor obtains multiple parameters, including the current temperature T n , the target temperature T d , the current intrinsically safe voltage V o and the current intrinsically safe current I o ;

[0012] A2. The controller obtains the temperature difference ΔT = |T n - T d |, and compares ΔT, T1 and T2; T1 and T2 are preset thresholds respectively, and T1 > T2;

[0013] If ΔT > T1, output the maximum voltage V i,max ;

[0014] If T2 ≤ ΔT ≤ T1, use the step prediction model established based on the temperature control device to output the step voltage V i,step ;

[0015] If ΔT < T2, compare the time when ΔT < T2 with the preset T adj,max time, and select the step prediction model or the continuous prediction model according to the comparison result. The continuous prediction model outputs the voltage V i,opt ;

[0016] A3. Obtain the final voltage V i,max , V i,step or V i,opt , and the controller adjusts the output voltage of the first power supply to V i . i .

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. Reduce the noise of the intrinsically safe circuit and improve the circuit stability;

[0019] 2. Improve the working efficiency of the intrinsically safe circuit;

[0020] 3. Improve the working efficiency and lifespan of the safety barrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Referring to the accompanying drawings, the disclosure of the present invention will become more understandable. It is easy for those skilled in the art to understand that these drawings are only used to illustrate the technical solutions of the present invention and are not intended to limit the protection scope of the present invention. In the figures:

[0022] Figure 1 is the power supply link design diagram of the prior art;

[0023] Figure 2 is the power supply link design diagram of the present invention;

[0024] Figure 3 This is a schematic flowchart of the temperature control method of the present invention;

[0025] Figure 4 This is a schematic diagram illustrating the expected results of Embodiment 2 of the present invention;

[0026] Figure 5 This is a schematic diagram of the measured temperature and voltage in Embodiment 2 of the present invention;

[0027] Figure 6 This is a schematic diagram of the measured temperature and voltage in Embodiment 3 of the present invention. Detailed Implementation

[0028] Figures 2-6 The following description illustrates optional embodiments of the invention to teach those skilled in the art how to implement and reproduce the invention. Some conventional aspects have been simplified or omitted to teach the technical solutions of the invention. Those skilled in the art should understand that variations or substitutions derived from these embodiments will be within the scope of the invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the invention. Therefore, the invention is not limited to the optional embodiments described below, but is defined only by the claims and their equivalents.

[0029] Example 1

[0030] This embodiment provides an intrinsically safe explosion-proof temperature control method, such as... Figure 2 As shown, a first power supply, a first safety barrier, and a controller are installed in the safe zone, while a second power supply, an intrinsically safe circuit, and a temperature control device are installed in sequence in the hazardous zone. The first safety barrier is connected to the second power supply.

[0031] like Figure 3 As shown, the temperature control method includes the following steps:

[0032] A1. The sensor acquires multiple parameters, including the current temperature T. n Target temperature T d Current intrinsically safe voltage V o and the current intrinsically safe current I o ;

[0033] A2. The controller obtains the temperature difference ΔT = |T n -T d | and compare ΔT, T1, and T2; T1 and T2 are preset thresholds, and T1>T2;

[0034] If ΔT>T1, the maximum output voltage V i,max ;

[0035] If T2 ≤ ΔT ≤ T1, the stepped voltage V is output using the stepped prediction model established based on the temperature control device i,step ;

[0036] If ΔT < T2, compare the time when ΔT < T2 with the preset T adj,max time, and select the stepped prediction model or the continuous prediction model according to the comparison result. The continuous prediction model outputs the voltage V i,opt ;

[0037] A3. Obtain the final voltage V i,max 、V i,step or V i,opt , and the controller adjusts the output voltage of the first power supply to V i . i .

[0038] To improve work efficiency, the selection method is as follows:

[0039] If the duration of ΔT < T2 exceeds T adj,max time, select the continuous prediction model;

[0040] If the duration of ΔT < T2 does not exceed T adj,max time, select the stepped prediction model.

[0041] To meet rationality, further, the change rates dV i and V i satisfy: i V i,min <Vi < V i,max , dV i,min < dV i < dV i,max i,min ;

[0043] i,min i,max V<000005 (V is the minimum voltage, and dV i,min 、dV i,max are the change rates of the minimum voltage and the maximum voltage respectively.

[0044] To obtain the accurate maximum voltage, further, the method for obtaining the maximum voltage V i,max is as follows:

[0045] Calculate the maximum total power consumption P of all circuits in the danger zone max , and based on the lowest output voltage V o,min at which it can work properly, calculate the current I o,max = P max / V o,min ;

[0046] Obtain the maximum voltage drop ΔV on the first safety barrier, ΔV = I o,max ·R is , R is is the impedance of the first safety barrier;

[0047] Obtain V i,max = V o,min +ΔV + V margin , V margin is the safety margin.

[0048] In order to obtain an accurate output voltage, further, the step prediction model is:

[0049] V i,step = V i,max -ΔV step,max ·[1 - ξ(m - 1) / n], ΔV step,max = V i,max - V i,opt ;

[0050] ΔV step,max is the maximum step adjustment voltage, ξ is the control time influence factor, m, n are the step temperature interval factors, V i,opt is the voltage corresponding to the first power supply when the temperature control is stable.

[0051] In order to obtain an accurate ξ, further, according to the calculation speed from high to low, the value-taking methods of ξ are respectively:

[0052] ξ = k, ξ = k(1 - T adj / T step,max ), ξ = k(1 - T adj / T step,max ); 2 ξ = k·exp(-n·T adj / T step,max );

[0053] 0 < T adj ≤ T step,max , k is a constant with 0 < k ≤ 1.

[0054] In order to obtain accurate m, n, further, the value-taking methods of m, n are:

[0055] Divide ΔV step,max into steps, divided into n linear intervals, and the interval m is [(m - 1)ΔV step,max / n, mΔV step,max / n], m = 1, 2 ··· n, and the corresponding temperature step interval division adopts Gaussian distribution division, so that V m = ΔV step,max is located at 3σ of the Gaussian distribution, and the Gaussian distribution probability density function ;

[0056] The temperature division ratio p(m) corresponding to the first m intervals is:

[0057] ;

[0058] The actual temperature division interval corresponding to the m-th interval is [p(m-1)ΔT]. max ,p(m)ΔT max The overlapping portion of the two temperature division intervals is taken as the hysteresis interval.

[0059] To obtain an accurate output voltage, the step prediction model is further as follows:

[0060] V i,step (m)=V o,min +I o,max ·R is +V margin -ΔV step,max ·[1-ξ(m-1) / n];

[0061] ΔT∈[p(m-1)ΔT max ,p(m)ΔT max ].

[0062] To obtain an accurate output voltage, the continuous prediction model is further defined as follows:

[0063] The preset temperature difference range T2 includes multiple stepped intervals. Each interval is smoothed using polynomial fitting. The input value is the temperature difference ΔT, and the output value is the continuously corrected voltage dV. opt ;

[0064] When the measured ΔT falls within the corresponding interval, dV is calculated using the polynomial corresponding to that interval. opt The output voltage V is obtained. i,opt =V i,max -dV opt .

[0065] Example 2

[0066] An application example of the intrinsically safe explosion-proof temperature control method in Embodiment 1 of the present invention.

[0067] In this application example, such as Figure 2 As shown, the parameters obtained by the sensors are transmitted directly to the controller wirelessly. The first safety barrier is a Zener barrier. The heating wire is a 10-ohm resistance wire with a maximum power of 1W. The ambient temperature is 25 degrees Celsius, and the target temperature is 40 degrees Celsius.

[0068] The intrinsically safe explosion-proof rating is ia. The Zener gate parameters are: current-limiting resistor R is 4.7 ohms, Uo is 5.9V, and the maximum intrinsically safe current limit Io = 5.9 / 4.7 = 1.25A. The expected temperature control result is as follows... Figure 4 As shown.

[0069] Maximum voltage V i,max The way to obtain it is:

[0070] The minimum operating voltage requirement for an intrinsically safe circuit is 3.3V, so the maximum operating current is (5.9-3.3) / 4.7=0.55A. Considering that the intrinsically safe circuit is a low-power circuit except for heating, the actual maximum current on the heating wire can reach 5.9 / (10+4.7)=0.4A<0.55A.

[0071] Since the maximum power of this heating wire is 1W, that is, the maximum voltage of the heating wire is V. t,max =(1W·10Ω) 0.5 =3.16V, the maximum current of the heating wire is I t,max =3.16 / 10 = 0.316A < 0.4A, which is reasonable. This means the intrinsically safe circuit can reach its maximum heating power, at which point the maximum voltage V can be obtained. i,max :

[0072] V i,max =V o,min +ΔV+V margin =3.3 + 3.16 · 4.7 + 0.1 = 4.9V.

[0073] Stepped prediction model design:

[0074] Through the closed-loop feedback control design of the heating wire, the average current is 0.2A when the control is stable.

[0075] V i,opt =3.3 + 0.2 · 4.7 + 0.1 = 4.34 V.

[0076] During control, the overshoot temperature reached a maximum of 45 degrees Celsius. The design temperature range (T1) is 6 degrees Celsius. The control step range is designed with three levels, i.e., n=3. The optimal control voltage V at stable operation is... i,opt =4.34V, then the corresponding voltage steps are [4.34V, 4.53V], [4.53V, 4.71V], [4.71V, 4.9V].

[0077] The temperature influence factors p(m) = ∫p(ΔV) are set to 0.68, 0.95, and 0.997, respectively. Therefore, the corresponding temperature ranges for each level are [0, 4.08℃], [4.08℃, 5.7℃], and [5.7℃, 6℃]. Finally, the time influence factor ξ is set to a constant value, ξ = 1.

[0078] Continuous prediction model design:

[0079] The design temperature is T2=2℃. Considering the computational complexity and the relatively small temperature difference in the actual system, the fitting function is chosen to be a first-order linear fit, i.e., y=a0+a1x+a2x. 2 In the given information, a2 = 0.

[0080] When [0, T2] is in the first-level interval [0, 4.08℃], the corresponding voltage is [4.34V, 4.53V], and the fitting function is:

[0081] V = 4.34 + 0.046 ΔT, that is, a0 = 4.34 V, a1 = 0.046 V / ℃.

[0082] Take T adj,max =10s.

[0083] The measured temperature control results are as follows Figure 5 As shown.

[0084] When control is stable, it is generally in the continuous prediction stage, and the efficiency of the conventional scheme is 0.2. 2 A·10Ω / (4.9V·0.2A) = 40.1%, the efficiency of this scheme is 0.2%. 2 A·10Ω / (4.34V·0.2A)=46.1%, the efficiency is relatively improved by (46.1%-40.1%) / 40.1%=15%.

[0085] During the control process, it is generally in the step prediction stage, and the relative efficiency improvement is less than 15%.

[0086] Example 3

[0087] An application example of the intrinsically safe explosion-proof temperature control method in Embodiment 1 of the present invention.

[0088] In this application example, such as Figure 2 As shown, the first safety barrier is a Zener barrier, and the temperature control device is a thermoelectric cooler. The thermoelectric cooler is equivalent to a 5Ω resistor and has a cooling power of 2W.

[0089] Design requirements: Ambient temperature is 25 degrees Celsius, target temperature is 20 degrees Celsius.

[0090] The intrinsically safe explosion-proof Zener barrier parameters are as follows: current-limiting resistor R is 4.0 ohms, U... o The voltage is 6.0V, and the intrinsically safe maximum current limit is I. o =6.0V / 4.0Ω=1.5A. The average current is 0.4A when the temperature control is stable.

[0091] Maximum input voltage calculation:

[0092] The minimum operating voltage requirement for an intrinsically safe circuit is 2.5V, so the maximum operating current is (6.0V-2.5V) / 4.0Ω=0.88A. Considering that the intrinsically safe circuit is a low-power circuit except for cooling, the actual maximum cooling current can reach 6.0V / (5Ω+4.0Ω)=0.67A<0.88A.

[0093] Since a thermoelectric cooler can be equivalent to a resistor, its maximum cooling power is 2W and its maximum current is I. t,max =(2W / 5Ω) 0.5 =0.63A < 0.67A. This means the intrinsically safe circuit can achieve its maximum cooling power, at which point the maximum input voltage V can be obtained. i,max .

[0094] V i,max =V o,min +I o,max ·Ris+V margin =2.5V+0.63A·4.0Ω+0.1V=5.13V.

[0095] Stepped prediction model design:

[0096] Through closed-loop feedback control design, the average current when the control is stable is 0.4A, that is, V when stable. i,opt .

[0097] V i,opt =2.5V+0.4A·4.0Ω+0.1V=4.2V.

[0098] During control, the minimum overshoot temperature reached 17 degrees Celsius. The design T1 = 3 degrees Celsius, and the control step range was designed with 3 levels (n = 3). The optimal control voltage V at steady state was determined. i,opt =4.2V, then the corresponding voltage steps are [4.2V, 4.51V], [4.51V, 4.82V], [4.82V, 5.13V]. The temperature influence factors p(m) = ∫p(ΔV) are 0.68, 0.95, and 0.997 respectively. Therefore, the corresponding temperature ranges for each level are [0, 2.04℃], [2.04℃, 2.85℃], and [2.85℃, 3℃].

[0099] Finally, assuming a linear relationship between the control time influence factor and the longest step model control time is T. step,max =30s, ξ=1-T adj / 30,0 <T adj <30.

[0100] Therefore, let ΔV step,max =0.9V, the voltage output of the step prediction model is:

[0101] V i,step(m) = 5.13V - 0.9V·[1 - (1 - T) adj [ / 30)(m-1) / n],0 <T adj <30.

[0102] Continuous prediction model design:

[0103] The design temperature is T2=1℃. Considering the computational complexity and the relatively small temperature difference in the actual system, the fitting function is chosen to be a first-order linear fit, i.e., y=a0+a1x+a2x. 2 In the given information, a2 = 0.

[0104] When [0, T2] is in the first-level interval [0, 2.04℃], the corresponding voltage is [4.2V, 4.51V], and the fitting function is:

[0105] V = 4.2 + 0.152 · ΔT, that is, a0 = 4.2V, a1 = 0.152V / ℃.

[0106] Take T adj,max =10s.

[0107] The measured temperature control results are as follows Figure 6 As shown.

[0108] When control is stable, it is generally in the continuous prediction stage, and the efficiency of the conventional scheme is 0.4. 2 A·5Ω / (5.13V·0.4A) = 39%, the efficiency of the patented solution is 0.4. 2 A·5Ω / (4.2V·0.4A)=48%, the efficiency is relatively improved by (48%-39%) / 39%=23%.

[0109] During the control process, it is generally in the step prediction stage, with a relative efficiency improvement of less than 23%, but higher than the constant step model.

[0110] In the above embodiments, the output parameters of the sensor are transmitted to the controller wirelessly. Of course, a second safety barrier can also be set in the safety zone. The parameters obtained by the sensor are first transmitted to the second safety barrier via wired means, and then transmitted to the controller.

Claims

1. An intrinsically safe explosion-proof temperature control method, comprising setting up a first power supply and a first safety barrier in a safe zone, and sequentially setting up a second power supply, an intrinsically safe circuit, and a temperature control device in a hazardous zone, wherein the first safety barrier is connected to the second power supply; characterized in that, The temperature control method includes the following steps: A1. The sensor acquires multiple parameters, including the current temperature T. n Target temperature T d Current intrinsically safe voltage V o and the current intrinsically safe current I o ; A2. The controller obtains the temperature difference ΔT = |T n -T d | and compare ΔT, T1, and T2; T1 and T2 are preset thresholds, and T1>T2; If ΔT>T1, the maximum output voltage V i,max ; If T2≤ΔT≤T1, the stepped prediction model based on the temperature control device is used to output the stepped voltage V. i,step ; If ΔT < T2, compare the time when ΔT < T2 with the preset time T, and select the step prediction model or the continuous prediction model according to the comparison result. The continuous prediction model outputs a voltage V adj,max ; i,opt ; A3. Based on voltage V i,max V i,step or V i,opt Obtain the final voltage V i The controller adjusts the output voltage of the first power supply to V. i ; The ladder prediction model is as follows: V i,step =V i,max -ΔV step,max ·[1-ξ(m-1) / n],ΔV step,max =V i,max -V i,opt ; ΔV step,max ξ is the maximum step adjustment voltage, ξ is the control time influence factor, m and n are the step temperature range factors, and V i,opt This is the voltage corresponding to the first power supply when the temperature control is stable; The continuous prediction model is as follows: The preset temperature difference range T2 includes multiple stepped intervals. Each interval is smoothed using polynomial fitting. The input value is the temperature difference ΔT, and the output value is the continuously corrected voltage dV. opt ; When the measured ΔT falls within the corresponding interval, dV is calculated using the polynomial corresponding to that interval. opt The output voltage V is obtained. i,opt =V i,max -dV opt .

2. The temperature control method according to claim 1, characterized in that, The selection method is as follows: If the duration of ΔT < T2 exceeds T adj,max time, select the continuous prediction model; If the duration for which ΔT < T2 does not exceed T adj,max in time, select the step prediction model.

3. The temperature control method according to claim 1, characterized in that, Voltage V i and V i rate of change dV i satisfy: V i,min <Vi<V i,max ,dV i,min <dV i <dV i,max ; V i,min It is the minimum voltage, dV i,min dV i,max These are the rates of change of the minimum and maximum voltages, respectively.

4. The temperature control method according to claim 1, characterized in that, Maximum voltage V i,max The way to obtain it is: Calculate the maximum total power consumption P of all circuits in the hazardous area. max Based on the minimum output voltage V required for normal operation o,min Calculate the current I o,max =P max / V o,min ; Obtain the maximum voltage drop ΔV=I on the first safety barrier o,max ·R is R is It is the impedance of the first safety barrier; Get V i,max =V o,min +ΔV+V margin V margin For safety margin.

5. The temperature control method according to claim 1, characterized in that, Based on the calculation speed from high to low, the values ​​of ξ are taken in the following ways: ξ=k,ξ=k(1-T adj / T step,max ),ξ=k(1-T adj / T step,max ) 2 ,ξ=k·exp(-n·T adj / T step,max ); 0 < T adj ≤ T step,max , where k is a constant with 0 < k ≤ 1.

6. The temperature control method according to claim 1, characterized in that, The values ​​of m and n are selected as follows: ΔV step,max The system is divided into n linear intervals, with interval m being [(m-1)ΔV step,max / n,mΔV step,max [ / n], m=1,2···n, the corresponding temperature step intervals are divided using a Gaussian distribution, so that V m =ΔV step,max Located at 3σ in a Gaussian distribution, the probability density function of the Gaussian distribution. ; The temperature division ratio p(m) corresponding to the first m intervals is: ； The actual temperature division interval corresponding to the m-th interval is [p(m-1)ΔT]. max ,p(m)ΔT max The overlapping portion of the two temperature division intervals is taken as the hysteresis interval.

7. The temperature control method according to claim 6, characterized in that, The ladder prediction model is as follows: V i,step (m)=V o,min +I o,max ·R is +V margin -ΔV step,max ·[1-ξ(m-1) / n]; ΔT∈[p(m-1)ΔT max ,p(m)ΔT max ]。 8. The temperature control method according to claim 1, characterized in that, The parameters are transmitted directly to the controller wirelessly, or first to the second safety barrier via a wired connection, and then to the controller.

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