CN202257322U - Temperature control device - Google Patents

Abstract

The utility model relates to a temperature control device, comprising a temperature detection circuit, an analog-to-digital conversion circuit, a central processing unit, an I2C communication circuit, and an on-off control circuit, wherein the temperature detection circuit is arranged in a container where a heater is located; the analog-to-digital conversion circuit is arranged in the locality of the temperature detection circuit; the analog signal input end of the analog-to-digital conversion circuit is connected with the analog signal output end of the temperature detection circuit; the digital signal output end of the analog-to-digital conversion circuit is connected with the digital signal input end of the central processing unit through the I2C communication circuit; the control end of the on-off control circuit is connected with the control signal output end of the central processing unit; the input end of the on-off control circuit is connected with a power supply; and the output end of the on-off control circuit is connected with the input end of the heater. The temperature control device improves the temperature control precision.

Description

Attemperating unit

Technical field

The utility model relates to the automated production field, in particular to a kind of attemperating unit.

Background technology

In various production runes, heating process becomes more efficient, energy supply is more accurate in order to make, and the temperature of well heater is controlled just become particularly important.In order to improve the accuracy of heter temperature control, generally can adopt the closed loop thermal control method.Conventional closed loop thermal control device generally comprises temperature signal collection circuit, analog to digital conversion circuit, microprocessor, ON-OFF control circuit etc.Temperature signal collection circuit and analog to digital conversion circuit are used to obtain temperature signal, export microprocessor to.This microprocessor is handled temperature signal, produces heater control signal, exports ON-OFF control circuit to, forms the closed-loop control to temperature.

Platinum resistance temperature sensor is to utilize its resistance to become certain funtcional relationship with temperature and the temperature sensor processed, because its accuracy of measurement is high, measurement range is big, stability is high, is widely used in temperature precision measurement field.PT100 is a kind of temperature element of widespread use, and the linearity is high, measurement is accurate, interchangeability is good, the anti-vibrating and impact performance is good, in-50 ℃～600 ℃ scopes, has other temperature sensor incomparable advantage.In the temperature survey field, can the PT100 temperature sensor directly be placed liquid environment, measure accurate, direct.

In the prior art; Produce analog electrical signal through PT100 temperature sensor detected temperatures, long-distance transmissions is carried out analog to digital conversion at the microprocessor end and is obtained digital signal to microprocessor then; By microprocessor digital signal is handled then, produced control signal.Yet the PT100 temperature sensor produces is generally fainter analog electrical signal, in long-distance transmissions, very easily is interfered the accuracy that influence is measured.

The utility model content

The utility model aims to provide a kind of attemperating unit, to solve the lower problem of existing attemperating unit precision.

In the embodiment of the utility model, a kind of attemperating unit is provided, comprising: temperature sensing circuit is arranged in the residing container of well heater; Analog to digital conversion circuit is arranged on this locality of temperature sensing circuit, and the input end of analog signal of analog to digital conversion circuit connects the analog signal output of temperature sensing circuit; CPU; The I2C communication line is connected to the digital signal output end of analog to digital conversion circuit the digital signal input end of CPU; ON-OFF control circuit, its control end connects the control signal output ends of CPU, and its input end connects power supply, and its output terminal connects the input end of well heater.

The attemperating unit of the utility model is a digital signal because of what transmit, thus overcome the lower problem of existing attemperating unit precision, and then improved accuracy of temperature control.

Description of drawings

Accompanying drawing described herein is used to provide the further understanding to the utility model, constitutes the application's a part, and illustrative examples of the utility model and explanation thereof are used to explain the utility model, do not constitute the improper qualification to the utility model.In the accompanying drawings:

The structural representation of a kind of attemperating unit that Fig. 1 provides for the utility model embodiment;

The principle schematic of the PT100 testing circuit that Fig. 2 provides for the utility model embodiment;

The circuit theory synoptic diagram of the PT100 testing circuit that Fig. 3 provides for the utility model embodiment;

The circuit theory synoptic diagram of the reference voltage source that Fig. 4 provides for the utility model embodiment;

The SCM peripheral reset circuit principle schematic that Fig. 5 provides for the utility model embodiment;

The schematic flow sheet of a kind of closed loop thermal control method that Fig. 6 provides for the utility model embodiment;

The Single-chip Controlling schematic flow sheet that Fig. 7 provides for the utility model embodiment;

The structural representation of a kind of attemperating unit that Fig. 8 provides for the utility model preferred embodiment;

The electrical block diagram of a kind of attemperating unit that Fig. 9 provides for the utility model embodiment;

The circuit theory synoptic diagram of the LCD backlight voltage that Figure 10 provides for the utility model embodiment.

Embodiment

Below with reference to accompanying drawing and combine embodiment, specify the utility model.

The structural representation of a kind of attemperating unit that Fig. 1 provides for the utility model embodiment comprises:

Temperature sensing circuit 14 is arranged in the well heater 12 residing containers 10;

Analog to digital conversion circuit 26 is arranged on this locality of temperature sensing circuit 14, and the input end of analog signal of analog to digital conversion circuit 26 connects the analog signal output of temperature sensing circuit 14;

CPU 18;

I2C communication line 16 is connected to the digital signal output end of analog to digital conversion circuit 26 digital signal input end of CPU 18;

ON-OFF control circuit 20, its control end connects the control signal output ends of CPU 18, and its input end connects power supply, and its output terminal connects the input end of well heater 12.

In the present embodiment, temperature sensing circuit is used for the actual temperature at the heater terminal tracer liquid, after analog to digital conversion, by I2C communication temperature value is reached CPU.In the attemperating unit of correlation technique, analog to digital conversion circuit is arranged on this end of CPU, so the simulating signal that temperature sensing circuit produces gets the long-distance CPU that is transferred to, and causes decay bigger, produces error.And in the present embodiment, analog to digital conversion circuit is arranged on this end of temperature sensing circuit, thus digital data transmission is arrived CPU, can not produce decay and error, improved accuracy of temperature control.

The attemperating unit that the utility model embodiment provides can be realized real-time detection and closed-loop control to temperature.Can find out that from circuit structure whole ON-OFF control circuit is simple in structure, realize with low cost.

Preferably, temperature sensing circuit comprises: 1 PT100 thermo-sensitive resistor R _TWith 3 conventional, electric-resistance R ₁, R ₂, R ₃, R _TAnd R ₃Resistance is identical under design temperature, R ₁And R ₂Resistance is identical under design temperature, with R _TAnd R ₁, R ₂, R ₃Connect into electric bridge, R ₁And R ₂Connect bias supply altogether, R _TAnd R ₃Be total to ground connection, and with R _TBe arranged in the residing container of well heater.

The principle schematic of the PT100 testing circuit that Fig. 2 provides for the utility model embodiment.The PT100 testing circuit that the utility model embodiment provides adopts typical unbalanced bridge to connect method, and the main effect of electric bridge is the change that the resistance value that the PT100 temperature sensor changes along with temperature variation is converted into magnitude of voltage.When selecting R ₁=R ₂=R ₃During=100om, bridge sensitivity is maximum.But, change into and select R because the PT100 electric current is crossed the accuracy that conference causes resistance heating and then influence to be measured ₁=R ₂=2Kom, R ₃=100om.

Under parameter current is selected, 1 ℃ of the every variation of temperature, the variation of output voltage is about 0.7mV, and is fainter, before getting into analog to digital converter, needs to increase the one-level filter amplifier.Fig. 3 further shows the circuit theory diagrams of the PT100 testing circuit that the utility model embodiment adopted, and comprises unbalanced bridge, electric bridge amplifying circuit and secondary LPF amplifying circuit.Wherein, the voltage signal computing formula of electric bridge amplifying circuit is following:

$V_{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="HSA00000587442700021.png,HSA00000587442700022.png"\; state="\{\{state\}\}">r</figure-callout>}1}=V_{\mathrm{DD}}\&CenterDot;\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="R\; t\; R"\; filenames="HSA00000587442700022.png,HSA00000587442700031.png"\; state="\{\{state\}\}">R</figure-callout>}}_t}{R_{}}\right)$

$\frac{V_{r2}}{{\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="HSA00000587442700022.png,HSA00000587442700031.png"\; state="\{\{state\}\}">R</figure-callout>}}_3}=\frac{V_{\mathrm{DD}}-V_{r1}}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HSA00000587442700021.png,HSA00000587442700022.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}+\frac{V_{o1}-V_{r1}}{{\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="HSA00000587442700021.png,HSA00000587442700022.png"\; state="\{\{state\}\}">R</figure-callout>}}_4}$

V _r1＝V _r2

Can draw by above 3 formulas:

$V_{o1}={\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="HSA00000587442700021.png,HSA00000587442700022.png"\; state="\{\{state\}\}">R</figure-callout>}}_4\&CenterDot;V_{\mathrm{DD}}((\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HSA00000587442700021.png,HSA00000587442700022.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}+\frac{1}{{\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="HSA00000587442700022.png,HSA00000587442700031.png"\; state="\{\{state\}\}">R</figure-callout>}}_3}+\frac{1}{R_4})\&CenterDot;\frac{{\mathrm{<figure-callout\; id="2"\; label="R\; t\; R"\; filenames="HSA00000587442700022.png,HSA00000587442700031.png"\; state="\{\{state\}\}">R</figure-callout>}}_t}{R_{}}-\frac{1}{R_1})$

$\frac{{\mathrm{dV}}_{o1}}{d{R}_t}=R_4\&CenterDot;V_{\mathrm{DD}}(\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HSA00000587442700021.png,HSA00000587442700022.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}+\frac{1}{R_3}+\frac{1}{R_4})\&CenterDot;\frac{R_2}{{(R_2+R_t)}^2}$

Under parameter current is selected, 1 ℃ of the every variation of temperature, output voltage V o1 becomes 51mV.Change the resistance of R4, can regulate enlargement factor, and change measurement range.

The second-order low-pass filter amplifying circuit of selecting homophase to amplify; Simultaneously because temperature signal changes slowly; And disturb for the power frequency of filtering 50Hz, the cutoff frequency that wave filter is set is 10Hz, and this cutoff frequency can be regulated through the value that changes R5, R6, C2, C3.After the filtering amplification, 1 ℃ of the every variation of temperature, output voltage changes more than the 51mV.For 10 analog to digital converter, can realize about 0.1 ℃ temperature resolution.

Preferably, it is the modulus conversion chip of MAX1238 that analog to digital conversion circuit adopts model, and this is a 12,10 passage ADC with 2 line serial line interfaces, can set up I2C with single-chip microcomputer and communicate by letter.

This attemperating unit also comprises and is used to the reference voltage source that analog to digital conversion circuit provides accurate reference voltage, prevents the harmful effect that mains fluctuations cause, and guarantees the precision and the degree of stability of whole measuring system.It is the accurate voltage reference chip of REF198ES that the reference voltage source that is used for analog to digital conversion circuit that the utility model embodiment provides is selected model, the reference voltage of output 4.096V.But it will be appreciated by persons skilled in the art that and to select other any suitable Voltage Reference chip.Fig. 4 further shows the circuit theory diagrams of the reference voltage source that the utility model embodiment adopted.Wherein, 2 pin are the voltage input pin, and 1,5,7,8 pin are unsettled, owing to do not need park mode, so 3 pin are connected to the voltage input pin.According to the recommendation circuit of chip data, input end uses the shunt capacitance combination of 10uF/0.1uF, and output terminal uses the shunt capacitance combination of 1uF/0.1uF.

Preferably, CPU comprises: model is 51 series monolithics of AT89C51ED2,18.432MHz external crystal-controlled oscillation and external reset circuit.The SCM peripheral reset circuit principle schematic that Fig. 5 provides for the utility model embodiment.MAX811 is 4 pin microprocessor voltage monitors, has the hand-reset input of shaking.3 pin of MAX811 are the hand-reset input end, and low level is effective, and this moment, reverse reset output terminal also was that low level is effective.Because AT89C51ED2 is that high level resets, added one-level reverser NC7S04 between the input pin so reset at MAX811 and single-chip microcomputer.

Preferably, CPU comprises: difference calculating module is used to calculate from the temperature value that digital signal reflected of I2C communication line and the difference of preset temperature; Warming module is used in difference sending the control signal that keeps heating during greater than threshold value (for example 5 ℃); PID (PID control) module is used for when difference is not more than threshold value, carries out pid control algorithm, sends pwm control signal.

Preferably, CPU also comprises: overtime alarm module is used for when heating is overtime, sending alerting signal.

Preferably; ON-OFF control circuit comprises relay drive circuit and ac solid relay; The control end of relay drive circuit connects the control signal output ends of CPU; Its drive signal output terminal connects the switch control end of ac solid relay, and the ac solid relay input end connects AC power, and its output terminal connects well heater.Relay drive circuit is used for converting the control signal that receives into the corresponding relays drive signal, and then the conducting and the shutoff of control ac solid relay, realizes the break-make of heater voltage, reaches regulation and control heater power and and then the purpose of control temperature.

The schematic flow sheet of a kind of closed loop thermal control method that Fig. 6 provides for the utility model embodiment.Wherein, in step S101, the actual value of PT100 testing circuit detected temperatures, after analog to digital conversion by the I2C communications to CPU.Subsequently, in step S102, single-chip microcomputer (the being CPU) setting value of accounting temperature and the difference of actual value.In step S103, when difference during greater than 5 ℃ (being threshold value), for example design temperature is 80 ℃, and when detecting temperature and being lower than 75 ℃, the shielding pid control algorithm, and the conducting that keeps heater voltage realizes the fast rise of temperature and near setting value.Monitor heating overtime situation simultaneously, when heat time heating time greater than the maximum time of setting, and temperature gap is during still greater than 5 ℃; Then think the heating system fault; Single-chip microcomputer will be notified the upper strata PC through the mode of serial communication, and close well heater, the safety of protection system.When difference smaller or equal to 5 ℃, open pid control algorithm, the break-make of output pwm signal control solid-state relay, thereby effective heating power of control heater realize the precise and stable control of temperature.Afterwards; Program gets into step S104, converts the pwm signal that receives the drive signal of ac solid relay into by control section, by the break-make of ac solid relay control heater voltage; Realize the adjusting of the effective heating power of well heater, realize the closed-loop control of temperature.Program is repeating step S101, S102, S103, S104 successively, to realize the accurate control to heater power.

Fig. 7 further shows the monolithic processor controlled schematic flow sheet that the utility model embodiment is adopted, and comprising:

Step S201 carries out initialization, and the control cycle of pwm signal is set at 2s, is divided into 100 parts to each PWM control cycle, and every section duration is realized through the interruption that timer produces 20ms.

Step S202 judges whether that 2s regularly;

Step S203 when having arrived 2s regularly, then obtains actual value;

Step S204, the difference of accounting temperature setting value and actual value;

Step S205 judges that whether difference is smaller or equal to 5 ℃;

Step S206, if not, then shielding pid control algorithm, output well heater normal open signal is to keep the conducting of heater voltage;

Step S207, otherwise, the operation pid algorithm;

Step S208, output pwm signal is got back to step S202 then with the heating amplitude of control heater.

The pid algorithm that the utility model embodiment is adopted is applicable to the interchange well heater of 220VAC/50Hz power supply.Call pid algorithm to this difference and draw an integer controlled quentity controlled variable H between 0～100, corresponding required dutycycle.In the 2s of next PWM control cycle, H 20ms of heater voltage conducting cuts off (100-H) individual 20ms, realizes the adjusting of dutycycle with this.The utility model embodiment through the PT100 system for detecting temperature, combine the introducing of the pid control algorithm etc. of PWM technology, realized closed-loop control to temperature, the fluctuation of temperature is controlled at ± 0.1 ℃ in.In addition, through restriction to the pid algorithm usable range, guarantee temperature control accurate and stable in, realized that also temperature reaches the requirement of setting value at short notice fast.

Preferably, this attemperating unit also comprises: ac solid relay employing model is that the plate of CXE240D5 carries relay, and it is the driver ic of ULN2803 that relay drive circuit adopts model.

The structural representation of a kind of attemperating unit that Fig. 8 provides for the utility model preferred embodiment.Preferably, this attemperating unit also comprises: display device 22, the demonstration output terminal of connection CPU; Serial communication circuit (RS232) 24; The serial ports that the serial ports of CPU is connected outer computer; The rs 232 serial interface signal that is used for level conversion CPU and outer computer realizes that CPU communicates by letter with standard RS-232 between the outer computer.Display device can show the various duties of this attemperating unit and the monitored results of temperature, and shows overtime warning.The serial communication circuit is used to set up the serial communication of CPU and PC, makes things convenient for the user that attemperating unit is debugged.

The electrical block diagram of a kind of attemperating unit that Fig. 9 provides for the utility model embodiment, comprising: PT100 testing circuit 201 is used for converting Current Temperatures into the correspondent voltage signal; Analog to digital conversion circuit 202 is used for converting voltage signal into digital signal corresponding, through I2C communication the temperature digital signal is reached CPU; Reference voltage source 203 is used to analog to digital conversion circuit accurate reference voltage is provided.This temperature control also comprises CPU, is used to receive the design temperature and the actual temperature of heating liquid, draws the ON time of well heater under the corresponding situation according to the two difference, regulates effective heating power of well heater, simultaneously temperature is monitored and is shown.

CPU comprises: single-chip microcomputer 204, be used for the reception and the storage of desired temperature, and calculate the difference of setting value and actual value, and draw the ON time of corresponding well heater according to this difference, export the corresponding relays control signal; Crystal oscillator and reset circuit 205 are used to provide single-chip microcomputer normal required external crystal-controlled oscillation signal, the hardware reset signal etc. of moving.

It is 51 series monolithics of AT89C51ED2 that the single-chip microcomputer of the utility model embodiment is selected model.Can desired temperature be write the inner EEPROM of single-chip microcomputer, will directly from EEPROM obtain current desired temperature after system powers at every turn.Through the serial communication of foundation, can new desired temperature be write single-chip microcomputer, and come into force at once with PC.Simultaneously, single-chip microcomputer will be exported the liquid crystal display control signal, be used for the normal demonstration of liquid crystal display.

The SCM peripheral circuit that the utility model embodiment provides comprises 18.432MHz external crystal-controlled oscillation and external reset circuit (seeing also Fig. 5).

This attemperating unit also comprises serial communication circuit 207, is used for the conversion of Transistor-Transistor Logic level and RS232 level, sets up the serial communication of CPU and PC.The serial communication circuit that the utility model embodiment provides is selected the MAX3232 chip, adopts proprietary low pressure differential transmitter output stage, supply voltage 5V or 3.3V, power consumption 0.3mA, external 4 0.1uF electric capacity.

This attemperating unit also comprises liquid crystal display circuit 208, is used for the demonstration of temperature control relevant information.

This attemperating unit also comprises the heating control section branch, is used to receive the relay control signal of CPU, the break-make of control heater voltage.

This heating control section branch comprises: relay drive circuit 209 is used to drive the normal folding of relay; Ac solid relay 210 is used for the break-make of control heater voltage.The ac solid relay selection model that the utility model embodiment provides is that the plate of CXE240D5 carries relay.Between control signal and CXE240D5, add driver ic ULN2803.When the ULN2803 input end is high level, corresponding delivery outlet output low level, CXE240D5 coil electricity, the adhesive of CXE240D5 contact; When the ULN2803 input end is low level, the CXE240D5 coil blackout, the CXE240D5 contact is broken off.

This attemperating unit also comprises power unit 206, and the system of being used to provides stable direct current supply voltage, and driving voltage and voltage backlight is provided for LCDs.

Display device can comprise liquid crystal display, is used for information and shows; The liquid crystal display driving circuit is used to liquid crystal display required driving voltage and voltage backlight is provided.Preferably, it is the LCD MODULE of 4 row, 20 characters of MDLS20464SP that display device adopts model, and it is the serial port chip of MAX3232 that the serial communication circuit adopts model.The selection that it will be appreciated by persons skilled in the art that LCD MODULE can be arbitrarily.The circuit theory synoptic diagram of the LCD backlight voltage that Figure 10 provides for the utility model embodiment.LT1963A is a low noise linear voltage regulator, has the adjustable voltage output of 1.21V～20V.Output voltage satisfies following relational expression:

$V_{\mathrm{LED}+}=V_{\mathrm{OUT}}=1.21V\&CenterDot;(1+\frac{R_{e2}}{R_{25}})+I_{\mathrm{ADJ}}\&CenterDot;R_{25}$

I _ADJ＝3μA?at?25℃

According to the selected parameter of reality, the output voltage range that this circuit is realized is 1.21V～4.235V.According to the device handbook of MDLS20464SP, it recommends voltage backlight is 4.1V, can realize this voltage backlight through the resistance of regulator potentiometer Re2 in the use.

The pin function table of the LCD MODULE that following table provides for the utility model embodiment:

Pin number	Symbol	State	Function
					1	Vss		Power supply ground
2	Vdd		+ 5V logic power
				3	V0		The liquid crystal drive power supply
4	RS	Input	Register selects 1; Data; 0; Instruction
				5	R/W	Input	The reading and writing operation selects 1: read; 0: write
6	E	Input	Enable signal (MDLS40466 is usefulness not, symbol NC)
				7	DB0	Ternary	Data bus (LSB)
8	DB1	Ternary	Data bus
				9	DB2	Ternary	Data bus
10	DB3	Ternary	Data bus
				11	DB4	Ternary	Data bus
12	DB5	Ternary	Data bus
				13	DB6	Ternary	Data bus
14	DB7	Ternary	Data bus (MSB)
				*15	E1	Input	MDLS40466 last two exercises can signal
*16	E2	Input	Two exercise the ability signal under the MDLS40466

Annotate: 15,16 liang of pins only are used for MDLS40466, and all the other models need not or be the input of LED-backlit power supply.

Can find out that from above description the utility model owing to introduced the close-loop feedback control of temperature, can be realized the accurate adjusting of temperature in temperature control system.The use of PT100 temperature sensor and replace original voltage signal with the digital temperature signal after the analog to digital conversion, the interference that can avoid the circuit transmission to cause to the full extent guarantees thermometric accuracy.Combining of pid control algorithm and PWM technology, realized the accurately control fast of temperature, the heating overshoot is little, temperature fluctuation can be controlled in ± 0.1 ℃ in.Because pid control algorithm will be brought into use less than the occasion of particular value (5 ℃) at temperature gap, than traditional method for heating and controlling, temperature control is quick, accurate, and it is little to fluctuate, good stability.Circuit is simple, cost is low, and stability is high.

The preferred embodiment that the above is merely the utility model is not limited to the utility model, and for a person skilled in the art, the utility model can have various changes and variation.All within the spirit and principle of the utility model, any modification of being done, be equal to replacement, improvement etc., all should be included within the protection domain of the utility model.

Claims (10)

1. an attemperating unit is characterized in that, comprising:

Temperature sensing circuit is arranged in the residing container of well heater;

Analog to digital conversion circuit is arranged on this locality of said temperature sensing circuit, and the input end of analog signal of analog-digital conversion circuit as described connects the analog signal output of said temperature sensing circuit;

CPU;

The I2C communication line is connected to the digital signal output end of analog-digital conversion circuit as described the digital signal input end of said CPU;

ON-OFF control circuit, its control end connects the control signal output ends of said CPU, and its input end connects power supply, and its output terminal connects the input end of said well heater.

2. device according to claim 1 is characterized in that, said temperature sensing circuit comprises: 1 PT100 thermo-sensitive resistor R _TWith 3 conventional, electric-resistance R ₁, R ₂, R ₃, R _TAnd R ₃Resistance is identical under design temperature, R ₁And R ₂Resistance is identical under said design temperature, with R _TAnd R ₁, R ₂, R ₃Connect into electric bridge, R ₁And R ₂Connect bias supply altogether, R _TAnd R ₃Be total to ground connection, and with R _TBe arranged in the residing container of said well heater.

3. device according to claim 1 is characterized in that, it is the modulus conversion chip of MAX1238 that analog-digital conversion circuit as described adopts model.

4. device according to claim 1 is characterized in that, said CPU comprises: model is 51 series monolithics of AT89C51ED2,18.432MHz external crystal-controlled oscillation and external reset circuit.

5. device according to claim 1 is characterized in that, said CPU comprises:

Difference calculating module is used to calculate from the temperature value that digital signal reflected of said I2C communication line and the difference of preset temperature;

Warming module is used in said difference sending the control signal that keeps heating during greater than threshold value;

The PID module is used for when said difference is not more than threshold value, carries out pid control algorithm, sends pwm control signal.

6. device according to claim 5 is characterized in that, said CPU also comprises:

Overtime alarm module is used for when heating is overtime, sending alerting signal.

7. device according to claim 1; It is characterized in that; Said ON-OFF control circuit comprises relay drive circuit and ac solid relay, and the control end of said relay drive circuit connects the control signal output ends of said CPU, and its drive signal output terminal connects the switch control end of said ac solid relay; Said ac solid relay input end connects AC power, and its output terminal connects said well heater.

8. device according to claim 7 is characterized in that, also comprises: the plate that said ac solid relay employing model is CXE240D5 carries relay, and it is the driver ic of ULN2803 that said relay drive circuit adopts model.

9. device according to claim 1 is characterized in that, also comprises:

Display device connects the demonstration output terminal of said CPU;

The serial communication circuit connects the serial ports of said CPU the serial ports of outer computer.

10. device according to claim 9 is characterized in that, it is the LCD MODULE of MDLS20464SP that said display device adopts model, and it is the serial port chip of MAX3232 that said serial communication circuit adopts model.

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