CN111273717A - System and method for realizing rapid water flow temperature control - Google Patents
System and method for realizing rapid water flow temperature control Download PDFInfo
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- CN111273717A CN111273717A CN202010241022.2A CN202010241022A CN111273717A CN 111273717 A CN111273717 A CN 111273717A CN 202010241022 A CN202010241022 A CN 202010241022A CN 111273717 A CN111273717 A CN 111273717A
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- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
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- G05D27/02—Simultaneous control of variables covered by two or more of main groups G05D1/00 - G05D25/00 characterised by the use of electric means
Abstract
The invention provides a system and a method for realizing rapid water flow temperature control, wherein the system comprises: the device comprises a water flow control element, a heating element, a water inlet temperature measuring element, a water outlet temperature measuring element, an MCU, a first high-power transistor and a second high-power transistor; the MCU is respectively electrically connected with the water inlet temperature measuring element and the water outlet temperature measuring element; the MCU is connected with the heating element through the first high-power transistor; the MCU is connected with the water flow control element through the second high-power transistor; a water flow control member for drawing water from the water tank into the heating member and controlling the flow rate and velocity of the water flowing into the heating member; the water inlet temperature measuring element is used for measuring the temperature T of water at the inlet0(ii) a And feeding back the temperature at the inlet to the MCU; the water outlet temperature measuring element is used for measuring the temperature T of water at the outlet1(ii) a Feeding back the temperature at the outlet to the MCU; the heating element is used for heating the water flow passing through the heating element.
Description
Technical Field
The invention relates to a temperature control technology, in particular to a system and a method for realizing rapid water flow temperature control.
Background
At present, the instant heating type water dispensers in the market are various in types, and on the basis of a water temperature control strategy, a method for adjusting the power of a heating element is basically adopted, and the working power of the heating element is controlled to enable the temperature of a water outlet to finally reach the target water temperature. The control strategy for adjusting the power of the heating element mainly has three disadvantages:
first, the hardware circuit needs to use a thyristor, which results in high cost of components and complex control method. A zero-crossing detection circuit needs to be designed on hardware, a zero point in each period of the 220V alternating current is found, then the size of a conduction angle of the silicon controlled element is controlled, power regulation and control of the heating element are carried out, and finally water temperature control is achieved. In addition, the heat dissipation of the thyristor is also a relatively difficult problem.
Secondly, inertia exists between the power and the temperature of the heating element, the adjustment of the power cannot rapidly cause the change of the water temperature, the real-time performance is poor, the inertia of the heating element needs to be compensated in a control algorithm, or a large number of experiments are carried out, the empirical value is used in a program, and the implementation is troublesome.
Thirdly, the heating effect of the heating element is not in a linear relation with the power, the influence of the power on the heating effect is larger at high temperature, and the resistance value of the heating element jumps after the heating element reaches a certain temperature. The reason is that the temperature deviation of the instant heating type water dispenser adopting the heating element power regulation and control method is large in the market at present.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a system and a method for realizing rapid water flow temperature control. The technical scheme of the invention is as follows:
a system for achieving rapid water flow temperature control, comprising: the water flow control element, the heating element, the water inlet temperature measuring element, the water outlet temperature measuring element, the micro control unit MCU, the first high-power transistor and the second high-power transistor;
the MCU is electrically connected with the water inlet temperature measuring element and the water outlet temperature measuring element respectively;
the MCU is connected with the heating element through the first high-power transistor and can be used for controlling the heating element to provide constant heating power;
the MCU is connected with the water flow control element through the second high-power transistor and can be used for controlling the working power of the water flow control element;
the water flow control element is used for pumping water from the water tank into the heating element and controlling the flow and the flow rate of the water flowing into the heating element;
the water inlet temperature measuring element is arranged at the inlet of the heating element and is used for measuring the temperature T of water at the inlet0(ii) a And feeding back the temperature at the inlet to the MCU;
the water outlet temperature measuring element is arranged at the outlet of the heating body and is used for measuring the temperature T of water at the outlet1(ii) a And feeding back the temperature at the outlet to the micro control unit;
the heating element for heating a water stream flowing therethrough;
the system corresponds to a plurality of target temperature values, the MCU sets constant heating power for the heating element corresponding to each target temperature value, and changes the water temperature at the water outlet of the heating element by adjusting the working power of the water flow control element so as to enable the water temperature to reach the target temperature value;
the MCU is according to a specific heat capacity formula: controlling the water flow control unit by Q-cm delta T; wherein:
q is the amount of heat absorbed by the water flowing through the heating element per unit time, c is the specific heat capacity of the water, m is the mass of the water flowing through the heating element per unit time, and Δ T is the amount of change in the temperature of the water after absorption of heat.
Optionally, the water flow control element comprises a diaphragm pump, wherein the anode of the diaphragm pump is connected with the power supply, and the cathode of the diaphragm pump is connected with the second high-power transistor; the MCU inputs a PWM pulse signal to the diaphragm pump through the second high-power transistor, and changes the working power of the diaphragm pump by changing the duty ratio or the PWM pulse frequency of the PWM pulse signal, so that the flow and the flow speed of water sent to the heating element by the diaphragm pump are changed;
the heating element comprises a relay, a plurality of groups of heating wires and a pipeline, and the plurality of groups of heating wires are arranged on the outer surface of the pipeline; the plurality of groups of heating wires are electrically connected with the relay;
the pipeline is a thick film heating pipe;
the relay is connected with the first high-power transistor; the MCU controls the opening and closing of the relay through the first high-power transistor so as to control the connection relation between the heating wires, and the heating power provided by the heating wires is changed by changing the connection relation between the heating wires;
the connection relationship among the heating wires at least comprises one of the following connection relationships:
only one heating wire works, the heating wire is not connected with other heating wires, and other heating wires do not work;
several heating wires are connected in series to work together;
several heating wires are connected in parallel to work.
Optionally, the water inlet temperature sensing element comprises: the first NTC thermistor and the first divider resistor are connected in series;
the first NTC thermistor has a first end connected with a power supply, a second end connected with one end of a first divider resistor, and the other end of the first divider resistor connected with the ground; an output voltage U1out is connected from the second end of the first NTC thermistor;
measuring the U1out, converting the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the first NTC negative temperature coefficient thermistor and the first voltage division resistor, and searching a thermistor temperature-resistance value characteristic curve to obtain the actual temperature;
the water outlet temperature measuring element comprises: the second NTC thermistor and the second divider resistor are connected in series;
the first end of the second NTC thermistor is connected with a power supply, the second end of the second NTC thermistor is connected with one end of a second divider resistor, and the other end of the second divider resistor is grounded; an output voltage U2out is connected from a second end of the second NTC thermistor;
and measuring the U2out, converting the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the second NTC negative temperature coefficient thermistor and the second voltage division resistor, and searching a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
Optionally, the MCU acquires the value of U1out, converts the resistance of the thermistor at the current temperature according to the known resistance voltage-dividing relationship between the first NTC negative temperature coefficient thermistor and the first voltage-dividing resistor, and finds the thermistor temperature-resistance characteristic curve to obtain the actual temperature;
and the MCU acquires the value of the U2out, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the second NTC negative temperature coefficient thermistor and the second voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
Optionally, the water inlet temperature measuring element further comprises: the first ADC chip acquires a U1out value, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the first NTC negative temperature coefficient thermistor and the first voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature;
the water outlet temperature measuring element further comprises: and the second ADC chip acquires the value of U2out, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the second NTC negative temperature coefficient thermistor and the second voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
Optionally, the method further comprises: the water level detection element is electrically connected with the MCU; the water level detection element is arranged on the inner wall of the water tank and used for detecting the water level in the water tank.
Optionally, the heating element further comprises a temperature-controlled switch, and the temperature-controlled switch is arranged on the outer side of the pipeline;
the temperature control switch is provided with a safety value, and if the temperature outside the pipeline exceeds the safety value, the temperature control switch automatically cuts off the power supply of the heating element.
A method for achieving rapid water flow temperature control, comprising the steps of:
s1: establishing a system as claimed in any preceding claim;
s2: determining a target effluent temperature value, and judging whether a pipeline of the heating unit is in a cold pipe state or a hot pipe state; the judgment is based on the following:
the cold pipe state refers to a state that the pipeline has no residual temperature after the system is powered on for the first time or is in standby for a long time;
the state of the heat pipe means that the system is electrified and residual temperature is remained in the pipeline, and the pipeline does not need to be preheated at the moment, so that the temperature is increased more quickly;
if the pipeline is in a cold pipe state, the process goes to step S3;
if the pipe is in the heat pipe state, the process goes to step S4;
s3: the water flow control member draws an initial water flow into the pipe and proceeds to step S5;
s4: judging whether the target outlet water temperature value has the 'optimal water flow' heated last time;
if the current water flow exists, the MCU directly calls the duty ratio or PWM pulse frequency of a PWM signal corresponding to the last heated optimal water flow to control a water flow control element, and the water flow control element extracts the optimal water flow to enter the pipeline and then enters step S5; the optimal water flow refers to the corresponding water flow when the temperature of the water outlet reaches the target temperature after the last heating;
if the above "optimal water flow" does not exist, the water flow control member flows into the pipe with a previously set empirical water flow, and proceeds to step S5;
s5: according to the target water outlet temperature, the MCU controls the heating unit to provide constant heating power to heat water flow in the pipeline;
s6: the MCU obtains the temperature of the water inlet and the temperature of the water outlet of the pipeline from the water inlet temperature measuring element and the water outlet temperature measuring element, and continuously changes the duty ratio or PWM pulse frequency of a PWM signal input into the water flow control element according to the temperature value so as to enable the temperature of the water outlet of the pipeline to be in a target temperature gear;
s7: when the temperature of the water outlet reaches a target temperature gear, the water flow is considered as the optimal water flow, and the MCU acquires the PWM duty ratio or PWM pulse frequency corresponding to the optimal water flow heated at this time for the next heating temperature control;
s8: the MCU controls the water flow control element to stop pumping water flow and controls the heating unit to stop heating.
Optionally, the step S7 further includes:
the MCU continuously collects PWM duty ratios or PWM pulse frequencies input into the diaphragm pump for multiple times, calculates the average value of the PWM duty ratios or the PWM pulse frequencies, and stores the average value as the PWM duty ratio or the PWM pulse frequency corresponding to the optimal water flow heated at this time for the next heating temperature control;
optionally, the step S7 further includes:
and the MCU collects the PWM duty ratio or PWM pulse frequency of the currently input diaphragm pump as the PWM duty ratio or PWM pulse frequency corresponding to the optimal water flow heated at this time for storage, and the PWM duty ratio or PWM pulse frequency is used for controlling the temperature for the next heating.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention is simpler, more efficient and more reliable.
2. The invention has simpler structural design, directly pumps cold water into the heating pipe for heating, instantly reaches the target temperature, and does not have complex pipelines for carrying out operations such as neutralization of cold water and hot water, steam discharge and the like.
3. The control method adopts water flow regulation, does not have temperature lag, and has quicker response and higher precision.
4. The heating element of the invention adopts a common relay to control the on-off, and does not need power regulation and control; the water flow element controls the high-power transistor to drive, and the circuit is simple.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic diagram of a system for implementing rapid water flow temperature control according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a hardware circuit of a system for implementing rapid water flow temperature control according to an embodiment of the present invention;
fig. 3 is a flow chart of a method for implementing rapid water flow temperature control in accordance with an embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
Referring to fig. 1 and 2, the present embodiment discloses a system for implementing fast water flow temperature control, including: the water flow control element, the heating element, the water inlet temperature measuring element, the water outlet temperature measuring element, the micro control unit MCU, the first high-power transistor, the second high-power transistor and the water level detection element.
The MCU is electrically connected with the water inlet temperature measuring element and the water outlet temperature measuring element respectively;
the MCU is connected with the heating element through the first high-power transistor and can be used for controlling the heating element to provide constant heating power;
the MCU is connected with the water flow control element through the second high-power transistor and can be used for controlling the working power of the water flow control element;
the water flow control element is used for pumping water from the water tank into the heating element and controlling the flow and the flow rate of the water flowing into the heating element;
the water inlet temperature measuring element is arranged at the inlet of the heating element and is used for measuring the temperature T of water at the inlet0(ii) a And feeding back the temperature at the inlet to the MCU;
the water outlet temperature measuring element is arranged at the outlet of the heating body and is used for measuring the temperature T of water at the outlet1(ii) a And feeding back the temperature at the outlet to the micro control unit;
the heating element for heating a water stream flowing therethrough;
the water level detection element is arranged on the inner wall of the water tank and is used for detecting the water level in the water tank; it is electrically connected with the MCU;
the system corresponds to a plurality of target temperature values, the MCU sets constant heating power for the heating element corresponding to each target temperature value, and changes the water temperature at the water outlet of the heating element by adjusting the working power of the water flow control element so as to enable the water temperature to reach the target temperature value;
the MCU is according to a specific heat capacity formula: controlling the water flow control unit by Q ═ cm Delta T, wherein:
q is the amount of heat absorbed by the water flowing through the heating element per unit time, c is the specific heat capacity of the water, m is the mass of the water flowing through the heating element per unit time, and Δ T is the amount of change in the temperature of the water after absorption of heat.
According to the formula of specific heat capacity, when the heating power Q of the heating element is constant, the size m of water flow in unit time determines the temperature T of the water outlet1. Wherein, the temperature of c and the water before heat absorption are both determined quantity, and the value of m is changed when the water temperature of the water outlet is changed. And the value of m is related to the flow rate and velocity of the water flowing into the heating element. Therefore, the water temperature at the water outlet can be controlled by controlling the flow and the flow speed of the water flowing into the heating element.
The water flow control element comprises a diaphragm pump, the positive electrode of the diaphragm pump is connected with a power supply, and the negative electrode of the diaphragm pump is connected with a second high-power transistor; the MCU inputs a PWM pulse signal to the diaphragm pump through the second high-power transistor, and the working power of the diaphragm pump is changed by changing the duty ratio or the PWM pulse frequency of the PWM pulse signal, so that the flow and the flow speed of water sent to the heating element by the diaphragm pump are changed. The accurate regulation and control of the power of the diaphragm pump can be realized by changing the duty ratio of the PWM pulse signal or the PWM pulse frequency, and the higher the power is, the larger the water flow is. In this embodiment, a dc miniature diaphragm pump is used, the power supply voltage is dc 12V, and the rated power is 5W.
The heating element comprises a relay, a plurality of groups of heating wires and a pipeline, and the plurality of groups of heating wires are arranged on the outer surface of the pipeline; the plurality of groups of heating wires are electrically connected with the relay;
it should be noted that the flow rate of water fed to the heating element is the flow rate of water fed to the heating element and the cross-sectional area of the conduit.
The pipeline is a thick film heating pipe;
the relay is connected with the first high-power transistor; the MCU controls the opening and closing of the relay through the first high-power transistor so as to control the connection relation between the heating wires, and the heating power provided by the heating wires is changed by changing the connection relation between the heating wires;
the connection relationship among the heating wires at least comprises one of the following connection relationships:
only one heating wire works, the heating wire is not connected with other heating wires, and other heating wires do not work;
several heating wires are connected in series to work together;
several heating wires are connected in parallel to work.
Of course, parallel and series relationships can also exist for several heating wires in operation. The present invention does not limit the connection relationship.
In this embodiment, the heating element has two sets of heating wires, which have 700W and 1300W power levels respectively, and can generate 700W, 1300W and 2000W power levels after combined use. Heating at the temperature of 45-55 ℃ by adopting 700W power; heating by using a 1300W power gear within the range of 55-70; 2000W power is used at 70-100 gears.
The heating element further comprises a temperature control switch, and the temperature control switch is arranged on the outer side of the pipeline; the temperature control switch is provided with a safety value, and if the temperature outside the pipeline exceeds the safety value, the temperature control switch automatically cuts off the power supply of the heating element so as to prevent the pipeline from being damaged by dry burning.
It should be noted that the MCU, the first high-power transistor, the second high-power transistor, and the relay are all disposed on a circuit board. The power supply part mainly comprises three parts of 220V alternating current, 12V direct current and 5V direct current, wherein the 220V alternating current is used as a working power supply of the heating element; 12V direct current voltage is used for attraction control of the micro diaphragm pump and the relay coil; the 5V direct current voltage is used for normal work of the MCU control chip.
Wherein, water level detection element includes hall element, and when water level was less than the threshold value in the water tank, water level detection element can send the early warning: on one hand, the early warning needs to supplement water to the water tank; on the other hand, the MCU receives the early warning signal and can control the water flow control element to stop sucking water from the water tank.
Wherein the water inlet temperature sensing element comprises:
the first NTC thermistor and the first divider resistor are connected in series;
the first NTC thermistor has a first end connected with a power supply, a second end connected with one end of a first divider resistor, and the other end of the first divider resistor connected with the ground; an output voltage U1out is connected from the second end of the first NTC thermistor;
and measuring the U1out, converting the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the first NTC negative temperature coefficient thermistor and the first voltage division resistor, and searching a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
It should be noted that the "temperature-resistance characteristic curve of the thermistor" belongs to a known curve, and the temperature-resistance characteristic curve of the NTC thermistor with the same specification is the same to all the persons skilled in the art, is fixed, belongs to the field of the prior art, and is not described herein again.
Wherein, delivery port temperature element includes:
the second NTC thermistor and the second divider resistor are connected in series;
the first end of the second NTC thermistor is connected with a power supply, the second end of the second NTC thermistor is connected with one end of a second divider resistor, and the other end of the second divider resistor is grounded; an output voltage U2out is connected from a second end of the second NTC thermistor;
and measuring the U20ut, converting the resistance value of the thermistor at the current temperature according to the known resistance voltage dividing relationship between the second NTC negative temperature coefficient thermistor and the second voltage dividing resistor, and searching a thermistor temperature-resistance characteristic curve to obtain the actual temperature.
The MCU collects the value of the U1out, the resistance value of the thermistor at the current temperature is converted according to the known resistor voltage division relation between the first NTC negative temperature coefficient thermistor and the first voltage division resistor, and the temperature-resistance value characteristic curve of the thermistor is searched to obtain the actual temperature.
And the MCU acquires the value of the U2out, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the second NTC negative temperature coefficient thermistor and the second voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
The temperature acquisition adopts a resistance voltage division circuit on hardware, uses an ADC inside the MCU to sample voltage, and calculates the accurate water temperature at the inlet and the outlet according to the voltage division relation.
In another embodiment of the present invention, the water temperature may also be obtained by using external ADC chips with different accuracies, which is as follows:
the water inlet temperature measuring element further comprises: the first ADC chip acquires a U1out value, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the first NTC negative temperature coefficient thermistor and the first voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature;
the water outlet temperature measuring element further comprises: and the second ADC chip acquires the value of U2out, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the second NTC negative temperature coefficient thermistor and the second voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
As shown in fig. 3, this embodiment also discloses a method for implementing fast water flow temperature control, which includes the following steps:
s1: establishing a system for realizing rapid water flow temperature control as described above;
s2: determining a target effluent temperature value, and judging whether a pipeline of the heating unit is in a cold pipe state or a hot pipe state; the judgment is based on the following:
the cold pipe state refers to a state that the pipeline has no residual temperature after the system is powered on for the first time or is in standby for a long time;
the state of the heat pipe means that the system is electrified and residual temperature is remained in the pipeline, and the pipeline does not need to be preheated at the moment, so that the temperature is increased more quickly;
if the pipeline is in a cold pipe state, the process goes to step S3;
if the pipe is in the heat pipe state, the process goes to step S4;
s3: the diaphragm pump draws an initial flow of water into the conduit and proceeds to step S5; wherein, the initial water flow is generally configured to be larger and is 60 to 80 percent of the rated power water flow of the diaphragm pump.
S4: judging whether the target outlet water temperature value has the 'optimal water flow' heated last time;
if the current water flow exists, the MCU directly calls the duty ratio or PWM pulse frequency of a PWM signal corresponding to the last heated optimal water flow to control a water flow control element, and the water flow control element extracts the optimal water flow to enter the pipeline and then enters step S5; the optimal water flow refers to the corresponding water flow when the temperature of the water outlet reaches the target temperature after the last heating;
if the above "optimal water flow" does not exist, the water flow control member flows into the pipe with a previously set empirical water flow, and proceeds to step S5;
s5: according to the target water outlet temperature, the MCU controls the heating unit to provide constant heating power to heat water flow in the pipeline;
s6: the MCU obtains the temperature of the water inlet and the temperature of the water outlet of the pipeline from the water inlet temperature measuring element and the water outlet temperature measuring element, and continuously changes the duty ratio or PWM pulse frequency of a PWM signal input into the diaphragm pump according to the temperature value so as to enable the temperature of the water outlet of the pipeline to be in a target temperature gear;
s7: when the temperature of the water outlet reaches a target temperature gear, the water flow is considered as the optimal water flow, and the MCU acquires the PWM duty ratio or PWM pulse frequency corresponding to the optimal water flow heated at this time for the next heating temperature control;
s8: the MCU controls the diaphragm pump to stop pumping water flow and controls the heating unit to stop heating.
In this embodiment, the step S7 further includes:
the MCU continuously collects the PWM duty ratio or the PWM pulse frequency input into the diaphragm pump for multiple times, calculates the average value of the PWM duty ratio or the PWM pulse frequency, and stores the average value as the PWM duty ratio or the PWM pulse frequency corresponding to the optimal water flow heated at this time for the next heating temperature control.
In another embodiment of the present invention, the step S7 further includes:
and the MCU collects the PWM duty ratio or PWM pulse frequency of the currently input diaphragm pump as the PWM duty ratio or PWM pulse frequency corresponding to the optimal water flow heated at this time for storage, and the PWM duty ratio or PWM pulse frequency is used for controlling the temperature for the next heating.
Both of the above two methods are examples, and in the specific implementation, it is critical to obtain the control parameter (PWM duty ratio or PWM pulse frequency in this embodiment) corresponding to the "optimal water flow" so that the control parameter is used as the "optimal" control parameter for the next temperature control. This "best" parameter is collected either by some kind of calculation or directly, and the invention is not limited thereto.
In this embodiment, in step S6, a PID algorithm is used to adjust the water flow flowing into the pipeline, specifically:
the PID algorithm continuously adjusts the water flow entering the pipeline according to the difference between the water outlet temperature and the target water outlet temperature, namely continuously changes the PWM pulse duty ratio or PWM input into the diaphragm pump, thereby achieving the final target temperature gear.
The position type PID formula is as follows:
wherein, U0: representing the initial water flow size of the system; kp: the proportional coefficient is used for determining the PID regulation speed; ki: the integral coefficient and the accumulated error coefficient can ensure that the system has no steady-state error after entering a steady state; kd: the differential coefficient can inhibit errors generated by the heating tube of the inertia component and the NTC thermistor of the hysteresis component and improve the dynamic characteristics of the system in the adjusting process; e (k): representing the temperature difference between the water outlet and the water inlet in the current sampling period; e (k-1) represents the temperature difference between the water outlet and the water inlet in the last sampling period.
It should be noted that, in the specific implementation, the temperature rise can also be achieved by reducing the water flow in equal proportion without using the PID algorithm; or the PID algorithm is simplified, the consideration of the inertia factor of the heating element is abandoned, and only the current water temperature error and the accumulated error are considered. The invention does not limit the specific algorithm for adjusting the water temperature. The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (10)
1. A system for achieving rapid water flow temperature control, comprising: the water flow control element, the heating element, the water inlet temperature measuring element, the water outlet temperature measuring element, the micro control unit MCU, the first high-power transistor and the second high-power transistor;
the MCU is electrically connected with the water inlet temperature measuring element and the water outlet temperature measuring element respectively;
the MCU is connected with the heating element through the first high-power transistor and can be used for controlling the heating element to provide constant heating power;
the MCU is connected with the water flow control element through the second high-power transistor and can be used for controlling the working power of the water flow control element;
the water flow control element is used for pumping water from the water tank into the heating element and controlling the flow and the flow rate of the water flowing into the heating element;
the water inlet temperature measuring element is arranged at the inlet of the heating element and is used for measuring the temperature T of water at the inlet0(ii) a And feeding back the temperature at the inlet to the MCU;
the water outlet temperature measuring element is arranged at the outlet of the heating body and is used for measuring the temperature T of water at the outlet1(ii) a And feeding back the temperature at the outlet to the micro control unit;
the heating element for heating a water stream flowing therethrough;
the system corresponds to a plurality of target temperature values, the MCU sets constant heating power for the heating element corresponding to each target temperature value, and changes the water temperature at the water outlet of the heating element by adjusting the working power of the water flow control element so as to enable the water temperature to reach the target temperature value;
the MCU is according to a specific heat capacity formula: controlling the water flow control unit by Q-cm delta T; wherein:
q is the amount of heat absorbed by the water flowing through the heating element per unit time, c is the specific heat capacity of the water, m is the mass of the water flowing through the heating element per unit time, and Δ T is the amount of change in the temperature of the water after absorption of heat.
2. The system of claim 1, wherein the water flow control element comprises a diaphragm pump having a positive electrode connected to a power source and a negative electrode connected to a second high power transistor; the MCU inputs a PWM pulse signal to the diaphragm pump through the second high-power transistor, and changes the working power of the diaphragm pump by changing the duty ratio or the PWM pulse frequency of the PWM pulse signal, so that the flow and the flow speed of water sent to the heating element by the diaphragm pump are changed;
the heating element comprises a relay, a plurality of groups of heating wires and a pipeline, and the plurality of groups of heating wires are arranged on the outer surface of the pipeline; the plurality of groups of heating wires are electrically connected with the relay;
the pipeline is a thick film heating pipe;
the relay is connected with the first high-power transistor; the MCU controls the opening and closing of the relay through the first high-power transistor so as to control the connection relation between the heating wires, and the heating power provided by the heating wires is changed by changing the connection relation between the heating wires;
the connection relationship among the heating wires at least comprises one of the following connection relationships:
only one heating wire works, the heating wire is not connected with other heating wires, and other heating wires do not work;
several heating wires are connected in series to work together;
several heating wires are connected in parallel to work.
3. The system of claim 1, wherein the water inlet temperature sensing element comprises: the first NTC thermistor and the first divider resistor are connected in series;
the first NTC thermistor has a first end connected with a power supply, a second end connected with one end of a first divider resistor, and the other end of the first divider resistor connected with the ground; an output voltage U1out is connected from the second end of the first NTC thermistor;
measuring the U1out, converting the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the first NTC negative temperature coefficient thermistor and the first voltage division resistor, and searching a thermistor temperature-resistance value characteristic curve to obtain the actual temperature;
the water outlet temperature measuring element comprises: the second NTC thermistor and the second divider resistor are connected in series;
the first end of the second NTC thermistor is connected with a power supply, the second end of the second NTC thermistor is connected with one end of a second divider resistor, and the other end of the second divider resistor is grounded; an output voltage U2out is connected from a second end of the second NTC thermistor;
and measuring the U2out, converting the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the second NTC negative temperature coefficient thermistor and the second voltage division resistor, and searching a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
4. The system of claim 3, wherein the MCU collects values of U1out, converts the resistance of the thermistor at the current temperature according to the known resistance voltage dividing relationship between the first NTC negative temperature coefficient thermistor and the first voltage dividing resistor, and finds the thermistor temperature-resistance characteristic curve to obtain the actual temperature;
and the MCU acquires the value of the U2out, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the second NTC negative temperature coefficient thermistor and the second voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
5. The system of claim 3, wherein the water inlet temperature sensing element further comprises: the first ADC chip acquires a U1out value, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the first NTC negative temperature coefficient thermistor and the first voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature;
the water outlet temperature measuring element further comprises: and the second ADC chip acquires the value of U2out, converts the resistance value of the thermistor at the current temperature according to the known resistance voltage division relation between the second NTC negative temperature coefficient thermistor and the second voltage division resistor, and searches a thermistor temperature-resistance value characteristic curve to obtain the actual temperature.
6. The system of claim 1, further comprising: the water level detection element is electrically connected with the MCU; the water level detection element is arranged on the inner wall of the water tank and used for detecting the water level in the water tank.
7. The system of claim 2, wherein the heating element further comprises a temperature controlled switch disposed on an outside of the conduit;
the temperature control switch is provided with a safety value, and if the temperature outside the pipeline exceeds the safety value, the temperature control switch automatically cuts off the power supply of the heating element.
8. A method for realizing rapid water flow temperature control is characterized by comprising the following steps:
s1: establishing a system according to any one of claims 1 to 7;
s2: determining a target effluent temperature value, and judging whether a pipeline of the heating unit is in a cold pipe state or a hot pipe state; the judgment is based on the following:
the cold pipe state refers to a state that the pipeline has no residual temperature after the system is powered on for the first time or is in standby for a long time;
the state of the heat pipe means that the system is electrified and residual temperature is remained in the pipeline, and the pipeline does not need to be preheated at the moment, so that the temperature is increased more quickly;
if the pipeline is in a cold pipe state, the process goes to step S3;
if the pipe is in the heat pipe state, the process goes to step S4;
s3: the water flow control member draws an initial water flow into the pipe and proceeds to step S5;
s4: judging whether the target outlet water temperature value has the 'optimal water flow' heated last time;
if the current water flow exists, the MCU directly calls the duty ratio or PWM pulse frequency of a PWM signal corresponding to the last heated optimal water flow to control a water flow control element, and the water flow control element extracts the optimal water flow to enter the pipeline and then enters step S5; the optimal water flow refers to the corresponding water flow when the temperature of the water outlet reaches the target temperature after the last heating;
if the above "optimal water flow" does not exist, the water flow control member flows into the pipe with a previously set empirical water flow, and proceeds to step S5;
s5: according to the target water outlet temperature, the MCU controls the heating unit to provide constant heating power to heat water flow in the pipeline;
s6: the MCU obtains the temperature of the water inlet and the temperature of the water outlet of the pipeline from the water inlet temperature measuring element and the water outlet temperature measuring element, and continuously changes the duty ratio or PWM pulse frequency of a PWM signal input into the water flow control element according to the temperature value so as to enable the temperature of the water outlet of the pipeline to be in a target temperature gear;
s7: when the temperature of the water outlet reaches a target temperature gear, the water flow is considered as the optimal water flow, and the MCU acquires the PWM duty ratio or PWM pulse frequency corresponding to the optimal water flow heated at this time for the next heating temperature control;
s8: the MCU controls the water flow control element to stop pumping water flow and controls the heating unit to stop heating.
9. The method of claim 8, wherein the step S7 further comprises:
the MCU continuously collects the PWM duty ratio or the PWM pulse frequency input into the diaphragm pump for multiple times, calculates the average value of the PWM duty ratio or the PWM pulse frequency, and stores the average value as the PWM duty ratio or the PWM pulse frequency corresponding to the optimal water flow heated at this time for the next heating temperature control.
10. The method of claim 8, wherein the step S7 further comprises:
and the MCU collects the PWM duty ratio or PWM pulse frequency of the currently input diaphragm pump as the PWM duty ratio or PWM pulse frequency corresponding to the optimal water flow heated at this time for storage, and the PWM duty ratio or PWM pulse frequency is used for controlling the temperature for the next heating.
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