A temperature control circuit for a heating sheet / heating wire

Abstract

The utility model discloses a kind of temperature control circuit for heating sheet / heating wire, including power supply circuit, commercial power zero-crossing acquisition circuit, synchronous drive external thyristor circuit, bidirectional thyristor drive circuit, 1st single-chip microcomputer function circuit, 2nd single-chip microcomputer function circuit, peripheral communication interface function circuit, voltage current acquisition function circuit, signal processing function circuit after heating sheet voltage current acquisition.The utility model is used for the temperature control circuit for heating sheet / heating wire temperature control precision no time delay, satisfy fast temperature control demand;Synchronous temperature measurement no lag, temperature feedback real-time is strong;Traditional thermocouple / thermal resistance exists heat conduction delay, and the utility model control circuit realizes heating and temperature measurement synchronous, completely eliminate temperature measurement lag, ensure that the actual temperature obtained by single-chip microcomputer and heating sheet real temperature are identical, avoid temperature control deviation caused by delay.

Description

Technical Field

[0001] This utility model relates to the technical field, and in particular to a temperature control circuit for a heating element / heating wire. Background Technology

[0002] Existing heating element temperature control mainly relies on thermocouples or resistance temperature detectors (RTDs). However, the heating element itself heats up quickly, and these sensors have thermal conduction delay characteristics, causing the temperature acquisition results to always lag behind the actual temperature change of the heating element. This ultimately leads to problems such as untimely temperature control response and large accuracy deviations.

[0003] In film sealing processes in the food and pharmaceutical industries, time relays are commonly used to indirectly adjust the sealing temperature by controlling the energizing time of the heating element. However, this method cannot monitor the real-time temperature of the heating element; both the initial temperature and the actual temperature at the end of the process are unknown, leading to two frequent problems: first, the heating element temperature is too low, resulting in an insecure seal; second, the heating element temperature is too high, causing the film at the sealing point to melt and become damaged. Utility Model Content

[0004] To address the shortcomings of the aforementioned technologies, the purpose of this invention is to provide a temperature control circuit for a heating element / heating wire. This control circuit functions to quickly and accurately control the temperature of the heating element. Because the heating element heats up rapidly, and conventional thermocouple / resistance temperature sensors exhibit thermal delay in temperature acquisition, an alternative method is needed for acquiring the temperature of the heating element.

[0005] The temperature control circuit for a heating element proposed in this utility model includes: a power supply circuit, a mains power zero-crossing acquisition circuit, a synchronous drive external thyristor circuit, a bidirectional thyristor drive circuit, a No. 1 microcontroller functional circuit, a No. 2 microcontroller functional circuit, a peripheral communication interface functional circuit, a voltage and current acquisition functional circuit, and a signal processing functional circuit for acquiring the voltage and current of the heating element; wherein...

[0006] The power supply circuit is used to convert the externally input voltage into the voltage required by the device.

[0007] The mains power zero-crossing acquisition circuit is used to acquire the zero-point of the AC sinusoidal wave through zero-crossing detection technology.

[0008] Synchronous drive external thyristor circuit, used to drive external high-power thyristor circuit;

[0009] The bidirectional thyristor drive circuit is used to connect to the primary side of the transformer. The PWM pulse signal from the microcontroller's I / O port drives the transformer through the bidirectional thyristor to energize and heat both sides of the heating element / heating wire.

[0010] The microcontroller function circuit is used to provide the microcontroller with operating conditions, input signal processing, and output drive capabilities.

[0011] The peripheral communication interface circuit is used to convert external input signals into signals that can be recognized by the microcontroller, and to convert the signals output by the microcontroller into external switching signals or analog signals.

[0012] The voltage and current acquisition circuit is used to convert the voltage signals on both sides of the heating element / heating wire and the current signal of the transformer into voltage signals within the range;

[0013] The signal processing circuit is used to convert digital signals into digital signals that can be read by a microcontroller through a digital potentiometer and operational amplifier circuit, and then through an ADC chip.

[0014] In this invention, the power supply circuit uses an LM2675M-5.0 chip with an integrated switching transistor.

[0015] In this invention, the mains zero-crossing acquisition circuit generates positive and negative power supplies using a resistor-capacitor voltage reduction method. It includes an operational amplifier TL061CDR and an operational amplifier TS912IDT. The TL061CDR, along with surrounding resistors and capacitors, forms a second-order active low-pass filter. The high-voltage mains power is input to the TL061CDR after being divided by resistors. After high-frequency interference is filtered out by the second-order active low-pass filter, the signal passes through one path of the TS912IDT, outputting a square wave. The signal then passes through the other path of the TS912IDT, driving the primary side of an optocoupler. The isolation secondary side of the optocoupler is connected to a pull-up resistor and an RC low-pass filter before being input to the microcontroller's I / O circuit to acquire the zero-crossing point.

[0016] In this invention, the microcontroller I / O port connected to the synchronous drive external thyristor circuit drives the primary side of the optocoupler and controls the conduction and shutdown of the secondary side DC.

[0017] In this invention, the bidirectional thyristor driving circuit includes: a bidirectional thyristor Q18, a varistor RV1, an absorption buffer circuit RC, a varistor RV2, a bidirectional thyristor isolation driver chip U13, an NPN transistor Q16, and a DC blocking capacitor C42. The varistor RV1 is applied between the L and N terminals to prevent high voltage spikes on the L and N terminals. The absorption buffer circuit RC at both ends of the thyristor suppresses voltage spikes across the thyristor. The varistor RV2, for protection, is applied between pins 1 and 2 of the bidirectional thyristor Q18 to prevent high voltage spikes on pins 1 and 2. The primary side of the bidirectional thyristor isolation driver chip U13 is driven by a microcontroller I / O. Due to the DC blocking effect of the DC blocking capacitor C42, the base current of the NPN transistor Q16 gradually decreases, but the bidirectional thyristor will continue to conduct even if the primary side drive is absent until it turns off after crossing zero. This mechanism, combined with zero-crossing detection, can control when the bidirectional thyristor turns on after crossing zero at the beginning of the cycle and turns off at the zero-crossing at the end of the cycle, thereby achieving accurate control of the heating wire temperature.

[0018] In this invention, the microcontroller functional circuit includes: a No. 1 microcontroller functional circuit and a No. 2 microcontroller functional circuit; the No. 1 microcontroller functional circuit includes: a microcontroller peripheral circuit and an encryption chip U7; the microcontroller peripheral circuit includes: a reset circuit, a power supply circuit, a crystal oscillator circuit, and a download port; the No. 2 microcontroller functional circuit includes: 8-bit DIP switch acquisition, rotary potentiometer acquisition, rotary encoder switch acquisition, LED indication, and EEPROM storage; screen communication uses a serial port with a baud rate of 115200 to communicate with the microcontroller serial port; the EEPROM stores key data using SPI communication.

[0019] In this invention, the peripheral communication interface functional circuit includes: a three-way control via an optocoupler, a 0-10VDC output, a 0-10VDC input, and a linear power supply; wherein, when the three-way control via the optocoupler receives a 24VDC peripheral input, the secondary side of the optocoupler is turned on, and the high level is input to the microcontroller's I / O port after being filtered by an RC low-pass filter; when the peripheral input is 0V or not connected, the low level is input to the microcontroller's I / O port; the 0-10VDC output and 0-10VDC input circuits and the linear power supply use 78L15 and 78L10 chips to power the circuit; the input of the 0-10VDC output circuit is the microcontroller's PWM pin; the 0-10VDC input signal is protected and filtered before being input to an operational amplifier, which forms a follower and then provides a voltage divider to the microcontroller's AD acquisition.

[0020] In this invention, the voltage and current acquisition circuit includes: a charge pump LM828, an analog switch DG442, and an inverting integrator; wherein, the charge pump LM828 supplies power to the analog switch DG442; the inverting integrator consists of two channels of a quad operational amplifier TSV914. The signal processing circuit includes: a digital potentiometer, a signal processing circuit, an ADC, and four 0-ohm resistors; the voltage and current signals after integrator enter the digital potentiometer, the setting and gating of which are controlled via an SPI bus, and its output signal passes through the signal processing circuit; the signal processing circuit consists of the other two channels of the quad operational amplifier TSV914; the processed voltage and current signals enter the ADC, which acquires the CH0 voltage signal and CH1 current signal respectively, and controls whether the signal passes through the digital potentiometer and operational amplifiers by whether the four 0-ohm resistors R12, R13, R14, and R15 are soldered.

[0021] In this invention, the microcontroller is also equipped with a U2 EEPROM for data storage.

[0022] The core principle of this control circuit is to sample the current flowing through the heating element / heating wire and the voltage across the heating element / heating wire, and calculate the resistance value of the heating element using Ohm's law R = U / I. Based on the relationship between the resistance value and temperature of the heating element, the actual temperature of the heating element is then determined. Using the set temperature and the calculated actual heating element temperature, proportional control in the microcontroller's PID program is employed. This control, through the PWM pulse width time, drives a bidirectional thyristor to energize and heat the heating element (the voltage and current processing and acquisition circuits must remain consistent), to achieve a setting temperature equal to the actual heating element temperature.

[0023] Unlike traditional temperature control circuits, the control circuit of this invention can simultaneously heat the heating element and read its temperature without delay.

[0024] The temperature control circuit for heating elements disclosed in this utility model has the following beneficial effects:

[0025] Precise and time-free temperature control meets the needs of rapid temperature control; synchronous temperature measurement is lag-free and provides strong real-time temperature feedback; traditional thermocouples / resistance devices have thermal conduction delay, while the control circuit of this utility model realizes simultaneous heating and temperature measurement, completely eliminating temperature measurement lag, ensuring that the actual temperature obtained by the microcontroller is consistent with the true temperature of the heating element, and avoiding temperature control deviation caused by delay. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the temperature control circuit for the heating wire in this utility model.

[0028] Figure 2 This is a circuit diagram of the power supply circuit in this utility model.

[0029] Figure 3 This is a circuit diagram of the mains zero-crossing acquisition circuit in this utility model.

[0030] Figure 4 This is a circuit diagram of the synchronous drive external thyristor circuit in this utility model.

[0031] Figure 5 This is a circuit diagram of the bidirectional thyristor drive circuit in this utility model.

[0032] Figure 6 This is a circuit diagram of the No. 1 microcontroller functional circuit in this utility model.

[0033] Figure 7 This is the circuit diagram of the No. 2 microcontroller functional circuit in this utility model.

[0034] Figure 8 This is a circuit diagram of the peripheral communication interface functional circuit in this utility model.

[0035] Figure 9 This is a circuit diagram of the voltage and current acquisition function circuit in this utility model.

[0036] Figure 10 This is a circuit diagram of the signal processing function circuit in this utility model.

[0037] Figure 11 This is a schematic diagram of the power supply circuit in this utility model.

[0038] Figure 12 This is a schematic diagram of the mains zero-crossing acquisition circuit in this utility model. Detailed Implementation

[0039] The utility model will be further described in detail below with reference to the specific embodiments and accompanying drawings. Except for the contents specifically mentioned below, the processes, conditions, and experimental methods for implementing this utility model are all common knowledge and general knowledge in the field, and this utility model has no particular limitations.

[0040] The power supply circuit described in this utility model is used to convert the externally input 24VDC voltage into the 5VDC voltage required by the device for use by the device.

[0041] The chip used is the LM2675M-5.0, which has a fixed output of 5VDC and an integrated switching transistor. Therefore, the external circuit is simplified, requiring only a freewheeling diode, an energy storage inductor, and some capacitors to ensure that the load device operates stably in complex power supply environments.

[0042] The mains power zero-crossing acquisition circuit is used for zero-point acquisition of AC sine waves, mainly through zero-crossing detection technology. The core is to detect the critical point when the voltage waveform changes from the positive half-cycle to the negative half-cycle or from the negative half-cycle to the positive half-cycle.

[0043] A resistor-capacitor (RC) step-down method is used to generate positive and negative power supplies, producing a voltage of ±6.2V relative to N (neutral line). The high AC voltage at LN is divided by resistors and input to the first operational amplifier TL061CDR. The surrounding resistors and capacitors form a second-order active low-pass filter (compensated in the feedback path because it drives a capacitive load) to filter out high-frequency interference. After passing through one path of a TS912IDT (forming a comparator), it outputs a square wave. After passing through the other path of a TS912IDT (forming a follower), the operational amplifier output drives the primary side of the optocoupler. The isolation secondary side of the optocoupler is connected to a pull-up resistor and an RC low-pass filter before being input to the microcontroller's I / O to collect the zero-crossing point.

[0044] The synchronous drive external thyristor circuit is used to drive an external high-power thyristor circuit.

[0045] TB_PB9 comes from the microcontroller's I / O port and its driving logic is consistent with that of the thyristor on the circuit board; it drives the primary side of the optocoupler and controls the conduction and shutdown of the secondary side 24VDC.

[0046] The bidirectional thyristor drive circuit is used to connect to the primary side of the transformer. The PWM pulse signal from the microcontroller's I / O port drives the transformer through the bidirectional thyristor to energize and heat both sides of the heating wire.

[0047] The RV1 varistor is placed between L and N for protection, preventing high voltage spikes on LN. The RC snubber circuit across the SCR suppresses voltage spikes across the SCR, and RV2 provides protection. U13 is a professional bidirectional SCR isolation driver chip. Its primary side is driven by the microcontroller's I / O. When the microcontroller outputs a high level, Q16 conducts briefly, and the bidirectional SCR conducts. Due to the DC blocking effect of C42, the base current of Q16 gradually decreases. However, even without the primary-side driver, the bidirectional SCR will continue to conduct after turning on until it turns off at the zero-crossing point. This mechanism, combined with zero-crossing detection, allows control over when the bidirectional SCR turns on after the zero-crossing point at the beginning of the cycle and turns off at the zero-crossing point at the end of the cycle, achieving accurate temperature control of the heating element.

[0048] The No. 1 microcontroller functional circuit is essential for building a complete and usable microcontroller application system. It provides the necessary operating conditions, input signal processing, and output drive capabilities for the microcontroller, enabling it to reliably execute preset tasks.

[0049] Besides the basic microcontroller peripheral systems, such as the reset circuit (Max6326), power supply circuit (AMS1117), crystal oscillator circuit, and download port, these components constitute the minimum system of a microcontroller and are necessary for its operation. It also includes a U7 encryption chip, which effectively prevents unauthorized cracking.

[0050] The second microcontroller functional circuit is used to ensure the operation of the microcontroller system, input signal processing and output driving capabilities, so that the second microcontroller can reliably execute preset tasks.

[0051] Besides the basic microcontroller peripheral system, such as the crystal oscillator circuit and the download port (the power supply and the first microcontroller share an AMS1117, and the reset is provided by the first microcontroller), these parts constitute the minimum system of the microcontroller and are necessary conditions to ensure the operation of the microcontroller.

[0052] The system acquires data from 8-bit DIP switches, rotary potentiometers, rotary encoder switches, and LED indicators. Screen communication utilizes a serial port with a baud rate of 115200 for fast and timely communication with the microcontroller. An EEPROM has been added to store critical data; EEPROM offers better stability than the STM32's internal FLASH storage and uses SPI communication to store key control circuit data.

[0053] The peripheral communication interface function circuit is used to convert external input signals into signals that can be recognized by the microcontroller, and to convert the signals output by the microcontroller into external switching signals or analog signals, etc.

[0054] The three-way control is achieved through an optocoupler. When the external input is 24VDC, the secondary side of the optocoupler is turned on, and the high level is input to the microcontroller's I / O port after passing through an RC low-pass filter. When the external input is 0V or not connected, the low level is input to the microcontroller's I / O port.

[0055] The circuit features 0-10VDC output and input, along with a linear power supply. The power supply utilizes classic 78L15 and 78L10 chips, providing stable 15VDC and 10VDC outputs. The input to the 0-10VDC output circuit is the microcontroller's PWM pin. After passing through two RC low-pass filters, it becomes a DC signal. This signal is then amplified by an operational amplifier (op-amp) to output a 0-10VDC signal for external devices. The final 0-10VDC output value can be controlled by adjusting the duty cycle of the microcontroller's PWM pin; for example, a 50% duty cycle results in a 5V output. The 0-10VDC input signal, after protection and filtering, is input to the op-amp. The op-amp forms a follower, and a resistor divider provides the voltage to the microcontroller's AD converter, transforming the 0-10VDC input signal into a 0-3.3VDC signal for microcontroller acquisition.

[0056] The voltage and current acquisition circuit is used to convert the voltage signals on both sides of the heating element and the current signal of the transformer into voltage signals within a certain range through an integrating circuit.

[0057] An LM828 charge pump powers the DG442 analog switch. Two channels of a TSV914 quad op-amp form an inverting integrator. J5-2 receives the voltage signal, which, after protection and filtering, is divided and then enters the inverting integrator. The output value of the integrator is the collected heating element voltage value, and its amplitude can be calculated from the relationship between J5-2 and the voltage signal. J5-3 and J5-4 are the output signals of the current transformer. The input signals, after protection and filtering, flow through a 6.2-ohm sampling resistor. The control of the integrator and the release of the integrating capacitor are controlled by a microcontroller. The output value of the integrator is the collected heating element current value, and its amplitude can be calculated from the relationship between J5-3 and J5-4.

[0058] The signal processing circuit after the heating element voltage and current are acquired is used to convert the voltage and current signals after integrator through digital potentiometer and operational amplifier circuit, and then through ADC chip into digital signals that can be quickly read by microcontroller.

[0059] The voltage and current signals after integrator enter a digital potentiometer. The setting and selection of the digital potentiometer can be controlled via the SPI bus. Its output signal passes through the other two channels of a TSV914 quad op-amp, which constitute a signal processing circuit. By setting the four potentiometers, the voltage and current signal output values ​​can be ensured to be within a reasonable range. The processed voltage and current signals enter the MCP3202 12-bit ADC, which has two channels to acquire the CH0 voltage signal and CH1 current signal respectively. The ADC reference is generated by a MAX6067 at 4.5VDC. Four 0-ohm resistors are added to the lower right to control whether the signal passes through the digital potentiometer and op-amp. A U2 EEPROM is also added to the microcontroller for data storage. Communication between these three chips and the microcontroller uses SPI communication.

[0060] Example

[0061] like Figure 2 The power supply circuit shown is crucial; its stability determines the overall stability of the circuit. The input voltage is 24VDC, and the output needs to generate 5V. Since 5V consumes approximately 400mA of current, a linear circuit would consume too much power. Therefore, a switching power supply is used here, specifically a Buck power supply topology. The chip used is the LM2675M-5.0, which provides a fixed 5V output and integrates a switching transistor, simplifying the external circuitry to include only a freewheeling diode, an energy storage inductor, and some capacitors.

[0062] In addition to the Buck power supply, the control circuit here includes a soft-start circuit and an overcurrent protection circuit. Because the 24VDC input filter capacitors are relatively large (two 2200uf capacitors), a soft-start electronic switch is implemented using Q4 PMOS to prevent inrush current. Transistor Q7 gradually turns off after power-on, which manifests as Vgs gradually turning on Q4, thus enabling Q4 to achieve a soft-start function and limit inrush current. Overcurrent protection is implemented using transistor Q6. When the current flowing through the three parallel 1R transistors becomes excessive, Q6 conducts, increasing the gate voltage of Q4, thereby turning off Q4 PMOS. Furthermore, Q6's conduction causes Q9 to turn off, Q8 to turn off, and Q5 to turn on, thus pulling down the ON / OFF control pin of the Buck chip, ultimately shutting down the Buck power supply for protection. When no overcurrent occurs, Q6 turns off, and Q9 conducts, setting the gate voltage of Q4 to approximately 8V. At this point, the ON / OFF control is normally ON, and the entire power supply operates normally.

[0063] like Figure 3The AC zero-crossing acquisition circuit shown uses a resistor-capacitor (RC) step-down method to generate positive and negative power supplies. The right side of the diagram represents the RC step-down circuit, which generates a positive and negative 6.2V voltage relative to N (neutral line). The high AC voltage at LN is divided by resistors and input to the first operational amplifier TL061CDR. The surrounding resistors and capacitors form a second-order active low-pass filter (compensated in the feedback path because it drives a capacitive load) to filter out high-frequency interference. After passing through one path of a TS912IDT (forming a comparator), it outputs a square wave. After passing through the other path of the TS912IDT (forming a follower), the operational amplifier output drives the primary side of the optocoupler. The isolation secondary side of the optocoupler is connected to a pull-up resistor and an RC low-pass filter before being input to the microcontroller's I / O to acquire the zero-crossing point.

[0064] like Figure 4 The synchronous drive external thyristor circuit shown has TB_PB9, which comes from the microcontroller's I / O port and has the same drive logic as the thyristor on the circuit board. It drives the primary side of the optocoupler and controls the conduction and shutdown of the secondary side 24VDC.

[0065] like Figure 5 The diagram shows the bidirectional thyristor drive circuit. Looking at the left, the varistor RV1 is applied between L and N for protection, preventing high voltage spikes on LN. The RC snubber circuit across the thyristor suppresses voltage spikes, and RV2 provides protection. U13 is a professional bidirectional thyristor isolation driver chip. Its primary side is driven by the microcontroller's I / O control. When the microcontroller outputs a high level, Q16 conducts briefly, and the bidirectional thyristor conducts. Due to the DC blocking effect of C42, the base current of Q16 gradually decreases. However, even if the primary side drive is absent, the bidirectional thyristor will continue to conduct after a zero-crossing point until it turns off. This mechanism, combined with zero-crossing detection, allows control over when the bidirectional thyristor turns on after the zero-crossing point at the beginning of the cycle and turns off at the zero-crossing point at the end of the cycle, achieving accurate temperature control of the heating element.

[0066] like Figure 6 The diagram shows the functional circuit of microcontroller No. 1. Besides the basic microcontroller peripheral systems, such as the reset circuit (Max6326), power supply circuit (AMS1117), crystal oscillator circuit, and download port, it also includes a U7 encryption chip. This chip runs some programs and important data, effectively preventing unauthorized cracking. These components constitute the minimum system of the microcontroller and are essential for its operation.

[0067] The top left corner shows the CH0 comparator circuit, which compares the CH0 voltage with a fixed voltage. When CH0 is greater than this fixed voltage, CMP outputs a low level. Next to it, U26 and the gate handle the voltage and current integration control are ANDed with CMP. Therefore, the CMP level controls the operation of the voltage and current acquisition integration circuit (whenever CMP goes low, the integration control also goes low). When CH0 is greater than a certain value, all integration controls go low and shut down.

[0068] like Figure 7 As shown, this is the functional circuit of microcontroller No. 2. In addition to the basic microcontroller peripheral system, such as the crystal oscillator circuit and the download port (the power supply and microcontroller No. 1 share an AMS1117, and the reset is provided by microcontroller No. 1), these parts constitute the minimum system of the microcontroller and are necessary conditions to ensure the operation of the microcontroller.

[0069] like Figure 8 The diagram shows the peripheral communication interface circuit. The three control channels in the upper left corner are connected via optocouplers. When the external input is 24VDC, the secondary side of the optocoupler conducts, and the high-level signal is filtered by an RC low-pass filter before being input to the microcontroller's I / O port. When the external input is 0V or not connected, a low-level signal is input to the microcontroller's I / O port. The upper right corner controls RS-485 communication; RS-458 uses differential signal transmission, offering stronger anti-interference capabilities and longer transmission distances, enabling effective communication with the PLC. The middle right corner controls relay control. When a fault signal is detected, the microcontroller outputs a high level, controlling Q26 to conduct, which in turn activates the relay. The lower left side features the 0-10VDC output and input circuits, along with a linear power supply. The power supply uses classic 78L15 and 78L10 chips, providing stable 15V and 10V outputs. The 0-10VDC output circuit's input is the microcontroller's PWM pin. After passing through two RC low-pass filters, it becomes a DC signal. This signal is then amplified by an operational amplifier (op-amp) to output a 0-10VDC signal for external devices. The final 0-10VDC output value can be controlled by adjusting the duty cycle of the microcontroller's PWM pin; for example, a 50% duty cycle results in a 5VDC output. The 0-10VDC input signal, after protection and filtering, is input to the op-amp. The op-amp forms a follower circuit, and a resistor divider provides the voltage to the microcontroller's AD converter, transforming the 0-10VDC input signal into a 0-3.3VDC signal for microcontroller acquisition.

[0070] like Figure 9The diagram shows the voltage and current acquisition circuit. The DG442 analog switch needs to control positive and negative signals, so a negative voltage power supply is required. An LM828 charge pump chip is used to convert +5V to -5V. Two channels of the TSV914 quad op-amp form an inverting integrator. Since it is powered by a single power supply, its input signal must be negative for effective output. J5-2 is the voltage signal. After protection and filtering, the input signal can be selected from one of the upper or lower channels based on its voltage amplitude. After voltage division, it enters the inverting integrator. The control of the integrator and the release of the integrating capacitor are controlled by the microcontroller. The output value after integrator is the acquired heating element voltage value, and its amplitude can be calculated from the relationship between J5-2. J5-3 and J5-4 are the current transformer output signals. After protection and filtering, the input signals flow through the two ends of a 6.2-ohm sampling resistor. Here, the phase is detected by the program's algorithm, and the logic of controlling the PC8 and PC9 pins makes the two NMOS of U15 turn on alternately. The input current signal for controlling the current is negative. The control of the integrator and the release of the integrating capacitor are controlled by the microcontroller. The output value after passing through the integrator is the collected heating element current value, and its amplitude can be calculated in relation to J5-3 and J5-4.

[0071] like Figure 10 The diagram shows the signal processing circuit after the voltage and current of the heating element / heating wire are acquired.

[0072] The voltage and current signals after integrator enter a digital potentiometer. The setting and selection of the digital potentiometer can be controlled via the SPI bus. Its output signal passes through the other two channels of a TSV914 quad op-amp, which constitute a signal processing circuit. By setting the four potentiometers, the voltage and current signal output values ​​can be ensured to be within a reasonable range. The processed voltage and current signals enter the MCP3202 12-bit ADC, which has two channels to acquire the CH0 voltage and CH1 current signals respectively. The ADC reference is generated by a MAX6067 at 4.5V. Four 0-ohm resistors are added to the lower right to control whether the signal passes through the digital potentiometer and op-amp. A U2 EEPROM is also added to the microcontroller for data storage. Communication between these three chips and the microcontroller uses SPI communication.

[0073] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0074] As used in this invention, the term "comprising" is an open-ended expression, meaning it includes the contents specified in this invention, but does not exclude other aspects.

[0075] As used in this invention, the term "and / or" includes any one and all combinations of one or more of the related listed items.

[0076] The scope of protection of this utility model is not limited to the above embodiments. Any variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the utility model are included in this utility model and are protected by the appended claims.

Claims

1. A temperature control circuit for a heating element / heating wire, characterized in that, include: The power supply circuit is used to convert the externally input voltage into the voltage required by the device. The mains power zero-crossing acquisition circuit is used to acquire the zero-point of the AC sinusoidal wave through zero-crossing detection technology. Synchronous drive external thyristor circuit, used to drive external high-power thyristor circuit; The bidirectional thyristor drive circuit is used to connect to the primary side of the transformer. The PWM pulse signal from the microcontroller's I / O port drives the transformer through the bidirectional thyristor to energize and heat both sides of the heating element / heating wire. The microcontroller function circuit is used to provide the microcontroller with operating conditions, input signal processing, and output drive capabilities. The peripheral communication interface circuit is used to convert external input signals into signals that can be recognized by the microcontroller, and to convert the signals output by the microcontroller into external switching signals or analog signals. The voltage and current acquisition circuit is used to convert the voltage signals on both sides of the heating element / heating wire and the current signal of the transformer into voltage signals within the range; The signal processing circuit is used to convert digital signals into digital signals that can be read by a microcontroller through a digital potentiometer and operational amplifier circuit, and then through an ADC chip.

2. The temperature control circuit for heating element / heating wire as described in claim 1, characterized in that, The power supply circuit uses the LM2675M-5.0 chip, which integrates a switching transistor.

3. The temperature control circuit for heating element / heating wire as described in claim 1, characterized in that, The mains power zero-crossing acquisition circuit generates positive and negative power supplies using a resistor-capacitor voltage reduction method. It includes an operational amplifier TL061CDR and an operational amplifier TS912IDT. The operational amplifier TL061CDR and surrounding resistors and capacitors constitute a second-order active low-pass filter. The high-voltage AC power is divided by resistors and then input to the TL061CDR operational amplifier. After high-frequency interference is filtered out by a second-order active low-pass filter, it passes through one channel of the TS912IDT operational amplifier and outputs a square wave. Then, it passes through the other channel of the TS912IDT operational amplifier, and the output of the operational amplifier drives the primary side of the optocoupler. The isolation secondary side of the optocoupler is connected to a pull-up resistor and an RC low-pass filter before being input to the microcontroller's I / O to collect the zero-crossing point.

4. The temperature control circuit for heating element / heating wire as described in claim 1, characterized in that, The synchronous drive external thyristor circuit is connected to the microcontroller's I / O port, which drives the primary side of the optocoupler and controls the conduction and shutdown of the secondary side DC.

5. The temperature control circuit for heating element / heating wire as described in claim 1, characterized in that, The bidirectional thyristor drive circuit includes: a bidirectional thyristor Q18, a varistor RV1, an absorption buffer circuit RC, a varistor RV2, a bidirectional thyristor isolation drive chip U13, an NPN transistor Q16, and a DC blocking capacitor C42; wherein... A varistor RV1 is applied between LN to prevent high spike interference on LN; The RC snubber circuit across the thyristor is used to suppress voltage spikes across the thyristor. The RV2 varistor is used for protection and is placed between pins 1 and 2 of the bidirectional thyristor Q18 to prevent high spike interference on pins 1 and 2 of the thyristor Q18. The bidirectional thyristor isolation driver chip U13 has a primary side that is a microcontroller I / O control driver; the DC blocking capacitor C42 is for DC blocking.

6. The temperature control circuit for heating element / heating wire as described in claim 1, characterized in that, The microcontroller functional circuit includes: microcontroller functional circuit No. 1 and microcontroller functional circuit No. 2; The No. 1 microcontroller functional circuit includes: microcontroller peripheral circuit and encryption chip U7; the microcontroller peripheral circuit includes: reset circuit, power supply circuit, crystal oscillator circuit and download port; The No. 2 microcontroller functional circuit includes: 8-bit DIP switch acquisition, rotary potentiometer acquisition, rotary encoder switch acquisition, LED indication, and EEPROM storage; The screen communicates via a serial port at a baud rate of 115200 with the microcontroller; the EEPROM stores key data and uses SPI communication.

7. The temperature control circuit for heating element / heating wire as described in claim 1, characterized in that, The peripheral communication interface functional circuit includes: three control channels via optocouplers, a 0-10VDC output, a 0-10VDC input, and a linear power supply; wherein... The three-way control is activated by the secondary side of the optocoupler when the external input is 24VDC. The high level is then input to the microcontroller's I / O port after being filtered by an RC low-pass filter. When the external input is 0V or not connected, the low level is input to the microcontroller's I / O port. The 0-10VDC output and 0-10VDC input circuits, as well as the linear power supply, are powered by 78L15 and 78L10 chips. The input of the 0-10VDC output circuit is the PWM pin of the microcontroller. The 0-10VDC input signal is protected and filtered before being input to the operational amplifier. The operational amplifier forms a follower and then provides a voltage divider to the microcontroller's AD acquisition.

8. The temperature control circuit for heating element / heating wire as described in claim 1, characterized in that, The voltage and current acquisition circuit includes: a charge pump LM828, an analog switch DG442, and an inverting integrator; wherein... The charge pump LM828 powers the analog switch DG442; the inverting integrator consists of two channels of the quad operational amplifier TSV914.

9. The temperature control circuit for heating element / heating wire as described in claim 8, characterized in that, The signal processing circuit includes: a digital potentiometer, a signal processing circuit, an ADC, and four 0-ohm resistors; The voltage and current signals after passing through the integrator enter the digital potentiometer. The setting and gating of the digital potentiometer are controlled by the SPI bus, and its output signal passes through the signal processing circuit. The signal processing circuit consists of the other two channels of the four operational amplifiers TSV914. The processed voltage and current signals enter the ADC, which collects the CH0 voltage signal and CH1 current signal respectively. Whether the signal passes through the digital potentiometer and operational amplifier is controlled by whether four 0-ohm resistors R12, R13, R14, and R15 are soldered.

10. The temperature control circuit for heating element / heating wire as described in claim 1, characterized in that, The microcontroller is also equipped with a U2 EEPROM for data storage.

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