CN112286253A - Temperature control system and method for hydrogen atomic clock - Google Patents

Temperature control system and method for hydrogen atomic clock Download PDF

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CN112286253A
CN112286253A CN202011127339.XA CN202011127339A CN112286253A CN 112286253 A CN112286253 A CN 112286253A CN 202011127339 A CN202011127339 A CN 202011127339A CN 112286253 A CN112286253 A CN 112286253A
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temperature
module
voltage
temperature control
atomic clock
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李锡瑞
封澳
陈翔
戚建宇
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Changzhou Institute of Technology
Shanghai Astronomical Observatory of CAS
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Changzhou Institute of Technology
Shanghai Astronomical Observatory of CAS
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/1902—Control of temperature characterised by the use of electric means characterised by the use of a variable reference value
    • G—PHYSICS
    • G04—HOROLOGY
    • G04F—TIME-INTERVAL MEASURING
    • G04F5/00—Apparatus for producing preselected time intervals for use as timing standards
    • G04F5/14—Apparatus for producing preselected time intervals for use as timing standards using atomic clocks

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Abstract

The invention provides a temperature control system of a hydrogen atomic clock, wherein a temperature control module of the temperature control system comprises a voltage stabilizing module, a reference voltage source, a bridge circuit, an ADC reading module and a temperature calculation and PID control module which are sequentially connected, the temperature calculation and PID control module is connected with a heating module through a PWM output module and is connected with an upper computer through a serial port communication module, and the heating module comprises heating wires wound in corresponding temperature control areas; the bridge circuit is provided with a first output end and a second output end, and the voltage dividing resistors of the bridge circuit are high-precision low-temperature drift resistors; the thermistor is embedded in the wall of the corresponding temperature control area and sealed by hot melt adhesive; the temperature calculation and PID control module determines the current temperature according to the voltage difference and determines the output quantity of PID control according to the current temperature. The invention also provides a corresponding temperature control method. The temperature control system improves the control precision and stability of the temperature and can be used for solving the problem of long-term stability of the hydrogen atomic clock.

Description

Temperature control system and method for hydrogen atomic clock
Technical Field
The invention relates to a temperature control system, in particular to a temperature control system and method of a hydrogen atomic clock.
Background
At present, the self-excited hydrogen atomic clock adopts the atomic storage bubble technology, so that the resonance spectral line is greatly narrowed, and the accuracy of the hydrogen atomic frequency standard can reach 3 multiplied by 10-13Stability of up to 10-16A day; at the same time, the resonant cavity adopts TE011The mode electromagnetic field structure has many good characteristics such as high quality factor, excellent signal-to-noise ratio and frequency discrimination capability.
However, the cavity bubble structure imposes a nearly strict requirement on the temperature environment, and the limitation requirement on the temperature fluctuation is tens of times or even hundreds of times higher than that of the cesium clock. Considering that temperature variation is an important factor influencing the long-term stability of the output frequency of the hydrogen atomic clock. Therefore, in order to achieve better long-term stability, it is necessary to improve the temperature stability of the bubble component[1]。
The temperature is an important factor for the hydrogen atomic clock, and poor temperature control can cause the stability of the hydrogen atomic clock to be poor; the temperature runaway can directly result in no intermediate frequency signal output of the hydrogen atomic clock. Therefore, the temperature control is reliable and stable in design.
The temperature-dependent influencing factors of the hydrogen atomic clock will be described in greater detail below.
1) Effect of cavity drag
The pulling effect of the temperature-induced intra-cavity frequency variation on the clock frequency can be represented by the following equation:
Figure BDA0002734048260000011
in the formula, QcIs the quality factor of the resonator; qlIs atomic 0-0 transition spectral line quality factor; Δ fcRepresenting the frequency variation of the resonant cavity; Δ f0Representing the amount of change in the output frequency of the hydrogen atomic clock.
Given Qc＝3.0×104，Ql＝1.5×109If Δ fc1Hz, then Δ f0＝±2.0×10-5. For f0＝1.4×109In the case of Hz, the relative frequency stability of the output frequency of the hydrogen atomic clock is:
Figure BDA0002734048260000012
when required
Figure BDA0002734048260000013
When, if
Figure BDA0002734048260000014
The allowable range of temperature variation is:
Figure BDA0002734048260000015
thus, the long-term stability is highly demanding for temperature control; aiming at the problem of cavity traction effect, a metal material with small thermal expansion and cold contraction rate is suitable to be selected in the design to manufacture the microwave resonant cavity so as to reduce the influence of temperature on the cavity frequency of the microwave resonant cavity.
2) Second order Doppler effect
The second order Doppler shift of the hydrogen atoms in the storage bubble can be expressed as follows:
Figure BDA0002734048260000021
in the formula,. DELTA.fDRepresenting the magnitude of the second order doppler shift of the stored atom; f. of0Represents the center frequency of a hydrogen atom; k represents a boltzmann constant; t represents the thermodynamic temperature of the storage bubble; m represents the total mass of hydrogen atoms.
For hydrogen atoms, the variation of this offset with temperature is:
Figure BDA0002734048260000022
in order to make the output frequency of the hydrogen atomic clock reach 10-15Relative frequency stability, the temperature of the storage bubble must be maintained at 7X 10-3The temperature is not changed.
3) Wall motion
When operated at about 40 deg.C, the amount of frequency shift (i.e., wall displacement) caused by a wall collision of a hydrogen atom with a storage bubble can be given by[2]：
Figure BDA0002734048260000023
In the formula,. DELTA.fwRepresents the magnitude of the wall displacement; a represents a temperature coefficient; k represents the coefficient of wall properties at 40 ℃ (values of approximately-324 to-390 mHz cm); d represents the diameter of the storage bubble; theta represents the temperature of the storage bubble (expressed in degrees centigrade).
Offset δ (Δ f) of wall displacement amount due to temperature change δ θw) Comprises the following steps:
δ(Δfw)＝aKδθ/D，
for a storage bubble diameter of 16cm, the wall displacement value is approximately 25mHz at a temperature of 313K.
4) Effect of electronics
The conventional size self-excited hydrogen pulse is hardly affected by the electronic effect. The microwave receiver is part of a phase locked loop, and possible thermal influences may not be taken into account, as the temperature of the microwave receiver and the phase locked loop is typically controlled to a level of 0.1 c.
When the mini-type hydrogen pulse device is operated in the active mode, the electronic effect is the same as that described above. But the Q enhancement electronics significantly increase the thermal sensitivity of the cavity resonant frequency due to the phase change of the re-injected signal. Although these hydrogen masers are equipped with cavity auto-tuning systems for eliminating cavity resonant frequency variations, these factors still need to be suppressed with excellent temperature control.
In the non-self-excited hydrogen pulse, any change in the load reactance of the cavity must be avoided, as is the case with the self-excited hydrogen pulse. But in the non-self-excited mode of operation there is an inherent additional frequency shift. If these frequency shifts are time-varying, they may also affect the long-term variation of the frequency.
In summary, the variation of the microwave cavity temperature is one of the important factors causing the variation of the frequency scale frequency of the hydrogen atom. Firstly, most frequency scales are provided with a resonant cavity, and the geometrical size of the resonant cavity is influenced by temperature; second, the frequency shift due to atomic phenomena (such as wall collisions, spin changes, and doppler effects) is also a function of temperature. According to the current practical work experience, the following steps are known: in order to achieve a long-term stability of the frequency standard of 10-15In order of magnitude, the stability of temperature control reaches 5 x 10-3K is very essential[3]。
The current situation of temperature control systems:
at present, in order to overcome the influence of factors such as larger thermal inertia of a controlled system, cavity temperature fluctuation and large temperature gradient caused by heat conduction and the like and improve the temperature control precision to the maximum extent, a temperature control system is often constructed by adopting a method of combining physical environment heat preservation and electronic closed-loop temperature control in the prior art.
As shown in fig. 1, the conventional hydrogen atomic clock includes a storage bubble 101 disposed at the innermost side, and a resonant cavity 102 (cylindrical shape), a vacuum bell jar 103 (cylindrical shape), a C field cylinder 104 (cylindrical shape), a 4-layer magnetic shielding cylinder 105 (cylindrical shape), and a neck 106 of the resonant cavity are sequentially sleeved on the outer side. The design of the existing precise temperature control system is realized by arranging a double-layer heating furnace from the outside of a resonant cavity to a shield, wherein the outer furnace provides an internal constant temperature environment which can resist the fluctuation of the external temperature relatively stably, and the inner furnace realizes the precise temperature control of each part. Therefore, the temperature control part comprises a heating wire which is wound on the vacuum bell jar and is used as the inner furnace part, and a heating wire which is wound on the magnetic shielding cylinder and is used as the outer furnace part; the thermistor is also attached to the corresponding cartridge.
In order to enable the temperature control to be more accurate, the inner furnace bell jar is divided into three units, namely a bottom unit, a barrel part and a top unit, and an outer furnace is divided into an upper unit and a lower unit. In addition, a novel heat insulation material is adopted between each layer structure, and an insulating film is added for preventing the local uneven heating from causing thermal current.
The hydrogen atomic clock has 7 temperature control areas at present by counting in weight: the device comprises a vacuum bell jar (inner furnace) bottom, a vacuum bell jar (inner furnace) cylinder part, a vacuum bell jar (inner furnace) top, an outer furnace cylinder part, a coaxial cable serving as a neck resonant cavity and an isolator, wherein the isolator is a processing part for outputting a coupling signal to a hydrogen clock. Temperature control is an important factor, for example, in recent years, temperature control is also designed for a hydrogen bottle (hydrogen gas supply source) so that the supply pressure of hydrogen gas is stable and the flow rate is stable. By subdividing each temperature control zone, the temperature gradient change is reduced and the temperature is kept constant. Specifically, temperature control is performed independently for a portion of the hydrogen atomic clock, which is susceptible to temperature, being substantially partitioned.
The existing temperature control system has the following defects:
1) the existing hardware temperature control installation mode is that the hardware temperature control installation mode is directly adhered to the outer wall of a resonant cavity, and the method cannot accurately read the actual temperature of the resonant cavity because the resonant cavity and a thermistor cannot be well contacted.
2) The temperature control system used at present sets a resistance value by adjusting the sliding resistor, and compares the resistance value of the thermistor at the current temperature with the resistance value of the sliding resistor, so as to roughly determine whether the target temperature is reached.
3) The current temperature control system adopts +15V direct current voltage and 1.5K +/-0.1% of resistance to divide voltage, and abstractly reads the temperature by comparing the voltage of the sliding resistor and the voltage of the thermistor, so that the method cannot directly read the current temperature, is easily influenced by power supply fluctuation and has low precision.
4) The currently used temperature control system reads the difference between the voltages of the sliding resistor and the thermistor to drive the NPN low-frequency high-power triode 3DD15, and directly adds the +24V voltage to the heating wire for heating, so that the defects of low temperature control precision, no feedback in open loop and the like are overcome.
5) The temperature control system used at present does not have a temperature display function and cannot visually display the current temperature.
6) The temperature control system used at present adopts an old-fashioned 3DD15 triode for temperature control, the three connecting pipes have obviously low conversion efficiency due to long time, the temperature control time is long, and the long-time temperature heating can cause serious heating.
Reference documents:
[1] nigula Demuoff hydrogen clock development technology and expectation [ J ] astronavigation measurement technology, 2007, Z1:6-14.
[2] Measurement and elimination of hydrogen atomic clock wall shift [ J ] journal of spectroscopy, 201128 (3): 378-382.
[3] Dial cause, hydrogen pulse cavity frequency-temperature effect analysis [ J ] astronavigation measurement technique, 200626 (5): 7-11.
Disclosure of Invention
The invention aims to provide a temperature control system and a temperature control method of a hydrogen atomic clock, which are used for realizing accurate temperature measurement, digital temperature control and feedback temperature regulation.
In order to achieve the purpose, the invention provides a temperature control system of a hydrogen atomic clock, which comprises at least one temperature control module which corresponds to the temperature control area of the hydrogen atomic clock one by one, wherein the temperature control module comprises a voltage stabilizing module, a reference voltage source, a bridge circuit, an ADC reading module and a temperature calculation and PID control module which are sequentially connected, the temperature calculation and PID control module is connected with the voltage stabilizing module, the temperature calculation and PID control module is also connected with a heating module through a PWM output module and is connected with an upper computer through a serial port communication module, the heating module comprises heating wires, and the heating wires are wound in the corresponding temperature control area; the power supply end of the bridge circuit is connected with the reference voltage source, the bridge circuit comprises a thermistor and a first divider resistor which are sequentially connected in series between the power supply end and the ground, and a second divider resistor and a third divider resistor which are sequentially connected in series between the power supply end and the ground, a first output end is arranged between the thermistor and the first divider resistor, a second output end is arranged between the second divider resistor and the third divider resistor, and the first divider resistor, the second divider resistor and the third divider resistor are all high-precision low-temperature drift resistors; the thermistor is embedded in the wall corresponding to the corresponding temperature control area and sealed by hot melt adhesive; the temperature calculation and PID control module is set to determine the current temperature according to the acquired voltage difference between the first output end and the second output end of the bridge circuit, and determine the output quantity of PID control according to the current temperature.
The voltage stabilizing module is set to supply power to the temperature calculation and PID control module and the reference voltage source, the voltage stabilizing module comprises a voltage stabilizing power supply and a voltage stabilizer which are sequentially connected, a voltage output end VOUT of the voltage stabilizer is connected with the temperature calculation and PID control module, and a direct-current voltage output end OUT of the voltage stabilizing power supply is connected with the reference voltage source.
The voltage-stabilized power supply is an LM2596S series chip, and the output voltage of the voltage-stabilized power supply is 5V direct-current voltage; the voltage stabilizer is an AMS1117-3.3 chip, the output voltage value of the voltage stabilizer is 3.3V, and the chip model of the reference voltage source is ADR 4525.
And the two channels of the ADC reading module are respectively connected with the first output end and the second output end of the bridge circuit.
The resistance value of the thermistor Rt of the bridge circuit is as follows:
Figure BDA0002734048260000051
the current temperature is:
Figure BDA0002734048260000052
wherein U1 is the voltage of the first output terminal of the bridge circuit, U2 is the voltage of the second output terminal of the bridge circuit, and Δ U is the voltage difference between the first output terminal and the second output terminal of the bridge circuit; u shapeDatumIs the voltage of the reference voltage source; rt is the resistance value of the thermistor at the current temperature T, and R1, R2 and R3 are the resistance values of the first divider resistor, the second divider resistor and the third divider resistor, respectively; r0To be at a reference temperature T0The resistance of the time-dependent thermistor; t is the current temperature; t is0Is a reference temperature; b is the material constant of the negative temperature coefficient thermistor,it is obtained by fitting; exp is an index with a natural number e as the base;
wherein, the output quantity of PID control is:
Figure BDA0002734048260000053
wherein u is the output quantity of PID control; kp1、Kp2Is the first and second proportionality coefficients, Kp1>Kp2；KiIs an integral coefficient; c1 is a first constant, C2 is a second constant, C1 is much larger than C2; e is an error value of the target temperature relative to the current temperature, and the target temperature is preset in the temperature calculation and PID control module; Σ e is the integral of the error; e1、E2、E3The first, second and third temperature error threshold values are decreased in sequence.
The temperature calculation and PID control module and the PWM output module are integrated in the same main control chip, the main control chip is a 32-bit ARM microcontroller, and the model of the main control chip is STM32F103C8T 6.
The master control chip is integrated with a DMA serial port sending module which is connected with the serial port communication module through a serial port, and the upper computer is set to receive and display the data of the current temperature sent by the temperature calculation and PID control module through the serial port communication module.
The heating module comprises a preceding triode and a rear triode, the base of the preceding triode is connected with the output end of the PWM output module through a protective resistor, the emitter of the preceding triode is connected with the base of the rear triode, and the collector of the preceding triode is connected with the output end of the regulated power supply through a fourth voltage-dividing resistor; and the emitter of the rear triode is grounded, and the collector of the rear triode is connected with an external power supply through the heating wire.
In another aspect, the present invention provides a method for controlling a temperature of a hydrogen atomic clock, including:
s1: dividing a hydrogen atomic clock into a plurality of temperature control areas, and establishing a temperature control system of the hydrogen atomic clock corresponding to each temperature control area of the hydrogen atomic clock;
s2: for each temperature control module, respectively initializing each module of the temperature control module, creating an initial task and starting task scheduling; creating an initial task including setting a target temperature of a temperature control zone;
s3: each temperature control module executes an initial task, creates a subtask, and deletes the initial task, wherein the subtask comprises subtasks sent by ADC reading, temperature control and serial ports;
s4: and creating a software timer in each subtask, setting corresponding timing time, ensuring that each subtask has determined execution time, and then executing the subtask.
The subtasks of ADC reading include:
step S41: acquiring a voltage difference delta U between a first output end and a second output end of the bridge circuit by using an ADC reading module;
step S42: converting the voltage difference in the step S41 into a current temperature by using a temperature calculation and PID control module;
step S43: performing window filtering processing on the current temperature by using a sliding window filtering module arranged in the temperature calculation and PID control module;
the subtasks of temperature control include:
step S41': calculating an error value of the current temperature relative to the target temperature;
step S42': determining the corresponding PID control output quantity according to the error value by utilizing a temperature calculation and PID control module;
step S43': outputting a corresponding PWM wave by a PWM output module according to the output quantity controlled by the PID;
the subtasks sent by the serial port comprise:
step S41 ″: a DMA serial port sending module is adopted to obtain the data of the current temperature sent by the temperature calculation and PID control module;
step S42 ″: the DMA serial port sending module compiles the data of the current temperature according to a corresponding protocol to become data which can be identified by an upper computer, and sends the data after being packaged;
step S43 ″: and the serial port transmission module is used for receiving the data sent by the DMA serial port sending module and then transmitting the data to the upper computer for the upper computer to identify.
The temperature control system of the hydrogen atomic clock adopts the high-precision, low-power-consumption and low-noise reference voltage source to output a high-precision voltage, adopts the bridge circuit to divide the voltage, and determines the current temperature through the voltage difference value of the bridge circuit by the temperature calculation and PID control module.
In addition, the temperature control system of the hydrogen atomic clock presets a fixed target temperature in software, and then performs temperature control through a PID control technology, and has the advantages of large target temperature setting range, accurate target temperature setting, quick target temperature adjustment and the like; moreover, the temperature control system of the hydrogen atomic clock has a fixed target temperature, adopts a sectional PID control algorithm to control the temperature according to the difference value between the current temperature and the target temperature, and has feedback in a closed loop, so the temperature control system of the hydrogen atomic clock has a smooth temperature control curve, small temperature data fluctuation, high precision and ideal control effect.
In addition, the temperature control system of the hydrogen atomic clock displays the current temperature obtained by the temperature calculation and PID control module through the upper computer, and can observe the current temperature condition in real time.
In conclusion, the temperature control system of the hydrogen atomic clock is optimized in the aspects of reading voltage by the electric bridge, setting fixed target temperature, adopting the PID control technology and displaying temperature, improves the control precision and stability of the temperature, and can be used for solving the problem of long-term stability of the hydrogen atomic clock.
Drawings
Fig. 1 is a schematic structural view of a conventional hydrogen atomic clock.
Fig. 2 is a heating schematic diagram of each temperature control module of the temperature control system of the hydrogen atomic clock of the present invention.
Fig. 3 is an overall block diagram of each temperature control module of the temperature control system of the hydrogen atomic clock of the present invention.
Fig. 4 is a circuit diagram of the voltage stabilizing module of the temperature control system of the hydrogen atomic clock of the present invention.
FIG. 5 is a circuit diagram of a bridge circuit of the temperature control system of the hydrogen atomic clock of the present invention.
FIG. 6 is a circuit diagram of a heating module of the temperature control system of the hydrogen atomic clock of the present invention.
Fig. 7A to 7D are flowcharts of a temperature control method of a hydrogen atomic clock of the present invention, in which fig. 7A shows a main flow of the temperature control method, and fig. 7B to 7D show a flow of executing three subtasks.
FIG. 8 is a graph comparing the results of different mounting locations on temperature measurements.
Fig. 9A to 9B are graphs showing comparison of heating times of the temperature control system of the conventional hydrogen atomic clock and the temperature control system of the hydrogen atomic clock of the present invention.
Fig. 10A to 10B are graphs comparing target temperatures of a conventional temperature control system for a hydrogen atomic clock and a temperature control system for a hydrogen atomic clock according to the present invention.
Fig. 11A to 11B are graphs comparing temperature control curves of a conventional temperature control system for a hydrogen atomic clock and a temperature control system for a hydrogen atomic clock according to the present invention.
Fig. 12 is a graph showing the effect of temperature control in a conventional temperature control system for a hydrogen atomic clock and in a temperature control system for a hydrogen atomic clock according to the present invention.
Fig. 13A to 13B are graphs comparing temperature control curves of a conventional temperature control system for a hydrogen atomic clock and a temperature control system for a hydrogen atomic clock according to the present invention.
Detailed Description
The temperature control system of the hydrogen atomic clock is arranged on the hydrogen atomic clock, and the hydrogen atomic clock comprises a storage bubble, a resonant cavity, a vacuum bell jar, a C field cylinder and 4 layers of magnetic shielding cylinders which are sequentially arranged from inside to outside. The temperature control system of the hydrogen atomic clock is also divided into a plurality of temperature control areas, in this embodiment, the number of the temperature control areas is 7, and the temperature control areas include: a bottom of the vacuum bell jar, a tube portion of the vacuum bell jar, a top of the magnetic shielding tube, a tube portion of the magnetic shielding tube, a coaxial cable as a resonant cavity of the neck portion, and an isolator (RF isolator).
As shown in fig. 2, the temperature control system of the hydrogen atomic clock includes at least one temperature control module corresponding to the temperature control regions one to one, and each temperature control module includes a heating wire wound around the corresponding temperature control region, a thermistor embedded in the wall corresponding to the corresponding temperature control region and sealed by a hot melt adhesive, and a temperature control circuit board connected to both the heating wire and the thermistor. In this embodiment, the number of the temperature control modules is 7, which corresponds to 7 temperature control areas, the heating wires are wound on the external grooves of the bottom, the cylinder part and the top of the vacuum bell jar of the hydrogen atomic clock, the top and the cylinder part in the outermost two-layer magnetic shielding cylinder, the coaxial cable of the resonant cavity and the isolator respectively, the heating wires wound on the external grooves of the vacuum bell jar form an inner furnace, and the heating wires wound in the outermost two-layer magnetic shielding cylinder form an outer furnace.
Since the temperature control circuit boards of the 7 temperature control regions have the same structure, in this embodiment, the temperature control regions take a vacuum bell jar as an example, the thermistor is embedded in an inclined jack arranged on the wall of the vacuum bell jar, and the temperature control circuit board adopts a completely new designed digital control mode.
Overall design of system hardware circuit:
as shown in fig. 3, each temperature control module in the temperature control system of the hydrogen atomic clock of the present invention includes a voltage stabilization module 1, a reference voltage source 2, a bridge circuit 3, an ADC reading module 4, and a temperature calculation and PID control module 5, which are connected in sequence, wherein the temperature calculation and PID control module 5 is connected to the voltage stabilization module 1, and the bridge circuit 3 is provided with the thermistor. The temperature calculation and PID control module 5 is also connected with a heating module 7 through a PWM output module 6 and is connected with an upper computer 9 through a serial port communication module 8, and the heating module 7 comprises the heating wire. All the structures except the thermistor Rt and the heating wire are provided on the temperature-controlled circuit board described above.
The voltage stabilizing module 1 is arranged to supply power to the temperature calculation and PID control module 5 and the reference voltage source 2, the voltage stabilizing module 1 comprises a voltage stabilizing power supply 11 and a voltage stabilizer 12 which are connected in sequence, a 24V external power supply is stabilized to be 5V direct current voltage by the voltage stabilizing power supply 11, the 5V voltage is stabilized to be 3.3V voltage by the voltage stabilizer 12, a voltage output end VOUT of the voltage stabilizer 12 is connected with the temperature calculation and PID control module 5, and the output 3.3V voltage is used for supplying power to the temperature calculation and PID control module 5; meanwhile, a dc voltage output terminal OUT of the regulated power supply 11 is connected to the reference voltage source 2, and the 5V voltage output from the regulated power supply 11 supplies a voltage to the precision reference voltage source 2. In addition, through the connection of the reference voltage source 2, the bridge circuit 3 and the ADC reading module 4, the reference voltage source 2 generates a 2.5V high-precision low-noise voltage to provide a reference power supply for the ADC reading module 4, and meanwhile, the resistance value variation of the thermistor Rt caused by the temperature is converted into a corresponding voltage value through the bridge circuit 3, and then converted into a digital value through the ADC reading module 4. Then the current temperature value is obtained through the temperature calculation and the corresponding calculation of the PID control module 5. The temperature calculation and PID control module 5 determines the output quantity of PID control again, and the PWM output module 6 generates PWM waves and adjusts the duty ratio of the PWM waves through the output quantity, so that the heating module 7 is controlled, and the temperature of the resonant cavity of the hydrogen atomic clock is changed. The serial port communication module 8 is connected with the upper computer 9, the serial port communication module 8 is set to receive the data of the current temperature sent by the temperature calculation and PID control module 5 and transmit the data to the upper computer 9 in real time, and the upper computer 9 is set to receive the data of the current temperature sent by the temperature calculation and PID control module 5 through the serial port communication module 8 and display the data so as to provide more visual current temperature and temperature change trend for people.
In the present embodiment, the regulated power supply 11 is an LM2596S series chip, and its output voltage is 5V dc voltage; the voltage stabilizer 12 is an AMS1117-3.3 chip and has an output voltage value of 3.3V. The chip model of the ADC reading module 4 is ADS 1256. The reference voltage source 2 is an ultra-low noise, high precision 2.5V reference voltage source ADR 4525.
The voltage stabilizing module 1 has the following specific structure:
the specific structure of the regulator module 1 is shown in fig. 4, and includes a regulated power supply 11 and a regulator 12.
In the present embodiment, the regulated power supply 11 is a regulated chip, preferably a chip of the LM2596S series, and its output voltage is a dc voltage of 5V. The LM2596S series chip is a 3A current output step-down switch type integrated voltage-stabilizing chip produced by Texas Instruments (TI), which contains a fixed frequency oscillator (150KHz) and a reference voltage stabilizer (1.23v), and has perfect protection circuit, current limitation, thermal cut-off circuit, etc. The device can form the high-efficiency voltage stabilizing circuit by only needing few peripheral devices.
As shown in fig. 4, the regulated power supply 11 includes a dc voltage input terminal IV, a dc voltage output terminal OUT, a ground terminal GND, a regulated sample voltage input terminal FB, and an enable control terminal ON/OFF. The maximum voltage value of the direct-current voltage input end IV can reach 40V, and the minimum voltage value is 4.5V; the DC voltage output end OUT is also an open-circuit output end of an emitter of the switching tube, the highest output of the DC voltage output end OUT is 37V, and the lowest value of the DC voltage output end OUT is 1.2V; the ground end GND is an input/output common end; the regulated sampling voltage input terminal FB is connected to the dc voltage output terminal OUT through a first inductor L1, which monitors the magnitude of the output voltage through a voltage divider network inside the chip of the regulated power supply 11; the enabling control end is ON/OFF, whether the voltage of the output end exists or not is controlled, when the enabling control end is ON/OFF higher than 1.23V, the internal switching tube is turned OFF, the output voltage is OV, when the enabling control end is lower than 1.23V, the output voltage is rated voltage, and in actual use, the enabling control end is ON/OFF and is generally grounded.
The voltage stabilizer 12 has a chip model of AMS1117-3.3 and an output voltage value of 3.3V. The AMS1117-3.3 chip is a forward low-voltage drop voltage stabilizer, an overheating protection and current limiting circuit is integrated in the forward low-voltage drop voltage stabilizer, the forward low-voltage drop voltage stabilizer is the best choice for battery power supply and portable computers, and a voltage stabilizing circuit formed by the forward low-voltage drop voltage stabilizer can completely meet the power supply requirement of the temperature control module.
As shown in fig. 4, the dc voltage input terminal IV of the regulated power supply 11 is connected to a +24V dc external power supply, and is grounded via a first capacitor C1 and a second capacitor C2, respectively, so that the +24V external power supply reaches the LM2596 chip after being filtered by the first capacitor C1 and the second capacitor C2. The ground terminal GND and the enable control terminal ON/OFF of the regulated power supply 11 are grounded. The regulated sample voltage input FB of the regulated power supply 11 is connected to the dc voltage output OUT through a first inductor L1, and the end of the first inductor L1 connected to the dc voltage output OUT is grounded through a reversed diode D1, so that the diode D1 and the first inductor L1 make the output current continuous in the off state of the LM 2596. The voltage-stabilizing sampling voltage input terminal FB of the voltage-stabilizing power supply 11 is further connected to the voltage input terminal VIN of the voltage-stabilizing power supply 12, the ground terminal GND of the voltage-stabilizing power supply 12 is grounded, the voltage output terminal VOUT of the voltage-stabilizing power supply 12 is grounded through the fifth capacitor C5 and the sixth capacitor C6, and the voltage output terminal VOUT is set to output a stable voltage of 3.3V.
The regulated sampling voltage input terminal FB of the regulated power supply 11 is grounded and connected with a magnetic bead L2 through a third capacitor C3 and a fourth capacitor C4, the other end of the magnetic bead L2 is the output terminal of the +5V dc voltage of the regulated power supply 11, and is connected with the analog ground AGND through a seventh capacitor C19 and an eighth capacitor C20, the magnetic bead L2 is dedicated to suppressing the signal line, the high frequency noise and the spike interference on the power line, and has the capability of absorbing the electrostatic pulse, the first capacitor C1, the third capacitor C3, the fifth capacitor C5 and the seventh capacitor C19 are electrolytic capacitors for eliminating the low frequency noise of the power supply, and the second capacitor C2, the fourth capacitor C4, the sixth capacitor C6 and the eighth capacitor C20 are common capacitors for eliminating the high frequency noise of the power supply. Therefore, the voltage is stabilized to be +5V direct current voltage by the voltage stabilizing power supply 11, then the direct current voltage reaches the voltage stabilizer 12 through the two filter capacitors C3 and C4, the +5V voltage is stabilized to be +3.3V, and then the power is supplied to the STM32F103C8T6 single chip microcomputer. The analog ground AGND is specially arranged for the ADC module, in order to reduce interference of current noise to the ADC module, GND of the ADC module is distinguished from GND of other modules, and the AGND and the GND are connected through a 0-ohm resistor.
Specific structure of the reference voltage source 2:
the model of the reference voltage source 2 is ADR4525, ADR4525 is a high-precision, low-power consumption, low-noise reference voltage source, the maximum initial error is +/-0.02%, the temperature drift is 2 ppm/DEG C (maximum), and the output noise is generated<1.25μVp-pIt has excellent temperature stability and low output noise. The reference voltage source 2 isHigh accuracy is achieved with innovative core topology while providing industry-leading temperature stability and noise performance. Low thermally induced output voltage hysteresis and low long term output voltage drift of the device also improve system accuracy over lifetime and temperature. A maximum operating current of 950 μ a and a maximum low voltage difference of 300mV make the device suitable for portable equipment.
The specific structure of the temperature measuring circuit (i.e. the bridge circuit 3) is as follows:
the resistance value of the thermistor changes along with the change of temperature, and the temperature measuring circuit needs to convert the change of the resistance value of the thermistor into the change of a voltage signal, and in order to realize the change, two circuits are generally used for realizing the change:
(1) a bridge temperature measuring circuit requiring a constant voltage;
(2) constant current source formula temperature measuring circuit.
Since the reference voltage source 2 used in the present system is the reference voltage source ADR4525, the voltage can be generated with the accuracy of ADR4525
0.02%, temperature drift of 2 ppm/DEG C (maximum), output noise<1.25μVp-pAfter voltage division by a high-precision low-temperature drift resistor, the voltage can be directly used as a voltage source of the bridge temperature measuring circuit, so that the system adopts the bridge circuit 3 as the temperature measuring circuit, and the power supply end of the bridge circuit 3 is connected with the reference voltage source 2.
As shown in fig. 5, the circuit diagram of the bridge circuit 3 is shown, the bridge circuit 3 includes a thermistor Rt and a first divider resistor R1 connected in series between a power supply terminal and the ground, and a second divider resistor R2 and a third divider resistor R3 connected in series between the power supply terminal and the ground, a first output terminal U1 is provided between the thermistor Rt and the first divider resistor R1, and a second output terminal U2 is provided between the second divider resistor R2 and the third divider resistor R3. The first voltage dividing resistor R1, the second voltage dividing resistor R2 and the third voltage dividing resistor R3 are high-precision low-temperature drift resistors with the precision of +/-0.1% and the temperature drift of 5 ppm/DEG C.
When the temperature changes, the resistance of the thermistor Rt changes, and the resistances of the first voltage dividing resistor R1, the second voltage dividing resistor R2, and the third voltage dividing resistor R3 do not change, so that the voltage at the second output terminal U2 does not change, the voltage at the first output terminal U1 changes, and the voltage difference between the two arms of the bridge circuit 3 is:
Figure BDA0002734048260000121
wherein Δ U is the voltage difference, U1 is the voltage of the first output terminal, U2 is the voltage of the second output terminal, UDatumIs the voltage of the reference voltage source; rt is the resistance of the thermistor, and R1, R2, R3 are the resistances of the first voltage dividing resistor, the second voltage dividing resistor and the third voltage dividing resistor, respectively.
Therefore, the output of the two arms of the bridge forms a differential signal, the differential signal is input to the input end of the ADC reading module 4 connected with the temperature calculation and PID control module 5, the resistance value of the thermistor Rt can be calculated through the voltage difference delta U in the temperature calculation and PID control module 5, and the temperature at the moment can be calculated through a temperature-resistance value relation formula fitted by the thermistor Rt.
The effect of thermistor self-heating on the selection of the resistances of the divider resistors R1, R2, R3:
when current flows through the thermistor Rt, certain heat is inevitably generated, and the heat causes the change of the resistance value of the thermistor, thereby affecting the stability of the hydrogen atomic clock control system of the present invention. The thermistor has an important parameter, namely dissipation ratio, which means the power required by the thermistor Rt to raise the temperature of the thermistor Rt by self-heating to 1 ℃ in a thermal equilibrium state, and the unit is mW/DEG C and is expressed by delta. The dissipation coefficient is different according to the packaging mode and the material of the thermistor Rt, and also changes with the temperature within the working temperature range. In order to suppress the influence of the self-heating effect of the thermistor Rt on the temperature measurement accuracy, the current flowing through the thermistor should be reduced as much as possible under the condition of ensuring sufficient signal sensitivity and signal-to-noise ratio, and the heat generated by the thermistor itself should be reduced, so as to suppress the influence of the temperature rise caused by self-heating on the control stability. For the bridge circuit shown in FIG. 5, the power P of the thermistor RtConsumption unitThe calculation formula of (a) is as follows:
Figure BDA0002734048260000122
wherein, UDatumIs the voltage of the reference voltage source; rt is the resistance of the thermistor at the current temperature T, and R1 is the resistance of the first divider resistor.
To ensure the temperature control stability of the system to be better than 1 x 10-3The temperature rise Δ T due to self-heating effect should be less than 1 × 10 deg.C-3℃。
In the present embodiment, the thermistor Rt has a model number of MFB 402-3470. The dissipation factor δ of the thermistor Rt in 25 ℃ still air is 2.5mW/° c, and therefore it yields 1 × 10-3The power P required by the temperature rise of the temperature is as follows:
P＝(2.5×10-3×1×10-3)W＝1×10-6W。
therefore, if the temperature rise caused by the power generated by the thermistor itself is less than 1 × 10-3The effect of the self-heating effect of the thermistor can be considered to be negligible, i.e. PConsumption unit<P，PConsumption unitThe power for increasing the temperature of the thermistor by the current flowing through the thermistor, P is 1 × 10-3The power required for temperature rise.
Substituting into the formula yields:
Figure BDA0002734048260000131
therefore, the resistor R1 at the lower arm position on the same side as the thermistor Rt should be properly selected. Due to the voltage value U of the reference voltage source 2Datum2.5V, the resistance of R1 should satisfy:
Figure BDA0002734048260000132
therefore, in the present embodiment, the resistances of the first divider resistor R1 and the second divider resistor R2 are 100K Ω, the resistance of the third divider resistor R3 is 4K Ω, the thermistor Rt is of the type MFB402-3470, and the resistance of the thermistor Rt is 4K ± 0.5% at normal temperature (25 ℃). In addition, in other embodiments, the resistances of the first divider resistor R1 and the second divider resistor R2 may be set to 150K Ω, or may be set to any value between 100K Ω and 150K Ω.
The specific structure of the ADC reading module 4:
in this embodiment, the chip model of the ADC reading module 4 is ADS 1256. ADS1256 is a 24-bit ADC conversion module. The ADS1256 high precision transducer accessible through the SPI. Has a data output rate of up to 30 kSPS; supporting 4-channel differential input or 8-channel single-ended analog input; an SPI serial interface; ultra low noise. In the present invention, the ADC reading module 4 adopts 8-channel single-ended analog input, and two channels of the ADC reading module 4 are respectively connected to the first output terminal U1 and the second output terminal U2 of the bridge circuit 3, and are configured to collect a voltage difference between the first output terminal U1 and the second output terminal U2 of the bridge circuit 3. In the present embodiment, since only two channels, i.e., the 0 channel and the 1 channel, are used, only data of two of the channels is read.
The temperature calculation and PID control module 5 and the PWM output module 6 have the following specific structures:
the temperature calculation and PID control module 5 and the PWM output module 6 are integrated in the same main control chip 100, and the main control chip 100 is a 32-bit ARM microcontroller. In this embodiment, the main control chip 100 is model number STM32F103C8T6, wherein the STM32F103 family belongs to a 32-bit ARM microcontroller, and the family of chips is available from the law Semiconductor (ST) corporation, and the core thereof is Cortex-M3.
The main control chip 100 has serial Single Wire Debug (SWD) and JTAG interfaces, 3 normal timers, 1 advanced timer (16 bits). Each common timer has four channels, each of which can be used for input capture, output comparison, PWM or pulse counting, and can also be used as input for an incremental encoder. The advanced timer not only has all functions of a common timer, but also has a 16-bit dead zone control and an emergency brake, which are used for timing and outputting PWM waves, so that one of the advanced timers of the main control chip 100 is used as a PWM output module 6 and is integrated in the main control chip 100; in this embodiment, the output port of the PWM output module 6 is a PA6 pin of the main control chip. In addition, the main control chip 100 further includes 2 watchdog timers (independent and window type), a system time timer, and a plurality of communication interfaces such as serial ports; the watchdog timer is used for resetting the program when the program is in error; the system time timer is a 24-bit self-reduction counter and is used for recording the working time of the current system; and a serial port in the communication interface is connected with the serial port communication module 8 and is used for communication between the temperature calculation and PID control module 5 and the upper computer 9.
The temperature calculation and PID control module 5 is configured to determine the current temperature according to the voltage difference Δ U between the first output terminal U1 and the second output terminal U2 of the bridge circuit 3, and determine the PID-controlled output U according to the current temperature.
Determining the current temperature specifically comprises: and calculating the resistance value of the thermistor Rt according to the voltage difference delta U between the first output end U1 and the second output end U2 of the bridge circuit 3, and calculating the current temperature according to the resistance value of the thermistor Rt.
Wherein, the resistance value of the thermistor Rt is as follows:
Figure BDA0002734048260000141
the current temperature is:
Figure BDA0002734048260000142
wherein U1 is the voltage of the first output terminal, U2 is the voltage of the second output terminal, Δ U is the voltage difference between the first output terminal U1 and the second output terminal U2 of the bridge circuit 3; u shapeDatumIs the voltage of the reference voltage source; rt is the resistance value of the thermistor at the current temperature T, and R1, R2 and R3 are the resistance values of the first divider resistor, the second divider resistor and the third divider resistor, respectively; r0To be at a reference temperature T0The resistance of the time-dependent thermistor; t is the current temperature; t is0Is a reference temperature; b is the material constant of the negative temperature coefficient thermistor, namely the thermal sensitivity index, which is determined by simulationSynthesized, here 3470; exp is the exponent with the natural number e as base.
PID (proportional-derivative-integral) control section:
if the temperature control module needs to ensure the rapidity of temperature response, the proportional coefficient Kp in the PID control parameter needs to be increased, but the stability margin of the temperature control module is reduced, and the system has larger static error due to the use of proportional adjustment; if only proportional-integral adjustment is adopted, although the static error can be eliminated and better control stability precision is obtained, for an object with larger lag, the proportional-integral adjustment time is too long, and the requirement of system rapidity cannot be met.
In order to ensure that the control scheme can meet the rapidity and obtain better control stability, the temperature control module adopts the idea of sectional control. And the temperature calculation and PID control module 5 determines the control rule to be adopted in the current control period according to the deviation signal.
A sliding window filtering module may be disposed inside the temperature calculation and PID control module 5 in the main control chip 100, and the sliding window filtering module performs window filtering processing on the current temperature, that is, the calculated current temperature is sampled only once, and the sampling value of one time and the sampling values of several times in the past are averaged together, so that the obtained effective sampling value can be used as the final output current temperature. If the N samples are averaged, N buffers of data must be created in the memory. Every time a new data is collected, storing the data into a temporary storage area, and simultaneously removing an oldest data, so that the N data are always the latest updated data. The sliding window filtering can well reduce the influence of error values on a system, has good inhibition effect on periodic interference, has high smoothness and is suitable for a high-frequency oscillation system.
The temperature calculation and the PID controlled output by the PID control module 5 can be described by the following equation:
Figure BDA0002734048260000151
wherein u is the output quantity of PID control, and is a numerical value, and in the embodiment, the output quantity range is 0-1000; kp1、Kp2Is the first and second proportionality coefficients, Kp1>Kp2；KiIs an integral coefficient; c1 is a first constant, C2 is a second constant, C1 is much larger than C2, in this embodiment, the first constant C1 is 1000, and the second constant C2 is 0; e is an error value of the target temperature relative to the current temperature (the error value is the target temperature — the current temperature), and the target temperature is preset in the temperature calculation and PID control module 5; Σ e is the integral of the error; e1、E2、E3A first, a second and a third threshold value of temperature error, which are decreased in turn, in this embodiment, a first, a second and a third threshold value of temperature error E1、E2、E 33, 0.8 and 0, respectively, and the three constants divide the temperature error into four intervals, namely (∞ -3), (3 ~ 0.8), (0.8 ~ 0) and (0 ~ infinity).
Thus, (1) when the actual temperature is much lower than the target temperature (E)1E) within the control interval, a constant and larger control quantity is used, so that the heating wire works at higher heating power, and the controlled temperature is increased to be close to the target temperature as fast as possible;
(2) when the actual temperature approaches the target temperature (E)2≤e≤E1) The actual temperature is lower than the target temperature, and in order to enable the actual temperature to be quickly increased to the target temperature and ensure that the controlled temperature does not generate large overshoot and oscillation, a control scheme of proportional adjustment is used in the control interval;
(3) when the actual temperature reaches the vicinity of the target temperature (E)3≤e≤E2) The difference value between the actual temperature and the target temperature is very small, fine adjustment is needed in the control interval, proportional-integral adjustment is adopted, and a differential link is not used in the control scheme in order to avoid the influence of external disturbance on the control stability;
(4) when the actual temperature reaches or exceeds the target temperature (e)<E3) A smaller output is used in this control interval.
The output u in the formula can change the duty ratio of the PWM, i.e. change the time of the high level in one period. In this embodiment, if a period of one PWM is 10ms (period value is 1000), the output quantity u is in the range of 0-1000, and if the output quantity u is 400, the duty ratio of the PWM is 40%, i.e. the high level time occupies 4ms and the low level time occupies 6ms in one period.
The PWM output module 6 is configured to generate a PWM wave and output the PWM wave of a specific duty ratio according to the output quantity u of the PID control.
The calculation formula is as follows: duty cycle is (output quantity/period value) 100%.
In addition, the master control chip 100 is integrated with a DMA serial port transmission module connected with the serial port communication module 8 through a serial port, which is preferably a DMA controller, the DMA controller is a unique peripheral integrated in the master control chip 100 (i.e. a single chip microcomputer) for transferring data inside the system, and can be regarded as a controller capable of connecting an internal memory and an external memory with each peripheral having a DMA capability through a set of dedicated buses. When the data is not transmitted by a DMA controller, the singlechips are required to participate in real time, and the singlechips transmit and monitor the data one by one. However, if the DMA controller is used, after parameters such as a starting address, data size and the like are set, data are directly transmitted by a special DMA serial port transmitting module, and a singlechip does not need to participate in the transmitting process, so that the resources of the singlechip can be saved, and the utilization rate of a system CPU (central processing unit) is improved. After the transmission is finished, interruption is generated to inform the single chip microcomputer. Therefore, the DMA is used for sending data through the serial port, so that the resource of the single chip microcomputer can be saved, the system structure is optimized, and the utilization rate of the single chip microcomputer is improved.
The specific structure of the heating module 7:
as shown in fig. 6, the heating module 7 includes a preceding transistor Q1 and a following transistor Q2, the base of the preceding transistor Q1 is connected to the output terminal of the PWM output module 6 (i.e. the PA6 pin of the main control chip 100) through a protection resistor R23, the protection resistor R23 is used for current limiting, the emitter of the preceding transistor Q1 is connected to the base of the following transistor Q2, and the collector is connected to the output terminal of the regulated power supply 11 through a fourth voltage-dividing resistor R24; the emitter of the rear triode Q2 is grounded, and the collector of the rear triode Q2 is connected with the +24V external power supply through the heating wire (R25 in the figure) described above. The heating module 7 is integrated on the above-mentioned temperature control circuit board except for the heating wire wound around the temperature control region (e.g., resonant cavity).
In this embodiment, the front-stage transistor Q1 is an NPN type low-power transistor, whose model is S9013; the rear stage transistor Q2 is a power transistor with model number 2SC 1969.
Under the ideal condition, when the triode is conducted, the voltage drop at two ends of the triode is zero, and no power is consumed, so that the output power of the heating voltage is equal to the heating power of the heating wire; when the triode is turned off, no current flows in the triode and the heating wire, and the heating power of the heating wire is zero. In practice, when the triode is conducted, the voltage drop between the two ends of the triode is not zero, so that the heating power of the heating wire is smaller than the output power of the heating voltage; when the triode is turned off, a tiny current flows through the triode and the heating wire, and the heating power of the heating wire is not zero. In practice, the heating power of the heating wire is smaller than that calculated by this formula, so that a sufficient margin is required in design (for example, it is calculated that 100J of energy is required for raising a certain temperature, and we output more than 100J of energy such as 110J and 120J of energy to leave a sufficient margin.
The selection of the two transistors needs to be noted that the output power and the collector current allowed by the rear-stage transistor Q2 are larger than the maximum power and the maximum current required by the heating wire. When the heating wire is in a heating state in the whole control period, the maximum heating power can reach 16W and the current is 0.67A, the output power of the rear triode Q2 (the model number is 2SC1969 in the embodiment) can reach 20W, and the maximum current allowed by the collector is 5A, so the requirement is met.
An upper computer 9 supporting a plurality of protocols:
according to the invention, the upper computer 9 of each temperature control module learns the communication protocols of various upper computers on the market, including frame head, frame tail, analysis frame and data transmission types, the data protocols are rearranged, classified and combined to write different serial port sending sub-functions for the plurality of upper computers 9, the main control chip 100 can send data to different upper computers through the same serial port communication module 8 only by calling the serial port sending sub-functions corresponding to various upper computers in the main control chip 100, and the online debugging of various upper computers can be supported simultaneously by sending through the plurality of serial ports, so that the debugging efficiency is greatly improved.
As shown in fig. 7A to 7D, a temperature control method can be implemented based on the above-described temperature control system of the hydrogen atomic clock. In this embodiment, the temperature control method is implemented based on the existing FreeRTOS operating system, and the FreeRTOS is a scalable small-sized RTOS system, and has functions of high portability, high efficiency, a software timer, a powerful trace execution function, a stack overflow detection function, unlimited task number, unlimited task priority, and the like. In today's environment, we do not need to worry about the RTOS being a performance penalty. In contrast, the RTOS provides an event-driven design such that the RTOS only runs when it is processing actual tasks, which enables more reasonable utilization of the CPU. In a real project, if a program waits for a timeout event, the conventional non-RTOS case either waits in place and cannot perform other tasks, or uses a complex state machine mechanism. If the RTOS is used, it is convenient to block the current task at the event and then automatically execute another task, which is obviously more convenient and makes efficient use of the CPU.
As shown in fig. 7A, the implemented temperature control method specifically includes:
step S1: dividing a hydrogen atomic clock into a plurality of temperature control areas, and establishing the temperature control system of the hydrogen atomic clock corresponding to each temperature control area;
step S2: for each temperature control module, respectively initializing each module of the temperature control module, creating an initial task and starting task scheduling;
wherein, carry out each module initialization of temperature control module, include: initializing the ADC reading module 4, initializing a serial port of the main control chip 100, and initializing a timer of the main control chip 100;
creating an initial task comprising: setting a target temperature of the temperature control area;
step S3: each temperature control module executes an initial task, creates a subtask, and deletes the initial task; thus, each temperature control module will then be scheduled cyclically in the created subtasks.
The subtasks include the subtasks of ADC reading, temperature control, serial port sending and the like.
Step S4: a software timer is created in each subtask, and a corresponding timing time is set to ensure that each subtask has a certain execution time (for example, a subtask sent by a serial port is executed every 100ms, a subtask read by an ADC is executed every 100ms, and a subtask controlled by temperature is executed every 10 ms), and then the subtask is executed. Wherein each sub-task is executed simultaneously.
As shown in fig. 7B, in step S4, the sub task of ADC reading is performed by the ADC reading module 4 and the temperature calculation and PID control module 5, which specifically includes:
step S41: collecting the voltage difference of the two channels (i.e. the voltage difference Δ U between the first output terminal U1 and the second output terminal U2 of the bridge circuit 3) by using the ADC reading module 4;
step S42: the voltage difference in step S41 is converted into the current temperature by the temperature calculation and PID control module 5.
Further, step S43 may be further included: and a sliding window filtering module arranged in the temperature calculation and PID control module 5 is used for carrying out window filtering processing on the current temperature. That is, the calculated current temperature is sampled once, and the sampled value of one time and the sampled values of the past times are averaged together to obtain an effective sampled value as the finally output current temperature.
When the subtask read by the ADC is executed, in order to avoid interruption of the read task, the task scheduling is closed at the moment, and when the task of reading the voltage by the ADC is executed, the task scheduling is opened.
As shown in fig. 7C, the subtask of temperature control is executed by the temperature calculation and PID control module 5, which specifically includes the following steps:
step S41': calculating an error value of the current temperature relative to the target temperature;
step S42': determining the corresponding PID control output quantity according to the error value by utilizing a temperature calculation and PID control module 5;
as described above, the output quantities of the PID control are:
Figure BDA0002734048260000191
wherein u is the output quantity of PID control, and is a numerical value, and in the embodiment, the output quantity range is 0-1000; kp1、Kp2Is the first and second proportionality coefficients, Kp1>Kp2；KiIs an integral coefficient; c1 is a first constant, C2 is a second constant, C1 is much larger than C2, in this embodiment, the first constant C1 is 1000, and the second constant C2 is 0; e is the error value of the target temperature relative to the current temperature; Σ e is the integral of the error; e1、E2、E3A first, a second and a third threshold value of temperature error, which are decreased in turn, in this embodiment, a first, a second and a third threshold value of temperature error E1、E2、E 33, 0.8 and 0, respectively, and the three constants divide the temperature error into four intervals, namely (∞ -3), (3 ~ 0.8), (0.8 ~ 0) and (0 ~ infinity).
Step S43': and outputting a corresponding PWM wave by using a PWM output module 6 according to the output quantity controlled by the PID.
As shown in fig. 7D, the subtask sent by the serial port is executed by using the DMA serial port sending module integrated in the main control chip 100, which specifically includes the following steps:
step S41 ″: a DMA serial port sending module in the main control chip 100 is adopted to obtain the data of the current temperature sent by a temperature calculation and PID control module (5);
step S42 ″: the DMA serial port sending module compiles the data of the current temperature according to a corresponding protocol to become data which can be identified by an upper computer, and sends the data after being packaged;
step S43 ″: the data is sent through the serial port, namely, the data sent by the DMA serial port sending module is received by the serial port transmission module 8 and then transmitted to the upper computer for the upper computer to identify.
Comparison of Experimental conditions
The invention takes a small designed bell as an example for simulation (the difference is that the actual bell of the hydrogen clock is larger, and the experimental bell is smaller). Specifically, adopt two small-size bell jar models that a mould is the same, the coiling mode of heater strip is the same completely, and the difference lies in:
one of the small-sized bells is the prior art thermistor-attached-to-bell-surface mounting mode and the original analog circuit control mode. And the other adopts the improved installation mode of embedding the thermistor in the hole of the bell jar through an inclined jack and a digital control mode of a brand-new design.
The technical effect of the improved temperature control module of the present invention compared to the temperature control module of the prior art is described in detail below.
Installation mode of the thermistor:
at present, the mounting position of a thermistor is changed, a hole is drilled in a resonant cavity, the thermistor extends into the hole, and then the hole is sealed by hot melt adhesive. As can be seen from fig. 8, the temperature difference between the thermistor adhered to the outer wall of the resonant cavity and the thermistor placed in the hole of the resonant cavity is more than one degree.
In terms of heating time:
as can be known from fig. 9A to 9B, the temperature control is performed on the hydrogen atomic clock and the heating module at the same time under the same time and the same conditions, because the conversion efficiency of the heating module adopted by the temperature control system (i.e., software temperature control) of the hydrogen atomic clock of the present invention is higher than that of hardware temperature control, the time for raising the temperature by the software temperature control is shortened by about one time compared with that of the temperature control system (i.e., hardware temperature control) of the hydrogen atomic clock of the prior art, the heating time is saved, and the heating efficiency is improved.
Target temperature setting aspect:
the value of the target temperature is very important to the whole temperature control, a determined target value is provided, the premise that the temperature control of the system is stable is provided, and the system can control the temperature of the resonant cavity according to the set target value only if an exact target value is set. The target value setting of the hardware temperature control is adjusted by changing the resistance value of the sliding resistor and is easily influenced by factors such as resistance aging or external factor change, so the method cannot set an exact target temperature, the target value changes within a range, the software temperature control can set a specific target value, and the target value is not influenced by factors such as resistance value and external factor change.
As can be seen from fig. 10A to 10B, the target temperature of the hardware temperature control fluctuates within a certain range, there is no accurate target value, and the target temperature of the software temperature control is very determined and is not affected by external factors. The temperature control system of the hydrogen atomic clock has the advantages of large setting range (20-100 ℃) of the target temperature, accurate setting of the target temperature, quick regulation of the target temperature and the like by setting a fixed target temperature in software and then controlling the temperature by the PID technology.
Temperature stability:
as can be seen from fig. 11A-11B, since the target temperature of the hardware temperature control is not an accurate value, and there is no algorithm in the temperature control aspect, and the temperature control is performed by using a voltage comparison method, the temperature control curve of the hardware temperature control is not smooth enough, the fluctuation of the temperature data is large, the error is obvious, and the control effect is not ideal enough. The temperature control system of the hydrogen atomic clock has the advantages of smooth temperature control curve, small temperature data fluctuation, high precision and ideal control effect because the temperature control system of the hydrogen atomic clock has fixed target temperature, adopts a sectional PID control algorithm to control the temperature according to the difference value between the current temperature and the target temperature and has feedback in a closed loop. As can be seen from fig. 12, the software temperature control can still maintain high stability after long-time operation, and the temperature stability is within thousandth of a degree.
Temperature reading aspect:
the temperature control system of the hydrogen atomic clock adopts a high-precision, low-power-consumption and low-noise reference voltage source ADR4525 to output a high-precision +2.5V voltage, the maximum initial error is +/-0.02%, then a bridge circuit consisting of high-precision resistors with the precision of one thousandth and the temperature drift of 5PPM is adopted to divide the voltage, meanwhile, a 24-bit high-precision ADC reading chip ADS1256 is adopted to read the difference value of the current voltage, and the temperature is calculated through a curve after temperature fitting by a temperature calculation and PID control module.
Temperature display aspect:
the temperature control system of the hydrogen atomic clock displays the current temperature obtained by the temperature calculation and PID control module through various upper computers, and can observe the current temperature condition in real time.
In the aspect of conversion efficiency:
the temperature control system of the hydrogen atomic clock adopts the novel 9013 triode and the 2SC1969 power tube for temperature control, has the advantages of high conversion efficiency, short temperature control time, half of temperature control time reduction compared with the prior temperature control time, and no heating caused by heating.
And (3) overall comparison:
by observing the temperature control curves of the hardware temperature control and the software temperature control, we can know that the overall temperature control of the hardware temperature control is inferior to that of the software temperature control, particularly the data stability is obvious, and as can be seen from fig. 13A-13B, the temperature control curve of the hardware temperature control is rough, and after the set value is reached, the temperature data still fluctuates with a large error, the data stability is poor, and the overall control effect is not ideal; the temperature control curve of the software temperature control is smooth, and after the temperature data reaches a set value, the temperature data is maintained on a straight line, the data stability is high, and the overall control effect is ideal.
The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.

Claims (10)

1. A temperature control system of a hydrogen atomic clock comprises at least one temperature control module which corresponds to temperature control areas of the hydrogen atomic clock one by one, and is characterized in that the temperature control module comprises a voltage stabilizing module (1), a reference voltage source (2), a bridge circuit (3), an ADC reading module (4) and a temperature calculation and PID control module (5) which are sequentially connected, the temperature calculation and PID control module (5) is connected with the voltage stabilizing module (1), the temperature calculation and PID control module (5) is also connected with a heating module (7) through a PWM output module (6) and is connected with an upper computer (9) through a serial port communication module (8), the heating module (7) comprises heating wires, and the heating wires are wound in the corresponding temperature control areas;
the power supply end of the bridge circuit (3) is connected with the reference voltage source (2), the bridge circuit (3) comprises a thermistor (Rt) and a first voltage-dividing resistor (R1) which are sequentially connected in series between the power supply end and the ground, and a second voltage-dividing resistor (R2) and a third voltage-dividing resistor (R3) which are sequentially connected in series between the power supply end and the ground, a first output end (U1) is arranged between the thermistor (Rt) and the first voltage-dividing resistor (R1), a second output end (U2) is arranged between the second voltage-dividing resistor (R2) and the third voltage-dividing resistor (R3), and the first voltage-dividing resistor (R1), the second voltage-dividing resistor (R2) and the third voltage-dividing resistor (R3) are high-precision low-temperature drift resistors; the thermistor is embedded in the wall corresponding to the corresponding temperature control area and sealed by hot melt adhesive; the temperature calculation and PID control module (5) is arranged to determine the current temperature according to the acquired voltage difference between the first output end (U1) and the second output end (U2) of the bridge circuit (3), and determine the output quantity of PID control according to the current temperature.
2. The temperature control system of a hydrogen atomic clock according to claim 1, characterized in that the voltage regulation module (1) is configured to supply power to the temperature calculation and PID control module (5) and the reference voltage source (2), the voltage regulation module (1) comprises a voltage regulation source (11) and a voltage regulation source (12) which are connected in sequence, a voltage output terminal VOUT of the voltage regulation source (12) is connected to the temperature calculation and PID control module (5), and a direct current voltage output terminal OUT of the voltage regulation source (11) is connected to the reference voltage source (2).
3. The temperature control system of the hydrogen atomic clock as claimed in claim 2, wherein the regulated power supply (11) is an LM2596S series chip, and the output voltage of the regulated power supply is 5V direct-current voltage; the voltage stabilizer (12) is an AMS1117-3.3 chip, the output voltage value of the voltage stabilizer is 3.3V, and the chip model of the reference voltage source (2) is ADR 4525.
4. The temperature control system of a hydrogen atomic clock according to claim 1, characterized in that the two channels of the ADC reading module (4) are connected to the first output terminal (U1) and the second output terminal (U2) of the bridge circuit (3), respectively.
5. The temperature control system of a hydrogen atomic clock according to claim 1, characterized in that the thermistor Rt of the bridge circuit (3) has a resistance value of:
Figure FDA0002734048250000011
the current temperature is:
Figure FDA0002734048250000021
wherein U1 is the voltage of the first output terminal of the bridge circuit (3), U2 is the voltage of the second output terminal of the bridge circuit (3), and DeltaU is the voltage difference between the first output terminal (U1) and the second output terminal (U2) of the bridge circuit (3); u shapeDatumIs the voltage of the reference voltage source; rt is the resistance value of the thermistor at the current temperature T, and R1, R2 and R3 are the resistance values of the first divider resistor, the second divider resistor and the third divider resistor, respectively; r0To be at a reference temperature T0The resistance of the time-dependent thermistor; t is the current temperature; t is0Is a reference temperature; b is a material constant of the negative temperature coefficient thermistor, which is obtained by fitting; exp is an index with a natural number e as the base;
wherein, the output quantity of PID control is:
Figure FDA0002734048250000022
wherein u is the output quantity of PID control; kp1、Kp2Is the first and second proportionality coefficients, Kp1>Kp2；KiIs an integral coefficient; c1 is a first constant, C2 is a second constant, C1 is much larger than C2; e is an error value of the target temperature relative to the current temperature, and the target temperature is preset in the temperature calculation and PID control module (5); Σ e is the integral of the error; e1、E2、E3The first, second and third temperature error threshold values are decreased in sequence.
6. The temperature control system of the hydrogen atomic clock according to claim 1, wherein the temperature calculation and PID control module (5) and the PWM output module (6) are integrated in the same main control chip (100), the main control chip (100) is a 32-bit ARM microcontroller, and the model of the main control chip (100) is STM32F103C8T 6.
7. The temperature control system of the hydrogen atomic clock according to claim 6, wherein the master control chip (100) is integrated with a DMA serial port transmission module connected with the serial port communication module (8) through a serial port, and the upper computer (9) is configured to receive and display data of the current temperature transmitted by the temperature calculation and PID control module (5) through the serial port communication module (8).
8. The temperature control system of a hydrogen atomic clock as claimed in claim 2, characterized in that, the heating module (7) comprises a preceding transistor (Q1) and a following transistor (Q2), the base of the preceding transistor (Q1) is connected with the output end of the PWM output module (6) through a protection resistor (R23), the emitter of the preceding transistor (Q1) is connected with the base of the following transistor (Q2), and the collector of the preceding transistor is connected with the output end of the regulated power supply (11) through a fourth voltage-dividing resistor (R24); and the emitter of the rear triode (Q2) is grounded, and the collector of the rear triode is connected with an external power supply through the heating wire.
9. A temperature control method of a hydrogen atomic clock is characterized by comprising the following steps:
step S1: dividing a hydrogen atomic clock into a plurality of temperature control areas, and building a temperature control system of the hydrogen atomic clock according to one of claims 1 to 8 corresponding to each temperature control area of the hydrogen atomic clock;
step S2: for each temperature control module, respectively initializing each module of the temperature control module, creating an initial task and starting task scheduling; creating an initial task including setting a target temperature of a temperature control zone;
step S3: each temperature control module executes an initial task, creates a subtask, and deletes the initial task, wherein the subtask comprises subtasks sent by ADC reading, temperature control and serial ports;
step S4: and creating a software timer in each subtask, setting corresponding timing time, ensuring that each subtask has determined execution time, and then executing the subtask.
10. The method for controlling the temperature of a hydrogen atomic clock according to claim 9, wherein the subtask of ADC reading comprises:
step S41: acquiring a voltage difference delta U between a first output end (U1) and a second output end (U2) of the bridge circuit (3) by using an ADC reading module (4);
step S42: converting the voltage difference in the step S41 into a current temperature by using a temperature calculation and PID control module (5);
step S43: a sliding window filtering module arranged in the temperature calculation and PID control module (5) is used for carrying out window filtering processing on the current temperature;
the subtasks of temperature control include:
step S41': calculating an error value of the current temperature relative to the target temperature;
step S42': determining the corresponding PID control output quantity according to the error value by utilizing a temperature calculation and PID control module (5);
step S43': outputting a corresponding PWM wave by a PWM output module (6) according to the output quantity controlled by the PID;
the subtasks sent by the serial port comprise:
step S41 ″: a DMA serial port sending module is adopted to obtain the data of the current temperature sent by the temperature calculation and PID control module (5);
step S42 ″: the DMA serial port sending module compiles the data of the current temperature according to a corresponding protocol to become data which can be identified by an upper computer, and sends the data after being packaged;
step S43 ″: and a serial port transmission module (8) is used for receiving the data sent by the DMA serial port sending module and then transmitting the data to an upper computer for the upper computer to identify.
CN202011127339.XA 2020-10-20 2020-10-20 Temperature control system and method for hydrogen atomic clock Pending CN112286253A (en)

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