CN109375291B - Temperature, air pressure and humidity measuring device and method suitable for sonde - Google Patents
Temperature, air pressure and humidity measuring device and method suitable for sonde Download PDFInfo
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Abstract
The invention provides a temperature, air pressure and humidity measuring device and method suitable for a sonde. The measuring device can be well matched with a low-resistance thermal resistance atmospheric temperature sensor, a piezoresistive bridge absolute air pressure sensor, a high-resistance dew point temperature sensor and a humidity-sensitive capacitance type humidity sensor for use. The invention utilizes the relation that the same reference current flows through the tested resistor and the reference resistor, and the voltage drop ratio of the reference resistor is irrelevant to the reference current; or the reference voltage directly acts on the measuring resistor network, the voltage division ratio of the reference voltage is irrelevant to the reference voltage, the performance of eliminating the measurement error caused by reference current or voltage drift is obtained, the voltage division coefficient of the measured resistor and the reference resistor or the resistor network is obtained through measurement, the resistance value of the measured resistor is calculated, and the measured values of the atmospheric temperature, the atmospheric pressure and the frost exposure point temperature can be further calculated.
Description
Technical Field
The invention relates to the technical field of electronic information, in particular to a temperature, air pressure and humidity measuring device and method suitable for a sonde.
Background
The working environment and working conditions of the sonde are greatly different from those of ground measurement. For an ascending sonde lifted by a balloon or a descending sonde lifted to a certain altitude by a rocket, an airplane and other methods, the response time of measurement is required to be fast enough due to a certain ascending or descending speed of the descending sonde; meanwhile, the temperature, air pressure and humidity in high altitude are greatly different, the dynamic range of measurement is required to be large enough, and the adaptability of the working environment condition of the measuring instrument is required to be wide enough; moreover, since the air is inevitably radiated by sunlight and microwave with different wavelengths, the measurement parameters of the sonde are required to be influenced to a small extent.
With respect to response time, the current technique is to reduce the size of the sensor so that it senses the magnitude of the measured parameter as quickly as possible.
For the dynamic range, at air temperature and pressure, the structure of the sensor has been improved, improving the measurement range and resolution of the sensor.
In terms of humidity, due to the limitations of the traditional humidity-sensitive capacitor with better performance in terms of resolution and precision, a physical method for measuring dew point or frost point is required to meet the requirements of dynamic range, resolution and precision. However, the latter method cannot be popularized and used in the conventional meteorological sounding service due to the relatively high cost, so that the two methods in humidity measurement are selected and used in different requirements.
For the adaptability of the working environment of the instrument, the main problem is that the temperature change range is too large, particularly the low temperature condition is very serious, and exceeds the working temperature range of most components, so that the instrument is difficult to work normally. The method for solving the problem is that foam materials with enough thickness are generally adopted to isolate the direct heat transfer between the instrument and the atmosphere, and the temperature change of the instrument does not exceed the working range within about 2 hours of measurement.
Because of this, in addition to the pressure sensor communicating with the outside air through the duct, the humidity and temperature sensors still need to be exposed to the air in order to obtain the best sensing results, i.e. response time and true amount of atmospheric air sensed.
For the influence of radiation, the currently used method is to coat special materials which do not have a great influence on the sensing of the measured variable and which reflect the radiation.
Thus, the temperature sensor has the same temperature measurement range as that of the conventional strain or filament, and the resistance and the variation range thereof are greatly reduced, so that the conventional measurement circuit hardly fully exerts the excellent performance of the improved temperature sensor, and the actual effect is not improved to an expected degree.
For humidity, in a humidity-sensitive capacitance measurement mode, due to the structural characteristics, an alternating current measurement technology is required in order to ensure that the performance of the humidity-sensitive capacitance measurement mode is not deteriorated in the measurement process, and the direct current component applied to the sensor is difficult to eliminate by a conventional measurement method. If the frost dew point measurement technique is adopted, it is necessary to accurately measure the current temperature value of the mirror surface for forming dew condensation or frost formation, i.e., the dew point or the frost point temperature. In order to reduce the sensor connecting lines and the AC excitation measuring technology as much as possible, and improve the measuring precision. The current measuring circuit does not use an alternating current excitation measuring technology in order to simplify the structure.
Therefore, it is necessary to develop a temperature, pressure and humidity measuring device suitable for a weather sonde.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provides a temperature, air pressure and humidity measuring device suitable for a sonde so as to accurately quantify and express the measuring results of temperature, air pressure and humidity sensors.
The invention adopts the following technical scheme:
a temperature, air pressure and humidity measuring device suitable for a weather sonde,
comprises a main controller, a constant current measuring module, an alternating current measuring module and an alternating current PWM measuring module, wherein,
a main controller having I in chip2Hardware interface of C bus, timing counter with capture function and UART serial interface, I2The C bus is used for communicating with the constant current measuring module and the alternating current measuring module, and the timing counter is used for exciting and measuring the alternating current PWM measuring module; the UART serial interface is set to two working modes of a fast mode and a slow mode, the fast UART is used for ground test and calibration, the slow UART is used for data transmission from the data in the sounding space to the transmitter, and all measurement and control operations are realized by the main controller and are connected with a ground computer through the transmitter;
constant current measuring module, which has current source excitation and programmable instrument amplifier, the current excitation connects with air pressure sensor and atmospheric temperature sensor, and connects with high precision reference resistance to form analog-to-digital conversion reference voltage, eliminates measuring error caused by constant current fluctuation and drift in measurement, the programmable instrument amplifier sets proper gain (2)n0,1,2, …,7, making the reference voltage higher than 1 time but not higher than 2 times the signal voltage), ensuring the analog-digital conversion part to work in the optimum voltage range;
AC measuring module with ACAn excitation and programmable instrumentation amplifier connected to a voltage-excited high-precision platinum resistance temperature sensor on the mirror surface of the condensation-type frost point apparatus and a platinum resistance temperature sensor on the heat sink in the semiconductor refrigerator, an AC reference voltage used as the excitation voltage of the measuring bridge and the reference voltage of the ADC, the programmable instrumentation amplifier setting an appropriate gain (2)n0,1,2, …,7, making the reference voltage higher than 1 time but not higher than 2 times the signal voltage), ensuring the analog-digital conversion part to work in the optimum voltage range;
and the alternating current PWM measuring module is used for processing a measuring time pulse sent by the main controller and a direction signal of polarity alternate change by a pulse processing circuit, performing polarity alternate charging and discharging on the connected humidity-sensitive capacitor, forming pulse width by charging time, and performing high-precision pulse width measurement by a timing counting unit of the main controller.
The further technical scheme is that the resistance value of an air pressure sensor externally connected with the constant current measuring module is 1-5 kilo-ohms, the resistance value of an atmospheric temperature sensor is 30-60 ohms, and the resistance value of a high-precision reference resistor is 1.25 kilo-ohms.
The further technical scheme is that the resistance value of a mirror surface high-precision platinum resistor temperature sensor of the condensation type frost point instrument connected in the alternating current measurement module is 1 kilo ohm at 0 ℃.
The further technical scheme is that a mirror surface high-precision platinum resistance temperature sensor of the condensation type dew point instrument and a platinum resistance temperature sensor on a radiating block in a semiconductor refrigerator are externally connected with a field effect tube to form an H-bridge switching circuit.
The further technical scheme is that the forward directions of two ends of the air pressure sensor and the atmospheric temperature sensor are both connected with a Schottky diode in parallel.
The further technical proposal is that the atmospheric temperature sensor adopts a 4-wire connection mode; a mirror surface high-precision platinum resistor temperature sensor of the condensation type dew point instrument adopts a 3-wire connection mode.
The further technical scheme is that the atmospheric temperature sensor is formed by repeatedly winding a 20-micrometer temperature-measuring tungsten wire.
The method for measuring the temperature, the air pressure and the humidity of the weather sonde in claim 1 is characterized by comprising
Step 1, processing an air pressure sensor, an atmospheric temperature sensor, a platinum resistor temperature sensor and a humidity-sensitive capacitor by a binary or multi-valued calibrating device to obtain a characteristic curve of the sensor;
step 2, connecting the air pressure sensor, the atmospheric temperature sensor, the platinum resistor temperature sensor and the humidity-sensitive capacitor to the constant current measuring module, the alternating current measuring module and the alternating current PWM measuring module through circuits, and connecting the modules to a main controller;
step 3, sending the measuring device to a position to be measured by using a sonde;
and 4, the measuring device obtains the measurement parameters, calculates the measurement results and sends the measurement results to the ground or sends the measurement parameters to a ground computer, and the ground computer calculates the measurement results through the floating points.
The further technical scheme is that during calibration, the output of the constant current measurement module is set to be 1mA, the amplification factor of the programmable instrument amplifier is set to be 16, the resistance value of the high-precision reference resistor is 1.25 kilo-ohm, and the ADC is a bipolar offset binary code.
The further technical scheme is that during calibration, the amplification factor of a programmable instrument amplifier of the alternating current measurement module is set to be 16, and the ADC is a bipolar offset binary code.
The invention has the beneficial effects that:
1) the voltage proportion formed on the air pressure sensor, the atmospheric temperature sensor (small resistance value) and the reference resistor (high precision) is not influenced by the current precision by small current flowing through the air pressure sensor, the atmospheric temperature sensor (small resistance value) and the reference resistor, and after the voltages are respectively amplified to the voltages of the same magnitude by the high-precision programmable instrument amplifier, analog-to-digital conversion and digital processing are carried out, so that the actual atmospheric temperature and the actual atmospheric pressure can be accurately restored.
2) The temperature measuring resistor with higher resistance value and the polarization effect and the thermocouple effect of the connecting circuit of the temperature measuring resistor are eliminated by using alternating current excitation, the influence of possible fluctuation and drift of the reference voltage is eliminated by using the consistent measuring bridge excitation voltage and ADC reference voltage, and the temperature of a measured object can be accurately reduced by performing analog-to-digital conversion and digital processing after the reference voltage is amplified by the high-precision programmable instrument amplifier.
3) Through alternating current pulse excitation, the influence of performance reduction caused by direct current electric field polarization on the humidity-sensitive capacitor is eliminated, and the atmospheric relative humidity value can be accurately calculated through high-precision pulse width measurement.
4) For any consistency differences that may exist in the sensor, the device can obtain the characteristic curve of the sensor through a two-value or multi-value verification device before use so as to calculate the real measured value.
Drawings
FIG. 1 is a schematic block diagram of a temperature, air pressure and humidity measuring device suitable for a weather sonde according to the present invention;
FIG. 2 is a schematic block diagram of an atmospheric temperature and pressure measurement module provided by the present invention;
FIG. 3 is a block diagram of a mirror temperature measurement module according to an embodiment of the present invention;
FIG. 4 is a graph showing the relationship between the temperature measuring resistor and the temperature and the error curve according to the embodiment of the present invention;
FIG. 5 is a graph showing the relationship between the temperature measuring bridge and the ADC and the error curve according to the embodiment of the present invention;
FIG. 6 is a graph of measured temperature versus ADC and error curves provided by an embodiment of the present invention;
FIG. 7 is a schematic block diagram and key waveform diagram of an atmospheric humidity measurement module based on a humidity-sensitive capacitive sensor according to an embodiment of the present invention;
fig. 8 is an ac humidity-sensitive capacitance measuring circuit based on pulse width modulation according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention are described below clearly and completely, and it is obvious that the described embodiments are some, not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The utility model provides a temperature atmospheric pressure and humidity measuring device suitable for meteorological sonde, includes main control unit, constant current measurement module, exchanges measurement module to and exchange PWM measurement module.
The main controller is composed of 32 high-performance embedded chips, STM320Fxx series models can be adopted, and hardware interfaces mainly use I in the chips2And the external resources comprise a bus C, a timing counter with a capture function, a UART serial and the like.
I2The C bus is used for communicating with the constant current measuring module and the alternating current measuring module; the timing counter is used for exciting and measuring the alternating current PWM measuring module; the UART serial interface is set to be in two conditions of a fast state and a slow state, the fast UART is used for ground test and calibration, and the slow UART is used for data transmission from the detection air to the emitter. All the measurement and control operations are realized by the controller, the calculation of the measured physical quantity formed by the measurement structure can be finished and the final result is returned, and the measurement parameters can also be returned to the ground and realized after being received by the ground computer.
Therefore, the ground computer adopts double-precision floating point calculation, thereby being more convenient.
The strong performance of the main controller is utilized to calibrate the sensor. For consistency difference possibly existing in the sensor, before the sensor is used, the characteristics of the sensor can be calibrated through one or more temperature calibrating devices, two-value or multi-value air pressure calibrating devices and two-value or multi-value humidity calibrating devices, and a characteristic curve of the sensor can be obtained and used for calculating a true value of a measured object.
The constant current measuring module is used for an air pressure sensor with kiloohm resistance value and a temperature sensor with ohm resistance value which are excited by current. The small current and the intermittent operation can greatly reduce the heating influence caused by the sensor. The same small current is used for flowing through a high-precision reference resistor to form a reference voltage of analog-digital conversion, and offset errors caused by constant current fluctuation and drift which can be generated in measurement are eliminated. The independently gain-settable high-precision programmable instrumentation amplifier can ensure that the analog-to-digital conversion part works in an optimal voltage range.
Programmable instrument amplificationThe gain setting range of the device is as follows: 2nAnd n is 0,1,2, …,7, so that the reference voltage is higher than 1 time but not higher than 2 times of the signal voltage.
The resistance value of the air pressure sensor is in the range of 1-5 kilo-ohms, the resistance value of the atmospheric temperature sensor is in the range of 30-60 ohms, and the resistance value of the high-precision reference resistor is 1.25 kilo-ohms.
The result of the working state machine of the constant current measuring module passes through I2The C bus is controlled and processed by the main controller.
The alternating current measuring module is used for a mirror surface high-precision platinum resistor temperature sensor of a condensation type frost point instrument excited by voltage and having a kiloohm resistance value and a platinum resistor temperature sensor on a radiating block in a semiconductor refrigerator. The alternating current measurement can counteract the effect of the polarization effect and thermocouple effect of the connecting line on the measurement. The AC reference voltage is used as the exciting voltage of the measuring bridge and the reference voltage of the ADC at the same time, so that the influence of the fluctuation and the drift which may occur to the AC reference voltage after the analog-to-digital conversion is automatically eliminated. Proper gain is set, and after the gain is amplified by the high-precision programmable instrument amplifier, the analog-digital conversion part can be ensured to work in the optimal voltage range.
The gain setting range of the programmable instrument amplifier is as follows: 2nAnd n is 0,1,2, …,7, so that the reference voltage is higher than 1 time but not higher than 2 times of the signal voltage.
The resistance value of a mirror surface high-precision platinum resistor temperature sensor of the condensation type dew point instrument is 1 kilo ohm at 0 ℃.
The working state and the result of the alternating current measurement module pass through I2The C bus is controlled and processed by the main controller.
The alternating current PWM measuring module processes a measuring time pulse sent by the main controller and a direction signal of polarity alternate change by a pulse processing circuit, and then carries out a charge and discharge process of polarity alternate on the humidity sensitive capacitor, so that the influence of the humidity sensitive capacitor on the performance reduction caused by the polarization of a direct current electric field is eliminated, the charging time forms a pulse width, and a timing counting unit of the main controller carries out high-precision pulse width measurement.
The alternating current PWM working process is controlled and processed by the main controller to obtain accurate measurement parameters.
The invention provides a technical means in 5, and the performance of the weather sonde is improved.
First, the use of sensor excitation directly correlates to the ADC reference voltage, eliminating additional measurement errors due to reference voltage or current fluctuations, drift.
For the case of the reference current, refer to fig. 1, the upper part of the schematic block diagram of the temperature, air pressure and humidity measuring device suitable for the weather sonde, and the actual schematic diagram of the part is fig. 2, the schematic block diagram of the atmospheric temperature and air pressure measuring module. The constant current source measurement module can be implemented using a 16-bit AD7792, or a 24-bit AD7793, or similar dedicated chips.
The current flows through the absolute air pressure sensor, and a Schottky diode is connected in parallel with the two ends of the absolute air pressure sensor in the forward direction, so that the situation that the measurement of the series-connected atmospheric temperature is influenced by a failure short circuit is prevented. When the circuit is broken, the diode plays a role of maintaining current.
Current flows through the atmospheric temperature sensor, which is likewise connected in parallel with a schottky diode in the forward direction across the sensor to prevent it from short circuiting in a failure that would affect the measurement of atmospheric pressure in series. When the diode is in normal state, the diode does not work, and when the diode is in short circuit, the diode plays a role of maintaining current.
Aiming at the measurement of the atmospheric temperature, the sensor can adopt a temperature measuring tungsten wire with the size of 20 mu m, the tiny tungsten wire is not sensitive to the radiation of the sun and other microwaves, one section of the tiny tungsten wire is cut and made into a zigzag shape to be repeatedly wound for a plurality of times, and the atmospheric temperature sensor R with good contact with the air is formedTThe resistance value of the sensor can be selected in the range of 30-60 ohms under normal temperature conditions, preferably 57 ohms, and the resistance value change of the sensor conforms to a linear temperature relationship.
In order to obtain good measurement performance, an atmospheric temperature sensor RTPreferably, a 4-wire connection is used. Due to the characteristics of the kelvin circuit, the line resistance of the current transmission loop (at both ends) is not affected in the voltage sampling line.
Example 1
Suppose, at a temperature t1When it is in the range of RA1AD7792 the measured data is D1 (considered to beIs a calibration step 1); at a temperature t2When it is in the range of RA2AD7792 measured data as D2 (which can be considered as calibration step 2); in practical measurement, the resistance is R at tAThe AD7792 measured data as D.
The reference voltage is R through a reference resistorrefIs converted to obtainref1.25 kilo ohm high precision resistor with low temperature coefficient is selected.
Setting AD7792 to IOUT2Constant current output and size of ItestThe instrument amplifier operates at a magnification beta (beta 16 corresponds to the present atmospheric temperature measurement). The ADC directly uses a bipolar offset binary code. According to the AD7792 characteristics, an atmospheric temperature measurement equation system, namely the equation (1), can be derived.
The first two terms of the formula (1) are calibration processes, namely, the slope K of the atmospheric temperature linear measurement is obtained through calibrationTAnd intercept BTAnd the item 3 is an atmospheric temperature measurement calculation formula.
Constant current source I in visible measurementtestIs eliminated and its drift and fluctuations no longer affect the measurement. For higher precision and minimized heat generation, in practical operation, the constant current source I is used for measurementtestIs set to a 1mA active output and the other conditions will be turned off.
Partial differentiation is carried out on the temperature measurement items to obtain an estimated temperature measurement error formula (2)
By embodying this equation as equations (3) and (4), it is possible to estimate the variation δ R due to the resistance value of the reference resistorrefResulting in a maximum measurement error deltatrefMeasurement error deltat formed from ADC nonlinearity error deltaDDThe case (1). The sum of the two is the total error.
If the constant current source measurement module uses AD7793, because its 24 is the data property, D1、D2D is 24 bits, 2 in formulae (1) to (4)-15Change to 2-23That is, other settings and values are unchanged.
The atmospheric pressure is measured by using an absolute air pressure sensor of NPC-1210-015A-3S or the like. The sensor is in a differential bridge form, the given parameter is that the driving current is 1.5mA, the output voltage is 100mV under the air pressure condition of a full range of 15PSI (approximately 1034.2hPa, slightly higher than 1 atmosphere of 1000hPa), and the differential impedance change value can be inferred to be 66.67 ohms. Obviously, if the current is 1mA, the corresponding output voltage is 66.67 mV.
Assuming that the output voltage and the pressure change conform to a linear relationship, at pressure P1When the corresponding resistance changes to deltaR1Output voltage of VO1AD7792 the measured data is D1(can be considered as calibration step 1);
at the air pressure P2, the corresponding resistance changes to delta R2, the output voltage is VO2, and the data measured by AD7792 is D2(which can be considered as calibration step 2); while in actual measurement, the air pressure is P, and the corresponding resistance change is deltaROutput voltage of VOThe AD7792 measured data as D.
Consistent with the principle of atmospheric temperature measurement, the working amplification factor beta of the AD7792 instrumentation amplifier is still set to be 16, and according to the AD7792 characteristics, the atmospheric pressure measurement formula (5) can be deduced, and other analysis and processing are consistent with the flow of atmospheric temperature measurement.
For the reference voltage, refer to fig. 1, which is a middle part of a schematic block diagram of a temperature, air pressure and humidity measuring device for a weather sonde, and a practical schematic diagram of the middle part is a schematic block diagram of a mirror temperature measuring module for a frost point detector in fig. 2. The ac measurement module may be implemented using a 24-bit AD7195, or similar dedicated chip.
In order to obtain good measurement performance, 4 reference resistors R constituting a bridgeREFThe 3 kilo-ohm resistor with the precision better than 0.1% is used to ensure the consistency of the resistance value and the measurement precision.
Specular temperature measurements were made using a model p1k0.232.3fw.a.010 or similar performance platinum resistor (see fig. 3 for details). The platinum resistor size is 2.3 x 2x 0.65/1.3 in length, width and height (mm). The small size is to reduce the corresponding time of the measurement as much as possible. According to the technical specification, the resistance value at 0 ℃ is 1 kilo-ohm. Suppose that at temperature tCWhen it is in the range of RMCAD7195 measured Data as Data. The resistance value change with temperature can be expressed in a polynomial manner as shown in equation (6).
Wherein, A is 3.9083 × 10-3【℃-1】，B＝-5.775×10-7【℃-2】，C＝-4.183×10-12【℃-4[ MEASURING THERMORESISTANCE ] belongs to the type of temperature measuring thermal resistance with a temperature coefficient of 3850 ppm/K.
FIG. 4 shows the relationship between the resistance and the temperature of the temperature measuring resistor (upper graph) and the error curve chart (lower graph).
The method of using the reference voltage as the measurement voltage is detailed in fig. 3. The N-channel and P-channel insulated gate field effect transistors in the figure are used as reversing switches, and the working states of the field effect transistors are saturated conducting or cutting off media. With forward drive model ACX1 and complementary drive model generated by an AC measurement module (e.g., using AD7195)And the inverted drive signal ACX2 and the complementary drive signalAnd respectively driving.
Thus, the device is provided withReference voltage VREFMeanwhile, the polarity of the excitation voltage is periodically changed, the average voltage is 0, and the excitation voltage is used as the excitation voltage of the measuring bridge and belongs to an alternating current measuring model. In order to reduce the additional influence caused by the lead wires, a 3-wire connection mode is adopted for a temperature measuring platinum resistor in the circuit.
To achieve the best range, the ac measurement module AD7195 has an operating amplification β set to 16, and its ADC is a bipolar offset binary.
From equation (6), the measured thermal resistance calculation can be expressed as: rMC＝f(tC) With an inverse function of tC＝f-1(RMC). According to the four-resistor bridge network, the measured voltage output is:
according to the characteristics of the AC measurement module AD7195, the ADC converts the numerical values as follows:
by using the formulas (6) and (8), the relationship between the resistance value of the temperature measuring resistor on the temperature measuring bridge and the ADC and an error curve chart can be calculated, which is shown in detail in FIG. 5. It can be seen that the reference voltage has no longer reacted on the output data and its possible instability has been eliminated.
Equation (8) can be expressed as: data is g (R)MC) The inverse function of which is RMC＝g-1(Data). The relationship of the converted value to the measured temperature can be derived: g (f (t) is Data ═ gC))＝h(tC) The inverse function is: t is tC＝f-1(g-1(Data))＝h-1(Data)。
By Matlab numerical calculation, the relationship between the set of temperature values in the measurement range and the corresponding set of ADC conversion final values, i.e., Data h (t), can be obtained in steps due to the accuracy requirementC). Data as argument, tCFor dependent variables, a 3 rd order polynomial relationship, i.e. t, can be fittedC＝h-1(Data) so that the temperature value t can be directly found from the measured Data, as shown in equation (9).
t＝p1Data3+p2Data2+p3Data+p4--------------------(9)
Wherein h is-1＝[p1 p2 p3 p4]And is and
p1＝-187304258.701497/1E20
p2＝25813142653524.273438/1E20
p3＝-2208570865245775360.000000/1E20
p4＝26443952875826686459904.000000/1E20
the fitting formula needs to be calculated by adopting double-precision floating point numbers, and the maximum additional error generated by the fitting formula is less than 0.03 ℃ and can be ignored. FIG. 6 shows the relationship between the resistance of the crossing temperature measuring resistor, the measured temperature and the ADC output offset binary code, and the error curve, and the analysis is corresponding to the upper and lower graphs.
So far, the accurate measurement of the mirror surface temperature of the dew frost point instrument is completed.
The temperature measurement of the radiating fins of the dew frost point instrument is completely the same as the temperature measurement of the mirror surface. In order to reduce the cost, the PT1000 type B-level temperature measurement platinum resistor with relatively large volume can be adopted for realization.
Secondly, a linear section of capacitor charging is adopted to form a linear relation between the pulse width and the capacitance, and the relative humidity is directly calculated through pulse width measurement.
Humidity sensitive capacitor CHThe volume is almost linear with the humidity of the environment, and if the capacitance measurement is also linear, the measurement data will be linear with the humidity.
As shown in FIG. 7, the input of the analog switch is DC, and the output is connected to form an "H-bridge" circuit to realize the control of the humidity-sensitive capacitor CHForward charging and discharging and reverse discharging. The charge-discharge circuit and a Schmitt trigger jointly form a pulse forming circuit. According to the humidity sensitive capacitance CHThe range of the capacity is evaluated by a suitable time constant, which can be determinedThe size of the charge and discharge resistor enables the Schmitt trigger to be in the voltage size before the Schmitt trigger is turned over and the humidity sensitive capacitor C in the charging processHIn a linear relationship, i.e. ensuring the output pulse width and the humidity-sensitive capacitor CHIn a linear relationship. After the pulse signal is shaped, the pulse signal is output to a main controller for counting, and pulse width data D is obtained.
Suppose, at humidity H1When it is, its corresponding pulse width data is D1(considered as calibration step 1), humidity H2When it is, its corresponding pulse width data is D2(which can be considered as calibration step 2); and when the humidity is actually measured, the humidity is H, and the corresponding pulse width data is D. From this, equation (10) can be derived.
The 1 st and 2 nd equations of the formula (10) are used for calibration, the third equation is an actual measurement equation, and the relative humidity value is directly calculated through the pulse width value.
And thirdly, the influence of the polarization effect and the thermocouple effect of the sensor and a connecting circuit thereof is eliminated or reduced by adopting an alternating current excitation technology, so that the measurement accuracy is higher.
An accurate measurement of the mirror temperature and the heat sink temperature of the frost point apparatus can be seen in fig. 3.
An H-bridge switching circuit is formed by externally connecting a field effect transistor, and extra forward and reverse errors caused by a polarization effect and a thermocouple effect formed by an external circuit are naturally offset in data accumulation through forward and reverse measurement, so that the measurement accuracy is improved.
In order to avoid the humidity-sensitive capacitor from being polarized to reduce the measurement performance and the service life, an alternating current excitation technology is required, and a conventional direct current charging and discharging circuit is not suitable for use.
The ac measurement circuit of the humidity sensitive capacitor is shown in fig. 8. The analog switch adopts ADG413BR or other devices with the same performance, and the difference of resistance values caused by the on-resistance and the discreteness of the on-resistance is negligible for the charge and discharge resistance due to the small on-resistance. Therefore, the forward and reverse charging parameters are completely consistent, so that the alternating current driving characteristic of complete 0 offset is ensured, and the consistency of forward and reverse measurement is also ensured.
Fourthly, the problem of large individual discreteness of the sensor is solved by adopting a binary linear calibration or multi-valued nonlinear fitting technology
For a thin tungsten wire atmospheric temperature sensor, an air pressure sensor and a humidity sensor, the individual discreteness is large, calibration is required before use, and otherwise, the error is large. The sensor used in the embodiment has better linearity, and can be calibrated by directly using a binary value under a linear fitting method, so that the operation and calculation process is simplified. If a sensor with poor linearity is used, a multi-valued nonlinear fitting technique needs to be used.
The specific method of binary linear calibration is as follows.
For calibration of atmospheric temperature measurements, the steps are as follows:
1) setting the working amplification factor beta of AD7792 to 16, and using the constant current output end IOUT2(Itest1mA), ADC is a bipolar offset binary code;
2) determining the resistance value of a reference resistor, generally taking 1.25 kilo-ohm, using a high-stability resistor, and enabling the precision to be 0.1%;
3) setting an ambient temperature t using a thermostat1Measuring to obtain ADC value D1；
4) Setting the ambient temperature t2Measuring to obtain ADC value D2；
5) Thus, using the 1 st and 2 nd terms of equation (1), the slope k can be calculatedTAnd intercept bTThe computer records the instrument and the corresponding binary value;
6) input kTAnd bTThereafter, the measurement can directly calculate the atmospheric temperature t using the 3 rd term of equation (1).
For calibration of atmospheric pressure measurements, the steps are as follows:
1) setting the working amplification factor beta of AD7792 to 16, and using the constant current output end IOUT2(Itest1mA), ADC is a bipolar offset binary code;
2) determining the resistance value of a reference resistor, generally taking 1.25 kilo-ohm, using a high-stability resistor, and enabling the precision to be 0.1%;
3) measuring the pressure P using a constant pressure tank arrangement1Measuring to obtain ADC value D1；
4) Setting the measured pressure P2Measuring to obtain ADC value D2；
5) Thus, using the 1 st and 2 nd terms of equation (2), the slope k can be calculatedPAnd intercept bPThe computer records the instrument and the corresponding binary value;
6) input kPAnd intercept bPThereafter, the measurement can directly calculate the atmospheric temperature P using the 3 rd term of equation (2).
For calibration of atmospheric humidity measurements, the steps are as follows:
1) humidity H was measured using a constant humidity cabinet setting1Measuring to obtain a pulse width value D1；
2) Setting the measured humidity to H2Measuring to obtain a pulse width value D2；
3) Using the 1 st and 2 nd terms of equation (3), the slope k can be calculatedHAnd intercept bHThe computer records the instrument and the corresponding binary value;
4) input kHAnd intercept bHThe measurement can then directly calculate the atmospheric humidity H using the term 3 of equation (3).
5) Fifthly, the method of directly fitting the measured physical quantity by using the measured value reduces the extra error caused by multiple conversions
6) For the measurement of the dew (or frost) point temperature of the dew-frost point instrument and the temperature of the radiating block thereof, a mature and stable platinum resistor temperature sensor is adopted, the resistance value of the resistor has a certain relation with the temperature, and after the measurement circuit is determined, the final ADC measured value has a certain relation with the resistance value of the resistor. Thus, the two are combined to form simple calculation of the formula (9), intermediate links are reduced, the peace reduces rounding errors generated by calculation of the intermediate links, and the calculation amount is reduced.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (6)
1. A temperature, air pressure and humidity measuring device suitable for a weather sonde is characterized in that,
comprises a main controller, a constant current measuring module, an alternating current measuring module and an alternating current PWM measuring module, wherein,
a main controller having I in chip2Hardware interface of C bus, timing counter with capture function and UART serial interface, I2The C bus is used for communicating with the constant current measuring module and the alternating current measuring module, and the timing counter is used for exciting and measuring the alternating current PWM measuring module; the UART serial interface is set to two working modes of a fast mode and a slow mode, the fast UART is used for ground test and calibration, the slow UART is used for data transmission from the data in the sounding space to the transmitter, and all measurement and control operations are realized by the main controller and are connected with a ground computer through the transmitter;
the constant current measurement module is provided with a current source excitation and a programmable instrument amplifier, the current source excitation is connected with the air pressure sensor and the atmospheric temperature sensor and is connected with the high-precision reference resistor to form a reference voltage for analog-to-digital conversion, so that measurement errors caused by constant current fluctuation and drift possibly generated in measurement are eliminated, the programmable instrument amplifier is provided with proper gain, and the analog-to-digital conversion component is ensured to work in an optimal voltage range;
the constant current measurement module is used for an air pressure sensor with kiloohm resistance value and a temperature sensor with ohm resistance value which are excited by current, and can greatly reduce the heating influence caused by the sensors by small current and intermittent work;
the atmospheric temperature sensor is formed by repeatedly winding a 20-micrometer temperature-measuring tungsten wire;
the AC measurement module is provided with an AC excitation and a programmable instrument amplifier, is connected with a mirror high-precision platinum resistance temperature sensor of a voltage-excited condensation type frost point instrument and a platinum resistance temperature sensor on a radiating block in a semiconductor refrigerator, adopts a reference voltage with periodically changed polarity as an excitation voltage of a measurement bridge, forms an 'H bridge' switching circuit through an external field effect transistor, eliminates or reduces the influence of the polarization effect and the thermocouple effect of a connecting circuit on the measurement in the data accumulation process through forward and reverse measurement, uses the AC reference voltage as the excitation voltage of the measurement bridge and the reference voltage of an ADC (analog-to-digital converter), eliminates the influence of fluctuation and drift possibly occurring in the measurement process on the analog-to-digital conversion, sets a proper gain by the programmable instrument amplifier, and ensures that an analog-to-digital conversion component works in an optimal voltage range;
the alternating current PWM measuring module processes a measuring time pulse sent by the main controller and a direction signal of polarity alternate change by a pulse processing circuit, and then performs polarity alternate charging and discharging on a connected humidity-sensitive capacitor through an H-bridge switching circuit formed by an external circuit, so that the influence of the polarization effect of a direct current electric field on the measuring precision of the humidity-sensitive capacitor is improved, the measuring accuracy is improved while the service life of the humidity-sensitive capacitor is prolonged, the pulse width is formed by the charging time, and the high-precision pulse width measurement is performed by a timing counting unit of the main controller;
the measuring method comprises the following steps:
step 1, processing an air pressure sensor, an atmospheric temperature sensor, a platinum resistor temperature sensor and a humidity-sensitive capacitor by a binary or multi-valued calibrating device to obtain a characteristic curve of the sensor;
step 2, connecting the air pressure sensor, the atmospheric temperature sensor, the platinum resistor temperature sensor and the humidity-sensitive capacitor to the constant current measuring module, the alternating current measuring module and the alternating current PWM measuring module through circuits, and connecting the modules to a main controller;
step 3, sending the measuring device to a position to be measured by using a sonde;
and 4, the measuring device obtains the measurement parameters, calculates the measurement results and sends the measurement results to the ground or sends the measurement parameters to a ground computer, and the ground computer calculates the measurement results through the floating points.
2. The device for measuring the temperature, the air pressure and the humidity of the weather sonde as claimed in claim 1, wherein the resistance value of the air pressure sensor externally connected with the constant current measuring module is 1 to 5 kilo-ohms, the resistance value of the atmospheric temperature sensor is 30 to 60 ohms, and the resistance value of the high-precision reference resistor is 1.25 kilo-ohms.
3. The device of claim 1, wherein the resistance of the high precision platinum resistance temperature sensor of the condensation type frost point detector connected to the AC measurement module at 0 ℃ is 1 kilo ohm.
4. The device for measuring the temperature, the air pressure and the humidity of the weather sonde as claimed in claim 1 or 3, wherein the high-precision platinum resistance temperature sensor on the mirror surface of the condensation type frost point detector and the platinum resistance temperature sensor on the heat dissipation block of the semiconductor refrigerator are externally connected with field effect transistors to form an H-bridge switching circuit.
5. The device for measuring the temperature, the air pressure and the humidity of the weather sonde as claimed in claim 1 or 2, wherein a schottky diode is connected in parallel with the air pressure sensor and the atmospheric temperature sensor in the forward direction.
6. The weather sonde-adapted temperature, air pressure and humidity measuring device of claim 5, wherein the atmospheric temperature sensor is connected by 4 wires; a mirror surface high-precision platinum resistor temperature sensor of the condensation type dew point instrument adopts a 3-wire connection mode.
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| CN112015219B (en) * | 2020-08-26 | 2022-04-01 | 广东电网有限责任公司广州供电局 | Humidity sensing circuit |
| CN112818528B (en) * | 2021-01-21 | 2021-09-24 | 河海大学 | Method for reconstructing dew point-frost point temperature field driven by ultrahigh frequency wireless microwave data |
| CN113465763B (en) * | 2021-07-15 | 2023-09-05 | 中国电子科技集团公司第四十九研究所 | Temperature and humidity sensor and temperature and humidity measurement method |
| CN113552655B (en) * | 2021-09-18 | 2021-12-10 | 成都信息工程大学 | Alternate switching continuous working dew-frost point instrument and dew-frost point continuous measuring method |
| CN115980884A (en) * | 2022-11-14 | 2023-04-18 | 福建师范大学 | Temperature anomaly detection method in high-altitude meteorological detection by secondary Bezier curve fitting |
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Effective date of registration: 20231127 Address after: No.2666, airport 4th Road, Southwest Airport Economic Development Zone, Shuangliu District, Chengdu, Sichuan 610200 Patentee after: Chengdu genbo Radar Technology Co.,Ltd. Address before: 610225, No. 24, Section 1, Xuefu Road, Southwest Economic Development Zone, Chengdu, Sichuan Patentee before: CHENGDU University OF INFORMATION TECHNOLOGY |