CN2594792Y - Capacitor-type moisture sensor for meteorological detection - Google Patents

Abstract

A capacitive humidity sensor for high-altitude weather detection, a humidity sensing element or a compensation capacitor is connected between a first Darlington circuit and a second Darlington circuit through a switch, and an RC filter is connected to the output end of the circuit. The utility model replaces the resistive humidity sensor currently used on the digital radiosonde with a capacitive humidity sensor, so that the humidity detection performance of the radiosonde is further improved, and it can be used in the high-altitude harsh environment with an ambient temperature of 45-90°C. Humidity can be detected under the environment, the range can reach 0-100%RH, the measurement accuracy is ≤5%RH, and the hysteresis coefficient is ≤1 second. Therefore, the utility model has a large measurement range, high measurement accuracy and high sensitivity, and can be used in high-altitude meteorological detection. The measurement of humidity can also be used in automatic weather stations on the ground. For example, its secondary development can also be applied in various fields of the national economy, such as automatic humidity control systems in papermaking, warehouses, libraries, textiles, tobacco and other industries.

Description

Capacitive humidity sensor for high-altitude weather detection

technical field

The utility model relates to a humidity sensor in an automatic humidity control system, in particular to a capacitive humidity sensor for high-altitude weather detection.

Background technique

There are many types of humidity sensors used for high-altitude meteorological detection in the prior art. Mechanical ones such as hair, curly hair, and casings are suitable for the detection of mechanical code type radiosondes and ground meteorological humidity. Due to their poor accuracy and adaptability , has now been phased out. The commonly used electronic types are resistive and capacitive, and they are generally composed of humidity sensing elements and measuring circuits. The advantage of resistive humidity sensor is high measurement resolution, and its measurement circuit is simple and easy; while the biggest advantage of capacitive humidity sensor is that its low humidity humidity measurement performance is much better than that of resistive type, and its stability is good, which is more suitable for high-altitude meteorological detection.

However, as a high-altitude meteorological detection instrument, the radiosonde is a one-time-use instrument that requires low cost, but its environmental requirements are very high, and the temperature range is +50 to -90°C. Therefore, the use of a capacitive humidity sensor must first solve the problem. The following two difficulties:

1. When the airsonde is in use, the humidity sensing element is exposed outside the body, and the wire leading into the body is very long. In this way, the distributed capacitance generated by the wire and the distributed capacitance of the line itself will affect the measurement accuracy and stability of the humidity sensor. sex.

2. At present, the operating temperature range of humidity sensing elements on the market is -40°C to +50°C, and the measurement performance will be greatly reduced below -40°C, while the minimum operating temperature range of radiosondes must reach -90°C. If the humidity sensing element is strictly required to reach -90°C, its manufacturing process will be very complicated and the cost will be greatly increased, which is not advisable.

In foreign countries, some manufacturers have adopted some measures to try to solve these difficulties. For example, Vaisala Company of Finland adopts the method of heating the humidity sensing element, and uses a multi-harmonic oscillator and a low-pass filter circuit to complete the capacitance-voltage conversion. But their methods are complex and costly.

Other manufacturers have made improvements in the measurement circuit, such as the German Fraunhofer company's patent "circuit and method for measuring parameters that affect the capacitance-voltage performance of capacitive elements" (patent number: US5,235,267), the measure is to apply a cycle to the capacitive element Voltage signal, the area of the capacitance-voltage characteristic curve is detected by the integration of the current of the capacitive element and the partial period of the voltage signal, and then the measured parameter value is determined from this area according to the relationship between the parameter and the capacitance. Although this patented technology can improve the measurement accuracy and Removes some distractions, but still doesn't solve the two puzzles above.

Contents of the invention

The technical problem to be solved by the utility model is to overcome the above-mentioned defects in the prior art, and provide a capacitive humidity sensor with temperature compensation and elimination of distributed capacitance, simple process and low cost for high-altitude meteorological detection.

The utility model adopts the following technical solutions to solve its technical problems: a capacitive humidity sensor for high-altitude weather detection, which is characterized in that: the first Darlington circuit composed of resistors R2, R3 and crystal transistors Q1, Q2 and the first Darlington circuit composed of resistors The second Darlington circuit composed of R4, R5 and crystal transistors Q3 and Q4 is connected to a humidity sensing element Cs or a compensation capacitor C1 through a switch K, and a filter composed of a resistor R6 and a capacitor C2 is connected to the output terminal of the circuit .

The utility model replaces the resistive humidity sensor currently used on the digital radiosonde with a capacitive humidity sensor, so that the humidity detection performance of the radiosonde is further improved, and it can be used in the high-altitude harsh environment with an ambient temperature of 45-90 ° C. Humidity can be detected under the environment, the range can reach 0-100%RH, the measurement accuracy is ≤5%RH, and the hysteresis coefficient is ≤1 second. Therefore, the utility model has a large measurement range, high measurement accuracy and high sensitivity, and can be used in high-altitude meteorological detection. The measurement of humidity can also be used in automatic weather stations on the ground. For example, its secondary development can also be applied in various fields of the national economy, such as automatic humidity control systems in papermaking, warehouses, libraries, textiles, tobacco and other industries.

Description of drawings

Accompanying drawing is the electrical schematic diagram of the utility model.

Detailed ways

The utility model will be further described below in conjunction with the accompanying drawings and embodiments.

Referring to the accompanying drawings, the utility model is composed of resistors R2, R3 and crystal triodes Q1, Q2, the first Darlington circuit is added between the voltage signal source and the humidity sensing element to add this Darlington amplifier circuit to eliminate long The integral effect produced by the distributed capacitance caused by the wire improves the front and rear edges of the voltage signal.

The second Darlington circuit is composed of resistors R4, R5 and crystal transistors Q3, Q4. A humidity sensing element Cs is connected between the first Darlington circuit and the second Darlington circuit through a changeover switch K, and a differential sensor can be used. The method measures the size of its capacitance, and uses the second Darlington amplifying circuit to generate a positive pulse. In addition, a compensation capacitor C1 is connected in parallel next to the humidity sensing element Cs, and is converted by a transfer switch K. In addition to eliminating the temperature coefficient of the measurement circuit itself, it can also cooperate with the main circuit board of the radiosonde to learn from the temperature sensor in the radiosonde. For the measured atmospheric temperature, the temperature coefficient of the humidity sensing element Cs is corrected to ensure the working accuracy of the sensor at low temperature.

The filter composed of resistor R6 and capacitor C2 is connected to the output end of the circuit, which can convert the positive pulse into a DC voltage, and indirectly measure the size of the capacitive humidity sensing element, that is, the humidity value, through the level of the DC voltage.

The working principle of the present utility model is set forth in detail below:

The voltage signal source Vs adds the positive pulse signal to the first Darlington circuit through the coupling resistor R1, and after amplifying, it generates a pulse signal with very steep front and rear edges, which is transferred to the humidity sensing element Cs or compensation capacitor C1 by the transfer switch K.

When the transfer switch K is connected to the humidity sensing element Cs, the humidity measurement value is output; when the transfer switch K is connected to the compensation capacitor C1, since the temperature performance of the compensation capacitor C1 has been measured in advance, it can be used as a reference capacitance value at different atmospheric temperatures. The microprocessor in the radiosonde performs processing related to temperature compensation (atmospheric temperature is detected by the temperature sensor in the radiosonde). Since the time constant between the resistor R4 and the humidity sensing element Cs (or compensation capacitor C1) is small, when the voltage signal jumps positively, the Darlington tubes Q3 and Q4 continue to maintain the conduction state (0 voltage), when the voltage signal jumps negatively When the time changes, the Darlington tubes Q3 and Q4 are cut off (high voltage), and the cut-off time depends on the size of the humidity sensing element Cs (or compensation capacitor C1), that is, the positive pulse width on the collectors of Darlington Q3 and Q4 and Humidity sensing element Cs (or compensation capacitor C1) is proportional. The positive pulse signal is converted into a DC voltage through the resistor R6 and the capacitor C2. The wider the positive pulse, the higher the DC voltage. Therefore, by measuring the level of the output terminal Vo, the capacitance of the humidity sensing element Cs can be indirectly measured, and then calculated properly. The required humidity value can be measured. Since the voltage is not affected by distributed capacitance during DC transmission, the humidity value is not affected by distributed capacitance.

Claims (2)

1. A capacitive humidity sensor for high-altitude weather detection, characterized in that: the first Darlington circuit made up of resistors (R2, R3) and transistors (Q1, Q2) and the resistors (R4, R5) and crystal The second Darlington circuit composed of transistors (Q3, Q4) is connected to a humidity sensing element (Cs) or a compensation capacitor (C1) through a switch (K), and is composed of a resistor (R6) and a capacitor (C2). A filter is connected at the output of the circuit. 2. The capacitive humidity sensor for high-altitude weather detection according to claim 1, characterized in that: the voltage signal source (Vs) is connected to the first Darlington circuit through a coupling resistor (R1).

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