CN2375963Y - Humidity sensor - Google Patents

Abstract

The utility model relates to a humidity sensor which can measure the humidity of the gas under the state of high temperature (the temperature is less than or equal to 250 DEG). The humidity sensor comprises two zirconia sheets, the center of each sheet is provided with a diffusion hole, both sides of the sheets are printed with first electrodes and second electrodes, the second electrodes of the two sheets are covered by the same covering element, and respective diffusion chambers are respectively formed between the two second electrodes and the covering element. The humidity sensor has the advantages that the humidity of the gas can be measured under the temperature range of 250 DEG.

Description

Humidity sensor

The utility model relates to a humidity transducer, in particular to a humidity transducer which is manufactured by utilizing the oxygen measuring principle of a solid electrolyte zirconia boundary current type oxygen sensor and can measure the moisture content in gas in the environment with the temperature not more than 250 ℃.

In many industrial processes or material handling processes where dry gases are used for protection, it is important to monitor the moisture content of these gases. In the field of humiditymeasurement, a plurality of humidity sensors are manufactured by applying various materials and adopting various principles. Such as an alumina humidity sensor (CN2129414Y), a ceramic humidity sensor (CN2168250Y), a polymer humidity sensor (CN2101237U), a composite humidity sensor (CN11777102A), a thermistor humidity sensor (CN1142263A) and the like, which utilize the physical adsorption phenomenon of humidity sensing materials to water molecules to realize the humidity measurement, when the environmental temperature is higher than 100 ℃, the adsorption amount of the humidity sensing materials of the various sensors to the water molecules becomes very small (close to the physical adsorption limit value), so that when the environmental temperature is higher than 100 ℃, the various humidity sensors cannot measure the humidity in the environment. The heat conduction type sensor (CN1142263A) has good long-term stability because it cannot absorb moisture, but it cannot measure the humidity in the gas at 100 ℃ or higher because the output voltage of the thermistor at 100 to 150 ℃ is independent of the humidity.

The utility model aims at providing a humidity transducer that both can be in the humidity of measuring in the gas under the environment that is less than 100 ℃, can measure humidity in the gas under the environment of 100 ℃ -250 ℃ simultaneously.

The utility model has the structural characteristics that two solid electrolyte zirconia limit current type oxygen sensors are combined together, and the following manufacturing process can be realized:

firstly, a zirconia sheet 1 is manufactured by mould forming, the zirconia sheet 1 is put into a high-temperature sintering furnace to be sintered, a diffusion hole 2 is manufactured on the sheet 1, then electrodes 3 and electrodes 4 are printed on two sides of the sheet, the electrodes 4 on the two zirconia sheets with the diffusion hole and the electrodes are covered by a same cover part 5, and the cover part 5 and the zirconia sheets where the two electrodes 4 are respectively arranged are sealed and bonded through glass enamel 6. A diffusion chamber 7 is formed between the cover 5 and the electrode 4, and communicates with the outside through diffusion holes in the zirconia sheet.

The utility model discloses utilize solid electrolyte zirconia limit current formula oxygen sensor's oxygen measurement principle to carry out humidity measurement. Fig. 1 is a working principle diagram of the oxygen sensor, which comprises a solid electrolyte zirconia sheet 1, electrodes 3 and 4 printed on two sides of the sheet 1, and a diffusion hole 2 in the center of the sheet 1. The cover member 5 covers the electrode 4, and a diffusion chamber 7 is formed between the electrode 4 and the cover member 5. As shown in fig. 1, when a voltage V is applied between the electrodes 3 and 4 and the solid electrolyte zirconia flake is heated to 350 ℃ or higher, the following reactions occur at the electrodes 3 and 4 (wherein the electrode 3 is an anode and the electrode 4 is a cathode):

cathode: ……………………(1)

anode: $O^{2-}\&RightArrow;\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="O"\; filenames="Y9923079200061.png"\; state="\{\{state\}\}">O</figure-callout>}}_2+{2e}^{-}\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\left(2\right)$

the reaction is represented by the current I generated on the loop, in dry air, as the voltage V continues to increase to V₁When the voltage V is increased, the current I is not increased any more but becomes a stable current value I₀However, as voltage V continues to increase beyond V₂When the current Iis from I₀The current-voltage characteristic of the phenomenon is shown in figure 2, which is a working principle characteristic diagram of the solid electrolyte zirconia boundary current type oxygen sensor. The current I is formed by the flow of oxygen ions, the I of different oxygen concentrations₀All of which differ in value, according to this property, by measuring I₀The value can be calculated to obtain the oxygen concentration value in the gas.

When water vapor exists in the air, the scientific research personnel increase the voltage V value to V₃When the current I has a first stable value I₁Until the voltage is increased to V₄Current value I from I₁Continue to useChange when the voltage continues to increase to V₅When the current I has a second stable value I₂Until the voltage increases to V₆When the current Iis from I₂Continuing, as shown in FIG. 3, the microscopic mechanism of this phenomenon is as follows:

cathode: ……………………(1)

…………………(3)

anode: $O^{2-}\&RightArrow;\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="O"\; filenames="Y9923079200061.png"\; state="\{\{state\}\}">O</figure-callout>}}_2+2e^{-}\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\&hellip;\left(2\right)$

the value of I is also formed by the flow of oxygen ions, only the oxygen ions are derived from the gas O₂And H₂The sum of the oxygen ions in O that are electrolyzed.

According to the gas diffusion pore restriction Ficks rule of the sensor, the first limiting current I is given on the assumption that the diffusion coefficient of oxygen is equal to that of water vapor₁Value and second limit current value I₂May be represented by the following formulae, respectively: ${\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="Y9923079200062.png"\; state="\{\{state\}\}">I</figure-callout>}}_1=-\frac{4\mathrm{FDSP}}{\mathrm{RTL}}\ln (1-\frac{P_{O_2}}{P})$ ${\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="Y9923079200061.png"\; state="\{\{state\}\}">I</figure-callout>}}_2=-\frac{4\mathrm{FDSP}}{\mathrm{RTL}}(1+\frac{P_{H_{2}O}}{2P_{O_2}})\ln (1-\frac{P_{O_2}}{P})$ ${\mathrm{<figure-callout\; id="2"\; label="P\; O"\; filenames="Y9923079200061.png"\; state="\{\{state\}\}">P</figure-callout>}}_{O_{}}=0.21(P-P_{H_{2}O})$ wherein F is a Faraday constant; d is the diffusion coefficient of the mixed gas molecules;

s is the area of the gas diffusion hole; p is the total pressure of the mixed gas;

is the partial pressure of oxygen

Is the water vapor partial pressure;

r is a gas constant; t is the working temperature (K) of the sensor;

l is the length of the gas diffusion hole; 0.21 is the oxygen content in air.

FIG. 3 shows the current of the humidity sensor as a function of voltage and ambient humidity, showing the first threshold current value I₁Value of oxygen partial pressure in the atmosphere

Proportional, the second limiting current law is proportional to the sum of the partial pressure of oxygen and the partial pressure of water in the atmosphere, and therefore, by measuring I₁Value and I₂The value is calculated, and the difference value delta I of the two-stage limit current is calculated, so that the partial pressure of the water vapor in the environment atmosphere can be conveniently detected

Values, FIG. 4 shows the water vapor partial pressureIs related to Δ I.

As the solid electrolyte zirconia limit current type oxygen sensor adopted by the humidity sensor can work at the temperature of 400 ℃ or above, the humidity sensor can work at high temperature, water molecules can react as shown in formulas (1), (2) and (3) as long as the water molecules are in contact with the electrode of the sensor, physical adsorption of the water molecules is not needed, and the contact between the water molecules and the surface of the electrode cannot be influenced by the high temperature, so that the humidity sensor can measure the humidity in a high-temperature environment.

The present invention will be more fully described with reference to the accompanying drawings in which:

FIG. 1 is a diagram of the operating principle of a solid electrolyte zirconia boundary current oxygen sensor.

FIG. 2 is a graph of current-voltage characteristics of an oxygen sensor in dry gas

FIG. 3 is a graph of current-voltage characteristics of an oxygen sensor in humid gas

FIG. 4 partial pressure of humid water vaporGraph of dependence on Δ I

FIG. 5 is a block diagram of a humidity sensor

FIG. 6 is another block diagram of a humidity sensor

Fig. 5 shows a preferred embodiment of the invention:

the two zirconia sheets 1 with the diffusion holes 2 and the printing electrodes 3 and 4 and the two diffusion chambers 7 are respectively positioned at two sides of the cover 5, the structure of the humidity sensor is symmetrical and compact, so the humidity sensor has small volume, is heated uniformly during working, has accurate measurement, and is easy to realize in process.

Another structure of the present invention is shown in fig. 6, in which two zirconia sheets 1 having diffusion holes 2 and printing electrodes 3 and 4 and two diffusion chambers 7 are located on the same side of the same lid 5.

The utility model has the advantages of as follows: the humidity sensor has the outstanding characteristic that the humidity sensor can work in the environment with the temperature below 100 ℃ and the environment with the temperature above 100 ℃ and high temperature, low humidity or high humidity, the highest working temperature is 250 ℃, and the humidity measuring range is 0-50 kPa, so that the blank that various existing humidity sensors of macromolecules, semiconductors, ceramics and electrolytes can not work in the environment with the temperature above 100 ℃ in the field of the current humidity sensor is filled.

Claims (3)

1. A humidity sensor is characterized in that the humidity sensor comprises two zirconia sheets 1, a diffusion hole 2 is formed in the center of each zirconia sheet 1, electrodes 3 and 4 are printed on two sides of each zirconia sheet 1, the two zirconia sheets 1 are respectively bonded with a cover piece 5 through glass enamel 6, and diffusion chambers 7 are respectively formed between the two zirconia sheets 1 and the cover piece 5.

2. The humidity sensor according to claim 1, wherein the two zirconia sheets 1 are symmetrically adhered to both sides of the cover member 5, and the same diffusion chamber 7 is formed at both sides, respectively.

3. The humidity sensor according to claim 1, wherein said two zirconia sheets 1 are symmetrically adhered to the same side of the cover 5, and two identical diffusion chambers 7 are formed on the same side.

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