CN1243949A - Humidity meter - Google Patents

Abstract

A humidity meter is composed of limit current type humidity zirconium oxide sensor, working voltage generator, heating voltage generator, preamplifier, humidity calculator, display and output unit. As the working voltage and heaing voltage generators work invidually, so the meter has stable performance. Said humidity sensor can work at 350-400 deg.C, so the meter can measure the humidity of gas in high-temp (lower than or equal 250 deg.C) environment.

Description

Humidity measuring instrument

The invention relates to an analyzer, in particular to a humidity tester capable of measuring the moisture content in gas in a high-temperature (less than or equal to 250 ℃) environment.

Currently, there are many kinds of moisture measuring devices used in industry and life, from hair moisture meters to moisture measuring devices using moisture sensitive elements made of polymer materials as probes, and moisture measuring devices made of ceramic and semiconductor material probes, all of which utilize physical adsorption of moisture sensitive elements to water molecules to change physical characteristics of probes, such as resistance, capacitance, and even length. The change signal of the physical characteristic is collected and processed by a circuit so as to achieve the aim of measuring the humidity in the environment. When the environmental temperature exceeds 100 ℃, the adsorption quantity of the humidity sensing probe to water molecules is very small (close to a physical adsorption limit value), so that a humidity testing instrument manufactured by utilizing the humidity sensing characteristic of the material cannot be suitable for working in a high-temperature (more than or equal to 100 ℃) environment or cannot be suitable for working in a high-temperature (more than or equal to 100 ℃) environment for a long time, and the humidity sensing probe in the humidity testing instrument is placed in a testing environment and is subjected to dynamic humidity measurement, so that the stability of the instrument can be influenced by environmental changes.

The invention aims to provide a high-temperature humidity tester with a probe capable of measuring in a high-temperature environment, simple circuit, strong anti-interference capability, good stability and long service life.

The object of the invention can be achieved by the following measures:

the power supply required by the invention is provided from the outside, the humidity sensor is provided with the heating voltage generating circuit, the working voltage generating circuit provides the required heating voltage and working voltage, and the generated current signal is transmitted to the preamplification circuit, amplified, transmitted to the humidity calculation unit, converted and processed, and then transmitted to the display unit and the output unit by the humidity calculation unit.

The invention comprises a zirconia boundary current type humidity sensor, a heating voltage generating circuit, a working voltage generating circuit, a humidity arithmetic unit, a display unit and an output unit. The connection relationship is as follows: the input end b of the humidity sensor is connected with the output end a of the heating voltage generating circuit, the input ends e and f of the humidity sensor are respectively connected with the output ends h and g of the working voltage generating circuit, the output ends c and d of the humidity sensor are respectively connected with the input ends i and j of the preamplification circuit, the output ends k and l of the preamplification circuit are respectively connected with the input ends m and n of the humidity arithmetic unit, the output ends o and p of the humidity arithmetic unit circuit are respectively connected with the input end q of the display unit, the input end r of the output unit is connected with the input end b of the humidity sensor, the output end a of the heating voltage generating circuit is connected with the input end b and f of the humidity sensor, the output ends e and f of the humidity sensor are respectively connected with the output ends h and g of the working voltage generating circuit, the output ends c and d of the humidity sensor are respectively connected with the, l are connected with the input end m and n of the humidity arithmetic unit respectively, and the output ends o and p of the humidity arithmetic unit circuit are connected with the input end q of the display unit and the input end r of the output unit respectively.

The principle of the zirconia boundary current type humidity sensor is as follows: when the zirconia thin sheet is in an environment with a working temperature (the working environment temperature of the limit current type humidity sensor is 350-400 ℃), the insulating material zirconia becomes a selective through conductor of oxygen ions, voltage is applied to two ends of the zirconia thin sheet, so that the oxygen ions or oxygen atoms generate oxidation-reduction reaction on electrodes at two ends of the zirconia thin sheet, and the following reactions can be generated by applying different voltages:

applying a voltage V_O1Time (V)_O1Provided for sensor definition), the reaction is:

cathode:

anode:

the sensor applies voltage V to two identical zirconia chips respectively_O1、V_O2Two opposite currents I can be obtained₁、I₂；I₁、I₂Are each O₂Current generated by electrolysis and O₂+H₂The current generated by O decomposition, and the two currents are processed to obtain H₂And O, generating a current signal delta I by electrolysis, and processing the current signal delta I to obtain the content of the moisture in the gas.

The heating voltage circuit supplies heating voltage to the humidity sensor, and the heating voltage circuit is composed of a DC/DC conversion chip IC₈Capacitance E₆、E₇、E₈、E₁₆、E₁₇、E₁₈、C₁₆、C₁₇、C₁₈、C₂₁、C₂₂、C₂₄、C₂₅Resistance R₁₆、R₁₇、R₁₈Inductor L₆And a linear potentiometer W₄Fast recovery diode D₈The connection relationship of the components is as follows: linear potentiometer W₄And R₁₆、R₁₇The connected points are connected to the IC₈Feedback F of_B Terminal 2, C₁₇And R₁₆Parallel, IC₈ Driving EXT terminal 7 connected to FET T₁Of the grid, field effect transistor T₁Source and IC of₈ CS terminal 6 of the power supply is connected to a power supplyInput terminal, field effect transistor T₁Drain electrode of and fast recovery tube D₈And C is₁₈One end of an inductor L is connected with D₈Positive electrode of (2) is grounded, C₁₈Is passed through a resistor R₁₈And (4) grounding. Capacitor E₁₆、E₁₇、E₁₈The negative electrode of the capacitor is grounded; capacitor E₆、E₇、E₈、C₂₁、C₂₂、C₂₄、C₂₅The negative electrode of the capacitor is grounded. By adjusting W₄And a stable voltage value is provided, and the required heating voltage value is obtained by adjusting the linear potentiometer.

The working voltage generating circuit provides the voltage V required by the humidity sensor during working_O1、V_O2In the present invention, the operating voltage generating circuit is a combined operational amplifier IC₁、IC₂Resistance R₁₀、R₁₁、R₁₂Potentiometer W₁、W₂Capacitor C₇、C₈、C₉And an integrated zener diode D₁The connection relationship of the components is as follows: w₁And one end of (D)₁The + terminal and C₉And one end of W₂Is one end of and R₁₀Are connected at one end to R₁₀Another end of (3) is connected to a power input terminal, W₁Is at the other end passes through R₁₁，W₂Is at the other end passes through R₁₂Ground, C₉The other end of (A) is also grounded, D₁Is grounded at the end, W₁And operational amplifier IC₁Is connected through the IC₁End 1 of (a) is connected with output end h, C₇Is connected to IC₁Between end 4 of (C) and ground, C₈Is connected to IC₁Between end 8 of (D) and ground, W₂And follower IC₂Is connected through the IC₂And end 7 is connected to output end g. By integrating a zener diode D₁Providing a stable voltage value by the linear potentiometer W₁、W₂Regulating supply of two required voltages V_O1、V₀₂In W₁And an output terminal C₃Interconnecting an operational amplifier IC₁As followers, in W₂And an output terminal C₄Interconnecting an operational amplifier IC₂As a follower, the stability of the output voltage can be ensured.

The sensor heating voltage generating circuit, the working voltage generating circuit and the preamplifier circuit are independent circuits, so that the anti-interference capability of the instrument is improved, and the zirconium oxide boundary current type humidity sensor can be used for measuring the humidity in the environmental gas in high-temperature (less than or equal to 250 ℃) occasions because the working temperature of the zirconium oxide boundary current type humidity sensor is 350-400 ℃.

The invention is further described below with reference to the following figures and examples:

FIG. 1: schematic block diagram of moisture meter

FIG. 2: circuit connection diagram of heating voltage generating circuit

FIG. 3: circuit connection diagram of working voltage generating circuit

FIG. 4: current-voltage characteristic diagram of humidity sensor

In the preferred embodiment of the present invention, the components of the humidity tester are shown in fig. 1, taking the humidity sensor model 98043149 as an example, the heating voltage is: v_HThe operating voltage of 2.2V is: v₁＝-1.2V，V₂-2.0V; e is selected for each element in the heating voltage generation circuit₆＝E₇＝E₈＝E₁₆＝E₁₇＝E₁₈＝100μ；C₂₁，C₂₄＝1μ；C₂₂，C₂₅＝C₁₆＝0.1μ；C₁₇＝220p；C₁₈＝1000p；R₁₆39K omega, linear potentiometer W₄＝20KΩ，R₁₈22 Ω, field effect transistor T₁The model is IRG 9540; rectifier tube D₈Model IN5817, operational amplifier IC₈Model number MAX 1627. The connection relationship is as follows: linear potentiometer W₄And R₁₆、R₁₇The connected points are connected to the IC₈Feedback F of_B Terminal 2, C₁₇And R₁₆Parallel, IC₈Driving EXT terminal 7 connected to FET T₁Of the grid, field effect transistor T₁Source and IC of₈ CS terminal 6 is connected to the power input terminal, field effect transistor T₁Drain electrode of and fast recovery tube D₈And C is₁₈One end of an inductor L is connected with D₈Positive electrode of (2) is grounded, C₁₈Is passed through a resistor R₁₈And (4) grounding. Capacitor E₁₆、E₁₇、E₁₈The negative electrode of the capacitor is grounded; capacitor E₆、E₇、E₈、C₂₁、C₂₂、C₂₄、C₂₅The negative electrode of the capacitor is grounded. The working principle is as follows: DC power supply+5V via E₆、E₇、E₈、C₂₁、C₂₂、C₂₄、C₂₅Filtered and then passed through IC₈Supply power due to IC₈-MAX1627EQR internal reference voltage of 1.3V, IC₈MAX1627 is pulse frequency control (PFM), and the feedback loop regulates output voltage $V_O=V_{\mathrm{REF}}\×(1+\frac{W_4+R_{17}}{R_{16}}),$ In this example: v₀Is the heating voltage V of the humidity sensor_HAdjusting W₄Thus obtaining the product. Since its output current depends mainly on T₁So that IC₈It also has hair perming effect.

The various components in the working voltage generating circuit are: r₁₀＝2KΩ，W₁＝5KΩ，R₁₁＝R₁₂＝200Ω，C₁₀＝C₉0.1 mu, operational amplifier IC₁，IC₂Are all LM358, integrate a voltage stabilizing diode D₁LM385-2.5V, and the connection relationship is as follows: w₁And one end of (D)₁The + terminal and C₉And one end of W₂Is one end of and R₁₀Are connected at one end to R₁₀Another end of (3) is connected to a power input terminal, W₁Is at the other end passes through R₁₁Ground, W₂Is at the other end passes through R₁₂Ground, C₉The other end of (A) is also grounded, D₁Is grounded at the end, W₁And operational amplifier IC₁Is connected through the IC₁End 1 of (a) is connected with output end h, C₇Is connected to IC₁Between end 4 of (C) and ground, C₈Is connected to IC₁Between end 8 of (D) and ground, W₂And follower IC₂Is connected through the IC₂And end 7 is connected to output end g. Since the humidity 2 sensor needs to provide two operating voltages, V_O1＝-1.2V，V_O22.0V, 2 voltage-stabilizing circuits are needed, the power supply is connected via R₁₀After current limiting and voltage dividing, V₀is-2.5V (D)₂LM336-2.5V), adjusting W₁The voltage between pins 6 and 7 of LM358 was set to-1.2V, and W was adjusted₂The voltage between pins 1 and 2 of LM358 is-2.0V, and the maximum current of LM336-2.5V operational amplifier is 10mA, R₁₀The resistance is selected as R ═

When I is 5mA and R is 500 omega, the voltage stabilizing effect is better.

Claims (4)

1. A humidity measuring instrument comprises a humidity sensor, a pre-amplification unit, a humidity calculation unit, a display unit and an output unit, wherein the output ends c and d of the humidity sensor are respectively connected with the input ends i and j of a pre-amplification circuit, the output ends k and l of the pre-amplification unit are respectively connected with the input ends m and n of the humidity calculation unit, the output ends o and p of the humidity calculation unit are respectively connected with the input end q of the display unit and the input end r of the output unit.

2. The hygrometer of claim 1, wherein the humidity sensor used in the hygrometer is a zirconium oxide boundary current humidity sensor.

3. The hygrometer according to claim 1, wherein the heating voltage generating circuit is a DC/DC conversion chip IC₈Capacitance E₆、E₇、E₈、E₁₆、E₁₇、E₁₈、C₁₆、C₁₇、C₁₈、C₂₁、C₂₂、C₂₄、C₂₅Resistance R₁₆、R₁₇、R₁₈Inductor L₆And a linear potentiometer W₄Fast recovery diode D₈The connection relationship of the components is as follows: linear potentiometer W₄And R₁₆、R₁₇The connected points are connected to the IC₈Feedback F of_BTerminal 2, C₁₇And R₁₆Parallel, IC₈Driving EXT terminal 7 connected to FET T₁Of the grid, field effect transistor T₁Source and IC of₈CS terminal 6 is connected to the power input terminal, field effect transistor T₁Drain electrode of and fast recovery tube D₈And C is₁₈One end of an inductor L is connected with D₈Positive electrode of (2) is grounded, C₁₈Is passed through a resistor R₁₈Ground, capacitor E₁₆、E₁₇、E₁₈The negative electrode of the capacitor is grounded; capacitor E₆、E₇、E₈、C₂₁、C₂₂、C₂₄、C₂₅The negative electrode of the capacitor is grounded.

4. As claimed in claim 1The humidity measuring instrument is characterized in that the working voltage generating circuit is an operational amplifier IC₁、IC₂Resistance R₁₀、R₁₁、R₁₂Potentiometer W₁、W₂Capacitor C₇、C₈、C₉And an integrated zener diode D₁The connection relationship of the components is as follows: w₁And one end of (D)₁The + terminal and C₉And one end of W₂Is one end of and R₁₀Are connected at one end to R₁₀Another end of (3) is connected to a power input terminal, W₁Is at the other end passes through R₁₁Ground, W₂Is at the other end passes through R₁₂Ground, C₉The other end of (A) is also grounded, D₁Is grounded at the end, W₁And operational amplifier IC₁Is connected through the IC₁End 1 of (a) is connected with output end h, C₇Is connected to IC₁Between end 4 of (C) and ground, C₈Is connected to IC₁Between end 8 of (D) and ground, W₂And follower IC₂Is connected through the IC₂And end 7 is connected to output end g.

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