KR940002513B1 - Humidity measuring apparatus - Google Patents

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Description

Humidity measuring device

1 is an overall configuration diagram of a humidity measuring apparatus of the present invention.

2 is a circuit diagram of the humidity measuring apparatus of the present invention.

3 is a flowchart illustrating the operation of the humidity measuring apparatus of the present invention.

4 is an explanatory diagram of charging conversion.

5 is a circuit connection diagram during discharge.

6 is a circuit connection diagram when the humidity sensor is selected.

7 is an explanatory diagram of a sensor switching means function.

8 is an explanatory diagram of humidity determining means.

9 is a view showing another example of the oscillation count counting means.

10 is a cross-sectional view of the humidity sensor.

11 is a humidity sensor characteristic diagram.

* Explanation of symbols for main parts of the drawings

101: humidity sensor 102: reference resistance

103: reference capacitor 104: charge switching means

105: voltage discrimination means 106: charge and discharge switching means

107: discharge resistance 108: sensor direction switching means

109: oscillation count counting means 110: humidity sensor resistance value calculation means

111: humidity determination means

The present invention relates to a humidity measuring apparatus for measuring relative humidity by using a humidity sensor of a resistance value change type. Background Art A method disclosed in Japanese Patent Application Laid-Open No. 58-15134 (Electronic Thermometer) is known as an electronic thermometer that performs temperature measurement using a resistance change type sensor. At first glance, it is thought that a humidity device is possible by using the device configuration of the electronic thermometer described above.However, a humidity sensor causes electrolysis and changes in humidity characteristics when a current flows in one direction for a long time, so that accurate humidity measurement is performed for a long time. Could not be realized over. In addition, the humidity sensor has a large dispersion of characteristics, takes time to adjust the measuring device, and is expensive.

Accordingly, an object of the present invention is to provide a humidity measuring apparatus which can realize accurate humidity measurement over a long period of time at low cost. In the humidity measuring apparatus of the present invention, as shown in the overall configuration diagram of FIG. 1, (a) humidity sensors 101 whose impedance changes with changes in humidity, (b) resistances are known reference resistances 102, and (c) capacitances. Charge switching means 104 and (e) the reference reference capacitors 103 and (d) which charge from a DC power supply in series with either the reference resistor or the humidity sensor in series with the known reference capacitors 103 and (d). Voltage discrimination means 105 for determining the height HL of the voltage between the capacitor terminals; (f) charge / discharge switching means 106 for switching between the reference capacitor charge and the capacitor discharge according to the output of the voltage discrimination means; g) the discharge resistance 107 which becomes the reference capacitor load resistance at the time of discharging the reference capacitor, and (h) the direction of the current flowing through the humidity sensor at the time of charging the reference capacitor by switching the connection direction of the humidity sensor at regular intervals. When discharging Is the sensor direction switching means 108, (i) the oscillation count counting means 109 for counting the number of repetitions of the reference capacitor charge / discharge within a predetermined time, and (j) the reference capacitor is connected and charged By the humidity sensor resistance value calculating means (110) and (K) the humidity sensor resistance value determining means for calculating the humidity sensor resistance value in the charging and discharging repetition number of times when the charging and discharging repetition number of times and the humidity sensor are connected to the reference capacitor. Humidity determination means 11 for determining the humidity from the obtained humidity sensor resistance value is characterized in that it is provided.

(2) The humidity sensor is characterized in that a porous silica film (main damp film) in which carbon particles are dispersed is formed on an insulating substrate on which a multilayer thin film electrode is formed.

(3) is characterized in that to use a brush containing 4wt% or less carbon particles in the main moisture-sensitive film raw material.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. 2 is a circuit diagram of the humidity measuring apparatus of the present invention. In FIG. 2, the humidity sensor 101 has a characteristic in which impedance is changed due to a change in humidity. At both ends of the humidity sensor, analog switches 208a and 208b are provided as sensor direction switching means. An analog switch 206 is provided at the terminal of the reference capacitor 103 as the charge / discharge switching means. In the humidity measurement method, first, the reference resistor 102 is selected by the analog switch 204 provided as the charge switching means, and the circuit connection state is as shown in FIG. The voltage Vc of the terminal of the reference capacitor 103 increases with time. At this time, the analog switch 206, which is the charge / discharge switching means, selects the charge and the connection state is as shown in FIG. The voltage discrimination means connected to the reference capacitor 103 is a logic inversion gate 205 having hysteresis, and when Vc reaches the threshold value VH above the logic inversion gate 205, Va becomes L level. Analog switch 206 selects the discharge. The circuit connection state at the time of discharge is shown in FIG. 5, and the reference capacitor 103 is connected to the inversion resistor 107, and Vc decreases with time.

As shown in FIG. 7, when Vc falls to the lower threshold VL of the logic inversion gate 205, Va becomes H level, and the analog switch 206 selects charging and repeats the charging and discharging. At this time, the oscillation count counting means 109 counts how many times the charge discharge of the reference capacitor 103 has been repeated between the predetermined time T set in advance. In the present embodiment, the count is counted by the microcomputer 212 composed of the CPU 209, the ROM 210, the RAM 211, and the like. As described above, the number of counts when the reference resistance is selected is N. Next, the humidity sensor 101 is selected by the analog switch 204, and the circuit connection state is as shown in FIG. As in the case of the reference resistor, charging and discharging of the reference capacitor 103 are repeated. Count the number of repetitions with a microcomputer. At this time, the count number is Ns. Here, the analog switch 208 provided as a sensor direction switching means is for switching the connection direction of the humidity sensor during charging. Specifically, as shown in FIG. 2, the analog switches 208a and 208b are controlled by a divider circuit by the flip-flop 213. FIG. For convenience, if the two terminals of the humidity sensor 101 are a and b, the direction of current flowing through the humidity sensor 101 is switched for each charge discharge cycle as shown in FIG. This switching is a function necessary to avoid the electrolysis of the humidity sensor 101, and is an extremely effective function for solving the conventional problems.

The resistance value Rs of the humidity sensor 101 is calculated by the following equation from N, Ns obtained as described above, and the resistance value Rn of the reference resistance 102.

Rs = (N / Ns) Rn (1)

Expression (1) is briefly described below. The charge time when the reference resistor 102 is used is Tnc, the charge time when the humidity sensor 101 is used is Tsc, the discharge time is Td, and the resistance value of the reference resistor 102 is determined by the Rn discharge resistance 107. When the resistance is Rd and the capacitance of the reference capacitor 103 is C, the following three expressions are established.

Tnc = CRn ln [(V-VL) / (V-VH)]

T5c = CRs' ln [(V-VL) / (V-VH)]

Td = CRd 'ln (VH / VL)

Here, in the definition of N, Ns, the following equation is established.

T = N (Tnc + Td) = Ns (Tsc + Td)

Here, if the resistance value Rd of the discharge resistance is set sufficiently smaller than Rn · Rs,

Tnc << Td, Ts << Td

Therefore, the following equation is established.

NTnc = NsTsc

NRn = NsRs

Therefore, the above formula (1) is delivered. It is the humidity sensor resistance value calculation means 110 which performs calculation of this Formula (1), and is implemented by the microcomputer 212. As shown in FIG. The reason why N is obtained by using the reference resistor 102 is to allow accurate humidity measurement even if the temperature changes because the capacitor is generally easy to change its capacity due to temperature change. The capacity of the reference capacitor 103 does not need to be measured strictly, but it is necessary to refer to it when determining the measurement time T described above. Next, the function of determining the humidity from the resistance value of the humidity sensor 101 is a humidity determination means 111. As shown in FIG. 8, a table 801 of humidity and resistance values is prepared, and the CPU 210 is stored in the ROM 210. Although a method of reading by the above method has been known in the past, in the present invention, since the humidity sensor having the characteristics as shown in FIG. 11 is used, the humidity can be determined by performing a simple calculation by a microcomputer. The formula for calculating the humidity Rh (%) from the resistance value Rs of the humidity sensor 101 is as shown below.

Rh = Plog Rs + Q (2)

However, P and Q are integers determined by the characteristics of the humidity sensor. 3 is a flowchart showing the above measurement procedure. In the figure, P1-P6 shows each step of the flowchart. The measurement is carried out according to an external command every fixed time. First, P1 determines whether measurement P2 by reference resistance or measurement P4 by humidity sensor is performed. Measurement P2 by reference resistance is performed only at the start of the apparatus when the temperature change in the measurement environment is small. In this case, the treatment time is short and it is effective when the humidity change is severe. It is also possible to repeat P2 several times in order to improve measurement accuracy and select P3. In P2 and P4, as described above, the repetition number N and Ns in a predetermined time T are calculated by a microcomputer. As shown in FIG. 9, the oscillation count counting means can also use a count circuit 901 which can control the reset 902 in the microcomputer, which is convenient when the microcomputer is used as a multitask. In P5, the resistance value of the humidity sensor is determined. Specifically, the formula (1) is calculated. After the resistance of the humidity sensor is calculated, the humidity is determined by P6. In the present invention, the formula (2) is calculated. The calculation of the pulse count equations (1) and (2), reading of RAM data, and the like are well-known techniques, and thus detailed descriptions thereof are omitted. Next, the humidity sensor manufacturing method of the present invention will be briefly described. A comb-shaped electrode made of Cr was formed on the alumina substrate by sputtering, and the portions to which the lead wires were connected were sputtered in this order again in order of Au, Ni, Cr, and Au. That is, the portion where the porous silica film in which the carbon particles are dispersed is formed is a comb-shaped electrode formed only of Cr, and the portion to which the lead wire is connected is a four-layer electrode formed in the order of Cr, Au, Ni, Cr, and Au near the substrate.

Next, 1300 g of ethanol and 240 g of 0.02N hydrochloric acid were added to 270 g of tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ), followed by stirring for 1 hour. Then, 76 g of glycerin and 81 g of fine powder silica were added and stirred for 30 minutes. After adding and stirring, ultrasonic dispersion was performed for 1 hour. A 25-lot sole was prepared and the viscosity was measured in exactly the same way. The result is shown in Table 1 (2.5 WT%), and the dispersion of the viscosity was extremely small. The result of changing the amount of carbon particles (activated carbon and carbon black) for comparison is shown in the same table. The reproducibility was good in the amount of carbon particles in the range of 1 to 4WT%.

Next, a porous silica film in which carbon particles were dispersed was carbon coated on the alumina substrate on which the electrodes were formed, and then dried at 100 ° C. for 10 minutes and sintered at 430 ° C. for 30 minutes to disperse the carbon particles. Moist film). Next, 35 ml of ethanol and 4 ml of 0.02N hydrochloric acid were added to 50 ml of tetraethoxysilane, followed by stirring for 30 minutes, 10 g of fine powder silica was added thereto, and the solution was stirred for 30 minutes on a main moisture-sensitive film, followed by drying at 120 ° C. for 30 minutes. Then, it sintered at 400 degreeC for 20 minutes, and the silica film was formed.

TABLE 1

10 is a cross-sectional view of the humidity sensor thus produced. In FIG. 1, 11 is a substrate, 12 is an electrode, 13 is a porous silica film in which carbon particles are dispersed, and 14 is a silica film. As shown in FIG. 10, the humidity sensor obtained as described above has a linear relationship between the relative humidity and the logarithm of the resistance value, and the humidity can be measured by performing a simple calculation as described above. In addition, since both silica and carbon, which constitute the humidity sensor, are very chemically stable, the humidity sensor is difficult to change the humidity characteristics against temperature changes, and the device can be sufficiently used even if a special temperature compensation circuit is not installed in the device. In addition, since the electrode is formed by sputtering, it is possible to make the gap between the electrodes extremely small, and it is practical because the resistance value of the humidity sensor is kept low.

In the above-described embodiment, the analog switch may use a small relay and other switch elements in some cases, and the division circuit used for switching the humidity sensor may use means other than flip-flop, and the voltage discrimination means It is also possible to think of a method such as using a radar element.

In addition, in the present embodiment, a humidity sensor having a structure in which a porous silica film in which carbon particles are dispersed is formed on an insulating substrate on which a multilayer thin film electrode is formed, has been described. It can be applied.

As described above, according to the present invention, the following effects can be expected.

(A) Since the means for changing the direction of the current flowing through the humidity sensor is provided, the characteristics change due to the electrolysis of the humidity sensor are small, accurate humidity can be measured over a long time, and a reliable humidity measuring device can be realized.

(B) As the humidity sensor uses a porous silica membrane in which carbon particles are dispersed, accurate humidity measurement can be performed in a high temperature and high humidity environment.

(C) Since the humidity sensor's humidity characteristics are stable against temperature changes, complicated temperature compensation circuits are unnecessary, and the device configuration is simple and low price.

(D) It is very easy to calibrate the device because the humidity sensor has the humidity characteristic that the number of impedances changes linearly with respect to the change in relative humidity.

(E) Since the silica and carbon constituting the humidity sensor are chemically stable, a long time humidity measurement can be performed in a high temperature and high humidity environment, which has been a problem in the past.

(E) By setting the amount of carbon particles in the sole, which is the raw material of the humidity sensor, to 4wt% or less, a humidity sensor with stable brush characteristics and stable humidity characteristics can be obtained, and the precision dispersion of the humidity measuring device can be reduced. have.

Claims (3)

A humidity measuring device for measuring humidity, comprising: (a) a humidity sensor whose impedance changes as the humidity changes, (b) a resistance value is a known reference resistance, (c) a capacity is a known reference capacitor, and (d) Charge switching means for charging from a DC current by connecting either the reference resistor or the humidity sensor in series to the reference capacitor; and (e) a voltage for determining the height (HL) of the voltage between the terminals of the reference capacitor. (F) charging and discharging switching means for switching the reference capacitor discharge in accordance with the output of the voltage discriminating means; (g) a discharge resistance that becomes the load resistance of the reference capacitor during the discharge of the reference capacitor; (H) sensor direction switching means for inverting the direction of current flowing through the humidity sensor when the reference capacitor is charged by switching the connection direction of the humidity sensor at regular intervals; Oscillation count counting means for counting the number of times of charge / discharge repetition of the reference capacitor within a predetermined time period; (d) the charge / discharge repeat count when the reference capacitor is connected and charged to the reference capacitor and the humidity sensor Humidity sensor resistance calculation means for calculating the resistance value of the humidity sensor in a repetitive number of times of charging the reference capacitor, and (k) humidity determination means for determining humidity from the humidity sensor resistance value obtained by the humidity sensor resistance value determination means. Humidity measuring device characterized in that. The humidity measuring apparatus according to claim 1, wherein the humidity sensor has a structure in which a porous silica film (hereinafter, referred to as a main humidity film) in which carbon particles are dispersed is formed on an insulating substrate on which a multilayer thin film electrode is formed. The humidity measuring apparatus according to claim 2, wherein a brush containing 4 wt% or less of carbon particles is used as the main moisture-sensitive film raw material.

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