JPS5840697B2 - humidity detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity detection circuit using a capacitive humidity detection element.

Specifically, the present invention provides a humidity detection circuit that has high accuracy and is capable of accurately detecting relative humidity even when the temperature fluctuates.

Conventional relative humidity detectors have used hair, changes in the ionic conduction of deliquescent salts due to humidity, and changes in electrical resistance based on the swelling properties of synthetic resins containing conductive particles. There are some, but none that satisfy me in terms of accuracy, responsiveness, stability, and price.

The present invention solves this problem by forming a dielectric anodic oxide film on a valve metal base, and then forming a semiconducting metal oxide film such as manganese dioxide on top of the dielectric anodic oxide film. The present invention provides a humidity detection circuit using a variable capacitance type humidity detection element.

Hereinafter, the content of the present invention will be explained using the drawings of FIGS. 1 to 5.

FIG. 1 shows a block circuit of a humidity detection circuit according to an embodiment of the present invention. In the figure, 1 is a fourth pulse generation circuit as a capacitance/time conversion circuit; This circuit charges and discharges the variable humidity detecting element 2, and generates a pulse with a time width of 1 when the electrostriction at both ends of the humidity detecting element 2 reaches the slice level voltage from the start of charging (or discharging).

The first pulse generation circuit 1 is composed of a humidity detection element 2, a fourth charge/discharge circuit 3, a first voltage generation circuit 4, and a first voltage comparison circuit 5. The voltage across the humidity detection element 2 becomes one input of the first voltage comparison circuit 5, and the output of the first voltage generation circuit 4 is used as the slice level voltage. This becomes the other input of the voltage comparator circuit 5 of No. 4.

Reference numeral 6 designates a second pulse generation circuit, and a capacitor 7 having a fixed capacitance value is used in the second pulse generation circuit 6, and a second charge/discharge circuit 8, a second voltage generation circuit 9, and a second The voltage comparison circuit 10 is composed of two voltage comparison circuits 10.

The capacitor 7 is charged and discharged by the second charging/discharging circuit 8, but since the slice level voltage of the second voltage generating circuit 9 changes depending on the temperature, the output of the second voltage comparing circuit 10 changes in pulse width depending on the temperature. will change.

11 is an arithmetic circuit, and this arithmetic circuit 11 is a circuit that creates a temporal difference (or sum) between the outputs of the fourth and second pulse generating circuits 1 and 6; A final output pulse is generated by taking the difference (or sum) of the output pulses of the pulse generation circuits 1 and 6.

FIG. 2 shows an example of the characteristics of the humidity detecting element described above, in which the horizontal axis is the relative humidity, and the vertical axis is the capacitance (shown on an arbitrary scale).

In Fig. 2, the three characteristic curves a, b, and c are pressed using temperature as a parameter, and the temperature decreases in the order of a, b, and c.

From this characteristic, the relationship between the relative humidity (X) and the capacitance C1 for each temperature can be approximated by a straight line.

Since the pulse length of the first pulse generation circuit 1 described above is proportional to the capacitance, in order to accurately make the relative humidity and pulse width proportional, the first pulse generation circuit 1 including the humidity detection element 2 must be It is sufficient to subtract the time corresponding to C6(T) in the above equation (1) from the output of .

Since Co(T) is the value at 0 coefficient of the Kinshi line,
It may be negative, so in that case, add that amount.

First, by adopting the configuration shown in FIG. 1, the relative humidity and the pulse width C (time) are accurately proportional.

The first and second charging/discharging circuits 3 and 8 may include a circuit that charges and discharges a capacitor with a constant current, and a CR charging/discharging circuit that connects a resistor in series with the capacitor and applies a constant voltage.

The constant current method includes a method in which a capacitive element is charged by a constant current power supply, and an integrator method in which a capacitive element is attached to the feedback circuit of an operational amplifier. In this case, the output pulse length is determined by changing the slice level voltage to Vs. Then, the output pulse width is directly proportional to the capacitance value, current value, and slice level voltage.

In addition, in the CR charging/discharging method in which a resistor is connected in series to a capacitive element and charged/discharged at a constant voltage, the pulse length becomes as follows, which is proportional to the capacitance value and resistance value, but not proportional to the slice level voltage.

By the way, looking at the electrical characteristics of the humidity detection element, tan δ as a capacitive element is quite large, and equivalently, tao δ due to the series resistance value occupies most of it.

Therefore, if the capacitance of this element is C2 and the equal series resistance is r, then in the constant current charging method, an error corresponding to iXr is included.

In such a case, in the CR charging/discharging method, the output pulse length is becomes.

FIG. 3 shows the pulse characteristics when logVr is plotted on the horizontal axis and α=Vs/Vcc is used as a parameter.

100 is α= (1-1/e) =0.6321・
..., 101 is α=0.7, 102 is α=0.6
, 103 is α>0.7, 104 is α<0.6, and 0
．． In the range of 6≦α≦0.7, T/C2R is logR
7γ has the least error over a wide range of values.

In the humidity detection element, r is large on the low humidity side, and γ is considerably small on the high temperature side. Therefore, the humidity detection element is charged and discharged in CR, and the slice level voltage Vs is set to 0.0% of the charging and discharging voltage Vcc.
By selecting 6 to 0.7 times, the measurement error can be reduced.

Note that the voltage curve when discharging is the same as when charging, so the slice level voltage Vs during discharging is the charging/discharging voltage V
It becomes 0.3 to 0.4 times cc.

FIG. 4 shows an example of a specific circuit configuration.

C is a humidity detecting element, R is a charging resistor, and when the switch S1 is closed, the humidity detecting element C is charged and discharged.

Note that this circuit outputs pulses during charging.

R1 and R2 are resistances for generating slice level voltage, and α is 0.6 to 0 according to the formula 2αF■S/Vcc=
．． The resistance value is set to be 7R1+R2.

12 is a first voltage comparator.

These constitute the first pulse generating circuit.

In addition, the second pulse generation circuit has a resistor R3# R4゜R6
and a slice level voltage generating section consisting of a positive characteristic thermistor R6, a second OCR charging/discharging section consisting of a resistor R', a capacitor C' (fixed capacitance) switch S2, and a second voltage comparator 13.

14 is an arithmetic circuit that calculates the difference in pulse width, which includes a gate, etc.;
15 is a control circuit.

The waveforms of each part of FIG. 5A to E are shown in a time chart, and the symbols AE of FIG. 5 indicate the waveforms of the part of A to E of FIG. 4.

The figure shows the waveform at the humidity detection element C end, and the dashed line shows the slice level voltage.

B shows the voltage waveform at the end of capacitor C' which is a fixed capacitor, C shows the output waveform of the first voltage comparator 12, D shows the output waveform of the second voltage comparator 13, and E shows the final output. It shows the waveform.

In this circuit of FIG. 4, the first. Second voltage comparator 12.1
3 is not a pulse output, but the output of the first voltage comparator 1
By taking the difference between the 2nd output and the 2nd voltage comparator 13 output, the result is exactly the same as when each voltage comparator output outputs a pulse from the start of charging until it reaches its respective determined slice level voltage. is obtained.

The circuit shown in FIG. 4 is an example of a circuit in which a positive temperature coefficient thermistor R6 is used to generate the second slice level voltage.

If the CR charging method is used in this way, the circuit configuration is very simple, and as is clear from Figure 4, the slice level voltage generation section and the CR charging/discharging section are in a bridge configuration, so that the power supply voltage is It also has the advantage that the pulse output width does not change even if it fluctuates.

Even when a constant current method is used as a charging method, it is possible to obtain a pulse width proportional to relative humidity.

If a pulse width proportional to relative humidity is obtained in this way, humidity can be immediately displayed digitally by counting clock pulses of a constant period during this pulse width.

Furthermore, this pulse signal can be converted into a voltage using an integral method or the like to control external electrical equipment.

As described above, according to the humidity detection circuit of the present invention, the humidity characteristics of the capacitive humidity detection element can be compensated for with a simple circuit configuration, and relative humidity can be detected with high accuracy, which is of great practical value. High effects can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a humidity detection circuit according to an embodiment of the present invention, and FIG. 2 is an isostatic diagram showing changes in capacitance with respect to relative humidity of a humidity detection element used in the humidity detection circuit of the present invention. Fig. 3 is a characteristic diagram showing the pulse output due to the series resistance of the CR charging/discharging circuit, Fig. 4 is an electric circuit diagram showing an example of a specific circuit configuration of the humidity detection circuit of the present invention, and Figs. FIG. 4 is a time chart showing the voltage waveforms at sections I to E in FIG. 4. FIG. 1...First pulse generation circuit, 2...
Humidity detection element, 3...First charging/discharging circuit, 4.
...first voltage generation circuit, 5 ...first voltage comparison circuit, 6 ...second pulse generation circuit,
7... Curved capacitor, 8... Second charging/discharging circuit, 9... Curved second voltage comparison circuit, 10... Second
Voltage comparison circuit, R6...Positive characteristic thermistor. 11... Arithmetic circuit,

Claims (1)

[Scope of Claims] 1. A first voltage for charging and discharging a humidity detecting element whose capacitance changes with humidity and comparing the voltage across the humidity detecting element and the slice level voltage of the first voltage generating circuit. a first pulse circuit that generates a pulse with a time width of 1 such that the voltage across the humidity sensing element reaches the slice level voltage i from the start of charging or discharging of the humidity sensing element; and a first pulse circuit that charges a fixed capacitor. A second voltage comparator circuit compares the voltage across the fixed capacitor with the slice level voltage that changes depending on the temperature of the second voltage generating circuit. a second pulse generation circuit that generates a pulse with a time width of 1 for the voltage to reach the slice level voltage; and a sum of the output pulse of the first pulse generation circuit and the output pulse of the second pulse generation circuit. or an arithmetic circuit that calculates a difference. 2. The humidity detection element is composed of a resistor connected in series to the humidity detection element and a switch connected in parallel.
When charging with the R charge/discharge circuit, the slice level voltage of the voltage generation circuit of straw 1 is set to 0.6 to 0.7 of the charge/discharge voltage.
The humidity detection circuit according to claim 1, characterized in that the humidity detection circuit is doubled. 3. The humidity detection element is composed of a resistor connected in series to the humidity detection element and a switch connected in parallel.
When discharging through the R charging/discharging circuit, the slice level voltage of the first voltage generating circuit is set to 0.3 to 0.4 of the charging/discharging voltage.
The humidity detection circuit according to claim 1, characterized in that the humidity detection circuit is doubled. 4. The humidity detection circuit according to claim 1, wherein the second voltage generation circuit uses a temperature detection element whose resistance value changes depending on temperature.