JPS6046451A - Humidity detecting circuit - Google Patents

Abstract

PURPOSE:To adjust an error due to variance among ceramic humidity sensor by composing a rectifying circuit with an absolute value circuit of a high-input impedance type and a smoothing circuit. CONSTITUTION:A sensor 5 changes variation in relative humidity into variation in resistance. A resistance-voltage converting circuit 2 outputs an AC voltage corresponding to the variation in relative humidity, and the voltage is converted by a rectifying citcuit 3 into a humidity detection signal, i.e. DC voltage. The rectifying circuit 3 consists of the absolute value circuit 31 and smoothing circuit 32, and the absolute value circuit is a high input impedance type, so the resistance in the resistance-voltage converting circuit 2 is increased in value. Therefore, even if the sensor 5 has variance, an adjustment corresponding to it is made.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity detection circuit, and more particularly to a humidity/detection circuit that can be applied to a detection circuit using a ceramic humidity sensor.

Conventional ceramic humidity sensors are roughly divided into those that require occasional cleaning during use and those that can be used without cleaning.
-L tZ nV 2Os-based ceramic humidity sensors are known to exhibit high reliability without requiring cleaning. However, even with the ceramic humidity sensor mentioned above, due to long-term use and other usage conditions,
Ceramic humidity sensors often need to be replaced because their properties can gradually deteriorate or become damaged, causing the humidity sensing circuit to malfunction. -It is clear that when replacing a ceramic humidity sensor, it must be replaced with one that has the same characteristics, but at present there are variations in this type of sensor.
Since it is difficult to avoid errors due to sensor variations, there has been a problem with sensor compatibility in the past, which has been a major obstacle in putting this into practical use.

In addition, humidity detection circuits using this type of ceramic humidity sensor have recently been constructed using, for example, high-density Toshiba circuit technology, but the rectifier circuits used in conventional humidity detection circuits are generally This is a rectifier circuit that uses semiconductor diodes as shown in Figure 1, or a rectifier circuit that combines an operational amplifier and a diode as shown in Figure 2. In this type of rectifier circuit, the forward voltage drop of diode 19 is and it changes depending on the temperature (for example, the temperature coefficient is about -2mV/℃ to -3mV/C)
Therefore, this often poses a problem in practical use, for example, when creating a measuring circuit with a high density or when creating a measuring circuit that operates at a low power supply voltage. In FIGS. 1 and 2, D is a diode, OP is an operational amplifier, and C is a capacitor.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to easily adjust errors caused by variations in ceramic humidity sensors, eliminate sensor compatibility problems +m, and achieve good performance even at low power supply voltages. It is an object of the present invention to provide a humidity detection circuit that can operate and eliminate practical problems associated with temperature changes.

The humidity detection circuit according to the present invention includes a ceramic humidity sensor whose resistance value changes according to changes in humidity, a resistance-voltage conversion circuit which converts the change in resistance value of the ceramic humidity sensor into a change in alternating current voltage, and a resistance-voltage conversion circuit that converts the change in resistance value of the ceramic humidity sensor into a change in alternating current voltage. A rectifier circuit that converts changes in the AC voltage output from the conversion circuit into changes in DC voltage, and a reference point adjustment and slope that manually outputs a humidity detection signal based on the changes in the DC voltage output from the rectifier circuit. and an adjustment circuit for adjustment, and the rectifier circuit is configured with a high human power impedance type absolute value circuit and a smoothing circuit, which solves the compatibility problem of conventional ceramic humidity sensors. Eliminate the problem and explain it against low power supply voltage and temperature changes.

FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention;
FIG. 4 is a characteristic diagram showing the relationship between relative humidity and resistance of the sensor of one embodiment shown in FIG. 3. FIG. 5 is a diagram showing the detailed configuration of each part shown in FIG. 3, and FIG. FIG. 3 is a diagram showing a comparison of the relationship between relative humidity and output voltage between the example shown in the figure and a conventional example.

In FIGS. 3 and 5, 1 is an oscillation circuit, 2 is a resistance-voltage conversion circuit, 3 is a rectifier circuit, 4 is an adjustment circuit for reference point adjustment and slope adjustment, and 5 is a ceramic humidity sensor. The oscillation circuit 1 is an oscillation circuit used to avoid polarization, which occurs when direct current is applied to the element of the ZnCr-LiZnV2O5 ceramic humidity sensor 5, for example, and is a type of Wien Brisso oscillation circuit. It is configured to apply an AC oscillation voltage to the ceramic humidity sensor 5. The oscillation voltage output from the oscillation circuit 1 is input via a capacitor 6 to a resistance-voltage conversion circuit 2 which converts a change in resistance of the sensor 5 into a change in alternating current voltage.

A sensor 5 is inserted into this resistance-voltage conversion circuit 2, and as shown in FIG. 4, for example, this sensor 5 converts a change in relative humidity into a change in resistance. Changes in AC voltage corresponding to changes in relative humidity output from the resistance-voltage conversion circuit 2 are input to a rectifier circuit 3, which converts changes in AC voltage into changes in DC voltage. As shown in FIG. 5, the rectifier circuit 3 is composed of a high input impedance type absolute value circuit 31 and a smoothing circuit 32. Changes in the DC voltage output from the rectifier circuit 3 are input to an adjustment circuit 4 for reference point adjustment and slope adjustment.
Zero level adjustment and full scale adjustment are performed, and a humidity detection signal is output. In FIG. 5, OP1 to OP5 are operational amplifiers, R1 to R4 are resistors, and D and D are diodes.

The operation of the above embodiment of the present invention will be explained.

3 and 5, the configuration and operation of the oscillation circuit 1, the resistance-voltage conversion circuit 2, and the adjustment circuit 4 for reference point adjustment and slope adjustment are those used in the fields of conventional various measuring instruments, etc. Since it is substantially the same as that shown in FIG.

In FIG. 5, the rectifier circuit 3 is composed of the absolute value circuit 3 and the smoothing circuit 32 as described above. Since this absolute value circuit 31 is of a high input impedance type, the value of the resistance in the resistance-voltage conversion circuit 2 (the resistance between the sensor 5 and the ground) can be increased. Here, if the voltage at the output end of the resistance-voltage conversion circuit 2 is 01, then
The absolute value circuit 3 has a gain of (1+) when el>0, and the diode D2 is turned off when el>0. , and when el(O, the voltage e at the output end of the absolute value circuit 312 R4 is eo = 8. (1-R18,)
If the town is 0, then of course it is e. =ei, so e. =
+e, + characteristics are obtained. Therefore, the humidity detection circuit according to the present invention operates satisfactorily even at a low power supply voltage.

On the other hand, in the case of using a rectifier circuit as shown in FIGS. 1 and 2, the forward voltage drop of the diode (approximately equal to the bending point 'fg pressure; 0.6~ for 0.2V%St diode
Even when rectifying a direct current signal with a large amplitude that can be ignored (0.7 V), when the power supply voltage decreases, the output amplitude oscillated by the oscillation circuit 1 shown in FIG. 5, for example, also decreases. As a result, the sheath e also becomes smaller. When this e becomes so small that it cannot be ignored compared to the forward voltage drop,
The conventional rectifier circuit described above cannot output a linear DC voltage with ei.

However, according to the above-mentioned embodiment of the present invention, even if the power supply voltage becomes low as described above and the voltage drop becomes so small that it cannot be ignored compared to the forward voltage drop, the characteristic of eo=1ei1 can be obtained. This means that it is possible to always output a linear DC voltage to el.

Furthermore, even if the power supply voltage does not decrease as described above, for example, the sensor 5 inserted into the resistance-voltage conversion circuit 2
However, even if its characteristics change due to variations due to its replacement etc., its resistance increases and ei becomes so small that it cannot be ignored compared to the forward voltage drop, according to the present invention, the rectifier circuit 3 Since a linear DC voltage is output as shown in <ei, even if the sensor 5 is unstable, adjustment can be made accordingly, which eliminates the drawback of not being compatible with conventional ceramic humidity sensors. This can be practically resolved.

Figure 6 shows the relative humidity-output voltage characteristics of the embodiment of the present invention shown in Figure 3 and the conventional example.
Change the relative humidity of the sensor atmosphere from 30 RH to 50 % F.
This shows the output voltage characteristics when changing from 70% RH to 90% RH. In Figure 6, the straight line A indicates the ideal output voltage characteristic, and the curved line indicates the rectifier circuit 3 in Figure 3. The output voltage characteristic when the conventional rectifier circuit is replaced as shown in FIG. 2, and the curve C shows the output voltage characteristic according to an embodiment of the present invention shown in FIG. It can be seen that output voltage characteristics close to the characteristics can be obtained.

As described above, according to the present invention, the rectifier circuit used in the humidity detection circuit using the ceramic humidity sensor is configured with the absolute value circuit of the ta input impedance type and the smoothing circuit, thereby reducing the variation in the ceramic humidity sensor. It eliminates the traditional shortcomings of sensor compatibility by making it easy to adjust for the errors caused by the noise, and also allows it to work well even at lower supply voltages, while reliably eliminating the traditional practical obstacles associated with temperature changes. It is possible to achieve excellent effects such as the ability to

[Brief explanation of the drawing]

1 and 2 are diagrams each showing the configuration of a conventional rectifier circuit, FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 4 is an embodiment shown in FIG. 3. Figure 5 is a diagram showing the detailed configuration of each part shown in Figure 3, Figure 6 is a diagram showing the relative humidity of the embodiment shown in Figure M3 and the conventional example. FIG. 3 is a diagram showing a comparison of the relationship between and output voltage. 1... Oscillation circuit, 2... Resistance-voltage conversion circuit, 3.
... Rectifier circuit, 4 ... Adjustment circuit for reference point adjustment and slope adjustment, 5 ... Ceramic humidity sensor, 6 ... Capacitor, 3 ... Absolute value circuit, 32 ... Smoothing circuit , OP1~oPs... operational amplifier, R1-R4...
Resistor, D11D2 river diode.

Claims (1)

[Claims] A ceramic humidity sensor whose resistance value changes according to changes in humidity, a resistance-voltage conversion circuit that converts changes in the resistance value of this ceramic humidity sensor into changes in AC voltage, and an output from this resistance-voltage conversion circuit. A rectifier circuit that converts changes in AC voltage into four changes in DC voltage, and an adjustment circuit for reference point adjustment and slope adjustment that inputs changes in DC voltage output from this rectifier circuit and outputs a humidity detection signal. A humidity detection circuit comprising: the rectifier circuit comprising a high input impedance type absolute value circuit and a smoothing circuit.