JPS6161628B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity detection circuit using a humidity sensor whose impedance changes exponentially with humidity.

Although humidity sensors are being actively developed,
Among these, many are seen whose impedance changes exponentially with humidity. Furthermore, most of these humidity sensors cannot detect with direct current, and must be operated with alternating current or pulse drive. Furthermore, the humidity-impedance characteristics are temperature dependent, so temperature compensation must also be performed. For these reasons, in general,
Highly accurate detection circuits using such elements are complex and expensive.

In view of these points, the present invention provides a detection circuit that can easily perform logarithmic conversion and temperature compensation.

Embodiments of the present invention will be described below with reference to the drawings. As a humidity sensor, there is, for example, the one shown in FIG. 1 developed by the applicant. FIG. 1 is a schematic diagram of the structure. The thin film 1 on the top surface is made of, for example, a styrene sulfonic acid polymer electrolyte membrane as a moisture sensitive membrane, and a resin coating membrane is laminated thereon to obtain excellent moisture resistance, water resistance, and good moisture sensitivity characteristics. The substrate 2 is made of, for example, alumina, and the electrode 3 is made of, for example, Au to form a comb-shaped electrode.

Figure 2 shows typical humidity-impedance characteristics of such a polymer electrolyte membrane humidity sensor, as an example, the humidity characteristics at temperatures of 15°C, 30°C, and 45°C, and here approximately -0.6%. It has a temperature dependence of RH/℃.

By the way, the forward current and forward voltage of a PN junction, and their temperature dependence are well known. Things that have a P-N junction include diodes and transistors, and the main material used is Si, but there are also things that use Ge or other semiconductors. There is also a Schottky diode that has such characteristics. Figures 3a and 3b show an example of diode characteristics. A is a characteristic diagram showing the relationship between forward current and voltage of a diode, and in the forward voltage range shown in the diagram L, the voltage versus current characteristic changes almost exactly according to an exponential function curve. Part b is a diagram showing the characteristics when the temperatures are set to 15° C., 30° C., and 45° C., respectively, as an example, in order to specifically explain temperature dependence.

The humidity detection circuit of the present invention utilizes such diode characteristics to combine a humidity sensor and a diode, logarithmically convert the output of the humidity sensor, and perform temperature compensation at the same time.

Examples of circuits of the present invention are shown in FIGS. 4 to 9.

4 and 5, a humidity sensor 4 and a diode 5 are connected in series, and the voltage at the connection point is applied to an operational amplifier 6. In FIG. The sensor 4 is driven by direct current, and in FIG. 5, the humidity sensor 4 is driven by a pulse generator 8 in pulses.

6 and 7, a diode 5 is inserted into the feedback loop of the operational amplifier 6. If the polarity of the applied voltage (constant voltage power source 7 or pulse generator 8) is changed, detection can be performed in the same way by reversing the direction of the diode 5.

FIG. 8 shows a case where an element preferably driven by alternating current (for example, a sine wave, a square wave, a triangular wave, etc.) is used as the humidity sensor 4, and two diodes 5, 5 are connected in antiparallel, and this is used as the humidity sensor. 4 and are connected in series to the oscillator 9.

Figure 9 shows the same AC drive, with diodes 5 and 5 connected in antiparallel connected to an operational amplifier 6.
into the feedback loop.

With the circuit configuration as described above, the humidity sensor 4
At the same relative humidity, the resistance decreases as the temperature increases. As a result, the current increases and the forward voltage of the diode 5 increases; however, the forward voltage of the diode 5 decreases as the temperature increases, so changes with respect to temperature are canceled out.

By the way, using the humidity sensor 4 developed by the applicant and the diode 5 with model number 1S1588 as shown in the characteristic diagram of FIG. 2, the humidity-output characteristics of the circuit of FIG. 8 are shown in FIG. 10. The exponential change in the humidity sensor 4 is logarithmically converted, and at the same time, temperature compensation is performed to suppress temperature changes.

As described above, the present invention can easily perform logarithmic conversion and temperature compensation, and can provide a humidity detection circuit that is inexpensive and has high practical value.

[Brief explanation of the drawing]

Fig. 1 is a schematic structural diagram of a humidity sensor used in an embodiment of the present invention, Fig. 2 is a typical humidity-impedance characteristic diagram of the humidity sensor, Fig. 3 a and b are characteristic diagrams of a diode, and Fig. 4 9 are electrical circuit diagrams showing different circuit examples of the present invention, and FIG. 10 is a humidity-output characteristic diagram in one embodiment of the present invention. 4... Humidity sensor, 5... Diode, 6...
Operational amplifier, 7... constant voltage power supply, 8... pulse generator, 9... oscillator.

Claims (1)

[Claims] 1. It has a humidity sensor whose impedance changes exponentially with respect to humidity and a diode, and uses the relationship between the forward current and voltage of the diode and its temperature dependence to calculate the output of the humidity sensor logarithmically. What is claimed is: 1. A humidity detection circuit that performs temperature compensation and temperature compensation at the same time.