JPS582732A - Humidity detection circuit - Google Patents

Abstract

PURPOSE:To correct fluctuations of detected value caused by the secular characteristic variation of a humidity sensitive element itself and a temperature characteristics simply, by converting the output of a pair of the humidity sensitive elements into frequency signals and detecting only a minute variation part of frequency by the humidity. CONSTITUTION:Electrostatic capacity of a humidity sensitive element 1b for environmental humidity measurement disposed on one chip of a semiconductor substrate etc. in very close vicinity and a standard humidity sensitive element 1a for reference sealed tightly so as not to be affected by the environmental temperature, is converted into each frequency signal by electrostatic capacity- frequency conversion circuits 2a, 2b. These frequency signals are passed through a phase difference detection circuit 3 and a low-pass filter circuit 4 and are made into beat signals of two signals excluding a high frequency component of a phase difference signal. This bear signal is sent to a threshold circuit 5 and is counted by a counter 6 after converting into a digital signal and then, is sent to a humidity display device 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a speciation detection circuit that converts the output of a pair of miniaturized lacrimal sensitive elements into a frequency signal, detects only the molten part of the frequency due to humidity, and outputs it as an electrical signal. It is related to.

The conventional technique is to turn humidity changes into electrical signals! Humidity detection devices that use a humidity sensing element that converts t" have had major problems such as changes in the characteristics of the humidity sensing element over time, and a decrease in detection accuracy due to K such as temperature II! characteristics. However, it is difficult to calibrate the characteristics of the moisture-sensitive element using a correction chart, or to calibrate the scale of the detected value display according to the characteristics of the element before measurement. In addition, the control device is complicated because it requires correction using an electric circuit, and it is difficult to correct gradual changes in sensitivity over time. In a 041 degree detection device that converts the capacitance of a temperature sensing element into the frequency of an electrical signal, the rate of change in the number of cycles due to the rate increase is small with respect to the center frequency of the output signal. A complicated circuit configuration was required to detect and amplify only the frequency cost component.In other words, it is difficult to detect the center frequency due to humidity and the same frequency accuracy. It is possible to detect frequency drifts due to moisture-sensitive operation without requiring an electrical circuit.

The present invention was created in order to eliminate the drawbacks of the conventional devices described above, and its purpose is to improve the behavior of moisture-sensitive elements due to environmental factors such as temperature changes, and to It is an object of the present invention to provide a humidity detection circuit that corrects characteristic changes with a simple circuit configuration and outputs only the amount of frequency adjustment caused by temperature sensing operation of a humidity sensing element as an electrical signal.

In order to achieve this object, the present invention combines a humidity sensing element for humidity measurement and a standard humidity sensing element for reference having the same characteristics as the humidity sensing element, and reduces the size of the elements and makes them under the same environmental conditions. The pair of moisture sensing elements were placed extremely close to each other. Further, the standard □ temperature-sensitive element was sealed so as not to sense changes in humidity.

Furthermore, a pair of capacitance-frequency converter circuits having the same KS411 characteristics of the pair of moisture sensing elements are combined to obtain two frequency signals at the same time, and a phase difference between these two frequency signals is detected. A phase difference detection circuit and a low-pass filter circuit were added to generate the beat frequency signal. Further, in order to count the frequency of this beat frequency signal with a digital frequency counter, a dark value circuit for analog-to-digital conversion was provided.

Next, the present invention will be specifically explained with reference to the embodiments shown in the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment. In the figure, 1 is a humidity sensing element, which is a pair of humidity sensing elements installed very close to each other on a single chip such as a semiconductor substrate, that is, a humidity sensing element 1 for measuring environmental humidity.
The standard humidity sensing element 11 for reference, which is sealed so as not to be affected by environmental humidity at all, is made to have a sharp change in temperature characteristics and to be easily improved over time. In addition, since these pairs of small temperature sensing elements are placed close to each other on one chip, they share an almost identical environment except for temperature.
Changes in the frequency difference between the two frequency signals are considered to be caused only by changes in humidity, and if this change in frequency difference is detected as a signal, temperature correction and other corrections are not necessary. Therefore, if the capacitance of these humidity sensing elements 1 m + lb is converted into each frequency signal by the capacitance -□ frequency conversion circuit 2a4bK, and the - frequency difference is detected, it directly corresponds to the environmental temperature. Detection of the zero-order frequency difference from which a frequency output signal is obtained will be described. The frequency signals output from the capacitance-frequency conversion circuits 2m and 2b are combined by a phase difference detection circuit 3 into a signal representing only the phase difference between these frequency signals, and the low-pass filter circuit 4 detects the phase difference. The high frequency component of the signal is removed, and a low frequency signal that is a beat signal of the two signals is output. This beat signal is sent to the threshold circuit 5 and converted into a digital signal.
The number of pulses of this digital signal is counted by the counter 6, and the counting result is sent to the humidity display or alarm generator 7, and the humidity f! ! The dark value circuit is provided with a direct output terminal 8, which allows the direct output of the digital signal, in addition to the generation of an alarm or an alarm.

FIG. 2 is a time chart of signal waveforms at each point A-H in FIG. 1. The output signal A of the capacitance-frequency conversion circuit 2a is a constant frequency signal and does not cause frequency adjustment with respect to adjustment of paper environment humidity. On the other hand, capacitance −
The output signal B of the frequency conversion circuit 2b has a frequency of C due to the adjustment of environmental humidity. Three phase difference oil circuits detect the phase difference between these two signals A and H, and output a digital signal C whose pulse length is proportional to the phase difference. The analog signal representing the average amplitude value of the digital signal C is the signal A.
, B are small with respect to each signal frequency, and h and h indicate the beat frequency of the two signals. Therefore, the analog signal is converted into a digital signal EK' by the dark value circuit 5.
If the pulse count is performed by the counter 6, changes in the output signal frequency caused by temperature changes can be detected. For clarity of explanation, the phase difference between the signals A and B is exaggerated.

In the actual device, as shown in Fig. 3, the beat 1
i-1) The frequency of D is often about one thousandth of the frequency of signals A and B, and in addition, the detection operating frequency that the moisture sensing element can follow is several thousandths of this beat signal frequency. It is about one.

Therefore, K, the digital signal E generated from the beat signal
The result obtained by counting the pulses of K can be considered to indicate the humidity value at the time of counting, if the time required for counting is sufficiently short compared to the detection operation time of the humidity sensing element.

Since the present VJ4 adopts the above-mentioned configuration, it is possible to use a pair of temperature-sensitive elements with different characteristics. Therefore, the force characteristics of the humidity-sensitive element itself over time are improved, and the temperature characteristics etc. This has the effect of being able to correct the drift of the detected value with a simple circuit configuration. In addition, the output frequency signal only represents the frequency adjustment caused by humidity changes, and it is possible to eliminate unnecessary bias frequencies. It has a feature that makes the circuit configuration of counters and indicators easy, and is suitable for industrial use.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a tie ζ diagram of signal waveforms at each part in the circuit, and Fig. 3 is a l! FIG. 3 is a diagram comparing the periods of the signal waveforms shown in FIG. 2 during actual humidity detection. In the figure, ta+lb is a pair of moisture sensing elements, 2a4b is a pair of capacitance-frequency conversion circuits, 3 is a phase difference detection circuit, 4 is a low-pass filter circuit, 5Fi floor value circuit, 6 is a counter, and 7 is a display 8 is a direct output terminal,
■, is the threshold voltage, 3rd Il! 1A and B indicate continuous waves. Patent Applicant Anritsu Electric Co., Ltd. Agent Patent Attorney Ryutabe Koike+'

Claims (1)

[Claims] A pair of humidity sensing elements (la, lb) whose capacitance changes when sensing humidity; a pair of capacitance-frequency conversion circuits which converts the change in capacitance of the humidity sensing elements into a frequency signal. (2a
4b); and; a phase difference detection circuit (3) that receives two frequency signals output from the pair of capacitance-to-circumference number conversion circuits, detects their phase difference, and outputs the signal; a low-pass filter circuit (4) that receives the output signal of the wrinkle phase difference detection circuit and outputs its low shoulder wave component; compares the output of the low-pass filter circuit with a predetermined dark value potential and generates a digital signal; 1. A IIJI detection circuit comprising: a dark value circuit (5) for converting into a dark value; and a counter (6) for counting the number of pulses of a digital signal outputted from the wrinkle value circuit.