JPH0222338B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, an integrating circuit is constructed by a humidity sensor whose capacitance changes depending on humidity and a resistor, and this integrating circuit and a comparative integrating circuit are provided in advance in the device. The same pulse is applied to the circuit, and the obtained 2
The present invention relates to a humidity measuring device that detects the maximum value of a difference signal between two integral waveforms and displays a change in humidity based on the amount of change in the maximum value of the difference signal.

Conventionally, capacitance changes have been detected by constructing a series circuit or bridge circuit with a known resistance and the capacitance under test, and detecting changes in the impedance of the capacitance, or by connecting the capacitance under test to a feedback circuit in an oscillation circuit. Methods such as installing a capacitor and detecting changes in oscillation frequency due to changes in capacitance have been used. These methods are based on continuous measurement using continuous sine wave signals or oscillation waves, and the stability of the signal amplitude and oscillation frequency greatly affects measurement accuracy.
Stabilizing these elements required advanced manufacturing techniques and complex circuits. In addition, when detecting capacitance changes that remain constant over a long period of time, such as with a humidity sensor when measuring humidity, intermittent measurements set at appropriate time intervals taking into account the response time of the humidity sensor may be sufficient. There are many
When the continuous measurement operation detection circuit is used, most of the power is wasted during non-measurement periods, and unnecessary heat generation is also generated. These points become disadvantages when it is considered that the detection circuit is integrated into a small size and operated with a finite micro power source such as a battery. Furthermore, operating the detection circuit intermittently does not only make it impossible to fully utilize the circuitry required to stably perform continuous measurement operations, but also requires the addition of a new circuit for intermittent measurement operations, and the influence of transient response on the output signal. It becomes necessary to consider the following, and even more advanced technology and complicated circuit configurations are required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a humidity measuring device which has a simple circuit configuration, performs intermittent measurement operation with low average power consumption, and allows the intermittent cycle to be arbitrarily varied, in addition to the above-mentioned drawbacks.

For this purpose, the present invention adopts an intermittent measurement method using a rectangular pulse signal, converts the capacitance change due to humidity change of the humidity sensor into a time constant change,
A capacitance detection circuit that outputs this as an electrical signal is provided, and a pulse oscillation circuit is also provided that can arbitrarily set the rectangular pulse width and repetition period optimal for detecting changes in capacitance. Furthermore, a maximum signal amplitude value holding circuit is provided, which holds the maximum value of the output signal of the detection circuit when not being measured to form a continuous step-like output waveform, and this circuit is operated in synchronization with the cycle of the rectangular pulse signal. A reset pulse circuit is provided for this purpose.

Next, this invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. Further, FIG. 2 shows voltage waveforms at points a to d in FIG. 1. A rectangular pulse a generated by a pulse oscillation circuit 2 whose oscillation period and pulse width can be arbitrarily varied is passed through a comparison integration circuit 4 installed in the device, and an integration circuit 1 consisting of a humidity sensor 1a and a resistor _R2 . added to. The time constant τ _S of the comparison integration circuit 4 is given by the resistance R ₁ and the variable capacitance C ₁ in the circuit as τ _S =R ₁ C ₁ . Also,
If the capacitance of the humidity sensor 1a is C ₀ , then the time constant τ _O of the integrating circuit 1 composed of the humidity sensor 1 a and the variable resistor R ₂ is τ _O =R ₂ C ₀ . These τ _S , τ _O
A rectangular pulse a of time width T is simultaneously applied to a circuit with a time constant of , and the voltage difference between the output signals b and c is
If we calculate Vd, we get V _d =ε ^-t/ 〓 ⁰ −ε ^-t/ 〓 ^s (0tT)...(1). However, the amplitude value of the rectangular pulse a is 1.0. Further, if both τ _S and τ _O are sufficiently smaller than T, V _d =ε ^−t/ 〓 ⁰ −ε ^−t/ 〓 ^s (Tt) ...(2) also holds true. The waveforms obtained from the above equations (1) and (2) are pulsed output signals as shown in FIG. 2d. The amplitude value Hm of the peak m of this pulse waveform d and the generation time t _n are given by the following equation.

H _n = (ε ^-tm/ 〓 ₀ −ε ^-tm/ 〓 ⁰ ) ...(3) t _n = logτ _S /τ _O / (1/τ _O -1/τ _S ) ...(4) (3 ) The relationship between the value of equation H _n and the time constant ratio (τ _O /τ _S ) is shown graphically in FIG. Time constant ratio (τ _O /τ _S )
is a numerical value proportional to C ₀ when R ₁ , R ₂ , and C ₁ are constants, so the graph in FIG. 3 shows the amount of change in H _n with respect to the change in C ₀ . In addition, Figure 4 shows t _n of equation (4) normalized by the value of time constant τ _S , time constant and τ _O
The relationship between (t _n /τ _S ) and (τ _O /τ _S ) is shown in a graph. The pulse waveform d whose apex is determined by these H _n and t _n is obtained as the output signal of the differential amplifier 3 in the embodiment shown in FIG.

Next, a circuit for converting the pulsed output signal d into a stepped output signal will be described. The purpose of this signal waveform processing is to hold the maximum amplitude value H _n of the output signal d obtained by the differential amplifier 3, and display a display device (display device or recorder) 8 that displays humidity changes.
To accurately indicate the value of H _n even when the response time of H n is much longer than the pulse width of the output signal d. Therefore, the pulsed output signal d obtained by the differential amplifier 3 is sent to the maximum signal amplitude value holding circuit 5. This maximum signal amplitude value holding circuit 5 has a signal input terminal, a reset terminal, and an output terminal. First, a reset pulse is applied to the reset terminal to make the signal voltage at the output terminal zero, and
Next, when an input signal is applied, the circuit continues to output an output signal voltage proportional to the maximum value of the input signal. That is, if the pulsed output signal d is added, a voltage signal proportional to its maximum amplitude value H _n continues to be output. This output signal returns to zero when a reset pulse is applied, and the circuit enters the state of waiting for an input signal. In the present invention, the reset pulse is generated by the reset pulse circuit 6 using the rising edge of the rectangular pulse a generated by the pulse oscillation circuit 2. Fifth
The figure shows a timing chart of the reset pulse e and the maximum signal amplitude value holding circuit output f when the rectangular pulse a is repeatedly generated in the pulse oscillation circuit 2 and the capacitance of the humidity sensor 1a changes. . As is clear from the figure, the time width T of the rectangular pulse a is the generation time of the pulsed output signal d.
larger than T _n , and reset pulse time width T _r
must be smaller than the above T _n . The humidity detection operation time of this device is T _n , and this value is determined by the values of τ _S and τ _O as shown in FIG. 4 above. The practical values of τ _S and τ _O are set to an arbitrary time greater than the rise time of the rectangular pulse a. Further, since the signal values of the output signal f at times T _n1 and T _n2 have no meaning as measured values, there is no need to display them. Furthermore, the amplitude value of the output signal f, that is,
As shown in FIG. 3, the value of H _n is not directly proportional to the capacitance change of the humidity sensor, and the humidity versus capacitance change characteristic of the humidity sensor is usually not linear. Therefore, in order to make this device directly connected to humidity, it is necessary to use a linear correction amplifier 7 that converts these non-linear characteristics into linear characteristics, or to adjust the scale of the display device 8.

As described above, the humidity measuring device according to the present invention has a simpler circuit configuration than conventional devices, and
Since intermittent measurement is performed using pulse signals, average power consumption can be reduced, making it possible to achieve smaller size and lighter weight. In addition, stabilizing the amplitude of a rectangular pulse signal is easier than that of a sine wave signal, and if the rise time of a rectangular pulse signal is constant, fluctuations in pulse width and repetition period will not affect the measured value. By keeping changes in the time constants of each circuit constituting the circuit to a small value, it is expected that measurement accuracy will be improved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing a measurement rectangular pulse a and pulse waveforms b and c after passing through a time constant circuit, and Fig. 3 is a diagram showing the maximum amplitude value of the pulse wave d. A graph showing the relationship between H _n and the time constant ratio (τ _O /τ _S ), Figure 4 shows the time at which the maximum amplitude value of the pulse wave d occurs.
A graph showing the relationship between t _n and τ _O normalized by τ _S. Figure 5 is a timing chart showing the waveforms of each part in the device. A is the measurement rectangular pulse a, B is the pulse after passing through the time constant circuit. Waveforms b, c, and c show the differential amplifier output signal d, d shows the reset pulse signal e, e shows the maximum signal amplification value holding circuit output signal f, and f shows the linear correction amplifier output signal g. 1 is an integration circuit, 1a is a humidity sensor, 2 is a pulse oscillation circuit, 3 is a differential amplifier, 4 is an integration circuit for comparison, 5 is a maximum signal amplitude value holding circuit, 6 is a reset pulse circuit, 7 is for linear compensation The amplifier and 8 indicate a display device (display or recorder). R ₁ and R ₂ are resistances, and C ₁ is variable capacitance.

Claims (1)

[Claims] 1. A humidity measuring device that uses a pulse signal as a measurement signal, comprising: a pulse oscillation circuit 2 that generates the pulse signal;
a comparison integration circuit 4 that receives and integrates the pulse signal from the pulse oscillation circuit 2 and outputs an integrated waveform signal for comparison; and a humidity sensor 1a whose capacitance changes depending on humidity and a resistor _R2 . An integrator circuit 1 configured; the output of the comparison integrator circuit 4 and the integrator circuit 1;
a differential amplifier 3 receiving the output of the differential amplifier 3 and outputting a difference signal thereof; receiving the output signal of the differential amplifier 3;
a maximum signal amplitude value holding circuit 5 that holds and outputs the maximum amplitude value; receives a pulse signal from the pulse oscillation circuit 2 and resets the operation of the maximum signal amplitude value holding circuit 5 in synchronization with this pulse signal; a reset pulse circuit 6; and a maximum signal amplitude value holding circuit 5.
Display device 8 for displaying or recording the output signal of
A humidity measuring device comprising: