JPS6257227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention configures an integrating circuit by the capacitance of the object to be measured and the resistance inside the device, and the integration circuit is identical to the comparison integrating circuit provided in advance in the device. A capacitance change method in which a rectangular pulse is applied, the maximum value of the difference signal between the two obtained integral waveforms is detected, and the capacitance change of the measured object is detected based on the amount of change in the maximum value of the difference signal. This invention relates to a detection device.

Conventionally, capacitance changes have been detected by configuring a series circuit or a bridge circuit with a known resistor and an object to be measured, and detecting changes in capacitance impedance, or by using a feedback circuit in an oscillation circuit. Methods have been used in which a measurement object is installed and changes in oscillation frequency due to changes in capacitance are detected. These methods are based on continuous measurement operations using continuous sine wave signals or oscillation waves, and the stability of the signal amplitude and oscillation frequency greatly affects measurement accuracy, so advanced manufacturing is required to stabilize them. It required technology and complex circuits. Furthermore, when detecting gradual changes in capacitance that persist over a long period of time, intermittent measurements set at appropriate time intervals are often sufficient; At times, most of the power is wasted, 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 effects 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 capacitance change detection device that has a simple circuit configuration, performs intermittent measurement operation with low average power consumption, and allows the intermittent cycle to be arbitrarily varied, eliminating the above-mentioned drawbacks. .

For this purpose, the present invention adopts an intermittent measurement method using a rectangular pulse signal, and is equipped with a capacitance detection circuit that detects changes in capacitance of the object to be measured in the form of time constant changes, and outputs an electrical signal. In addition, a pulse signal generation circuit is provided that can arbitrarily set the rectangular pulse width and repetition period that are optimal for the amount of change in capacitance. Furthermore, the present invention further includes a signal maximum value holding circuit that holds the maximum output signal value of the detection circuit when not measuring and forms a continuous step-like output waveform; A reset pulse circuit is provided.

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 adjusted to a predetermined amplitude by variable resistors /R ₃ and R ₄ , and then passed through a comparison integration circuit 4 installed in the device, and DUT 1 and variable resistance/
R ₂ is added to the integrator circuit. The time constant τ _s of the comparison integration circuit 4 is determined by the variable resistance /R ₁ and variable capacitance /C ₁ in the same circuit, so that τ _s =
Given by R ₁ C ₁ . Furthermore, if the capacitance of the object to be measured is C ₀ , then the time constant τ ₀ of the circuit composed of the object to be measured and the variable resistor R ₂ is τ ₀ =R ₂ C ₀ .
If we simultaneously apply a rectangular pulse a of time width T to these circuits with time constants τ _s and τ ₀ and find the voltage difference Vd between the respective output signals b and c, Vd=ε−t/τ ₀ − ε-t/ _τs (OtT)...
(1) becomes. However, the amplitude value of the rectangular pulse a is 1.0. Further, if both τ _s and τ ₀ are sufficiently smaller than T, Vd=ε−t/τ _s −ε−t/τ ₀ (Tt) (2) also holds true. The waveform obtained by the above equations (1) and (2) is a pulse waveform as shown in FIG. 2d. This pulse wave d
The amplitude value Hm of the vertex m and the occurrence time tm are given by the following equation.

Hm=(ε-tm/ _τ0 -ε-tm/ _τs )...(3) m= _logτs / _τ0 /(1/ _τ0-1 / _τs )...(4) Equation (3) The relationship between the value of Hm and the time constant ratio (τ ₀ /τ _s ) is shown graphically in FIG. Time constant ratio (τ ₀ /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 Hm with respect to the change in C ₀ . Further, FIG. 4 shows a graph of the relationship between equation (4) tm normalized by the value of τ _s and τ ₀ , that is, the relationship between (tm/τ _s ) and (τ ₀ /τ _s ). In the embodiment of FIG. 1, the pulse wave d whose apex is determined by these Hm and tm is as follows:
It is obtained as the output signal of the differential amplifier 3.

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 Hm of the output signal d obtained by the differential amplifier 3, and output the response time of the display or recorder connected to this device to display capacitance changes. To be able to accurately indicate the value of Hm even when the pulse width of the signal d is much longer than the pulse width of the signal d. Therefore, the differential amplifier 3
The pulsed output signal d obtained 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 then when an input signal is applied, the input signal is This circuit continues to output an output signal voltage proportional to the maximum value of . That is, when the pulsed output signal d is added, a voltage signal proportional to the maximum amplitude value Hm 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 portion of the rectangular pulse a generated by the pulse oscillation circuit 2. FIG. 5 shows a timing chart of the reset pulse e and the output of the maximum signal amplitude value holding circuit when the rectangular pulse a is repeatedly generated and the capacitance of the object to be measured changes. As is clear from the figure, the time width T of the rectangular pulse a is larger than the generation time Tm of the pulsed output signal d, and the reset pulse time width Tr needs to be smaller than the Tm.
The detection operation time of this device is Tm, and this value is determined by the values of τ _s and τ ₀ as shown in FIG. 4 above. The practical values of τ _s and τ ₀ are the rectangular pulse a
Set to an arbitrary time greater than the rise time of . Further, since the signal values of the output signal at times Tm ₁ and Tm ₂ have no meaning as measured values, there is no need to display them. Furthermore, the amplitude value of the output signal, that is, the value of Hm, is as shown in FIG.
Since it is not directly proportional to the capacitance change of the object to be measured, in order to make the device directly connected to the capacitance change, use the linear compensation amplifier 7 shown in FIG. 1, or change the scale of the display meter etc. Create according to the characteristics of the diagram.

As described above, the capacitance change detection device according to the present invention has a simpler circuit configuration than conventional devices, and because it performs intermittent measurement using pulse signals, it is possible to reduce the average power consumption, making it smaller and lighter. can be realized. 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, measurement accuracy can be expected to improve. Furthermore, since the basic operation of the present invention is to detect a change in the time constant of a circuit including an object under test,
Electrical elements that are involved in the time constant when configuring a circuit,
For example, it is easy to modify it into a measuring device for resistance, inductance, etc.

[Brief explanation of the drawing]

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 Hm and the time constant ratio (τ ₀ /τ _s ), FIG. 4 is a graph showing the relationship between the maximum amplitude value generation time tm of the pulse wave d and τ ₀ normalized by τ _s ,
Figure 5 is a timing chart showing the waveforms of various parts in the device, where A is the measurement rectangular pulse a, B is the pulse waveforms b and c after passing through the time constant circuit, C is the differential amplifier output signal d, and D is the reset signal. Pulse signal e, E shows the maximum signal amplitude value holding circuit output signal, and F shows the linear correction amplifier output signal g. Reference numeral 1 indicates an object to be measured, 2 a pulse oscillation circuit, 3 a differential amplifier, 4 an integration circuit for comparison, 5 a maximum signal amplitude value holding circuit, 6 a reset pulse circuit, and 7 a linear correction amplifier. R ₁ , R ₂ , R ₃ , and R ₄ represent variable resistances, and C ₁ represents variable capacitance.

Claims (1)

[Claims] 1 A capacitance change detection device that uses a pulse signal as a measurement signal, comprising a pulse oscillation circuit 2 that generates the pulse signal; and a pulse oscillation circuit 2 that receives and integrates the pulse from the oscillation circuit to generate an integrated waveform signal for comparison. a comparison integrator circuit 4 that outputs; a differential amplifier 3 that receives the output of the comparison integrator circuit and an output signal from an integrator circuit including the object under test and outputs a difference signal; and an output signal of the differential amplifier. a maximum signal amplitude value holding circuit 5 that receives the signal, holds the maximum amplitude value, and outputs it; a reset pulse that receives the output pulse of the pulse oscillation circuit and resets the operation of the amplitude value holding circuit in synchronization with this pulse; A capacitance change detection device comprising a circuit 6.