JPS5840125B2 - Seidenyouriyou - Chiyokuryuden Atsuhen Kansouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitance-to-DC voltage converter that converts a change in a measured quantity into a change in the capacitance of a variable capacitor such that a movable electrode moves, and converts it into a change in DC voltage. It is.

Generally, when measuring capacitance, a method is used that uses an AC circuit, such as various AC bridges, but special measures such as synchronous rectification are required to convert the measurement output to DC.

However, this method requires a complicated circuit configuration and is not highly reliable.

As a means of increasing reliability and simplifying the circuit, synchronous detection methods using frequency detection, phase detection, etc. have been proposed, but as long as the output of the AC bridge is used,
No significant improvements were made in either reliability or circuit simplification.

Especially recently, electromagnetism, capacitance, etc. are widely used as non-contact detection methods to measure changes in minute physical and mechanical quantities. The effects of irregular distribution of lines, stray capacitance, and changes in the dielectric constant of the interelectrode material cannot be ignored.

In view of the above, this invention adds a new idea to the arrangement of electrodes, and also has a new configuration for electrostatic capacitance that can directly measure minute changes in physical and mechanical quantities even though it has capacitance. This provides a capacitive displacement-to-DC voltage converter.

The gist of this configuration is that it has a movable electrode that is placed in the center of two fixed electrodes and is displaced according to the physical quantity to be measured, and that when one increases, the capacitance value increases due to the displacement of this movable electrode. Two silk capacitances are configured such that the capacitance decreases, a charging circuit charges each capacitance via a resistor, and a charging circuit is configured to discharge each capacitance separately. A discharge circuit, a pulse generation circuit that generates a timing pulse when the charging voltage value of each capacitance reaches a certain voltage value, and two outputs that perform a reversal operation each time they receive this timing pulse and are in a reverse state with respect to each other. It is equipped with a flip-flop circuit for outputting a signal and a smoothing circuit for smoothing the output voltage pulse of the flip-flop circuit, and the discharge circuit is alternately operated to discharge with the output of the flip-flop circuit. The flip-flop output has a duty cycle corresponding to the change in capacitance.

In other words, three equal-shaped electrodes are arranged at equal intervals, the central electrode is movable, and the electrodes at both ends are fixed. Since the effects are completely removed, this difference in capacitance changes linearly as the center electrode moves.

Since this capacitance change is electrically measured using the simplest circuit configuration, it is possible to obtain extremely high accuracy, stability, linearity, and economy.

Next, embodiments of the present invention will be described.

In Figure 1, 1 and 2 are resistances, 3 and 4 are capacitances that change differentially as the measured quantity changes, and 5 and 6 are set voltages that charge the capacitances 3 and 4. When it becomes
This is a switch for short-circuiting and discharging the capacitances 3 and 4, and a discharge circuit that includes the switches and operates alternately is formed.

This switch can be a field effect transistor or a 0-M
OS analog switch is enabled.

7 and 8 are comparators that generate one pulse when the capacitances 3 and 4 change and the charging voltage reaches the set voltage, and the charging voltage value of each capacitance reaches a constant voltage value. This is a pulse generation circuit that generates each timing pulse when the

Reference numeral 9 denotes a bistable circuit, such as a flip-flop circuit, which receives the timing pulses from the pulse generation circuits 7 and 8 and converts it into a rectangular wave voltage pulse with a pulse width proportional to the measured quantity, and includes the switches 5 and 6. Drives the discharge circuit.

10 is the output terminal -FB of this flip-flop 9, for example.
A smoothing circuit connected to the flip-flop circuit 9 smoothes the output pulse of the flip-flop circuit 9 and converts it into a DC voltage.

Eo is the output voltage value of the converter of this example, and E
is the charging voltage and the reference voltage source as the power source.

FIG. 2 shows the signal waveforms at the output end of each of the above circuits, with each waveform A, B, 0. D.E.

F and G indicate examples of voltage values at the input/output terminals with the same names in FIG. 1.

It is assumed that the common central electrode of the variable capacitors 3 and 4 is movable, and as shown in the example, it is moved by the pressure difference P1-P2, and when P1=P2, the capacitances of the capacitors 3 and 4 are equal. At the same time, resistors 1°2 are selected to be equal to each other (that is, the relationship between the resistance value R1 of resistor 1 and the resistance value R2 of resistor 2 is R1 = R2 = R), and the set voltage of comparator 7.8 is constant. It is assumed that the adjustment is made to take the value Vs.

When the switch 5 is open and the switch 6 is closed in the initial state of the flip-flop circuit 9, the waveform at point A in FIG.
As shown in Figure A, the capacitance 3 is charged from the reference voltage E through the resistor 1 until it reaches the set voltage Vs of the comparator 7.

If the time it takes for the potential at point A to reach Vs is 11, then t
10R (kl is a constant), and when the charging voltage reaches Vs at this time, one pulse as a timing pulse is output from the comparator 7.

The pulse operates the flip-flop circuit 9, and the polarity of its output is reversed.

Therefore, the switches 5 and 6 connected to each output terminal -FB' and F are also reversed, and the capacitance 3 is discharged, while charging of the capacitance 4 is started.

Therefore, as shown in Figure 2, the potential at point A becomes 0 after <11 hours have elapsed, and the potential at point B changes from Vs to O after t1+t2=T time has elapsed (the capacitance 4 reaches a constant potential Vs). (The time at which the discharge starts is t2).

The waveform at point B is as shown in FIG. 2B.

The waveforms shown in FIG. 2 C-D are the timing pulses of the pulse generating circuits 7 and 8, respectively, and in response to this timing, the output of the terminal -FB-F of the flip-flop circuit 9 is as shown in FIG.
-F, for example, it becomes a rectangular pulse of voltage value Es,
Occurs alternately depending on the occurrence of timing pulses.

At this time, if the capacitances 3 and 4 are equal, then <E-
The generation pulse intervals of F are equal (11=12), for example, from one output terminal E of the flip-flop to the smoothing circuit 10
The output voltage E after

Hato becomes.

This output voltage E.

is the value when the common central electrode of the capacitance is stationary at the center and the capacitances 3 and 4 are equal.

However, if this common central electrode moves to one side, a difference will occur between the capacitances 3 and 4, and the time required to be charged to a constant voltage value Vs will change, resulting in a difference in the output pulse interval of the pulse generation circuit. As a result, each end of the flip-flop circuit 9 -7
The pulse interval of the output voltage of E-F changes.

(t to t2) As a result, the smoothing circuit 10 is connected to the end 7.
Although an embodiment in which only F is provided has been described, when the output from each terminal -7E-F is smoothed, the output voltage value is E as described above.

This results in different values.

This displacement of the center electrode allows the voltage values obtained from the two ends -i'E-F of the flip-flop circuit to be added individually or differentially and used.

Note that if the discharging time of the capacitances 3 and 4 is long, charging of the other one starts before the discharging of the other one is completed, so the forward resistance of the semiconductor switches 5 and 6 is compared to the resistance value of the resistor 1°2. It needs to be small enough.

Figure 3 shows the structure of the variable capacitor section in Figure 1, with an area of 3
It consists of two flat parallel electrodes.

The two electrodes 11 and '13 on both ends are fixed electrodes, and the one in the center 12
is a movable electrode.

When the movable electrode 12 is located between the fixed electrodes 11 and 13, the distance between the capacitance 3 and the fixed electrode is dl, the distance between the capacitance 4 and the fixed electrode is d2, and ε is the dielectric constant of the interelectrode material. Considering when the electrode moves △d to the right, the gap between the electrodes becomes d1 + △d for capacitance 3, d2 - △d for capacitance 4, and each capacitance is as follows for period T: R1 = R2 = R. Then, the output E from the capacitance 3 side.

1 is as shown in the following equation.

Similarly, output E from the capacitor 4 side.

2 is also the following formula% formula% Furthermore E.

1 and E. If you extract the difference between 2 and 2 as output,
Its output e.

is as follows. Then, if the distance between the electrodes is chosen so that d, = d2 = d, then e.

= lid, and the difference output voltage e. It is clear that Δd increases or decreases in proportion to the moving distance Δd of the movable electrode, and the two have a completely proportional relationship.

According to the above, according to this conversion transmitter, as shown in equation (5), not only the displacement amount △d but also all physical and mechanical quantities that are proportional to the amount of movement of the central movable electrode can be calculated using the simplest static method. This is a capacitance measurement method that makes it possible to convert it into an electrical quantity. According to this measurement method, changes in the dielectric constant of the interelectrode material and changes in output due to the effects of stray capacitance are completely compensated for. In particular, since this is a method of alternately charging and discharging two capacitances, the influence of variations in discharge time on the output voltage can be ignored.

The above technology can be used, for example, as a differential pressure converter/transmitter that takes advantage of the fact that the difference in pressure on both sides of a single diaphragm is proportional to the amount of deformation of the diaphragm. Similar effects can be achieved in measurement, conversion and transmission.

Regarding the circuit configuration, the semiconductor switch used for charge/discharge switching is of a type other than the device in the example, and the pulse generation circuit uses an inverter in addition to the comparator to adjust its threshold voltage. A similar conversion effect can be obtained using a set voltage.

Moreover, the same effect as the present invention can be obtained not only in the shape of the capacitance shown in FIG. 3 but also in the case where the center electrode is fixed and the electrodes on both sides are displaced together.

As detailed above, the present invention utilizes capacitance in order to accurately detect minute displacements due to changes in physical and mechanical quantities without contact. By making these capacitances work differentially, removing the effects of dielectric constant and stray capacitance, and measuring the amount of charging and discharging of this capacitance, we use it as a representative value of displacement. It is optimal for accurately measuring small minute displacements.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is an operational waveform of each part of the circuit diagram of FIG. 1, and FIG. 3 is a diagram showing the configuration of the variable capacitor shown in FIG. 1. 1.2...Resistor, 3,4...Variable capacitor, 5.6...Switch, 7,8...
... Comparator, 9 ... Flip-flop circuit, 10 ... Smoothing circuit, 11, 13 ...
...Fixed electrode, 12...Movable electrode.

Claims (1)

[Claims] A movable electrode is placed in the center of the 12 fixed electrodes and is displaced according to the physical quantity to be measured, and the capacitance of the movable electrode is changed so that when one increases, the other decreases. capacitance, a charging circuit that charges each capacitance via a resistor, a discharging circuit configured to discharge each capacitance separately, and a charging voltage of the capacitance. A pulse generation circuit that generates a timing pulse when the voltage reaches a certain voltage value, a flip-flop circuit that inverts each time it receives this timing pulse and outputs two output signals that are in reverse states, and and a smoothing circuit for smoothing the output voltage pulse of the flip-flop circuit, and the output of the flip-flop circuit causes the discharge circuit to perform a discharge operation alternately, so that the output of the flip-flop changes depending on the change in capacitance. A capacitance-to-DC voltage converter having a corresponding duty cycle, wherein the DC voltage output from the smoothing circuit increases or decreases in proportion to the displacement of the movable electrode.