JPH0549947B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an impedance change detector that uses a pair of impedance elements whose impedance changes depending on the amount of displacement to obtain an electrical output signal according to the amount of displacement.

FIG. 1 is a schematic diagram of a conventional impedance change detector. Reference numerals 11 and 12 denote impedance elements built into a pressure receiving capsule or the like whose impedance changes according to the amount of change, and whose capacitances C ₁ and C ₂ change according to changes in the amount of displacement. Resistors 21 and 22 are connected in series to each impedance element 11 and 12, respectively, and these series circuits are connected in parallel to form a so-called bridge circuit. The connection point between the resistors 21 and 22 is connected to a resistor 23, and an alternating current signal is supplied from the oscillator 3 to this circuit. Here, the currents flowing through the resistors 21 and 22 are respectively i ₁ and i ₂ and the resistor 23
Let i ₃ be the current flowing through the resistors 21, 22, 23, and R ₁ , R ₂ , R ₃ be the resistance values of the resistors 21, 22, 23.
Let the voltages generated at 3 be e ₁ , e ₂ , and e ₃ . Also,
If 1/jωC ₁ , 1/jωC ₂ ≫R ₁ , R ₂ , R ₃ , the following equation holds true.

i ₁ = i ₃ /C ₂ (1/C ₁ + 1/C ₂ ) = i ₃ C ₁ /C ₁ +C ₂ i ₂ = i ₃ /C ₁ (1/C ₁ + 1/C ₂ ) = i ₃ C ₂ / C ₁ + C ₂ Therefore, finding the difference between e ₁ and e ₂ , that is, e ₂ − _{e 1} , R ₁ =
When R ₂ = R ₃ , the following formula holds true.

e ₂ −e ₁ = C ₂ − C ₁ /C ₂ +C ₁・e ₃ e ₃ = i ₃ R ₃ Therefore, the current i ₃ flowing through the resistor 23, i.e., i ₁ + i ₂
If the voltage is kept constant, the difference in voltage generated between the resistors 21 and 22 becomes a value proportional to the amount of impedance displacement of the impedance element described above.

In this way, in the conventional conversion method, if the sum current i ₃ of the currents i 1 and i ₂ flowing in the series circuit of a pair of impedance elements and _two resistors constituting a bridge circuit is always constant, the resistors 21 and 22 The change in impedance of the impedance element can be measured by measuring the difference in voltage generated between the impedance elements.
However, in such a conventional system, when the capacitance values C ₁ and C ₂ of the impedance elements 11 and 12 change, the current values i ₁ and i ₂ change, and the sum current i ₃ supplied from the oscillator 3 changes. Therefore, in the conventional method, as shown in FIG. 1, in order to keep the sum current i ₃ =i ₁ +i ₂ constant, the detection control unit 31 detects the fluctuation in the voltage e ₃ generated in the resistor 23. holds the current supplied by the oscillator 3 constant.
Therefore, there is a drawback that the circuit configurations of the oscillator 3 and the detection control section 31 become complicated.

The present invention aims to eliminate the drawbacks of the prior art and to realize a displacement transducer that detects impedance changes with an extremely simple configuration. Its configuration is characterized by using a current transformer having primary and secondary coils with the same number of turns, and connecting the terminals of the primary and secondary coils with the same polarity to the impedance element. The structure is such that alternating current voltages of equal amplitude and opposite phases are applied to the series circuit of Narufuo. With this configuration, the current flowing through the primary and secondary coils is always equal, and if the amplitude of the oscillator's AC voltage is always kept constant, an output signal corresponding to impedance changes can be obtained from the current transformer. . An embodiment of the present invention will be described below with reference to FIG.

In Figure 2, 11 and 12 are the same as in Figure 1, for example, a pair of impedance elements whose capacitances C ₁ and C ₂ change, and 4 is the same number of windings on the primary and secondary sides. A current transformer, 3' is an oscillator that generates an alternating current voltage _e0 with a constant amplitude, 5 is a signal detection unit that detects the voltage generated on the primary side (or secondary side) of the current transformer 4, and extracts it as an output signal, 6 is a transformer having an intermediate tap 62 on the secondary coil 6b. In addition, the terminals 41 and 42 of the primary coil and the coil terminals 43 and 44 of the secondary side of the current transformer 4 are terminals 41 and 43, and terminal 42, respectively.
and 44 have the same polarity.

These elements are connected as follows.
That is, one ends 112, 122 of the pair of impedance elements 11, 12 are connected to the terminals 41, 41, and 41 of the primary and secondary coils 4a and 4b of the current transformer 4, respectively, which have the same polarity.
43, and the other terminals 42 and 44 of the primary and secondary coils of the current transformer 4 are respectively connected to terminals 61 and 63 of the secondary coil 6b having an intermediate tap 62 of the transformer 6. . Also, the intermediate tap 6 of the secondary coil 6b of the transformer 6
2 is connected to the other terminals 111, 121 of the impedance elements 11, 12, and 1 of the transformer 6.
An alternating current voltage e of constant amplitude is applied to the next coil 6a from an oscillator 3'. Also current transformer 4
The voltage generated in the primary side (secondary side) coils 4a and 4b is detected by the signal detection unit 5, and it is possible to know the impedance change of the impedance element from this voltage.

Next, the operation of the present invention will be explained. Now let the impedances of the pair of impedance elements 11 and 12 be Z ₁ and Z ₂ , and currents flowing through the primary and secondary sides of the current transformer 4 are generated at i ₁ and i ₂ in the primary coil of the current transformer 4. Let the voltage be e.
Although the number of windings on the primary and secondary sides of the current transformer 4 are equal in phase, the phases of the voltages applied to the primary and secondary sides are opposite to each other, so the coils on the primary and secondary sides are A voltage e is generated which is opposite in direction and equal in magnitude, and currents i ₁ and i ₂ flowing therein are equal in magnitude and in opposite directions, that is, i ₁ =i ₂ .

Here, terminals 61-62 on the secondary side of the transformer 6
The voltages generated between 63 and 62 have opposite polarities and are equal in magnitude, so if we define this as e ₁ - e ₀ , e ₀ = i ₁ Z ₁ + e......(1) e ₀ = i ₂ Z ₁ - e ...(2) i ₁ = -i ₂ ...(3) From the above equations (1), (2), and (3), the voltage e generated in the primary coil of the current transformer 4 is e = Z ₁ −Z ₂ /Z ₁ +Z ₂・e ₀ ...(4), and between the primary terminals of the current transformer 4 41
-42, it is possible to obtain an output voltage proportional to the variation of the impedance element. Furthermore, when the impedance elements are capacitances C ₁ and C ₂ that change differentially, Z ₁ = 1/jωC ₁ and Z ₂ = 1/jωC ₁ , so e=C ₂ −C ₁ /C ₁ As +C ₂ ·e ₀ , a voltage e corresponding to the change in capacitance is generated between the terminals 41 and 42 of the current transformer. This voltage e is extracted from the signal detection section 5.

FIG. 3 is a graph showing voltage waveforms generated in impedance elements 11 and 12 when rectangular alternating current is supplied from oscillator 3'. Figure a shows the voltages e ₁₀ and e ₂₀ generated in the impedance elements 11 and 12, and when Z ₁ = Z ₂ , e ₁₀ = e ₂₀ = e ₀ , which is generated in the pair of impedance elements. The voltage becomes equal to the AC voltage applied to the bridge circuit, indicating that the voltage e ₃ generated in the primary or secondary coil of the current transformer becomes zero. Diagram b
Then, impedance element 1 when Z ₁ > Z ₂
1 and 12, and for the voltage _{e 3 generated} in the primary coil of the current transformer, e ₁₀ = e ₀ + e, e ₂₀ = e ₀ - e, and the _primary side and 2
The property of a current transformer in which the number of turns of the next coil is equal indicates that a voltage increase occurring in one impedance element results in a voltage decrease occurring in the other impedance element.

In addition to the configuration for extracting the voltage generated between the terminals of the primary coil or the secondary coil, as shown in FIG. 4, a third sense winding 4C is provided in the current transformer 4 to extract the output signal. , the voltage generated in the sense winding 4C may be detected by the signal detection section 5.

As described above, the present invention uses a current transformer with the same number of windings on the primary and secondary sides,
This is an extremely novel configuration in which a pair of impedance elements constitutes a bridge circuit so that the currents flowing through the primary and secondary coils are always equal. Therefore, if the amplitudes of the alternating current voltages of equal amplitude and opposite phase given by the alternating current source are kept constant, that is, if the alternating current voltage of the oscillator 3' is kept constant in amplitude, the impedance elements 11 and 12
It is possible to obtain an output according to the impedance change. Furthermore, a circuit that maintains the AC voltage of the oscillator 3' at a constant amplitude can be easily designed by, for example, creating a reference voltage using a Zener diode within the oscillator 3', so that the sum current can be kept constant as in the conventional case. The circuit can be simplified compared to a configuration in which it is maintained.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing a conventional impedance change detector, Fig. 2 is a schematic diagram showing an embodiment of the present invention, Fig. 3 is a graph showing a voltage waveform generated in a pair of impedance elements, and Fig. 4 FIG. 2 is a diagram showing another output signal extraction configuration of the present invention. 11, 12... Impedance element, 3'...
Oscillator, 4... current transformer, 5... signal detection section.

Claims (1)

[Claims] 1: a pair of impedance elements whose impedance changes at least on one side; a current transformer having coils with the same number of turns on the primary and secondary sides; and an AC source that generates AC voltages with equal amplitude and opposite phases; a signal detection unit that measures the voltage generated in the coil of the current transformer, and one terminal of the pair of impedance elements is connected to terminals of the same polarity on the primary side and secondary side of the current transformer, respectively. and the pair of impedance elements and the primary and secondary sides of the current transformer.
AC voltages of equal amplitude and opposite phases are supplied from the AC source to a circuit connected in series with the next coil, and
An impedance change detector characterized in that the voltage generated in the next coil is detected by the signal detecting section to measure an impedance change of the impedance element.