JP7117512B2 - Concentration sensor - Google Patents

Description

The present disclosure relates to concentration sensors.

A concentration sensor for detecting the concentration of a fluid is composed of a conductive outer pipe forming a fluid flow path and a conductive inner pipe disposed within the flow path. The concentration sensor is formed by an outer pipe and an inner pipe, detects capacitance, and outputs a signal corresponding to the capacitance as concentration information.

For example, Patent Document 1 is known as prior art document information related to the disclosure of this application.

Japanese Patent Publication No. 2009-505074

However, the fluid to be detected is not a little electrically conductive. The conductivity in the fluid is included in the detection results as a resistance component in the capacitance detection. This resistance component causes an error in concentration detection, resulting in a problem of deteriorating detection accuracy.

Accordingly, an object of the present disclosure is to solve such problems and improve the detection accuracy of the concentration sensor.

A concentration sensor according to one aspect of the present disclosure includes a cylinder, a lead wire, and a circuit processing section, and the circuit processing section includes a reference oscillator, a first frequency divider, a phase comparator, a low-pass filter, a voltage-controlled oscillator, and a second divider. A voltage controlled oscillator has a variable capacitance diode, an oscillator and an amplifier, and the first output port is voltage controlled via the detector. It is connected to an oscillator, the second output port is connected to the rear stage of the low-pass filter, the cylinder and the lead wire jointly form a resonator, and the resonator is connected between the cathode of the variable capacitance diode and the oscillator. It is

This configuration can improve the detection accuracy of the density sensor.

FIG. 1 is a configuration diagram schematically showing a concentration sensor of the present disclosure. FIG. 2 is an equivalent circuit diagram of the concentration sensor of the present disclosure. FIG. 3 is a cross-sectional view schematically showing a modification of the resonator.

A density sensor according to an embodiment of the present disclosure will be described below with reference to the drawings. It should be noted that each of the embodiments described below is a preferred specific example of the present disclosure. Therefore, the shapes, components, arrangement of components, connection modes, and the like shown in the following embodiments are examples, and are not intended to limit the present disclosure. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in independent claims representing the highest concept of the present invention will be described as optional constituent elements.

Each figure is a schematic diagram and is not necessarily strictly illustrated. In each figure, substantially the same structures are denoted by the same reference numerals, and overlapping descriptions are omitted or simplified.

FIG. 1 is a configuration diagram schematically showing the density sensor 100. As shown in FIG. The concentration sensor 100 has a resonator 10 and a circuit processing section 20 . The resonator 10 has a TEM mode waveguide configuration with a tube 11 and a conducting wire 12 disposed inside the tube 11 . The tube 11 has a through hole 13 arranged on its side surface. One end side of the conducting wire 12 is led out to the outside of the cylinder 11 through the through hole 13 . An insulator 14 is provided in the through hole 13 . Conducting wire 12 is fixed to tube 11 via insulator 14 .

The tube 11 is made of a conductor such as iron or stainless steel. Cylinder 11 is grounded when the concentration of fluid X is measured. An inner peripheral portion of the tube 11 serves as a flow path 15 for the fluid X to be inspected. The fluid X to be inspected is a liquid such as gasoline or a gas such as carbon dioxide.

The conducting wire 12 is made of a conductor such as copper or aluminum. The conducting wire 12 has an extending portion 12A extending in the extending direction of the tube 11 and a lead portion 12B led out through the through hole 13 to the outside.

The inductance component of resonator 10 is composed of the inductance component of conductor 12 . The capacitance component of the resonance circuit is composed of the electrostatic capacitance component generated when the conducting wire 12 and the tube 11 face each other. That is, the resonant frequency of the resonator 10 is determined by the length of the extended portion 12A and the dielectric constant of the fluid X. FIG. The dielectric constant of the fluid X changes according to the fluid X concentration. Therefore, the concentration sensor 100 can output a signal containing the concentration information of the fluid X by detecting the resonance frequency of the resonator 10 .

The circuit processing section 20 has two output ports 21 and 22 . FIG. 2 shows an equivalent circuit of the concentration sensor 100. As shown in FIG.

The circuit processing unit 20 includes a reference oscillator 23 , a frequency divider 24 , a phase comparator 25 , a low-pass filter 26 , a voltage controlled oscillator 27 , a frequency divider 28 and a detector 29 . The output port 21 is connected after the wave detector 29 . Output port 22 is connected between low pass filter 26 and voltage controlled oscillator 27 . A coil 36 is a choke coil, and a capacitor 37 is a bypass capacitor. A crystal oscillator, for example, can be used as the reference oscillator 23 . Frequency divider 24 is arranged after reference oscillator 23 . The phase comparator is arranged after the 25 frequency divider 24 . A low-pass filter 26 is connected after the phase comparator 25 . The voltage controlled oscillator 27 is connected after the low pass filter 26 . Frequency divider 28 is placed in feedback loop 30 from voltage controlled oscillator 27 to phase comparator 25 . A detector 29 is connected after the voltage controlled oscillator 27 .

The voltage controlled oscillator 27 has a variable capacitance diode 31 , an oscillator 32 and an amplifier 33 . The variable capacitance diode 31 has a cathode connected to the rear stage of the low-pass filter 26 and an anode grounded. The oscillator 32 is connected after the low pass filter 26 . Amplifier 33 is connected after oscillator 32 . A resonator 10 is connected between the cathode of the variable capacitance diode 31 and the oscillator 32 . Also, the capacitor 34 is a DC cut capacitor. A capacitor 35 is a capacitor for coupling.

In the circuit processing unit 20, the reference oscillator 23, the frequency divider 24, the phase comparator 25, the low-pass filter 26, the voltage controlled oscillator 27, and the frequency divider 28 form a phase-locked loop (hereinafter referred to as PLL). there is As a result, signals corresponding to changes in the resonance frequency of the resonator 10 are output from the output ports 21 and 22 . A signal containing conductivity information of the fluid X is output from the output port 21 . A signal containing information on the dielectric constant of the fluid X is output from the output port 22 .

The PLL functions to lock to a constant frequency as the resonance frequency of the resonator 10 changes. For example, when the dielectric constant of the fluid X decreases and the resonant frequency of the resonator 10 increases, the PLL adjusts the control voltage to the voltage controlled oscillator 27 so as to decrease the frequency. Specifically, the anode of the variable capacitance diode 31 is grounded. By adjusting the control voltage so as to increase the capacitance of the variable capacitance diode 31, the resonance frequency of the resonator 10 can be lowered. A change in this control voltage is reflected in the output signal of the output port 22 . In other words, the output signal from the output port 22 contains information on the dielectric constant of the fluid X. FIG.

Also, the output signal of voltage controlled oscillator 27 is determined by the excitation levels of oscillator 32 as well as amplifier 33 and resonator 10 . For example, when the conductivity of the fluid X increases, the Q value of the resonator 10 decreases. As the Q value of the resonator 10 decreases, the excitation level of the resonator 10 decreases and the output signal of the voltage controlled oscillator 27 decreases. As a result, the voltage of the output signal of detector 29 drops. A detector 29 converts the output signal of the voltage controlled oscillator 27 into a DC voltage signal. In other words, the information on the electrical conductivity of the fluid X is included in the output signal from the output port 21 connected after the detector.

As described above, the concentration sensor 100 outputs information about the dielectric constant and information about the conductivity of the fluid X according to changes in the concentration of the fluid X. FIG. Therefore, since the resistance component can be removed in detecting the concentration of the fluid, the detection accuracy of the concentration sensor can be improved.

Note that the resonator 10 has an open end at the leading end of the conducting wire 12 . In this case, since the resonator becomes a λ/2 type resonator, the Q value is increased. As a result, the detection accuracy of the density sensor is enhanced. In addition, since the conductor wire has a one-end support structure, it is easy to attach the conductor wire to the cylinder.

A modification of the resonator 10 is shown in FIG. In the resonator 40, the leading end of the lead wire 42 (the right end portion of the extending portion 12A in the drawing) is connected to the cylinder 41 at the connecting portion 41C. Since the cylinder 41 is grounded in the measurement stage, the resonator 40 becomes a λ/4 type resonator. The conducting wire 42 has a double end support structure in which both ends of the extending portion 41A are supported by the tube 41 by the supporting portion 42B and the connecting portion 42C. According to this structure, the conducting wire 42 can suppress external influences such as fluid flow and external vibration. Furthermore, resonator 40 is smaller than resonator 10 .

The concentration sensor of the present disclosure is particularly effective in internal combustion engine applications such as automobiles.

10, 40 resonator 11, 41 tube 12, 42 conducting wire 15 channel 20 circuit processing unit 23 reference oscillator 24, 28 frequency divider 25 phase comparator 26 low pass filter 27 voltage controlled oscillator,
29 detector 30 feedback loop 31 variable capacitance diode 32 oscillator 33 amplifier 21, 22 output port X fluid

Claims (3)

a cylinder whose interior constitutes a fluid flow path;
a conducting wire arranged inside the channel;
a circuit processing unit to which one end of the conducting wire is connected,
The circuit processing unit
a reference oscillator;
a first frequency divider connected after the reference oscillator;
a phase comparator connected after the first frequency divider;
a low-pass filter connected after the phase comparator;
a voltage controlled oscillator connected after the low-pass filter;
a second frequency divider placed in a feedback loop from the voltage controlled oscillator to the phase comparator;
a detector connected after the voltage controlled oscillator;
a first output port connected after the detector;
a second output port connected between the low pass filter and the voltage controlled oscillator;
The voltage controlled oscillator is
a variable capacitance diode whose anode is grounded and whose cathode is connected to the rear stage of the low-pass filter;
an oscillator connected after the low-pass filter;
an amplifier connected after the oscillator,
The cylinder and the conducting wire jointly form a resonator,
The concentration sensor, wherein the resonator is connected between the cathode of the variable capacitance diode and the oscillator. 2. The concentration sensor according to claim 1, wherein the other end of said conducting wire is connected to said tube. 2. The concentration sensor according to claim 1, wherein the other end of said conducting wire is an open end.

Images