JPH06222032A - Capacitive alcohol concentration measuring equipment - Google Patents

Abstract

PURPOSE:To detect capacitance of fluid highly accurately by eliminating the internal resistance contained in a signal detected by a capacitance sensor. CONSTITUTION:A bridge circuit 2 is constituted including a capacitance sensor 1 and connected, on the input side thereof, with an oscillation circuit 5 for applying an AC voltage E and a DC power supply 11 for applying a DC voltage V whereas connected, on the output side thereof, with an A-D converter 8 for converting AC into DC through a differential amplifying circuit 7 and an LPF 12 outputting DC. A detecting voltage VB detects only the capacitance C and a detecting voltage V2 detects internal resistance RC. Consequently, alcohol concentration can be detected while eliminating the internal resistance RC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type alcohol concentration measuring device suitably used for measuring the concentration of alcohol contained in a liquid such as alcohol-blended gasoline, fountain solution for a printing machine or the like.

[0002]

2. Description of the Related Art Here, a concentration detecting circuit as a capacitance type alcohol concentration measuring device according to a conventional technique is shown in FIG. 7 and explained.

In the figure, reference numeral 1 denotes an electrostatic capacitance type sensor serving as an electrostatic capacitance sensor. The electrostatic capacitance type sensor 1 is composed of parallel plate type or coaxial cylindrical type electrodes and the like, and alcohol is mixed between the electrodes. The fluid to be measured such as alcohol mixed gasoline is circulated, and the capacitance type sensor 1 detects the capacitance C of the fluid to be measured.

Reference numeral 2 denotes a bridge circuit, which is composed of reference resistors 3 and 3 having a resistance value R, a capacitance type sensor 1 and a compensation capacitor 4, and a connection point a of each reference resistor 3 will be described later. Is connected to the output side of the oscillation circuit 5 via a buffer 6, and the connection point b between the capacitance type sensor 1 and the compensation capacitor 4 is short-circuited to the ground. In addition, a connection point c between one reference resistor 3 and the compensation capacitor 4
A connection point d between the other reference resistor 3 and the capacitance type sensor 1 is connected to an input terminal of a differential amplifier circuit 7 described later. Then, the bridge circuit 2 is configured as an AC bridge circuit by applying the AC voltage E.

Reference numeral 5 denotes an oscillation circuit, which applies an AC voltage E having a frequency f (f = 1 MHz) from a connection point a of the bridge circuit 2 via a buffer 6.

Reference numeral 7 denotes a differential amplifier circuit which is composed of an operational amplifier and is connected to the latter stage of the bridge circuit 2, and the connection point c of the bridge circuit 2 is non-inverted at the inverting input terminal of the differential amplifier circuit 7. The connection points d of the bridge circuit 2 are connected to the input terminals, respectively, and when the balance of the bridge circuit 2 is lost, the difference is amplified by α times and output as the output voltage E0.

Reference numeral 8 denotes an AD converter as a conversion means for converting AC into DC. The AD converter 8 is connected to the output terminal of the differential amplifier circuit 7 and has an AC output voltage E.
0 is converted to DC output voltage VA.

Reference numeral 9 denotes an amplifier circuit, which is A-
It is connected to the output side of the D converter 8 and amplifies the DC output voltage VA from the AD converter 8 and outputs it as a detection voltage VB to an external control device or the like.

In the concentration detection circuit thus constructed, air (dielectric constant =
When 1) is present, the bridge circuit 2 is configured to maintain a balanced state.

Here, for example, when a fluid to be measured (for example, dampening water mixed with isopropyl alcohol (hereinafter referred to as "IPA" used in a printing machine)) flows between the electrodes of the capacitance type sensor 1. The capacitance sensor 1 detects the capacitance C corresponding to the concentration of IPA (that is, the relative permittivity), the balance of the bridge circuit 2 is disrupted in accordance with the detection signal, and this disruption is detected by the differential amplifier circuit 7 Is output as an output voltage E0 and is detected as a DC detection voltage VB via the AD converter 8 and the amplifier circuit 9. Since this detection voltage VB corresponds to the concentration of IPA, it can be easily detected. You can know the concentration.

[0011]

By the way, when tap water is used as the water in the dampening water, the shade water in the dampening water is used. The internal resistance RC as shown in FIG. 3 is detected by the capacitance type sensor 1.

Therefore, the connection points b and d of the bridge circuit 2 are
In between, the concentration of IPA detected by the capacitance type sensor 1,
Since the detection signals of the electrostatic capacitance C and the internal resistance RC due to the concentration of anions are output, the output voltage E0 output from the differential amplifier circuit 7 is not only the concentration change of IPA but also the concentration of anions. It also includes the amount of change due to.

Therefore, since the internal resistance RC changes due to the conductivity of the anions in the dampening water, not only the electrostatic capacitance C but also the internal resistance RC is involved in the detection signal from the electrostatic capacitance sensor 1. The value of the detection voltage VB output to the outside is an output due to changes in the electrostatic capacitance C and the internal resistance RC.

Therefore, the capacitance type alcohol concentration measuring device according to the prior art has a problem that the alcohol concentration cannot be accurately detected.

When this density measuring device is used to measure the IPA density in the dampening water of the printing machine, the density cannot be adjusted accurately and the printed matter cannot be finished neatly. There is.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention provides a capacitance type alcohol concentration measuring device capable of eliminating a detection error due to anions contained in a fluid to be measured. The purpose is to do.

[0017]

In order to solve the above-mentioned problems, a capacitance type alcohol concentration measuring apparatus adopted by the present invention determines the capacitance by the relative permittivity of a fluid to be measured in which alcohol is mixed. Capacitance detecting means for detecting, resistance detecting means for detecting a resistance value by the conductivity in the fluid to be measured, and resistance detecting means when the alcohol concentration and the conductivity of the known fluid to be measured are variable. Created based on each detection signal from the capacitance detection means,
Based on the detection signal from the resistance detection means for a storage means storing a plurality of characteristics in which the detection signal of the capacitance detection means with respect to the alcohol concentration is created for each detection signal of the resistance detection means, and an unknown fluid to be measured. And a selection unit for selecting one characteristic of the storage unit, and an alcohol concentration for calculating an alcohol concentration corresponding to the one characteristic selected by the selection unit based on a detection signal from the capacitance detection unit. It consists of an arithmetic means.

Further, the capacitance detecting means is formed by a pair of electrode plates, and a capacitance sensor in which a fluid to be measured flows between the electrode plates and an electrode plate of the capacitance sensor. The resistance detecting means is composed of an oscillating circuit for applying an AC voltage and a converting means for converting only an AC output of the output from the capacitance type sensor into a direct current, and the resistance detecting means is each electrode of the capacitance type sensor. A DC power supply for applying a DC voltage to the plate,
It is preferable that the electrostatic capacitance sensor is constituted by a DC voltage output means for outputting only a DC output.

[0019]

With the above structure, since the change in the resistance value due to the conductivity is constant regardless of the alcohol concentration, the capacitance detecting means for the alcohol concentration is based on the detection signal detected by the resistance detecting means by the selecting means. It is possible to calculate the alcohol concentration corresponding to this characteristic from the detection signal detected by the electrostatic capacitance detecting means by selecting the characteristic of the detection signal.

Further, the alternating voltage by the oscillation circuit and the direct current voltage by the direct current power source are superposed, the electrostatic capacity and the resistance output from the electrostatic capacity type sensor are detected, and the conversion means and the direct current voltage output means respectively detect them. The output signal corresponding to the electrostatic capacity and resistance can be detected.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

First, a concentration detection circuit of a capacitance type alcohol concentration measuring apparatus according to an embodiment of the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 11 denotes a DC power source, which is connected to the input side of the oscillation circuit 5 so that the DC voltage V is superimposed on the AC voltage E.

Reference numeral 12 denotes a low-pass filter (hereinafter referred to as "LPF12") as a DC voltage output means, which is L
The PF 12 is connected to the output side of the differential amplifier circuit 7 in a branched manner from the A / D converter 8 and has a cut-off frequency f0 (f0 = f0 =
It is set to be 1 kHz). And the L
The PF 12 outputs a DC output voltage V1 to an amplifier circuit 13, which will be described later, by passing a voltage of the cutoff frequency f0 or less in the output voltage E0. A smoothing circuit may be connected to the latter stage of the LPF 12.

Reference numeral 13 denotes an amplifier circuit, which has the same amplification factor as the amplifier circuit 9 connected to the output side of the A / D converter 8 and outputs a detection voltage V2 obtained by amplifying the DC output voltage V1. Output.

In the concentration detecting circuit thus constructed, as described in the prior art, the change in the capacitance C of the capacitance type sensor 1 is detected by the AC voltage E from the oscillating circuit 5 as the detection voltage VB. The operation of detecting as is similar to the conventional technique.

Further, the DC power source 1 added in this embodiment
1, a voltage of (AC voltage E + DC voltage V) is applied to the bridge circuit 2 by the LPF 12 and the amplifier circuit 13, and the differential amplifier circuit 7 changes the capacitance C and the internal resistance RC in the bridge circuit 2. Is output as an output voltage E0, and the output voltage E0 is output from the A / D converter 8 and L.
The AC component and the DC component are distinguished by the PF 12, and the detected voltages V are detected by the amplifier circuits 9 and 13 as the DC output voltages VA and V1, respectively.
It is output as B and V2.

The output voltage E0 output from the differential amplifier circuit 7 can be divided into an AC component E0 (AC) and a DC component E0 (DC) shown in the following equation 1.

[0029]

[Equation 1]

Further, in the concentration detecting circuit according to the present embodiment, the detecting circuit for the AC component (E0 (AC) of the equation 1) (that is,
Oscillation circuit 5, bridge circuit 2, differential amplifier circuit 7, A-D
The converter 8 and the amplifying circuit 9 become the AC impedance detecting means A, and the detecting circuit (that is, the DC power source 11, the bridge circuit 2, the differential amplifying circuit 7, the LPF 12 and the amplifying circuit) for the DC component (E0 (DC) of the equation 1). 13) becomes the DC resistance detecting means B. Further, the detection voltage VB by the AC impedance detection means A is the relative permittivity (capacitance C) in dampening water.
Detection signal by the DC resistance detection voltage V by the DC resistance detection means B
Reference numeral 2 shows a detection signal based on the conductivity (internal resistance RC) in the dampening water.

Next, the concentration measurement processing circuit of the electrostatic capacitance type alcohol concentration measuring device will be described with reference to FIGS.

In FIG. 2, reference numeral 14 denotes a control unit as a concentration measurement processing circuit, and the control unit 14 is made up of a microcomputer or the like and is generally composed of an input / output control circuit 15, a processing circuit 16 and a storage circuit 17. . Further, the input side of the input / output control circuit 15 is connected to the above-mentioned AC impedance detecting means A and DC resistance detecting means B via the respective amplifying circuits 9 and 13, and the detection voltages VB and V2 are inputted and output. IP on the side
A display 18 for displaying the A concentration is connected. Further, a detection processing program as shown in FIG. 6 which will be described later is built in the storage circuit 17, and characteristic data as shown in FIG. 5 is stored in the storage area 17A.

Based on the characteristic diagrams shown in FIGS. 3 and 4 and the characteristic data shown in FIG. 5, the detected voltage VB,
The relationship of V2 will be described.

First, tap water (including anions) and I
A large number of types of dampening water in which the mixing ratio of PA is 100% as a whole and the IPA and anion are changed at a known ratio are prepared. The AC impedance detecting means A,
Measured by the DC resistance detection means B, and detected voltage V
B, detection voltage V2 is obtained.

In the characteristic diagram shown in FIG. 3, I is plotted on the horizontal axis.
Based on the measurement results of a large number of types of dampening water measured by the DC resistance detection means B with the PA concentration and the detection voltage V2 on the vertical axis, characteristic lines L1, L2, L3, ...
x, ... Ln was obtained. Since the change in the resistance value of the internal resistance RC due to the anion in the dampening water is independent of the IPA concentration, the characteristic lines L1, L2, L3, ... Lx ,.
n is parallel to the horizontal axis.

In the characteristic diagram shown in FIG. 4, IP is plotted on the horizontal axis.
Based on the measurement results of a large number of types of dampening water measured by the AC impedance detection means A with the A concentration and the detection voltage VB on the vertical axis, characteristic lines LA, LB, L for each concentration of anion.
By obtaining C, ... L0, ... LN, a characteristic line peculiar to each concentration of each anion can be obtained.

The characteristic lines L1 to L shown in FIGS. 3 and 4 are used.
Of n, LA to LN, L1 and LA, L2 and LB, ...,
Since Ln and LN are the results of measuring the same dampening water,
Characteristic data as shown in FIG. 5 can be obtained. That is, since the characteristic lines L1, L2, L3, ... Ln detected by the DC resistance detecting means B do not depend on the IPA concentration in the characteristic data, if the voltage value v of the detection voltage V2 is detected,
One of the characteristic lines L1 to Ln can be determined. Since the characteristic lines L1 to Ln and the characteristic lines LA to LN correspond to each other on a one-to-one basis, if one of the characteristic lines L1 to Ln in FIG. 3 can be determined, the characteristic lines LA to LN in FIG. One of them can be confirmed. As shown in FIG. 5, this relationship is based on the voltage value v of the detected voltage V2 and the characteristic lines LA and LB shown in FIG.
, LC, ... LN (gradients α1, α2, α3 ... αn and intercepts β1, β2, β3 ... βn) have a one-to-one relationship. Further, this characteristic data is stored in the storage area 17A, and this characteristic data is a specific example of the storage means.

Next, a method of detecting the IPA concentration will be described with reference to FIG.

First, in step 1, the direct current resistance detecting means B reads the voltage value v0 as the detection voltage V2 which is the change in the electrical conductivity due to the anion in the dampening water.
In step 2, based on the characteristic data shown in FIG. 5, the slope α0 and the intercept β corresponding to the voltage value v0 of the detection voltage V2 are obtained.
0 (characteristic line L0) is selected and read.

In step 3, the AC impedance detecting means A reads the voltage value v0B as the detection voltage VB which changes the capacitance C due to the dielectric constant in the dampening water,
In step 4, the IPA concentration is calculated from the slope α0 and the intercept β0 read in step 2 as shown in the following equation 2.

[0041]

[Equation 2]

Then, in step 5, the IPA concentration (about 50% in FIG. 4) is displayed on the display unit 18.

Therefore, in the capacitance type alcohol concentration measuring apparatus according to the present embodiment, even when the fluid to be measured contains conductivity such as anion, as in the case of dampening water, the internal resistance RC causes The error can be removed, and the alcohol (IPA) concentration can be accurately detected.

Thus, according to the present embodiment, the AC circuit E and the DC voltage V are superposed and applied to the bridge circuit 2 including the capacitance type sensor 1 to provide a simple circuit configuration. The voltage VB is detected, and the change in the conductivity (anion) in the dampening water can be detected as the detection voltage V2 by the change in the DC voltage V.

Further, as shown in FIG. 3, the detected voltage V2 always shows a constant voltage value without depending on the IPA concentration even when the anion concentration is changed. Therefore, as shown in FIG. The IPA concentration can be easily detected by various processing operations. Moreover, whether or not the influence of conductivity of the dampening water due to anions is removed from this IPA concentration, or the IPA concentration can be accurately measured, and the IPA concentration of the dampening water can be adjusted appropriately, and the printed matter The finish can be done neatly.

Further, step 2 in the processing program shown in FIG. 6 in the above embodiment is a selection means for reading out one characteristic data (inclination α, intercept β) from the storage area 17A, and the operation in step 4 is the alcohol concentration calculation. Specific examples of the means are shown.

Further, in the above-mentioned embodiment, the electrostatic capacity type alcohol concentration measuring device is described as being used for measuring the IPA concentration in the dampening water of the printing machine. However, the present invention is not limited to this, and it is applicable to automobiles and the like. It may also be used to measure the alcohol concentration of alcohol-blended gasoline.

Further, in the above embodiment, the detection signals from the electrostatic capacitance detection means and the resistance detection means are converted into detection voltages VB,
Although V2 is used, the capacitance C and the internal resistance RC may be detected as the relative permittivity and the conductivity.

Furthermore, in the selection program of step 2 in the processing program of FIG. 6 according to the embodiment, one of the characteristic lines LA to LN is selected and the inclination α
However, the present invention is not limited to this, and the slope α and the intercept β may be calculated and calculated by an interpolation method or the like.

[0050]

As described above in detail, according to the present invention, the capacitance detecting means for detecting the capacitance of the fluid to be measured and the resistance detecting means for detecting the resistance value in the fluid to be measured are provided. , Selecting one characteristic of the storage means by the selection means based on the detection signal from the resistance detection means based on the storage means storing a plurality of characteristics and selecting the detection signal from the electrostatic capacitance detection means Since the alcohol concentration corresponding to one of the characteristics described above is detected by calculating with the alcohol concentration calculating means, even if the conductivity in the fluid to be measured changes, this change is removed to determine the alcohol concentration. Can be accurately detected.

The capacitance detecting means and the resistance detecting means apply an AC voltage and a DC voltage to a common capacitance type sensor, and the output from the capacitance type sensor is divided into an AC component and a DC component. Since the electrostatic capacity and the resistance can be detected by separately detecting the electrostatic capacity and the resistance, it is possible to separately detect the electrostatic capacity and the resistance with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a capacitance type alcohol concentration measuring device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control unit according to the present embodiment.

FIG. 3 is a characteristic diagram showing a detection voltage from a resistance detection unit with respect to alcohol (IPA) concentration.

FIG. 4 is a characteristic diagram showing a detection voltage from an electrostatic capacitance detection means with respect to alcohol (IPA) concentration.

5 is a diagram showing characteristic data created by FIGS. 3 and 4. FIG.

FIG. 6 is a flowchart showing an IPA concentration detection process.

FIG. 7 is a circuit configuration diagram of a capacitance type alcohol concentration measuring device according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitance type sensor 2 Bridge circuit 5 Oscillation circuit 8 A-D converter (Conversion means) 11 DC power supply 12 LPF (DC voltage output means) 14 Control unit 15 Input / output control circuit 16 Processing circuit 17 Storage circuit 17A Storage area VB , V2 detection voltage (detection signal)

Claims (2)

[Claims] 1. A capacitance detecting means for detecting a capacitance by the relative permittivity of a fluid to be measured mixed with alcohol, and a resistance detecting means for detecting a resistance value by the electrical conductivity of the fluid to be measured. When the known alcohol concentration and conductivity of the fluid to be measured are variable, it is created based on the respective detection signals from the resistance detection means and the capacitance detection means, and the capacitance detection means detects the alcohol concentration. Based on the detection signal from the resistance detection means for a storage means in which a plurality of characteristics are created for each detection signal of the resistance detection means and an unknown fluid to be measured, one characteristic of the storage means is stored. An alcohol concentration calculator for calculating the alcohol concentration corresponding to one characteristic selected by the selecting means based on the selecting means for selecting and the detection signal from the capacitance detecting means. Capacitance type alcohol concentration measuring device composed of steps. 2. The capacitance detecting means is formed by a pair of electrode plates, and a capacitance sensor in which a fluid to be measured flows between the electrode plates and an electrode plate of the capacitance sensor. The resistance detecting means is composed of an oscillating circuit for applying an AC voltage and a converting means for converting only an AC output of the output from the capacitance type sensor into a direct current, and the resistance detecting means is each electrode of the capacitance type sensor. 2. A capacitance type alcohol concentration according to claim 1, comprising a DC power source for applying a DC voltage to the plate, and a DC voltage output means for outputting only a DC output of the output from the capacitance type sensor. measuring device.