JPS61151475A - Apparatus for measuring conductivity of solution - Google Patents

Abstract

PURPOSE:To make it possible to detect only an electromagnetically induced signal, by receiving the detection coil opposed to an exciting coil in a hermetically closed container and providing an AC signal applying means and a detection means to the electromagnetic induction pair immersed in a solution to be measured. CONSTITUTION:Because the resistance RX of a liquid channel coil X is changed by the conductivity of a solution to be measured, if an AC signal is applied to an exciting coil L1 and the signal electromagnetically induced to a detection coil L2 through a liquid channel coil LX is measured, the conductivity of the solution to be measured can be measured from the amplitude value of said AC signal. Because the exciting coil L1 and detection coil L2 in an electromagnetic induction coil pair utilize an electromagnetic induction phenomena, the direct contact with the solution of both coils are not required. Because the control signal of the exciting AC signal is detected, the noise signal between the exciting coil L1 and the detection coil L2 and be perfectly cut off.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a solution conductivity measuring device for measuring the conductivity of a solution to be measured.

[Prior art] A conventional solution conductivity measuring device is shown in FIG.

An alternating current power source is used as the measuring power source AC, and an alternating current signal from the measuring alternating current power source AC is amplified by a buffer amplifier A1 and applied to the measuring cell GE. As shown in FIG. 13, the measurement cell GE has two opposing electrodes T1. It has T2,
The solution to be measured is caused to flow in and out between these opposing electrodes T1.72. When the conductivity of the solution to be measured differs, the resistance RX between the opposing electrodes varies. The AC output of the measurement cell CE is amplified by an AC amplifier A2. The amplified AC signal is passed through diode D
It is rectified by and input to DC amplifier A3. A thermistor TH is connected to the DC amplifier A3 in parallel to the operational resistor R, thereby performing temperature compensation.

When a solution to be measured is placed in the measurement cell GE and the output voltage of the measurement AC power source AC is applied to the counter electrodes Tl, T2 of the measurement cell GE via the buffer amplifier A1, the counter electrodes T1. T2
An output signal corresponding to the resistance RX of the solution to be measured between the two is sent to the output terminal To via the AC amplifier A2 and the DC amplifier A3. The resistance RX varies depending on the conductivity of the solution to be measured, but also varies depending on the temperature of the solution to be measured, so the thermistor TH performs temperature compensation.

However, in such a conventional solution conductivity measurement device, the counter electrodes TI, T2 made of metal directly touch the solution to be measured, so when measuring the conductivity of salt water, etc., the counter electrodes T1. There was a problem that the blade 2 was attacked by the solution and deteriorated.

Furthermore, in the conventional solution conductivity measuring device, the counter electrode Tl is used to detect the output AC signal with a diode.

There has been a problem in that the signal induced in the counter electrode T2 due to the capacitance that inevitably exists between the two electrodes is also considered to be a signal due to the solution. In particular, when the resistance RX is large at low concentrations, errors and fluctuations increase, so there is a limit to its use at low concentrations.

(Object of the Invention) The present invention has been made in consideration of the above circumstances, and is a solution conductivity measurement device that can detect only the signal induced by the electric charge without the measurement cell being corroded by the solution to be measured and deteriorating. The purpose is to provide

(Summary of the Invention) In order to achieve the above object, a solution conductivity measuring device according to the present invention includes an excitation coil and a detection coil opposite to the excitation coil, and includes a pair of electromagnetic induction coils immersed in a solution to be measured. , an alternating current signal applying means for applying an alternating current signal to the excitation coil of the electromagnetic induction coil pair, and detecting the detection signal induced in the detection coil via the solution to be measured in synchronization with the alternating current signal. The method is characterized by comprising a detection means and a measurement means for measuring the electrical conductivity of the solution to be measured based on the output signal of the detection means.

[Embodiments of the invention]

The solution conductivity measuring device according to the first embodiment of the present invention is
As shown in the figure.

The solution conductivity measuring device according to this embodiment measures the conductivity of a solution using a pair of electromagnetic induction coils. The 11 induction coil pair is composed of an excitation coil L1 and a detection coil L2 that face each other, as shown in FIG. 2(a). These coils L1
When L2 and L2 are immersed in the solution to be measured, a solution coil LX passing through the center of the coils L1 and L2 is formed as shown in FIG. 2(a).

The resistance RX of the liquid path coil L3 changes depending on the conductivity of the solution to be measured, so if an AC signal is applied to the excitation coil L1 and the signal electromagnetically induced to the detection coil L2 via the liquid path coil LX is measured, this The conductivity of the solution to be measured can be measured from the amplitude value of the signal. The excitation coil L1 and the detection coil L2 in this electromagnetic induction coil pair utilize the electromagnetic induction phenomenon, so there is no need to directly touch the solution. Therefore, the second
As shown in Figure (a), each coil L1. L2 is placed in the sealed cases C31 and C82, and the coils L1. It is possible to prevent L2 from being attacked by the solution.

An alternating current signal to the excitation coil L1 is generated by an oscillation circuit composed of a solution amplifier OP1, a capacitor C1, and resistors R1, R2, R3°R4.

In this oscillation circuit, a grounded capacitor C1 is connected to the negative input terminal of the operational amplifier OP1, and a resistor R1 is connected between the negative input terminal and the output terminal.

Resistors R2 and R are connected in series between the output terminal and ground.
3 and R4 are inserted. The connection point between the resistor R3 and the resistor R4 is connected to the positive output terminal of the operational amplifier OPI.

This oscillation circuit is a connection point (point A) between resistor R2 and resistor R3.
Its amplitude changes depending on the voltage.

A diode D1 is connected to the output terminal of the operational amplifier OP1 to rectify the alternating current signal. The rectified signal is smoothed by capacitor C2. The smoothed DC signal is resistor R
5 and is applied to the operational amplifier OP2 and amplified.

A temperature detection element Rt is connected between the negative input terminal and the output terminal of the operational amplifier OP2. The temperature detection element Rt is an element whose resistance value changes depending on the temperature. This temperature detection element Rt is connected to the excitation coil L1 and the detection coil L2 as much as possible.
It is desirable to be located near . With this configuration, the voltage at the output ends (8 points) of the operational amplifier OP2 becomes a temperature-compensated negative DC signal.

A resistor R6 is connected to the output terminal of the operational amplifier OP2, and this resistor R6 is connected to the negative input terminal of the operational amplifier OP3. A resistor R7 is inserted between the output terminal and the negative input terminal of the operational amplifier OP3. Output terminal of operational amplifier OP3 (0 point)
The cathode of the diode D3 is connected to the point A, and the anode of the diode D3 is connected to the point A. A diode D2 is inserted between point A and point B. The anodes of diodes 1 and 2 are connected to point 'A, and the cathodes are connected to point B. If resistance R6 and resistance R7 are made equal, 0 point and B
The point is a DC signal with the same field but a different sign. Therefore, the absolute value of the voltage at point A is equal to the temperature-compensated voltage at point B, and the amplitude of the square wave oscillation circuit changes depending on the temperature.

An operational amplifier OP is installed in the detection coil L2 of the electromagnetic induction coil pair.
5 is connected to AC amplify the detection signal electromagnetically induced in the detection coil L2. A resistor R9 is inserted between the negative input terminal and the output terminal of the operational amplifier OP5. Further, the negative input terminal and the positive input terminal of the operational amplifier OP5 are connected to a grounded resistor R8,
Each is connected to R10.

The AC amplified detection signal is sent to switches SW1, SW2. S
W3. It is detected by SW4. Switch SW1 and SW
2 has one end connected to the output end of the operational amplifier OP5. The other end of the switch SW1 is connected to a point on one output line, and the other end of the switch SW2 is connected to a point G on the other output line. One ends of the switches SW3 and SW4 are grounded. The other end of switch SW3 is connected to point G, and the other end of switch SW4 is connected to one point. Switches SWI, SW2. SW3 and SW4 are turned on and off in synchronization with the AC signal applied to the excitation coil L1. That is, the AC signal applied to the excitation coil L1 is amplified by the operational amplifier OP4. The amplified signal,
Control φ1 for switches SW1 and SW3 is assumed. Switches SW2 and SW4 convert control signal φ1 to inverter INV.
It is controlled by a control signal φ2 inverted by .

Switch SW1. SW2. SW3. The signal applied by SW4 is DC amplified by operational amplifier OP6, and the differential output is converted into a single output. The signal at one point is smoothed by resistor R11 and capacitor C3,
It is input to the negative input terminal of operational amplifier OP6. The signal received at point G is smoothed by resistor R12 and capacitor C4, and is input to the positive input terminal of operational amplifier (1) P6. Operational amplification i1! ! : A grounded resistor R14 is connected to the positive input terminal of OP6, and a resistor R1 is connected between the negative input terminal and the output terminal.
3 has been inserted. The signal output from the output terminal of the operational amplifier OP6 is a measurement signal for the conductivity of the solution to be measured.

Next, the operation of the solution conductivity measuring device according to this embodiment will be described in more detail using an example in which the concentration (salinity) of seawater is measured.

First, the temperature compensation ta operation will be explained.

The relationship between the salinity of seawater and the electrical conductivity varies by 4 degrees as shown in FIG. Even if the salinity is the same, the conductivity increases as the temperature increases. If temperature compensation tm is not performed as in this embodiment, the output signal will become too large as the temperature rises, making it impossible to accurately measure salinity. For this reason, in this embodiment, temperature compensation is performed using the temperature detection element Rt.

As shown in FIG. 4, the resistance of the temperature detection element Rt has a characteristic that it decreases as the temperature rises. Therefore, if the temperature rises, the resistance Rt decreases, and therefore the amplification factor of the operational amplifier OP2 decreases. Then, the absolute value of the voltage at point B becomes smaller.

Since the voltages at point B and point A have the same absolute value, the voltage at point A becomes lower as shown in FIG. Then, the amplitude of the AC signal output from the generation circuit becomes smaller. That is, the amplitude of the alternating current signal applied to the excitation coil 1 becomes smaller as the temperature rises. If an alternating current signal with a constant amplitude is applied to the excitation coil L1, as the temperature of the solution rises, the detection signal and the signal detected from 2 will increase; however, in this embodiment, as the temperature rises, the signal added to the excitation coil L1 Since the amplitude of the detection signal at point D of the detection coil L2 becomes smaller, if the circuit constants of each resistor etc. are adjusted to offset the increase due to the temperature rise, the width of the detection signal at point D of the detection coil L2 becomes smaller as shown in Fig. 6. It remains constant regardless of temperature.

Next, the detection operation of the detection signal electromagnetically induced to the detection coil L2 via the solution to be measured will be described.

The detection signal of the detection coil L2 is an alternating current signal with a small amplitude, as shown in FIG. 7(a). This is the operational amplifier OP5
When AC amplification is performed, the result is as shown in FIG. 7(b).

- SW1 and 8W3 controlled by the force control signal φ1 are turned on when the potential at point E is positive, as shown in FIG. 7(C). Therefore, the voltage at point E remains at one point, and point G becomes OV. Conversely, sw2.3W4, which is controlled by the control signal φ2, turns on when the potential at point E is negative, as shown in FIG. 7(d). Therefore, the potential at one point is OV
Therefore, the potential at point G is the same as the potential at point E. Therefore, point 1 and point G are shown in Fig. 7(e), (f>
It becomes as shown in . By smoothing this and converting the differential output to a single output, a detected output signal as shown in FIG. 7 (CI) is obtained.

As described above, according to this embodiment, since temperature compensation is performed on the AC signal applied to the excitation coil, there is a sufficient signal level and there is no influence from external noise. In addition, since detection is performed using a switch that uses an excitation AC signal as a control signal instead of a diode, it is possible to completely block out noise signals induced by the distributed capacitance between the excitation coil L1 and the detection coil 2, which is impossible with a diode. Even minute signals of 0.3V or less can be detected.

The solution conductivity measuring device according to the second embodiment of the present invention is
As shown in the figure. The AC signal applied to the excitation coil L1 is directly applied from the AC signal source AC without temperature compensation. If the temperature of the solution to be measured is constant, the concentration of this solution can be measured correctly.

A ninth embodiment of the solution conductivity measurement device according to the third embodiment of the present invention
As shown in the figure. This embodiment differs from the first embodiment in that DC amplification by the operational amplifier OP6 is omitted. Furthermore, switches SW3 and S
One end of W4 is connected to the detection coil L2, and the other end is grounded. As a result, the signal that appears at one point is similar to a full-wave rectified waveform as shown in FIG. This full-wave rectified waveform is smoothed by capacitor C5 to obtain an output signal.

The solution conductivity measuring device according to the fourth embodiment of the present invention is
Shown in Figure 1. The operational amplifier OP6 for direct current amplification and the operational amplifier OP5 for alternating current amplification are also omitted.

Even if the signal is not amplified, the signal induced by the capacitance is not detected, and only the signal electromagnetically induced via the liquid path coil L3 is detected, so that sufficient accuracy can be obtained.

Alternatively, AC amplification of the detection signal may be omitted and only DC amplification may be performed.

Note that the present invention can also be used to measure the 2J electric rate of solutions other than seawater.

〔Effect of the invention〕

As described above, according to the present invention, the measurement cell is not corroded or deteriorated, and the measurement cell is not damaged or deteriorated. ! Only the induced signal can be detected, and therefore extremely accurate measurements can be made even at low solution temperatures.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a solution conductivity measuring device according to the first embodiment of the present invention, and FIGS. 2(a), (b) and f are perspective views of a pair of electromagnetic induction coils used in the solution conductivity measuring device. and circuit diagrams, Figures 3 to 6 [Graphs for explaining the temperature compensation operation of the same solution conductivity measuring device, Figures 7 (a) to (g)
) is a time chart for explaining the detection operation of the solution conductivity measuring device, FIG. 8 is a circuit diagram of the solution conductivity measuring device according to the second embodiment of the present invention, and FIG. 10 is a time chart for explaining the detection operation of the solution conductivity measuring device according to the fourth embodiment of the present invention. FIG. 11 is a circuit diagram of the solution conductivity measuring device according to the fourth embodiment of the present invention. Figure 12 is a circuit diagram of a conventional solution conductivity measuring device, and Figure 13 is a circuit diagram of a conventional solution conductivity measuring device.
Figures (a) and (b) are a perspective view and a circuit diagram of a measurement cell used in the solution conductivity measuring device. OP1 to OP8... operational amplifier, R1-R17...
Resistance, Rt...temperature detection element, RX...resistance of liquid path coil, 01-C4...condenser Isu, Ll...excitation coil, [2...detection coil, LX...liquid path coil, SW1 to SW4... switch, 081. C32・
...Sealed case. Applicant's agent Kiyoshi Inomata Figure 3 Figure 5 Figure 4 Turtle M6 Figure Exhibition Figure 9 Figure 10 Figure 11 Figure M 12, TH Figure 13

Claims (1)

[Claims] A pair of electromagnetic induction coils that includes an excitation coil and a detection coil opposite to the excitation coil, and is immersed in a solution to be measured, and an alternating current signal is applied to the excitation coil of the pair of electromagnetic induction coils. an alternating current signal applying means; a detection means for detecting a detection signal electromagnetically induced in the detection coil via the measuring solution in synchronization with the alternating current signal; 1. A solution conductivity measuring device comprising: a measuring means for measuring conductivity.