JPS61151474A - Apparatus for measuring solution conductivity - Google Patents

Abstract

PURPOSE:To make it possible to compensate the temp. in the measurement of conductivity, by receiving the detection coil opposed to an exciting coil in a hermetically closed case and providing the exciting coil AC signal applying means of an electromagnetic induction coil pair immersed in a solution to be measured and a temp. compensation means for compensating temp. by changing the amplitude of an AC signal. 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 L and the signal magnetically 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. The exciting coil L1 and detection coil L2 in an electromagnetic induction coil pair utilize an electromagnetic induction phenomena and, therefore, the direct contact with the solution thereof is not required. Because the compensation of temp. is performed to the AC signal applied to the exciting oil, the effect of external noise is not received.

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 the alternating current signal from the measuring alternating current power source AC is amplified by the N amplifier #A device A1 and applied to the measuring cell CE. The measurement cell GE is the 11th
As shown in the figure, two opposing electrodes T1. T2, and the solution to be measured flows in and out between these opposing electrodes T1, T2. When the conductivity of the solution to be measured differs, the resistance RX between the opposing electrodes varies. The AC outputs of measurement cells C and E are amplified by AC amplifier A2. The amplified AC signal is rectified by diode D 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.

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 buffer amplifier No. 1 through the counter electrode T1. of the measurement cell CE. When applying 1° to T2, the counter electrode T1.7
The 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.
is sent. 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 temperature compensation is performed by the thermistor Tt-(.

However, in such a conventional solution conductivity measuring device, the counter electrode T1. Since T2 directly contacts the solution to be measured, when measuring the conductivity of salt water, etc., the counter electrode T1. There was a problem that T2 was attacked by the solution and deteriorated.

In addition, in conventional solution conductivity measurement devices, temperature compensation is performed on the output side of the measurement cell, but because the signal level is low on the output side, it is easily affected by external noise, making it difficult to perform sufficient temperature compensation. Met.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to provide a solution conductivity measuring device that can perform appropriate temperature compensation without causing the measurement cell to deteriorate due to being corroded by the solution to be measured.

[Summary of the invention]

In order to achieve the above object, the solution conductivity measuring device according to the present invention has 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, and the electromagnetic induction coil. an alternating current signal applying means for applying an alternating current signal to a pair of excitation coils; a temperature detecting means for detecting the temperature of the solution to be measured; Temperature compensating means for temperature compensation by changing the amplitude of an alternating current signal; and measuring means for measuring the conductivity of the solution to be measured using a detection signal electromagnetically induced to the detection coil via the solution to be measured. It is characterized by:

[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. As shown in FIG. 2(a), the electromagnetic induction coil pair is composed of an excitation coil L1 and a detection coil L2 that face each other. When these coils L1 and 2 are immersed in the solution to be measured, the centers of the coils L1 and L2 are tightly coiled with the solution to form a shape X, as shown in FIG. 2(a).

Since the resistance RX of the liquid path coil L3 changes depending on the conductivity of the solution to be measured, 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 is measured, The conductivity of the solution to be measured can be measured from the amplitude value of this signal. Since the excitation coil L1 and the detection coil L2 in this Vit1 induction coil pair utilize electromagnetic induction phenomena, there is no need to directly touch the solution. Therefore, as shown in FIG. 2(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 OP1.

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 this operational amplifier OP2. The temperature detection element R1 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 [2] as much as possible.
It is desirable to be located near . With this configuration, the voltage at the output terminal (point B) 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 end of operational amplifier 50P3 (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 anode and cathode of the diode D2 are connected to point A and point B, respectively. If the resistors R6 and R7 are made equal, the 0 point and the B point will be DC signals with the same value but different signs. 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, and a voltage V! is applied to the detection coil L2. 1. AC amplify the induced detection signal. A resistor R9 is inserted between the negative input terminal and the output terminal of the operational amplifier OP5. Furthermore, the negative input terminal and the positive input terminal of the operational amplifier OP5 are connected to a grounded resistor R.
8, each connected to RIO.

The AC amplified detection signal is sent to the switch SWI.

SW2. SW3. It is detected by SW4. switch S
One end of W1 and SW2 is connected to the output end of 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. switch SW3
and SW4 are grounded at one end. The other end of switch SW3 is connected to point G, and the other end of switch SW4 is connected to one point. Switch SW1. SW2. SW3゜SW
4 is 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 is used as control φ1 for switches SW1 and SW3. The switches SW2 and SW4 are controlled by a control signal φ2 obtained by inverting the control signal φ1 by an inverter INV.

The signals detected by the switches SWI and SW2.8W3.8W4 are DC amplified by the 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 OP6. The positive input terminal of the operational amplifier OP6 is grounded and connected to an IC resistor R14, and the resistor R13 is inserted between the negative input terminal and the output terminal. The signal outputted from the output terminal of the operational amplifier OP6 is a signal for measuring 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 temperature (salinity) of seawater is measured.

First, the temperature compensation operation will be explained.

The relationship between the salinity and electrical conductivity of seawater changes depending on the temperature, as shown in FIG. Even if the salinity is the same, the conductivity increases as the temperature increases. If temperature compensation is not performed as in this embodiment, the output signal will increase as the temperature increases, 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 AC signal applied to the excitation coil L1 becomes smaller as the temperature rises. If an AC signal with a constant amplitude is applied to the excitation coil L1, the signal detected from the detection signal L2 increases as the temperature of the solution increases, but in this example, as the temperature increases, the excitation coil L
Since the amplitude of the signal applied to 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 detection signal at the point D of the detection coil L2 becomes smaller as shown in FIG. The amplitude of is 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 SW3 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, SW2.8W4, 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) and (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(g) 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 noise signals induced by the distributed capacitance between the excitation coil L1 and the detection coil 12, and it is also possible to completely block out noise signals that are not possible with diodes. It can also detect minute signals of 0.3V or less.

Next, a solution conductivity measuring device according to a second embodiment of the present invention is shown in FIG. The circuit for detecting the detection signal electromagnetically induced in the detection coil L2 is different from the first embodiment. That is, the detection signal induced in the detection coil L2 is AC amplified by an operational amplifier OP7 having a resistor R15 connected between the input and output terminals. The amplified AC signal is rectified and detected by diode D4.

The rectified signal is DC amplified by an operational amplifier OP8 with a resistor R16 connected between the input and output terminals, and an output signal is obtained.

Next, a solution conductivity measuring device according to a third embodiment of the present invention is shown in FIG. The detection signal electromagnetically induced in the detection coil is passed through the diode D5. D6. A DC signal that has been fully square-wave rectified by a diode bridge circuit consisting of D7 and D8 is measured by a DC ammeter AMP. Measurement signals can be obtained extremely easily. Note that the present invention can also be used to measure the conductivity of solutions other than seawater.

〔Effect of the invention〕

As described above, according to the present invention, highly accurate temperature compensation can be performed without the measurement cell being attacked by the solution to be measured and deteriorating.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a solution conductivity measuring device according to a first embodiment of the present invention, and FIGS. 2(a) and 2(b) are perspective views of a pair of electromagnetic induction coils used in the solution conductivity measuring device. The circuit diagram, Figures 3 to 6 are graphs for explaining the temperature compensation operation of the solution conductivity measuring device, and Figures 7 (a) to (g) show the detection operation of the solution S conductivity measuring device. A time chart for explanation, FIG. 8 is a circuit diagram of a solution conductivity measuring device according to a second embodiment of the present invention, and FIG. 9 is a circuit diagram of a solution conductivity measuring device according to a third embodiment of the present invention. Figure 10 is a circuit diagram of a conventional solution conductivity measuring device, and Figure 11 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. OPI~OP8... operational amplifier, R1-R17...
Resistance, -Rt...Temperature detection element, RX...Resistance of liquid path coil, C1-C4...Capacitor, Ll...Excitation coil, L2...Detection coil, UX...Liquid path coil , SW1 to SW4...switch, C81, C32...
...Sealed case. Figure 3] Degrees - Figure 5 0610°20@30' Temperature Figure 4 Figure 6

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. AC signal applying means; temperature detecting means for detecting the temperature of the solution to be measured; and temperature compensation by changing the amplitude of the AC signal applied by the AC signal applying means based on the detection signal of the temperature detecting means. and a measuring means for measuring the conductivity of the solution to be measured using a detection signal electromagnetically induced to the detection coil via the solution to be measured. Device.