JPS6018943B2 - conductivity meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conductivity meter for measuring the conductivity of an aqueous solution containing impurities.

In this specification, "conductivity" is also used to refer to a certain resistivity as its reciprocal. In general, the conductivity G of an aqueous solution to be measured is calculated based on the ionization of pure water as shown in the following equation. and the impurities it contains (mainly salts)
It is expressed by the sum of the conductivity G2 due to ionization.

G=G, 10G2...
・'1) The conductivity G of the aqueous solution to be measured changes depending on the temperature, and exhibits temperature characteristics as shown in FIG.

Therefore, if the conductivity of the aqueous solution to be measured at the converted temperature tm, which generally indicates 25 zero, is Gm, the conductivity based on the ionization of water is G,m, and the conductivity due to the ionization of impurities is G2m, the formula {1} is as follows. It can be rewritten as G
m=G, m×G2m ・・・・・・
...■The conductivity G of the aqueous solution to be measured has the characteristic of showing different values depending on the temperature, as shown in Figure 2.
Conduction rate G at converted temperature (generally indicates 25qo)
It is expressed in terms of m.

At the time of this conversion, it is necessary to correct the temperature change in the conductivity G, but since this change is nonlinear, it is difficult to accurately correct it. By the way, if a is a coefficient indicating the ratio of the electrical conductivity G2 at a certain temperature t (≠tm) of the aqueous solution to be measured to the electrical conductivity G2m at the converted temperature tm, then a=conductivity.・・・．・・・． - side, so the conductivity ○2m becomes G2m = G2 hand ...---...'41.

From formulas [1}, '2) and [4}, the electrical conductivity Gm of the aqueous solution to be measured at the converted temperature daytime m is Gm=G(G-GI)+
Represented by GIm -...--[51.

Since the electrical conductivity G, m based on the ionization of water can be known in advance, when the first term on the right side of equation '5, which indicates the conductivity of impurities, is sufficiently larger than the second term, the electrical conductivity Gm is Gm=
Wife (G-GI) -...--'61.

Furthermore, if the conductivity ○, m based on the ionization of water is small enough to be ignored with respect to the conductivity G of the aqueous solution to be measured,
(6) The electrical conductivity Gm in equation (6) is approximately as follows: Gm=;G
...----It can be expressed as '7'.

This invention was made with attention to the points mentioned above.
A measured conductivity signal with a small temperature change rate is obtained by multiplying the measured aqueous solution by the reciprocal of a coefficient consisting of the ratio between the conductivity at an arbitrary temperature and a preset converted temperature of the measured aqueous solution containing ionizable impurities. and correcting the measured conductivity signal using the water conductivity signal multiplied by the reciprocal of the coefficient and at least one of the converted temperature and the conductivity of the water. An object of the present invention is to provide a conductivity meter that can accurately correct a conductivity signal over a wide temperature range.

Hereinafter, one embodiment of the present invention will be described in detail.

FIG. 1 is a circuit diagram of a conductivity meter shown as an embodiment of the present invention, and is constructed based on formula 5'. The detection cell D has a pair of electrodes immersed in the aqueous solution to be measured whose conductivity is to be measured, one electrode is connected to the AC power supply 1 and the other electrode is connected to the first input of the operational amplifier 2. be done.
The detection cell D has a constant K determined by the structure of the pair of electrodes.
has.

Now, rd is the resistance value of the detection cell D in the aqueous solution to be measured, G
When is the conductivity of the aqueous solution to be measured, the constant K is K rd ×
G......[Represented by 81. The operational amplifier 2 functions as a first operational circuit, has a first input connected to a temperature-sensitive resistor 4 to be described later, a second input grounded, and has a gain terminal.

However, G is the electrical conductivity of the aqueous solution to be measured, and a is the ratio of the electrical conductivity ○2 at a certain temperature t of the aqueous solution to be measured containing ions due to impurities to the number m of moths that can be converted into warm-up moths, as shown in equation 3. 'This is the coefficient. The output of the operational amplifier 2 is input to a synchronous rectifier circuit 3.

The synchronous rectifier circuit 3 may be of a known type, and has a configuration as shown in FIG. 3, for example. In FIG. 3, the field effect transistor Q, functions as a switch, and its drain is connected to the output terminal of the operational amplifier 2, and its source is connected to the resistor R4.
It is connected to the output end of the synchronous rectifier circuit 3 via the synchronous rectifier circuit 3, and its gate is connected to the signal source S.

The signal source S performs half-wave rectification of the AC voltage of the AC power source 1, that is, obtains a waveform of the positive period of the AC voltage, and further converts this waveform into a rectangular wave to generate pulses every 1800, and converts these pulses into an electric field. is applied to the gate of the effect transistor Q, turning it on or off. The field effect transistor Q2 has a drain connected to the first input of the operational amplifier 2, and a source connected to the field effect transistor Q. The gate is connected to the source of the signal source S2, and the gate is connected to the signal source S2. The signal source S2 has the same configuration as the signal source S, but outputs pulses of opposite polarity to the signal source S. A temperature sensitive resistor 4 is connected between the drain and source of the field effect transistor Q2. Temperature sensitive resistor 4
For example, a fixed resistor and a thermistor are connected in series or parallel, and the resistance value r4 at a certain temperature t and the converted temperature t
The ratio of its resistance value r to m: the sheep is selected to be equal to the coefficient a.

That is, a=sheep.・・・．・・・． Therefore, the output voltage 3 of the arithmetic circuit consisting of the operational amplifier 2, the synchronous rectifier circuit 3, and the temperature-sensitive resistor 4 is expressed as follows: the voltage of the AC power supply 1 is es, the resistance value of the detection cell D is rd, and the overflow-sensitive resistor If the resistance value of 4 is r4, then e3=-ki-r4
----------{10.

Therefore, (IQ formula is e
3=-eS-long-ki-r control......(11) The values of es, K, and r4m in equation (9) are the measurement range,
Since the detection cell D and the temperature-sensitive resistor 4 can take values specific to the detection cell D and the temperature-sensitive resistor 4, the equation (11) can be expressed as e3.

Equation (12) shows that by measuring e3, the electrical conductivity G2m at the converted warm-up m is found. Note that m, [2
}, {Using the 3' formula, the formula (12) becomes e3戊-KiG=
− Wife (G. 10G2) = − (G2m + Ashigoko.)……(1
3) When ○2m》G, e3 is -G2m...,. ,…(14
).

Returning to the explanation of FIG.

The output of the synchronous rectifier circuit 3 is connected to the operational amplifier 5 via a resistor R3.
is supplied to the first input of. On the other hand, the direct current e is connected to a first input of an operational amplifier 9 via a temperature-sensitive resistor 8, and its second input is grounded.

The output of the operational amplifier 9 is also connected to its first input via a resistor R, and to the first input of an operational amplifier 10 via a resistor R2 and a switch S. Here, the temperature-sensitive resistor 8 is constructed by connecting temperature-sensitive resistive elements such as a thermistor and a fixed resistor in series or in parallel, and its resistance value r8 is aG, m. ．． ．． ．． ．． ．． ．． ．． ．． (
15) Selected to satisfy r8=rtm・-a.

However, rtm is the resistance value of the thermistor at the converted temperature tm.

The operational amplifier 10 has a first input connected to a switch S and a resistor R.
2 to the three output terminals of the operational amplifier 9, and is connected to the DC power supply e2 via the switch S2 and resistor R3, the second input is grounded, and the output device is connected to the first input and the output terminal via the resistor R7. It is connected to the first input of the operational amplifier 5 via a resistor R6.

Here, the first signal generation circuit composed of a DC power supply e, a temperature-sensitive resistor 8, a resistor R, and an operational amplifier 9 has the following equation: If the output of the operational amplifier 9 is e3, then from equation (15), e3=
-e.・Black = -a magazine. ...(16) Since R, , r, and e in equation (16) are known constants, (16
) formula is e3 is - thing ・・・-・---・(1
7).

That is, when the switch S of the operational amplifier 9 is closed, the output e6 shown from the nose is inputted to the operational amplifier 101 via the resistor R2 and the switch S. Further, the DC power supply e2 functions as a second signal generation circuit, and the switch S
2 is closed, a signal indicated by G, m is input to the operational amplifier 10 via the resistor R3 and the switch S2.

Therefore, the signal is input through the operational amplifier 1, switch S, (or S2) and resistor R2 (or R3), and is inverted and amplified. . The operational amplifier 5 has a first input connected to one end of the resistors R5, R8 and R9, a second input connected to ground, an output end connected to the other end of the resistor R9, and an output terminal 7 via the indicator meter 6. Connected.

Output terminal 7 is connected to resistor R. grounded via o. In the measurement, for example, when both switches S and S2 are set to ON, the output of the operational amplifier 5 is calculated to satisfy the equation {5).

In addition, when the conductivity of impurities in the aqueous solution to be measured is high, only switch S can be turned on.
At this time, the output of the operational amplifier 5 satisfies equation (6).Furthermore, when the conductivity G and m of water can also be ignored, the switches S and S2 can be turned off; The output of the operational amplifier 5 is calculated to satisfy the formula '7-.In this way, the operational amplifier 5 functions as a function of the conductivity G of the aqueous solution to be measured as a second calculation circuit, and the output of the operational amplifier 5 is calculated as follows.
Through the credit resistance R5 indicated by G. Input the mata'ma (koto-G.m), kokotogari o'ko small signal through the resistor insect 8, and invert the sum of both, that is, {movement, '6
- or [7-] and supplies the signal indicated by Gm to the output terminal 7 via the indicator meter 6.

The signal at the output terminal 7 is a signal indicating the corrected conductivity of the aqueous solution to be measured. Note that it is known that the thermistors that form the basis of the temperature-sensitive resistors 4 and 8 are generally evaluated by a constant B, and are expressed by the following relational expression.

R=RoeXPB(壬-≠) ‐‐…‐‐‐‐(18
) However, B is the resistance value of the thermistor at temperature TK,
R. is the resistance value of the thermistor at temperature To. Therefore, the constant B is, and usually takes a value of about 300 to 400 blood dishes.

As described above, according to the present invention, since the measurement signal is multiplied by a coefficient and corrected so that the change in the conductivity signal becomes small with respect to temperature change, the aqueous solution to be measured is Even if the coefficient is large, it is possible to maintain high conductivity measurement accuracy over a wide temperature range, and the sensitive resistor used to obtain such a coefficient is easy to manufacture and its cost is low. , it can be an economical device.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conductivity meter according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the temperature characteristics of the conductivity of the liquid to be measured, and FIG. 3 is a circuit diagram of the synchronous rectifier circuit shown in FIG. 1. 1... AC power supply, 2, 5, 9, 10...
・Operation amplifier, 3...Synchronous rectifier circuit, 4, 8...
・Temperature-sensitive resistor, 6... Indication meter, D... Detection cell, e
,,e2'es...DC power supply. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 Detector D having a pair of electrodes to which a voltage is applied for measuring the conductivity by being immersed in an aqueous solution whose conductivity Gm is to be measured, and using the voltage passed through the electrodes as a detection signal G. and a first calculation in which the detection signal G is multiplied by a coefficient 1/a determined by the ratio between the conductivity of the object to be measured at a preset converted temperature tm and an arbitrary temperature t different from this converted temperature. Circuits 2, 3, 4 and the value obtained by multiplying the standard conductivity G_1 of pure water by the above coefficient (G_1
)/a, and a second signal generating circuit that generates a second correction signal corresponding to the conductivity G_1m of water in the measurement object at the converted temperature. A signal generation circuit e_2, a switch circuit S_1, S_2 that selects at least one of the first and second correction signals outputted from the first and second signal generation circuits, and an output signal of the first arithmetic circuit and the above. Second arithmetic circuit R_5, R_8, R_ which adds the output signal of the switch circuit
9 and 5, wherein the output signal of the second arithmetic circuit is used as a measurement signal indicating the conductivity of the object to be measured.