JPS5830231Y2 - Pure water conductivity measuring device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an apparatus for measuring the conductivity of pure water, which has extremely low conductivity.

In water purification equipment that produces pure water with extremely low conductivity (0.05 to 0.5 μυ/cm) used in nuclear power plants, etc., there is a purification process and impurities from the vessel walls and tube walls through which the water flows. Since it is considered that the elution of

K=Ki+Ko...(1) Where, Ki: Electrical conductivity caused by elution of electrolyte from the vessel wall, tube wall, etc. of a pure water device Ko: Ideal pure water, i.e. vessel wall, tube wall, etc. The electrical conductivity of pure water under the assumption that there is no elution of electrolytes, etc., and the electrical conductivity of water has a positive temperature coefficient, and it is customary to calculate it as a value converted to a temperature of 25°C, so (1) The following equation is derived from the equation.

K25=Ki25+Ko25 (2) Kt
=Ki25 f (t) 10Ko 25 g (j)
``'' (3) Here, K 25 : Value Ki of the conductivity of pure water at 25°C
25: Ki value KO25 at 25°C: 25
Value of Ko at °C Kt: Value of K at arbitrary temperature t °C f(t): Function representing temperature characteristics of Ki g(t): Function representing temperature characteristics of Ko From equations (2) and (3) By eliminating K125, the following equation is obtained.

In equation (4), Ko25 is a known value, and f(
1) and g(t) are also known functions; f(t) is approximately 2% per 1°C, and g(t) is approximately 6% per 1°C.

Therefore, by measuring the value Kt of K at an arbitrary temperature t°C and applying the calculation of equation (4) to this, it is possible to obtain 25 as the conductivity of pure water in terms of 25°C.

The present invention was made based on the above study results, and has a simple configuration that automatically measures Kt and calculates equation (4), thereby quickly and accurately measuring the 25°C equivalent conductivity of pure water. The aim is to realize a measuring device that can determine the

The figure is a wiring diagram showing an embodiment of the present invention, where Sl is an AC constant voltage source, which is a commercial power source or a square wave voltage source whose amplitude can be easily stabilized.

S2 is a direct current constant voltage source, MC is a cell for measuring the conductivity of pure water to be measured, and includes an inflow/outflow pipe and an on/off valve thereof (none of which are shown) to allow the pure water to be measured to flow continuously into and out of the cell. In addition, a counter electrode for measuring conductivity is provided inside the cell.

A11 to A6 are operational amplifiers, R1, R3, R4, R
5, R7, R9, R13, and R17 are feedback resistors, R2
, R6, R8, RIO, R11, R12, R14, R1
5 and R16 are input resistances, C is a capacitor, Dl and D
2 is a diode, and O is an output terminal.

The feedback resistor R4 is a temperature-sensitive resistance element having negative temperature characteristics, such as a so-called thermistor, and is connected in series and parallel with the resistors R5 and R5 to form a temperature compensation circuit.

The input resistor R10 is also a temperature sensitive resistive element having a negative temperature characteristic, and is connected in series and parallel with the resistors R12 and R11 to form a temperature compensation circuit.

The temperature sensitive resistance elements R4 and R10 are conductivity measurement cells MC.
For example, it is provided as close as possible to the conductivity measurement cell MC so as to maintain the same temperature at all times.

Further, operational amplifier A3 constitutes a rectifier circuit together with diodes D1 and D2, resistors R6 and R7, and capacitor C, and operational amplifier A6 constitutes a rectifier circuit together with input resistors R14, R15, and R1.
6. Configure an adder circuit together with feedback resistor R17.

Now, the voltage of the power source S1 is El, the container constant of the conductivity measurement cell MC is C1, the resistance value of the pure water to be measured between the opposite electrodes for conductivity measurement built in this cell is rt, and the feedback resistance R
If the resistance values of input resistors R2 and R7 are rl and rl, respectively, the combined resistance value of the temperature compensation circuit consisting of feedback resistors R3, R4, and R5 is r3(t), and the resistance values of input resistors R2 and R6 are r2 and r6, respectively, The output voltage Eo3 of the rectifier circuit consisting of the operational amplifier A3, the diodes DI and D2, the resistors R6 and R7, and the capacitor C is as follows.

Next, the voltage of the power supply S2 is set to El, and the resistance values of the input resistance R8 and the feedback resistance R9 of the operational amplifier A4 are set to r8 and r9, respectively.
Then, the output voltage Eo4 of the operational amplifier A4 is as follows.

In addition, the input resistances RIO, R11 and R1 of the operational amplifier A5
2(7) When the combined resistance value is rlO(t) and the resistance value of the feedback resistor R13 is r13, the output voltage Eo5 of the operational amplifier A5 is as follows.

Furthermore, if the respective resistance values of the input resistors R14 to R16 and the feedback resistor R17 of the operational amplifier A6 are all selected to be equal, the output voltage of the operational amplifier A6, that is, the output voltage Eo of the output terminal O
is Eo=-(Eo3+Eo4+Eo5), and operational amplifier A3. The respective output voltages of A4 and A5 are added.

Substituting equations (5) to 7) into the above equation yields.

In the above equation, if we set each constant so that 25 can be calculated as the electrical conductivity at 25°C.

As is clear from the above description, the device of the present invention has a simple configuration and is capable of automatically, quickly and accurately measuring the 25° C. equivalent conductivity of pure water, and has a great practical effect.

[Brief explanation of drawings]

The figure is a wiring diagram showing an embodiment of the present invention, in which Sl: AC constant voltage source, S2: DC constant voltage source, MC: cell for measuring conductivity,
A1 to A6: operational amplifier, R1, R3, R4, R5
, R7, R9, R13 and R17: feedback resistance, R2, R
6, R8, R10, R11, R12, R14, R15 and R16: Human resistance, C: Capacitor, Dl and Dl
: Diode, O: Output terminal.

Claims (1)

[Scope of utility model registration request] The function representing the temperature characteristic of electrical conductivity in pure water in which electrolyte is dissolved is f(t), and the electrical conductivity at a temperature of 25°C of ideal pure water assuming no dissolution of electrolyte is Ko 2
5. If g(t) is a function representing the temperature characteristic of conductivity in the ideal pure water, then the first a second operational amplifier having an input/output characteristic of the reciprocal of the function f(t) and to which the output of the first operational amplifier is added; and a rectifier to which the output of the second operational amplifier is added. a circuit, a third operational amplifier to which a DC voltage is applied so as to obtain an output voltage proportional to 025 to the conductivity, and an input/output characteristic of the ratio of the function g(t) to the function f(t). and a fourth operational amplifier to which the output of the third operational amplifier is added, and an addition circuit to which the output of the rectifier circuit and the outputs of the third and fourth operational amplifiers are added. Pure water conductivity measuring device.