SU1346994A1 - Method of precision conductometric checking of liquid media - Google Patents

Abstract

The invention relates to chemical process control and can be used to solve a wide class of high frequency conductometric analysis of liquid media. The aim of the invention is to improve the measurement accuracy, which is achieved by adapting the use of measurement tools in the form of a capacitive conductometric cell with partial dielectric filling included in the frequency-generating circuit of the auto-oscillating measuring converter. The dielectric constant of the medium to be analyzed is preliminarily measured. The dielectric fill cell is established with a dielectric constant equal to the value found. The choice of the interelectrode distance is the operating point of the maximum steepness of the conversion characteristic where the measurement of the complex electrical resistance is made. 1 silt, (L: o 4; 35 x with 4:

Description

The invention relates to chemical process control and can be used for highly accurate conductometric analysis of liquid media in industrial and laboratory conditions.

The aim of the invention is to improve the measurement accuracy.

The drawing shows the construction of a capacitive cell, which is a primary conductometric transducer included in the frequency-generating circuit of an auto-oscillating measuring transducer,

The cell consists of two parallel p dielectric plates 1, a Moving device in the form of a stud 2 with precision thread and nuts 3 mounted on the plates I, on which electrodes 4 with partial dielectric filling in the form of plates 5 of the same size as . electrodes. Plates are removable. The resistors 6 are connected to the electrodes D and form a frequency-determining KS circuit.

The frequency w of the oscillator with a frequency homing circuit of this type is defined as

with 1, ()

R. C,

R ,, C.

chain resistance. Ohm; capacitance associated with an electric double layer formed at the interface between the phases of the dielectric — the medium under study, F.

The change in frequency over the entire range of the characteristic curve is expressed by the ratio

  -. (:

 R,

-i; (2)

where c

- capacitance associated with the dielectric constant of the medium being analyzed. Therefore, the measurement accuracy is greatest when the values of C and Cj are equal. For example, when measuring aqueous solutions of potassium chloride, adopted as standards in conductometry, in the range from 10 to 3 M solutions, its relative static dielectric constant changes accordingly from

69942

77.4 to 58.2; Therefore, by varying the dielectric capacitance of the plate 5 within these limits, the maximum value of the measurement accuracy is reached.

The method is carried out as follows.

The capacitance of the empty cell is measured, setting the initial (reference) value of the frequency of the measuring transducer,

The dielectric constant of the test compound is preliminarily measured.

ten

media p. From the working bank of dielectric plates choose the latter from the condition „„ “, fix them on the electrodes of the cell (dielectric permittivity of the cell).

I

The cell is immersed in the test medium, and the impedance of the cell changes, which leads to a change in the frequency at the output of the measuring transducer. The interelectrode distance is changed while simultaneously monitoring the frequency at the output of the transmitter and the slope of the conversion characteristic as a function of displacement. When the last maximum value is reached, the adjustment is stopped. This point corresponds to the maximum stability of the measured frequency values. At this point, the impedance is measured. Next, the concentration of the desired substance is determined from the previously obtained calibration dependence.

Claims (1)

Invention Formula The method of precision conductometric control of liquid media using a capacitive cell with partial dielectric filling included in the frequency-response circuit of an auto-oscillating measuring transducer, which consists in measuring the capacity of a cell without a liquid, installing a cell in the medium under study, measuring the complex resistance and determining the concentration of the desired substance from the previously obtained with a calibration curve, so that, in order to improve accuracy, the dielectric constant of the test medium is preliminarily measured, the dielectric filling of the cell is chosen equal to the dielectric constant of the medium, after the cell is placed in the test medium, the electrode the distance, the slope of the conversion characteristic, and the impedance measurement at the point of maximum slope.