SU1659821A1 - Conductometer - Google Patents

Abstract

The invention relates to the field of measurement technology. The aim of the invention is to improve the measurement accuracy. The conductometer contains a transformer conductivity sensor with excitation and measurement transformers, an additional winding, the circuit of which includes an exemplary resistor connected in series with the key, a computing device and a control unit, the output of which is connected to the control inputs of the key and the computing device. The dielectric channel of the transformer sensor is made in the form of two coaxial tubes, the invention relates to information-measuring equipment and is designed to determine the electrical conductivity, which is used to judge the concentration of the liquid medium solution. The purpose of the invention is to improve the measurement accuracy. FIG. 1 shows the developed conductivity meter; in fig. 2 - transformer conductivity sensor. In case 1, an excitation transformer 2 is located, measuring the transformers in one case, at a distance from each other. The field transformers and metering transformers are on the same tube. At the outer ends of the tubes, the first and second hemispherical electrodes are located with the center at the point of intersection of the axis of the tubes with the planes of external cuts, and in the gap between the tubes there is a third hemispherical electrode with the center at the point of intersection of the axis of the tubes with the second plane of the cut off tube. the winding of the excitation transformer is connected to the generator, the winding of the measuring transformer is connected to the input of the analog-digital converter, the output of which is connected to the input of the computing device The third hemispherical electrode is connected to the common terminal of the switch, the other two terminals of which are connected to the first and second hemispherical electrodes, and the control input to the control unit. In order to ensure the performance of the conductometer in the fluid flow, the hemispherical electrodes are made of mesh 1 s. f-ly, 2 ill. Matrix 3, they are located on the first tube 4, the second tube 5 is coaxial with it. The first electrode 6 is located at the outer end of the first tube, and the second electrode 7 is at the outer end of the other tube. with planes of their external cuts. In the gap between the tubes there is a third hemispherical electrode 8 with a center at the point of intersection of the axis of the tubes with the second cut plane of the first, on which are located (/)

Description

transformers. Moreover, the winding of the excitation transformer 2 is connected to the generator 9, the windings of the measuring transformer 3 to the input of the analog-digital converter 10, the output of which is connected to the input of the computing device 11. The reference resistor 12 connected in series with the key 13, the second and the third, is connected to the additional winding circuit. Electrodes 6 and 7, respectively, are connected to a metallic open conductor through a switch 14. The control unit 15 ensures synchronized operation of the key, the switch and the analog-to-digital transducer.

The device conductivity of the liquid medium occurs in three cycles.

The control unit 15 provides synchronized operation of the key 13, the switch 14 and the analog-digital converter 10. The generator 9 provides a signal to the excitation transformer 2, which induces an emf in a water coil, and a signal proportional to the electrical conductivity of the water is removed from the measuring transformer 3. In the first measurement cycle, the control unit 15, by means of the synchronization signal, switches the key 13, and the switch 14 closes it on the electrode 7 (upper position). The electrical conductivity of the liquid column enclosed between the first and second electrodes 6 and 7 is measured. The measured signal is fed to the analog-to-digital converter 10, and the measured value in digital form is not supplied to the computing device 11, i.e. the following dependency is obtained1

Uz a + b + a, ki, (1)

where Oz is the measured voltage corresponding to the conductivity of the liquid column between the electrodes 6 and 7;

a and b are the coefficients of the conversion function of the entire measuring channel:

Ki is a coefficient depending on the cross sectional area of the dielectric channel and the distance between electrodes 6 and 7;

7 | - specific electrical conductivity of the liquid medium.

In the next cycle, the key 13 is closed by means of the control unit 15 and the switch 14 is closed to the second electrode 7 (upper position).

The electrical conductivity of the liquid column enclosed between the first and second electrodes 6 and 7 and the circuit with the reference resistor 12 and the key 13 is measured. The signal is similarly fed to the analog-to-digital converter 10, and then the computing device 11.

The following dependency is obtained

Ua a + b (Ki 01 + сгобр), (2) where U2 is the measured voltage corresponding to the total conductivity of the liquid column between the electrodes 6 and 7 and the circuit with the reference resistor 12 and the key 13;

7edr - exemplary conductivity, inversely proportional to the resistance of the model resistor 12 and the resistance of the key 13 connected in series.

In the last cycle, the switch 14 is closed to the electrode 9 (lower position), and the key 13 is open. We measure the electrical conductivity of a liquid column enclosed between electrodes b and 8. We obtain the following relationship:

Uza + b en G2

(3)

where U s is the measured voltage corresponding to the conductivity of the liquid column between the electrodes 6 and 8;

K2 coefficient depending on the cross-sectional area of the dielectric channel and the distance between electrodes 6 and 8. According to the obtained data, we determine the specific electrical conductivity of the liquid medium, expressed by the dependence

thirty

but

Ui -Uz Ki-K2 U2-Ui

It is clear from the last expression that the accuracy of measuring the specific electrical conductivity does not depend on the stability of the parameters of the electronic units: the generator, the analog-digital converter, but is determined only by the stability of the reference resistor 12 and the geometric constant Ki and K2.

When developing the design of a transformer sensor, one should take into account the error introduced by the capacity of the double layer at the interface of the electrode - liquid.

Given the magnitude of the error, you can determine the design parameters of the transformer sensor. For example, this can be done as follows.

0 way. Given the area of the electrodes 5el and knowing the specific capacitance of the double layer Court for the selected material of the electrodes, you can determine its impedance

52lt - 5elSud.

Coefficient 2 appears due to the effect of double layer capacitances on two electrodes.

Suppose, asking 5El 10 cm

i

the capacity of the double layer Court -20 microfarads / cm and a frequency of 10 kHz, we get Z 0.159 Ohms.

If you specify that the error due to the capacity of the double layer should not exceed 0.025%, then the resistance of the water column in the tube should not be less than Rb 636.6 Ohms. From here it is possible to determine the geometric constant, while taking the highest conductivity, for example 5.5 Sim / m:

where i is the length of the tube;

S is the area of the inner section.

So, with a tube length of 5 cm, the diameter of the internal cross section should be 3.9 mm. i

Claims (2)

1. A conductometer containing a transformer conductivity sensor with excitation and measurement transformers, an additional winding, the circuit of which includes an exemplary resistor connected in series with the key, a computing device and a control unit, the outputs of which are connected to the control inputs of the key, and a computing device differing from that, in order to improve measurement accuracy, The dielectric channel of the transformer sensor is made in the form of two coaxial tubes placed in one housing with a gap relative to each other; the excitation and measurement transformers are located on the same tube, with the first and second hemispherical electrodes with the center at the intersection point of the axis at the outer ends of the coaxial tubes. 10 tubes with planes of their external cuts, and in the gap between the tubes a third hemispherical electrode is placed with the center at the point of intersection of the axis of the tubes with the second cut plane of the tube, on which 15 transformers are located, the excitation transformer winding is connected to the generator, the measuring transformer winding is connected to the input of the analog-digital converter, the output 20 of which is connected to the input of the computing device, and the third hemispherical electrode is connected to the common terminal of the switch, the other two terminals of which are connected to the remaining first and second 25 to hemispherical electrodes, and a control input to the control unit, the output of the control unit is connected to the input of the analog-digital converter. 2. The conductivity meter according to claim 1, about 30 and 30 so as to ensure. work in the flow of fluid, spherical electrodes are made of mesh. one/ Fig 2