RU122777U1 - DEVICE FOR MEASURING ELECTRIC CONDUCTIVITY OF A LIQUID - Google Patents

Abstract

A device for measuring the electrical conductivity of a liquid, containing a sinusoidal voltage generator, a supply transformer with an excitation winding, a measuring transformer with a measuring winding, a closed loop from the test liquid, covering the cores of both transformers, characterized in that it includes a phase-sensitive zero-organ, additional compensation multisection windings , keys, a store of conductivity, a control circuit, moreover, a sinusoidal voltage generator is connected to the excitation winding of the supply transformer, a store of conductivity is connected to the sections of the compensation windings through the keys, to the input of which a control circuit is connected, which is connected to a phase-sensitive zero-element, to the input of which the measuring the instrument transformer winding and the sinusoidal voltage generator, and the keys connecting the conductivity store with the compensation winding sections are also connected to the control circuit.

Description

The utility model relates to the field of electrical measurements and can be used to measure the electrical conductivity of liquid media.

A device for measuring the electrical conductivity of a liquid, containing an AC voltage source, a supply transformer with an excitation winding, a measuring transformer with a measuring winding connected to the measuring circuit, a loop of electrically conductive material covering both transformer cores, a closed coil of electrically conductive liquid, a comparison circuit and an adder, moreover, the comparison circuit compares (subtracts) the excitation signal supplied to the exciting winding and the signal received from loops covering both cores, and the signal from the comparison output is summed on the adder, while the adder output is connected to the excitation winding [USSR Author's Certificate No. 1427272, cl. O01N 27/02, 1984].

In this device, there is an error associated with a change in the voltage of the generator, compensation of the dynamic error is possible only with certain transfer coefficients of the adder and the comparison circuit, which makes it difficult to regulate the voltage within the field winding within the necessary limits (for example, to set different sensitivity ranges).

The closest in technical essence to the proposed utility model is a conductometer consisting of a sinusoidal voltage generator, a supply transformer with an excitation winding, a measuring transformer with a measuring winding, a loop of electrically conductive material and a closed loop of the test fluid, covering the cores of both transformers, the first and second peak detectors, comparison circuits, voltage amplifier, measuring circuit, attenuator, power amplifier, reference source voltage and regulator, and the loop through the first peak detector, measuring circuit, regulator and attenuator is introduced into the generator feedback circuit, the supply transformer winding is connected to the generator through a power amplifier and attenuator, and the measuring transformer winding is connected to the measuring device through a voltage amplifier and a second peak detector [Author's certificate of the Russian Federation No. 2079851, cl. G01R 27/22].

The implementation of this device requires a particularly stable AC voltage regulator, which allows you to simultaneously maintain constant the amplitude, shape and frequency of the generated voltage. Changing one of these parameters leads to a distortion of the measurement results. For example, the variability of the amplitude of the generated voltage leads to the appearance of an error of the order of 5%. In addition, the change in the magnetic permeability of the transformer cores under the influence of temperature affects. Even if you select thermostable ferrite 2000НМ3, then a temperature change of 10 ° C will lead to a change in magnetic permeability of 2%, which affects the inductance of the windings, and therefore the measurement result.

The essence of the proposed utility model consists in the fact that a phase-sensitive zero-organ, additional compensation multi-sectional windings are introduced into the device containing a sinusoidal voltage generator, a supply transformer with an excitation winding, a measuring transformer with a measuring winding and a closed loop of the test fluid covering the cores of both transformers , keys, conductivity store and control circuit.

In this case, the generator is connected to the excitation winding of the supply transformer, the conductivity store is connected to the sections of the compensation windings through the keys, to the input of which a control circuit is connected, which is connected to a phase-sensitive zero-organ, to the input of which the measuring winding of the measuring transformer and the generator are connected. The keys connecting the conductivity store to sections of the compensation windings are also connected to the control circuit.

In general, the proposed utility model allows to increase accuracy, expand the limits of measurements, and also improve the dynamic properties of the device.

The essence of the utility model is illustrated in figure 1. A device for measuring the electrical conductivity of a liquid consists of a sinusoidal signal generator 1, an excitation winding 2, a supply transformer 3, a closed loop of an electrically conductive test fluid 4, a measuring transformer 5, a measuring winding 6, a phase-sensitive zero-organ 7, sections of the compensation windings 8, 9, 10 , 11, keys 12, 13, 14, 15, control circuits 16, conductivity store 17.

The device operates as follows. The voltage from the generator 1 is supplied to the excitation winding 2 of the supply transformer 3. In this case, an EMF is induced in the liquid coil 4 and the compensation winding. The EMF acting in the liquid coil 4 causes a current, the value of which depends on the electrical conductivity of the liquid and which induces a voltage in the measuring winding 6 of the measuring transformer 5. The EMF acting in the compensation winding causes a current whose value depends on the selected conductivity in the conductivity store. The liquid coil and the compensation winding are included so that the voltages induced in the measuring winding have different signs. As a result of the operation of the control circuit on the measuring winding, zero voltage is achieved. Using a control circuit, the phase-sensitive null organ changes the value of the conductivity magazine and the position of the keys until the voltage across the measuring winding is zero. The code generated by the control circuit, which is supplied to the store and to the keys, is an output signal that determines the conductivity of the liquid coil. Consider the operation of the device in the diagram (figure 2):

The system of equations describing the operation of the circuit

where U ₁ is the voltage of the power source;

U ₂ - voltage in the measuring winding of the measuring transformer;

I ₁ - current in the exciting winding of the supply transformer;

I _x - current in a liquid loop;

I _d is the current in the compensating winding;

L ₁ is the inductance of the exciting coil;

L _x is the inductance of the liquid loop;

L _d is the inductance of the compensating winding;

M ₁₂ is the mutual inductance of the exciting winding and the liquid coil;

M ₂₃ - mutual inductance of the measuring winding and the liquid coil;

M ₁₄ - mutual inductance of the exciting and compensating windings;

M ₃₄ - mutual inductance of the measuring and compensating windings;

R _x is the resistance of the liquid loop;

R _d is the resistance of the compensating winding;

ω is the frequency of harmonic sinusoidal oscillations.

Express the currents I _d and I _x equations (2) and (3):

at the moment when the output voltage U ₂ = 0, from equation (4) we obtain:

from here

From equations (5), (6), (8) we obtain the relationship between the resistances at the voltage across the measuring winding U ₂ = 0:

Replacing G _{x with} and G _d on where G _x , G _d is the conductivity of the liquid coil and the conductivity from the conductivity store, we obtain:

Given that << 1 and << 1, we can deduce the relationship between G _x and G _d :

in equation (12) M ₂₃ , M ₁₂ = M, since the exciting and measuring windings of the transformers have the same number of turns, and the liquid round is common for the supply and measuring transformers. The mutual inductance between the transformer winding (excitation or measuring) and the compensation coil is equal to the mutual inductance between the transformer winding and the liquid coil, since the inductance of the liquid coil and the compensation winding are equal, and the inductances of the measuring and exciting windings contain a constant number of turns. this implies

where N ₁ and N _{2 are the} number of turns in the additional windings connected via keys to the conductivity store. We get the equation

follows from it

Equation (16) explains the main advantage of this device - the absence of factors affecting the error of the device, such as amplitude, frequency, shape of the generated voltage and temperature of the transformers.

Based on equation (16), we can uniquely determine the conductivity of the liquid coil.

where σ _x is the electrical conductivity, k is the constant of the electrolytic cell.

As can be seen from formula (16), it is possible to achieve zero voltage on the winding not only by changing the conductivity of the store, but also by changing the number of turns of additional compensation windings. As you can see, the introduction of multi-sectional compensation windings allows you to expand the range of measurements of the electrical conductivity of the liquid.

The phase-sensitive null-organ determines the direction of the change in conductivity, which allows to improve the dynamic properties of the device, which is very important for measuring the conductivity in a fluid flow, where the conductivity can vary significantly and at high speed. The control circuit generates signals to control the conductivity store and the keys that connect the sections of the compensation windings to the conductivity store. At the output of the control circuit, a code is generated corresponding to the value of the store conductivity and the position of the keys. The control scheme allows you to automate the measurement process, which improves dynamic properties and extends the measurement range. The conductivity store allows you to change its conductivity over a wide range and is a working standard. Its qualities largely determine the metrological properties of the device. The keys controlled by the control circuit connect the conductivity store to sections of the compensation windings. Their presence allows to increase the limits of measurements. Multi-sectional windings allow you to expand the range of measurements of the electrical conductivity of liquid media.

Claims (1)

A device for measuring the electrical conductivity of a liquid, containing a sinusoidal voltage generator, a supply transformer with an excitation winding, a measuring transformer with a measuring winding, a closed loop of the test liquid, covering the cores of both transformers, characterized in that it includes a phase-sensitive zero-organ, additional compensation multi-section windings , keys, conductivity store, control circuit, moreover, the sinusoidal voltage generator is connected to the winding circuit of conductors, to the input of which a control circuit is connected, which is connected to a phase-sensitive zero-organ, the input of which is connected to the measuring winding of the measuring transformer and the sinusoidal voltage generator, and the keys connecting the conductivity store to the sections compensation windings are also connected to the control circuit.