RU2498284C1 - Comparator unit for measurement of sea water salinity - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: according to the invention, a comparator unit includes a primary temperature converter and a primary inductance transducer of electrical conductivity with input and output toroidal transformers, a feed generator of sine voltage, a transformer voltage divider, digital and analogue current compensators with a two-cycle balancing mode, an electronic unit connected to a computer, a thermostat of the electronic unit; with that, an inductance cell is placed in an active water thermostat with fixed temperature and has flow-type structure, in the inner cavity of which there arranged are primary converters of temperature and electric conductivity.

EFFECT: improvement of measurement accuracy of salinity and temperature of a sea water sample.

5 cl, 1 dwg

Description

The invention relates to the field of hydrophysical measurements and can be used as a working and reference means for measuring the salinity of sea water in accordance with the scale of practical salinity 1978 (ShPS-78) [1. GSSSD 77-84. Sea water .. Scale of practical salinity. - M., Gosstandart, 1986]

Known devices of the type of comparators for measuring the relative electrical conductivity of sea water by comparison with a reference sample of sea water, which is the international standard sample “normal” sea water, certified by the value of salinity 35 PES and the value of relative electrical conductivity K ₁₅ [2. Seawater Standards URL. http://www.osil.co.uk/Products.…. Date of treatment: 02/09/2012]. The basis of such comparators is the conductometric cell of the contact or non-contact principle of operation. For example, the salimeter is known [3. SOLEMER .. Patent RU 2365909 C2 dated 08/27/09 IPC G01N 27/22 (2006.01)], containing two contactless inductive cells, one of which contains a reference sample of “normal” sea water, and the other a test sample of water. Water salinity is determined by the ratio of the specific conductivities of the reference and studied water samples. To achieve high measurement accuracy, the device uses a code-voltage transformer, operating mode switches, amplifiers, a synchronous detector, and an indicating unit. The device provides improved measurement accuracy by increasing the conversion coefficients of inductive cells. The disadvantage of this device is the manual method for measuring the electrical conductivity of water samples by switching the modes of the transformer converter code-voltage, focusing on the readings of a dial indicator. Subsequent calculation of salinity by the ratio of the measured electrical conductivities, in accordance with ShPS-78, is also performed manually, which drastically reduces work productivity.

There is also a known method and device for measuring the relative electrical conductivity of sea water with an inductive type cell [4. METHOD AND DEVICE FOR MEASURING SPECIFIC ELECTRICAL CONDUCTIVITY OF SEA WATER Patent RU 2366937 C2 dated 10.09.2009 IPC G01N 27/06]. In this device, a high resolution of conductivity measurements of water is achieved by measuring the output signal of the cell in two cycles. In the first cycle, the main part of the signal is digitally measured by discrete balancing from a reference voltage divider. In the second cycle, the residual part of the signal is measured by analog balancing with the zero method, followed by converting the result to digital form. The final measurement result is obtained by summing the samples of the first and second cycles. To implement the two-cycle measurement method, this device contains a sinusoidal generator supplying an inductive cell, a transformer voltage divider, and an electronic circuit coupled to a computer.

The advantage of this method and device is its high resolution and automatic measurement mode through the use of a computer included in the product. The disadvantage of this device is the lack of measurement accuracy required for the reference comparator, due to the imperfection of the design of the device and in particular the inductive cell. The main disadvantage is the lack of thermal stabilization of the cell and insufficient mechanical rigidity of the cell body, which is manifested in the instability of its "geometric constant" during the life of the cell.

The closest technical solution to the claimed invention in terms of features is the model GM-2007 electro-salt meter, manufactured by the Safonovsky Gidrometpribor plant [4. State registry of measuring instruments. Electrosolemer 2007. No. 42444-09 of 08/10/2009]

The electric salt meter is designed to measure the relative electrical conductivity and temperature of seawater samples and calculate salinity in accordance with ShPS-78 from the measured values using the computer included in the electric salt meter. To carry out measurements, the electric salt meter must be calibrated with a “normal” sea water reference sample.

The composition of the electric salt meter includes the following nodes: a bulkless contactless inductive cell, a supplying sinusoidal voltage generator, a transformer voltage divider, an electronic circuit that implements a two-cycle measurement mode, a resistance thermometer that measures the temperature of the water sample in the cell and an electronic circuit thermostat.

According to the passport data, the error in measuring the salinity of this device is 0.005 practical units of salinity (PES), which is only 2 times less than the best foreign counterparts (for example, the Autosal-8400 device of the Canadian company Guildline

[5. "Autosal" Laboratory Salinometer - URL Autosal 8400 / manuals / Date of access: 9.02.2012].

The disadvantages of the GM-2007 electric salt meter, limiting the potential measurement accuracy, are, in particular:

- insufficient washing of the bulk cell, requiring repeated rinsing;

- insufficient rigidity of the cell made of transparent plastic;

- lack of temperature control of the water sample;

- not the optimal operating frequency of the toroidal transformers of the electronic circuit and inductive cell.

The present invention is to improve the accuracy of measuring the salinity of sea water to the level of world standards. This goal is achieved by improving the design of the prototype and optimizing the mode of operation of the inductive cell by selecting elements with optimal operating frequency.

The technical result is achieved by the fact that the inductive cell is placed in an active water thermostat with a fixed temperature and is made flow-through with inlet and outlet fittings, and primary converters of temperature and electrical conductivity are placed in its internal cavity. In addition, the following improvements are introduced into the inductive cell:

- the cell body is made of quartz glass or ceramic with a low temperature coefficient of expansion;

- the cell is supplemented by a heat exchanger connected to its inlet fitting and placed in the water thermostat along with the cell;

- two toroidal transformers of the inductive cell and transformers of the voltage divider are made on twisted tape cores made of permalloy or transformer steel, intended for use at low sound frequencies;

- windings of two transformers of the inductive cell are distributed around the entire perimeter of the tape cores with a uniform pitch regardless of the number of turns.

These improvements provide the claimed effect for the following reasons:

- the implementation of the inductive flow cell in comparison with the bulk type cell in the prototype provides quality control of washing from the remnants of the previous sample during the measurement process. As a result, the accuracy and reproducibility of measurements of salinity of seawater samples are increased;

- thermostating of the flow cell in a water thermostat, in comparison with the bulk cell in contact with the environment, eliminates the temperature and electrical conductivity gradients in the sample volume and thereby significantly increases the measurement accuracy;

- thermostating the cell at a temperature of 22 ° C with a stability of 0.02 ° C allows you to increase the accuracy of temperature measurement to the desired level of 0.001 ° C by reducing the measuring range;

- the manufacture of a cell body made of quartz glass or ceramic with a low temperature coefficient of expansion, as well as with greater mechanical rigidity compared to a plastic case, provides a multiple increase in the stability of the so-called "geometric constant" of the cell, which directly affects the accuracy of measuring the conductivity of the sample;

- complementing the design of the comparator with a heat exchanger, through which a water sample is pumped into the cell, accelerates the onset of temperature equilibrium of the sample with the temperature of the thermostat. As a result, labor productivity increases in the production of measurements;

- the execution of toroidal transformers of the primary converter of electrical conductivity on tape cores made of permalloy or transformer steel, instead of cores made of ferrite grade 6000NM, allows you to change the operating mode of the cell and switch to using the operating frequency of 250 Hz instead of the frequency of 8 kHz used in the prototype. This measure eliminates the influence of the so-called skin effect in the cell volume. The skin effect is manifested in the fact that when current flows through a conductor, the current density is unevenly distributed over the cross section of this conductor. The current density in the deep layers of the conductor is attenuated with respect to the current density on the surface. The current distribution over the cross section of the conductive channel depends on the electrical conductivity, current frequency, and the geometric dimensions of the cross section. The greater the electrical conductivity, the geometric dimensions of the cross section and the frequency of the current, the stronger the skin effect is manifested. In seawater, the skin effect is relatively weak due to low electrical conductivity. The thickness of the skin layer at a frequency of 10 kHz is 1.15 m, at a depth of which the current density decreases 2.7 times. As applied to a conductometric cell, the skin effect is manifested in the fact that its “geometric constant” changes depending on the salinity of the water. In a cell with a conducting channel diameter of 30 mm, at an operating frequency of 8 kHz, in the salinity range from 0 to 40 PES, the skin effect causes a nonlinearity of the calibration characteristic of about 0.1%.

At a low frequency of 250 Hz, the influence of the skin effect on the linearity of the characteristic can be neglected, therefore, in foreign reference installations (for example, the Autosal 8400 salinometer), this frequency is used

- The design of the cell with a uniform distribution of turns of the windings significantly reduces the parasitic effect of the input and output transformers on each other through an external magnetic field. It is known that a toroidal core with a winding does not have an external part of the magnetic field if the magnetic characteristics of the core are uniform along its length, and the winding is made with a uniform pitch along the entire perimeter. If the winding consists of only one or two turns, then resort to the use of a wiring method of winding with a parallel connection of turns.

In the proposed design of transformers, the homogeneity conditions are satisfied sufficiently, which virtually eliminates the mutual influence of transformers. In turn, this design allows you to simplify the design of the cell, eliminating dull electromagnetic screens on top of the windings. Recommended measures can almost completely eliminate the so-called “quadrature interference” and the additional measurement error caused by this interference.

Figure 1 shows a block diagram of a comparator for measuring salinity of sea water.

The device contains an inductive flow cell 1 with input and output fittings, primary converters of electrical conductivity 2 and temperature 3, located in the internal cavity of the inductive cell and connected to an electronic circuit that implements the measurement of the output signals of the primary converters and pairing with a computer, an active water thermostat 4, providing predetermined temperature stabilization, heat exchanger 5 connected to the inlet fitting of the cell and to the flow rate of the seawater sample 6, drain cup 7 connected to the outlet fitting of the cell.

The device operates as follows. A test sample of sea water or a reference standard sample from a supply tank 6 enters a 30 cm ³ cell 1 through a heat exchanger 5, in which the electrical conductivity and temperature of the test sample in the cell are measured using primary converters of electrical conductivity 2 and temperature 3 . From the measured temperature and relative electrical conductivity, the salinity of the sample is calculated using a computer. The water temperature in an active thermostat with a volume of 2 l is maintained at a predetermined level (22 ± 0.1) ° C with stability of ± 0.02 ° C. When passing through the heat exchanger, the water sample is brought to the temperature of the thermostat. A water sample enters the cell with a small but adjustable speed of the order of 0.5 cm ³ / s. The cell is filled within 1 minute. After filling the cell, water continues to flow, and its excess is slowly dropped into the drain cup 7 in the drip mode.

Before taking measurements, the comparator is calibrated using a standard solution of “normal” seawater.

The conductivity and temperature in the flow cell are measured continuously in automatic mode with a given cyclicity, for example 15 s.

The water temperature in the cell is measured by a primary temperature transducer with an accuracy of 0.001 ° C. Thermostating facilitates the task of accurate temperature measurement due to the narrow measuring range.

The salinity calculation result is read from the computer screen after a stable reading is established, which occurs within about two minutes at a sample pumping rate of 0.1 cm ³ / s.

After completing the salinity measurements of one sample, the cell is emptied into the drain cup by blowing air for a sufficient time necessary to remove its traces. Then the cell is filled with a new breakdown.

Claims (5)

1. A comparator for measuring the salinity of seawater samples by the relative electrical conductivity of sea water, comprising a primary temperature transducer and an inductive primary transducer of electrical conductivity with input and output toroidal transformers, a power supply for a sinusoidal voltage generator, a transformer voltage divider, digital and analog current compensators with a two-cycle balancing mode , an electronic unit coupled to a computer, an electronic unit thermostat characterizing I in that the inductive cell is placed in an active water bath with a fixed temperature, flow formed in the inner cavity of which has primary transducers temperature and electrical conductivity, 2. The comparator according to claim 1, characterized in that the cell body is made of quartz glass or ceramic with a low temperature coefficient of expansion. 3. The comparator according to claim 1, characterized in that the cell is supplemented by a heat exchanger connected to its inlet fitting and placed in a water thermostat with the cell. 4. The comparator according to claim 1, characterized in that the two toroidal transformers of the inductive cell and the voltage divider transformers are made on twisted tape cores made of permalloy or transformer steel, designed for use at low sound frequencies. 5. The comparator according to claim 1, characterized in that the windings of the two transformers of the inductive cell are distributed along the entire perimeter of the tape cores with a uniform pitch regardless of the number of turns.

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