The method of determining the level of liquid media and device for its implementation

 

(57) Abstract:

The essence of the invention: control object placed thermoresistive Converter in the form of three series-connected resistive sensing elements (SE) measurement and compensation, of different length and with different resistances. Measure the voltage drop across re, whose values are used to calculate the desired value level. Previously in the same conditions of heat transfer for all SE determine the normalizing coefficients, which eliminates calibration. Thermoresistive the Converter is implemented in the form of cables with mineral insulation. Current and potential conclusions SE form with them a U-shaped electrical branch with a loop-like arrangement of the conductors in the connection. thermocouple is connected to the measuring circuit. 2 S. p. f-crystals, 1 Il.

The invention relates to measuring technique and can be used for level measurement of liquids in chemical, power, metallurgical and other industries.

A known method of measuring the liquid level thermal sensor that uses the difference in conditions of heat exchange between podogrevaemyj are converters with resistive sensors. At the same time to reduce the influence of measurement conditions (medium, pressure, temperature) on the readings of the sensor is also sensitive measuring element, use one or two helper.

In the known method level value is calculated by the ratio of the two difference signals determined by the resistances of the two auxiliary and sensitive measuring elements, all three thermoresistive element have equal resistance and flow the same current.

To implement the method requires the equality of all three sensing elements, which requires them to customize and create a measuring transducer or three times longer than the measurement range, or very complex designs.

Closest to the claimed method according to technical essence is a way of determining the level of liquid media, including accommodation in the testing object thermoresistive Converter in the form of three series-connected resistive sensing elements measuring and compensation, of different length and with different resistances in different conditions of heat transfer and the measurement of the fall is fast device, containing thermoresistive Converter with three sensors connected with their current and potential conclusions respectively to the power unit and computing unit (2).

The disadvantage of this method is the need to pregraduate sensor when changing from one liquid medium to another, or when the difference of the physical properties of the resistive elements of gauges of different parties.

A disadvantage of the known device is that you cannot use for a variety of liquids in a wide range of temperatures and pressures.

The technical result produced by the invention is to improve accuracy in the measurement of any liquid medium in a wide range of temperatures and pressures.

This result is achieved in that in the known method pre-measure the voltage drop Uè0U10U20on the sensitive elements in the same conditions of heat transfer, determine the correction coefficients Kand, K1, K2as the ratio of the voltage drop across any of the sensing elements to the voltage drop across the corresponding sensitive element, and the value of urosticte specified result in the known device for determining the level of liquid media sensitive resistive elements are placed within the cable mineral insulated metal sheath, hermetically closed at one end, current and potential conclusions sensitive elements withdrawn from the sheath of the cable with its other end with the formation together with sensors installed along the cable, U-shaped electrical branch contacts which, in the points of connection of all conductors, formed by the loops of the latter.

The drawing schematically shows a device for determining the level.

The device comprises a cable thermoresistive level Converter comprising a sealed metal shell 1 is made of stainless steel, the current findings 2, potential findings 3, compacted electrically insulating and thermally conductive powder 4 from magnesium oxide, sensitive measuring element (SE) 5, compensatory SE 6, 7 of the single core conductor, made for example from alumel or Nickel. To ensure high reliability of cable thermocouple level during operation all communication between the SE and outputs generated by loop-like arrangement of conductors. The end of the transducer immersed in the measuring environment, hermetically sealed, and current and potential findings go in the same direction, forming a U-shaped electric is Artie not shown).

The measuring circuit consists of power supply, switch, ADC and computing unit indicator.

Resistance measurement and compensation (SE) are determined by the particular dimensions of the measurement objects and measurement range of the level.

To determine the level carry out the normalization of the signals of the three SE in the same conditions of heat exchange, for which cable thermocouple placed horizontally in the water, air, oil, etc. thus determine the relationship of the voltage drop across each of the three SE on any of these voltage drops, taken as a measure for rationing, for example, compensatory SE 7, always in fluid U20. Then normalizing (correction) coefficients are equal to, respectively:

< / BR>
In computing the block all signals from the measuring SE 5 are multiplied by the Kandand with compensatory SE 6, which is located in the gas (vapor phase) - K1, K21.

Normalization eliminates the influence on the measurement results of the differences in the length, cross-section and the resistance of the sensitive element, which take place in the manufacture of the level Converter.

Further, in the computing unit is CC>1U2Uandthe current values of the voltage drop across the compensating and measuring SE.

Of the invention allow the measurement level for almost any object and the measurement conditions, without prior calibration.

Cable run resistive thermal Converter allows to obtain a monolithic structure, small size (diameter 5-7 mm), tough enough to withstand high pressures (up to 40 MPa), and flexible enough to be located in almost any object made of materials capable of operating at temperatures from -200 to +1000oC.

The use of compressed powdered material with high thermal conductivity between the SE and the protective sheath and the small size of thermocouple can significantly reduce thermal resistance between the SE and the medium, and this allows to increase the temperature difference between the parts of the measuring sensitive element located in the liquid and in the gas, and consequently to improve the accuracy and robustness. In addition, the small size and good thermal conductivity between the SE and the medium improves the dynamic properties of the Converter.

Accommodation all vintagee hole.

1. The method of determining the level of liquid media, including accommodation in the testing object thermoresistive Converter in the form of three series-connected resistive sensing elements measuring and compensation, of different length and with different resistances, and measuring the voltage drop UandU1U2on the sensitive items in different conditions of heat exchange, wherein the pre-measure the voltage drop Uand0U10U20on the sensitive elements in the same conditions of heat transfer, determine the correction coefficients Kand, K1, K2as the ratio of the voltage drop across any of the sensing elements to the voltage drop across the corresponding sensitive element, and the level value determined by the formula

< / BR>
where L is the length measuring sensor element.

2. Device for determining the level of liquid media containing thermoresistive Converter in the form of three resistive sensing elements of different lengths and different resistance compensation and placed between the measuring connected in series and podkluchitsa fact, that sensitive resistive elements are placed within the cable mineral insulated metal sheath which is sealed at one end, current and potential conclusions sensitive elements withdrawn from the sheath of the cable with its other end with the formation together with sensors installed along the cable, U-shaped electrical branch, the contacts of which are at the points of connection of all conductors are formed by loops of the latter.

 

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