RU2653165C2 - Method of contact temperature sensor shells temperature and thermal inertia measuring and device for its implementation - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measuring equipment and is intended for use in oceanography. Claimed is a method of contact temperature sensor shells temperature and thermal inertia measuring. For this, three sensors are used, consisting of sensitive elements with different thermal inertia parameters, placed into external shells with the same thermal factor values and internal heat-conducting medium with different thermal inertia parameters. Based on the of sensor sensing elements θ_t1, θ_t2 and θ_t3 current temperature determining the medium θ_tc current temperature, thermal inertia current parameter of the sensors ε_t3 outer shell, sensitive elements ε₁₁, ε₂₁ and ε₃₁, inner shells ε₁₂, ε₂₂ and ε₃₂ using solutions x_j

of linear algebraic equations system of the form of

,

,N≥18, where a _tj and C_t are coefficients, calculated from N values of the θ_t1, θ_t2 and θ_t3 current temperatures and derivatives thereof up to the third one.

EFFECT: technical result is an increase in the dynamic temperature measurements accuracy and metrological durability by determining the sensitive elements and sensor shells thermal inertia parameters in the operating mode.

2 cl, 2 dwg

Description

The invention relates to measuring technique, is intended for use in oceanography and can be used for accurate measurement of non-stationary temperatures and physical parameters of the medium, affecting the heat exchange of sensors with the medium.

Known methods G. Pfrim and their development for measuring the dynamic temperature and heat transfer coefficient of the sensor with the environment using two different in dynamic parameters of the sensors, equivalent to the inertial links of the first and second order [N. Yaryshev Theoretical basis for measuring unsteady temperature. - 2nd ed., Revised. - L .: Energoatomizdat. Leningra. Otdel., 1990 .-- 256 p.: ill. ISBN 5-283-04474-2].

However, the practical implementation of these methods is difficult due to the need to know the design parameters of the sensors that determine their inertial parameters. Identification of these parameters is difficult and not possible in known methods. This limits the accuracy of dynamic measurements and metrological durability.

Real sensors contain a sensitive element placed in a protective shell filled with a heat-conducting filler. The model of such sensors is the sequential inclusion of three inertial links of the first order.

The aim of the invention is to increase the accuracy of dynamic measurements of temperature and metrological durability by determining the thermal inertia of the sensitive elements and shells of the sensor in the operating mode.

This goal is achieved by using three sensors, consisting of sensitive elements with different thermal inertia indices and placed in external shells with the same values of the thermal factor and internal heat-conducting medium (filler) with different thermal inertia indices, and placing the sensors in the measuring medium with the same conditions flow around the flow to ensure equality of the coefficients of convective heat transfer of the outer shells of the sensors with the medium, simultaneously measure the current sensing temperatures integral elements of the sensors θ _t1 , θ _t2 and θ _t3 , determine the current medium temperature θ _tc by the formula

,

,

current indicator of thermal inertia of the outer shell of the sensors ε _t3 according to the formula

,

,

thermal inertia indicators of internal sensitive elements of sensors

,the first

,

,second

,

,third

,

indicators of thermal inertia of the inner shells (fillers) of the sensors

the first ε _l2 = x ₁ -ε ₁₁ ,

second ε ₂₂ = x ₃ -ε ₂₁ ,

third ε ₃₂ = x ₅ -ε ₃₁ ,

,Where

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из решения системы линейных алгебраических уравнений видаx _j

from solving a system of linear algebraic equations of the form

,

, N≥18,

,

, N≥18,

,Where

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.

The construction of a temperature sensor with three sensing elements is shown in FIG. 1. A block diagram of a temperature measuring device and a thermal inertia index of sensor shells is shown in FIG. 2.

Consider the essence of the proposed method. We write the heat balance equation for a passive sensor having two shells around the sensing element (SE) and three heat exchange surfaces, in terms of thermal inertia of these surfaces. This equation will be the 3rd order inertial link.

For the inertial link of the first order corresponding to the SE of the sensor without a shell, it is known [N. Yaryshev Theoretical basis for measuring unsteady temperature. - 2nd ed., Revised. - L .: Energoatomizdat. Leningra. Otdel., 1990 .-- 256 p.: ill. ISBN 5-283-04474-2] equation

where θ _tc is the current temperature of the external environment, as the first shell of the SE;

θ _t1 is the current temperature of the SE;

, где m₁ - масса ЧЭ; c₁ - удельная теплоемкость;ε _t1 is the indicator of thermal inertia of the SE, depends on time, since it depends on the variable heat transfer coefficient α _{t1 of the} SE with the medium, and

where m ₁ - mass of SE; c ₁ - specific heat;

является консервативным конструктивным параметром, иногда называемым тепловым фактором [Азизов A.M., Гордов А.Н. Точность измерительных преобразователей. - Л.: Энергия, 1974. - 256 с]. Его нельзя определить экспериментально, в отличии от показателя термической инерции ε_t1.S ₁ is the surface area of the contact of the CE with the medium. Value

is a conservative design parameter, sometimes called a thermal factor [Azizov AM, A. Gordov Precision measuring transducers. - L .: Energy, 1974. - 256 s]. It cannot be determined experimentally, in contrast to the thermal inertia index ε _t1 .

When a SE is placed in a certain first shell (in our case, a filler with a thermal inertia index ε _t2 ), which takes the place of the external medium in temperature θ _t2 , and the external temperature θ _tc is counted from the temperature θ _t3 and instead of formula (1) we can write

Moreover, from the formula (1)

taking into account the replacement of ε _t1 by ε ₁ , since the thermal inertia index ε ₁ SE has become internal conservative due to the quasi-constancy of the heat transfer coefficient α _t1 → α ₁ SE with the first shell.

We differentiate expression (3) and find

в выражение (2) и получимWe substitute the expressions for θ _t2 and

into expression (2) and get

We place the SE in the first shell from the filler into the second shell (tube) with the thermal inertia index ε _t3 and temperature θ _t3 .

For the ambient temperature θ _t4 = θ _tc, by analogy with expressions (2-4), we write

In expression (8), the thermal inertia indices of the SE ε ₁ and filler ε ₂ are conservative and can be considered constant over a certain period of time; the thermal inertia index of the outer shell ε _t3 changes over time due to the variability of heat transfer coefficient α _t3 with the external environment and is subject to definition in the current time. We write expression (8), highlighting the unknowns θ _tc and ε _t3

To achieve this goal, we use three sensors in which the indices ε _t3 coincide, and the indices ε ₁ and ε ₂ differ. Denote them by ε ₁₁ , ε ₁₂ , ε ₂₁ , ε ₂₂ , ε ₃₁ , ε ₃₂ .

We denote the quantities calculated from the measurements

for ε _i1 + ε _i2 = b _i1 , ε _i1 ε _i2 = b _i2 .

- номер датчика.

- sensor number.

For three sensors, we obtain a system of equations for the unknown θ _tc and ε _t3

The first and second equations from system (12) give an expanded matrix of the form

and first values for unknowns

The first and third equations from system (12) give an expanded matrix of the form

and second values for unknowns

These pairs of unknown values for the same time moment in the absence of errors in measuring the temperature of the SE and determining their derivatives should coincide. Since the indicated errors always occur, there will be no coincidence and it is advisable to take the average of the two values obtained above for the estimates of the unknown

и

To find the thermal inertia indicators of the internal shells of the sensors after manufacturing or in the operating mode, we equate the expressions for

and

Substituting the expressions for A _t1 , A _t2 , A _t3 and C _t1 , C _t2 , C _t3 in (21) we obtain

Using time samples, we form a system of linear algebraic equations, for which we open the brackets, give similar ones, group the unknowns and their coefficients, introduce notation for new unknowns

For coefficients with unknowns, we obtain

. Получили систему линейных алгебраических уравнений видаFor free members we write

. Got a system of linear algebraic equations of the form

, остальные неизвестные x_j являются избыточными, но могут вычисляться для контроля правильности решений.Of interest are the first six unknowns x _i

, the remaining unknown x _j are redundant, but can be calculated to verify the correctness of the solutions.

получимAfter finding x _i

we get

In the second expression we substitute ε ₁₂ = x ₁ -ε ₁₁ and we obtain

By analogy, we get

Thus, the proposed method allows to measure without dynamic error the current medium temperature θ _tc , common for three sensors current indicator of thermal inertia of the outer shell of the sensors ε _t3 , as well as quasi-constant slowly varying thermal inertia indicators of sensitive elements ε ₁₁ , ε ₂₁ , ε ₃₁ and fillers ε ₁₂ , ε ₂₂ , ε ₃₂ , which ensures metrological durability.

A device for implementing the proposed method, in contrast to the known ones, should contain three temperature sensors from the sensitive elements in the tubes with filler, the design of which should provide a difference in thermal inertia ε ₁₁ , ε ₂₁ , ε _{31 of the} sensitive elements and fillers ε ₁₂ , ε ₂₂ , ε ₃₂ and the equality of the current thermal inertia of the outer shells ε _t13 = ε _t13 = ε _t33 = ε _t3 .

These requirements are met if the design of the sensors is performed as shown in the drawing of FIG. one.

и конвективный коэффициент теплообмена с внешней средой α_t3(t) для всех датчиков совпадают, следовательно, равны и показатели термической инерции внешних оболочек

.Sensitive elements 1, 2 and 3 are distributed in equal areas inside a common tube 4 filled with a heat-conducting medium (filler) 5. The difference in thermal inertia ε ₁₁ , ε ₂₁ , ε _{31 of the} distributed sensitive elements is achieved by changing their mass (respectively, and volume), for example, by laying a different number of longitudinal loops of the passive wire 6. This automatically, due to a change in volume in the tube with a fixed inner diameter, provides a difference in the thermal inertia of the fillers ε ₁₁ , ε ₂₂ , ε ₃₂ . Since the outer shells of all sensitive elements are identical and equally located in the flow in the external environment, the thermal factor

and the convective heat transfer coefficient with the external medium α _t3 (t) for all sensors coincide, therefore, the thermal inertia of the outer shells are equal

.

. Устройство работает параллельным опросом датчиков, преобразованием их параметров в код и вычислением измеряемых величин по предложенному способу.The device for implementing the proposed method (Fig. 2) in addition to the three sensors 1i with the above differences also contains framing electronics, which can be performed in a known manner, for example, as part of secondary measuring transducers 2i, analog-to-digital converters 3i and microprocessor 4

. The device works by parallel polling of sensors, converting their parameters into code and calculating the measured values by the proposed method.

Claims (41)

1. A method of measuring temperature and thermal inertia of the shells of a contact temperature sensor using more than one sensor with different inertial parameters, characterized in that three sensors are used, consisting of sensitive elements with different thermal inertia indicators, placed in external shells with the same values of the thermal factor and filled with a heat-conducting medium (filler) with different indicators of thermal inertia, place the sensors in the measurement medium with the same conditions about flow to ensure the equality of the convective heat transfer coefficients of the outer shells of the sensors with the medium, measure the current temperature of the sensitive elements of the sensors θ _t1 , θ _t2 and θ _t3 at the same time, determine the current temperature of the medium θ _tc by the formula

current indicator of thermal inertia of the outer shell of the sensors ε _t3 according to the formula

thermal inertia indicators of sensitive elements of sensors the first

second

third

indicators of thermal inertia of the shells (fillers) of the sensors first ε ₁₂ = x ₁ -ε ₁₁ , second ε ₂₂ = x ₃ -ε ₂₁ , third ε ₃₂ = x ₅ -ε ₃₁ , Where

from solving a system of linear algebraic equations of the form

N≥18, Where

2. The device for implementing the method according to claim 1, consisting of three contact sensors, the outputs of which are fed to the inputs of the secondary measuring transducers, connected at the outputs to the inputs of the analog-to-digital converters, the outputs of which are fed to the input of the microprocessor, characterized in that the sensitive elements of the sensors made distributed with different volumes, placed in a uniform protective tube along the axis in different areas, and the tube is filled with a heat-conducting medium.

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