SU901851A1 - Method of determination of thermal converter thermal lag index - Google Patents

Description

(54) METHOD OF DETERMINATION OF THE INDICATOR OF THERMAL INERTIA OF A THERMAL SPREATER

one

The invention relates to a measuring technique and can be used in metrological calibration and testing of thermocouples, and also in laboratory and industrial practice in measuring devices for measuring the temperature of the error correction class of the sensor, due to thermal inertia of thermocouples.

There is a known method of rendering, psi-heat thermal inertia of thermal conversions, consisting in a double reading of the readings of the two sensitive elements of the temperature sensor and the subsequent calculation of the heat and energy indicator.

The disadvantage of this method is the need to use identical, i.e. with identical characteristics of thermocouples. In practice, it is difficult to realize such a condition and in practice the divergence of the parameters of sensitive elements introduces a noticeable error in the definition of the thermal inertia index.

The closest to the present invention is a method for determining a thermal inertia indicator, including placing a thermal converter in an environment with a constant temperature, recording two values of its temperature, measuring the time interval between them, and calculating the thermal inertia index 2.

Show thermal inertia is calculated by the formula

t2 -

-.

ti

her

tc-t, where b (and - (, 2. sensor readings;

T (V (TSL of the moment of reading), an arbitrary moment of the transient response measured from the moment of contact of the thermal converter with the medium, and Tj is calculated by the formula

,

Claims (2)

where M is a constant characterizing the thermal conversion of the type. The disadvantages of this method are the complexity and large measurement error of the thermal inertia index of thermal converters, which is due to the fact that the accuracy of fixing the moment of contact of the thermal converter with the medium is limited by the sensitivity threshold of the recording device. In addition, the determination of the moment tTj is associated with preliminary calculations (introducing additional errors in determining the thermal inertia index) of the coefficient M, which, in turn, depends on a number of factors, such as size, shape, material, and thermal physical properties , heat transfer condition of the thermocouple with medium. The purpose of the invention is to improve accuracy while simplifying the process of determining the thermal inertia index. This goal is achieved by additionally registering the temperature of the thermocouple with the bluetooth time interval equal to the measured one, and the thermal inertia index of the thermocouple is determined by the nQ formula--T where DT is the time interval between two adjacent recorded temperature values; -t.to t a- the temperature values of the thermocouple of the former corresponding to the three measurement points. FIG. 1 shows a block diagram of a device implementing the proposed method; in fig. 2 is a plot of T 01 -fc (T-current value of time, -t-value of the temperature of the thermoconverter, proportional to the change in its output signal). The device contains test thermocouple 1 connected to the input of indicator 2. As indicator 2, an oscilloscope with a tube having a long afterglow time can be used. The scale of the screen along the scan line is graduated according to the SG time, along the vertical scan line - proportional to the values of the transient response of the thermal transducer. The method is carried out as follows. Thermoconverter under investigation 1, 1 is placed in an environment with a constant temperature and from its output a 1F electrical signal, which, before reaching the stationary mode, changes exponentially (Fig. 2), which is a transitional characteristic of the thermoconverter caused by it inertia. The output signal of the thermocouple is fed to the input of the indicator 2, on the screen of which a graph of the transient response is displayed (Fig. 2). On a scale of indicator 2 at an arbitrary point in time, three values of the transient characteristic of the thermoconverter i fc and H are equal to each other in the interval b.f are recorded. Then, calculate the rate of thermal inertia of thermocouple 1 by formula (1). The process of calculating the thermal inertia indicator can be automated by connecting, for example, an analog computing device connected to the output of a time interval generator to the output of a thermal transducer. You can also -pea-. To use the proposed method using a digital computing device connected to the output of thermal conversion using an analog-digital converter. The derivation of formula (1) is based on a known ratio of the theory of the regular thermal regime,. 4. (r) - te (.le, where is the indicator of thermal inertia of the thermal converter; Bj is the true value of temperature T is the current value of time; fete) is the current value of the temperature of the thermal converter, provided that each of the time points T, TZ I. differs by the value of DT, i.e. Tga T + tr iT i- r T Ziicr. Thus, to determine the thermal inertia indicator, it is necessary to dawn, to locate three values of the thermoconverter signal at any part of the transient response through two equal in-4 time intervals and to calculate the thermal inertia index ps by formula (1). The invention eliminates the need to predict the time when the thermoconverter enters the medium, and also eliminates the need to take into account such factors as defrosting, shape, material, heat4. 590, physical properties and heat transfer conditions of the thermal converter with the medium. As a result, the accuracy of the sensor is greatly increased and the process of determining the thermal inertia index of thermal converters is simplified. TaiK, for a known method, as not shown by experimental studies, the error in determining the thermal inertia index is 24.1%, and for the proposed one - 2, O5%, therefore, the proposed method allows to reduce the measurement error by about 12 times. In addition, by simplifying the process of determining the rate of tep inertia, the response speed is no less than 2 times. The invention The method of determining the thermal inertia index of a thermal converter, including placing a thermal converter in an environment with a constant temperature, regenerating two temperatures of its temperature, measuring the time interval between them and calculating the thermal index and operating theory that differs in that, with an increase in accuracy while simplifying the process of determining the thermal inertia indicator, the temperature value of the temperature transducer is additionally recorded after a time interval equal to CB and heat index "howling inertia termopreobraeovately def & cases dissolved by the formula - / it where LT - the time interval between two adjacent registrable zna Cheney mi temperature; - - - - temperature values of the thermoprv-A of the former, corresponding to the thundering measurement points. Sources of information taken into account in the examination 1. The author's certificate of the USSR N5 174813, cl. Q01 K 15 / OO. 1965. 2. USSR author's certificate - s1 .G.V. V OJnMCI tSUtol IBU, 1,267123 cl. QO1.K 15/00, 1970 (photo type).