SU384028A1 - METHOD FOR AUTOMATIC MEASUREMENT OF THERMAL CONSTANT TIME OF THERMAL SENSOR - Google Patents

Description

one

The invention relates to the field of measurement technology and can be used in laboratory or manufacturing practice for measuring high temperatures or rapidly varying in temperature temperature, outgoing processes for correcting measurement errors caused by thermal inertia of such thermal sensors as thermocouples and resistance thermometers.

There is a method of measuring thermal constant temperature of a thermal sensor based on the use of an analytical relationship describing the process of simple heating (or cooling) a body introduced into a medium with a constant temperature of 0 ° C in the integral form of the form

/ -in (4-in), (1)

where t is the cooling rate, i.e., the reciprocal of the thermal time constant T; to - the initial body temperature (thermal sensor), from where after logarithmization we get

ln (f - &) - t- + in (4 - Q). (2)

From equation (2), you can see that the logarithm of the temperature difference t of the body (thermal sensor) and its environment is a linear function of time m with an angular coefficient equal to-m, since 1n () const.

However, with this method it is difficult to obtain a high accuracy of the measuring path and it is difficult to automate the measurement process on the basis of dependence (2), since its main operation is a logarithm: the voltage from the output of the temperature sensor of the temperature sensor to an electrical signal.

According to the proposed method, the voltage at the output of the converter after the temperature sensor is inserted into a predetermined medium in one channel of the measurement setup is amplified and fed to the vertical scanning terminals of the beam of the electronic oscilloscope, and in the other channel it is differentiated, amplified and supplied

The 5 horizontal sweep terminals, photograph the image on the screen, after which the thermal constant value is calculated from the slope of the rectilinear portion of the curve obtained in the photograph.

Thanks to this, the measurement accuracy is improved and the measuring path is simplified.

The method of measuring the thermal constant of the T thermometer sensor is also based on the analytical relationship (1), but not only in the integral forum, but in the differential forum, which has the form

in - D - (- in). (3)

0

d

It is obvious that the graph of equation (3) is a linear function with an angular coefficient equal to: M - T. At FIG. 1 shows a block diagram of an installation for carrying out the proposed method for automatically measuring the thermal time of a thermal sensor; on, fit. 2 - photo-screen of the oscilloscope. The installation contains a vessel / with a predetermined medium having a constant software with a volume of known temperature in ° C, a linear transducer 2 of the temperature of the temperature sensor to a direct voltage with a conversion factor Ki (t / Bbix) np Ki - (- 6) V, amplifier 3 DC voltage from the output of the converter with a gain of K2 2 K2-Ui Ki-K2- (ti-Q) in, an optical amplifier 4 voltage of the direct current performing the operation of differentiation and amplification of the input signal from the output of the inverter with the coefficient Кз КгК, - (-9) v, the elec- trot 5 oscilloscope sweep with scale factors of the input voltage signal lo vertical / Su mm / a and go.rizontali Kx mm / a Y KyU. KYK, K (t - in) mm; X KxU, / Cx / SLS (- Q) MM And block 6 for photographing the image on the screen of the electronic oscilloscope. To measure the thermal constant of the time of the thermal sensor to the proposed methods, a thermal sensor connected to the converter 2 is placed in the vessel I, and the signal from the output of the converter caused by heating (or cooling) the thermal sensor is amplified in one channel by the Hia terminal vertical scanner of the electronic oocythograph 5, and in another channel with the help of the operational amplifier 4 is differentiated, amplified and then fed to the horizontal scan terminals of the oscilloscope. The resulting image on the screen of the electronic oscilloscope is photographed and then the value of the measured thermal constant of the temperature sensor is calculated from the magnitude of the tangent, the angle of inclination of the linear plot obtained in the image photograph. The tangent of the angle of tilt is expressed by the Kyff ratio. tg - (o) (i -I, from where KiKs t - Q or T / 4 follows) Equation (6) allows calculating the value of the thermal constant of the time of a thermode .chik. If you choose the coefficients so that the ratio is obtained,. The proposed method makes it possible to automatically determine the value of the thermal time of a thermal sensor. As transducer 2 you can use, for example, two thermocouples of one calibration. Included are differential differential thermocouples, and for wire, resistance thermometers, two identical resistance thermometers included in the adjacent arms of the measuring bridge. To determine the thermal constant of the temperature of the sensor by the proposed method, it is necessary after installation of the measurement setup 1 according to the scheme of FIG. 1, first, one of the thermal sensors (thermocouple or resistance thermometer), put in a predetermined wed, food with a constant known temperature of 6 ° C. After the first temperature sensor warms up to a temperature in ° C, place the second thermal sensor in the same medium and take a picture on the screen of the electronic oscilloscope when the second thermal sensor is heated, Ika, whose thermal constant is measured. Then, using the formula (6), calculate the value of the constant T. The measurements of the thermal constant of the time, pr, are ed, m, by the method according to | the block diagram of FIG. 1 can also be carried out with only one thermal sensor, imitating the output signal of the converter 2, which corresponds to the temperature of the heating of the thermal sensor of 6 ° C using one of the methods known in measurement technology. The subject of the invention is a method of automatically measuring the thermal time constant of a thermal sensor in an environment with a constant coefficient of heat transfer, characterized in that, in order to improve measurement accuracy and simplify the measuring path, the voltage at the output of the converter after the thermal sensor is applied to a predetermined the medium in one channel of the measuring unit, amplifies and serves up the vertical scanning terminals of the beam of the electronic oscilloscope, and in the other, the corner of the beam is amplified, amplifies and serves to the terminals of the horizontal spread The camera captures the image on the screen, after which the value of the thermal constant is calculated at the slope of the rectilinear section of the curve obtained in the photograph.

FIG. 2