SU1377621A1 - Method of measuring temperature - Google Patents

Abstract

This invention relates to thermometry. The purpose of the invention is to simplify the method and expand the range of measured temperatures. In the device implementing the method, the electrodes 5 are placed in a controlled environment 6. The temperature of the electrodes 5 must not exceed the measured temperature of the medium. To do this, when measuring low temperatures, the necessary measures are taken to prevent unwanted overheating of the electrodes 5 due to the influx of heat through the wires connecting the electrodes 5 to a high voltage source (secondary winding of step-up transformer 2). After the onset of thermal equilibrium between the electrodes 5 and the medium, a voltage is applied to the electrodes 5 and is increased by means of the regulator 1 until the medium is broken in the gap between the electrodes 5. The magnitude of the voltage on the electrodes. 5 at the time of the breakdown is recorded by the device 4. The medium temperature is determined from the measured value of the breakdown voltage. 2 Il. with

Description

5 i

SAE

Фа9.1

The invention relates to thermometry and can be used to determine the temperature of gases and gas outflows, non-conductive liquids to solid dielectrics in the temperature range of U-ZOOO K.

The purpose of the invention is to simplify the method and expand the range of the measured temperature.

Fig. I shows the electrical circuit of the device for carrying out the proposed method; Fig. 2 shows the results of studies for several lengths of discharge intervals S (S 2 and 3 mm).

The device contains a voltage regulator 1, a step-up transformer 2, a current-limiting resistor 3, a voltage meter 4 (kilovolt-meter) and electrodes 5,

The method is carried out as follows.

The electrodes 5 are placed in a controlled medium 6 (Fig.), While the temperature of the electrodes themselves must certainly exceed the measured temperature of the medium. For this, when measuring temperatures, take the necessary measures to prevent undesirable overheating of the electrodes due to the influx of heat through the wires connecting the electrodes 5 to the high voltage source (secondary winding of the step-up transformer 2). Thermal equilibrium between the electrodes and the medium on the electrodes the voltage is applied and its voltage is controlled by regulator 1 until the breakdown of the medium in the gap between the electrodes 5 The value of the voltage on the electrodes at the time of the breakdown is recorded by the device 4 "By measuring The temperature of the medium is determined by the magnitude of the breakdown voltage.

It has been established by research that the breakdown voltage and the gases, at temperatures from room to at least I500 K, is subject to

and f (2-)

Chrr i h .-

where S is the interelectrode distance;

p is the gas pressure;

T is the gas temperature

known for normal temperatures. Gases are subject to this dependence and at low temperatures up to their liquefaction temperatures. Quantitatively, this relationship, for example, for air is expressed by the formula

and

etc

(IN 1)

Q

five

0

5 0 cr 0

five

0

where S is expressed by BCMjp-najT-K.

If the pressure in the process is measured. If it does not change, but the pattern of its change is known, then it is easy to take into account when measuring temperature using the formula and P if the change in p occurs within narrow limits (0.5 p / p, 2.0). Here Up is the breakdown voltage at a given pressure p; n, jn, - is the measuring breakdown voltage, i.e., the voltage from which T is determined from the calibration curve determined at the initial pressure r0. As a rule, p is the atmospheric pressure,

Thus, the medium temperature is determined from the measured breakdown voltage with the help of formulas similar to those written down, or from the grading curves. The highest accuracy of the method is achieved with equal temperatures of the electrodes and the medium. The difference in temperature of the medium and electrodes by 20-30% increases the error in temperature measurement to 5: 10%. For accuracy, use the calibration curves Upp f (T), taken at different temperatures of the medium and electrodes,

The shape of the electrodes must be such that a uniform or quasi-uniform electric field is provided in the perforation gap. In this case, the measurement accuracy is higher and the given calculation formula is suitable for determining the temperature.

Example. The temperature dependence of the breakdown voltage of heated air was investigated in the temperature range from 20 to 1700 ° C. Studies were carried out in a discharge chamber where the electrodes and gas had the same temperature. The shell of the chamber served as a ceramic tube of alumina, inside of which cylindrical electrodes were placed, providing a uniform electric field in the discharge gap. Stainless steel, brass, Pt, ZrOg, MoSij, were tested as the material of the electrodes. The heating was carried out using an electric resistance furnace, in

which was placed the camera. The gas temperature in the gap was determined with a thermocouple. Measurements were conducted at constant current. The test voltage growth rate did not exceed 1000 V / s.

In Figure 2, the values of breakdown voltages obtained by using electrodes and various materials are indicated by differently indicated points. Each point on the graph is a result of averaging Unp values for five or more breakdowns.

It has been established that the change in breakdown voltages to temperatures of 1500 ° C with all the electrode materials studied is subject to a dependence known for normal temperature and obtained with a change in air pressure:

and „p 24.55 & s + e.ee-isT, (q), (2)

about rtv

where о ™ is the density of air, FROM i

worn to a normal level (, 013-Yu Pa; T ,,

 293 K);

T - absolute temperature. TO; p is the gas pressure, Pa; - S is the interelectrode distance, see. The change in accordance with this dependence is shown in Figure 2 by solid lines. The greatest deviation of the experimental Unp values from those calculated by (2) is observed in the range of 400-700 ° C and is + 5%. At temperatures above 1400-1500 ° C, the experimental data deviate from the calculated ones.

Claims (1)

Invention Formula The method of measuring the temperature, which consists in placing two electrodes in a controlled environment, which are set at a fixed distance from each other, and between the electrodes, applying an electrical voltage to them, creates an electric field that, in order to simplify and extending the range of measured temperatures, the strength of the electric field is increased until the occurrence of an electrical breakdown of the medium in the gap between the electrodes, and the voltage between the electrodes is measured at which An electrical breakdown occurs and the temperature of the medium is determined by it, while the temperature of the electrodes is kept below or equal to the expected temperature of the medium. nf), About 800 800 yuo sho to ° Fce.g