SU363874A1 - DEVICE FOR MEASURING NONSTATIONARY - Google Patents

Description

one

The invention relates to temperature measurements and can be used for accurate measurements of non-stationary temperatures with inertial resistance thermometers under conditions of slowly changing heat exchange.

Devices for measuring non-stationary temperatures by means of non-stationary thermal receivers are known, in which appropriate automatic correction is introduced to reduce the error and inertia.

The disadvantages of these devices are the need for high gain to obtain optimal signal levels derived from small heat transfer coefficients, when the time of the thermal receiver is large, the need for powering the thermal receiver with alternating current, since the device contains differentiating units; the complexity of these devices, as they contain complex calculating blocks.

The aim of the invention is to provide the possibility of automatic correction of dynamic measurement errors resulting from a change in the constant time of the resistance thermometer.

The goal is achieved by the fact that the thermal receiver is equipped with an auxiliary resistance thermometer, both of which are connected to a corrective link in a counter.

Most technical thermometers of resistance consist of a platinum platform placed in a certain way in the channels of the ceramic frame protected by metal fittings. The leads of the platinum wire are protected from reinforcement with a ceramic insulator. The framework channels are filled with alumina powder. Since the thermophysical parameters of alumina are close to those of ceramics, such a construction can be considered as a two-layer body, the central part of which consists of ceramics and the outer part of metal. The constant time of such a receiver is equal to

  ,(one)

20 where s is the minimum value of the index of thermal inertia, provided that the heat transfer coefficient tends to infinity;

EO is a measure of thermal inertia of a thermal receiver, if the temperature distribution in it was uniform over the entire volume. Ultimately, expression (1) results in the form

 (2)

where L and B are the generalized coefficients determined only by the design parameters of the thermal receiver.

Overheating of the auxiliary sensing element heated along the axis results in

D. l D, (3)

where C and D are coefficients of the same nature as A and B.

Determining from (3) the value of a and putting it in (2), we find that 1 constant; at the time of the thermal receiver, it is unambiguously determined by the temperature difference between the heated sensing element and the medium or, equivalently, between the heated and the basic sensing elements

 f IR P-L / -g-S-DH in FIG. 1 shows the proposed device for measuring non-stationary temperatures with dimensions according to A-A and BB; in fig. 2 is a block diagram of the device.

The thermal receiver contains a main / and auxiliary 2 resistance thermometers. Heater 3 is made of wire with zero temperature coefficient of resistance, which ensures constancy of mopdnost in all the necessary temperature range for a given voltage. The main and auxiliary thermometers are separated by an isolator 4. The ceramic frame of the auxiliary thermal receiver has several channels, where the heater is located along the axis, and the remaining heat-sensitive wires 5 and leads 6, which extend from the main thermometer. The auxiliary thermometer (see r-ig. 1, section bb) has five channels. All free space in the protective reinforcement is filled with alumina, including the framework channels. The ends of the frames, as usual, sealed with glaze.

The block diagram of the device (see Fig. 2) shows the main (and auxiliary) 2 resistance thermometers, amplifier 7, covered by feedback 8, tuned by means of an executive unit 9.

The device works as follows. With a constant time of the thermal receiver and the corrective element located in the feedback circuit, the voltage at the output of the amplifier is proportional to temperature. When the heat transfer conditions or the heat transfer coefficient change, the overheating temperature of the thermometer 2 changes, which

defined as the temperature difference between the primary and secondary thermometers. In accordance with this change, the actuator 9 changes the time constant of the corrective element so that

the equality of the time constant of the thermal receiver and the corrective element will always be observed due to the proportional dependence of S on 4 in accordance with equation (4). The power of measuring circuits can be applied both on constant and alternating current. Since the power supplied to the heater is small, and the heat distribution along the thermal receiver is insignificant, additional heating of the main

thermal receiver is practically excluded.

Subject invention

A device for measuring non-stationary temperatures, containing a main resistance thermometer, an amplifier with a correction link in the feedback circuit, and an actuator, characterized in that

automatic correction of dynamic measurement errors resulting from a change in the constant time of the resistance thermometer, the latter is equipped with an auxiliary heated resistance thermometer, both of which are connected to the corrective link counter. 1 2 3

/

A a

6-6

FIG. one