SU1747968A1 - Method of metering a rarefied gas pressure and device thereof - Google Patents

Abstract

This invention relates to a measurement technique. The goal is to increase speed and expand functionality by simultaneously measuring the gas temperature. Measurements are taken in three consecutive time ticks. In the first cycle, the temperature-sensitive pressure sensor is overheated by the first overheating current from the first to the second fixed temperature value of the temperature-sensitive sensor, the second one turns off the overheating current and cools it from the second to the first fixed temperature, turns on the second overheating current not equal to the first one to the second one fixed temperature, U) C

Description

2

NJ

during each cycle, the amount of heat released in the thermal sensor when it is heated and cooled is measured and the current temperature is integrated over time. The temperature and pressure of the medium are determined according to certain corresponding mathematical dependencies. An apparatus for carrying out the method comprises a temperature-sensitive sensor 1, a discretely controlled current source 2, an amplifier 10 with a discretely controlled gain factor, a comparator 19, a voltage divider 20 with a discretely controlled transmission coefficient, a reference voltage source 25, a voltage converter 26, counters 27 and 28 pulses, pulse generator 29, storage unit 30, computing unit 37 and control unit 38. On signals from control unit 38, the overheating current is switched on and off. 2 sec. f-ly, 2 ill.

The invention relates to a technique of thermophysical measurements and can be used to measure low gas pressures and its temperature.

There is a known method for measuring vacuum using a thermal converter, including its overheating by a constant-power current, measuring the temperature of a temperature-sensitive resistor at regular intervals and further determining pressure using a mathematical formula,

The disadvantage of this method is the impossibility of carrying out with its help complex measurements of the parameters of rarefied gases — pressure and temperature. The combination of individual types of measurements leads to a considerable duration of these measurements.

Closest to the proposed method of measuring vacuum and a device for its implementation, based on the use of a temperature-sensitive resistor. The thermistor is heated and cooled by periodically turning on and off the electric direct current that heats it up against the temperature of the gas medium, while measuring the heating time of the thermometer from the first initial value by a normalized value, cools the thermistor to a temperature below the second initial value not equal to the first, measured the heating time of the thermistor from the third fixed temperature to the fourth, then periodically turn on and off the superheating current, giving possibly In order to change the temperature of the thermistor to the normalized increment and adjusting its value until the duration of the second interval is equal to the duration of the first one, the powers allocated to the thermistor in the first and second time intervals are determined, the pressure is determined by a mathematical formula.

A device for measuring vacuum contains a thermistor included in one of the branches of the measuring bridge, an amplifier, a driver of reference pulses, a block

timing, voltage regulator, electronic key and bias voltage adjuster.

The disadvantage of the known method and device is low speed.

when measuring vacuum, which is associated with the need for power control to obtain a given heating time, which requires several heating-cooling cycles of the thermistor. With a rapid change in pressure, this deficiency is exacerbated. The speed of a known method is also deteriorated due to the need to periodically calibrate the heating time when measuring

ambient temperature, for which the thermistor is removed from the measurement mode.

In addition, there is no possibility to simultaneously determine the temperature.

ambient gas.

The purpose of the invention is to increase speed and enhance functionality by simultaneously measuring the gas temperature.

As follows from the theory of a calorimetric experiment, if a body placed in a gas with a temperature of bp and having an initial temperature of # 1 0Cp, for some burden, heat the power Pi to the final temperature vg. for heat exchange by radiation and thermal conductivity on structural elements minimized and not taken into account) can be determined from the heat balance equation

SI H (ft -0 |) + a (0 - ftp) dt

ti

(one)

45 where N tC (t is the mass; C is the heat capacity);

or - heat transfer coefficient; ti, t2 are the time points of reaching the temperatures, respectively;

A-7

T1

Pidt - heat reported by ter- g

to the sea diver.

The first member of the right-hand side of (1) is equal to the amount of heat stored by the body when it is heated from in to –2.

The heat balance equation for the day of the body cooling section from the temperature 9g to the instant of time tc reaches its temperature # 1 can be written as

Q2 H (% - ft) + «/ (at - 0cp) dt,

12

t3

where Oi - J Padt - heat reported ter12

to the seismistor with measuring current with power P2 «Pi

The heat balance equation for the heating section with the power Рз Р2, by analogy with equation (1), is written as

H

Q3 H (0i -fc) + a / (0-0cp) dt (3)

13

Solving the system of equations (1) - (3) with respect to "under the condition

a (0 | + fe) (T2 + T3) - (Q2 + Q3) (Tl-fT2)

(T2 + T3) tf0dt- (Ti + T2) j 0dt

Cta

(four)

Since the thermal conductivity of the medium is directly proportional to pressure (P K u), then

p „(Q1 + Q2) (T2 + Tz) - (02 + 03) (T1 + T2)

K - | l- - .-- .. t.-.-..- J-- .. -l, e

(T2 + T3) j #dt - (Ti + T2) / # dt

And 12

(AT)

Solving the system of equations (1} - (3) relatively vr. We get

(Qi4-Q2) t / 0dt- (Q2 + Q3) 55

t2 t2

(01 + Q2) (T2 + T3) - (Q2 + Q3) (T1 + T2)

(6)

g

 Q

20

25

thirty

wasp

U

45

50

55

)

FIG. 1 shows diagrams of temperature measurement on a thermistor; 2 is a block diagram of a device for measuring vacuum and temperature.

The method is carried out as follows.

The resistance thermocouple placed in the measured medium is overheated with respect to the ambient temperature # Cf (Fig. 1) with the first superheating current I to the first fixed temperature in and since it reaches ti they measure the amount of heat QI released in the thermistor until reaching time t2 The second fixed temperature is b # i At the moment of time t2, the overheating current is turned off and the time of its cooling to the temperature Qi is measured, fixing the time TK and the amount of heat Q2 supplied to the thermistor during measurements. At the same time, over time periods Ti t2-tt and T2 - Ш2 integrate over time the current temperature of the thermistor at time t3 turn on overheating current 2, for example h It, and measure the amount of heat released on the thermistor until t4 reaches its second fixed temperature & 2, integrating the current temperature over time. At time T4, the current is turned off, and the medium temperature and pressure are calculated using formulas (5) and (6).

A device for carrying out the proposed method comprises a thermistor 1 of a pressure converter and a discretely controlled current source 2 consisting of keys 3-5, resistors 6-8 and amplifier 9, an amplifier 10 with discretely controlled gain factor, consisting of resistor 11, keys 12- 14 resistors 15-17 and amplifier 18, comparator 19, voltage divider 20 with discretely controlled gain, consisting of resistors 21 and 22 and switches 23 and 24, reference voltage source 25, voltage-to-frequency converter 26, counters 27 and 28 pulses, a pulse generator 29, a storage unit 30 consisting of memory registers 31-36, a computing unit 37 and a control unit 38. On signals from control unit 38, the overheating current is turned on and off. Information is processed in the computing unit. The output codes of the computational unit are directly proportional to the values of Vsr and R f o rmu l and z o b rie

1. A method for measuring a rarefied gas pressure based on heating and cooling a thermistor by periodically turning on and off an electric current, measuring the duration of heating and cooling time intervals during which the temperature of the thermistor changes at a predetermined fixed range, and determining the amount of heat generated in the thermistor during each time interval, characterized in that, in order to increase speed and enhance functionality by simultaneously measurement of the gas temperature, measurements are made during the first, second and third time intervals, with the first time including the superheating current of the first magnitude and integrating the temperature of the thermistor in time, the second heating time turning off the temperature of the thermistor, the third time interval includes the superheating current of the second value, not equal to the first value, and integrate the temperature of the thermistor with time, then turn off the superheating current and determine the pressure P of the gas and its average temperature # cf by the ratio

pg (.31 + Q2XT2 + Tz) - (02 + Oz) (T1 + T5) Tsi + S2} (T2 + T3) - (Si + S2) (Ti + TT)

ftp

 (Q + Q2KS + S-Q- (Q2 4-Cn) (Sl-f 52) (01 + Q2) (T2 + Tz) - (02 + Q3) (T1 + T2)

where K is the calibration coefficient;

Ti, Ta, T3 - the duration of the first, second and third time intervals;

Qi.Q2, Q3 - the amount of heat measured in the first, second and third time intervals;

Si, S2, S3 - integrals of the temperature of the thermistor in the first, second and third time intervals.

2 A device for measuring the pressure of a rarefied gas, which contains a resistive thermoconverter and a source of voltage, characterized in that, in order to increase speed and enhance functionality by simultaneously measuring the gas temperature, a discretely controlled current source is introduced into it, adjustable ratio

gain, voltage divider with discretely controlled transmission coefficient, voltage to frequency converter, first and second pulse counters, pulse generator, storage unit, computing unit, comparator and control unit, while the thermal converter is connected to the output of the discrete controlled current source, the first, second and third control inputs of which are connected respectively to the first, second and third outputs of the control unit, which are also connected respectively to the first, second and third at a control input of the amplifier to discretely

adjustable gain, the information input of which is connected to the thermal converter, and the output to the first input of the voltage to frequency converter and to the first input of the comparator,

The second input of which is connected to the output of a divider with discretely controlled transmission coefficient, the first and second inputs of which are connected respectively to the fourth and fifth outputs of the control unit, the input of which is connected to the comparator output and the sixth output to the first inputs of the first and second pulse counters, moreover, the output of the reference voltage source is connected to the third input

voltage divider with discretely controlled transmission coefficient and to the fourth input of the controlled current source, the first output of the pulse generator is connected to the second input of the second pulse counter, and the second output to the second input of the voltage to frequency converter, the output of which is connected to the second input of the first pulse counter connected to the output of the first memory

unit, the second input of which is connected to the output of the second pulse counter, and the third, fourth and fifth of its inputs are connected respectively to the seventh, eighth and ninth outputs of the control unit, with

this outputs of the storage unit connected to the inputs of the computing unit.

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Claims (2)

.Claim 1. A method of measuring the pressure of a rarefied gas, based on heating and cooling the thermistor by periodically turning the electric current on and off, measuring the duration of the heating and cooling time intervals during which the temperature of the thermistor varies in a given fixed range, and determining the amount of heat released in a thermistor during each time interval, O t characterized in that, in order to improve performance and expand functionality by simultaneously gas temperature measurement, measurements are made during the first, second and third time intervals, moreover, in the first time interval, the overheating current of the first magnitude is turned on and the temperature of the thermistor is integrated over time, in the second time interval the overheating current is turned off and the temperature of the thermistor is integrated over time. in the third time interval, an overheating current of a second value not equal to the first value is turned on, and the temperature of the thermistor is integrated over time, then the overheating current is turned off and the gas pressure P and its average temperature 0 _C p are determined by the ratios p (l + a2) (T2 + Tz) - (ar + az) (t1 + tz) (si + S2) (t ₂ + T ₃ ) - (si + S2) (τι + τ ₂ ) 0av ⁼ = (Q 4-Q2) (S2 + sa) ~ (Q2 4-Q3) (S1 + S2) (Q1 + Q2) (T2 + Тз) - (Q2 + Q3) (T1 + T?) 'Where K is a calibration factor; T 1, Tg, Tz - the duration of the first, second and third time intervals; Q1.Q2.Q3 - the amount of heat measured in the first, second and third time intervals; S1.S2.S3 - temperature integrals of the thermistor in the first, second and third time intervals. 2. A device for measuring the pressure of a rarefied gas, comprising a resistance thermoconverter and a reference voltage source, which is ensured by the fact that. in order to increase speed and expand functionality by simultaneously measuring the gas temperature, a discretely controlled current source, an amplifier with a discretely adjustable gain 5, a voltage divider with a discretely controlled transfer coefficient, a voltage to frequency converter, first and second pulse counters are introduced into it , a pulse generator, a storage unit, a computational unit, a comparator, and a control unit, while the thermal converter is connected to the output of a discrete a direct current source, the first, second and third control inputs of which are connected respectively to the first, second and third outputs of the control unit, which are also connected respectively to the first, second and third control inputs of the amplifier with a discrete 20 adjustable gain, the information input of which is connected to thermoconverter, and the output is to the first input of the voltage to frequency converter and to the first input of the comparator, 25 the second input of which is connected to the output of the divider with discrete control transfer coefficient, the first and second inputs of which are connected respectively to the fourth and fifth outputs of the control unit, whose input is connected to the output of the comparator, and the sixth output to the first inputs of the first and second pulse counters, and the output of the reference voltage source is connected to the third input 35 a voltage divider with a discretely controlled transmission coefficient and to the fourth input of a controlled current source, the first output of the pulse generator is connected to the second input of the second counter of 40 pulses, and the second to output - with the second input of the voltage to frequency converter, the output of which is connected to the second input of the first pulse counter connected to the output of the first input of the memory block 45, the second input of which is connected to the output of the second pulse counter, and its third, fourth and fifth inputs are connected respectively, with the seventh, eighth and ninth outputs of the control unit, with 50 of which the outputs of the storage unit are connected to the inputs of the computing unit. Vut.i