SU502223A1 - Method for determining gas flow at low pressures - Google Patents

Description

one

The invention relates to vacuum technology, in particular to the measurement of gas flows at low pressures.

The known methods of continuous measurement of gas flow when pumping gas from the chamber with their advantages have one major drawback: the release of gas or the pumping of gas from the measuring chamber in which the pressure gauge transducer is installed, which gives a signal on the flow rate, will introduce an error in the measured flow value pressure in the working chamber.

The purpose of the present invention is to improve the measurement accuracy. This can be achieved if the modulating device — a variable-section element — is not installed between the measuring chamber of known volume and the discharge port, but between the measuring chamber and the camera with the flow source. In other words, if you modulate the non-effective rate of pumping gas from the measuring chamber and make the gas flow entering the measuring chamber pulsating, i.e., modulate the gas flow before entering the measuring chamber of constant volume.

A schematic diagram of the implementation of the method is shown in the drawing, where the following symbols are adopted: 1 — a chamber with a volume Vi — a source of gas flow Q, the value of which is to be determined; 2 - measuring

a chamber of known constant volume Vz, 3 a manometric transducer, QM - a gas flow from a maometric transducer 3; 4 - a pipeline (pin) connecting the chamber 1 with the chamber 2; 5 - a damper modulating the flow at the entrance to the measuring chamber 2.

The gas flow from chamber 1, the passage through the rotating flap 5, becomes pulsating. The variable component of the pressure D / in the measuring chamber 2 is proportional to the magnitude of the measured gas flow Q, equal to

Q K-Vz-f- p,

where / C is a constant coefficient, f is the rotational speed of the valve. The constant flow QM of the manometric transducer 3 results in an increase or decrease in the constant component of the pressure in the measuring chamber 2 and does not affect the transient component of the pressure.

This method of fully interrupting the effects of leakage, gas evolution or gas pumping out in the measuring chamber 2, in which the pressure gauge 3 is installed, allows the use of more reliable than ionization, electric discharge manometers. This increases the reliability of the device, makes it a breakdown machine, in particular when it comes to

pressure to atmospheric.

For this method of measuring the flow of rarefied gas, the sensitivity of the useful signal is less characteristic of the note (dn / dQ) than when measuring the flow by modulating the pumping rate. However, the lower sensitivity of the useful signal can be compensated for by applying a selective amplifier tuned to double the frequency of the damper 5.

FORUMY; i a and 3 o breteni

The method of determining the magnitude of the gas flow at low pressures by measuring the variable component of the pressure in the constant volume chamber, characterized in that, in order to improve the measurement accuracy, the gas flow is modulated before entering the chamber: a constant volume.

five

 f

H i

 f ,.

..: g A