SU1281984A1 - Device for preparing the calibrating mixtures - Google Patents

Abstract

This invention relates to methods for producing gas or para-gas mixtures for the calibration of gas analyzers. The purpose of the invention is to simplify the procedure for the preparation of mixtures over the entire calibration range of concentrations and to increase the accuracy of preparation in the field of low concentrations. The goal is achieved by introducing a diluent gas source 1, a diluent gas source 2, a metering vessel in the form of chambers 4, 5, a mixing vessel 6 and a six-way switching valve 3, an additional four-way switching valve 8 and supplying the mixing vessel with a mixing device , made in the form of a pulsed heater 7. 1 Il. x-x-: § (L

Description

This invention relates to methods for producing gas or vapor-gas mixtures for the calibration of gas analyzers.

The purpose of the invention is to simplify the procedure for the preparation of mixtures over the entire calibration range of concentrations and to improve the accuracy of the preparation of mixtures in the region of low concentrations of the reference substance.

The drawing shows a diagram of the proposed device.

A device for preparing calibration mixtures contains a source 1 of gaseous reference substance, a source 2 of a diluent gas, a switching valve 3, a metering vessel in the form of two chambers 4 and 5, a mixing vessel 6 equipped with a heater 7, a switching valve 8, a flow regulator 9 the diluent gas, the pressure regulator 10 and the air throttle 11 installed on the line of the reference substance.

The diagram also shows the connection points of the control manometers 12 and the calibrated gas analyzer 13.

The device works as follows.

Before the start of the dosing cycle, the switching valves 3 and 8 set such positions in which gas flows through channels indicated by solid lines. In this case, the reference gas from source 1 passes through valve 8, chamber 4 of the metering vessel, mixing vessel 6, chamber 5 and is discharged through valve 8 and throttle 11, and the dilution gas from source 2 through valve 3 enters the gas analyzer 13, which time registers the zero level of the output signal of its detection system.

After the vessels are filled with the reference gas, they are switched off with the help of the crane 8 from the source 1. In this case, the reference gas flows through the valve 8 (through the channel indicated by the dotted line) and the choke 11 to the discharge. If necessary, it can be closed.

Then the valve 3 is switched, and the diluent gas from the source 2, the passage through the channels indicated by the dotted lines, displaces the reference gas from the mixing vessel to the analyzer 13, and part of the reference gas remains in the dosing chambers 4 and 5

12819842

vessel. The amount of the reference t-az entering the analyzer can be determined from the Mendeleev equation

PV RT

or gj

PMV RT

(one)

where Gj, is the mass of the reference gas in the mixing vessel;

P, V and T are the pressure, volume and temperature of the reference gas (V V (, is the volume of the mixing vessel);

M is the molecular mass of the reference gas;

R

P v

 pn

universal gas

273.2

constant (Р - normal pressure, V, - volume 1 of gas under normal conditions).

Substituting in equation (1) value

get

G,

- PMVg

273.2 + t

(2)

where t is the gas temperature. WITH; V - volume, dm;

P - pressure, kPa. Accordingly, the amount of reference gas remaining in the dosing vessel is determined by the expression:

 0.12U4 RMU 1,273.2 + t

;

(3)

40

where Va is the volume of the dosing vessel. After displacing the reference gas

and purging the mixing vessel 6 with a diluent gas switch the valve 3 to its original position, together with the chambers 4 and 5 of the dosing vessel with the mixing vessel 6.

At the same time, the heater 7 is powered by a pulse voltage generator (not shown).

The reference gas from the dosing vessel (chambers 4 and 5) through the valve 3 (through channels marked with solid lines) diffuses into the volume of the mixing vessel 6. At the same time, the diluent gas flows from the mixing vessel 6 into the dosing vessel. The mixing process is promoted by the operation of the heater 7, which creates

gives pulsation of pressure and temperature, which provides convective mixing of gases. /.1d1 The nature of the mixing process can be determined by calculation or experimentally and is determined by the design and circuit parameters of the device. - However, for practically tubular doses up to 10 cm long, the mixing time should not exceed 1 minute. The amount of reference gas in the mixing vessel after the first dosing cycle is

A4

The court (chambers 4 and 5) is filled with a reference gas, which comes from source 1 through the channels of the crane 8, indicated by solid lines, 1 after the completion of these operations, switch valve 8, the compartment of the dosing vessel from the source 1 of the reference gas. Then switch the valve 3 to its original position, together

metering and mixing 6 vessels (through channels marked with solid lines) and transferring the diluent gas flow to the analyzer 13.

 G.y,

V. +. У „

(four)

  Accordingly, the amount of reference gas in the dosing vessel after the first dosing cycle

Cia.Va

V, + V

(five)

Using the indicated dependencies, a formula can be obtained for determining the amount of a reference substance in a mixing vessel after each dosing cycle of previously prepared mixtures from the dosing vessel:

g - a Ue with; (V + v,)

ABOUT

(6)

where i 1, 2, 3, ..., p

Thus, repeatedly repeating the dosing and displacement operations described, obtain the required set of mixtures with concentrations of the reference substance decreasing from cycle to cycle.

To calculate the concentrations of the mixtures obtained, one can use the well-known formulas that take into account the pressure of gases in the metering and mixing vessels.

Using the proposed device, it is possible to prepare mixtures with any one given concentration of the reference substance. In this case, the selection of the volumes of the metering and mixing vessels sets the degree of dilution of the reference gas. Before starting the dosing cycle, the mixing vessel is purged with a diluent gas. At this time, the diluent gas stream passes through the channels of the crane 3, indicated by dotted lines. Simultaneously dosing with

After the mixture is obtained, the valve 3 is switched to the purge position and the mixture is forced out into the analyzer 13. Then, with the help of the crane 8, the dosing vessel is connected to the source 1, after which the described dosing cycle is repeated.

five

0

five

0

Claims (1)

Invention Formula A device for preparing calibration mixes containing a source of gaseous reference substance, a source of diluent gas, metering and mixing vessels, a six-way switching valve, the first and fourth fittings of which are connected to the inlet and outlet of the mixing vessel, and the second and third fittings to a diluent gas source and a calibrated analyzer, characterized in that, in order to simplify the procedure of preparing mixtures over the entire calibration range of concentrations and to increase the preparation accuracy in Low concentrations, it is equipped with an additional four-way switching valve, the first fitting of which is connected to the source of the reference substance, and the dispensing vessel is made in mind of two chambers, one of which is connected with its output to the second fitting of the additional tap, and the output to the sixth fitting of the main crane, the second chamber is connected with its output to the pin of the main valve, and the output to the third one of the additional valve, the fourth one of which is connected to the discharge line, and mixes flax vessel equipped with a stirrer, designed as a pulsed heater.