DE1943645A1 - Method and device for measuring the partial pressure of oxygen - Google Patents

Description

BROWN, BOVERI & CIE. SHARED COMPANY

MANNHEIM BROWN BOVERI

Mp. No. 632/68 'Mannheim, July 31, 1969

Pat / P / Bu,

. _{__;} - "Method and apparatus for measuring the oxygen partial druckes'- '·.

The invention relates to a method and a device for measuring the oxygen partial pressure of a high vacuum, in particular an ultra-high vacuum with a heated one Electron-emitting, arranged in a heating circuit emitter electrode and a collector electrode ,, which in are arranged in an electrical circuit.

The measurement of pressures is generally carried out with a Ionization vacuum meter in which the gas molecules ionize and the ion current is measured '(E.A. Trendelnburg, • Ultra high vacuum, Verlag G.Braun, Kalrsruhe, 1963). The measured ion current is proportional to the total pressure. One However, measurement of the oxygen partial pressure, for example, is not possible in this way.

It is known (E.A. Trendelnburg, Ultra-Hochvakuum, Verlag G.Braun, Kalrsruhe, 1963) to separate the ionized gas molecules from one another with a mass spectrometer, whereby the quotient of charge and mass is always determined. the measured ion currents are then a measure of the partial pressures. However, the effort is very high and above all then not justified if only the partial pressure of oxygen should be measured.

It is still known (vacuum technology, 10th year, p.110), the individual gas components on a heatable surface adsorb. By slowly increasing the temperature of the surface, desorb from a certain temperature the individual gas components, each with a short-term

009813/1525 BADORtGINM.

Pressure rise in the vicinity of the surface occurs. From the 'concerned If the pressure increases, the density of the gas component in question is then determined · However, this method is not industrial applicable, since on the one hand it requires great care and experience and on the other hand easily leads to wrong conclusions. This method still assumes a finite volume, so the pressure rise can be measured,

The invention is based on the object of the partial oxygen measure pressure in a high vacuum or ultra-high vacuum room, without the other gas components affecting the measured values, a Have influence, the method also used to determine the Oxygen partial pressure in space is applicable. In addition, the measurement should focus on the determination of the oxygen differential pressure be expandable in gases and vapors under normal, positive and negative pressure outside the measuring room

This object is achieved according to the invention in that the Oxygen partial pressure ρ according to a relationship

■ in ρ _β f (I, T)

is measured, the temperature T of the emitter electrode is always so high that only oxygen is adsorbed, and I the Circuit is flowing current.

In particular, with a constant current I, the temperature T can Emitter electrode from the relationship between T and. the heating current! j ™ of the emitter electrode. . \

can be determined »For this purpose, the Emitter electrode arranged an ammeter.

The invention assumes that above one of the oxygen partial pressure Depending on the temperature, only oxygen is adsorbed but not all other gases. Depending on the temperature T of the metal surface, it then arises a certain surface occupancy Θ, which is determined by the oxygen

009813/1525 " ₃ V

■ ■. - 3 -

partial pressure depends on ^v

β = f ₂ (T, ρ)

As a result of this occupation, the work function of the surface for electrons changes according to the relationship

ψ = ± ₃ (ο) = -f ₃ (f ₂ (τ, p)) = f ₄ (τ, p)

For this reason, the current I changes with the work function according to the Richardson equation I = PA _n T ² exp (-J. .Φ) = F AT ² exp (- 1. F. (T, p))

kT kT

■ 2

F = emitting area of the emitter electrode in cm

\ A = Richardson's constant
k = Boltzmann constant

This equation can be solved for ρ, so that with constant Current I the oxygen partial pressure ρ is a puncture of the temperature T. '

In ρ = f (T) ₁ _

const

The method is accordingly carried out in such a way that, at constant current I, the change in the temperature of the emission, electrode is measured.

Because the temperature of the emitter electrode is a puncture of its heating current!

follows

in ρ -% (I _HZ ) _{lB oonst}

With a constant current I, the oxygen partial pressure is thus determined from the heating current. For this purpose .ein at well-known ionization manometers can be used, with an ammeter arranged in the heating circuit *

0098137152Ö _ ₄ _

'. ■■■' ■■ '. ■■■. ■ ': ■■■ -

Based on the measurement method described and that of the Device for leak detection applied idea can be the partial pressure of oxygen can be determined outside the measuring area by marking the high vacuum vessel with a normal · * · »over or Vacuum space is connected by a defined leak and the oxygen partial pressure is determined in the latter. During the measurement, a constant is generated by means of a pump Working pressure kept in the high vacuum vessel. Particularly when using a tungsten emitter, it is recommended that the Reduce the working pressure to less than 10 torr. That a defined leak can be a metering valve through which the gas to be examined enters.

In the drawings, exemplary embodiments for the method are given, which are described below * They show:

Fig. 1 shows an arrangement for performing the method at (constant current I.

2 shows a registered family of curves, where the current I Parameter is.

• Pig. 3 an arrangement for determining the oxygen partial pressure outside the measuring room "

! In the heating circuit of an emitter electrode 1, which is in front of a j collector electrode 2 is arranged, there is a current

"! meter 3. The heating current is supplied by a voltage source 4 ■ '.

supplied In the circuit of the collector electrode and the emitter

Another ammeter 5 and a further voltage source 6, the positive pole of which is connected to the collector electrode, are located at the end of the electrode. A regulator 7 keeps the current I ί at an adjustable value. The collector electrode and the: emitter electrode are eioh in the space 8, the oxygen: to be determined partial pressure · ■

Q 0 98 iy j 5.2 p

The ammeter 5 is used to monitor the constant current. To calibrate the arrangement, various oxygen partial pressures are determined by means of a mass spectograph and the associated values of the heating current 1 ^ _{2 are recorded} at a constant current I. In this way, Pig. 2 a family of curves, where the current I is a parameter

The method according to the invention is also particularly advantageous when searching for leaks in a vacuum system through a leakage point penetrating air always has a certain oxygen concentration, so that a certain oxygen partial pressure is set in the vacuum system

If you direct a stream of oxygen at the leak, then the oxygen partial pressure increases. The leak detection passes accordingly in that a nozzle, from which oxygen flows, is guided along the parts of the apparatus. Any leaky Place is then indicated by a very rapid increase in oxygen par tialdruekes.

The arrangement shown in Fig. 3 is used to determine the oxygen partial pressure outside the space 8, or of the high vacuum vessel. The high vacuum vessel is via a defined leak 9, e.g. a valve with a linear flow characteristic 8 connected to an outer caterpillar 10, which to contains gas to be investigated. Another known connection Cross section 11 leads to a pump 12.

The pressure in the high vacuum vessel is kept constant by means of the pump 12 held. The amount of gas withdrawn from outside space 1 ο for this is negligibly small compared to the total amount, so that the conditions in the outer space 10 do not change. With known total external pressure can be measured by measuring the Easily determine the Saueratoffpartialdruckes in the high vacuum 8 that in the outer space.

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■ - β -

To get from Saueratoffpartialdruck: in the high vacuum vessel 1 to the to be able to conclude in an outside space 5 of small dimensions, the amount of gas withdrawn from the outer space 5 must be known. The high vacuum flowing into the high vacuum in a certain unit of time The amount is proportional to the opening of the dosing valve The flow rate is proportional to the amount generated by the pump Pressure difference between the pressure in the pump line and in a high vacuum / The change in quantity that occurred in the same time unit in a high vacuum results from the difference of inflow and outflow and is proportional to the change in pressure in a high vacuum. By means of previous measurements and / or calculations, one will determine the flow rate in order to also be able to use this Case of being able to determine the partial pressure of the oxygen by measuring at constant working pressure · '·

The advantage of the method according to the invention lies in its simple feasibility and, above all, that any known ionization vacuum meter can be used, in the heating circuit of which an ammeter is arranged. Afterward A one-time calibration in the manner described is sufficient.

Such ionization manometers can also be used on space flight devices for measuring the partial pressure of oxygen in space.

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Claims (6)

.- 7 claims Method for measuring the partial pressure of oxygen in a high vacuum, in particular an ultra-high vacuum with a heated electron emitting emitter electrode arranged in a heating circuit and a collector electrode arranged in an electrical circuit, characterized in that that the partial pressure of oxygen (p) according to an equation. In ρ = f (I, T) is measured, the temperature T of the emitter electrode Ci) is always so high that only oxygen is adsorbed on it and I is the one flowing in the circuit Electricity is. 2. Apparatus for performing the method according to claim 1, characterized by the use of a Ionization vacuum meter with one in the heating circuit arranged ammeter (3) 3 * Use of the device according to claim 2 as a leak detector for vacuum systems. 4. The method according to claim 1, characterized in that the high vacuum vessel (θ) with a normal, positive or negative pressure space do) through a defined leak (g) is connected and that the oxygen partial pressure in the latter do) is determined. BAD ORIGfNAL 009813/1525 5. The method according to claim 4, characterized in that in the high vacuum vessel (β) by means of a pump (12) constant working pressure is established ! 6. The method according to claim 4 and 5, characterized in that the working pressure is less than 10 ~ ⁴ T.orr. 009 * 13715 2.5 Read more