ppt intro vacuum gauging

Copyright 1998 MKS Instruments, Inc.

Introduction to Vacuum Gauging

Neil Peacock

MKS Instruments, HPS Products

Boulder Colorado

[email protected]

23 Sept 2010


Introduction to

Vacuum Gauging

Techniques

Copyright 1998 by MKS Instruments, Inc.

All rights reserved. No part of this work may be reproduced or

transmitted in any form or by any means, electronic or

mechanical, including photocopying and recording, or by any

information storage or retrieval system, except as may be

expressly permitted in writing by MKS Instruments, Inc.


Topics

Units and Conventions

Thermal Conductivity Gauges

Thermocouple

Pirani

Ionization Gauges

Hot Cathode

Cold Cathode

The Spinning Rotor Gauge

Capacitance Manometers

Residual Gas Analyzers

Indirect

GaugingTotal

Pressure

Gauging

Direct Gauging

Partial Pressure Gauging


Rough

Medium

High

Ultra

High

Thermal

Conductivity

of Residual Gas

Ionization of Residual Gas Drag Induced by

Residual Gas on

Moving Object

Force Applied

to Surface

Hot &

Cold Cathode

Ion Gauges

Residual

Gas

Analyzer

Gas

Composition

Analysis

System

Total

Pressure

Measurement

Spinning

Rotor

Gauge

Capacitance

Manometer

Ranges of Vacuum Gauges

Thermo-

couple &

Pirani

Gauges

Convection

Pirani

Atm

100

10-3

10-8


Thermal Conductivity Gauges

Total Pressure - Indirect

Conduction Independent of

Pressure

0.0001 0.001 0.01 0.1 1.0 10

Gas Pressure (Torr)

Heat

Transfer

H

E

A

T

S

E

N

S

E

Thermos

Bottle

Radiation & Lead Losses Dominate

hνννν

Thermal

Conductivity

Varies with

Pressure


Thermocouple Gauge

Separate Heater & Sense Elements

Constant Current Applied to Heater

Pressure Related to Thermocouple

Output

Thermocouple

Junction

milliVolt Meter

Heater

Power Source


Pirani Gauge

A filament with a high temperature coefficient

of resistance forms the sensing element.

The tube with sensor forms one leg of a bridge

circuit. A temperature compensating resistor

is located in the adjacent leg.

Changing resistance of the filament due to

pressure changes causes an imbalance

and a corresponding indication on the meter.

Circuit for Constant

Temperature Operation


0.0001 0.001 0.01 0.1 1.0 10

Gas Pressure (Torr)

Dry Nitrogen, Air

Xenon

Argon

Hydrogen

Helium

Krypton

Heat

Transfer

Water

10 Torr FS

Gas Sensitivity of Thermal

Conductivity Gauges

HeH

NeFONC

Si P S Cl Ar

Br Kr

Xe

1.0 4.0

14.012.0 16.0 19.0 20.2

28.1 31.0 32.1 35.5 39.9

79.9 83.8

131.3

Xe

AirHe


Convection Pirani Gauge

FilamentOrientation

Mark

Convection

Current

Pressure

(Torr)

Pirani Transducer Output Voltage

10-3

10-2

10-1

1

10

100

1000

Convection Mode

Pirani Mode

(Molecular Conduction)

Transition Region

(Reduced Sensitivity)

0 61 2 3 4 5


Micro Machined Pirani Gauges

n MicroMachined

– Conceptually the same,

– Different method of

manufacture

Temperature measurementresistors Rt

Silicon cover

Silicon cover

Measuring resistors Rm

Rm1

Rt1

Rm2Ro

Uout


Micromachined Pirani Cross Section


High Vacuum Gauges

Indirect - Total Pressure

Hot Cathode (Thermionic) Ion Gauges

Cold Cathode Ion Gauges


Operating Principle of a Hot Filament Ion Gauge

+

e -

i+i-

-

+

30 Volts

150 Volts

Filament

Constant

Emission (Electron)

Current

Ion Current


Bayard-Alpert Ion Gauge

Collector

Grid LeadsFilament Leads


Nude Ion Gauge

Filament

Grid Cage

Collector Guard

CF Flange

Collector

Ceramic Insulator


Grid

Filament

Collector

e -

+

+

e -

e -

Processes within the Bayard-Alpert Ion Gauge

An electron loops around the grid

and ionizes a molecule which is then

attracted to the collector.

An electron strikes the grid,

producing an x-ray. The x-ray

reaches the collector where a

photoelectron is produced. This

photoelectron may or may not

produce another ion.

An electron strikes the grid,

desorbing an ion which is then

attracted to the collector. An x-ray

may also be produced.

e -


10-3 -9

10-6

10-12

10

10-3

-910

-610

-1210

0.1mA

1 mA

Ion Current

(Amps)

Pressure (Torr)

The Ion Gauge Equation

Spurious

Currents

May be Worse

with Poor

Degassing

Triode Gauge

B-A Gauge

Ion Current = Gauge Constant x Electron Current x Pressure + Spurious Currents

i = K i P + i-+ r

Ion Current vs Pressure for

Various Electron Currents,

Gauge Factor = 10


Filament Materials

Tungsten Coated Iridium

LifeExpectancy

Long life in vacuumenvironment

Survives exposure to atmospheric air

Reactivity Less reactive with most residuals

Can be "poisoned" by hydrocarbons, halogens.May produce interesting

by-products

Stability More stable KLess stable K

E-beam degas maychange emission

OutgassingMore power required

for given emission - moretendency to outgas

Lower powerconsumption - less

outgassing


Ionization Cross Sections

10 100 1000 10,000

Ion Yield

Incident Electron

Energy (eV)

C2 H2

O2 ,CO

Ar

Ne

H2

He


Gas TypeSensitivity Relative to Nitrogen

Helium 0.15

Hydrogen 0.46

Water 0.89

Neon 0.24

Nitrogen 1.00

Carbon Monoxide 1.07

Oxygen 0.84

Argon 1.19

Carbon Dioxide 1.37

Krypton 1.86

Xenon 2.73

Ion Gauge Gas Sensitivity


Some Other Factors Affecting

Accuracy or Repeatability

Distortion of Internal Elements

Charging of the Glass Envelope

Gas Composition

Outgassing

Controller Stability

Gauge Pumping

Presence of Magnetic Fields


+

e -

-

+

Pole Pieces

Magnetic

Field

Cold Cathode Ion Gauge

Several kV

µA


Inverted Magnetron Gauge

Anode

Electrometer Connection

Demountable

End Seal

Cylindrical

Magnet

High Voltage Connection


Electron Processes within an inverted magnetron gauge

Inverted magnetron

High cathode-anode potential or

cosmic ray generates “first”

electron/ion

Electron accelerates to anode but is

“caught” in crossed E and B fields

Electron strikes atom, produces ion,

secondary electron(s)

Ion strikes cathode (because it is

heavier and will not spin as much), is

counted, and generates secondary

electron(s)


Vacuum

Chamber

2-3/4" CF

Flange

Gauge Head with

Rotor and

Positioning, Drive &

Sense Coils

To

Electronics



Spinning Rotor GaugePermanent Magnets (2)

Vertical

Stabilization

Coils (2)

Drive

Coils (4)

Sense

Coils (2)

Cylindrical

Vacuum Tube

Rotor

Case &

Magnetic

Circuit

Lateral

Damping Coils (4)


SRG Equation:

−1

ω

dω

dt= σ

10

π

1

ad

p

c

– Ball is accelerated to 400 Hz and then allowed to decelerate

– Ball decelerates about 10 Hz, data obtained, re-accelerated

– The equation is

– where� ω is angular rotation

� σ is tangential momentum accommodation coefficient of the ball

� a is the radius of the ball

� d is the density of the ball

� c is the average speed of the molecules

� p is the pressure

σ, a, d depend on ball

σ, c depend on gas



Direct-Total Pressure

Development

Differential & Absolute Manometers

Ranges, Outputs & Adjustments

Accuracy

Thermal Transpiration

Configurations

Gauge Isolation

Installation & Troubleshooting

Calibration


An Early Capacitance Manometer

Lower Pressure

or Reference

Higher Pressure

or Unknown

Air-Tight Insulating

Housing

Clamped & Flat

Metal Diaphragm

Metal Spacer

Electrode


The Modern

Capacitance Manometer -

Differential

To Electronics

Electrode

Assembly

Diaphragm

Baffle

Reference

Side

Measurement

Side


The Modern

Capacitance Manometer -

Absolute

Getter Pump to

Maintain Low

Reference Pressure

Reference Side Evacuated to

Very High Vacuum


Bridge

Oscillator Reference

Buffer,

Scaling,

Amplifi-

cation

Output

Span Pot

Linearity Pot

Zero Pot

Px

Electronics

Pr

A Complete Transducer: Pressure Sensor with Signal Conditioning Electronics


10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10

100

1000

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

Pressure (Torr)

Four Decade Manometer -

Ranges & Output

in Hg

mmHgmbars

KPa

in H O2 cm H O2ZERO

x10-3

1 Torr Full Scale

General Purpose

Capacitance Manometer


10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10

100

1000

1000 Torr

10 Torr

0.1 Torr

A "Family" of Capacitance Manometers

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV


Zero, Span, Linearity

Full Scale

Zero

Properly

Adjusted

Not

Zeroed

Span

Out of

Adjust.

Linearity

Out of

Adjust.

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mVResolution

Actual

PressureOutput

Indicated Pressure


Zeroing

Screwdriver

for Zero

Adjustment

Vacuum at or

Below Maximum

Zeroing Pressure

in Hg

mmHgmbars

KPa

in H O2 cm H O2ZERO

Output Signal

Or, Zero at Display or

Controller


1.010100

100

10V 1.0 0.1 .01 1mV

1

10

0.1

0.1 0.01

Zeroing

Pressure

Control

Range

Reading

Range

Reading as % of Full Scale

Output Voltage

Error

(% of Reading)

Total Error with

10 degree C Temperature

Change

Base Accuracy

(0.25% of Rdg.)

Effect of the Temperature Coefficients


Indicated

Pressure

True Pressure

Full

Scale

Full Scale

% of Reading Error

Band

% of Full Scale Error

Band

Non-Linearity

Hysteresis

Non Repeatability

Span Temp Coefficient

Resolution

Zero Temp Coefficient

0

0

Error Summary


Temperature Regulated and Bakeable


Constant

Temperature

OvenHigh Temperature with Heated

or Bakeable Sensors & Remote

Electronics

Heated

Sensor

Signal

Conditioning

Heated

Sensor

Signal

Conditioning

100-150 Degrees C

125-200

Degrees C

45-100 Degrees C


High Accuracy Capacitance Manometers

Oven Encloses Sensor

Vibration Isolation with

Fixed Orientation

Connection via Metal

Bellows Tubing

To Signal

Conditioner


10V

1.0

0.1

.01

1mV

.1mV

Control

Range

Reading

Range

Zeroing

Pressure

4 Decade

General Purpose

Capacitance

Manometer

5 Decade

High Accuracy

Capacitance

Manometer

Range Comparison: General Purpose, Temperature

Controlled and High Accuracy Capacitance Manometers

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10-8

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

Temperature

Controlled

Capacitance

Manometer


A "Family" of Heated

Temperature Controlled


Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

10

100

1000

1000 Torr

10 Torr

0.1 Torr

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

Zeroing

Pressure

Control

Range

Reading

Range

10V

1.0

0.1

.01

1mV

0.02 Torr


1.010100

10V 1.0 0.1 .01 1mV

0.1 0.01 Reading as % of Full Scale

Output Voltage

Error

(% of Reading)

100

1

10

0.1

0.01

0.25% Rdg.

Acc.

Temp .Coeff.

Induced Error

0.05% Rdg.

Acc.

Temp .Coeff.

Induced Error

Total Error with

10 degree C Temperature

Change

Control

Range

Reading

Range

Accuracy Comparison: Non-Temperature Regulated

vs High Accuracy


Zero Shift

Observed as an offset in the output, increasing over

a period of time. Almost always due to

a build-up of material on the diaphragm.

Direct Impingement - Sputtered

Particles, Radiation (Heat)

Condensables and Particulates

Contamination

(Surface Area Effects)

Diaphragm Contamination

(Zero Effect)


Thermal Transpiration

Manometer is Warmer than the

Attached Chamber and

the Connection is

in Molecular Flow.

Usually Seen with Heated

Manometers at

Pressures <<1 Torr.


Micromachined Piezo Gauge

Micro-Machined Piezo Resistive Gauges

Transforms mechanical stress due to

pressure to electric signal

Resistance change of mono crystalline

semiconductor

Fast response to pressure changes

Differential or absolute

Available with stainless steel membrane


Combination or Wide Range Gauges

PiezoSensor

uProcessor50 msec50 msec50 msec50 msecuPiraniSensor

HCSensor

(master)uProcessor

uProcessor

SPISPISPISPISPISPISPISPI PC

485485485485Controller

250 msec250 msec250 msec250 msecPiezoSensor

50 msec50 msec50 msec50 msecupdateupdateupdateupdatetimetimetimetimeuPiraniSensor

HC

Sensor

(master)uProcessor

Controller

PC

48548548548550 msec50 msec50 msec50 msec999

@2006

999@2005


Thank you for your interest in this presentation.

If you have questions, current or future chamber

needs, please contact me or your local MKS

Instruments office.

ppt intro vacuum gauging

Documents

gas pressure torr dry

pressure changes

pirani gaugea filament

adjacent leg

sensor forms

hps productsboulder

sensing element

arbr krxe1