ppt intro vacuum gauging
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Copyright 1998 MKS Instruments, Inc.
Introduction to Vacuum Gauging
Neil Peacock
MKS Instruments, HPS Products
Boulder Colorado
neil_peacock@mksinst.com
23 Sept 2010
Copyright 1998 MKS Instruments, Inc.
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.
Copyright 1998 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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
Thermocouple Gauge
Separate Heater & Sense Elements
Constant Current Applied to Heater
Pressure Related to Thermocouple
Output
Thermocouple
Junction
milliVolt Meter
Heater
Power Source
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
Micromachined Pirani Cross Section
Copyright 1998 MKS Instruments, Inc.
High Vacuum Gauges
Indirect - Total Pressure
Hot Cathode (Thermionic) Ion Gauges
Cold Cathode Ion Gauges
Copyright 1998 MKS Instruments, Inc.
Operating Principle of a Hot Filament Ion Gauge
+
e -
i+i-
-
+
30 Volts
150 Volts
Filament
Constant
Emission (Electron)
Current
Ion Current
Copyright 1998 MKS Instruments, Inc.
Bayard-Alpert Ion Gauge
Collector
Grid LeadsFilament Leads
Copyright 1998 MKS Instruments, Inc.
Nude Ion Gauge
Filament
Grid Cage
Collector Guard
CF Flange
Collector
Ceramic Insulator
Copyright 1998 MKS Instruments, Inc.
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 -
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
Ionization Cross Sections
10 100 1000 10,000
Ion Yield
Incident Electron
Energy (eV)
C2 H2
O2 ,CO
Ar
Ne
H2
He
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
+
e -
-
+
Pole Pieces
Magnetic
Field
Cold Cathode Ion Gauge
Several kV
µA
Copyright 1998 MKS Instruments, Inc.
Inverted Magnetron Gauge
Anode
Electrometer Connection
Demountable
End Seal
Cylindrical
Magnet
High Voltage Connection
Copyright 1998 MKS Instruments, Inc.
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)
Copyright 1998 MKS Instruments, Inc.
The Spinning Rotor Gauge
Copyright 1998 MKS Instruments, Inc.
Vacuum
Chamber
2-3/4" CF
Flange
Gauge Head with
Rotor and
Positioning, Drive &
Sense Coils
To
Electronics
The Spinning Rotor Gauge
Copyright 1998 MKS Instruments, Inc.
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)
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
Capacitance Manometers
Direct-Total Pressure
Development
Differential & Absolute Manometers
Ranges, Outputs & Adjustments
Accuracy
Thermal Transpiration
Configurations
Gauge Isolation
Installation & Troubleshooting
Calibration
Copyright 1998 MKS Instruments, Inc.
An Early Capacitance Manometer
Lower Pressure
or Reference
Higher Pressure
or Unknown
Air-Tight Insulating
Housing
Clamped & Flat
Metal Diaphragm
Metal Spacer
Electrode
Copyright 1998 MKS Instruments, Inc.
The Modern
Capacitance Manometer -
Differential
To Electronics
Electrode
Assembly
Diaphragm
Baffle
Reference
Side
Measurement
Side
Copyright 1998 MKS Instruments, Inc.
The Modern
Capacitance Manometer -
Absolute
Getter Pump to
Maintain Low
Reference Pressure
Reference Side Evacuated to
Very High Vacuum
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
Temperature Regulated and Bakeable
Capacitance Manometers
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
Copyright 1998 MKS Instruments, Inc.
High Accuracy Capacitance Manometers
Oven Encloses Sensor
Vibration Isolation with
Fixed Orientation
Connection via Metal
Bellows Tubing
To Signal
Conditioner
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
A "Family" of Heated
Temperature Controlled
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
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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)
Copyright 1998 MKS Instruments, Inc.
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.
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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
Copyright 1998 MKS Instruments, Inc.
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.
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