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Boston Technical Center (BTC)

Te-Yang Liu, Ph.D. 劉得洋senior scientist, Research & Development

tliu@servomex.com個人網頁 : http://56123.info

Woburn, MA USA

InsightsInto

H2O MeasurementsCRDS, TDLS

2013 March (v.1.012

水

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• DF-700 Model lineup• H2O spectral characteristics• Cavity ring down spectroscopy (CRDS)• Tunable diode laser spectroscopy (TDLS)

wavelength modulation (WM)• Real World Data • 700 series performance• Live demo on 745SG GSF editor• BTC Facility Photo Tour

Contents

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Servomex TDLS – H2O analyzer models

Model No. bkgrd gas LDL Full RangeDF 750 semi 0.2 ppb 20 ppmDF 760 Dual semi 0.2 ppb H2O 20 ppm

0.075 ppb O2DF 749 semi 0.4 ppb 20 ppmDF 745 semi 2 ppb 20 ppmDF 730* HCl, H2, N2 10 ppb 10 ppm DF 740* NH3, N2 10 ppb 10 ppmDF 745SG specialty 100 ppb 100 ppm

semi: N2, O2, H2, He, ArSpecialty (12): + CO, CO2, SF6, N2O, N2, Kr, Xe; adding new gases…

*: no blending

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Instruments vs. Analyzers

Laboratory instruments:• non-continuous/discrete: requires calibrations before use:

x-ray, APIMS, UV-Vis, FTIR, NMR, GC … etc• performance spec: statistically established – long term stability

Process analyzers:• online 24 hr/7 days, no calibrations:

Servomex DF-700 series• performance & stability spec: empirically challenged & verified

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O

H

H

Transitions:• Electronic: UV-Vis (C)• Vibrational: IR (B)• Rotational: microwave (A)

EV

R

H2O Transitions - spectrum origin

http://chemwiki.ucdavis.edu

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H2O IR Spectrum - fingerprints

1.4 mm region1.9 mm region

Popular detection wavelength at 1392 nm & 1854 nm

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with a lamp source

http://www.iup.uni-bremen.de

http://www.chem.ualberta.ca

Cavity Ring Down Spectroscopy (CRDS)

Perpetual likenumber of passes

Single wavelength detection

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CRDS Simplicity

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R = (t0 c – d) / t0c = (100E-6*2.99792458E10 – 30) / (100E-6*2.99792458E10) = 0.999989993 = 99.998993%

CRDS – mirror reflectivity, & t

for t0 = 100 µs, d = 30 cm,

100 µs = 30 km = 100, 000 passes

TO web

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CRDS – extremely sensitive to R t

Graph 1: Mirror Reflectivity vs. t0

at d = 30 cm

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t0 (µs) R10 ppb of moisture sample

A: t1 (µs) B: Dt (µs) C: eq. res.

200 0.9999950 195.069 4.931 10150 0.9999933 147.209 2.791 18100 0.9999900 98.752 1.248 41

50 0.9999800 49.686 0.314 173

CRDS – reducing resolution vs. tTable 1: resolution vs. t0

Easier to resolve 4.9 µs at 200 µs than at 100 µs.

A resolution Dt = 4.9 µs in time -> 10 ppb at t0 = 200 µs. The same D t can only resolve 173 ppb at t0 = 50 µs.

CRD Optics

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CRDS – reducing resolution vs. t

Graph 2: 1ppb equivalent resolution vs. mirror reflectivity

If a new analyzer with a t0 = 200 µs has a 1 ppb (D t = 0.50 µs) resolution, when t0 decreases to = 50 µs, with same D t = 0.50 µsits resolution is reduced to 16 ppb.

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CRDS – baseline drift vs. R & t0

Graph 3: baseline up-drift due to decaying R , resulting in decaying t0

Graph 4: baseline up-drift due to decayingt0

If not zeroed, reading drifts upwith decaying R.

Q: when?(auto 0?)

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Know CRDS

available: know crds.exe (http://56123.info/56123/?p=725)

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CRDS Limitation – mirror reflectivity

CRDS analyzer’s health indicator: where is the t0? the mirror reflectivity?

Analyzer’s readingAnalyzer’s resolutionAnalyzer’s zero

depends on t0

Two parallel mirrors, infinite passes =>>> Conundrum:

Higher reflectivity -> better resolution ?Higher reflectivity -> less light escape -> less signal

Perpetual-like ∞ number of passes …

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Servomex TDLS - implementation

• H2

O vial

• LASER • Multi-

pass• Herriott

Cell

• Mirrors

• Cell • Wi

ndow

• sample

• Detector

• Focusin

g• Mirr

or

• Gas• Outl

et• G

as

• Inlet

• Io/I

• Wavelength• modulation • Partiall

y reflected reference beam

• reference

• DetectorHerriott cell: resilient self-focusing multi-passesWavelength modulation: S/N enhancementH2O spectrum: absorption peak capture

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2.00

0.01

0.50

1.00

1.50

wavelength (bin)1990 20 40 60 80 100 120 140 160 180

Tunable Wavelength (nm)Laser Current mA

100

50

75

125 LaserWavelengthmodulation

Wavelength vs. current plot

Servomex TDLS – detection scheme (sim)Artfully scan (16 Hz), gather and capture an absorption peak area and shape.

Modulation at ~43 kHz.

The laser wavelength is lockedto reference H2O line center.Checked every 2 seconds.

Laser wavelength tuning: fine: current coarse: temperature

Software monitors more than 25 pars every 2 – 30 seconds

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Servomex TDLS – Voigt profile (sim)

Gaussian: thermal Doppler broadeningLorentzian: pressure broadeningVoigt line shape: convolution of Gaussian + Lorentzian

1.0

0.0

0.2

0.4

0.6

0.8

wavelegth bin2000 20 40 60 80 100 120 140 160 180

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Servomex TDLS – peak profiles (sim)

0.02

-0.03

-0.02

0.00

wavelength (bin)1990 25 50 75 100 125 150 175

1.00

0.00

0.50

1990 25 50 75 100 125 150 175

0.16

-0.16

0.00

1990 25 50 75 100 125 150 175

Original absorptionprofile

1f Voigt profile

2f Voigt profile

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Data and spectra in the presentation are from our customers’ DF-700 units with a standard released firmware.

(unless otherwise stated)

Real World Data

Servomex: DF-700 series H2O analyzers: 1.5 decades of makingDF series O2 analyzers: 4 decades of making

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X: wavelength indexY: 2f H2O intensity Blue: ~200 torrRed: ~760 torr

H2 PB: 2.1E-4, 1.5xH2O/H2: 900 ppb

N2 PB: 3.2E-4, 1xH2O/N2: 350 ppb

Background Gas Pressure Broadening

0.177

0.765

Laser line width << 1/100 absorption peak

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Servomex TDLS – profile modeling

H2O in semi-conductor background gases: N2(3.2E-4, hardest), O2(1.5E-4),

N2 350 ppb 200 torrN2 350 ppb 1 atm

O2 400 ppb 1 atmO2 450 ppb 200 torr

Blue: experimentRed: model

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Servomex TDLS - performance

0.7 ppb of H2O in He background gas2011-04-15 ND-10489

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Servomex TDLS – ppb step linearity

Courtesy: APCI

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Servomex TDLS – sub ppb steps

Courtesy: APCI

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Moisture in Argon

Courtesy of SAES Getters S.P.A.

Servomex TDLS – 2 ppb steps

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Courtesy of SAES Getters S.P.A.

Moisture in Argon

Servomex TDLS – large ppb steps

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Servomex TDLS – long term stability 1

~ 8 years

~ 7 years

~ 8 years

3 customer units

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Servomex TDLS – long term stability 2aTrend period: ~6.5 yr (2,348 days, 4:01:23 ), background: He

User reading:

Raw reading:

1 year:

Summer/fall

1 customer unit

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Servomex TDLS – long term stability 2bContinued from previous page

Ambient temp:

Laser intensity:

Raw reading:

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745SG GSF editor live demo

Easy, very easy to useUser templatesGas blendingExpandable

*PH3: no longer supported in 745SG

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Servomex – visual photo tourrds2

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