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Cambridge Particle Meeting
The Traceable Calibration of Condensation Particle Counters
Hans-Georg Horn+, Oliver F. Bischof+, Wei Liu++
+TSI GmbH, Aachen, Germany++TSI Incorporated, Shoreview MN, USA
Cambridge Particle Meeting - 2006
Why calibrate CPCs?
Condensation particle counters (CPCs) have been used to measure number concentration of ultrafine particles for almost 30 years
As part of scanning mobility particle sizer (SMPS™) to measure size distributions as well
Currently new regulations involving particle number concentration measurements are discussed Hence, calibration of CPCs using a traceable method to ensure proper performance is required
Method to calibrate smallest particle size detection limit, counting efficiency & concentration linearity
What is a Calibration?
Calibration:2)
The set of operations that establish, under specific conditions, the relationship between values for quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values realized by standards.
2) International Vocabulary of Basic and General Terms in Metrology, 2nd ed.,BIPM/IEC/IFCC/ISO/IUPAC/IUPAP/OIML, International Organization for Standardization (ISO), 1993 (VIM), 6.11
Calibration Method
The calibration method at TSI follows the well-known ‘primary absolute calibration’ method first described by leading aerosol scientists B. Liu and D. Pui in 1974 3)
3) Liu, B.Y.H. and D.Y.H. Pui [1974]. A Submicron Aerosol Standard and the Primary Absolute Calibration of the Condensation Nucleus Counter.J. Coll. Int. Sci., Vol. 47, pp. 155–171
Calibration Setup
Compressed Air Filtered Air
Supply
Electrospray Aerosol
Generator
Electrostatic Classifier with
nano-DMAAerosol
Electrometer
Test CPC1.5 L/min
Make-up Air
1.5 L/min
Po-210 Neutralizer
Flow Meter
FlowSplitter
CO2
Electrospray AG generates (emery oil) particlesDMA selects singly-charged, monodisperse particles of known size Monodisperse aerosol mixes with filtered air & splits equally into aerosol electrometer and CPCCounting efficiency: ratio CPC / electrometer readings
Calibration Details
This presentation discusses calibration results for standard TSI model 3010 and 3010D (PMP) CPCs.
Smallest particle size detection limit & Counting efficiency
Concentration linearity
CPC intercomparison
Traceability of Calibration Method
Traceability of the CPC calibration method depends on:
The ability of generating singly-charged, monodisperse particles of known size
The ability of measuring particle concentration accurately using a reference aerosol detector
Monodispersity of Particles
Step 1: Particles generated by electrospray(22 nm, GSD = 1.46) Step 2: Particles generated by
electrospray and selected by DMA (22 nm, GSD = 1.04)
Electrospray-generated, DMA-selected particles: 50 nm: GSD = 1.0490 nm: GSD = 1.11
Traceability – DMA
VL2)rrln()]qq(2/1q[
Z 12mptp π
+−=
Flow rates (qt=qs+qp) – NIST traceable flow metersSheath flow rate (qs)Polydisperse/Monodisperse aerosol flow rate (qp = qm)
Geometric parameters – NIST traceable bore gage, micrometer, and caliper
r1 / r2 = inner / outer electrode radiusL = characteristic length between aerosol inlet/outlet slits
Voltage on center electrode (V) – calibrated with NIST traceable kilovolt divider
In a cylindrical DMA, Zp of selected particles is
Aerosol Electrometer
where: N = particle number concentrationV = electrometer voltage reading (IR)e = unit charge, 1.602 x 10-19 CR = resistance of resistornp = number of charges per particleqe = air flow rate
ep qnReVN
⋅⋅⋅=
InducedCharge Flow(Current)
Particle Filter
Charged Aerosol Particles
I
Air Flow
Resistor
VR
Traceability – Aerosol Electrometer
Unit charge (e) – is a constant (1.602 x 10-19 C)Resistor (R) – 1% precision, measured by manufacturer using NIST traceable standard Particle charge (np) – verified to be unity (1.0) by SMPSFlow rate (qe) – NIST traceable flow meter
Aerosol Electrometer Inlet Losses
Particle losses as a function of particle size and flow rate
0.00%
1.00%
2.00%
3.00%
4.00%
5.00%
6.00%
7.00%
1 10 100
Particle Size (nm)
Diffu
sion
Los
s (%
)
1 l/min3 l/min5 l/min
Laminar flowTube length 10 cmT = 293 KP = 101.3 kPa
Inlet tubing to the Faraday cage must be kept as short as possible or losses must be quantified and corrected.
Calibration Details
Smallest Particle Size & Counting EfficiencyDepending on CPC model, 10 – 14 particle sizes below 100 nm used for counting efficiency curve Particle concentration < 104 P/cm3
CPCs 3010, 3010D (or other models) can be tested simultaneously• Model 3776 is tested one by one due to low concentration at
their smallest particle sizesTo eliminate need for diffusion loss correction• Equal tube lengths from flow splitter to electrometer & CPCs• Equal flow rates for electrometer & CPCs
CPC concentrations corrected for coincidence
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1 10 100Particle Size, nm
Cou
ntin
g Ef
ficie
ncy,
%SN2311_StandardSN2454_StandardSN2460_StandardSN70419349_StandardSN70419353_Standard
Results: Counting Efficiency of 3010
SN2311_S SN2454_S SN2460_S SN70419349_S SN70419353_S Size RangeD10, nm 7.2 6.5 6.4 6.9 6.5 6.8 ± 0.4D25, nm 8.3 7.6 7.5 8.0 7.4 7.9 ± 0.5D50, nm 9.9 9.1 9.1 9.7 8.9 9.4 ± 0.5D75, nm 11.9 11.0 11.0 11.7 11.1 11.4 ± 0.4D90, nm 14.0 13.0 13.0 13.8 13.6 13.5 ± 0.5
Standard 3010 CPC
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1 10 100Particle Size, nm
Cou
ntin
g Ef
ficie
ncy,
%SN2454_ModifiedSN2460_ModifiedSN70419351_ModifiedSN70419352_ModifiedSN70419354_ModifiedSN2311_StandardSN2454_StandardSN2460_StandardSN70419349_StandardSN70419353_Standard
PMP Range
Modified 3010D CPC
SN2454_M SN2460_M SN70419351_M SN70419354_M SN70419352_M Size Range PMP RangeD10, nm 15.9 16.2 15.8 16.4 16.5 16.1 ± 0.4 16 ± 1
18 ± 223 ± 337 ± 4
D25, nm 17.9 18.2 17.9 18.5 18.4 18.2 ± 0.3D50, nm 21.3 21.6 21.5 22.1 21.9 21.7 ± 0.4D90, nm 34.9 35.3 33.4 33.9 34.8 34.3 ± 1.0
Results: Counting Efficiency of 3010D
Standard 3010 CPC
Counting Efficiency 3010D
0%10%20%30%40%50%60%70%80%90%
100%110%
1 10 100Particle Diameter, nm
Cou
ntin
g Ef
ficie
ncy
705070037050700470507005705081457050814670515208705170757051707670517077705242097052421070524211
CPC Efficiency
PMP Lower Limit (nm)
PMP Mid Diameter (nm)
PMP Upper Limit (nm)
10% 15 16 17 25% 16 18 20 50% 20 23 26 90% 33 37 41
Counting Efficiency Results for Twelve 3010D Production CPCs.
Concentration Linearity
Concentration LinearitySetup for concentration linearity response 4)
50 nm particles chosen for ~100% counting efficiency for CPCSix to ten concentrations levels, depending on CPC model• Higher concentrations reduced by dilution bridge
Equally spaced from 0 - 104 P/cm3 (CPC 3010) and 2,000 to 300,000 P/cm3 (UCPC 3776) respectivelyReference instrument• Aerosol Electrometer 3068A (for 3776 only for validation)
- From April 2006 new aerosol electrometer model 3068B
4) Liu, W., B.L. Osmondson, O.F. Bischof and G.J. Sem (2005). Calibration of Condensation Particle Counters. SAE Paper No. 2005-01-0189.
Linearity Response of 3010 & 3010D
Slope = 0.953 to 0.973R2 > 0.9988
2454: y=0.9569x, R2=0.99912460: y=0.9676x, R2=0.9991
70419349: y=0.9731x, R2=0.998870419353: y=0.9532x, R2=0.998870419351: y=0.9693x, R2=0.998870419352: y=0.9670x, R2=0.998870419354: y=0.9668x, R2=0.9988
0
2000
4000
6000
8000
10000
12000
0 2000 4000 6000 8000 10000 12000
Electrometer Reading, particles/cm3
CPC
Rea
ding
, par
ticle
s/cm
3
2454_30102460_301070419349_301070419353_301070419351_3010D70419354_3010D70419352_3010D
Linearity of 3010D (Production)
70515208y = 1.02x
R2 = 0.9967
70507003y = 0.9666xR2 = 0.9997
70507004y = 0.9508xR2 = 0.9999
70507005y = 0.9713xR2 = 0.9997
70508145y = 0.9593xR2 = 0.9997
70508146y = 0.9657xR2 = 0.9997
70517076y = 0.968x
R2 = 1
70517077y = 0.9757x
R2 = 1
70524209y = 0.9804xR2 = 0.9996
70504210y = 0.9822xR2 = 0.9996
70524211y = 0.9861xR2 = 0.9997
70517075y = 0.9667xR2 = 0.9999
0
2000
4000
6000
8000
10000
12000
14000
0 2000 4000 6000 8000 10000 12000 14000Electrometer Reading, particles/cm3
3010
D C
PC R
eadi
ng, p
artic
les/
cm3
705070037050700470507005705081457050814670515208705170757051707670517077705242097052421070524211
Linearity Response of Twelve 3010D Production CPCs.