Volodya Savastiouk [email protected] 13 th Brewer User Workshop. Beijing, China September 12-16, 2011 Brewer calibrations: what do they accomplish? Volodya Savastiouk

13th Brewer User Workshop. Beijing, ChinaSeptember 12-16, 2011

Volodya [email protected]

Brewer calibrations: Brewer calibrations: what do they accomplish?what do they accomplish?

Volodya SavastioukVolodya SavastioukInternational Ozone Services Inc.International Ozone Services Inc.

Full Spectrum Science Inc.Full Spectrum Science Inc.



•Why do Brewers need calibrations?

•What is done during calibrations?

•Recommended calibration frequency.

Presentation outline:



1. The most important aspect of Brewer calibrations: maintaining the same ozone reference for all Brewersa) The world’s reference for Brewers is the triad of Brewers

in Torontob) Traveling reference Brewers with the triad either directly

in Toronto or using traveling references #017 and #1452. Keeping the Brewers in working condition and fixing what’s

broken3. Measuring Brewer characterization parameters

a) Dead time, dispersion, UV response, ND filtersb) Optimal high voltage, SL power

4. Training and educating local personnel

Why do Brewers need calibrations?



Extra Terrestrial Coefficients (ETC):Only a few Brewers are in locations that allow reliable absolute calibrations using the Langley extrapolation technique (Mauna Loa, Izana); the majority of instruments require comparisons with calibrated Brewers for establishing the ETC.

Why do Brewers need calibrations?

Remember how ozone is calculated in the Brewer software?

X=(R6-ETC)/(a*mu)

Measured CalEstablished CalEstablished Calculated

Ozone absorption coefficient (a):established using the results of the dispersion test and the

laboratory-measured ozone cross-sections.



What is done during calibrations?

1. Initial comparison with the traveling standard (if the Brewer is working) Analysing available historical data Collecting solar/sky data side-by-side with the standard Applying the necessary corrections to the ozone calculations

2. Brewer inspection/maintenance Tracker plate, micrometers, push rod, etc. The extent of this is based on the history of the Brewer

3. Characterization tests Dispersion, UV response, ND filters, dead time

4. Final comparison with the standard Adjusting the ETC if needed



Data evolution

Calibration

ETC SL ratio R6cal

Run/Stop

Dead Time

Steps per revolution

High voltage

Data collection: 1. Observations2. Tests3. Notes (log-file)



Red marks indicate that the Run/Stop test was not ideal

Any individual test result does not necessarily describe the state of the instrument.Looking at the historical record is a much more reliable way to diagnose a Brewer.

Overall, this instrument is working fine.



A calibration visit and maintenance improved the RS results



o3 DEADTIME TEST AT 03:46:45, sep 08, 07Deadtime (ns) for filter position 0 (high intensity) 3.787239E-08 (at 03:47:05) 3.875278E-08 (at 03:47:26) 3.93215E-08 (at 03:47:46) 3.742871E-08 (at 03:48:06) 3.821398E-08 (at 03:48:26) Mean = 38.317 Std Dev = .7 Deadtime (ns) for filter position 1 (low intensity) 3.635986E-08 (at 03:49:07) 3.64374E-08 (at 03:49:27) 3.58004E-08 (at 03:49:47) 3.638064E-08 (at 03:50:07) 3.434979E-08 (at 03:50:27) 3.624829E-08 (at 03:50:47) 3.821146E-08 (at 03:51:07) 4.033888E-08 (at 03:51:27) 3.89437E-08 (at 03:51:47) 3.515724E-08 (at 03:52:07) Mean = 36.822 Std Dev = 1.8



Dead time slowly changed from 34 ns to 32 ns



Look for sudden changes in the SL test results



A/D Values for sep 09/07 at 00:24:56 for instrument number ###

Channel# Name Value Value (Lamps off) (Lamps on) 0 Brewer temp 1 (deg C) 23.75 22.81 1 Brewer temp 2 (deg C) -10.94 -10.94 2 Brewer temp 3 (deg C) 21.88 21.88 3 H.T. voltage (V) 1446.46 1446.46 4 +15V power supply (V) 14.87 14.87 5 + 5V power supply (V) 5.03 5.00 6 -15V power supply (V) -15.05 -15.05 7 +24V power supply (V) 23.40 23.75 8 Rate meter (kc/s) 0.00 15.60 9 Not used (bits) 0.00 0.00 10 Not used (bits) 0.00 0.00 11 Not used (bits) 0.00 0.00 12 + 5V ss (V) 4.95 4.95 13 - 8V ss (V) -8.11 -8.15 14 Std lmp current (A) 0.07 1.68 15 Std lmp voltage (V) 0.00 10.23



Sun scan test – final wavelength setting for the Brewer

Cal.step



Data evolution

Calibration DS ozone observations

SL tests

ETCReal-time ozone values

SL-corrected ozone values

SL ratio R6cal

ETC*=ETC+(R6-R6cal)Calibration

ETC SL ratio R6cal



Data evolution

Calibration

Observation

Calibration

Observation

When to do maintenance to preserve calibration history?

Calibration



Recommended calibration frequency

This is a difficult one. From our experience, a calibration every two years is enough for most Brewers. However, we definitely see the most stability with Brewers that are visited every year.

Historical data are often a good indicator on whether the Brewer may benefit from annual calibrations.

Of course, all of this is based on the assumption that regular normal maintenance is done to the Brewer between the calibration visits, but that’ll be the topic of another talk.



In order to maintain (and improve) the quality of the Brewer ozone data regular calibration and maintenance visits are required.

It is extremely important to keep the Brewer network traceable the the main Brewer reference, the triad.

Conclusions:



Thank you!

Eureka, Canada, February 2011

Documents

Volodya Savastiouk [email protected] 13 th Brewer User Workshop. Beijing, China September 12-16, 2011 Brewer calibrations: what do they accomplish? Volodya Savastiouk