1. CALIBRATION
CALIBRATION OF AIR POLLUTION MONITORING INSTRUMENTS
Monitoring instruments used for assessment of air pollution are prone to drift and may
show variations in measured parameters. Hence it is a false expectations that their
calibration is stable over long period of time. Therefore, these instruments are need to
be calibrated at indicated frequency for reliable estimates.
Calibration is checking of any scale, reading or value, digital or analogue by comparing
it with an absolute standard and observed drift /variation must be account for while
measurement/calculation for reliable estimation of parameters. This is also one of the
basic necessity tor ISO-14000 accreditation where more and more stress is given for
ensuring reliability of value measured by instrument. Thus by adopting regular
calibration practices one can get precise and accurate measurement of parameters.
Calibration need to be adopted.
• When instrument is newly installed
• When instrument is transported to a new location and in different climatic
condition.
• If instrument is operated after interruption of several months.
• After observing significant drift either in zero or in span value
Besides, it is necessary to check the calibration - relationships of all monitoring
instruments on a pre-determined schedule.
Recognising the vital need of calibration across the country for air pollution monitoring
so that reliable quality data are generated, Envirotech has set-up following reference,
calibration facilities for calibration of Envirotech air pollution monitoring instruments.
( I ) Set-ups for calibration of flow
a Standard critical orifice - fitted calibrator
» Soap bubble meter
• Dry gas meter
• Wet gas meter
( ii ) Set - up for calibration of temperature
• Standard thermometer
® Digital Pyrometer using thermocouple
2. (iii ) Set-up for Calibration of Relative Humidity
• Standard Humidity Chambers
( iv ) Set-up for calibration of vacuum
• Standard vacuum gauge
( v) Set-up for calibration of time
• Standard stop watch & time totalizer unit.
( vi ) Set-up for calibration of differential pressure.
• Standard digital differential pressure monitor.
( vii ) Pitot tube calibration set-up
• Wind tunnel Set-up available at I.I T. Delhi
( viii) Wind - velocity calibration Set-up
• Wind Tunnel Set-up available at l.i.T. Delhi
All above reference set-ups are calibrated to a traceable national standard at highest
possible accuracy's. To ensure this the measurements for these Set-ups are done at
least one order better than the least count of the instrument.
CALIBRATION PRACTICES AT ENVIROTECH
Following calibrations are performed at Envirotech for various type of instruments using
forbid set-ups. These set-ups are available at Envirotech with valid tractability for
recalibration of Envirotech Instruments as per requirements at nominal cost of
calibration
( 1 ) High Volume Sampler / Respirable Dust Sampler
• Orifice plate based flow metering adopted in the instruments is calibrated against
basic system available at Gas Dynamics Lab I.I T Delhi
9 Individually certified Top loading calibrator is used for further checking of
instruments
• Time totalizer unit is calibrated against standard certified clock.
Rotameter of gaseous attachment is calibrated using NPL certified soap film
calibrator.
3. ( 2 ) STACK MONITORING KITS
• Each pyrometer and thermocouple is calibrated against standard certified
system traceable to national standard.
• Each Pitot is tested at l.l.T. Delhi thus Pitot calibration constant of each tube is
certified.
• rotameter are calibrated against standard certified dry gas meter and soap film
calibrator.
• Vacuum gauge is calibrated against standard certified gauge.
( 3 HANDY AND PERSONAL SAMPLER
• Rotameter is calibrated against standard NPL certified soap film calibrator.
( 4 ) WIND MONITORING SYSTEMS
• Wind speed is calibrated using standard l.l.T. Certified wind speed sensor.
B Reference set-up is available for wind direction calibration.
• Temperature and humidity sensors are calibrated using reference standard
thermometer and fixed humidity chambers.
B Rainfall sensor is calibrated by known quantity of water.
B Each solar sensor is calibrated against a standard certified solar sensor.
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