Quick Answer
Dissolved oxygen meter calibration uses the air-saturated water method (100% saturation at known temperature and pressure) as a reference point, and oxygen-free water (sodium sulphite solution) for zero check. The NABL certificate states DO accuracy at defined temperature and pressure.
Key Takeaways
- DO meter calibration uses water-saturated air reference (100% saturation at defined T and P).
- Zero point calibrated using oxygen-free water (sodium sulphite solution, 0% saturation).
- Temperature compensation verification is part of DO meter calibration.
- GPCB requires DO > 4 mg/L in treated effluent discharged to inland surface water.
- Prism calibrates Clark-type (membrane) and optical luminescence DO sensors.
DO Meter Calibration Methods
Air Saturation Method (100%)
Probe placed in water-saturated air (moist air in calibration chamber). DO meter set to 100% saturation at measured temperature and barometric pressure.
Zero Point (0%)
Probe submerged in freshly prepared sodium sulphite (Na₂SO₃) solution which chemically removes all dissolved oxygen. DO meter should read 0.00 mg/L.
2-Point Calibration
Using both 0% and 100% saturation points to verify full-scale linearity. Required for high-accuracy DO measurements in pharma and research.
Applications in Gujarat Industries
- ETP/STP aeration tank DO monitoring (GPCB compliance)
- Drinking water quality monitoring (BIS 10500: min 6 mg/L DO)
- Aquaculture and fish farming (minimum 5 mg/L for fish health)
- Pharmaceutical fermentation DO control
- BOD (Biological Oxygen Demand) testing for wastewater characterisation
- River and lake water quality monitoring
Frequently Asked Questions
What is the NABL uncertainty for DO meter calibration?
Prism achieves expanded uncertainty of ±0.1 mg/L (k=2) for dissolved oxygen meters at the 8 mg/L range (near saturation at 25°C).
How often should DO meters be calibrated?
Annual NABL calibration is standard. DO meters used in GPCB compliance monitoring should be calibrated every 6 months. Daily calibration against air saturation is recommended before field use.
Does Prism calibrate optical (luminescence-based) DO sensors?
Yes. Optical DO sensors (Hach LDO, YSI Pro30, Mettler-Toledo) are calibrated using the same air saturation method as membrane electrodes.
Is temperature compensation important for DO measurement?
Yes. DO saturation decreases as temperature increases: water holds ~9.1 mg/L at 25°C but only ~7.7 mg/L at 30°C. Temperature compensation corrects for this. Prism verifies ATC accuracy as part of DO meter calibration.
Can Prism calibrate DO meters on-site at ETP plants?
Yes. Prism offers on-site DO meter calibration at ETP/STP plants using portable calibration equipment and freshly prepared reference solutions.
Written by
Er. Parthiv Kinariwala
Managing Director · Prism Calibration Centre · NABL CC-2480 · Ahmedabad
Er. Parthiv Kinariwala founded Prism Calibration Centre in 2004 and has over 20 years of hands-on experience in calibration engineering, NABL accreditation, and industrial compliance. His team performs 10,000+ calibrations annually from the Vatva GIDC laboratory, serving 5000+ industries across Gujarat.
Prism Calibration Centre — Vatva GIDC, Ahmedabad
Prism Calibration Centre
F-101, Rudraksh Complex 2, Phase 3, GIDC Vatva, Near Jasoda Nagar Cross Road, Ahmedabad — 382445, Gujarat, India
Phone: +91 98245 26444
Email: info@prismcalibration.com
NABL: CC-2480 · ISO/IEC 17025:2017
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