4.5
Zero Calibration
In theory, the oxygen sensor is linear over its measurement range and has no signal output when ex-
posed to an oxygen free environment. However, in reality expect the analyzer to generate a small signal
in an oxygen free environment due to one or more of the following:
Minor leakage in the sample gas connections, contamination or quality of zero gas, small amounts of
dissolved oxygen in the sensor electrolyte, tolerance of electronic components in the analyzer.
When is a ZERO Calibration Recommended:
A zero calibration is recommended for online and portable oxygen analyzers in applications where a
continuous and precise measurement of oxygen is required below 5% of the lowest 2 ranges (i.e. when
measuring 0.5 ppm or below on the 0 - 10 ppm range and 5 ppm or below on the 0 - 100 ppm range).
A zero calibration is only recommended when these conditions are met and when the user is installing a
new oxygen sensor.
For most applications a ZERO calibration is not necessary, if you are unsure if a ZERO calibration is re-
quired for your installation, contact the factory and consult with our application specialists for a recom-
mendation.
CAUTION: Prematurely zeroing the analyzer can cause erroneously low readings and extra caution
should be taken to make sure a zero is performed accurately.
Determining the zero point is met: the user should allow the analyzer to be purged on zero gas for ap-
proximately 24 hours to stabilize the flowing gas. There should be no downward trend of the reading.
Zero Calibration Procedure:
Zero Calibration should proceed the span calibration and once performed should not have to be repeat-
ed with subsequent span calibrations. The zero calibration should only be performed once and when a
new sensor is installed or if changes are made to the sample system connections.
The maximum zero calibration adjustment permitted is 45% of the lowest full scale range availability
(roughly 4.5 ppm). As such, the analyzer ZERO has not been performed at the factory prior to shipment
as the factory gas connections and application conditions are different than the user’s installation.
Allow the analyzer to be purged with a zero gas for 24 hours, verify that the oxygen reading is stable.
Once Confirmed, and the reading is below 4.5 ppm, proceed to the menu to perform a zero calibration:
Once the ZERO Calibration procedure is complete, the display will show “PASSED” or “FAILED”. If
Failed, your reading was most likely above the 4.5ppm threshold or the 24 hour purge on zero gas was
not complete. Check your connections and zero gas and verify the unit is stable and not still trending
down. Contact the factory for additional troubleshooting techniques.
Maintenance
OMD-625 Oxygen Analyzer
Designed, Tested and Assembled in California, USA
4045 E. Guasti Rd. #203 Ontario, CA 91761 USA : 1-949-398-2879 : [email protected] : www.sso2.com
MAIN MENU
AUTO RANGE
MANUAL RANGE
SPAN CAL
ZERO CAL
ALARM 1
ALARM 2
SYSTEM
ZERO CAL
1.25 PPM
ENTER TO CAL
ESC TO EXIT
