Chapter 4 Calibrate; Zero Point Calibration; Full Scale - Emerson Rosemount 499ADO Quick Start Manual

4 Calibrate
4.1

Zero point calibration

Even in the absence of oxygen, the Rosemount 499ADO sensor generates a small signal
called the zero current. Failing to correct for the zero current can introduce a bias,
particularly if the oxygen concentration is small (<1 ppm). Zero the sensor when it is first
placed in service and every time the fill solution is changed.
To zero the sensor:
Procedure
1.
2.
3.
4.
5.
The zero current should be <200 nA.
4.2

Full scale

The Rosemount 499ADO sensor is best calibrated by exposing the sensor to water-
saturated air.
1.
2.
3.
4.
Quick Start Guide
Pour a cup of deionized or bottled water.
Add a teaspoon of sodium sulfite to the water.
Place the sensor in the water.
Wait until the sensor current has reached a stable low value (at least two hours).
Follow the transmitter prompts for zeroing the sensor.
Note
Refer to the manual for the transmitter you are using (56, 1056, 5081, or 1066).
Pour a small amount of water into a cup.
Suspend the sensor, keeping the membrane dry, about 1/4 in. (6 mm) above the
surface of the water.
Once readings are stable, follow the analyzer prompts to complete the calibration.
The analyzer automatically calculates the equilibrium solubility of atmospheric
oxygen in water under the prevailing temperature and barometric pressure.
After calibration, go to the Diagnostics menu and check the sensitivity.
The sensitivity should be between 1,800 and 3,000 nA/ppm.
For more information, refer to the transmitter manual.
Calibrate
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