Calibrate - Emerson Rosemount 499Atrdo Quick Start Manual

November 2019
4

Calibrate

4.1 Zero point calibration
Even in the absence of oxygen, the sensor generates a small signal called the
zero current. Normally, the zero current is less than 5 nA, which introduces
nor more than a 0.5 ppb error in measurement. Zero the sensor when it is
first placed in service and every time the fill solution is changed.
To zero the sensor:
Procedure
1. Pour a cup of deionized or bottled water.
2. Add a teaspoon of sodium sulfite to the water.
3. Place the sensor in the water.
4. Wait until the sensor current has reached a stable low value (at least
two hours).
5. Measure the current.
4.2 Full scale
The best way to calibrate the sensor is to expose it to to water-saturated air.
Procedure
1. Pour a small amount of water into a cup.
2. Suspend the sensor, keeping the membrane dry, about ¼-in. (6 mm)
above the surface of the water.
3. Once readings are stable, which should take no longer than 20
minutes, follow the transmitter prompts to complete the calibration.
The transmitter automatically calculates the equilibrium solubility of
atmospheric oxygen in water under the prevailing temperature and
barometric pressure.
4. After calibration, go to the Diagnostics menu and check the
sensitivity.
The sensitivity should be between 3,600 and 6,100 nA/ppm.
For more information, refer to the transmitter manual.
Quick Start Guide
a) If it is less than 5 nA, do not zero the sensor.
b) If it is between 5 and 10 nA, allow the sensor to run overnight.
Zero the sensor if the reading is still between 5 and 10 nA and
is stable.
c) If it is greater than 10 nA, call the factory.
Quick Start Guide
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