Emerson Rosemount5081, Instruction Manual, Page: 118 / 152

Ozone process readings erratic
If the ozone process readings are erratic, see the information below.
1. Readings are often erratic when a new sensor or a rebuilt sensor is first placed in
service. The current usually stabilizes after a few hours.
2. Is the sample flow within the recommended range? High sample flow may cause
erratic readings. Refer to the sensor instruction sheet for recommended flow rates.
3. Are the holes between the membrane and the electrolyte reservoir open? Refer to
Ozone zero reading unstable
4. Verify that wiring is correct. Pay particular attention to shield and ground
connections.
5. Is the membrane in good condition, and is the sensor filled with electrolyte solution?
Replace the fill solution and electrolyte. Refer to the sensor instruction manual for
details.
Ozone readings drift
1. Is the sample temperature changing? Membrane permeability is a function of
temperature. The time constant for the 499AOZ sensor is about five minutes.
Therefore, the reading may drift for a while after a sudden temperature change.
2. Is the membrane clean? For the sensor to work properly, ozone must diffuse freely
through the membrane. A coating on the membrane will interfere with the passage
of ozone, resulting in a slow response. Clean the membrane by rinsing it with a
stream of water from a wash bottle, or gently wipe the membrane with a soft tissue.
3. Is the sample flow within the recommended range? Gradual loss of sample flow will
cause a downward drift.
4. Is the sensor new, or has it been recently serviced? New or rebuilt sensors may
require several hours to stabilize.
Sensor not responding to ozone changes
1. Is the grab sample test accurate? Is the grab sample representative of the sample
flowing to the sensor?
2. Is the membrane clean? Clean the membrane and replace it if necessary. Check that
the holes at the base of the cathode stem are open. Use a straightened paper clip to
clear blockages. Replace the electrolyte solution.
3. Replace the sensor.
Ozone readings too low
1. Was the sample tested as soon as it was taken? Ozone solutions are highly unstable.
Test the sample immediately after collecting it.
Diagnostics and troubleshooting
108 Rosemount 5081