Emerson Rosemount5081, Instruction Manual, Page: 117 / 152

3. Has adequate time been allowed for the sensor to reach a minimum stable residual
current? It may take several hours, sometimes as long as overnight, for a new sensor
to stabilize.
4. Check the membrane for damage and replace it if neccessary.
Ozone zero reading unstable
1. Is the sensor properly wired to the transmitter? Verify that all wiring connections are
tight.
2. Readings are often erratic when a new or rebuilt sensor is first placed in service.
Readings usually stabilize after about an hour.
3. Is the space between the membrane and cathode filled with electrolyte solution,
and is the flow path between the electrolyte reservoir and membrane clear? Often
the flow of electrolyte can be started by simply holding the sensor with the
membrane end pointing down and sharply shaking the sensor a few times as though
shaking down a clinical thermometer.
If shaking does not work, try clearing the holes around the cathode stem. Hold the
sensor with the membrane end pointing up. Unscrew the membrane retainer and
remove the membrane assembly. Be sure the wood ring remains with the
membrane assembly. Use the end or a straightened paper clip to clear the holes at
the base of the cathode stem. Replace the membrane.
Verify that the sensor is filled with electrolyte solution. Refer to the sensor
instruction manual for details.
Sensor current less than 350 nA/ppm
If the sensor current is less than 350 nA/ppm at 25 °C (77 °F), see the following
information.
1. Sensor current is a strong function of temperature. The sensor current decreases
about 3% for every °C drop in temperature.
2. Sensor current depends on the rate of sample flow past the sensor tip. If the flow is
too low, ozone readings will be low. Refer to the sensor instruction sheet for
recommended sample flows.
3. Low current can be caused by lack of electrolyte flow to the cathode and membrane.
See Step 3 in
Ozone zero reading unstable .
4. Is the membrane fouled or coated? A dirty membrane inhibits diffusion of ozone
through the membrane, reducing the sensor current and increasing the response
time. Clean the membrane by rinsing it with a stream of water from a wash bottle or
gently wipe the membrane with a soft tissue.
If cleaning the membrane does not improve the sensor response, replace the
membrane and electrolyte solution. If necessary, polish the cathode. See the sensor
instruction sheet for details.
Diagnostics and troubleshooting
Instruction Manual 107