Emerson Rosemount MCL-220 Reference Manual page 78

Troubleshoot
May 2019
4. Check to see if a bubble is trapped against the membrane.
5. If the sensor is new or has been recently serviced, wait several hours for it to
6. Replace the fill solution and membrane.
9.5.6 Sensor does not respond to changes in monochloramine
level.
1. Is the grab sample test accurate? Is the grab sample representative of the sample
2. When was the sensor fill solution last replaced? The monochloramine sensor loses
3. Is the membrane clean? Clean the membrane with a stream of water and replace it
4. Replace the sensor.
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controller is level with the central overflow tube and that excess sample is flowing
down the tube. If necessary, disassemble and clean the overflow sampler.
See Constant head flow controller.
For the sensor to work properly, monochloramine must continuously diffuse
through the membrane. Bubbles block monochloramine in the sample from
reaching the membrane, so readings drift downward as bubbles form and grow.
The nozzle at the bottom of the flow cell pushes bubbles to the edges of the
membrane, where they do no harm. In cold samples, the nozzle may not be as
effective.
a) If you see bubbles, confirm that they are blocking the membrane by
removing the sensor from the flow cell and replacing it.
Removing the sensor breaks the bubbles, so when the sensor is replaced,
readings return to normal.
b) Confirm that the nozzle is properly positioned in the flow cell. Line up your
eye with the bottom of the membrane retainer.
No gap should be visible between the end of the nozzle and membrane
retainer.
stabilize.
Gradual downward drift is caused by a depletion of the fill solution. Noramally,
calibrating the sensor every week adequately compensates for the drift. After the
sensor has been in service for several months, you may need to replace the fill
solution and membrane. Refer to
flowing to the sensor?
sensitivity, that is, it generates less current per ppm of monochloramine, as it
operates. After about two or three months of operation, the sensitivity may start to
drop rapidly. If the fill solution is extremely old, the sensor may be completely non-
responsive to monochloramine. Replace the fill solution and membrane. See the
sensor instruction manual for details.
if necessary.
Replacing the electrolyte solution and
Reference Manual
00809-0100-3414
membrane.
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