Emerson Rosemount MCL-220 Reference Manual page 76

Troubleshoot
May 2019
9.5.1 Zero current is too high.
1. Is the sensor properly wired to the transmitter? See
2. Is the zero solution monochloramine free? Take a sample of the solution and test it
3. Has adequate time been allowed for the sensor to reach a minimum stable residual
4. Check the membrane for damage and replace it if necessary. Be careful not to touch
9.5.2 Zero current is unstable.
1. is the sensor properly wired to the transmitter? See
2. Readings are often erratic when a new or rebuilt sensor is first placed in service.
3. Is the space between the membrane and cathode mesh filled with electrolyte
4. Verify that the sensor is filled with electrolyte solution. Refer to
9.5.3 Sensor can be calibrated, but the current is too low.
1. Is the temperature low? The sensor current decreases about 5% for every °C drop in
2. Sensor current depends on the rate of sample flow past the sensor tip. If the flow is
3. Is a bubble trapped against the membrane? If a sample flow becomes too low
4. Low current can be caused by lack of electrolyte flow to the cathode and
5. When was the sensor fill solution last replaced? The monochloramine sensor loses
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for monochloramine level. The concentration should be less than about 0.02 ppm.
current? It may take several hours, sometimes as long as overnight, for a new
sensor to stabilize.
the membrane or cathode. Touching the cathode mesh may damage it.
connections are tight.
Readings usually stabilize after about an hour.
solution? 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.
sensor for details.
temperature.
too low, monochloramine readings will be low. Be sure the liquid level in the
constant head flow 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
(because dirt or slime has built up in the flow controller), bubbles have a tendency
to collect on the membrane. The bubble reduces the active area of the membrane
and readings drop. The design flow (2 gph) is adequate to push away bubbles. See
Constant head flow controller
membrane. See step 3 in
sensitivity, that is, it generates less current per ppm of monochloramine, as it
operates. Gradual loss of sensitivity can usually be compensated for by calibrating
the sensor weekly. After about two or three months of operation, the sensitivity
controller.
for the cleaning procedure
Zero current is unstable..
Reference Manual
00809-0100-3414
Wire sensor.
Figure 4-2. Verify that all wiring
Monochloramine
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