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13.3.4 Process readings are erratic or wander
A. Is the sensor properly wired to the analyzer? See Section 4.3. Verify that all connections are tight.
B. Readings can be erratic when a new sensor is first placed in service. Readings usually stabilize aver about an
hour.
C. Is the air pump working? There should be a vigorous stream of bubbles in the flow cell. The bubbles help mix
the sample and keep carbon dioxide bubbles off the membrane. Carbon dioxide forms when bicarbonate alka-
linity in the sample reacts with acetic acid. The bubbles accumulate on the membrane and eventually break
away, causing total chlorine reading to wander.
D. Is the membrane damaged or loose? Replace the membrane if necessary.
D. Is the space between the membrane and cathode filled with electrolyte solution and is the flow path between
the electrolyte reservoir and membrane clear? Refer to Section 13.3.2C for more information.
13.3.5 Readings drift
A. Is the sample temperature changing? Membrane permeability is a function of temperature. The time constant
for the 499ACL-01sensor is about five minutes. Therefore the reading may drift for a while after a sudden tem-
perature change.
B. Is the membrane clean? For the sensor to work properly, iodine must diffuse freely through the membrane. A
coating on the membrane will interfere with the passage of iodine, resulting in a gradual downward drift in read-
ings. The coating will also slow the response on the sensor to step changes. Clean the membrane by rinsing
is with a stream of water from a wash bottle. Wipe the membrane with a soft tissue.
C. Is the sensor new or has it recently been serviced? New or rebuilt sensors may require several hours to sta-
bilize.
D. Is the flow of sample past the sensor about 11 mL/min? See Section 13.3.3D for more information.
E. Is the reagent flow about 0.2 mL/min? See Section 13.3.3E for more information.
FIGURE 13-1. Disconnecting sample (A) and reagent (B) tubing prior to checking flow.
MODEL TCL SECTION 13
TROUBLESHOOTING