the cathode stem. Hold the sensor with the membrane end pointing up. Unscrew
the membrane retainer and remove the membrane assembly. Use the end of a
straightened paper clip to clear the holes at the base of the cathode stem.
13.5.3 Readings drift
1. Is the sample temperature changing? Membrane permeability is a function of
temperature. The transmitter automatically corrects for changes in sensor current
caused by temperature changes. The time constant for 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, must diffuse freely
through the membrane. A coating on the membrane will interfere with the passage
of , resulting in a .
13.5.4 Readings are too high
1. Is the sample conditioning reagent clear and colorless? If the reagent is pale yellow,
results will be high. The pale yellow color is caused by iodine, which comes from
the reaction between atmospheric oxygen and potassium iodide. The reaction is
catalyzed by sunlight. The purpose of the blue carboy is to protect the reagent from
sunlight.
2. Is the sensor fill solution fresh? An old, discolored fill solution may produce a high
reading.
13.6 Other troubleshooting - general
Problem See Section
Current output is too low. Current output too low
Alarm relays do not operate properly. Alarm relays don't work
13.6.1 Current output too low
Load resistance is too high. Maximum load is .
13.6.2 Alarm relays don't work
13.7 Simulating inputs
To check the performance of the transmitter, use a decade box and 1.5 V battery to
simulate the current from the sensor. The battery, which opposes the polarizing voltage, is
necessary to ensure that the sensor current has the correct sign.
Procedure
1. Disconnect the anode and cathode leads from terminals and connect a decade box
and 1.5 V battery as shown in Figure 13-2.
Reference Manual Troubleshoot
00809-0200-3415 January2023
Rosemount TCL 56 69
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