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MODEL TCL SECTION 11
TROUBLESHOOTING
11.5.6 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 potas-
sium 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.
11.5.7 Temperature measured by standard thermometer was more than 3°C different from analyzer.
1. Is the standard thermometer, RTD, or thermistor accurate? General purpose liquid-in-glass thermometers, par-
ticularly ones that have been mistreated, can have surprisingly large errors.
2. Is the temperature element in the sensor completely submerged in the liquid?
3. Is the standard temperature sensor submerged to the correct level?
11.5.8 Current Output Too Low.
Load resistance is too high. Maximum load is 550 Ω.
11.5.9 Alarm Relays Do Not Work
1. Verify the relays are properly wired.
2. Verify that deadband is correctly set. See Section 7.4.
11.6 SIMULATING INPUTS
To check the performance of the analyzer, use a decade box and 1.5V 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.
1. Disconnect the anode and cathode leads from terminals 8 and 10 on TB1 and connect a decade box and 1.5V
battery as shown in Figure 11-2. It is not necessary to disconnect the RTD leads.
2. Set the decade box to 1.4 MΩ.
3. Note the sensor current. It should be about 960 nA. The actual
value depends on the voltage of the battery. To view the sensor
current, go to the main display and press DIAG. Choose sensor 1.
The input current is the second line in the display. Change the
decade box resistance and verify that the correct current is shown.
Calculate current from the equation:
current (nA) =
The voltage of a fresh 1.5 volt battery is about 1.6 volt (1600 mV).
66
V
battery
— 250 (voltages in mV)
resistance (MΩ)
FIGURE 11-2. Simulating Chlorine
7
ANOD SHLD
CATH SHLD
CATH
ANOD
8
9
10
R