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MODEL TCL SECTION 9
CALIBRATION
SECTION 9. CALIBRATION
9.1 INTRODUCTION
The calibrate menu allows the user to do the following:
1. Calibrate the temperature sensing element in the total chlorine sensor.
2. Calibrate the chlorine sensor.
3. Calibrate the analog outputs.
9.2 CALIBRATING TEMPERATURE
9.2.1 Purpose
The total chlorine sensor is a membrane-covered amperometric sensor. As the sensor operates, iodine, produced
by the reaction between total chlorine and the vinegar/potassium iodide reagent, diffuses through the membrane
and is consumed at an electrode immediately behind the membrane. The reaction produces a current that depends
on the rate at which iodine diffuses through the membrane. The diffusion rate, in turn, depends on the concentra-
tion of the iodine and how easily it passes through the membrane (the membrane permeability). Because
membrane permeability is a function of temperature, the sensor current will change if either the concentration
or temperature changes. To account for changes in sensor current caused by temperature alone, the analyzer
automatically applies a membrane permeability correction. The membrane permeability changes about 3%/°C at
25°C, so a 1°C error in temperature produces about a 3% error in the reading.
Without calibration the accuracy of the temperature measurement is about ±0.4°C. Calibrate the sensor/analyzer
unit if...
1. ±0.4°C accuracy is not acceptable
2. the temperature measurement is suspected of being in error. Calibrate temperature by making the analyzer
reading match the temperature measured with a standard thermometer.