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MODEL SOLU COMP II
SECTION 6.0
CALIBRATION
SECTION 6.0
CALIBRATION
6.1
INTRODUCTION
6.2 CALIBRATING
TEMPERATURE
6.3
CALIBRATING OZONE
6.1 INTRODUCTION
The Calibrate Menu allows the user to calibrate the ozone sensor. Both the ppm reading and the temperature can
be calibrated.
Ozone sensors require periodic full-scale calibration. The purpose of the full-scale standard is to establish the
slope of the calibration curve. Because stable ozone standards do not exist,
the sensor must be calibrated
against a test run a grab sample of the process liquid.
Several manufacturers offer portable test kits for this
purpose.
New ozone sensors must be zeroed before being placed in service. Sensors should also be zeroed every time the
electrolyte solution is replaced. Zeroing involves placing the sensor in an ozone-free sample until the sensor cur-
rent drops to its lowest stable value.
6.2 CALIBRATING TEMPERATURE
6.2.1 Purpose
The ozone sensor is a membrane-covered amperometric sensor. As the sensor operates, ozone diffuses through
the membrane and is consumed at an electrode immediately behind the membrane. The reaction produces a cur-
rent that depends on the rate at which ozone diffuses through the membrane. The diffusion rate, in turn, depends
on the concentration of ozone 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 concen-
tration or temperature changes. To account for changes in sensor current caused by temperature alone, the ana-
lyzer 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
.
