Choosing Temperature Units And Manual/Automatic Temperature Compensation - Emerson Rosemount Analytical FCLi Instruction Manual

MODEL FCLi
5.6 CHOOSING TEMPERATURE UNITS AND MANUAL OR AUTOMATIC TEMPERATURE
COMPENSATION
5.6.1 Purpose
This section describes how to do the following:
1. Choose temperature display units (°C or °F).
2. Choose automatic or manual temperature compensation for membrane permeability.
3. Choose automatic or manual temperature compensation for pH.
4. Enter a temperature for manual temperature compensation.
5.6.3 Definitions — chlorine
1. AUTOMATIC TEMPERATURE COMPENSATION - CHLORINE. The chlorine sensor is a membrane-covered
amperometric sensor. The permeability of the membrane is a function of temperature. As temperature increas-
es, membrane permeability increases. Thus, an increase in temperature will cause the sensor current and the
analyzer reading to increase even though the chlorine level remained constant. A correction equation in the
analyzer software automatically corrects for changes in membrane permeability caused by temperature. In
automatic temperature compensation, the analyzer uses the temperature measured by the sensor for the cor-
rection.
2. MANUAL TEMPERATURE COMPENSATION - CHLORINE. In manual temperature compensation, the ana-
lyzer uses the temperature entered by the user for membrane permeability and pH correction. It does not use
the actual process temperature. Do NOT use manual temperature compensation unless the measurement and
calibration temperatures differ by no more than about 2°C. Manual temperature compensation is useful if the
sensor temperature element has failed an a replacement sensor is not available.
5.6.3 Definitions — pH
1. AUTOMATIC TEMPERATURE COMPENSATION — pH. The analyzer uses a temperature-dependent factor
to convert measured cell voltage to pH. In automatic temperature compensation, the analyzer measures the
temperature and automatically calculates the correct conversion factor. For maximum accuracy, use automat-
ic temperature compensation.
2. MANUAL TEMPERATURE COMPENSATION — pH. In manual temperature compensation, the analyzer con-
verts measured voltage to pH using the temperature entered by the user. It does not use the actual process
temperature. Do NOT use manual temperature compensation unless the process temperature varies no more
than about ±2°C or the pH is between 6 and 8. Manual temperature compensation is useful if the sensor tem-
perature element has failed and a replacement sensor is not available.
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SECTION 5.0
PROGRAMMING THE ANALYZER