Rosemount SOLU COMP II, Инструкция по эксплуатации

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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 TWO-POINT BUFFER CALIBRATION (AUTO CALIBRATION)
6.4 TWO-POINT BUFFER CALIBRATION (MANUAL CALIBRATION)
6.5 MAKING THE ANALYZER READING MATCH A SECOND
INSTRUMENT (STANDARDIZATION)
6.6 ENTERING A KNOWN SLOPE
6.7 ORP CALIBRATION
6.1 INTRODUCTION
The Calibrate Menu allows the user to calibrate the pH, ORP (or redox), and temperature response of the sensor.
For pH sensors, two-point buffer calibration is standard. In auto calibration the Solu Comp II calculates the actual
pH of the buffer from the nominal value entered by the user and does not accept calibration data until readings are
stable. In manual calibration the user enters buffer values and judges when readings are stable. The pH reading
can also be standardized, that is, forced to match the reading from a referee instrument. Finally, if the user knows
the electrode slope (at 25°C), he can enter it directly.
The ORP calibration is a single-point calibration against an ORP standard.
6.2 CALIBRATING TEMPERATURE
6.2.1 Purpose
Temperature affects the measurement of pH in three ways.
1. The analyzer uses a temperature dependent factor to convert measured cell voltage to pH. Normally, a slight
inaccuracy in the temperature reading is unimportant unless the pH reading is significantly different from 7.00.
Even then, the error is small. For example, at pH 12 and 25°C, a 1°C error produces a pH error less than ±0.02.
2. During auto calibration, the Solu Comp II recognizes the buffer being used and calculates the actual pH of the
buffer at the measured temperature. Because the pH of most buffers changes only slightly with temperature,
reasonable errors in temperature do not produce large errors in the buffer pH. For example, a 1°C error caus-
es at most an error of ±0.03 in the calculated buffer pH.
3. The Solu Comp II can be programmed to calculate and display pH at a reference temperature (25°C). The max-
imum change in solution pH with temperature is about ±0.04 pH/°C, so a 1°C temperature error does intro-
duce a small error. However, the major source of error in solution temperature compensation is using an incor-
rect temperature coefficient.
Temperature affects the measurement of ORP in a complicated fashion that is best determined empirically.
Without calibration the accuracy of the temperature measurement is about ±0.4°C. Calibrate the sensor/analyzer
combination 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.