eDAQ EA168, User Manual

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Chapter 3 — Electrode Calibration 21
Calibration Temperature
You must also enter the temperature of the standard buffer solutions,
. Please remember that the pH value of a buffer
solution is temperature dependent and that the correct buffer value
should be used at that temperature.
Temperature Compensation
For the most exacting work, both calibration and experimental
measurements are performed in a thermostatted glass reaction vessel
maintained at a known temperature to within ±0.05 °C. Under these
conditions temperature compensation is NOT required.
When pH, or other ISE measurements, will be made at temperatures
(
T
m
) other than the temperature under which calibration was performed
( T
c
), the Nernst equation can be used as a basis for compensation of
the readings.
The pH extension offers two types of temperature compensation:
• manual temperature compensation (MTC). Used where the
measurements are made at a constant temperature, but where
T
m
≠ T
c
.
• Automatic temperature compensation (ATC). Used where
temperature fluctuations are expected to occur during the
experiment, that is, when
T
m
is not constant. In these cases
temperature should be monitored on a second channel. Note that
the calibration must still be performed at a known constant
temperature.
Both MTC and ATC corrections can be removed if required, so that the
original, raw data can be re-displayed.
Manual Temperature Compensation
The manual temperature compensation (MTC) option is for use when
you need to measure ionic concentration at a temperature other than
that at which the electrode was calibrated. For example, the calibration
may have taken place at 25°C, but the subsequent samples might be at