Aquaprobe
®
AP-5000 Instruction Manual
10401-00906 Rev M
When taking a set of readings, gently stir the Probe, or raise and lower it in the sample (if
there is no natural water flow) until the global stability icon appears. The initial display of the
global stability icon will be accompanied by a double beep. When this occurs, all values are
stable and ready for reading or saving.
6.4. Temperature Compensation
The electrochemical properties of all solutions change with the solution's temperature. In
addition, the response of electrochemical measuring electrodes change with temperature. It
is a fundamental, practical requirement in the field of water quality monitoring that test
measurements taken at different temperatures can be compared.
In order to facilitate this, the AP-5000 automatically applies corrections for temperature
wherever required.
During three point calibration of the ISE electrodes, the variation in response of the
electrodes due to temperature is automatically calculated. During measurement, the
variation in response of the electrodes due to temperature is automatically compensated
for.
During calibration of the EC electrode, the variation in the calibration buffer solution due to
temperature is automatically corrected for. During measurement of EC, the readings can be
displayed without any temperature correction, corrected to 20
C, or corrected to 25
C. See
section 9 for more details.
During calibration of the DO electrode, variations due to temperature and air pressure are
automatically compensated for. During the measurement of DO, temperature, air pressure
and salinity are automatically compensated for.
During calibration of the ORP electrode, the variation in the calibration buffer solution due
to temperature is automatically corrected for. During measurement of ORP however,
temperature corrections are not applied as the correction factors are system and chemical
dependent and are not easily determined.
ORP potential measurements are mostly made to follow reactions rather than for their own
sake. The completion of an ORP reaction is normally accompanied by a sharp change in
the ORP millivolts reading. This change is usually much larger than the errors induced by
temperature side effects.
During calibration of the optical electrodes, variations in the calibration solutions due to
temperature are automatically compensated for. During the measurement, temperature is
automatically compensated for.
During calibration of the pH electrode, the small variation in the calibration buffer solutions
due to temperature is not compensated for due to the differences in thermal coefficient
between various buffer manufacturers. For this reason, the three pH points should be
calibrated as close to the buffer manufacturer's specified temperature as possible (usually
20ºC or 25ºC) although a variation of up to +/-10ºC makes very little difference in reality.
During pH measurement, temperature variation is automatically compensated for.
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®
Ltd.
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