SECTION 4 - Calibration and Measurement
Before performing a measurement the instrument must be calibrated. It is
recommended that the instrument is calibrated daily to achieve consistent and
accurate results. Model 570 has a 2 point calibration process. The first calibration
point MUST be buffer pH 7.00. The second calibration point depends on the
acidity of the solution which is to be measured. For samples with a pH around
5 the second calibration point should be 4.01 pH buffer. For samples with a pH
around 8 the second calibration point should be 10.01pH buffer. Always rinse
the pH and temperature probes in de-ionised water before placing in each buffer
solution. If the ATC probe is connected the instrument automatically compensates
for the resulting change in electrode response due to temperature during the
calibration process.
Press the ON/OFF key to switch the instrument on. If the temperature probe
is not connected ‘MANUAL’ will be displayed above the temperature value. If
manual temperature adjustment is being used, the temperature of the solution
must be measured using a thermometer so that the temperature can be manually
adjusted.
Place the pH electrode and temperature probe into 7.00 pH buffer solution and
allow the reading to stabilise. Stir then press and hold down the CAL key for 3
seconds. Auto-Cal will flash up on the display and then the current reading will be
displayed. Once the reading has stabilised press the CAL key, rinse the electrode
and temperature probe in deionised/distilled water and place them into 4.01 pH
or 10.01 pH solution and allow the reading to stabilise, again stir the solution to
remove any air bubbles. To finish press the CAL key, ‘Calibrated Ok’ will flash up
and the display will show the solution value of the buffer.
To abort the calibration point at any point press the ON/OFF key and the meter will
revert back to any previous calibration values.
During the calibration process the instrument will automatically detect the buffer
solution. However if you know the exact pH value for the buffer at a given
temperature (temperature coefficient) you can change the offset BS (buffer
solution 7.00pH) and slope BS (buffer solution 4.01 or 10.01) by using the Up
or Down arrow keys. Refer to your calibration solutions/capsules temperature
coefficients before any alterations are carried out.
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