Orion Lab Star PH111 pH/mV Bench Meter 25
Chapter 4
Calibration
4.1 pH Calibration
4.1.1 pH Calibration Overview
For best results, periodic calibration with known, accurate
and fresh pH buffers is recommended. Calibrate with pH
buffers that bracket the expected measuring range and
include a neutral buffer. For example, if samples will be pH
6.2 to 9.5, calibrate with pH 4.01, 7.00, and 10.01 buffers.
Perform one to five point pH buffers. The non-volatile meter
memory retains the most recent, active calibration data
when powered off.
During the pH calibration, the meter will automatically
recognize each pH buffer value using the pH buffer set
selected in the setup menu and the mV signal measured
by the pH electrode. Once the reading is stable, the meter
will automatically display the buffer value at its measured
temperature from the selected buffer set.
The following pH buffers are automatically recognized:
•
USA: 1.68, 4.01, 7.00, 10.01, 12.46
•
DIN: 1.68, 4.01, 6.86, 9.18, 12.46
Refer to the
pH buffer group.
If the mV value does not correspond to within
±
60mV of a
pH buffer in the selected buffer set, once the pH reading is
stable, the meter will display the theoretical pH value of the
buffer according to the last pH calibration that was
performed or, if no calibration has been performed, the
meter will display the theoretical pH value of the buffer
according to the Nernst equation.
The pH buffer values can be manually entered for each
calibration point. If the pH buffer value needs to be
manually adjusted, use the
or
key to edit the value of
the pH buffer at its measured temperature.
To eliminate temperature errors associated with pH, use an
automatic temperature compensation (ATC) probe with pH
electrode for best accuracy.
Press the “Cal” key to start and end the calibration. This
allows pH calibrations to be performed using one to five
points without having to program the number of points
before starting the calibration.
4.1.2 pH Calibration Procedure
Ensure the active measure mode is pH.
Press the “Cal” key to start the calibration.
Rinse the pH electrode and ATC probe and place
into the pH buffer.
Wait for the pH value to stabilize.
a.
While the reading is stabilizing, the stopwatch
icon is shown and the reading flashes.
b.
When the reading is stable, the checkmark icon
is shown, and the reading is solid.
Once the reading is stable, accept or edit the
displayed pH buffer value:
a.
To accept the pH buffer value, press the
“Enter” key.
or
b.
To edit the pH buffer value, press the
or
key to change the value and then press the
“Enter” key to save the value.
i.
Press the
key to increase by one
digit. Press and hold the
key to
quickly increase.
ii.
Press the
key to decrease by one
digit. Press and hold the
key to
quickly decrease.
Proceed to the next calibration point or save and
end the calibration:
a.
To proceed to the next calibration point, repeat
steps 3-5.
or
b.
To save and end the calibration, press the
“Cal” key.
i.
When performing a one point pH
calibration, press the
or
key to
edit the slope value and then press the
“Enter” key to accept.
The meter will display the calculated slope value and
then proceed to the main measure mode.
Note: Press the “Measure” key at any time to abort the
calibration and return to the main measure mode.
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