Thermo Fisher Scientific Alpha pH 2000 - Manual (Page 23)

5.2 pH Calibration
This controller unit features one-point or two-point calibration with five preset
buffer sets. Buffer values refer to 25 °C. To calibrate the instrument, you
need a standard pH buffer solution that matches one of these values.
two-point calibration
SETUP
HOLD
PH
CAL
HOLD
PH
P H CAL
HOLD
P H P H
CAL MEAS
P H
O C
atc
CAL
CAL
one-point calibration
1. Enter Calibration mode as described in section 5.1. The display should
read “CAL PH” (for pH calibration).
Note: If the display reads “CAL OrP”, see section 6.9 for procedures on how
to switch from ORP to pH readings.
2. Press the ENT key to start calibration. The “CAL” indicator appears at the
top of display and the buffer indicator appears in the bottom corner of the
display. The display shows the actual pH reading (upper value) and the
buffer value for zero point (lower value). For the offset (zero point)
calibration, there are two values to choose from. They are pH 7.00 or pH
6.86. Using the
▲ and ▼ keys, choose the value that matches with the
buffer used.
3. Place the electrode in the first buffer solution. In ATC mode, you must also
immerse the temperature probe in the buffer solution. Likewise for
symmetrical mode, you must also immerse the potential matching pin in
the buffer.
4. You can conduct either a one-point or a two-point calibration: Press the
ENT key for two point calibration or the CAL key for one point
calibration. The electrode indicator and CAL indicator both flash. The
controller automatically adjusts the reading to match the buffer value.
5. If one-point calibration was selected, the display will show the slope and
offset. If two-point calibration was selected, the lower section of the display
will now show its next lower “pH” buffer. Use
▲ and ▼ keys to select the
second buffer from one of these preset values: - pH 1.68, pH 4.01, pH
9.00, pH 9.18 and pH 10.01. Remove the electrode from the first buffer,
wash and then immerse it into the second buffer. Press the ENT key, the
electrode and CAL indicators will flash. The controller adjusts the reading
to the second buffer.
6. After calibrating with the second buffer value, the controller will
automatically display the slope in the upper and the zero point in the lower
section of the display.
Note: You can also view the values for zero point and slope without
calibration (see section 5.1.2 for instruction). The zero point and slope are re-
determined after each calibration.