7. Rinse the pH and Conductivity/TDS or Temperature sensors in distilled water and blot them
dry.
8. Place both sensors into a small sample of secondary buffer (pH4.00, 9.23 or 10.06), so that the
bulb and reference junction are both covered as per the diagram in step 5.
DO NOT place the electrodes directly into the buffer bottle.
NOTE: pH9.23 and pH10.06 buffers are highly unstable. Avoid using these buffers if
possible. Discard immediately after use.
9. Select pH calibration ( →→ F1:Calibrate →→ F3:pH).
The display should now look similar to the example shown in step 6. Note that the 90-FL has
automatically recognised the second buffer.
Wait for the displayed reading to stabilise before attempting to calibrate the 90-FL.
Press to calibrate to the displayed buffer.
Otherwise, enter an alternative buffer using the Numeric Keypad, and then press .
10. The 90-FL is now pH calibrated and is ready for use in this mode. Discard the used samples of
buffer.
Rinse the pH and Conductivity/TDS or Temperature sensors in distilled water and blot them
dry before placing them into unknown samples.
6.3 pH Calibration Notes
1. A 1-point calibration should be performed at least weekly. In applications where the electrode
junction can become blocked such as dairy products, mining slurries etc, a 1-point calibration
may have to be done daily.
2. A full 2-point calibration should be performed at least monthly. Of course, more frequent
calibration will result in greater confidence in results.
3. All calibration information is retained in memory when the 90-FL is switched off, even when
the power supply is removed. This information can be recalled or printed later using the GLP
function (see section 8).
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