IM 12B6B3-E-H
7-2 Maintenance
Calibration procedures are described in step-by-step detail in chapter 6. However, follow these guidelines.
1. Before starting a calibration, make sure the electrode system is properly cleaned so that electrodes are
fully functional. They must then be rinsed with clean water to avoid contamination of the calibration solu-
tion.
2. Always use fresh buffer solutions to avoid the possibility of introducing errors from contaminated or aged
solutions. Buffers supplied as liquids have a limited shelf life, especially alkaline buffers which absorb
CO2 from the air.
3. Yokogawa strongly recommends NIST (primary) buffer standards in order to ensure the best accuracy
and best buffer capacity is available. Commercially adjusted buffers (e.g. 7.00, 9.00 or 10.00pH) are a
compromise as a standard, and are often supplied without the temperature dependency curve. Their
stability will be much worse than for NIST solutions.
NOTE:
NIST (formerly NBS) buffers are available as consumable items from any Yokogawa sales office under the
following part numbers:
6C232 4.01 pH at 25°C}
6C237 6.87 pH at 25°C} A box contains 5 packets of powder. Each makes a 200 ml solution.
6C236 9.18 pH at 25°C}
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