Yokogawa EXA PH202 2-Wire pH/ORP Analyzer - Manual (Page 82)

IM 12B07D02-01E
7-2 maintenance
7-3. 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 solution.
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 CO
2
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 10.00 pH) 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}