Hach-Lange PHC725 - Manual (Page 3)

5. Add the filling solution to the probe as necessary (refer to Fill the probe
on page 11). The filling solution must be above the standard solution or the sample
level during measurement or calibration (
Figure 2 ).
6. For Red Rod probes, make sure that there is approximately 0.5 cm (0.2 in.) of KCl
crystals in the filling solution in the probe. Refer to Table 1 . For measurements at
temperatures higher than 60 °C (140 °F), add KCl crystals through the filling hole.
Refer to
Table 1 to calculate the quantity of KCl crystals to add. The quantity of
necessary KCl crystal increases linearly from 60 to 100 °C.
7. For Red Rod probes, make sure that the KCl crystals move freely through the liquid
when the probe is inverted. If necessary, shake the probe to loosen the crystals.
8. Make sure that the filling hole is open during measurement for the correct flow of the
filling solution.
Note: For the best stabilization time, condition the probe for 2 hours in pH buffer 4.01 before use, if
the probe was not used for 3 weeks or more. In low ionic strength (LIS) samples, condition the
probe for a maximum of 5 minutes in the sample before use. In all other cases a condition before
use is not necessary.
Figure 2 Filling solution level
1 KCl crystals 1 3 Filling solution
2 Filling solution level 4 Standard solution or sample level
1 Red Rod probes only
Table 1 KCl crystal level for Red Rod pH probes
Temperature Amount of KCl crystals Add Temperature Amount of KCl crystals Add
60 °C (158 °F) 0.5 g (0.5 cm) 0 g 90 °C (194 °F) 0.875 g 0.375 g
70 °C (158 °F) 0.625 g 0.125 g 100 °C (212 °F) 1.0 g (1.0 cm) 0.5 g
80 °C (176 °F) 0.750 g 0.25 g
Calibration
Before calibration:
The probe must have the correct service-life time stamp. Set the date and the time in the meter before the probe is attached.
It is not necessary to calibrate again if a calibrated probe is moved from one HQd meter to another. Make sure that the
additional meter is configured to use the same calibration options.
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