E-18-
8205
pH CONTROLLER 8205
ENTER
ENTER
HOLD
HOLD NO
HOLD YES
Press Enter for
5 seconds
PH CALIB
4.2.2 HOLD function
A continuous 4-20 mA output corresponding to the last value measured before this option
was entered is generated. The relays are blocked in their last state. This allows the
electrode to be cleaned without interruption of the process. The display in the operation
mode is flashing and there is no access to the parameter definition or the test menu, as
long as the HOLD-function is activated. To disactivate HOLD function, enter again "
HOLD
"
option and confirm "
HOLD NO
".
4.2.3 Calibration of pH electrode
1 or 2 measuring points calibration methods are available.
1 measuring point method: enables a quick control calibration with pH=7 buffer solution.
2 measuring points method: enables a precise calibration of zero and slope of the pH
electrode. 2 buffer solutions are required. The first solution is usually pH=7. Use the
second buffer solution as close as possible of the assumed final pH value. Before each
calibration, clean the electrode (see §5.2). The temperatures of the buffer solutions must
be equal. The pH controller must be calibrated regularly.
This maintenance procedure is very important to ensure a reliable control operation.
The frequency of calibrations depends upon the degree of contamination of the measuring
fluid: in normal conditions, calibration should be repeated once a week.
4 OPERATION
