Xylem MULTI 3500i HANDHELD MULTIPARAMETER METERS - Manual (Page 65)

Multi 3500i Operation
63
4.7.5 Determining the cell constant (calibration in the control
standard)
Why determine the cell
constant?
Aging slightly changes the cell constant, e. g. by coatings. As a result,
an inexact measured value is displayed. The original characteristics of
the cell can often be restored by cleaning the cell. Calibration deter-
mines the current value of the cell constant and stores this value in the
instrument.
Thus, you should calibrate at regular intervals (we recommend: every
6 months).
Procedure You can determine the actual cell constant of the conductivity measur-
ing cell by calibrating with the control standard in the following ranges:
z 0.450 ... 0.500 cm -1
(e.g. TetraCon 325, nominal cell constant 0.475)
z 0.800 ... 1.200 cm -1
(cells with a cell constant of approx. 1)
The cell constant is determined in the control standard, 0.01 mol/l KCl.
Cell constants outside the ranges quoted above cannot be calibrated.
In the delivery condition, the calibrated cell constant of the measuring
instruments is set to 0.475 cm
-1
(conductivity measuring cells,
TetraCon 325 and ConOx).
AutoRead The calibration procedure automatically activates the AutoRead func-
tion.
Display calibration data
and output to interface
You can have the data of the last calibration displayed (see
section 4.8.5). Subsequently, you can transmit the displayed calibra-
tion data to the interface, e. g. to a printer or PC, with the key.
Note
The calibration record is automatically transmitted to the interface after
calibrating.
Sample record:
3.11.03 07:14
CALIBRATION Cond
03.11.03 07:13:22
Multi 3500i ser. no. 12345678
Cal. interval 14 d
Cell constant 0.975 1/cm 25.0 °C
Sensor +++