4 ph calibration, Ph calibration – Xylem MULTI 1970I PORTABLE MULTIPARAMETER METERS User Manual
Page 23
Multi 1970i
Operation
21
4.3.4
pH calibration
Why calibrate?
pH electrodes age. This changes the asymmetry (zero point) and slope
of the pH electrode. As a result, an inexact measured value is dis-
played. Calibration determines the current values of the asymmetry
and slope of the electrode and stores them in the measuring instru-
ment. Thus, you should calibrate at regular intervals.
When to calibrate?
z After connecting another electrode
z When the sensor symbol flashes, i.e. after the calibration interval
has expired
Calibration points
Calibration can be made with one or two buffer solutions (single-point
or two-point calibration). The measuring instrument determines the fol-
lowing values and calculates the calibration lines as follows:
AutoCal TEC
is specially matched to the WTW technical buffer solutions as a fully au-
tomatic two-point calibration. The buffer solutions are automatically
recognized by the measuring instrument. Depending on the instrument
setting (see section 4.9 C
), the instrument displays the
relevant buffer nominal value or the current electrode voltage in mV.
The calibration can be terminated after the first buffer solution. This cor-
responds to a single-point calibration. To do this, the instrument uses
the Nernst slope (-59.2 mV/pH at 25 °C) and determines the asymme-
try of the electrode.
AutoRead
The calibration procedure automatically activates the AutoRead func-
tion.
The current AutoRead measurement can be terminated at any time
(accepting the current value) by pressing
Displaying the calibra-
tion data
You can view the data of the last calibration on the display. The pro-
ceeding is described on page 50.
Printing the
calibration protocol
The calibration protocol contains the calibration data of the current cal-
ibration. You can transmit the calibration protocol to a printer via the se-
rial interface (see O
Determined values
Values of the calibration lines
1-point
ASY
z Asymmetry = ASY
z Slope = Nernst slope (59.16 mV/
pH at 25 °C)
2-point
ASY
SLO
z Asymmetry = ASY
z Slope = SLO