4 calibration, Calibration – Xylem Lab 870 User Manual
Page 26
Operation
Lab 870
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11/2009
4.4
Calibration
Why calibrate?
pH electrodes age. This changes the zero point (asymmetry) and slope
of the pH electrode. As a result, an inexact measured value is
displayed. Calibration determines the current values of the zero point
and slope of the electrode and stores them. Thus, you should calibrate
at regular intervals.
For non-ID sensors, the calibration data is stored in the meter. For ID
sensors, the calibration data is stored in the sensor.
When do you have to
calibrate?
z After connecting another electrode
z If the CalClock has expired and flashes
Buffer sets for
calibration
You can use the buffer sets quoted in the table for an automatic
calibration. The pH values are valid for the specified temperature
values. The temperature dependence of the pH values is taken into
account during calibration.
No.
Buffer set*
pH values
at
1
SI Analytics GmbH DIN buffers
according to DIN 19266/NBS
1.679
4.006
6.865
9.180
12.454
25 °C
2
SI Analytics GmbH Technical
buffers according to DIN 19267
2.000
4.010
7.000
10.011
25 °C
3
Merck1*
4.000
7.000
9.000
20°C
4
Merck2 *
1.000
6.000
8.000
13.000
20°C
5
Merck3 *
4.660
6.880
9.220
20°C
6
DIN 19267 *
1.090
4.650
6.790
9.230
25 °C