wtw pH 1970i, Руководство по эксплуатации

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Operation pH 1970i
20 ba75690e01 01/2007
4.3 Calibrating
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
After the calibration interval has expired (when the sensor symbol
flashes)
Calibration interval The calibration interval (Int 3) is set to 7 days in the factory. You can
select the interval in the range of 1 ... 999 days (see
section 4.6 C
ONFIGURATION
).
Calibration points Calibration can be made with one or two buffer solutions (single-point
or two-point or three-point calibration). The measuring instrument de-
termines the following values and calculates the calibration lines as fol-
lows:
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
3-point ASY
SLO
ASY2
SLO2 The center buffer divides the
calibration range into two sub-
ranges with separate calibration
lines.
Range 1:
z
Asymmetry = ASY
z
Slope = SLO
Range 2:
z
Asymmetry = ASY2
z
Slope = SLO2
The calibration values of the
respective sub-ranges are used for
the measurement.