Metrohm 781 pH/Ion Meter - Manual (Page 71)

6 Methods / Parameters
780/781 pH/Ion Meter, Manual
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buffer type: mixed
A further way of using the stored buffer table is to combine a
maximum of five different buffer types to form a new series. You
can make your selection from all the stored buffers described in
Section 9.4.
A general rule is that you can only calibrate in defined temperature
ranges, as otherwise the error message:
buffer not defined
appears. If you use more than two buffers for the calibration then you
can use certain buffers several times in order to give them a better sta-
tistical weight.
low lim.slope 0.1...95.00...999.9 %
up lim.slope 0.0...103.0...999.9 %
low lim.pH(0 -99.999...6.40...99.999
up lim.pH(0) -99.999...8.00...99.999
)The most important calibration data such as slope and pH(0) must lie
within the limits defined here in order for them to be automatically
adopted. The given default values for the slope correspond to the quali-
ty criteria of a "passing electrode" in the electrode test (see Section 8.6).
If one of the values of the calibration data lies outside these limits then
at the end of the calibration the following message will appear: cal.
data out of limits ; you can then accept or reject the results.
offset Uoff state: OFF, ON
offset Uoff -2200.0...0.0...2200.0 mV
The automatic buffer recognition of the pH/Ion Meter assumes an
offset potential of 0 ± 30 mV for the electrode used. Ag/AgCl ref-
erence electrodes normally meet this requirement. If other refer-
ence systems are used, e.g. a calomel electrode, then the offset
potential may be outside this range. This means that for correct
buffer recognition this variation must be compensated by entering
the specific offset potential Uoff. For the pH measurement itself
this parameter is unimportant.