LTH Electronics HPT63, Руководство по эксплуатации

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10 Calibration
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10.3 Calibration Practices
Observe normal good practices when calibrating electrode systems against standard
solutions.
•
Always clean the electrode system before inserting in the standard solution to
avoid contamination and to obtain the best response from the electrode
system.
•
Rinse the electrode system in clean (preferably demineralised) water between
standard solutions.
•
Allow time for the electrode system temperature to stabilise in each standard
solution.
•
Use standard solutions of known quality. If in doubt make up fresh solutions.
•
Use clean beakers and bottles for standard solutions.
•
The HPT63 can be taken offline, which de-energises the relays and holds the
current outputs at their last values. This facility is useful when calibrating the
system, however the operator must ensure the relays are in a safe state when
using this feature.
10.4 pH Electrode Condition
Depending on the measurement environment, sensor sensitivity (slope) can vary with
age and, hence, periodic slope recalibration may be required. The buffer (offset)
value can also be adjusted, but this should not require regular adjustment once the
unit has been set up for a given sensor.
For a glass electrode, the buffer (offset) adjustment after calibration will be displayed
as 7 pH
±
2 pH. For antimony electrode, the adjustment will be displayed as 0 pH
±
2
pH. The Slope Limit adjustment for a glass electrode is 80% to 110%, for an
antimony electrode 75% to 115%.
10.4.1 pH Buffers
LTH supplies buffer powders which are prepared from pure dry chemicals, sealed in
a sachet or capsule which prevents the absorption of moisture and subsequent
deterioration. Prepare buffer solutions in accordance with the instructions supplied
with the buffer powders.
Using the
Buffer and Slope menu items, it is possible to do single ( Buffer only) or
two-point calibration,. It is important to do the calibration in the correct order:
1. Buffer (Offset) adjustment at 7
±
2 pH
2. Slope (Gain) adjustment at another pH – normally 4 or 9 pH (for two point
calibration only)
The output from an ideal glass/reference electrode pair will normally be 0mV at 7pH.