Navigator 600 Silica
Single-stream 7 Calibration & Maintenance
IM/NAV6S/SS–EN Rev. E 45
7.2 Secondary Calibration
During the Secondary calibration a known value silica
(secondary) standard is passed through the normal sample
flowpath, allowing a full chemical reaction to take place. The
silica chemistry is so reproducible that this response can be
compared to a theoretical response built into the analyzer. The
theoretical response has an ideal calibration factor of 1.0.
If the response is not perfect, compensation is applied to make
the readings correct and the resulting Calibrating factor provides
an indication of how much compensation is required – see
Fig. 7.5.
If this is within acceptable limits, the calibration passes and the
necessary compensation is applied. If the results are outside
acceptable limits the analyzer shows a calibration fail.
Calibration options comprise:
Baseline (2-point, resets zero) – runs both a zero and a
secondary calibration. Perform this routine only after the
reagents have been replaced or after an annual service.
This routine can only be initiated manually.
Zero (1-point) – required to compensate for any zero drift.
Performed weekly or as required to ensure accurate silica
measurement.
Secondary (1-point) – to verify sensitivity (as required) or if
the secondary calibration solution has been replaced.
Zero & Secondary (2-point) – can be performed instead of
a weekly zero calibration to compensate for drift and verify
sensitivity.
The zero, secondary and zero & secondary sequences can be
initiated manually or at programmed intervals.
Table 7.1 shows the timings for the full calibration sequence.
7.3 Cleaning
The analyzer can be programmed to introduce an alkaline
cleaning solution through the normal solution flowpath
automatically.
The alkaline solution has 2 main functions:
to remove the build up of precipitation or deposits in the
system due to the acidic chemistry conditions inside the
reaction block and optical unit. If cleaning is carried out
frequently, build up, and its effects on the zero offset, are
minimized.
to keep all the surfaces very clean and wetted, reducing
the effects of bubble formation due to sample and reagent
degassing.
Cleaning can be initiated either manually or automatically at
pre-programmed intervals with an adjustable duration.
The ideal frequency and duration of cleaning is determined by
monitoring the zero offset parameter at the end of each
calibration sequence. If the zero offset is not increasing by more
than 1 ppb from one zero calibration to the next, cleaning can
be less frequent.
The recommended initial starting point is to clean frequently for
a short period, for example, weekly for 30 minutes.
Fig. 7.5 Secondary Calibration
100 %
0 %
Theoretical Response –
Calibration Factor 1.0
Analyzer Response
Calibration Factor 0.9
Display and Reading ppb SiO2
Zero Offset –
2 ppb
Absorbance
Baseline
Activity
Zero
(if required)
Stability
Secondary Cal
(if required)
Stability
Recovery
(introduce sample)
Normal
Operation
Valve Energized Zero Zero Secondary Secondary None None
Timing (minutes)
Default
35 Up to 10 18 Up to 10 18 N/A
Calibration Relay Energized Energized Energized Energized Energized De-energized
Table 7.1 Calibration Sequence
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