4 69 0 S E R I E S |
T U R B I D I T Y SEN S O R | O I/AT S 410 - EN R E V. A
11
5 Calibration
A key feature of the 4690 Series Turbidity system is the dry
secondary calibration standard. This is designed to simplify
routine calibration verification and minimizes the need for
chemical standards.
Each dry calibration standard is verified against a primary
formazine standard before delivery, and the nominal turbidity
value is indicated on the label.
For regulatory monitoring, use the secondary calibration
standard for monthly calibration verification and periodically
monitor it for deterioration using a primary standard.
Definitions
•
Primary standards
Turbidity standards that are traceable and equivalent to
the reference turbidity standard, within statistical errors.
Formazine is the most commonly acceptable form of
primary standard. The other is a commercially
manufactured liquid suspension of styrene divinylbenzene
polymer beads (SDB). Primary standards are used to
calibrate a turbidity analyzer directly or to calibrate a
secondary standard.
•
Secondary standards
Standards that the manufacturer (or an independent
testing organization) has certified give analyzer
calibration results equivalent (within certain limits) to the
results obtained when the analyzer is calibrated with a
primary standard.
•
Calibration
A procedure that checks or adjusts an analyzer’s accuracy
by comparison with a defined standard or reference.
•
Calibration verification
A procedure used to check whether or not the calibration
of the analyzer is within certain limits.
Care and maintenance of secondary
standards
ABB’s secondary standards may be used repeatedly but must
be monitored for deterioration.
All secondary standards can change gradually with time.
Deterioration can be detected by measuring the turbidity value
of the secondary standard after calibration of the analyzer with
a primary calibration standard.
It is recommended that secondary standards are checked every
three months against a primary standard on the analyzer they
are intended to be used with.
If the comparison with a primary standard shows that the
turbidity value of the secondary standard has changed, the
secondary standard can be assigned a new turbidity value for
use in future calibration verification.
Included with each sensor is a calibration record card kit for
recording the value of the secondary standard compared to the
primary calibration data for each individual analyzer with which
the secondary standard is used.
Additional calibration record card kits can be purchased from
ABB (part no. 7998190 for pack of 3).
Turbidity Monitor Primary Calibration Card
Sensor Serial Number:
Dry Standard Serial Number:
Time/Date of Primary
Calibration
Dry Standard
Reading after
Primary Calibration
(NTU)
Performed By
Reorder Code: 7998190
Issue A, 08/06/2011
ABB Limited, Oldends Lane, Stonehouse, GL10 3TA
Time/Date of Primary
Calibration
Dry Standard
Reading after
Primary Calibration
(NTU)
Performed By
Figure 8 Example of calibration record card
To minimize deterioration of the secondary standard:
• Carefully clean any residual moisture after use.
• Clean the prism with a cloth that has no lint.
• Do not touch the dry standard rod. Fingerprints on the
surface can have an effect on its stated value.
• Keep it in the container provided when not in use, and keep
it in a dry place.
