HF scientific Micro1000 Laboratory Turbidimeter - 0-10,000 NTU - Manual (Page 15)

Rev. 3.2 9
Under normal conditions, re-calibration is recommended at least once every three months 1 . You
may select a predetermined calibration interval for automatic prompting for calibration: if you
exceed the selected calibration interval, the "Cal" block will flash until the instrument is re-
calibrated.
During calibration, the instrument performs several system self-diagnostics. As such, several
warning messages may be displayed. If the instrument detects an irregularity with the instrument
(detectors or lamp) a warning message will be displayed on the lower row of the display on exit from
the calibration mode. If this occurs please attempt to rectify the warning message yourself, or
contact the HF scientific technical services department. In any event, the instrument will continue to
monitor the turbidity of the process water with a decreased accuracy until the error is
rectified.
In addition, if the instrument remains in the calibration mode for longer than 5 minutes with no
activity, it will time out and return to the automatic measuring mode.
Note: The instrument must be re-calibrated after lamp replacement.
5.1. Calibration Standards
HF scientific, inc. recommends that you use the following materials during calibration to achieve the
accuracy stated in this manual:
1. 0.02 NTU ProCal Calibration Standard available from HF scientific inc.
2. 10.0 NTU ProCal Calibration Standard available from HF scientific, inc.
3. 100 NTU ProCal Calibration Standard available from HF scientific, inc.
4. 1750 NTU ProCal Calibration Standard available from HF scientific, inc.
5. 10000 NTU ProCal Calibration Standard available from HF scientific, inc.
It is well known that diluted Formazin is unstable. If you choose to use Formazin to calibrate the
instrument, ensure that you are using a fresh stock suspension of Formazin to achieve the accuracy
quoted for the instrument. A Formazin Stock Solution Kit is available from HF scientific (Catalog
No. 50040). The HF scientific
ProCal , primary calibration sets (Catalog No.19927 or 19928) are
more stable than Formazin and have a minimum shelf life of 12 months. If you use the stable HF
calibration standards to calibrate the instrument, review the expiration date to ensure that the
standards have not expired.
Note: The 1750 NTU & 10000 NTU calibration standards must be inverted (well mixed) prior to use
to ensure the homogeneity and repeatability of the suspension for measurement. Do not shake.
5.2. Indexing the Calibration Standard(s)
The United States Environmental Protection Agency (US EPA) recommends that cuvettes used for
instrument calibration or sample measurement be indexed. To comply with this recommendation,
each HF scientific, inc. calibration standard is supplied with an indexing ring for quick and
repeatable indexing of the calibration standards. To index a calibration standard perform the
following two steps:
1 The EPA recommends that on-line turbidimeters be calibrated with the primary standard at least once every three months if they
are to be used for EPA reporting.