8
4.1 Calibration Standards
We recommend that you use the following materials during calibration to
achieve the accuracy stated in this manual:
1.
CAL 1
: 1000 NTU Calibration Standard
2.
CAL 2
: 100 NTU Calibration Standard
3.
CAL 3
: 10.0 NTU Calibration Standard
4.
CAL 4
: 0.02 NTU Calibration Standard
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.
Calibration standards offered are more stable than Formazin and have a
limited shelf life of 6 months. If you use the stable calibration standards to
calibrate the instrument, review the expiration date (indicated on cap label)
to ensure that the standards have not expired.
4.2 Indexing the Calibration Standards
The United States Environmental Protection Agency (US EPA)
recommends that cuvettes used for any instrument calibration or sample
measurement be indexed. To comply with this recommendation, each
calibration standard is supplied with an indexing ring and each instrument
has a reference point for quick and repeatable indexing of the calibration
standard. To index a calibration standard perform the following steps:
1. While holding down the
↵
↵
button, slowly rotate the calibration standard
one complete revolution (360°) pausing between increments to allow the
display to update.
2. While rotating the standard, observe the turbidity reading and locate the
cuvette position with the lowest turbidity reading.
3.
With the calibration standard positioned at the location having the
lowest turbidity reading
, install the Indexing Ring over the black light
shield on the standard so that the pointer of the Ring aligns with the
reference arrow on the instrument.
4.3 Calibration Procedures
1.
Select the calibration function of the instrument by pressing the
CAL
button once. The “CAL” block will be illuminated on the display with
“1” indicating the standard required for this step of the calibration. This
is the first standard that should be used in a full calibration.