Hach Lange 2100AN, Instrument Manual

Page: 45 / 108

SECTION 3,
continued
45
3.3.3 Preparing Formazin Dilutions - User Selected
Hach Company recommends using 20, 200, 1000, 4000 and 7500-NTU formazin
standards for calibrating the 2100AN Turbidimeter. Other dilutions can be
prepared and used, but if problems occur when using these alternative solutions,
use the dilutions specified in Section 3.2.3 on page 37.
Prepare Formazin dilutions from well-mixed, 4000-NTU stock solution as
specified in section Section 3.2.3 on page 37 and dilution water as specified in
section Section 3.2.2 on page 37.
Prepare Formazin dilutions to span the entire range of the instrument. Four
standards are required. The following are suggested:
a. one in the range of 10 to 30 NTU
b. one in the range of 180 to 220 NTU
c. one in the range of 900 to 1,100 NTU
d. one of 4000 NTU.
Standards must have a difference of at least 60 NTU. In addition, make a blank
measurement using the same dilution water used in making the Formazin
dilutions, and entered as the 00 calibration point.
Prepare standard solutions immediately before use, and discard the standards
when calibration is complete.
3.3.4 Calibrating the 2100AN (user selected standards)
Instrument calibration is accomplished as described in Section 3.2.4 on page 39
with two exceptions:
1. Standards are values other than those used in steps 6, 9, 10, 11 and 12.
2. Before pressing
ENTER
to measure each standard, edit the displayed value to
agree with the actual turbidity of the standard. This is done by using first the
right arrow to get into the editing mode and then using the right, up and down
arrow keys to edit the number.
Note: For best accuracy, use the same sample cell or four matched sample cells for all
measurements during calibration. Abort the calibration procedure at any time without
changing any stored value by pressing the
UNITS/Exit
key.