Secondary Turbidity Standards - Hach 2100AN Instrument Manual

SECTION 3,
continued
3.2.4.1 Reviewing Calibration Data
®
3.2.5 Using Gelex
Note: Reassign values to the Gelex
standards each time the instrument
is calibrated with Formazin.
Note: Consistent orientation of the
Gelex standards is critical each time
they are used to check the
instrument calibration.
To review calibration data currently in effect, press the
the up arrow key to scroll through the standards. Pressing the
of the calibration data in effect. Press the
mode. The stored calibration data is not affected.

Secondary Turbidity Standards

Gelex Secondary Standards, supplied with the instrument, are metal-oxide particle
suspensions formulated to correspond to Formazin primary turbidity standards in
their light scattering characteristics. NTU values marked on the Gelex standards
indicate the range for which they are to be used. Minor variations in glass and
individual instrument optical systems dictate that the true value of the secondary
standard must be determined on the instrument on which they are used. To
calibrate the Gelex standards:
1. Calibrate the instrument with Formazin (refer to Section 3.2 on page 36).
2. Verify that the instrument is set for the NTU mode, ratioing on and Automatic
Ranging. For the 0-2 and 0-20 range standards, select either Ratio on or off.
Choose the Ratio function that the instrument will be operated in. If
measurements will be performed with Ratio on and off, assign a separate
value for each.
3. Thoroughly clean the outside of the Gelex vials, and apply a thin coating of
silicone oil.
4. Place the lowest NTU Gelex Standard in the sample compartment. Align the
Gelex vial orientation mark with the sample cell compartment orientation
mark. This ensures the best possible repeatability. Close the sample holder
cover.
5. Press
ENTER
instrument, and mark this value on the vial.
6. Repeat steps 3 through 5 for the other Gelex standards.
A Stray Light Standard is included with each Gelex Secondary Standard Kit. Use
of the Stray Light Standard helps monitor the integrity of the instrument's optical
system. If an optical component begins to degrade over time, the value of the
Stray Light Standard will change significantly. If the value changes significantly,
contact Hach Customer Service for more information.
Determine the Stray Light Standard value when the instrument is first received.
Clean the outside surface of the Stray Light sample cell, apply silicone oil (see
Section 2.3.2.1 on page 19) and measure the value in the NTU measurement
mode. Make sure the sample cell is aligned in the cell holder the same way each
time. Hach recommends using the vertical line that extends upward from the
diamond symbol on the vial as a reference mark. Align this mark with the sample
cell compartment orientation mark, and measure the value in the
Record this value on the sample cell. Store the Stray Light Standard at room
temperature.
. Record the value displayed. Remove the standard from the
42
key, and then use
CAL/Zero
PRINT
key to return to the operating
UNITS/Exit
key prints all
Ratio on mode.