42
SECTION 3,
continued
3.2.4.1
Reviewing Calibration Sequence
To review calibration data currently in effect, press the
CAL
key, and then use the
UP ARROW
key to scroll through the standards. If the instrument is connected to a
printer, pressing the
key prints all of the calibration data in effect. Press the
UNITS/EXIT
key to return to the operating mode.
3.2.5
Using Gelex
®
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 3.2 on page 37).
2. Verify that the instrument is set for the NTU mode and Automatic Ranging.
Select either Ratio on or off for the 0–2 and 0–20 range standards. Choose the
Ratio function that the instrument is intended to operate in. If measurements
will be made 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 with the
triangle on the vial aligned with the index mark on the instrument sample
compartment. Close the sample-cell cover.
5. Press the
ENTER
key. Record the value displayed. Remove the standard from
the instrument, and mark this value on the vial.
6. Repeat steps 3–5 for the other four Gelex standards.
Note: Reassign new values to the
Gelex standards each time the
instrument is calibrated
with Formazin.
An empty vial (Cat. No. 25891-00) is included with each Gelex Secondary
Standard Kit. Use the vial to monitor the integrity of the instrument’s optical
system. If an optical component begins to degrade over time, the value of the vial
will change significantly. If the value changes significantly, contact Hach
Customer Service or your distributor for more information.
Note: Consistent orientation of the
Gelex standards is critical each time
they are used to check the
instrument calibration.
Determine the vial value when the instrument is first received. Clean the outside
surface of the glass cell, apply silicone oil (Section2.6 on page 23) 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 RATIO on mode. Record this value on the sample cell. Store the
vial at room temperature.
Tài liệu sưu tầm của Trung Sơn - www.tschem.com.vn - 028.3811.9991 - [email protected]
Tài liệu sưu tầm của Trung Sơn - www.tschem.com.vn - 028.3811.9991 - [email protected]
