Hach-Lange SURFACE SCATTER 7 sc Turbidimeter - Manual (Page 34)

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Operation
8. If no selection is made for a set period of time, the screen will
prompt to remix the standard to avoid a change in the value of
the standard.
a. Open the SS7 sc and remix the standard.
b. Close the door and confirm to continue.
9. Confirm to calibrate. When the calibration is completed
successfully, confirm to accept the calibration.
10. Enter the initials of the user performing the calibration
and confirm.
Note: After confirmation of return to measurement mode, the instrument
will equilibrate for 2 minutes before the output mode changes. Instrument
measurements will show on the display, but the value will flash and a “OUT
MODE WARN” warning will display until the 2-minute equilibration period
is complete.
5.5.2.1 Calibration cylinder method
A calibration cylinder and a 500-mL bottle of 4000 NTU formazin
primary standard solution are included for convenient calibration of
the SS7 sc. After the formazin standard is added to the cylinder, the
instrument is set to the value of the standard.
1. Prepare the formazin standard solution at the desired NTU
value. The 4000-NTU standard supplied with the instrument
can be used at full strength and only requires mixing (by
inverting the bottle repeatedly). If a dilution of the 4000-NTU
standard is desired, the manufacturer recommends it be no
lower than 300 NTU. Dilutions must be made just prior to use.
Dilute formazin solutions are unstable and should be discarded
when calibration is complete. Use filtered sample or
demineralized water for dilution.
2. Turn off sample flow to the instrument and drain the
turbidimeter body. Insert the calibration cylinder into the top of
the body (
Figure 16 on page 33 ).
a. Select the PERFORM CAL menu entry and confirm.
b. Select the Active, Hold or Transfer output mode
and confirm.
c. Edit the standard value and confirm.
3. Follow the display prompts and pour the formazin standard
solution into the cylinder, allowing it to overflow. Only allow the
solution to stand long enough to allow bubbles on or near the
surface to dissipate.
4. Close the sample unit door tightly. Confirm to continue.
5. The TURB value displayed is the standard value determined
using the gain from the previous calibration. Confirm to accept
and continue with the calibration.
6. If no selection is made for a set period of time, the screen will
prompt to remix the standard to avoid a change in the value of
the standard.
a. Open the SS7 sc and remix the standard.
b. Close the door and confirm to continue.