Hach 1720E, User Manual

Page: 19 / 42

17
Operation
• Stop sample flow, drain, and clean the turbidimeter body before beginning the
calibration procedure.
• Always clean the photocell window per the instructions in section 6.4.1 on page 24 .
Rinse the photocell with deionized water and dry with a soft, lint-free cloth before
calibrating.
• Always clean the turbidimeter body or calibration cylinder per the instructions in
section 6.4.2 on page 24 . Rinse with deionized water before calibrating.
• Store the calibration cylinder upside-down to minimize contamination between
calibrations.
• Pour the calibration standard into the turbidimeter body at the inflow end (left side
when facing the instrument).
• Gently invert StablCal standards for 1 minute before opening. Do not shake. This
ensures a consistent turbidity of the standard.
• If the 20.0 NTU StablCal standard is allowed to sit in the calibration cylinder or
turbidimeter body for more than 15 minutes, it must be remixed (gently swirled in the
calibration cylinder) before use to ensure a consistent turbidity.
• Discard all standards after use per the instructions on the container. Never transfer the
standard back into its original container. Contamination will result.
• Always recalibrate after restoring default settings.
5.5.1 User-prepared Calibration
The user-prepared calibration is a two-step calibration in which the difference between the
DI water and the standard value is used to determine the gain of the instrument. The water
used for the standard solution must be from the same source as that which the DI water
measurement is made. Variation in dilution of the water source could negatively impact the
accuracy of the calibration.
The manufacturer does not recommend calibrating below
1.0 NTU, and instrument specifications are based on the calibration point at 20 NTU.
Before starting the calibration, read and apply the tips in section 5.5 on page 16 .
Follow the procedure as written (using 1 L of deionized water and 5.0 mL of 4000 NTU
formazin)
if using a calibration cylinder for calibration.
If using the turbidimeter body for the user-prepared calibration follow the procedure
below using 20.0 NTU formazin in step
12 . Follow the steps below for proper calibration:
1. Stop the sample flow, then drain and clean the body.
2. Prepare a 20.0 NTU standard by adding 5.0 mL of 4000 NTU formazin to a 1-L flask.
Dilute to the mark with deionized water and invert gently to mix.
3. Drain the deionized water and pour the prepared 20.0 NTU standard into the
turbidimeter body at step
12 . Do not add additional 4000 NTU formazin.
4. From the Main Menu, select SENSOR SETUP and confirm.
5. Select the appropriate sensor if more than one is connected and confirm.
6. Select CALIBRATE and confirm.
7. Select USER PREPD CAL and confirm.
8. Select the available Output Mode (Active, Hold, or Transfer) from the list and confirm.