Hach-Lange SURFACE SCATTER 7 sc Turbidimeter - Manual (Page 36)

34
Operation
calibrated. Take a grab sample from the on-line instrument drain or
sample inlet line and immediately measure its turbidity in the
laboratory instrument. If the on-line instrument reading is off by
more than 5%, use the calibration procedure detailed in
section 5.5.2 on page 31 to input the new standard value. If this
calibration method is used, it is not necessary to use the
calibration cylinder.
5.5.2.3 Calibration failure
If gain criteria for the calibration are not met, the screen will display
BAD CAL! Confirm to repeat the calibration.
5.5.3 Setting the verification baseline
When the SS7 sc has been successfully calibrated, a baseline can
be determined using standardization plates. The standardization
plates are composed of opaque backing, a plate glass covering and
a center filling of Gelex, a stable secondary turbidity standard. The
standardization plates are not calibrated when shipped from the
factory. The value of the plate is determined after calibration and
stored internally in the SS7 sc.
The calibration can be verified later
by reading the plate value and comparing it to the value
following calibration.
Important Note: Always verify calibration with the same
standardization plate that was used to establish the baseline. The
manufacturer recommends assigning a serial number (up to 4
characters) to each plate. The serial number can be marked on the
back of the plate.
1. Perform a calibration ( section 5.5.2 ).
2. Confirm to perform a baseline using a standardization plate.
3. The serial number for the last standardization plate used will
appear on the display. Confirm to accept or enter the serial
number of the plate to be used and confirm.
4. Follow the controller prompts:
a. Remove the calibration cylinder and wipe off the top of the
sample cylinder.
b. Place the standardization plate on top of the sample
cylinder so that the light beam strikes the center of the
plate. Note the orientation of the plate and always place it
in the same position when using it to check standardization.
c. Close the door to eliminate stray light. Confirm to continue.
5. When the measured value becomes stable, confirm to establish
an expected value for the plate.
Note: Future measured values will be compared to the stored
expected value. If the established PASS criteria are not met, a new
calibration should be performed.