YOKOGAWA WE440, User Manual

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<5. Calibration of the Instrument for Measurement Analysis>
5-2
IM 12Y18A04-01EN 1st Edition : Oct. 04, 2019-00
The analyzer uses a 10 ppm concentration standard solution for calibration. The absorbance
of the standard solution is measured and the slope is calculated and stored upon user’s
confirmation.
5.4 Base Line Calibration
After calibrating using the single point, improved accuracy around the base or zero point may be
further tuned by executing a base line calibration.
A low concentration solution is used and its absorbance is measured in the instrument. Only the
intercept is recalculated as:
Intercept = Concentration (Low) – [Slope X Absorbance (Low)]. This is used along with the slope
for single point calibration.
The calibration data is available for editing. From the MAIN MENU, follow the sequence:
MENU → SETUP → CALIBRATION PARAMETERS
The menu screen shows two columns labeled REFERENCE and CURRENT. The data in the
current column is the active data being used for slope and intercept, and the data in the reference
column is the data that the system relies on when comparing the new calibration result to check
its allowed deviation per the specified limit specified for the tolerance value.
5.5 High Range Dilution-Factor Calibration
The analyzer uses a dilution method for measurement of high concentrations. The cycle is
automatic and has been programmed at the factory. In most cases the factory default values are
sufficient for the specified range of the product. For improved accuracy, the user may calibrate
the dilution factor using a high concentration standard like a 100 ppm. This calibration is only
allowed in manual mode, with user prompts and confirmation required at the end of the cycle.
Extended range calibration:
MENU → SETUP → (+) CALIBRATION PARAMETERS
Set the STANDARD CONC = 100 ppm and calibration:
MAIN MENU → MEASUREMENT → CALIBRATE → CALIBRATE STANDARD
When the system detects a high absorbance level of the reacted solution, above the set limit, it
initiates the dilution cycle using the standard.
At the end of the cycle the dilution factor is calculated based on the value of the standard used
and the existing slope and intercept.
At the end of the calibration cycle the user is presented with the new calculated dilution factor to
accept or reject. The default dilution factor is 9.0 (range 8 to 10). The range depends on the pump
flow rate (pump #1) used to add the standard used for dilution dosing.
The user may edit the dilution factor in the ANALYSIS PARAMETERS menu:
MENU → SETUP → ANALYSIS PARAMETERS → (+) (+) PAGE 3 OF 4 → DILUTION
PARAMETERS
Consult before modifying the default dilution steps. Press (+) to access the dilution steps.
The automatic dilution cycle may be turned off using either a higher than expected AU limit:
ABS HIGH LIMIT= 5 AU or by de-selecting the dilution event
DILUTION EVENT = NOT ASSIGNED
During the analysis of high concentration samples, the system checks the final absorbance value
of the reacted solution and if it exceeds the set limit (ABS HIGH LIMIT) it will execute the dilution
steps and use the calibrated dilution factor to calculate the final concentration.