YOKOGAWA WE440, User Manual

Page: 34 / 67

<5. Calibration of the Instrument for Measurement Analysis>
5-1
IM 12Y18A04-01EN 1st Edition : Oct. 04, 2019-00
5. Calibration of the Instrument for
Measurement Analysis
In the analysis mode, the WE440 Phosphate Analyzer measures the absorbance of light through
the sample, and compares the result with the absorbance of light through a standard solution of
known concentration.
5.1 Theory of Calibration
Using two known standards, one of low concentration and the other of high concentration, the
absorbance for each concentration is measured and the slope and intercept are calculated from
the calibration curve as shown below:
Absorbance
∆ Absorbance
∆ Absorbance
Absorbance of Low Standard
Absorbance of High Standard
Concentration
∆ Concentration
∆ Concentration
Slope =
Concentration of
Low Standard
Intercept
Concentration of
High Standard
Figure 5.1
The Measured Absorbance is the result absorbance after subtracting the Blank Absorbance.
5.2 Methods of Calibration
Two methods of calibration are provided in the WE440 Phosphate Analyzer.
SINGLE POINT calibration uses high concentration standard alone, and BASE LINE calibration
uses either very low or zero standards.
The base line calibration is provided to improve accuracy for low level measurements and trace
analysis.
For setting up the calibration method, from the MAIN MENU, follow the sequence:
MAIN MENU → SETUP → CALIBRATION PARAMETERS
Set the MODE for SINGLE POINT or BASE LINE.
For Calibration, from the MAIN MENU, follow the sequence:
MAIN MENU → MEASUREMENT → CALIBRATE → CALIBRATE STANDARD
5.3 Single Point Calibration
For single point calibration, typically the intercept value is zero. Therefore,
Concentration = Slope x Absorbance.
The technician may modify the intercept value.