YOKOGAWA WE440, User Manual

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<5. Calibration of the Instrument for Measurement Analysis>
5-3
IM 12Y18A04-01EN 1st Edition : Oct. 04, 2019-00
5.6 Theory of Measurement
Measurement in the WE440 Phosphate Analyzer is done by measuring the absorbance of a
single wavelength of light through the sample, and comparing the result with the absorbance
of the same wavelength of light through a standard solution of known concentration. If the two
absorbencies match, then the sample concentration is equal to the standard solution.
To facilitate the comparison, the analyzer is first calibrated with standards to determine the
slope and intercept of the range of concentration it can analyze, and then the measurement
of the unknown sample is interpolated along the calibration curve to calculate the unknown
concentration.
i.e., Concentration = (Slope x Absorbance) + intercept. Where Slope and Intercept - Determined
from Calibration. Absorbance - Calculated through measurement.
The two variables (Slope and Intercept) are available for editing in the calibration parameters
menu screen.
Absorbance
Measured Absorbance
of Sample
Concentration
Concentration
of Sample
Figure 5.2
5.7 Mode of Measurement
The WE440 Phosphate Analyzer is designed to provide on-line process measurements, and has
two modes of operation. The mode is always displayed at the bottom right, i.e., below the Info
field and above the status field of the display.
The two modes of the instrument are AUTO restart mode (the instrument resumes auto analysis
mode after 0.5 Hr of inactivity) and MANUAL restart mode. The instrument awaits the user to
initiate the RUN or AUTO ANALYSIS mode by pressing the RUN key.
To change the instrument mode, from MAIN MENU follow the sequence:
MENU → SETUP → (+) ANALYSIS PARAMETERS → MODE
The instrument has two special keys to start and stop the measurement. Pressing the RUN
key starts the auto analysis immediately and analysis repeats at the rate of the time set in
measurement frequency, which is selectable. During this mode, the instrument displays RUN
MODE indicating that the instrument is running continuously.
To edit the measurement frequency, from the MAIN MENU follow the sequence:
MENU → SETUP → (+) ANALYSIS PARAMETERS → SAMPLE FREQUENCY
The STOP key aborts the measurement at any stage irrespective of the mode of the instrument.
NOTE
RUN is not the mode of the instrument. It indicates that the instrument is performing
measurement continuously, at the rate of measurement frequency.