Evoqua WALLACE & TIERNAN DEOX/2000, Instruction Manual

Page: 42 / 86

W3T331759 / WT.050.585.003.UE.IM.1014 38
MICRO/2000® AND DEOX/2000® MODULE
4.4.2.4 DEOX/2000® BIAS calibration
In performing the BIAS calibration, the slope is calibrated by directly measuring
the residual “bias” resulting from the reagents (iodine) added to the cell. This
bias can be directly determined only by operating the analyser on zero residual,
chlorine demand free water (distilled water), so that the iodine bias residual is
the only source of residual. The full procedure is discussed below.
CAUTION: For the BIAS calibration to be accurate the sample water and
the distilled water should be at the same temperature.
A full slope calibration of the analyser is generally preformed upon start-up
and periodically thereafter.
The nominal Bias value is 1½ times the range of the analyser. Due to
variations in feed rate, the actual Bias can vary ± 25%.
a. Place 500 ml of demand free water in a 500 ml flask, and place the
flask in the wet side on top of the flow cell. This will cause a small
pressure (head) a flooded suction. A 500 ml beaker will not fit.
b. Attach two feet of 1/8-inch ID flexible tubing to the calibration leg
(middle leg) of the calibration valve. Put the end of the calibration
leg (middle leg) tubing of the calibration valve into the flask.
c. Move to the BIAS calibration function in the calibration menu of
the user interface.
d. Move the calibration valve lever to the calibrate position. This
closes the valve inlet from the process sample and opens the inlet
to the contained sample.
TO
METERING
PUMP
TO
METERING
PUMP
FLOW
FROM
CALIBRATION
SAMPLE
TO CALIBRATE TO RUN
FROM
PROCESS
SAMPLE
STREAM
FLOW
Figure 4.4
Figure 4.4