27
SECTION 3, continued
Note: After entering a reagent blank adjust, the display may flash “limit”
when zeroing if the sample used for zeroing has a lower absorbance
value than the reagent blank.
To disable the Reagent Blank adjust feature, press SETUP, scroll
to
BLANK and press ENTER twice. The concentration readings
will be displayed without subtracting the blank. The sample cell
icon will no longer appear in the display.
Do not attempt to use the Reagent Blank Adjust feature if the
procedure uses a reagent blank for zeroing.
3.4 Adjusting the Standard Curve
The DR/890 Colorimeter has over 90 Hach Programs
permanently installed in memory (other models have fewer
programs). A program usually includes a preprogrammed
calibration curve. Each curve is the result of an extensive
calibration performed under ideal conditions and is normally
adequate for most testing. Deviations from the curve can occur
from using compromised testing reagents, defective sample cells,
incorrect test procedure, incorrect technique, or other correctable
causes. Interfering substances or other causes may be beyond the
analyst’s control.
In some situations, using the preprogrammed curve may not
be convenient:
• Running tests where frequent calibration curve checks
are required.
• Testing samples which give a consistent test interference.
Consider the following before adjusting the calibration curve:
1. Will future test results be improved by adjusting the curve?
2. Are interfering substances consistent in all the samples that
you will test?
Any precision and test range information provided with the
procedure may not apply to an adjusted curve calibration.
You can adjust many of the calibration curves by following the
steps found in the test procedures. Working carefully is
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