Electro-Chemical Devices (ECD) CA6 Hardness Analyzer - Manual (Page 40)

7.0 CALIBRATION
(1 st level password SERVICE)
Colorimetry is a relative method and a calibration is needed before
quantitative measurements can be performed. This is done using
standard solutions and analyzing them in the same way as the
samples will be analyzed. To ensure accurate measurements, the analyzer should be calibrated
periodically. A Calibration entails two measurement points, a zero point and a slope. The zero point is
referred to as the blank and is accomplished using distilled or De-Ionized water. The system slope is
determined using a standard solution of known concentration.
- Blank: Zero point of the system
- Factor: Slope of the system
The calibration can be done manually or automatically.
Initial calibration takes place at the factory (see analyzer final test results, Section 11.3). These values
should be used on a comparison basis for all subsequent calibrations.
7.1 Blank Calibration (Zero Point)
The Blank calibration should be performed whenever the reagent(s) are replaced and every time a
manual calibration is required.
This procedure is for a manually performed blank calibration. (See section 7.3 below for a step by step
guide) Before performing a manual calibration the operator should disable the 4-20 mA output. To
disable the 4-20 mA output press PROGRAM → SETTINGS → OUTPUT SIGNAL → ENABLE/DISABLE.
• Turn OFF sample flow
• Disconnect the sample #1 tubing from the sample vessel or the fast-loop reservoir,
• Place it in a container of distilled or de-ionized water (500-1000 ml). When the next analysis
cycle begins the analyzer will sample the DI water.
• The Blank absorbance detected by the analyzer is assumed to be the absorbance produced by
the reagent(s) and De-Ionized water with no ammonia present. This is the BLANK value, the zero
concentration point.
• Manually enter the new Blank value in PROGRAM → CALIBRATION MENU by pressing and
holding the BLANK key (3-10 seconds) until the value changes. This operation will replace the
stored BLANK value. It can only be executed after a completed analysis cycle, with the analyzer
in Stand-By (Wait) condition.
It is recommended that at least three analysis cycles be run with DI water before proceeding to a new
BLANK calibration.
The Blank Calibration can be overwritten in the Service Menu by entering a user determined value. This
could be an average of the absorbance values determined by several cycles of deionized water. Place
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