Span Calibration Procedure; Relative Probe Sensitivity - Hach 8450 Instrument Manual

3.15.3 Span Calibration Procedure

3.16 Relative Probe Sensitivity

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If the probe was immersed in deionized water for several hours prior to the
zero and this span calibration, allow the display to stabilize for 60 minutes
(with the probe immersed in the concentration) before span calibrating.
Enter into the Span Calibration sequence by selecting "SPAN" from the "CAL"
menu.
Note: You may abort the calibration at anytime by activating the
1. Immerse the probe in a flowing solution of known Cl
using a flow cell, install the probe into the flow cell with chlorinated water
running at the 14 to 16 gph flow rate through the cell as indicated under
section 3.15.2 on page
(> 1.00 ppm) are best. Wait for the displayed reading to become positive
and stable.
Note: The stability of the reading may be increased by increasing the "Damp"
parameter value in the RDG menu. Do not proceed if the concentration reading is
below zero.
2. When the concentration reading is positive and stable, initiate the
calibration by activating the
to blink, indicating that you may adjust its value. Use the arrow icons until
the concentration value displayed matches the known concentration value
and activate the icon.
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3. The timer will set to 10:00 minutes and begin counting down while the
instrument monitors the probe signal stability. These variances must be
less than 0.02 ppm over 60 seconds before the instrument will accept the
reading as stable. This will take at least 60 seconds. If the timer expires
(reach 0:00), an error message will scroll until it is acknowledged by
activating any icon.
Although not recommended, you may bypass this phase by activating the
icon. Bypassing this phase will display a "Span Calibration Complete"
scrolling message. This merely indicates that the spanning sequence has
been exited; do not misinterpret this to mean a valid span calibration has been
performed.
Note: It is important not to activate any icon during the AGC phase indicated in the
next step.
4. The instrument will now begin its auto-gain phase. During this phase, the
instrument will set the proper amount of gain based on the probe's input
signal and the known concentration of chlorine. The timer is reset to
15 seconds to permit the input signal to settle. When the count-down
timer reaches zero, the input is stored and the instrument updates the
relative probe sensitivity percentage displayed in the lower right hand
corner (see section 3.15). The message "Span cal complete..." is
displayed.
Chlorine probes vary in their sensitivity to residual chlorine and, as probes
age, their sensitivity will naturally decrease as internal components are
consumed. Upon calibration, the Model 8450 determines a relative probe
sensitivity (the percentage is derived from an average known output of all
38. In this regard, higher concentrations
icon. The concentration value will now begin
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Relative Probe Sensitivity
Section 3
icon.
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concentration or, if
2
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