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234 UDA2182 Universal Dual Analyzer Product Manual January 2009
15.17 Appendix P – AutoClean and AutoCal Theory and Piping
Overview
Periodic calibration of pH electrodes is necessary for best system performance because
electrode outputs change over time. One-point calibration (standardization) is a zero
adjustment to compensate for electrode drift. Two-point calibration (standardization and
slope adjustment) includes a span adjustment to match the gain of the
Analyzer/Controller to the electrode response. Standardization and slope each depend on
the electrode measuring a reference solution (buffer) of known pH.
The AutoClean and AutoCal features periodically rinse and calibrate pH electrodes
automatically as described in this section. To take advantage of these features you must:
• Select them during I/O setup (Section 6.15)
• Set the clock (Section 6.18), and specify the frequency and duration of the cleaning and
calibration operations. (Section 6.15)
• Configure the system to use automatic buffer recognition. (Section 8.5.2).
•Wire the relays assigned to these operations during system setup to operate the
necessary valves. (Section 7.3).
• Install piping and valves as diagrammed in this section.
AutoClean Sequence and Piping
Rinse sequence
The AutoClean operation occurs at the configured intervals. The sequence is described
below.
1 All alarm action is held at existing levels. The output(s) can be held or be active, depending on
configuration. Even if the outputs are not held, “HOLD ACTIVE” is displayed on the alarm stripe
because alarms are always held.
Also, “AUTOSEQUENCE” is displayed. Pressing the DISPLAY key will call up a special display that
shows how much time is left in the operation.
2 Relay 1 activates 3-way solenoid valve S1 (see Figure 15-11) to direct rinsing fluid to the electrodes
for the configured rinse duration (1 to 1999 seconds). If the measured sample is normally returned
to the process but quantities of rinsing fluid cannot be tolerated there, use an additional 3-way
solenoid valve S4. It is activated simultaneously with S1 to divert the discharge to drain.
3 At the end of the configured rinse time Relay 1 de-activates the solenoid valve S1 (and S4, if used).
After the configured delay period (1 to 1999 seconds) the Analyzer/Controller resumes sampling the
process. (Note that even with S4 for diversion, one system volume of washing fluid will pass to the
process at this point.)
4 The “HOLD” and “AUTOSEQUENCE” messages are cleared.
Note that the operator can make the operation pause using the special AutoClean display.
If the operator does not remove the pause by pressing the PAUSE soft key again, the
Analyzer/Controller will resume normal operation after 20 minutes.