Honeywell UDA2182 manual Appendix P AutoClean and AutoCal Theory and Piping

Index

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.

1All 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.

2Relay 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.

3At 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.)

4The “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.

234 UDA2182 Universal Dual Analyzer Product Manual January 2009