Yokogawa 2-Wire Dual Channel Transmitter/Analyzer FLXA21 - Manual (Page 199)

<16. COMMISSIONING OF SENCOM pH/ORP>
16-16
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
Wash time/measure time: Set the wash time in minutes. In a continuous wash, wash time is
replaced by measure time.
Recovery time: Set the recovery time in minutes.
Manual wash:
Select “Disabled” or “Enabled.”
When this item is enabled, a wash cycle can be activated manually. On the
Calibration/Wash screen, press the “Start manual wash cycle” to perform a
manual wash.
Imp2 wash: Select “Disabled” or “Enabled.”
When this item is enabled, a wash cycle can be started if the “Impedance 2
too high” error occurs with respect to the reference electrode.
Continuous wash: Select “Disabled” or “Enabled.”
A continuous wash cycle is started at the instant when this item is enabled.
In a continuous wash, the “Measure time” and “Interval time” are reversed
(see Figure 16.4).
Tw Tr
Tint
Tw Tr
Tint
Tw Tr
Tint Tint
Tw’ Tw Tr Tw’
F050605_2.ai
Tint: Interval time
Tw: Wash time
Tr: Recovery time
Tint: Interval time
Tw: Measure time
Tw’: Wash time
Tr: Recovery time
When a continuous wash is disabled
When a continuous wash is enabled
Figure 16.4
The instrument has a function for checking whether measurements are normally made after
wash, allowing you to check a sensor response.
The wash recovery check is performed by making use of the time to recover half the wash-cycle
pH change. The half the wash-cycle pH change recovery time replaces the relaxation time by the
recovery time.
Whether to conduct the wash recovery check can be set on the Error settings 2/3 screen. Half
the wash-cycle pH change refers to half the value (1/2∆pH) of the difference (∆pH) between the
pH value during normal measurement of an example in Figure 16.5 and the pH value detected
during wash. If the pH value during wash is greater than 1/2∆pH when 1/3 tR has elapsed, the
electrode is assumed to be good. If it is smaller than 1/2∆pH, then the electrode is assumed to be
bad.
However, for applications where the pH during wash shows almost the same value as the normal
pH, the difference will be approximately zero. In such a case, disable the wash recovery check.
An example of such applications is the monitoring of waste water pH. If you select water jet
cleaning in such a case, the normal pH as well as the washing time pH will be around pH 7; the
difference will be approximately zero, so the recovery time check will not work normally.
This function is available either for ORP measurement only.