Yokogawa 2-Wire Dual Channel Transmitter/Analyzer FLXA21 - Manual (Page 70)

<4. COMMISSIONING OF pH/ORP>
4-16
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
l Wash contact
Select Disabled or Enabled.
When this item is enabled, items for a wash can be set on the Wash settings screen.
In the Wash settings screen, set the interval time, wash time, and recovery time and setup of
various washes.
Interval time: Set the wash interval in hours.
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 4.5).
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 4.5
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 4.6 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.