Yokogawa EXAxt PH450 4-Wire Analyzer for pH and ORP - Manual (Page 50)

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IM 12B07C05-01E
Termination of a wash cycle
The user can decide to terminate the current
wash cycle. This is done in the main screen (all
other screens are deactivated) by pressing the
wash flag (once or twice). The wash cycle has
two time intervals (T
W
and T
R
) and depending
on the moment of pressing the “wash” flag the
current interval is ended (see fig. 6-1)
Note! Recovery time is intended to let the
sensor system recover to “Normal”
process conditions.
Measuring
Mode
Wash
Mode
Recovery
Mode
W
ash time
T
W
ended
W
ash flag pressed
Recovery time
T
R ended
W
ash flag pressed
WASH
HOLD
WASH
HOLD
Interval time ended
Figure 6-1. Wash cycle
Manual wash
When enabled in the “generic wash settings”,
wash cycles can be activated manually via
the user interface: Calibration/Wash >> Start
manual wash cycle or via an input contact (if
provided for.)
Continuous wash during sample/hold meas-
urement
Some processes scale the electrodes in such a
way that the electrodes need continuous wash
in order to keep on performing well. In this
configuration, a “recovery time” and a “interval
time” interrupt the continuous wash (cleaning).
The continuous wash cycle is started the
moment “Continuous wash” is enabled. First
with “measuring mode” which has the duration
of “wash time”, followed by the “wash mode”
which has the duration of “interval time”.
The “interval time” and “wash time” are
reversed!
The wash cycle is terminated the same way
as described above; pressing the wash flag in
the main display (once or twice). When the
cycle is terminated “Continuous wash” should
be re-enabled to start the wash cycle.
Note! When this setup is chosen special care
should be taken in reference to scaling
when the wash cycle is terminated.
Note! In this configuration manual wash is
not applicable.
Diagnostics
The response time is a good diagnostic tool
to see the condition of the electrode system.
During the recovery time the response is moni-
tored and an error is generated when the “half
time value” was not reached within 1/3 of the
recovery time.
pH
7.0
4.5
2.0
GOOD SENSOR
AGED SENSOR
T
W
T
R
1 /
3
T
R
time
Figure 6-2. Chemical cleaning of sensors
Input Contact
The input contact is always enabled when an
output contact is configured as wash. The input
contact can be used to enable a wash after the
detection of an Impedance High error.