Yokogawa EXA PH202 2-Wire pH/ORP Analyzer - Manual (Page 104)

IM 12B07D02-01E
Appendix 11-7
You can individually set the wash period "interval between wash cycles", tl; the wash time "length of
the wash phase", tw; and the recovery time, tR
During the recovery phase of the wash cycle, the detector checks if the sensor response is sluggish -
- the detector checks if the time to recover half the wash-cycle pH change (1/2∆pH) is within one third
of the recovery time (1/3tR) setting -- to determine if the sensor requires manual cleaning or is near
the end of its useful life. Determine the recovery time setting accordingly. To disable this check, you
need to set service code 60 accordingly.
The wash cycle pH change is ∆pH, the difference between the pre-wash pH and the pH during the
wash.
If the difference between the normal pH value in process and the pH during the wash is small, then
half the difference (1/2∆pH) will be too small to measure reliably, so this check should be disabled in
this case. The monitoring of waste water pH is an example of such an application.
If you select water jet cleaning in such a case, the normal pH as well as the washingtime pH will
be around pH7; the difference will be approximately zero, too small for the recovery time check to
measure, so the recovery time check will not work normally and should be disabled.
pH
Time
Good Electrode
Bad Electrode
tR : Recovery Time tW : Wash Time
tI : Wash Period
1/2∆pH
∆pH
1/3tR
tI : Wash Period (0.1 to 36.0 hours, default=6.0 hours)
tW : Wash Time (0.1 ... 9.9 minutes, default : 0.5 minutes)
tR : Recovery Time (0.1 ... 9.9 minutes, default : 0.5 minutes)
F5.0.eps