K-Patents PR-01-S - Manual (Page 73)

INSTRUCTION MANUAL FOR K-PATENTS PR-01-S (-AX/FM/CS) DOCUMENT/REVISION No. INM 1/14
Effective: May 15, 2009
71
8. PRISM WASH SYSTEMS
Three alternatives of prism wash systems can be provided:
– Steam wash with integral nozzle, Section 8.2.
– High pressure water with integral nozzle, Section 8.3.
– Steam and water wash for flow cell mounting, Section 8.4.
In most of the applications the prism wash is not necessary. However, installing the wash nozzle should
always be considered.
A prism wash nozzle (Sections 8.2, 8.3, 8.4) can be useful in cases where normally no prism coating
occurs, e.g. to clean the prism after a process stop using a manual wash valve. Washing can also be used
for operational check (output signal decreases during wash) or as a part of maintenance schedule.
There is an own prism wash nozzle for Isolation and Retractor Valve HIMP-2 for LPH sensor, see
Chapter 11.
8.1. PRISM COATING
Deposit build up on the prism surface disturbs measurement. Look out for the following indications of
coating:
– Abnormally high concentration reading or upward CONC% drift.
– Low TEST values, even TEST = 8.
– High LED current (press Calibrate/Optical image), especially LED = 255 (max) (See Section 6.5).
– Prism wash (e.g. by press Start prism wash) does not increase the TEST value the appropriate amount:
For steam wash TEST should be close to 248; for water wash close to the TEST value for water.
In most of the applications the prism will keep clean, but if coating occurs, check the following:
– Sensor mounted correctly in respect to flow direction (arrow on sensor head).
– Sufficient flow velocity, Section 3.1.
– A temperature difference between process fluid and sensor probe may cause coating. This may happen
for small flows if the thermal insulation is inadequate. In some cases it helps to insulate also the
connection flange, Figure 3.10.
If there is a coating problem, it is recommended to try to increase the flow velocity, e.g. by installing a pipe
portion with smaller diameter. If this cannot be done, the prism should be automatically washed at regular
intervals, e.g. by steam or hot water.
A prism wash nozzle (Sections 8.2-8.4) can be useful also in cases without coating problems, e.g. to clean
the prism after a process stop using a manual wash valve.