66
MI instruction manual
Document/Revision No.
IM-EN-MI
/2.00
Effective: September 2, 2019
7 Prism wash
In some applications the process flow does not keep the prism clean because flow ve-
locity is not enough to keep the prism clean, or the process medium is sticky. In these
applications the prism can be automatically cleaned by installing a wash system (see
the refractometer manual).
7.1 Configuring prism wash
The prism wash settings for different refractometers are independent of each other.
The wash system is active if a relay has been configured to be a wash relay (see Sec-
tion 6.3.1) and the wash time is not zero. An automatic wash function can be configured
so that all refractometers connected to MI have different wash parameters. The wash
parameters can be configured at Refractometer app -> Configuration -> Wash.
7.1.1 Wash cycle
The wash logic is shown in Figure 7.2 as a flow diagram. The automatic prism wash cycle
(Figure 7.1) consists of three phases:
precondition
,
wash
and
recovery
. The optional
preconditioning function is used to e.g. blow out the condensate from the washing
line before washing. After the preconditioning there is a one-second pause to avoid
having both precondition and wash relays active at the same time.
The wash cycle is initiated when the wash interval has elapsed. The wash can also
be started by configuring a general input for external wash (Section 6.5.2) or manually
from the user interface at Refractometer app -> Calibration menu. The order of priority
for these wash triggers is
1. manual wash
2. external wash request
3. wash interval timer
The wash relay is closed for the wash time specified in the wash settings.
After the wash phase is completed, a recovery time is spent. During the wash cycle (pre-
condition, wash, recovery) the measurement result is in hold unless otherwise speci-
fied.
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