K-Patents PR-21-S - Manual (Page 71)

7 Regular maintenance 65
7 Regular maintenance
The need for regular maintenance is minimal, due to the construction with no
moving parts, no mechanical adjustments, no trimpots and with a solid-state light
source. The following rules apply:
− Keep the sensor head and the Indicating transmitter clean and dry.
− Check that the ambient temperature is not above +45 °C (113 °F). The sensor
head should not be too hot to keep a hand on.
− If your refractometer has prism wash, check that it works, see Section 5.1.3.
7.1 Checking the sensor humidity level
The PR-21-S sensor head has an internal humidity detector. The humidity reading
can be checked on the Indicating transmitter display, select
3 SENSOR STATUS from the
Main menu. Check the humidity reading once in every three months.
Increasing humidity level indicates either condensate forming in the sensor head
(if the process temperature is below ambient) or prism leakage. If the humidity
reading exceeds 30 %, replace the dryer. If the reading exceeds 50 %, check the
prism seals. Relative humidity exceeding 60 % will produce a diagnostic message
HIGH SENSOR HUMIDITY (see Section 8.1.7).
The dryer (desiccant) is 2 pieces inside the sensor head cover, see Figure 10.2 (G).
The dryer cannot be reactivated by any means, it must be replaced. You can or-
der new dryer packages (drying agents/desiccants), spare part number PR-9108,
from either K-Patents or a K-Patents representative.
For instructions on how to open the sensor head to replace the dryer, see Sec-
tion 7.3.
7.2 Checking the prism and prism gaskets
Once a year check that the prism surface is smooth and clean and free of erosion
and small holes or digs.
7.3 Disassembling and assembling the sensor
!
Warning! Wear appropriate protective clothing and be careful when remov-
ing the sensor! Always check that the pipeline is empty before removing a sensor
from the process line. Never remove the sensor if there is process liquid in
the pipe (except when removing PR-21-S...LPH type sensors with isolation valve
HIMP-2/HIMP-3/. See Section 10.3).
7.3.1 Disassembling the sensor
Cover Open the clamp using a 11 mm wrench. Lift cover carefully, the O-ring seal
causes some friction.