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<7. INSPECTION AND MAINTENANCE>
7-3
IM 11M03A02-00E
7.1.2 Replacing the Sensor Assembly
The performance of the sensor (cell) deteriorates as its surface becomes soiled during operation.
Therefore, you have to replace the sensor when its life expectancy expires, for example, when
it can no longer satisfy a zero-gas ratio of 100±30 % or a span-gas ratio of 0±18 %. In addition,
the sensor assembly is to be replaced if it becomes damaged and can no longer operate during
measurement.
If the sensor becomes no longer operable (for example, due to breakage), investigate the cause
and remedy the problem as much as possible to prevent recurrence.
CAUTION
• If the sensor assembly is to be replaced, allow enough time for the detector to cool down
from its high temperature. Otherwise, you may get burned. If the cell assembly is to be
replaced, be sure to replace the metal O-ring and the contact together. Additionally, even in
a case where the cell is not replaced, if the contact becomes deformed and cannot make
complete contact with the cell, replace the contact.
• If there is any corroded or discolored area in the metal O-ring groove in which the contact
is embedded, sand the groove with sandpaper or use a metal brush, and then sand further
with a higher grade of sandpaper (no. 1500 or so), or use an appropriate metal brush
to eliminate any sharp protrusions on the groove. The contact’s resistance should be
minimized.
• Use sensor assemblies manufactured in or after Sept. 2000: the serial number on the side
of the sensor assembly should be 0J000 or later (for example: OK123, 1AA01 etc)
1. Identifying parts to be replaced
In order not to lose or damage disassembled parts, identify the parts to be replaced from among
all the parts in the sensor assembly. Normally, replace the sensor, metal O-ring and contact
together at the same time. If required, also replace the U-shaped pipe, bolts, filter and associated
spring washers.
2. Removal procedures
(1) Remove the four bolts and associated washers from the tip of the detector probe.
(2) Remove the U-shaped pipe support together with the U-shaped pipe. Remove filter also.
(3) Pull the sensor assembly toward you while turning it clockwise. Also, remove the metal
O-ring between the assembly and the probe. Remove filter also.
(When replacing the assembly, be careful not to scratch or dent the tip of the probe with
which the metal O-ring comes in contact (the surface with which the sensor flange also
comes in contact). Otherwise, the measurement gas will not be sealed.)
(4) Use tweezers to pull the contact out of the groove in the tip of the probe.
(5) Clean the sensor assembly, especially the metal O-ring contact surface to remove any
contaminants adhering to that part. If you can use any of the parts from among those
removed, also clean them up to remove any contaminants adhering to them.
(Once the metal O-ring has been used, it can not be reused. So, be sure to replace it.)