2 replacing the sensor assembly, 5 stopping and re-starting operation -8, Caution – Yokogawa Single Channel Oxygen Analyzer System ZR22/ZR402 User Manual

Page 175

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IM 11M12A01-03E

11-3

11.

Inspection and Maintenance

11.1.2

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

Ϯ30 % or a span-gas ratio

of 0

Ϯ18 %. 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: 0K123, 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.
(When replacing the assembly, be careful not to allow any flaws on 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.
(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 tightened, it can no longer be used. So, be sure to

replace it.)

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