YOKOGAWA DT450G Series, User Manual, Page: 35 / 41

<5. Inspection and Maintenance>
5-2
IM 11K01C01-01E
5.1 Periodic Maintenance
If the sensor probe is contaminated with a large amount of dust or significantly worn out by
dust, the output signal level for the same dust concentration may differ from the level when the
DT450G was initially put into operation. To be able to revert to the initial output signal level, the
sensor probe must be cleaned or the measurement range must be reset. Do not disassemble
such components as the printed circuit board from the internal unit of the DT450G; otherwise, the
DT450G may fail to operate correctly.
5.1.1 Cleaning the Sensor Probe
If the sensor probe tends to gather a significant amount of dust, it is advisable that the probe be
cleaned periodically. If dust accumulation is not very serious, its effect on the output signal is in
most cases negligible; therefore, it is not necessary to clean the sensor probe frequently.
Remove dust on the sensor probe with a dry cloth. For correct and normal measurement, keep
the insulation resistance of the purge-air outlet at a high level. To ensure this, completely remove
contaminants from the outlet. When cleaning the sensor probe, also remove dust that has
accumulated on the probe inlet.
5.1.2 Correcting (Resetting) the Measurement Range
The sensor probe may be worn out by dust contained in the gas under measurement.
Although wear in the sensor probe may not directly lead to the inability to measure, the level of
current arising from frictional electricity may change, affecting the output signal. If you need to
know precise dust concentration, correct (or reset) the measurement range according to your
degree of necessity. Correct (reset) the measurement range according to the procedure of
measurement range setting discussed in subsection 4.2.4. If the wear on the sensor probe is
extreme, it must be replaced.
5.2 Replacing Parts
In order to keep the DT450G serviceable over a prolonged period, you must replace parts that
are worn out or have deteriorated as a result of the gas under measurement.
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Replacing the O-rings
The O-ring that needs replacement is the one that prevents leakage of the gas under
measurement from the probe inlet. If the O-ring is found to be damaged in any way, such as
scratches, or cracks or permanent deformity due to deterioration, replace it.
Note: O-rings are also used in the DT450G main unit and on the contact surfaces of the sensor probe, though they are not visible from
outside. Ask Yokogawa Electric Corporation for replacement of these O-rings.