YOKOGAWA DO70G, User Manual

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<4. Maintenance>
4-1
IM 12J05D04-01E
4. Maintenance
4.1 Routine Inspection
n
Cleaning of Sensor (Sensor Cap)
A visual inspection of the sensor cap must be made whenever the sensor is calibrated. Any dirt
on the sensor cap adversely affects your measurements.
If the dirt is spread over the sensor cap, dip the sensor cap into clean water and gently wipe
the dirt off with a soft cloth or lint-free paper. If the dirt does not come off easily, apply a neutral
detergent to the sensor cap so it can be easier to remove the dirt. Wash the sensor cap with
clean water.
Before every calibration, check that the sensor cap is not loose. If it is loose, retighten it. When
you retighten or repalce the sensor cap, use an attached silicon tube and so forth.

Sensor Cap
(*): When you attach or detach the sensor cap, use an attached silicon tube and so forth.
Silicon Tube (
*)
4.2 Inspection If Failure Occurs
When the sensor cap ages and comes to the end of its service life, troubles such as failed span
adjustment may occur. DO402G Dissolved Oxygen Converter or FLXA402 4-Wire Converter
detects these failures.
If a sensor error code appears on the display, follow one of the procedures below.
1. Clean the sensor (sensor cap), by following the direction of 4.1 above.
2. Replace the sensor cap and the attached O-ring together with new ones.
3. Replace DO70G sensor unit with a new one if resistance temperature detector (RTD) fails
or the error still occurs even after the procedure 1 or 2 above is applied.
When DO402G is connected, troubles may be found by measuring the resistance value of
RTD.
Another possibility is that the error may be caused by defects of RTD.
A NTC 22k resistance temperature detector (RTD) is incorporated in the DO70G sensor.
This RTD indicates a resistance value of about 22 kΩ at 25°C. Check the RTD by measuring
the resistance value between the white wiring and the green wiring. If the resistance value
differs greatly from the 22 kΩ, the sensor must be replaced.
For further information on the error code, refer to the user’s manual IM 12J05D02-01E for
DO402G Dissolved Oxygen Converter, IM 12A01F03-01EN for FLXA402 4-Wire Converter
Operation of Converter.
8th Edition : July 11, 2023