Yokogawa DO202 2-Wire Dissolved Oxygen Analyzer - Manual (Page 58)

IM 12J05C01-01E
It is important for maintaining the measurement
accuracy of the EXA DO series of wire dissolved-
oxygen metering system to perform inspection and
maintenance at fixed intervals. It also serves to pre-
vent problems from arising.
This chapter describes daily inspection and main-
tenance for the purpose of maintaining system per-
formance.
7-1. Overall dissolved-oxygen metering system
Tables 7-1 and 7-2 show the inspection and main-
tenance items for equipment composing dissolved-
oxygen metering system. The procedure of inspec-
tion and maintenance for the dissolved-oxygen
transmitter is described in Section 7-2. For inspec-
tion and maintenance of the sensors and holders,
see each instruction manual respectively.
7-1-1. Inspection and maintenance to be imple-
mented periodically
Table 7-1. shows the items which are recommended
to be inspected and maintained periodically.
7-1-2. Inspection and maintenance to be imple-
mented on occasion
Occasionally implement the maintenance that is not
directly related to measurement functions and main-
tenance associated with errors.
Maintenance 7-1
7. MAINTENANCE
Table 7-1. Items for periodic inspection and maintenance of dissolved-oxygen metering system
Instrument or apparatus Item Recommended Interval
All equipment a. Calibration a. 1 to 2 months
Dissolved oxygen sensor a. Cleaning of membrane a. 1 to 2 months
b. Polishing of silver electrode b. 6 to 8 months
surface and replacement of electrolyte
c. Replacement of membrane assembly c. 6 to 8 months
Dissolved oxygen transmitter a. Inspection of temperature indication a. 6 months
(error check)
Float holder a. Sweeping of winch mechanism a. (depends on installation environment)
Immersion holder a. Inspection of sensor holding O-ring a. 6 months
b. Sweeping of cleaner nozzle b. 1 to 2 months
c. Inspection for leakage from the solenoid c. 6 months
valve for cleaning utility
7-2. Periodic maintenance for the EXA DO202
transmitter
The DO202 transmitter requires very little periodic main-
tenance. The housing is sealed to IP65
(NEMA 4X) standards, and remains closed in normal
operation. Users are required only to make sure the
front window is kept clean in order to permit a clear
view of the display and allow proper operation of the
pushbuttons. If the window becomes soiled, clean it
using a soft damp cloth or soft tissue. To deal with more
stubborn stains, a neutral detergent may be used.
Note: Never used harsh chemicals or solvents. In
the event that the window becomes heavily
stained or scratched, refer to the parts list
(Chapter 9) for replacement part numbers.
When you must open the front cover and/or glands,
make sure that the seals are clean and correctly fit-
ted when the unit is reassembled in order to maintain
the housing’s weatherproof integrity against water and
water vapor. The DO measurement uses small signal
currents and may otherwise be prone to problems
caused by exposure of the circuitry to condensation.
Table 7-2. Items for occasional inspection and maintenance of dissolved-oxygen metering
Faulty phenomenon System content of inspection
Error E2 occurrence Check whether the dissolved oxygen sensor membrane is contaminated or not.
Check whether the nozzle is clogged or not.
Error E3 occurrence Polish the silver electrode surface of the dissolved oxygen sensor and replace the
electrolyte.
It is difficult to see the inside of the transmitter Wipe off the dirt on the transparent window using tissue paper or
through the window
the like. (Use detergent for hard-to-clean dirt.)