Maintenance; Periodic Maintenance For The Exa 202 Transmitter - YOKOGAWA SC202G (S) User Manual

7. MAINTENANCE

7-1. Periodic maintenance for the EXA 202 transmitter

The EXA transmitter requires very little periodic maintenance. 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 10) for replacement part numbers.
When you must open the front cover and/or glands, make sure that the seals are clean and correctly fitted
when the unit is reassembled in order to maintain the housing's weatherproof integrity against water and
water vapour. The measurement otherwise may be prone to problems caused by exposure of the circuitry
to condensation (see page 10-1).
The EXA instrument contains a lithium cell to support the clock function when the power is switched off.
This cell needs to be replaced at 5 yearly intervals (or when discharged). Contact your nearest Yokogawa
service centre for spare parts and instructions.
7-2. Periodic maintenance of the sensor
NOTE:
Maintenance advice listed here is intentionally general in nature. Sensor maintenance is highly application
specific.
In general conductivity/resistivity measurements do not need much periodic maintenance. If the EXA
indicates an error in the measurement or in the calibration, some action may be needed (ref. chapter 8
trouble- shooting). In case the sensor has become fouled an insulating layer may be formed on the surface
of the electrodes and consequently, an apparent increase in cell constant may occur, giving a measuring
error. This error is:
Rv
2 x x 100 %
Rcel
where:
Rv = the resistance of the fouling layer
Rcel = the cell resistance
NOTE:
Resistance due to fouling or to polarization does not effect the accuracy and operation of a 4-electrode
conductivity measuring system. If an apparent increase in cell constant occurs cleaning the cell will restore
accurate measurement.
Cleaning methods
1. For normal applications hot water with domestic washing-up liquid added will be effective.
2. For lime, hydroxides, etc., a 5 ...10% solution of hydrochloric acid is recommended.
3. Organic foulings (oils, fats, etc.) can be easily removed with acetone.
4. For algae, bacteria or moulds, use a solution of domestic bleach (hypochlorite).
* Never use hydrochloric acid and bleaching liquid simultaneously. The very poisonous chlorine gas will
result.
Maintenance 7-1
IM 12D7B3-E-E