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7 MAINTENANCE
7.1 Scheduled Maintenance
The following servicing schedule has been produced as a
general guide only. Because the systems are designed for a wide
range of applications, where the nature of the sample can vary
considerably, it may be necessary to amend the schedule to suit
the particular installation and sample conditions.
7.1.1 Sensor Cleaning
Model 7997 202
The Model 7997 202 sensor unit is generally used on clean
water samples and maintenance should be limited mainly to
manual monthly cleaning of the flow chamber, under normal
conditions. If there is a high turbidity breakthrough, clean the
chamber immediately to ensure accurate readings.
Models 7997 200 Series, 300 and 400 Series
The required automatic cleaning frequency of the flow chamber
and optical windows of Models 7997 200 Series, 300 and 400
Series can only be determined by plant experience. It is
recommended that checks are made at appropriate intervals.
7.1.2 Calibration
A key feature of the system is the optional Dry Calibration
Standard, which simplifies routine calibration and virtually
eliminates the need for formazine standard solutions to be
produced.
These dry standards are safer, ensure repeatable accurate
results and eliminate operator error. However, the software is
designed to cater for both methods if the use of formazine
standards are preferred.
7.1.3 Using Dry Calibration Standards
Dry Calibration Standards are used to verify system accuracy.
They provide a means of verifying the integrity of the loop without
the need for chemical standard solutions.
Note.
•
The Dry Calibration Standard for the 7997 300 and 400
are specific to the sensor unit with which they are
supplied.
•
Always store the Dry Calibration Standard in the
container provided, and keep in a dry place.
•
Avoid touching the light reflecting parts of the standard.
Each Dry Calibration Standard is verified against a formazine
standard before delivery, and the turbidity value is indicated on
the label.
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