wtw Multi 9420, Руководство по эксплуатации

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Multi 9420 Dissolved oxygen (D.O.)
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Criteria for a stable
measured value
The Stability control function checks whether the measured values are stable
within the monitored time interval.
The minimum duration until a measured value is assessed as stable is the mon-
itored time interval. The actual duration is mostly longer.
7.1.2 Measuring the temperature
For reproducible D.O. measurements, it is essential to measure the tempera-
ture of the test sample.
IDS D.O. sensors measure the temperature with a temperature sensor inte-
grated in the IDS sensor.
7.2 FDO
®
Check procedure
7.2.1 Why should you check the sensor?
With the FDO
®
Check procedure, you can find out in a simple manner
whether the
FDO
®
925 D.O. sensor should be cleaned or calibrated.
7.2.2 When should you check the sensor?
Checking can be useful in the following cases:
 When the check interval has expired
(the [check] status indicator is displayed).
 If the measured values seem to be implausible

If you assume that the sensor cap is contaminated or at the end of
its lifetime

After the sensor cap was exchanged
 Routinely within the framework of the company quality assurance
7.2.3 Carrying out the FDO
®
Check procedure
FDO
®
Check
procedure
Check in water vapor-saturated air.
Use the check and storage beaker (FDO
®
Check) to carry out theFDO
®
Check
procedure.
Measured parameter Time interval Stability in the time
interval
D.O. concentration 20 seconds ∆ : better than 0.03 mg/l
D.O. saturation 20 seconds
∆
: better than 0.4 %
D.O. partial pressure 20 seconds ∆ : Better than 0.8 mbar
Temperature 15 seconds
∆
: Better than 0.5 °C