Endress+Hauser SpectraSensors OXY5500, Руководство по эксплуатации

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BA02195C OXY5500 Optical Oxygen Analyzer
Hauser B
–
17
Signal drifts due to oxygen gradients
It is important to remember that the sensor only measures the oxygen content
near its surface. The formation of a bio-film during long-term measurements,
or the accumulation of other sample components like oil or solid substances,
may lead to an oxygen gradient.
Signal drifts due to temperature gradients
A further source of imprecise measurement is insufficient temperature
compensation. If temperature compensation is used, ensure that no
temperature gradients exist between the oxygen sensor and the temperature
sensors. If measurement is conducted without temperature compensation,
bear in mind that the OXY5500 only measures correctly if the sample
temperature is constant during measurement and the temperature is the same
as the entry at the beginning of the measurement. A temperature
measurement error of +/-0.3

C will result in a measurement error of about +/-
1% of reading. The temperature probe provided with the unit has excellent
precision, but large gas temperature gradients will result in an offset between
the oxygen probe and temperature probe. To avoid an offset, ensure that the
gas temperature has been stabilized prior to passing over the oxygen probe.
SCS systems provided by Hauser are designed to ensure that this is
not a problem.
Signal drift due to photo-decomposition
The oxygen-sensitive material may be subject to photo-decomposition
resulting in a signal drift. Photo-decomposition takes place only during
illumination of the sensor tip and depends on the intensity of the excitation
light. Therefore, the excitation light should be minimized. Continuous
illumination of a OP-3 oxygen sensor over a period of 24 hours may lead to a
phase drift of up to + 0.4% of reading at 20

C. However, this effect of photo-
decomposition can be minimized by changing the measuring mode to the 30-
second or minute interval mode. In these modes, the software switches off the
excitation light after recording the data point and switches it on after the
interval chosen. Use the interval method whenever possible to increase the
operational life of the sensor. Refer to Table B–2 below.
Table B–2 Sensor drift at zero reading (0 ppb)
recording 3,600, 50,000 and 100,000 data points
Drift per 3600
Points
Drift per 50000
Points
Drift per 100000
Points
OP-3 <0.15% air-sat. <0.15% air-sat. <0.25% air-sat.
OP-6 <1 ppb <2 ppb < 3 ppb