Raw signal of the oxygen sensor: Difference between revisions
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For trouble shooting purposes of the [[polarographic oxygen sensor]] (POS), for choosing an appropriate [[gain]] setting (default is Gain 2), but also to understand how the O2k actually works, it is helpful to observe the raw signal (on-line or off-line). ย | For trouble shooting purposes of the [[polarographic oxygen sensor]] (POS), for choosing an appropriate [[gain (O2 channel)|gain]] setting (default is Gain 2), but also to understand how the O2k actually works, it is helpful to observe the raw signal (on-line or off-line). ย | ||
== Observing the Raw Signal == | == Observing the Raw Signal == |
Revision as of 12:53, 14 September 2010
For trouble shooting purposes of the polarographic oxygen sensor (POS), for choosing an appropriate gain setting (default is Gain 2), but also to understand how the O2k actually works, it is helpful to observe the raw signal (on-line or off-line).
Observing the Raw Signal
Depending on your DatLab version, a predefined layout called โB Trouble shootingโ is in the โGraph layoutโ menu. If not, you can easily generate this Graph layout. To do so, take the following steps in DatLab [MiPNet12.07]:
- From the main menu select โLayoutโ menu and choose โ1 Calibration Exp. G3-Tempโ
- From the main menu select โGraphโ / โSelect Plotsโ, by default you will see the โplotsโ tab from the drop down menus for the oxygen signals. Select โO2 raw signalโ instead of โO2 concentrationโ for both chambers.
- Select the โscalingโ tabs: adjust the scaling for the oxygen signal to 0 โ 10 Volt (Start at 0, Range 10)
- At the bottom of the window insert a name for the new layout (โB Trouble Shootingโ); press โSave Graph Layoutโ.
Remember to select the period of the experiment your are interested in or select โGraphโ / โAutoscale Time Axisโ to view the entire experiment. The maximum signal is 10 volt. Above 9.99 V, the amplifier is in the saturation range, the apparent signal will remain constant at this value, and the flux will appear to be zero. The raw signal can be modified by choosing an appropriate gain setting. We recommend a gain of 2 as a default for experiments at and below air saturation, to avoid reaching the upper 10 volt limit without noticing. Typical recorded voltages at air saturation, in pure water or experimental media, should be
- at Gain 8: offscale ( โ9.99Vโ)
- at Gain 4 : ca. 8 - 10 V (do not use at air saturation, especially if your lab is situated at or near sea level)
- at Gain 2: ca. 4 - 5 V
- at Gain 1: ca. 2 V
The actual value of the raw signal at air saturation (during calibration) depends on experimental temperature, barometric pressure, and the sensitivity of the individual POS. At or near sea level higher values are recorded than at higher altitudes. The raw signal is converted to oxygen concentration [ยตM or nmol/ml] or partial oxygen pressure [kPa] by calibration of the POS [MiPNet12.08]. Each gain requires a separate calibration of the oxygen signal. Therefore, after changing the gain you should not only perform a calibration at air saturation (as always before an experiment), but also a new zero oxygen calibration.