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| [[Image:BB-Bioblast.jpg|left|40px|link=http://www.bioblast.at/index.php/Bioblast:About|Bioblast wiki]] | | [[Image:BB-Bioblast.jpg|left|40px|link=http://www.bioblast.at/index.php/Bioblast:About|Bioblast wiki]] |
| == Popular Bioblast page ==
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| ::: [[MiPNet17.12 Bioblast 2012]] has been accessed more than
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| ::::* 5,000 times (2016-06-22)
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| The voltage recorded at air saturation and with an open chamber is an important instrumental quality parameter. It is one result of a full Oxygen sensor test. To access just this parameter observe the Raw signal.
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| Fill the chamber with water or medium
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| Establish an open chamber (or when using a closed chamber be sure that the O2 concentration is still very near to atmospheric saturation)
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| Wait for stabilization
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| The recorded value will depend on the gain.
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| Typical recorded voltages at air saturation, in pure water or experimental media, should be
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| at Gain 8: off scale ( “9.99V”)
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| at Gain 4 : ca. 8 - 10 V (do not use at air saturation, especially if your lab is situated at or near sea level)
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| at Gain 2: ca. 4 - 5 V
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| at Gain 1: ca. 2 V
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| The actual value of the raw signal at air saturation (during calibration) depends on, the medium, 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 [µM 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.
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| If the recorded value is too high first of all the zero current should be checked. A high zero current will also give a corresponding higher voltage at air saturation. E.g. If a sensor produced a zero current of 1 Volt at gain 2, the voltage at air saturation will typically be 5 to 6 V instead of 4 to 5 V. Please see the entries under zero current for acceptable values of this parameter.
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| Whether or not a high zero current is found the problem has to be further located by switching components. Typically the problem will be located either on the POS or on the POS connector.
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| If the zero current if ok, consider the following potential reasons:
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| The stirrer speed (rpm) may have been changed, or the stirrer may have been left in the off mode. - Re-set the stirrer speed and re-calibrate.
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| The gain setting may have been changed. - Compare calibration values at identical gain settings.
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| The block temperature may have been changed. - Compare calibration values at identical temperatures.
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| R1 is similar, but the oxygen calibration factor, Fc, may have changed, due to the use of a different oxygen solubility factor of the medium, FM. - Compare calibration factors, Fc, at identical values of FM.
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| R1 has changed, but the oxygen calibration factor, Fc, remains similar, if the barometric pressure has changed (e.g. experiments carried out at different altitude). - Compare calibration values, R1, at identical barometric pressure.
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| The problem occurred after application of a new membrane:
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| Lower R1: The membrane thickness may have changed, possibly by inadvertently using two superimposed membranes.
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| Lower R1: The membrane may have wrinkles in the area of the cathode.
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| Lower R1: The black butyl rubber gasket may have not been applied properly in the centre, now partially blocking the cathode.
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| Higher R1: The membrane may have been overstretched, or a thinner membrane is used.
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| The problem occurred after re-assembly of the O2k chamber:
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| Lower R1: The chamber may have been improperly positioned, with the blue POS holder (on the left or right side of the copper block) screwed too far into the chamber housing. This would allow only partial contact between the stirred medium and the cathode. - Follow the O2k-Start instructions (MiPNet12.06, Section 3.1) to insert the chamber properly.
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| The electrolyte in the POS may have partially dried out. - Apply a new membrane, following POS-Service instructions (MiPNet08.04).
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