Zero current

Each polarographic oxygen sesnor has a certain zero current, i.e a current that flow even at a oxygen concetration of zero. This current is takin into acount by the zero calibration. The zero current is displaed as a gain depndednt volatage. This voltage at zero oxygen can be expressed as % of the volatge at air saturation. While new sensors have a zero voltage of below 1% of the voltage at air saturation (for the same gain), used denors may have higher zero currents up to ca 10% of volatge at ais saturation without negative consequences, provided the zero current is stable. The stability of the zero current can be assesed by keeping tryk of calibrtion values using the "O2k-Calibration-list.xls" template. The template and the calibrtion procedure can be found at [MiPNet12.08]. A high or unstable zero current is usualy caused either by the POS or by the POS connector. Therefore the problem has to be localized by switching components. Frequentyl cleaning an dapplying conatct oil to the gold pin and thread conecting the POS head and the POS conector will solve the problem. If the problem is located on the POS head an inteniseve sesnor service should be applied at least two times. If this does not help the sesnor proable has to be replaced. If the problem is located at the POS connector cleaning the connection as desribed above is frequently succesfull. If the problem was desceased but not solved by clenaing and applying conat oil, the clenaing process may have to be repeted severl times. If cleaning the conector does not help

Like the voltage at air saturation the zero depends on the gain. It can be expresseda % of