Locating a problem

The two chamber approach of the O2k has among other benefits also advantages for Troubleshooting. By switching components between sides it usually is possible to locate a problem specifically at one component. This component can then be serviced by the user or replaced by OROBOROS Instruments without the need to ship the entire oxygraph.

Locating a Problem by Switching Components

It is always important to access the performance of the instrument in a well defined manner. Therefore, at each stage of this process a full Sensor test has to be done. In such a sensor test all hardware problems are visible. Biological experiments are not suitable for trouble shooting purposes. For troubleshooting it is very helpful to observe the Raw signal rather than a calibrated signal.

1. Perform a Sensor test.
2. Switch the Sensor heads (POS) between right and left side. This is also a good opportunity to clean and apply contact oil to the gold pin and thread connecting the Sensor connectors and proper Sensor heads. When disconnecting a sensor from the sensor connector remember to observe the guidelines to prevent damage by ESD, see [MiPNet14.1].
3. Repeat the full Sensor test. If the problem moved together with the sensor from one side to the other, the problem is located in the sensor head (POS).
4. If the problem remained on the same side, switch the Sensor connector together with the attached sensors between right and left side.
5. Repeat the full Sensor test. If the problem moved together with the sensor connector, it is located at the Sensor connector. If the problem still stays on the same side check carefully the DatLab settings for this side. There may be wrong settings for Gain, Polarization voltage or Scaling. Or there may be a wrong calibration for this channel (this is easily detected by observing the Raw signal). When these problems have been ruled out an electronic defect in the main unit for this channel must be considered. This should be confirmed by removing components as described below

Locating a Problem by Removing Components

The approach described above reached its limitations when more then one component is damaged. In this case some information can be gained by sequentially removing components. This approach can also be used to confirm a suspected defect in the main unit. When removing components from the running instrument is is of special importance to observe the ESD guidelines, see [MiPNet14.1]

Start with a fully assembled chamber, filled with some medium, e.g. water.

1. Record the Raw signal at open chamber (same conditions as at the beginning of a Sensor test. If the signal is off scale (9.99 V) try to decrease the gain (Gain = 2 for atmospheric saturation).
2. Empty the chamber. Remove the Sensor connector plus the still attached Polarographic oxygen sensor. Leave the sensor attached to the Sensor connector. Set an event, describing what you did and record the signal for a short time.
3. Remove the Polarographic oxygen sensor from the Sensor connector. Set an event, describing what you did and record the signal for a short time.
4. Remove the Sensor connector from the Main unit. Set an event, describing what you did and record the signal for a short time.

Tested states and expected results

State	Description	Expected Result
I	fully assembled, sensor in chamber, air saturation, Gain =2	stable signal, 3 to 5 V
II	sensor connector + senor removed from chamber, sensor still connected to sensor connector	initial decrease in voltage
III	sensor removed from sensor connector	stable signal at 0 V
IV	sensor connector removed from main unit	stable signal at 0 V

I	II	III	IV	Comment
expected behaviour observed? yes/no
no	yes	yes	yes	may indicate proble in the chamber assembly, or defect in the sensor, continue testing
no	no/yes	yes	yes	probable defect in the sensor. This indication is not so srong as a loclaisation obtained via switching components. The sesnor conncetors amy still be defect but this may be onyl visible when a signal is present.
no	no	no	yes	indicates defect in the sensor connector
no	no	no	no	possible defect in the main unit; contact OROBOROS Instruments