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 POS connectors and proper Sensor heads. When disconnecting a sensor from the POS 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 POS connector together with the attached sensors between right and left side.
5. Repeat the full Sensor test. If the problem moved together with the POS connector, it is located at the POS connector.
6. 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 settings have been ruled out consider next a problem related to Chamber assembly. Check by disassembling and reassembling the chamber. If there is any doubt about the glass chamber or the stirring bar they can be switched to the other chamber to confirm /localize a problem. Finally, when a malfunctioning chamber has 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.
   

Summary

Problem moves with	Problem situated at
POS	POS
POS connector	POS connector
not at all	Chamber assembly or Main unit

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 POS connector plus the still attached Polarographic oxygen sensor. Leave the sensor attached to the POS connector. Set an event, describing what you did and record the signal for a short time.
3. Remove the Polarographic oxygen sensor from the POS connector. Set an event, describing what you did and record the signal for a short time.
4. Remove the POS connector from the Main unit. Set an event, describing what you did and record the signal for a short time.

Tested states and expected behavior

State	Description	Expected behavior
I	fully assembled, sensor in chamber, air saturation, Gain =2	stable signal, 3 to 5 V
II	POS connector + sensor removed from chamber, sensor still connected to sensor connector	initial decrease in voltage
III	sensor removed from POS connector	stable signal at 0 V
IV	POS connector removed from main unit	typically signal off scale (+/- 9.99 V), may vary, a gain independent stable signal of 0.4 V is a strong indication of a electronic problem in the main unit

State expected behavior observed? yes/no				Interpretation / Comment
I	II	III	IV
no	yes	yes	yes	may indicate a problem in the Chamber assembly, or a defective sensor, continue testing
no	no/yes	yes	yes	probable defect in the Sensor. This indication is not so strong as a localization obtained via switching components. The POS connector (not the Sensor) may be defect, but this may be only visible when a signal is present.
no	no	no	yes	indicates a defect in the POS connector
no	no	no	no	indicates a problem with Chamber assembly or a defect in the Main unit; if the problem can not be solved by reassembling the chamber, contact OROBOROS Instruments.