Contact quality is measured for each position and displayed in the sensor map as shown below.
There are four states:
If a sensor is not in green, please check that it is making a good contact with the scalp and the sensor is wet. If the subject has thick hair, try to work the sensor under the hair and add additional fluid. Bad positioning and dry sensors are the two most common reasons for poor contact quality. Other reasons could be that the sensor housing isn’t locked in place or the felt pad has been recently replaced which might not be pushed far enough into the sensor housing.
If a sensor is persistently not making a good contact, you can test its functionality by tapping on the sensor and observe if anything appears in the EEG data steam. You can also try measuring your ECG by touching both references with one hand and the sensor with the other. You should be able to clearly see the QRS and T-wave.
If all of the channels are showing the same level of poor quality, the likely cause is the reference sensors are dry or the reference sensors are not making a good contact to the scalp. Before adjusting any of the recording electrodes, it is recommended that you have a good contact (green) for the reference sensors.
If the felt sensors are moistened for the first time, the sensors take time to absorb the fluid. The best solution is to apply a small amount onto each sensor and then top up each sensor so that they are wet.
For users with thick hair, skin contact can be improved by working the sensors through the hair to make a better contact onto the scalp.