Even with our active noise cancellation technology, there are factors that might lead to too much line noise or 50/60 Hz interference. Please refer to our EEG User Guide for all the necessary steps to perform EEG measurements.
Make sure to:
- always use the ground cable when measuring EEG.
- use the same type of electrode for the ground cable as well as for the EEG sensor.
- prepare the skin properly (with Nuprep or alcohol), as per the EEG User guide. In case you redo skin preparation, try redoing the ground electrode first.
- check electrode usage. Recommended usage of EEG disc electrodes is 10-20 times, as the Ag/AgCl layer will gradually wear off. Sintered electrodes can be used hundreds of times.
- check all supplies for expiration date (conductive pastes and skin preparation gels).
- check if the snap-on connectors (see image) are clean. Improper cleaning (snap-on will be covered by left-overs and often appear green) may affect signal quality.
- use enough paste or gel to cover the electrode, but prevent excessive use. Excessive paste will increase the chance of picking up 50/60Hz interference.
In the event these steps do not work, try:
- putting the system close to (e.g. on the lap of) the person being measured.
- unplugging the laptop from the power supply.
- NeXus-32: unplug the power adapter and use batteries instead.
In the unlikely event 50/60Hz interference is still present:
- Turn of wireless and electronic equipment one by one, like lights, desk lamp with adapter/transformer, electrically motorized chair, air-conditioning. Check for possible power lines/cables.
- Let the person who is being measured walk around in the room, carrying the NeXus, to find possible spots where the interference is lower/higher and pinpoint the source.
- Verify the ground cable is not defective by:
- Recording EEG and unplugging the ground cable after 30 seconds. Check if the interference increased after unplugging the ground cable. This means that the ground cable is working properly.
The last resort is setting a notch filter in the BioTrace+ software to filter out line noise. Please, refer to the “How to set Notch filter (50/60 Hz)” article for detailed information.
About 50/60 Hz interference
Electrophysiological activity has very low voltages, expressed in microvolts. Electrical interference can arise from electrical devices, lighting, etc. Electrical devices and cables transport electrical power at a level of 110-230 Volts AC. This power is alternating 50 or 60 times per second and therefore called “alternating current” or AC. This 50 or 60 Hertz activity can show up in the EEG, especially where the electrode does not make good contact, or where there are simply too many cables and electrical devices around. This is a very common artifact.
The BioTrace+ versions in English (EN) and German language contain 50Hz indicators and Notch filters.
The BioTrace+ version in English (US) contains 60Hz indicators and Notch filters.
In the BioTrace+ software 50 or 60Hz interference can be recognized in several ways:
Therapist screen
Frequency spectrum object indicating strong 50Hz interference
Line graph object showing strong 50Hz interference
Signal Check screen
Access the Signal Check screen from any therapist screen, clicking this icon:
The line graph as well as the second traffic light indicates 50Hz (or 60Hz) interference