Ensuring high-quality EEG recordings

Some users have difficulty getting a clean EEG.  When proper techniques are followed, and the environment does not have excessive interference, there should be no problem getting excellent EEG's.  Please refer to the information below, if you need to improve the quality of your EEG's.

In extreme cases when using your Discovery, you might notice a 15-16Hz and/or approximately 28 Hz noise that does not seem natural, and is more or less sustained.  It might be on one channel, possibly Fz or Pz, or on more than one channel.  It is due to a combination of extreme environmental noise, and non-optimal sensor placement.  If the electro-cap "puffs" up, it can also cause this problem.  Technically, it is due to a 240 Hz power line harmonic that is aliased by the 256 sps sampling rate to look like 16 Hz.  This noise is now entirely avoidable, using a free firmware update to the Discovery, available for all Discoveries June 29, 2011.  The update can be done remotely, without having to send your Discovery to BrainMaster.  Please contact BrainMaster at 440 232-6000 or at support@brainm.com to ensure that your Discovery has the latest firmware.  We will schedule a time to get you this update.  This new firmware pre-samples the EEG at 512 Hz, and then filters and reconstructs it at 256 Hz.  This operation reduces this type of noise by a factor of at least 100,000.

If you have the new firmware, and still seem to have problems with noise, please refer to the following:

 

Cap

  • Please be sure that the cap is properly on -  Impedances at all sites should be less than 5kohms.  DC Offsets should be less than 25mV.  When measuring these numbers, please be sure that there are no drastic discrepancies between any sites.
  • Make sure that the cap is completely on - Some caps do not sit on a persons head properly, and can puff at the frontal and perietial positions.  If enough conductive material is placed at these positions, it can occasionally have a ribbon effect giving you the false belief of a good connection.  If you notice this, please use a cap that properly fits and does not do this.
  • Do not use older caps - Caps by any company are considered to be expendable items.  Most companies will not warranty caps longer than 90 days.  With proper care and maintainance, caps should be good for up to 6 months.  After this time, performance might decline, and results are not guaranteed.
  • Take care of your cap - Please be sure to properly maintain your cap, per the directions that is provided by the manufacturer.  Failing to do so, can cause abnormal affects.
  • Make sure that the cable is not pulling the cap off - This is dependent on the placement of the Discovery.  Please make sure of proper placement of the Discovery to prevent this from occuring.

Device Position/Office Arangement

  • Discovery position - For proper performance, the Discovery should be about 4 feet away from the PC.  It is highly recommended to be placed behind the client for optimal performance.  A 10Ft. USB Cable is provided to help with this.
  • Do not use old surge protectors or power supplies - Over time, both Laptop power supplies and Surge protectors lose their protective coating, introducing noise into your environment.  Please make sure if you notice this, to be sure that these devices are up-to-date.  If you are using a Laptop, it might be necessary to run on the battery of the laptop.
  • Make sure the customer is not touching any electrical devices - If a surge protector is under your desk, and the clients feet are resting on top of this, this introduces noise directly through the client.  Please make sure that your office is set up to prevent this from happening.
  • Do you have the Snap Chokes on the Cable? - BrainMaster Technologies provides all USB Cables with Snap Chokes for the most optimal performance.  Using these is recommended.  If you are not using these, please contact BrainMaster Technical Support for a complimentary set of these.

 

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