How to check an electrode set for defects ?
 
What does it mean: The Bucket Test ?
When the Blue LED turns off, or when your electrodes are becoming noisy, you can use the 'Bucket Test' to test your electrode sets for defects. This test is done as following:
Fill a glass or plastic bowl or plastic bucket (no metal) with tap water and add a teaspoon of table salt (NaCl).
Connect a CMS/DRL cord to the front of the AD-box, or connect a P32 electrode set with integrated CMS/DRL to the "A" SCSI connector on the top of the AD-box.
Now first submerge only the CMS and DRL electrodes into the water. The Blue LED should now turn on. If the Blue LED turns off (blinking) then most likely the CMS/DRL electrodes are defect.
Now submerge the offending electrode(s) into the water, one by one and observe the Blue LED.
If there are any kinked wires, then moving/bending the electrodes and wires, will reveal them quicker.
If the Blue LED turns off, then you have found the problematic electrode(s).

What does it mean: Blue LED turns off ?
The CMS/DRL circuitry inside the AD-box constantly checks whether the AD-box and all the electrodes are working safely t
o comply with the 50uA max. value specified for the IEC-601 CF type isolation used in Europe.
If the Blue LED turns off (It will be blinking at about 1 Hertz) when an electrode is connected to the subject or during the bucket test, then this can be caused by:
An electrode wire is kinked internally. When a kinked wire is detected by the CMSDRL safety circuitry, then the CMS/DRL will turn-off the Blue LED (Blue LED will start blinking). The CMS/DRL will also turn-off all powers going to all electrodes. No measurement will be possible anymore, all channels will display maximum offset on the offset tab-page in ActiView.
There is gel inside the SCSI connector of the electrode set or inside the SCSI connector of the AD-box.
There is no CMS/DRL cord connected to the AD-box, or there are 2 CMS/DRL electrodes connected at the same time: (a CMS/DRL cord at the front of the AD-box, and at the same time, a P32 electrode set with integrated CMS/DRL at the "A" SCSI connector on the top of the AD-box)

What does it mean: Kinked wires ?
After long time use, it is inevitable that electrode sets will have to be replaced.
The most delicate place of the flatcable is the place where the wire exits the electrode housing of the electrode. At this place the flatcable has a lot of stress due to the handling/bending of the electrodes/wires. Bending of the wires often happens when:
Users pull out the electrodes out of the cap while pulling at the wires.
Grabbing the electrode housing at the place where the wire exits the housing, so the wire gets bend when pulling the electrode out of the headcap.
Bending/stressing the wires to much during the cleaning/washing process of the electrodes.up

The number of measurements which can be achieved with electrode sets, solely depends on the carefulness with which the electrode sets are handled. If a customer bends the wires, pulls out the electrodes out of the cap at the wires, or bends the wires every time when inserting the electrodes in the cap, then an electrode set will not last as long as when care would have been taken with regards to prevent kinked wires from appearing.

 
What does it mean: Gel inside the SCSI connector ?
When there is gel inside the SCSI connectors of the AD-box or gel inside the SCSI connector of the electrode set then the AD-box goes into 'power-down'. All 3 Led's on the AD-box turn of, or all 3 Led's start blinking.

When there is gel inside the SCSI connector of the AD-box, the gel can create a bridge between the pins inside the SCSI connector and the metal shielding around the SCSI connector. When this happens, the Guard protective circuitry will detect that the current running through the guard is to high and as a result the AD-box will be shut down and all 3 LED's will turn off or will start blinking. When there is gel inside the SCSI connectors, use alcohol and a cotton cloth to remove the gel.
When doing the 'Bucket test' with only the CMS and DRL in the water, the Blue Led should be on. If this is not the case, either the CMSDRL is defect, or there is gel inside a SCSI connector. Please read more here about how to solve this: AD-box shuts down or the acquisitions stops.

 
What does it mean: Noisy electrodes ?
Noise during a measurement can be caused by several causes:
Electrode tip is contaminated with metal particles.
Check your electrodes with the 'Bucket test' in water. After 15 minutes in water, the AgAgCl pellets must have stabilized. If an individual electrode tip is contaminated, then its noise is always seen as high frequency noise with quick jumps in baseline. Grinding the tip carefully with the finest grinding paper can sometimes grind away the contaminating metal particles.
EMG.
Check your electrodes with the 'Bucket test' in water. If there is no noise during the bucket test, the noise could have been caused by EMG. Noise caused by EMG is always only on a few electrodes and only at electrodes located around muzzles.
Hum (50/60Hz).
Hum is often seen as a low frequency noise with constant amplitude.
When the CMS or DRL electrodes do not make good enough contact, then all electrodes will show hum.
When an individual electrode does not make good enough contact, then only this electrode will show hum.
Perform the 'Bucket test' to check your electrode set. Put all electrodes in the bucket and group them all together with the CMS electrode at one side in the bucket. Place the DRL electrode at the other side in the bucket. (the CMS electrode should always be located in the middle of the measuring electrodes and the DRL should always be located away from the measuring electrodes).
Hum problems can be solved by: improving electrode contact (more gel), bundling the cable better to prevent magnetic interference, locating the subject away from the not isolated parts, placing the AD-box closer to the subject.

 

I found defective electrodes: Will BioSemi repair them, what should I do now ?
You can sent the sets to us for inspection. When we think the sets are still in good condition, then we'll repair them for free. If we think the problem is not only in 1 electrode, but problems are to be expected in more electrodes in the near future, then we'll no longer repair. When a set shows 2 kinked wires or more, the set will be labeled as being beyond repair.