How do I perform the one-bucket test to identify faulty electrodes? Or, why does the blue CM in Range flicker and the signals pulsate once every half second?

Posted by & filed under .

The blue CM in Range light reflects two things: 1) whether the CMS and DRL electrodes are adequately connected to the participant’s body, and 2) whether all of the other active electrodes, cables and connectors are intact.  If any of these are NOT true, then the blue CM in Range light will flicker and the signals and offsets will pulsate once every half second until the problem is rectified.  We call this state CM Out of Range (CMOR).  The blue LED labeled CM in Range on the front panel of the AD box is reflected on the top right of the ActiView software display. This makes it easy to recognize there is a problem.  To identify which electrodes are involved, use the one-bucket test.

One bucket test:
  1. Fill a plastic or glass container with about 1/2 gallon of tap water with roughly a teaspoon of Na/Cl (non-iodized table salt): this represents a virtual patient
  2. Connect CMS/DRL to the system, turn power on and submerge only those two electrodes in water. If the CM in range light (blue LED) does not come on, then CMS/DRL is faulty or something inside the box is broken. Stop the test. If the blue LED light does come on, continue to the next step.
  3. Connect the questionable electrode set to the system and submerge all electrode contacts in water and observe the electrode offsets in ActiView>Electrode Offsets tab. If the CM in range light goes out, then remove half of the electrodes in that set from the water. If the CM in range light comes on, then there is a problem in one of the electrodes that was removed from the water. In that case, switch the two sets of electrodes (take out those that are in the water and replace them with those that were out of the water).
  4. Repeat this step of removing half the electrodes until one or more faulty electrodes has been identified. 

Once you identify the faulty electrodes, contact us at via the Request Info form and let us know the serial number of the electrode, and if it is a set of electrodes on a ribbon cable let us know which electrode is (or electrodes are) causing the problem.  On occasion, this type of problem may be caused by a loose or damaged connector on the ribbon cable, but this is rare.  Most often, the problem is caused by a single broken wire on an electrode.  If both wires on an electrode are broken, then the CM in range light will not go off, but the offset on that channel will read -262 mV (the negative extent of the input range).