Recently our lab has been having some difficulty obtaining a clean signal and yesterday we noticed that one of our external electrodes was possibly the problem. We also noticed that the blue, CM in Range, indicator was blinking. Is this an indicator of the problem? What's typically wrong when this light blinks?
The main symptom of our problem is difficult to describe but I'll try. In ActiView instead of the steady relatively parallel signals we see a segmented signal with all electorde signals dropping to the bottom. Not sure if that make sense but that's what it looks like. It looks like a typical DRL issue but could it also be caused by any single problem electrode? Any help would be appreciated. Thanks
Pete S.
'CM in range' indicator
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Guest
We've had this problem a few times too. The problem (as far as we know) seems to be that one of the external (EXG) electrodes has a lead that is bare or broken. You should be able to figure out which one by systematically unplugging the external electrodes one-by-one. When the bad one is unplugged, the CM light should stay on.
I'm not sure if this problem could be due to a cap/strip electrode being bad, because we haven't had that problem. Maybe Coen can shed light on that issue.
Jeff
I'm not sure if this problem could be due to a cap/strip electrode being bad, because we haven't had that problem. Maybe Coen can shed light on that issue.
Jeff
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Coen
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The current flow via the DRL is constantly monitored by the safety circuitry inside the AD-box. The current flow is limited to 50 uA (IEC 601 safety limit). If the current runs into the limit, the CMS/DRL circuit cannot keep the Common Mode value within its normal working range, and the blue LED turns off. The safety circuitry reacts on this error situation by shutting the power supply to ALL active electrodes off. Consequently, no meaningful signals can be measured so long as the blue LED is off.
The circuit operation described above implies that any electrode can be the cause of a CM out of range error. Examples of errors are broken wires, bad connector contacts (pollution of connector with gel), defect IC inside the electrode, bare electrode wire contacting the subject (damaged cable isolation) etc.. For example, if one of the active electrode wires is broken, the electrode input circuit is not anymore biased correctly, and the input resistance may fall below its specified value of 10^12 Ohm. The resultant extra input current is detected by the CMS/DRL circuit, and the blue LED goes off.
Save operation of the system is ensured because the power supply to the active electrodes is only restored if ALL electrodes connected to the subject work correctly. In other words, both cap en EX electrodes can in principle cause CM out of range errors.
Best regards, Coen (BioSemi)
The circuit operation described above implies that any electrode can be the cause of a CM out of range error. Examples of errors are broken wires, bad connector contacts (pollution of connector with gel), defect IC inside the electrode, bare electrode wire contacting the subject (damaged cable isolation) etc.. For example, if one of the active electrode wires is broken, the electrode input circuit is not anymore biased correctly, and the input resistance may fall below its specified value of 10^12 Ohm. The resultant extra input current is detected by the CMS/DRL circuit, and the blue LED goes off.
Save operation of the system is ensured because the power supply to the active electrodes is only restored if ALL electrodes connected to the subject work correctly. In other words, both cap en EX electrodes can in principle cause CM out of range errors.
Best regards, Coen (BioSemi)