ADS1298: AC lead off

Aaron Spaete

Expert 4527 points

Part Number: ADS1298

Team,

My customer has the following question.

I am using the AC lead off feature of this device, however this is providing me with different values for impedance measured by each input channel. However, as far as I can work out all these channels have the same input components and should be identical.

Is this a correct assumption?

Regards,

Aaron

over 5 years ago

0 Alexander Smith over 5 years ago

TI__Guru 55312 points

Hi Aaron,

Thanks for your question.

Ryan and I wrote an article covering a similar topic: https://www.planetanalog.com/signal-chain-basics-149-how-to-accurately-measure-electrode-impedance-for-lead-off-detection-in-ecg-systems/#

The two main sources of error will be the lead off current which has a +/-20% tolerance from channel to channel as per datasheet specifications table and the electrode connections. We typically recommend using the largest lead-off current that does not violate the system protection specifications. If the electrode is not properly secured on one channel, the resistance will be higher. Using wet electrodes often provides the most secure connection. Then of course there is the variable impedance of wherever on the body they are performing the measurement.

Data converters

Data converters forum

ADS1298: AC lead off