Multiple DRL devices

[mcip]

Hi,

What would happen if a subject were using a second device simultaneously (not an active2) that also had a DRL circuit.

For example if you were measuring EMG with the Active 2 (and obviously using the DRL) on one arm, and at the same time using (for example) a separate GSR device which also used a DRL circuit. on the opposite arm..

Would these two DRL circuits continually disrupt each other, or would they be able to establish an equilibrium?

Thanks

[Coen]

Because of the battery power supply and fiber optic data transfer, the ActiveTwo front-end is fully floating (galvanically isolated from the environment). Therefore, the ActiveTwo does not "know" whether other measurement devices are connected to the subject. So, there won't be any problem when you connect other measurement devices to the same subject (either with DRL or with passive ground/neutral electrode). There are two further remarks however:

- Do not attempt to make a "ground" connection between the ActiveTwo and other measurement devices. With such an extra connection, the the ActiveTwo and other devices will not anymore be floating with respect to each other. The DRLs of different devices may then try to drive the subject to different potentials, which will lead to saturation (CM out of range) problems.

- The added measurement device may increase the isolation capacitance between subject and environment, which may lead to increased levels of interference in the ActiveTwo signals. For example, if a mains powered GSR device is added, the isolation capacitance in this GSR device will be the determining factor for the amount of leakage current, and advantages by the very high isolation offered by the ActiveTwo setup will be lost, also see http://www.biosemi.com/faq/battery_and_fiber.htm. In any case, be sure that the isolation of the subject remains high enough to ensure electrical safety (added measurement devices must conform with IEC 601-1).

Best regards, Coen (BioSemi)