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Multiple amplifiers per subject or multiple subjects per system

SAFETY

There is no intrinsic safety problem which results from connecting multiple subjects to a single MP150 system. However, all such subjects are galvanically connected to each other when they are properly connected to the same MP System through wired biopotential amplifier modules. All subjects remain galvanically isolated from earth ground.  (For more on this last point, see Galvanic Isolation Guidelines for the MP150 System.)

If there is a possibility that some such subjects may be exposed to Mains line voltage (120-240 VAC), while others may be exposed to earth ground, then the possibility exists for electrical shock hazard to all subjects connected to the single MP System. In this situation, use the IPS100C/HLT100C/OUTISO combination, in conjunction with respective subject amplifier module(s), to isolate each subject from both earth ground and from each other, or use BioNomadix modules.

PERFORMANCE

See “Grounding guidelines” for information about ground loops and how to avoid them for individual subjects.  Note that if proper procedures are followed, any subject connected to a wired system for the purpose of biopotential measurements will be grounded to that system.  There is no intrinsic performance problem when connecting multiple subjects to a single MP System via amplifier modules. However, since all subjects undergoing biopotential measurements are galvanically connected to the system’s ground, they are galvanically connected to each other.  Consequently if two such subjects come into direct contact with each other*, they may create a ground loop.

* Skin to skin.  Most clothing is made of electrically insulating material, so two subjects touching through clothing will not present the same concerns as two subjects touching directly.

If EDA measurements are being performed on multiple subjects, all of whom are connected to the same MP System, and if the subjects touch each other, galvanic currents will flow between the subjects, thus disturbing the measurement. The same situation holds true with the EBI100C or NICO100C amplifiers. If this situation is not acceptable, use the IPS100C/HLT100C/OUTISO combination to isolate the amplifiers from one another.  Alternatively data may be acquired with wireless BioNomadix modules.  The BioNomadix transmitters are fully isolated thus there will be no interaction possible between the EDA and Impedance Cardiography on the same subject or between subjects.

There is no intrinsic performance problem which results when conducting multiple biopotential measurements on the same subject. In this case, it’s only important to have simply ONE ground lead attached to the subject. There are some special cases to consider for certain amplifier modules and combinations of certain modules.

Special Cases

See “Grounding guidelines” for information about the use of EDA100C (GSR100C) and other biopotential amplifiers.

When performing mulitple EDA (GSR) measurements on the same subject

All EDA100C (GSR100C) amplifiers should share the same ground connection point on the subject. That is, only one of these amplifiers should have a lead wire connecting VIn- to the subject.  The current from each of the EDA amplifiers will return through this one site.  If this situation is not acceptable, then each additional EDA100C amplifier should be galvanically isolated from the others using the IPS100C/HLT100C/OUTISO combination, or BN-PPGED wireless modules should be used in place of EDA100C or GSR100C.

When using the EBI100C or NICO100C amplifier

Use the EBI100C or NICO100C ground lead (the I IN connecction) as the ground for all attached amplifiers.  As an alternative, it’s always possible to galvanically isolate the EBI100C or NICO100C from the other attached amplifiers by connecting through  IPS100C/HLT100C/OUTISO/CBL100.  Alternatively the BN-NICO may be used instead of the EBI100C (as long as phase information is not needed) or NICO100C.

When using multiple EBI100C or NICO100C amplifiers on the same subject

All EBI100C or NICO100C amplifiers should share the same ground connection point on the subject. That is, only one module should have a lead wire connecting I IN to the subject.  The current return path for all bioimpedance amplifiers will return through this one site.  If this situation is not acceptable, then each EBI100C or NICO100C amplifier should be galvanically isolated from the others using the IPS100C/HLT100C/OUTISO combination.  Again, BN-NICO modules may be used to replace one or all of these modules (as long as phase information is not required).

When using the EDA/GSR100C in combination with a EBI100C or NICO100C

Use the EBI100C or NICO current return (I IN) to ground the EDA100C too. In this case, the EDA100C will effectively be measuring conductance between the chosen fingertip and the ground position for the EBI100C or NICO100C (typically the abdomen). For relative EDA (GSR) changes, this configuration is functional. However, for fingertip-to-fingertip EDA (GSR) measurements, while also performing EBI100C or NICO100C measurements, the EDA100C should be galvanically isolated from the other amplifiers by using the IPS100C/HLT100C/OUTISO combination.  Alternatively BN-NICO or BN-PPGED may be substituted for the corresponding 100C modules.

Page last modified 31Dec2014

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Associated Application Notes

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