BIOPAC® Systems, Inc. Logo

Grounding guidelines

When a single subject is connected via wires to a single MP system, there should generally be one and only one ground connection to that subject*. When multiple subject grounds are used, ground loops can occur: current will flow between the different grounds. This will result in distorted data.

When recording with the EDA100C (GSR100C), EBI100C, or the NICO100C, a ground is already provided through the VIn- or I IN connection (in these three cases as well as their -MRI brethren, an internal connection makes VIn- for EDA amplifiers or I IN for the bioimpedance amplifiers electrically identical to ground).  Consequently, no other ground connection to the subject* need be used. In some cases, particularly when power line noise is apparent despite the presence of a single ground, it is beneficial to have more than one ground.  In the case of the EDA100C (or GSR100C), additional connections can be made through AC-coupled lead adapters (CBL205).

* “To the subject” meaning specifically an electrical connection to the subject.  Many other BIOPAC components, such as the respiratory effort transducer and photoplethysmogram transducer have ground connections to the equipment but are not relevant to this topic because these devices do not make electrical connections to the subject and thus will not produce ground loops through the subject.

To record EDA (GSR) simultaneously with other biopotential signals (for instance, ECG, EEG, EOG, EGG, EMG, or ERS) using 100 series amplifiers (e.g., GSR100, GSR100C, EDA100C, etc.), BIOPAC suggests using CBL205 connected to one ground on any of the biopotential amplifiers.

The AC coupled lead will not influence the EDA measurement when all electrodes are connected, but it will continue to function as a ground for the ECG amplifier if the electrode connected to VIn- on the GSR100C is disconnected from the subject.

For more on this topic see “Special Cases” under “Multiple amplifiers per subject or multiple subjects per system.”

Note—If using any two of the following on the same subject connected directly to the same MP system at the same time: EDA100C (GSR100C), EBI100C, or NICO100C, ground loops will be a problem; you will not be able to make absolute measurements (such as SCL). BIOPAC recommends the use of BioNomadix modules in this case as these transmitters do not share a common ground. Alternatively, one or more of the measures may be made through an additional MP150 system or with an IPS100C/HLT100C/OUTISO to optically isolate the ground connections.  More information may be found under Galvanic Isolation Guidelines.

Updated 12-31-2014

Associated Applications

Spotlight On
BIOPAC training

T4 Human Physiology Conference

Register Today! T4: Tools, Trends, Techniques, and Technology Monday, July 24, 2017 – Wednesday, July 26, 2017 Join BIOPAC for three days of hands-on, small-group human physiology workshops, presented by renowned experts, on the beautiful University of California at Santa Barbara campus in Santa Barbara, California, USA. Who should attend Anyone who records and analyzes […]

View All
Latest News

Mobita Advances Prestimulus EEG Research

The Mobita 32-Channel EEG recording system was used in research examining if physiological data can be used to predict truly random events that correspond to perceptual stimuli. Baumgart, et al. from the University of California Santa Barbara utilized a quantum random number generator (qRNG) to choose from three randomized conditions: light, sound, and no stimulus. […]

News Citations—Respiration and Cardiovascular Activity

BIOPAC provides software and hardware that allow for research teams to record and analyze respiration activity in physiological experimentation. Here are a few notable studies in monitoring respiration and cardiovascular activity. The coupling between peripheral microcirculation and slow breathing: The purpose of this study was to investigate the coupling of breathing movements and microcirculatory blood […]

Read All
Request a Demonstration
Request a Demonstration