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).

If using BioNomadix wireless transmitters, the subject requires one ground per transmitter. This only applies to units making an electrical connection with the subject. In addition, the BN-PPGED does not require an extra ground, as the VIN- of the EDA already acts as a ground. However, BN-ECG2, BN-EMG2, BN-EEG2, BN-EOG2 and BN-EGG2 all require separate ground connections.

* “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 MP system or with an IPS100C/HLT100C/OUTISO to optically isolate the ground connections.  More information may be found under Galvanic Isolation Guidelines.

Associated Applications

Spotlight On

FEMG Smart Amplifier

The fEMG Electromyography Smart Amplifier is designed specifically for recording facial EMG signals and electrical activity from other small muscle groups. Use with AcqKnowledge™ software to analyze facial expressions and startle paradigms. BIOPAC’s new Smart Amplifiers are designed for great data. Smart Amplifiers improve performance by amplifying the physiological signal close to the subject, which allows a high-level […]

View All
Latest News

New Citations | Combat Helicopters: Luxury Cars of the Sky

Recent psychophysiological studies feature BIOPAC’s MP Research series of Data Recorders and AcqKnowledge software. Creating Adaptive Assistants for helicopter crews based on Real-time Physiological Data In the Mercedes S-Class, biometric tools track a driver’s eyes, heart rate, and other physiological data, with one goal in mind: Making sure drivers are alert and safe on the […]

Electrocardiography Guide Now Available

BIOPAC’s just released Introductory ECG Guide addresses fundamental to advanced concerns to optimize electrocardiography data recording and analysis. Topics include: ECG Complex; Electrical and Mechanical Sequence of a Heartbeat; Systole and Diastole; Configurations for Lead I, Lead II, Lead III, 6-lead ECG, 12-lead ECG, precordial leads; Ventricular Late Potentials (VLPs); ECG Measurement Tools; Automated Analysis Routines […]

Read All
Request a Demonstration
Request a Demonstration