The terminology for electrical connections to human subjects is not universally agreed upon. “Ground” and “reference” are often used interchangeably. This is not a good practice as there are different purposes for different connections.
Ground and reference are better understood as two different types from the perspective of both physiology and amplifier design. BIOPAC uses a relatively pervasive terminology here.
The ground is used for common mode rejection. The primary purpose of the ground is to prevent power line noise from interfering with the small biopotential signals of interest. By design, amplifiers should not be affected by large changes in potential at both the active and reference sites. A ground electrode for EEG recordings is often placed on the forehead (but could be placed anywhere else on the body; the location of the ground on the subject is generally irrelevant).
The reference lead is the lead that connects the reference electrode; in EEG recordings, this electrode is usually placed at the ear or, in the case of “summed ears,” to a pair of electrodes, one at each ear. The measured electrical potential differences are ideally the voltage drops from the active electrode (connected to Vin+ on the amplifier) to the reference electrode (connected to Vin- on the amplifier).
In a unipolar setup, there will be one reference electrode, and the potential difference between this electrode (connected to Vin-) and every other electrode on the head (connected to Vin+ on separate amplifiers) will be measured.
For bipolar recordings, each active (Vin+) electrode will have its own reference (Vin-) connection.
BIOPAC Systems use a common ground connection for all amplifiers that are electrically connected to each other (i.e., part of the same MP system and not passing through a wireless stage as the BioNomadix modules do). In these cases, there should not be more than one ground connection to the subject unless all but one of the ground connections are through AC coupled leads. For instance, recordings made through a single MP36 system should have only one ground connection to the subject. Similarly, recordings made through EEG100C or EEG100C-MRI amplifiers all connected to a single MP150 system should have only one ground connection (total!) to the subject. BioNomadix wireless physiology data systems necessarily have a separate ground for each transmitter (note that each transmitter has two amplifiers on it). In this case, each transmitter should have one ground connection to the subject even if all transmitters communicate with the same MP150 system.
Basic principles of physiological data collection covers fundamentals of data collection and equipment configuration equipment to help you refine experiment protocols and avoid costly missteps. Frazer Findlay, CEO of BIOPAC, discusses common mistakes with physiology recording and shares his secrets for collecting great data. Topics include: How to prep a subject and where to place electrodes; Which type of electrodes work for different body signals; Analog to Digital Conversion; Sample rates (correct vs. incorrect); Filtering; and Scaling and calibration.Watch On Demand Now!
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 […]
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 […]