Reducing Interference During XDAQ Recordings

Reducing Interference During XDAQ Recordings

In electrophysiological experiments, even very small changes in voltage or current—occurring on millisecond or microsecond timescales—can reveal critical neuronal signaling mechanisms. Capturing these subtle electrical events requires highly sensitive equipment designed for precision measurement.

However, experimental sensitivity can often be compromised by the noise, not by inherent instrument noise, but by interference from external electromagnetic fields. Common sources of such interference include AC power lines (50/60 Hz), fluorescent and LED lighting systems, and electromagnetic emissions from nearby electronic devices. These external signals are frequently introduced due to suboptimal wiring practices within electrophysiology rigs.

This article covers grounding, shielding, and REF/GND connection best practices to minimize external interference pickup.

Grounding 

A recommended practice for grounding electrophysiology apparatus is the star grounding technique. This involves connecting all equipment grounds to a single, common grounding point, typically called the “star” node. From this central node, a single grounding conductor is connected to a dedicated earth ground or grounded wall outlet.

Each XDAQ includes chassis ground and system ground ports on the rear panel by the power input. Here’s how they differ:
  1. Sys GND: Referenced (not directly bonded) to Protective Earth (PE) via AC/DC adapter.
  2. Chassis GND: Connected to the instrument enclosure; when bonded to PE (or to system ground at a single point), it serves as an RF shield and shunts high-frequency common-mode noise away from the signal path.
The two-port design gives users flexibility while enabling a clean single-point ground when bonded together.
You may use the ground port on the XDAQ as the common grounding point for all apparatus in your electrophysiology rig. We recommend star grounding to avoid ground-loop formation and electric-field interference—run a dedicated ground lead from each instrument to the common point (the XDAQ ground port).

IdeaTips:
Users can try shorting (bonding) these two ports and then connecting the Faraday cage and rest of the instrumentation within the rig to that bonded point—this arrangement has eliminated most noise pickup in our lab environment.

Shielding 

Effective shielding is crucial for reducing interference from external electric fields, particularly those originating from mains power lines. Although notch filters can attenuate the fundamental 50/60 Hz mains frequency, higher-order harmonics often persist and may cause analog-to-digital converter (ADC) saturation and signal distortion.

A Faraday cage—typically constructed from conductive materials—can block these electromagnetic disturbances by enclosing the experimental apparatus and redirecting external electric fields. When integrated properly, a Faraday cage enables more accurate and stable signal acquisition.

We recommend conducting electrophysiological recordings within a Faraday cage to minimize electromagnetic interference.

Suggestions for constructing a faraday cage:

  1. Use conductive materials such as aluminum foil, copper mesh, or steel sheets.
  2.  Focus on the design of doors and cable entry points. Use conductive gasketing or mesh sleeves to preserve shielding effectiveness.
  3. Ground the Faraday cage to the true ground using the star grounding method. 

Establishing reference and ground connection between headstage and animal

XDAQ is designed with isolated headstage ports, which means the electrical circuits at the headstages (connected via the headstage ports) are protected, or isolated from that of the acquisition system.  This minimizes any electrical noise propagating from the XDAQ system and its connected instrumentations. Proper connection of the REF/GND lines from the headstage to the electrode probe and the animal's reference is essential for ensuring signal integrity and minimizing noise.

Suggestions for connecting the headstage REF/ and GND  to the animal:

  1. Establish a stable REF/GND point at the animal site using a bone screw or Ag/stainless steel wire and verify contact to the cerebrospinal fluid (CSF) or tissue.
  2. Incorporate a quality control step during  the surgery to verify the connectivity and stability of the REF/GND point.  Some users have adapted surgical protocol to leave access points on the craniotomy so that post surgery verification of the REF/GND connectivity can be easily done.
  3. Short all unused headstage channels to the headstage ground to prevent stray signal pickup and reduce noise.
  4. Provide the animal no ground path other than the headstage reference/ground leads.
  5. Avoid contact between the animal and grounded metal (stereotaxic frame, bite bar, earth-referenced heating pad, Faraday cage mesh).
  6. Keep hardware within the behavioral arena insulated or floating relative to mains earth, or reference them only through the same single-point ground—never directly to facility earth.
  7. Use stock KonteX HDMI cables for a trusted connectivity that minimizes noise and electrical connectivity. 

Info
INFO:
For establishing a stable REF/GND point at the animal site, we recommend experiment with various headstage GND/REF configuration and locations for your prep and always verify reliable signal is supplied to the headstage.  Shorting GND and References together is a common practice and could be a good starting point.  Once gaining a base baseline recording quality from a shorted GND-REF configuration, users could consider experimenting with separating these signals.  For example, one might use the metal canular from the probe as REF, as it is close to the recording sites, and use a bone screw as a GND.  Some neural probes have dedicated electrode sites that are designed for use as REF.  


Idea
Tips:
When adapters are used, check the entire signal path for GND and REF between the electrode and the headstage.  Check out v2 KonteX headstage adapters for added flexibility in GND/REF configuration.


    • Related Articles

    • What is the purpose of the ground ports in the back of the XDAQ ONE?

      These ports are designed to help troubleshoot and establish an optimal grounding scheme for the XDAQ acquisition hardware and thus minimize noises in the neural recordings. Most instrumentation ties all grounds - digital or analog - together, which ...

    • Optimizing Digital noise issue with XDAQ with X6R128 or Intan RHD2164

      Issue Description Some XDAQ users have reported noise affecting blocks of 32 channels, particularly when using longer cables with KonteX's X6R128 or Intan RHD2164 chip/probes. This issue is likely due to nanosecond-scale timing inconsistencies in ...

    • How to connect the XDAQ IO Expander to the XDAQ

      To use the XDAQ IO Expander, connect the XDAQ’s EXP1 port to the Expander’s EXP1 port and the XDAQ’s EXP2 port to the Expander’s EXP2 port. The XDAQ’s powering sequence is not critical; it can be powered on before or after plugging in to the ...

    • XDAQ supported headstages

      In addition to the ultra-small X-Headstages, XDAQ supports existing Intan-compatible headstages (from Intan, NeuroNexus, and more). To run these headstages with their corresponding accessories, you will need an adapter to properly remap the control ...

    • Updating the Gen2 XDAQ Firmware

      KonteX periodically releases new firmwares for bug fixes and new functionalities. Additional capabilities may be enabled if they were not selected in the initial purchase(e.g. adding the SR32 capability or Neuropixels support). To update the ...