5 Ways To Eliminate Ground Loops-Part II

In part I, we explored the frustration caused by ground loops. This phenomenon manifests as unwanted electrical noise – audible hums in speakers, jitter on screens, noisy measurements, and bad measurement data – and can even lead to unexpected communications loss and equipment shutdowns. Understanding the root cause of ground loop feedback allows users to implement effective mitigation strategies.

The Balancing Act of Grounding

Proper grounding not only prevents electrical shock but also minimizes electrical noise in electronic systems, maintaining signal quality. Achieving optimal system performance requires a well-designed grounding scheme that balances safety and noise reduction. It’s a critical yet delicate task.

The Culprits: Different Ground Potentials, Multiple Paths to Ground

In a perfect world, all grounding points would be at the exact same electrical potential. Unfortunately, reality paints a different picture. Factors like temperature, soil moisture, and even the number and type of devices connected to the ground can introduce slight variations in resistance between grounding points. When current flows through the ground path of a system, these resistance differences can create minute voltage variations and ground loop problems are created.

Ground loops commonly occur when multiple interconnected devices are plugged into separate circuits with different grounding paths. When these devices are connected using a ground conductor or shield, it creates a closed loop where electrical current can induce unwanted noise. Nearby sources of electromagnetic interference can worsen these issues.

Mitigating Ground Loop Feedback

Combating ground loop feedback requires a multi-pronged approach:

1. Prevention is Paramount: A well-designed system with attention to proper grounding and wiring practices is the first line of defense. Ideally, all grounds for sensitive equipment should be brought back to a single point in a star topology, and from this point, a low resistance cable runs back to a good earth ground. Prior to installation, a thorough inspection for any faults in the electrical system is crucial.
2. Separate Ground by Function: Ground circuits related to measurements should be kept separate from safety grounds or ground that are connected to high-power equipment. Ideally, each of these should have their own ground “tree” and only be coupled together at a low impedance physical ground point.
3. Avoid Multiple Connections to Ground: One of the most common group loop issues is caused by connecting the shield of a cable to the ground at each end. This will immediately create a ground loop such that any EMI in the area will induce a current in the shield.
4. Reducing Interference: Try to reduce or remove nearby EMI interference from AC power lines or high-power equipment. If this is unavoidable, use a shielded cable with one end of the shield connected to the ground.
5. Isolation is Your Ally: In situations where multiple grounding points are unavoidable, employing signal isolation techniques can prevent current flow through unintended paths. Shielded cables can further enhance noise reduction for low-current applications but see #2 above.

Galvanic Isolation for Data Acquisition: When working with data acquisition systems, consider utilizing data loggers equipped with galvanic isolation. This design feature provides isolation between the sensitive measurement circuitry and the power supply circuits and communications interfaces. It makes them less susceptible to creating ground loops between the sensors, measurement circuitry, and computers used to process the data, ensuring accurate measurements.

Conclusion

Understanding the root causes of ground loop feedback and implementing mitigation strategies significantly reduces the likelihood of encountering this issue. A well-grounded system, meticulous planning, and proper equipment lead to accurate measurements and trouble-free data acquisition.