Ground Loop Noise

February 12, 2020

In electrical and electronic systems, the word “ground” has two meanings depending on the context.

In power electricity, ground is a physical connection to the earth. It is commonly called earth ground.

In electronics, ground is not a connection to the physical earth but a reference point to 0 volts.

The Need for a Ground

Electrical grounds are used for human safety, to protect electrical circuitry from damage, and to provide a baseline for voltage measurements.

In power electricity, the earth ground is a third wire: it minimizes the chance of electrocution by shorting any potentially hazardous electricity—such as a high voltage surge—to the physical ground.

In electronics, ground is used throughout the circuitry and is critical to proper function.

Grounding and Ground Loops

Each component of a vibration testing system has a ground reference in the control circuitry. It may also have an electrical ground connection to the earth for safety. The combination of these grounds can potentially cause ground loops.

What is a Ground Loop?

A ground loop occurs when multiple devices that have an individual ground to the electrical power system are connected to each other with a signal or communications cable that also carries a reference ground connection. Multiple paths to ground through multiple devices can form a loop or loops. The loop(s) pick up interference currents and create electrical noise.

VRU: Ground loop noise

Figure 1.2. A simple ground loop.

In a vibration testing system, this electrical noise can cause physical motion on the shaker. In other cases, it only affects the measurement system. Ground loops are very common; with the appropriate steps, the effects can be minimized or completely eliminated.

The following lessons will explore how ground loops can occur in a vibration test system and the steps you can take to eliminate them.