Ground Loops can be mysterious. They reveal themselves in a variety of ways, from a "buzz" in your home stereo to malfunctioning electronic equipment. A definite answer can not always be given as to why they occur, but several suggestions can be offered to help locate and minimize ground loop effects. First, we must analyze exactly what a ground loop is.

A ground loop, very basically, is two or more electrically grounded points at different potentials. Because there are two different potentials, current will flow between them, causing "electrical noise" -commonly referred to as ground loop. Specifically, in process control equipment, ground loops can cause readings to offset from the actual value, saturating the input. This event can cause readings to "peg" up scale or down scale, or it may cause the instrument to lock up at one particular reading while the process is changing.

There is a simple, but not altogether foolproof test for detecting a ground loop in process control equipment. First, with the system under normal operating conditions, place the sensor into a plastic or glass beaker filled with the process solution, and note the reading on the display. This procedure isolates the sensor from the process ground since the beaker is electronically isolated from the process itself. Next, place one end of a wire into the beaker. The other end of the wire should be connected to the metallic piping that the sensor would normally be mounted in. If plastic piping is used, immerse the wire directly into the process fluid. (Note: Make sure both ends of the wire have the insulation stripped away, at least one-quarter inch in length). If the reading on the analyzer changes from the original value, there is a ground loop present.