Grounds loops come about when the measurement system installation has more than one ground point (see Figure 1). In electrical systems, we often assume that all "grounds" are at the same potential. In reality, this is often not the case, especially with installations outside of the laboratory environment, or in which long distances are involved between the positioning of the accelerometer and signal conditioner. If the grounds are at different potentials, a current flow will result, completely unrelated to measurement signal current.
Diagnosing ground loop problems can be a difficult and frustrating exercise, depending upon actual installation conditions. The best proactive approach for ground loop prevention is to utilize the single-point ground system approach. The idea behind the single-point ground system is to ensure that throughout the entire measurement system (accelerometer, cable and signal conditioner), only one ground point exists. In general, Meggitt recommends that the designated single-point ground be located at the signal conditioner.
Most signal conditioners are grounded via their power supply. The trick, then, is to ensure that the rest of the system is not additionally grounded at any point. The accelerometer must be examined. In particular, is the transducer case isolated, or case grounded?