there are several techniques that can be used to eliminate or reduce the interference signals caused by ground loop and common-mod voltages. They include the following ones:(1) single-point grounding, (2) use of differential-input amplifiers, (3) input guarding ,and (4) use of battery-powered instruments. We shall see that the use of differential-input amplifiers equipped with input guard shield (i.e., a combination of methods (2) and (3) provides the most complete solution for reduction of interference signals due to ground loop and common-mode voltage).
Prior to the widespread availability of differential amplifiers in the 1950s, single-point grounding implemented with heavy conductors was the most effective technique used for combating ground-loop interference problems. The single-point grounding method for eliminating ground-loop interference relies on the fact that current cannot flow in any path unless a complete loop exists. Therefore, to reduce ground-loop interference, we must avoid establishing any complete ohmic ground-loop paths and break up any such loops that already exist. The best way to ensure that no effective ohmic ground-loop paths exist is to design the measuring system so that only one point of the system is ever ohmically connected to ground. In that way, although other closed loops through the ground plane may still exist (due to capacitive coupling), their circulating currents will be much smaller than those in a low-impedance complete ohmic loop. In system for which single-point grounding provides an effective reduction in ground-loop interference signals, single-ended rather than differential-input amplifiers can be safely used. Single-ended amplifiers are less complex and costly to employ than differential-input amplifiers.