INPUT GUARDING TO REDUCE GROUND-LOOP INTERFERENCE
Input guarding is a technique in which the entire measuring or input-circuit section of a differential amplifier is enclosed within a metallic guard. The guard shield is also insulated from the rest of the system (and ground), as shown in Fig. 16.12. An isolation device (such as an isolation transformer or optoelectronic isolator) is used to couple the signal from the input circuit of the amplifier to its output circuit. The entire "amplifier guard shield isolation device" assembly is referred to as an isolation amplifier (see Chapter 15)