2 General Considerations

As the use of automation continues to grows, so too does the amount of information that needs to be monitored and processed. More data means more sensors and actuators and correspondingly more PLC I/O modules. However, space inside a factory is also at a premium. Hence, PLC and DCS manufacturers would like to offer more compact modules with higher and higher channel densities as a benefit to their customers. With many high-channel density modules packed close together, the power consumed by all the channels can lead to high module temperature, potentially causing reliability issues. Thermal concerns force each module to be designed for lower power dissipation than before. Also with increased electrification and cabling, the possibility of electromagnetic interference goes up, leading to an increased focus on electromagnetic compatibility (EMC).

These general considerations hold for group isolated and channel-to-channel isolated analog input modules. Group-isolated modules are lower cost, whereas channel-to-channel isolated modules offer robustness and flexibility of use. Careful choice of Isolation solutions is an important decision in each case and is a major factor that decides module size, power and electromagnetic compatibility.