The need to monitor remote sensors is common among factory automation control systems. For example, an analog input module or mixed module (AI, AO, DI, and DO) of a programmable logic controller (PLC) will interface to a field transmitter to monitor various process sensors at remote locations around the factory. A switch or multiplexer is often used to connect multiple inputs from the system and reduce the number of downstream channels.

There are a number of fault cases that may occur that can be damaging to many of the integrated circuits. Such fault conditions may include, but are not limited to, human error due to miswiring, component failure, wire shorts, electromagnetic interference (EMI), transient disturbances, and more.

Figure 9-1 Typical Application