In analog input programmable logic controllers (PLC) a multiplexer is often used to switch multiple sensors to a single ADC. By using a multiplexer, the number of components in the system can be reduced to save system cost and size. In a PLC module a ±10 V input signal range is common for interfacing with external field transmitters and sensors; however, 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 from wiring connections incorrectly, component failure or wire shorts, electromagnetic interference (EMI) or transient disturbances, and so forth.

Figure 10-1 Typical Application