Industrial Maintenance Technician Practice Test

The typical range for analog signals in a Programmable Logic Controller (PLC) is predominantly 4 to 20 milliamps. This range is widely used in industrial applications due to its advantages in terms of signal integrity and noise resistance.

When an analog signal is measured, having a minimum of 4 milliamps allows for distinguishing between a zero signal and a failure mode, such as a broken wire. If the signal drops below 4 milliamps, it can be easily interpreted as a fault condition, ensuring that the system can alert operators or take corrective actions. The range extends to 20 milliamps, allowing for a full scale of analog data transmission which can be proportional to various physical parameters like temperature, pressure, or flow.

Other ranges, such as 0 to 10 volts or 0 to 5 volts, may also be used, but they are less common in industrial contexts relative to the current loop standard established by the 4 to 20 milliamp range. The 10 to 30 volts option is not a standard for analog signals in PLCs, making the 4 to 20 milliamps the most typical choice in the industry. This standardization helps in integrating sensors and actuators into PLC systems