Which analog signal input is accepted by a PLC?

The 4-20 mA current signal is widely accepted as the standard for analog input in Programmable Logic Controllers (PLCs). This range provides several advantages that make it the preferred choice for transmitting analog signals.

First, the 4-20 mA signal is less susceptible to electrical noise than voltage signals, such as those measured in volts. Since current remains relatively constant over long distances, it is less affected by resistance in the wiring, making it reliable for communication in industrial settings where sensors and controllers can be spaced far apart.

The range of 4-20 mA also has a built-in "live zero" feature, where the minimum signal level (4 mA) indicates that the sensor is operational. This is beneficial for diagnostic purposes; if the signal drops below 4 mA, it can indicate a fault condition or that the circuit is open.

In contrast, the other options present issues that make them less ideal for PLC input. The 0-10 mV (DC) and 4-10 mV (AC) choices are too low in voltage, leading to poor signal integrity and increased susceptibility to noise. The 0-10V (AC) option, while potentially usable, does not offer the