What is the output range of a 4-20 mA transmitter when it is at its minimum setting?

The output range of a 4-20 mA transmitter is designed specifically to utilize a minimum output of 4 mA and a maximum output of 20 mA. This operational range is particularly important because it helps distinguish between a zero signal condition and a fault condition. When the transmitter is at its minimum setting, it outputs 4 mA, which indicates the lowest part of the measuring range.

The 4 mA value serves as a "live zero," meaning that even at its minimum, the transmitter is still actively providing a measurement signal, which is crucial for ensuring that monitoring and control systems can accurately interpret a real, functioning signal. If the output were to drop to 0 mA, it could be difficult to determine whether the signal was meant to represent zero flow or if there was an issue with the transmitter itself. Thus, 4 mA is established as the minimum output to prevent ambiguity in the readings provided by the transmitter when measuring process variables.