What is the common output of a typical 4-20 mA transmitter in terms of signal when measuring a variable?

The typical output of a 4-20 mA transmitter is represented by the current signal range of 4 to 20 milliamperes. This standard is widely used in industrial control systems for transmitting process variables such as temperature, pressure, and flow.

The reason this specific range is chosen stems from its ability to provide an accurate indication of system behavior. A current signal has distinct advantages, such as being less susceptible to signal degradation over long distances compared to voltage signals. The minimum output of 4 mA represents the lowest limit of the measurement range, while the maximum of 20 mA corresponds to the highest limit. The range is designed this way to allow the detection of signal loss; if a transmitter fails or if the circuit breaks, the output will drop below 4 mA, indicating a problem in the transmission.

Additionally, using this current loop standard aids in minimizing potential issues, such as interference from electrical noise, which is often more pronounced with voltage signals. Overall, the 4-20 mA output is a robust and reliable method for process variable communication in control systems.