What can you do more in 4-20 mA ?

NAMUR NE 43

Well as per API 551 recommendation following things can be distinguished when signal levels are properly defined

When the process variable has increased beyond transmitter calibrated range and transmitter has gone into saturation

When the transmitter is faulty and it is not the process variable range that is driving transmitter to saturation

When the transmitter wire is short circuited.

When the Transmitter wire is open

How this happens !

1. Transmitter Failure Identification :-

On failure of transmitter , The Transmitter is configured to output LOW or HIGH

This LOW Range can be between 3.6 to 3.8 mA

This HIGH Range can be between 20.5 to 22 mA

NOTE:-This between means we select a value as per our requirement .

E:G :- Factory setting for E+H Transmitter is 22mA

2. Process Variable has gone under-Range or Over Range :-

Under-Range :-

Between 3.8 to 4 mA would state that process variable has gone below the calibrated range but THE TRANSMITTER IS NOT FAULTY

Over-Range:-

Between 20 to 20.5 mA would state that process variable has gone above the calibrated range but THE TRANSMITTER IS NOT FAULTY