Transmitters emit current loop signal outputs of 4 to 20mA. Industrial systems often utilise transmitters with 4 to 20mA sensor signals because they provide noise immunity, support use with long cable lengths, and require only two-wire connectivity. However, if all the factors of a loop transmitter system are not taken into account the system could fail or have limited functionality. Fortunately, Druck has produced a paper that offers instructions and tips on how to calculate the requirements and limitations of loop transmitter systems.
Druck’s paper, titled ‘Tech Tip: Why doesn’t my pressure transmitter read full scale?’, is available here.
The paper includes helpful tables, diagrams, and equations for calculating the voltage loop supply, measurement limitations, cable lengths, and the voltage at the transmitter. If the voltage at the transmitter is too low, due to long cable lengths or a low voltage supply, the transmitter will cease to operate.
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