Hei Lars Petter,

Strøm-instrumentsignaler har en bedre immunitet mot elektromagnetiske forstyrrelser enn spenning-instrumentsignaler. Vi kunne ha lengre avstander mellom feltinstrumentet (transmitteren) og kontrollsystemet ved bruk av mA-signaler.

Fordeler med 4-20 mA:

The 4-20 mA current loop is the dominant standard in many industries.It is the simplest option to connect and configure.It uses less wiring and connections than other signals, greatly reducing initial setup costs.Better for traveling long distances, as current does not degrade over long connections like voltage.It is less sensitive to background electrical noise.Since 4 mA is equal to 0% output, it is incredibly simple to detect a fault in the system.

Ulemper med 4-20 mA:

Current loops can only transmit one particular process signal.Multiple loops must be created in situations where there are numerous process variables that require transmission. Running so much wire could lead to problems with ground loops if independent loops are not properly isolated.These isolation requirements become exponentially more complicated as the number of loops increases.

Og, her kan du lære om 4-20 mA (Youtube)

https://youtu.be/0v9ZCD3oL1M