Difference between Live Zero and Dead Zero?

A 4 - 20 mA system uses a live zero, where zero signal is equal to 4 mA.

A 0 - 20 mA system uses a dead zero, and isn’t nearly as popular.

The advantage of a live zero system is that a broken wire (0 mA) is easily distinguished from a zero signal (4 mA). The continuous 4 mA current also allows the transmitter to be powered by the loop current, rather than needing a separate power supply.

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