Editing Current loop (section)

{{Short description|Electrical signalling scheme}}
{{About|an analog electrical signaling scheme|digital serial communications|Digital current loop interface|the oceanic phenomenon|Loop Current|the network analysis variable|loop current}}

In electrical [[Signal (electrical engineering)|signalling]] an analog '''current loop''' is used where a device must be monitored or controlled remotely over a pair of conductors. Only one current level can be present at any time.

A major application of current loops is the industry [[de facto standard]] '''4–20&nbsp;mA''' current loop for [[process control]] applications, where they are extensively used to carry signals from process [[instrumentation]] to [[Proportional–integral–derivative controller|proportional–integral–derivative (PID) controllers]], [[Supervisory control and data acquisition|supervisory control and data acquisition (SCADA)]] systems, and [[Programmable logic controllers|programmable logic controllers (PLCs)]]. They are also used to transmit controller outputs to the modulating field devices such as [[control valves]]. These loops have the advantages of simplicity and noise immunity, and have a large international user and equipment supplier base. Some 4–20&nbsp;mA field devices can be powered by the current loop itself, removing the need for separate power supplies, and the "smart" [[Highway Addressable Remote Transducer Protocol| Highway Addressable Remote Transducer (HART) Protocol]] uses the loop for communications between field devices and controllers. Various [[List of automation protocols|automation protocols]] may replace analog current loops, but 4–20&nbsp;mA is still a principal industrial standard.