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A digital current loop uses the absence of current for high (space or break), and the presence of current in the loop for low (mark). [1] This is done to ensure that on normal conditions there is always current flowing and in the event of a line being cut the flow stops indefinitely, immediately raising the alarm of the event usually as the heavy noise of the teleprinter not being synchronized ...
A major application of current loops is the industry de facto standard 4–20 mA current loop for process control applications, where they are extensively used to carry signals from process instrumentation to proportional–integral–derivative (PID) controllers, supervisory control and data acquisition (SCADA) systems, and programmable logic ...
Mesh analysis (or the mesh current method) is a circuit analysis method for planar circuits. Planar circuits are circuits that can be drawn on a plane surface with no wires crossing each other. A more general technique, called loop analysis (with the corresponding network variables called loop currents ) can be applied to any circuit, planar or ...
The HART Communication Protocol (Highway Addressable Remote Transducer) is a hybrid analog+digital industrial automation open protocol. Its most notable advantage is that it can communicate over legacy 4–20 mA analog instrumentation current loops, sharing the pair of wires used by the analog-only host systems.
Two-wire circuits in new installations are limited to intercom and military field telephone applications, though these too are being supplanted by modern digital communication modes. To communicate in both directions in the same wire pair, conversion between four-wire and two-wire was necessary, both at the telephone and at the central office .
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Keying is a family of modulation forms where the modulating signal takes one of a specific (predetermined) number of values at all times. The goal of keying is to transmit a digital signal over an analog channel.
"Practical Costas loop design" (PDF). RF Design. Electronic Design Group. Archived from the original (PDF) on 2012-02-11; Nicoloso, Steven P. (June 1997). An Investigation of Carrier Recovery Techniques for PSK Modulated Signals in CDMA and Multipath Mobile Environments (PDF). Thesis (Thesis). Virginia Polytechnic Institute and State University.