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Note that a 4-wire instrument has a power-supply input separate from the current loop. Panel mount displays and chart recorders are commonly termed "indicator devices" or "process monitors". Several passive indicator devices may be connected in series, but a loop must have only one transmitter device and only one power source (active device).
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 ...
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.
Like other early DEC terminals they were equipped with both an RS-232 port as well as a 20mA current loop, an older serial standard used with teletype machines that was more suitable for transmission over long runs of twisted-pair wiring. Data was read into a small buffer, which the display hardware periodically read to produce the display.
Transistor electronics enabled wiring to replace pipes, initially with a range of 20 to 100mA at up to 90V for loop powered devices, reducing to 4 to 20mA at 12 to 24V in more modern systems. A transmitter is a device that produces an output signal, often in the form of a 4–20 mA electrical current signal, although many other options using ...
A digital loop carrier (DLC) is a system which uses digital transmission to extend the range of the local loop farther than would be possible using only twisted pair copper wires. A DLC digitizes and multiplexes the individual signals carried by the local loops onto a single datastream on the DLC segment.
The pneumatic control signals are traditionally based on a pressure range of 3–15 psi (0.2–1.0 bar), or more commonly now, an electrical signal of 4-20mA for industry, or 0–10 V for HVAC systems. Electrical control now often includes a "Smart" communication signal superimposed on the 4–20 mA control current, such that the health and ...
This list includes LCD, OLED and microLED display manufacturers. LCD uses a liquid crystal that reacts to an electric current blocking light or allowing it to pass through the panel, whereas OLED/microLED displays consist of electroluminescent organic/inorganic materials that generate light when a current is passed through the material.