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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 ...
To allow the construction of hybrid systems, where the 4–20 mA is generated by the controller, but allows the use of pneumatic valves, a range of current to pressure (I to P) converters are available from manufacturers. These are usually local to the control valve and convert 4–20 mA to 3–15 psi (or 0.2–1.0 bar).
Other signals are sent digitally on top of the 4–20 mA signal. For example, pressure can be sent as 4–20 mA, representing a range of pressures, and temperature can be sent digitally over the same wires. In point-to-point mode, the digital part of the HART protocol can be seen as a kind of digital current loop interface.
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 ...
4-channel stereo multiplexed analog-to-digital converter WM8775SEDS made by Wolfson Microelectronics placed on an X-Fi Fatal1ty Pro sound card AD570 8-bit successive-approximation analog-to-digital converter AD570/AD571 silicon die INTERSIL ICL7107. 3.5 digit (i.e. conversion from analog to a numeric range of 0 to 1999 vs. 3 digit range of 0 to 999, typically used in meters, counters, etc ...
In an analog-to-digital converter (ADC) application, signal conditioning includes voltage or current limiting and anti-aliasing filtering. In control engineering applications, it is common to have a sensing stage (which consists of a sensor ), a signal conditioning stage (where usually amplification of the signal is done) and a processing stage ...
An analog signal to discrete time interval converter (ASDTIC) is a specialized kind of an analog-to-digital converter, which converts the analog input signal (e.g. voltage or current) to time intervals between pulses. This conversion is a type of Pulse-width modulation (PWM). The origin of the term ASDTIC lies with NASA around 1970. [1]
Analog-to-Digital Conversion; Understanding Flash ADCs "Integrated Analog-to-Digital and Digital-to-Analog Converters", R. van de Plassche, ADCs, Kluwer Academic Publishers, 1994. "A Precise Four-Quadrant Multiplier with Subnanosecond Response", Barrie Gilbert, IEEE Journal of Solid-State Circuits, Vol. 3, No. 4 (1968), pp. 365–373