Current loop

Summary

In electrical 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 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 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 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 (HART) Protocol uses the lo

Official source

https://en.wikipedia.org/wiki/Current_loop

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Enhanced current and voltage regulators for stand-alone applications

Federico De Bosio

State feedback decoupling permits to achieve a better dynamic response for Voltage Source in stand-alone applications. The design of current and voltage regulators is performed in the discrete-time domain since it provides better accuracy and allows direct pole placement. As the attainable bandwidth of the current loop is mainly limited by computational and PWM delays, a lead compensator structure is proposed to overcome this limitation. The design of the voltage regulator is based on the Nyquist criterion, verifying to guarantee a high sensitivity peak. Discrete-time domain implementation issues of an anti-wind up scheme are discussed as well. Laboratory tests in compliance with the standard for UPS systems (IEC 62040-3) are performed to validate the theoretical analysis.

Ieee2016

Implementation issues on the design of current loops based on resonant regulators for isolated microgrids

Federico De Bosio

This paper analyzes the influence of state feedback coupling between the capacitor voltage and inductor current in voltage source inverters (VSI) operating in stand-alone microgrids. A decoupling technique is proposed as an effective measure to enhance the dynamics. Further implementation issues and control structures are also considered. Lab-scale experimental results prove the validity of the approaches.

IEEE2016

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Contactless current measurement based on Hall-effect sensors can be performed in either closed-or open-loop configuration. In this paper an open-loop sensor system with a current-mode output is described. The system measures the magnetic field induced around the current path targeting high linearity, accuracy and speed. As the accuracy of the Hall sensor microsystem is affected by temperature-dependent offset and sensitivity of the sensing element, system-level solutions are developed to minimize these effects. The full system integration represents a design challenge as both voltage and current references are directly involved in the sensitivity calibration and both contribute to the system sensitivity drift. The measurements show a sensitivity drift lower than 80ppm/degrees C, the offset drifts less than 300nT/degrees C and the non-linearity is less than +/- 0.08%. The effects of the varying external field on the calibration loop are analyzed and the theoretical prediction is validated by measurement.

Ieee2012