Enabling Smarter, Integrated Protection for 4-20mA Current Loops with eFuses
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1 Introduction
The Programmable Logic Controllers (PLC) are widely used for automation in industries. The PLC collects data from sensors, analyze this data, and controls the industrial process through actuators. One way of collecting data from different sensors is through current loops. The sensor transmitters convert the measured parameter in to a current output and the current is transmitted over a cable to analog input module for measurement. The analog input module converts the analog current value in to a digital value by measuring the voltage drop across burden resistor. Figure 1-1 illustrates an analog input module with current inputs.
Figure 1-1 Current input protection in Analog
Input modules
2 Protection Required for Current Inputs in Analog Input Modules
2.1 Over-Current Protection from Miswiring to Field Power Supplies
In the factory environment, a voltage source for example, 24 V power supply, can be miswired to a current input. The voltage source will lead to excessive current flow through the burden resistor and may burn the burden resistor. An over-current protection device with bi-directional current limiting (similar to PTC) is used traditionally to limit the current in the burden resistor.
