This is a simple circuit that can be used to convert a 4-20mA signal to a 0V to 5V analog voltage. It is ideal conversion to digital with an analog-to-digital converter (ADC). In this circuit, a current-sense amplifier (IC1) is used to monitor the loop current. To generate a ground-referenced output that ranges from 0V at 4mA to 5V at the full-scale loop current (20mA), a reference/op-amp/comparator device (IC2) is employed. Here is the circuit :
Using the resistor values shown (R2-R6), the output of IC at pin 8 is approximately 6.25V at 20mA and 1.25V at 4mA. An output range of 0.05V to 5.045V is generated by IC2 that is configured as unity-gain difference amplifier. Beside that, IC2 comparator can be used to flag a pre-set loop current or monitor input voltage.
Using 1% resistors, this circuit will perform well. The worst-case output error is 5% based on Monte Carlo analysis. However, the performance with unmatched components was better than 1% at full-scale. The accuracy of this circuit is better than 1% across the operating range, that can be done by compensating for the dominant error. [Source: maxim-ic.com]
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