4mA thru 20mA Loop to 0V thru +5V Converter
by ericgibbs , 7th May 2012 at 12:08 PM (2728 Views)
This is a simple circuit for converting a 4mA thru 20mA Loop signal to 0V thru +5V, suitable for an ADC input.
When using a LM358 OPA, the closest specified lowest swing is approx 20mV above 0V.
Take care when using with a ADC that will not accept excessive outputs voltages from theLM358.
For example with a PIC if the OPA output could exceed 5V in operation, using a limiting resistor, that will limit the ADC input current to less than ~10mA.
The internal clamp diodes of the PIC are rated at ~20mA max.
A series 470R connected between the LM358 output and the ADC input pin will limit the clamp current to ~10mA, if the OPA output reached +10V.
NOTE: 16 May2012
Added a 0V to +10Vout version of the converter
NOTE: 17 May2012
Added a 0V to +5/10Vout version of the converter for a 0mA to 20mA input.