Building a 4–20mA current transmitter and receiver for some upcoming automation projects.

After building the 4–20mA current transmitter, it was time to build a receiver. I used the companion Burr-Brown (TI) RCV420 precision current-loop receiver IC. The RCV420 is a monolithic circuit that converts a 4–20mA input signal into a 0–5V output signal, and has a 0.1% overall conversion accuracy.

The RCV420 utilizes a plus and minus 15 volt DC supply, and is not loop powered. I used a Recom RB-1215D, DC to DC converter that uses a 12 VDC input, and outputs +/- 15 VDC at up to 33 mA. I also used a Polymeric 150 mA PTC Resettable Fuse for the 12 volt input to the DC to DC converter along with some capacitors for EMC Filtering.

For filtering the +/- 15V power busses I used some United Chemi-Con 120 uF at 20 volt capacitors. These are Aluminum — Polymer capacitors with an ESR of 20 mOhms and a lifetime rating of 15000 Hrs @ 105°C. Each buss also has a 0.1 uF and 10 nF ceramic capacitor located close to the IC power pins.
To protect the input sense resistor, I chose to use a 0.032A, Lifflefuse Series 217 fast-acting fuse, as this introduced the least amount of loop voltage drop of the three recommended solutions from the datasheet.
The only other item of note is capacitor C9, a 1 uF ceramic on the IC’s voltage reference Noise Reduction pin #7 to reduce high frequency noise of the internal 10 volt reference.

I did attach an Assmann WSW Components V5619A 16 pin DIP heatsink to the RCV420 IC to reduce the affects of self-heating affecting the precision of the circuit.
I did try something new with 4–20mA transmitter and receiver boards in that I used a hatched polygon pour for the non-ground sides of the board. I used a width of 10 mils and a spacing of 40 mils for the hatch pattern with a 18 to 20 mil isolation from other traces.

For the most part, it is a simple circuit that works very well for my intended use. I will mount this board in a enclosure with several other boards and power supplies including the loop 24 volt DC supply

EagleCAD V7.7 board & schematic ZIP file for 4–20mAReceiver

OSH Park printed circuit boards for the 4–20mA Current Receiver