4–20mA Current Receiver

4-20mA Receiver Assembly
4–20mA Receiver Assembly

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.

4–20mA Receiver V1.0

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.

4–20mA Receiver Eagle CAD schemat­ic V 1.0

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.

4-20mA Receiver completed assembly
4–20mA Receiver com­plet­ed assembly

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

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