Circuit Review

If you are comfortable posting your circuits on the forum, I'm sure you will get lots of feedback.

Ok here is the 4-20ma part. Dont pay attention to the SPI items

So, it looks like you have 4 inputs setup for 4-20ma range, generating a 1-5V output to be read by the analog inputs.  What would you like to do with the inputs?

Gene

Ok so here’s the Idea for the 4-20ma, I`m looking to read general 4-20ma sensors loops.

The board has a 12volt power supply for the transmitter (if needed). I want to connect these inputs to a feather type proto board.

You might need to modify your 4-20ma loop front end somewhat.  First, the circuit as shown does not have a return path for the current loops.  Also, the current loop may not necessarily be directly referenced to ground (a lot are not, some are completely isolated).  A more typical solution is to differentially sense the voltage drop across a resistor that is directly connected to the two signal lines of the loop.

Gene

Wow missed that one. Completing the loop would be nice....

Tom,

Again, I am not sure that you can count on the second leg of the 4-20ma loop to be at ground potential.  You might end up shorting out a driver or introducing ground noise into the circuit.

Here is a link to some information on the risks of assuming a ground potential on the low side of the loop.

https://www.dataq.com/blog/data-acquisition/4-20-ma-current-loop-measurements/

Also, not all 4-20ma loop devices are actually supplying current.  There are passive devices that act as a variable resister, and the measuring circuit actually supplies the drive.

On the outside simple.  But potentially quite complex.  If you know the devices that you will be receiving from, then you can make some simplifications to the measuring circuit.

Gene

Tom,

Here is an even better link.  This shows how to differential sense the loop current.

https://www.sensorsmag.com/components/implementing-a-4-ma-to-20-ma-sensor-interface

Good luck!

Gene

Another useful source I found was instrumentation amplifier data sheets - the AMP04 from Analog Devices has a suggested 4-20mA receiver circuit that also shows some TVS protection diodes being used to protect the inputs, which could be useful in an industrial application?

A

Great info but I have a problem with the shunt resistors. My goal is to create something general to be used with most 4-20ma sensors.

Is this possible?

I checked out the AMP04 like the circuit but the -15 +15VDC supply becomes an issue.

I also found the RCV402 but there are expensive (old chip too). Anyone know of something newer and similar?

I though making a general 4-20 industrial loop would be easy…… well. Simple concept….. so many options….. lol

We sometimes use the Libelium 4-20ma device to connect to theses Siemens sensors. For sure the libelium board is not the complex.

https://www.google.com/search?q=libelium+4-20&client=firefox-b-ab&source=lnms&tbm=isch&sa=X&ved=0ahUKEwigmbOI2sHbAhVDlJAKHRdBCLQQ_AUICigB&biw=1093&bih=482#imgrc=cbzOIBxvMb2TTM:

Sensor:

https://w3.siemens.com/mcms/sensor-systems/en/process-instrumentation/level-measurement-with-level-measuring-instruments/continuous/ultrasonic/transducers/pages/echomax-xps.aspx

Control unit

  https://w3.siemens.com/mcms/sensor-systems/en/process-instrumentation/level-measurement-with-level-measuring-instruments/continuous/ultrasonic/controllers/Pages/MultiRanger-100-200.aspx