Clarifying 4-20mA Output wiring for Industrial Automation HAT v3.2

ericabboud

New member
Hello, I've got an Industrial Automation HAT that I'm using to drive an electronically controlled pressure regulator expecting a 4-20mA control signal. The documentation in the seems to show that I should have an external supply in my loop. I was running into some issues and started working with a benchtop supply and multimeter and found that even when my supply's output wasn't on, my multimeter was registering the current that I'd configured on the Pi. This led me to try and cut out the supply completely and I found that actually got my setup working!
My loop is now just composed of the HAT (powered with it's 24V supply) going directly to my regulator's input and it seems to be working... but the documentation makes me think it shouldn't be. Can I get some clarification on how things should be wired and if it is necessary to have the external supply in the loop?
 

alexburcea

Moderator
Staff member
Hi,

This mean you have the last version of the Industrial Automation Card which does not require external power supply because is using his own 24V.
Unfortunately, or not :) , we are very busy developing some custom cards and new products and we are behind with the manuals on a few cards.
We will update the manual shortly.
 

ericabboud

New member
Oh! I'm pretty pleased with that since it simplifies a bit of my wiring. So is that the case for all of the outputs like the Open Drain output? I'm using it to drive a solenoid that needs about 250mA. I've currently got a 24V supply in that loop as instructed by the user manual but do I still need that?
 

ericabboud

New member
Gotcha! Thanks so much for a clarification. Is there any way I could get notified when he newest manuals/schematics get posted for the hardware I have?
 

gman

New member
Hello,
I previously encountered a similar issue with the power supply, which I resolved after discovering this post. It appears I'm using the most recent version of the Industrial HAT.

However, I've now encountered a new problem while employing the Industrial Automation HAT to produce three distinct 4-20 mA signals. Each signal is directed to a separate PCB designed to interpret these 4-20 mA inputs. On this PCB, all the inputs share a common ground. Everything operates smoothly with a single signal, but issues arise when I attempt to use two (or more) signals. As far as I can tell, all the positive terminals (4-20 mA outputs) on the HAT are linked to the same node? Consequently, this causes the PCB to read an average value as soon as the second signal is connected. The signal entering the negative terminal on the HAT seems to be correct. Do you have any suggestions for resolving this problem or/and if there are any revised board schematics available. I would greatly appreciate your guidance and support. Thank you!
 

alexburcea

Moderator
Staff member
Hi,
The 4-20mA outputs are "open-collector" type so your behavior is normal. You can not measure with common GND between channels.
Checkout the attached schematics page 8.
 

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