4-20ma loops with multiple supply's on different inputs can you the commons together

[Vaughan91]

Hello this is my first post. Looking forward to being more involved in this community to learn and hopefully help others.

Any help or guidance would be appreciated.

I am building a pump station controller board. (Below photo has more details in the link.)

The board has
A kingfisher plc with IO-3 model card
A schnieder VSD/VFD
1x tank level sensor

There is a 4-20ma speed reference signal coming from the plc to the vsd.

There needs to be a 4-20ma motor current signal coming from vsd to plc.

There needs to be a 4-20ma tank level signal coming to the plc.

I'm a bit concerned if I have a external power supply supplying the power for the level sensor. Is it possible to share the same common ?

I did read in the kingfisher plc manual not to have multiple power sources onto he digital input side.

I'm.a bit lost.

To help explain, Please see link to my onedrive shared photo for wiring diagram

https://gitteljed-my.sharepoint.com...pMgTgJk_9oTA0B1ZqA-Z1XuKT4DtpMNCz-dQ?e=WWVL5c

 

[Vaughan91]

 

[BryanG]

Can you add a link to the Kingfisher PLC. Unfortunately Kingfisher PLC is Kingfisher Public Limited Company here in the UK so a web search finding a Programmable Logic Controller made by a company called Kingfisher is problematic

 

[Vaughan91]

Hey @BryanG
thanks for you message mate,

here is a link to my one drive with the manuals I'm using for this PLC & VSD.

https://gitteljed-my.sharepoint.com/:f:/g/personal/vaughangittel_gitteljed_onmicrosoft_com/Em6RANaCTKdIufOTi3iGPjYBUw3YP3RT15lXRCwfIkLGeg?e=CYK2CX

 

[Cheeseface]

The commons are already internally connected according to block diagram in section 9.1.1 page 133 of that 4th PDF, "kingfisher plus"

 

[diat150]

just use a 4-20 ma barrier/isolator to make sure you have no issues.

 

[Puddle]

Can you add a link to the Kingfisher PLC. Unfortunately Kingfisher PLC is Kingfisher Public Limited Company here in the UK so a web search finding a Programmable Logic Controller made by a company called Kingfisher is problematic

Honestly I had a moment of confusion thinking that Screwfix and B&Q had suddenly branched out into automation!

Those are general DIY / trade suppliers for anybody non-UK.

 

[lfe]

There should be no problem if all these power supplies are isolated and all the commons are joined at a single point, for example in the input/output module.

You never have to add another cable that joins those common ones at other connection points.

There should be no common loops.