How to prevent using a current loop isolator?

[KalleOlsen]

is this caused because the instrument earth and plc earth are at different potentials? and how do u prevent this?

1: Exactly
2: Quickfix seen from the PLC side, is as you've done; a loop isolator.
It should be prevented with proper equipotential bonding and earthing. This is an electricans job.

Kalle

 

[Theboss]

@silva. im not making things difficult here but the signal isolator works just fine and it is powered. the ai card is setup for 4 wire mA input.
i had a problem with the 4 wire mA signal being detected on AI but it wasn't so only after i installed the mA loop isolator, it resolved my problem.
NOW BACK TO MY QUESTION, HOW IS THIS CAUSED AND HOW DO I PREVENT THIS FROM HAPPENING AGAIN?

 

[Theboss]

Tnx Kalle.

 

[Regine]

Hi, I am also experiencing trouble with my SM431 AI 16X13-bit module, wherein I have configured the channels to 2-wire tranducer. My sources are analog outputs from level controller, and brix controller, which I presume are "active" devices. Upon power-up, I could not get normal reading at my analog channels, all indicate an overflow which is 7FFF. After reading the manuals, I learned that I have to configure the channels to 4-wire transducers for active devices. However, the manuals do not provide wiring diagrams for 4-wire setting of this module. Also, does this mean that the capacity of my module for reading 4-wire transducers also reduces? Originally, I have 16 AI slots available, does this count only for overall 2-wire configuration or not? Please help me with this. Thanks.

 

[Lancie1]

hi. im not with you on this, because its a 4-20mA that im transmitting to the plc, where is the 0V or do u mean the -ve lead of the 4-20mA?

Yes that is it, the -V lead. Many people are under the mistaken assumption that one side of a DC circuit can be a theoreticaly-impossible 0 volts. What you can do is make two separate DC circuits have a common node, usually the (-) terminal and also grouded so that it will measure 0 volts to earth ground.

 

[nonuke]

Regine,
Can you please start a new thread with your problem.
you don't want to get mixed up in this one.

And this thread is tooooooooooo old.

 

[Regine]

I have already started a new thread on this, please check. Thanks. Looking forward to your responses.

Regine

 

[danw]

What did you title the new thread? Link to it?

 

[Regine]

Here's the link:http://www.plctalk.net/qanda/showthread.php?t=82787