4-20ma signal from 1 plc to another

[bushmonkee]

Can someone help?

I have AB L32E with a OF4CI analog output card and need to send a 4-20ma signal to another guys PLC with an analog input card. He has 24vdc common and return input signal coming into my OF4CI but we cant get it to work. Any ideas where to start?

 

[Mickey]

I would install an isolator, see link below for one brand. There are many more.

http://www.miinet.com/products/ca_signal.shtml

 

[bushmonkee]

Thanks for the reply

I thought the card was isolated. But it could be an idea to get a separate isolator.

Its working the other way round as he is sending me a 4-20 and i am reading it ok on an analog input card.

 

[danw]

>He has 24vdc common and return input signal coming into my OF4CI
Here's the wiring for your OF4CI card:

Your reference to power supply common makes no sense to me

Your Iout(+) should go to his AI (+)
Your Iout(-) should go to his AI (-)

With that, you should be able to read a dc voltage across his AI(+) and AI(-). Can you do so?

 

[bushmonkee]

Danw

Hope you can see the drawing! I think I know whats wrong.

 

[sthompson]

I have to agree with Dan, it should be a no brainer. It would also help to know the Brand and Model of his Analog Input Card.

Stu......

 

[danw]

The notations on the wiring schematic are unreadable.

"Passive" loop powered transmitters or analyzer analog outputs need a connection to a power supply in order to power the current loop.

But your analog output card is 'active', its ouptut is not loop powered.

In fact, the 1769-OF4CI manual has a warning:

Miswiring of the module to an AC/DC source will damage the module.

 

[Dua Anjing]

Mt Two cents worth

I would install an isolator, see link below for one brand. There are many more.

http://www.miinet.com/products/ca_signal.shtml

I'm voting with Mickey. A good isolator will prevent you from accidentally "blowing up or either PLC and will allow you to calibrate both ends simply.

 

[danw]

A-B's claim is that the outputs are isolated, "Compact 1769-OF4CI Isolated Analog Output Module"

As much as I advocate isolation, I don't think ground loops or common mode are the problem, I think the AO wiring is not connecting to an AI on the other end, because AI connections are not called "24vdc common and return input signal" and I find the schematic unreadable.

 

[danw]

I suspect that there's some confusion over loop powering the analog output.

The A-B AO is 'active', its outputs are powered from the I/O card.

Passive outputs are loop powered, like below, where S+, S(-) are an analog input:

The A_B Analog Output is not passive, it does not need or want a power supply in the loop it is driving.

 

[Mickey]

I suspect that there's some confusion over loop powering the analog output.

The A-B AO is 'active', its outputs are powered from the I/O card.

Passive outputs are loop powered, like below, where S+, S(-) are an analog input:

The A_B Analog Output is not passive, it does not need or want a power supply in the loop it is driving.

I agree. All the more reason to isolate it from the outside world (whatever it is the OP is connecting it to).

 

[m.sohail20]

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[Jeff23spl]

if anyone interested to purchase step 7 and wincc contact me at:
[email protected]
Tel: 00923457842005

What are you doing here? it is an AB post about a wiring problem....Can someone re-direct this pub to a better place and delete this post next
Thanks

 

[Jeff23spl]

We need both side connections to figure it out...an multimeter with a working MA scale (Must of the time the fuse is blown...)

Making sure your module is well configured is needed and check is the card give something and if yes look at the other end with the other side disconnected...if there still 4-20mA signal your side is proved healty and you can stop there or help the other guy...


Your AB isolated card is a sourcing device and should be connected this way on the other side....no other powersupply inline needed and maybe you need to referrence your Analog- signal to his VDC negative reference....
This is why an isolator is suggested, it can work without but if something wrong happend in the other side, your isolated input will blow up and you will need to replace the whole card even if your PLC remain healty