What's the advantage of isolated DI/DO card?

[RobinWang11]

Hi All,

Who can tell me what's the benifit to use isolated DI/DO module.

Our customer spec 2 modules in a project:

ALB1769IA8I
ALB1769OW81​

Actually, all input/output power is from a same source, so i don't understand why they choose isolated card. Anyone can expain it to me? By the way, there is two terminals (NC) on the card. What's these terminals should connect with? Power supply? why no L and just N?
Thanks.​

 

[Roy Matson]

They are much easier to interface with a Motor Control Center because each starter usually has it's own control transformer.
Easier to mix output voltages e.g. you might have a 120AC circuit next to a 24VDC circuit.
Easier to interface with equipment that has non zero based I/O
That's to name a few reasons.
The disadvantage is you need two pins per circuit so it's harder to make High Density I/O for example 32 point
Regards
Roy

 

[ndzied1]

By the way, there is two terminals (NC) on the card. What's these terminals should connect with? Power supply? why no L and just N?
Thanks.​

"NC" Stands for No Connection so there is no use or function for these terminals.

The power to run the cards comes from the backplane of the chassis.

For an input card, there will only be the signal and neutral for each terminal. The power or L signal comes from the field device.

For an output card, there will only be the signal and power for each output. The neutral gets connected at the field device.

Check out the installation manuals for the cards for examples of connections:

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1769-in012_-en-p.pdf
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1769-in053_-en-p.pdf

 

[kamenges]

Originally posted by RobinWang11:

Actually, all input/output power is from a same source, so i don't understand why they choose isolated card. Anyone can expain it to me?

In your specific application there may be no need for isolated I/O. However, your customer may have other machines on site that do need these modules and they are just trying to manage spare count. They may also be trying to limit any confusion from having multiple modules with apparently identical functions with significantly different wiring.

Then again, they may not understand what 'isolated' means in this context and they think they are getting something special that is really not all that special.

Keith

 

[The Plc Kid]

Easier to interface with equipment that has non zero based I/O

What are non zero based I/O?

 

[The Plc Kid]

They are much easier to interface with a Motor Control Center because each starter usually has it's own control transformer.
Easier to mix output voltages e.g. you might have a 120AC circuit next to a 24VDC circuit.
Easier to interface with equipment that has non zero based I/O
That's to name a few reasons.
The disadvantage is you need two pins per circuit so it's harder to make High Density I/O for example 32 point
Regards
Roy

What are non zero based I/O?

 

[jimbo3123]

Easier to interface with equipment that has non zero based I/O

What are non zero based I/O?

I think that he meant ungrounded circuits (where the neutral is not tied to ground). Ungrounded control circuits are becoming less common, but I still see them occasionally.