wiring sourcing DC output module

unsaint32 · Oct 23, 2012

An AC output module has VAC and output terminals. Why does a DC output module have VDC, output terminals, and DC COM? Why does the DC output circuit need the return path beside the path through the field device?

Tharon · Oct 23, 2012

Solid State, Transistors vs Relays.

The DC Output cards with a VDC and DC COM are likely transistors. The ones with just the VDC and the Output are likely physical relay contacts.

mendonsy · Oct 23, 2012

It depens on the manufacturer but DC modules are generally opto-isolated so the need a common for the output side of the opto chip.

unsaint32 · Oct 23, 2012

mendonsy said:
It depens on the manufacturer but DC modules are generally opto-isolated so the need a common for the output side of the opto chip.

If that is the case, why doesn't a DC input module need a separate DC+ for the opto-chip?

sthompson · Oct 23, 2012

Not all Output Cards have a connection for a Common (-24VDC/L2/N). I believe it depends on how the power side of the Opto-isolated Outputs are wired.

In the Case of Allen Bradley, all the Energized Indicator LEDS/Pilots come from the PLC Bus side of the Card. However, I have worked on older Output Cards where the Output Energized LEDS/Pilots came from the Power Side of the Output Card, thus they needed a Common connection.

For an Input Card, as long as you have a Common, you can operate an LED/Pilot for Input Energized on the Power Side of the Input Card.

As an example, see the wiring for Allen Bradley SLC500 Cards.

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1746-in027_-en-p.pdf

Stu....

unsaint32 · Oct 23, 2012

sthompson said:
Not all Output Cards have a connection for a Common (-24VDC/L2/N). I believe it depends on how the power side of the Opto-isolated Outputs are wired.

In the Case of Allen Bradley, all the Energized Indicator LEDS/Pilots come from the PLC Bus side of the Card. However, I have worked on older Output Cards where the Output Energized LEDS/Pilots came from the Power Side of the Output Card, thus they needed a Common connection.

For an Input Card, as long as you have a Common, you can operate an LED/Pilot for Input Energized on the Power Side of the Input Card.

As an example, see the wiring for Allen Bradley SLC500 Cards.

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1746-in027_-en-p.pdf

Stu....

Are you saying, some (newer) DC output modules come without the DC_COM terminal? If so, the bottom diagram in my picture only pertains to older DC output modules?

Thanks.

sthompson · Oct 23, 2012

unsaint32 said:
Are you saying, some (newer) DC output modules come without the DC_COM terminal? If so, the bottom diagram in my picture only pertains to older DC output modules?

Thanks.

I'm saying it depends on how the Manufacturer decided to build the Output Card, and what is required for it to work properly based on how it is built.

Every Manufacturer has their own ideas on how to build an Output Card.

Stu....

bernie_carlton · Oct 24, 2012

Some manufacturers only give a block style diagram and you get no clue about the circuit. Others at least give a stylized idea of the circuitry so you can at least understand. But in any case just follow the directions.

wiring sourcing DC output module

unsaint32

Member

Tharon

Member

mendonsy

Member

unsaint32

Member

sthompson

Lifetime Supporting Member + Moderator

unsaint32

Member

sthompson

Lifetime Supporting Member + Moderator

bernie_carlton

Lifetime Supporting Member + Moderator

Similar Topics